mineral trioxide aggregate: a review of clinical usage and ...689794/s... · school of dentistry ....

Mineral Trioxide Aggregate: A review of clinical usage and

investigations of the effects of modifying particle size

William Nguyen Ha

BDSc GradCert Research Commercialisation

A thesis submitted for the degree of Doctor of Philosophy at

The University of Queensland in 2017

School of Dentistry

ii

Abstract

Introduction

Mineral trioxide aggregate (MTA) is a dental cement used in various endodontic and pulp

therapy procedures. MTA takes longer to set than other dental cements or bulk dental

restoratives such as glass ionomer cement (GIC). The long setting time and the cost of the

material are often described as problems of MTA. A method to accelerate reaction speed

is to reduce particle size. As a smaller particle size will accelerate the setting reaction, the

next consideration was how particle size influences the physical properties of the set MTA

cement. In the literature on MTA, the setting time has been assessed using an indentation

method involving arbitrary weights and needle diameters as defined by the International

Organization for Standardization (ISO), in particular, ISO 9917-1 for water-based cements

and ISO 6876 for endodontic cements. Both of these standards define a dental cement as

‘set’ based on arbitrary needle weights applied to the MTA, to which a complete

indentation is ‘set’ and an incomplete indentation is ‘unset’. This resulting definition of set

versus unset lacks validity, since the response to indentation pressure does not relate to

the material’s clinical properties nor its progress in hydration. Elastic modulus is a

parameter which can be measured over time as a material sets which can be used to test

MTA and other dental cements.

Methods

To understand MTA, a review of the chemistry of MTA and its relationships with other

related dental cements was performed. As MTA is 80% Portland cement, a review was

performed utilising knowledge from the concrete industry. A review of the clinical

knowledge of MTA was performed as well as a review of the testing methodology used in

the literature. To understand how MTA was used by clinicians, a survey was performed of

general dentists (GDs), endodontists (EDs) and paediatric dentists (PDs) in Australia.

Laser diffraction analysis (LDA) was used to assess the particle size distribution (PSD) of

ProRoot MTA (MTA-P) and MTA Angelus (MTA-A). The data obtained were analysed

using the non-linear least squares method to deconvolute the PSD into the constituents of

Portland cement (PC) and bismuth oxide (BO). The three key parameters of PSDs, namely

the 10th percentile (D10), the 50th percentile (D50) and the 90th percentile (D90) were

plotted against the setting times of 11 commercial MTA cements, 6 PC products and

against the cumulative heat release of the PC products.

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To assess the influence of reduced particle size on setting time, experimental MTAs with

varying particle size had their indentation setting time measured, elastic modulus tested

over time and comparisons of strength over time.

Results

The review of MTA and related cements revealed the use of vague or inaccurate terms in

the literature, which led to a formal creation of the term ‘hygroscopic dental cement’

(HDC). New MTA-like cements, often called ‘bioceramics’, fall under the category of HDCs

and share similar properties, all of which, can be influenced by storage, mixing, placement

and curing. The testing of HDCs often does not correlate well to the clinical usage of HDCs

as its setting time and curing is not considered.

A lack of experience with MTA was the greatest barrier to its use for GD (48.7%), followed

by its high cost (31.6%). A majority of GD (82.5%) desired additional hands-on training in

the use of MTA.

LDA documented a different PSD for each material, and also showed that because of the

hygroscopic nature of the cement, there were changes in the PSD when the powder was

exposed to room air. This point has important implications for how MTA powder is

packaged. MTA-P was shown to have both fine and large PC particles, with intermediate

size particles for BO. On the other hand, MTA-A had small BO with large PC particles.

Of the three key markers, the D90 showed the strongest correlation with the setting time

and the cumulative heat release. Curing under dry conditions gave a lower CS than when

samples were cured under wet conditions (in PBS). Cements with smaller particle sizes

gave greater initial CS and FS. However, this advantage was lost over time (1-3 weeks).

The cements tested were Fuji VII, Fuji IX, MTA-P, Biodentine, AH 26, AH Plus Jet and

Real Seal SE Sealer.

Discussion

Despite proposed advantages in handling, ‘bioceramics’ illustrate compromises in their

resultant properties which could have implications on clinical outcomes. These

compromises can be difficult to identify as the results of many published tests for MTA and

‘bioceramics’ are not reflective of clinical use of the material.

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Significant differences existed in how MTA was being used between GDs and EDs that

was reflected in the different levels of training. Thus, lack of knowledge of the material is a

larger barrier to its use, rather than its high cost or any inherent problems with the material.

The use of smaller particle sizes in MTA and PC correlate with faster setting times. Elastic

modulus provides a better method for testing setting time than indentation testing. Our

testing with experimental MTA illustrated faster setting times with no advantages to the

final strength of the cement. Testing of endodontic cements using rheology illustrated that

the proposed setting time by manufacturers can be an underestimation as the material is

still reacting.

v

Declaration by author

This thesis is composed of my original work, and contains no material previously published

or written by another person except where due reference has been made in the text. I

have clearly stated the contribution by others to jointly-authored works that I have included

in my thesis.

I have clearly stated the contribution of others to my thesis as a whole, including statistical

assistance, survey design, data analysis, significant technical procedures, professional

editorial advice, and any other original research work used or reported in my thesis. The

content of my thesis is the result of work I have carried out since the commencement of

my research higher degree candidature and does not include a substantial part of work

that has been submitted to qualify for the award of any other degree or diploma in any

university or other tertiary institution. I have clearly stated which parts of my thesis, if any,

have been submitted to qualify for another award.

I acknowledge that an electronic copy of my thesis must be lodged with the University

Library and, subject to the policy and procedures of The University of Queensland, the

thesis be made available for research and study in accordance with the Copyright Act

1968 unless a period of embargo has been approved by the Dean of the Graduate School.

I acknowledge that copyright of all material contained in my thesis resides with the

copyright holder(s) of that material. Where appropriate I have obtained copyright

permission from the copyright holder to reproduce material in this thesis.

vi

Publications during candidature

Peer-reviewed papers

1. Ha WN, Kahler B, Walsh LJ. Classification and nomenclature of commercial

hygroscopic dental cements. Euro Endod J. In press 2017 (accepted 9 Sep 2017).

2. Ha WN, Kahler B, Walsh LJ. Clinical manipulation of mineral trioxide aggregate:

Lessons from the construction industry and their relevance to clinical practice. J

Can Dent Assoc 2015;81:f4.

3. Ha WN, Nicholson T, Kahler B, Walsh LJ. Mineral trioxide aggregate – a review of

properties and testing methodologies. Materials. In press 2017 (accepted 26 Sep

2017).

4. Ha WN, Kahler B, Walsh LJ. Dental material choices for pulp therapy in paediatric

dentistry. Eur Endod J; 2017, 2:1-7.

5. Ha WN, Duckmanton P, Kahler B, Walsh LJ. A survey of various endodontic

procedures related to MTA usage by members of the Australian Society of

Endodontology. Aust Endod J; 2016; 42; 132-138.

6. Ha WN, Kahler B, Walsh LJ. Particle size changes in unsealed mineral trioxide

aggregate powder. J Endod 2014;40:423-426.

7. Ha WN, Shakibaie F, Kahler B, Walsh LJ. Deconvolution of the particle size

distribution of ProRoot MTA and MTA Angelus. Acta Biomater Odontol Scand

2016;2:7-11.

8. Ha WN, Bentz DP, Kahler B, Walsh LJ. D90: The strongest contributor to setting

time in mineral trioxide aggregate and Portland cement. J Endod 2015;41:1146-

1150. An abstract from this also appeared in the Australian Dental Journal

Research Supplement 2015; S11-12.

9. Ha WN, Kahler B, Walsh LJ. The influence of particle size and curing conditions on

testing Mineral Trioxide Aggregate cement. Acta Biomater Odontol Scand

2016;2:130-137.

10. Ha WN, Nicholson T, Kahler B, Walsh LJ. Methodologies for measuring the setting

times of mineral trioxide aggregate and Portland cement products used in dentistry.

Acta Biomater Odontol Scand 2016;2:25-30.

Database publication

1. Ha WN. Registrant of GMDN Term ‘Hydraulic dental cement’, (now Hygroscopic

dental cement), Term P60510. Available from https://www.gmdnagency.org/

vii

Conference proceedings

Australian and New Zealand College of Veterinary Scientists (Dental Section)

Gold Coast, Australia 2015

Conference abstracts

UQ School of Dentistry Research Day presentations

UQ School of Dentistry

Brisbane, Australia 2011, 2012, 2013, 2014, 2015, 2016, 2017

Storage of MTA

IADR Conference, Asia Pacific Region

Bangkok, Thailand 2013

Setting time of MTA

IADR Conference, Australia and New Zealand Division

Brisbane, Australia 2014

Survey on the usage of MTA by members of the Australian Society of

Endodontology

Annual Meeting of the Japanese Association of Dental Research

Fukuoka, Japan 2015

Rheology of MTA

IADR Conference, Australia and New Zealand Division

Dunedin, New Zealand 2015

Dental material choices for pulp therapy by ANZSPD members

World Congress on Dental Traumatology

Brisbane, Australia 2016

viii

Publications included in this thesis

1. Ha WN, Kahler B, Walsh LJ. Classification and nomenclature of commercial

hygroscopic dental cements. Euro Endod J. In press 2017 (accepted 9 Sep 2017).

- Incorporated in Chapter 1

Contributor Statement of contribution

William Ha (Candidate) Construct idea (50%)

Design methodology (100%)

Data collection (100%)

Analysis (100%)

Literature review (100%)

Writing of manuscript (50%)

Bill Kahler Writing of manuscript (50%)

Critical review (50%)

Supervision (50%)

Laurence J Walsh Construct idea (50%)


Supervision (50%)









Analysis (100%)





Supervision (50%)



Supervision (50%)

ix

1. Ha WN, Nicholson T, Kahler B, Walsh LJ. Mineral trioxide aggregate – a review of

properties and testing methodologies. Materials. In press 2017 (accepted 26 Sep

2017).






Analysis (100%)





Supervision (50%)



Supervision (50%)


dentistry. Eur Endod J; 2017, 2017; 2:1-7.

- Incorporated as Chapter 2





Analysis (100%)





Supervision (50%)



Supervision (50%)

x


procedures related to MTA usage by members of the Australian Society of

Endodontology. Aust Endod J; 2016; 42; 132-138.






Analysis (100%)



Peter Duckmanton Construct idea (25%)


Supervision (25%)



Supervision (50%)



Supervision (25%)

xi








Analysis (100%)





Supervision (50%)


Funding (100%)


Supervision (50%)

xii



2016;2:7-11.







Fardad Shakibaie Analysis (100%)





Supervision (50%)



Supervision (50%)

xiii


time in mineral trioxide aggregate and Portland cement. J Endod 2015;41:1146-

1150. An abstract from this also appeared in the Australian Dental Journal

Research Supplement 2015; S11-12.






Analysis (75%)



Dale Bentz Construct idea (25%)



Analysis (25%)





Supervision (50%)


Funding (100%)


Supervision (50%)

xiv


testing Mineral Trioxide Aggregate cement. Acta Biomater Odontol Scand

2016;2:130-137.






Analysis (100%)





Supervision (50%)


Funding (100%)


Supervision (50%)

xv









Analysis (75%)



Tim Nicholson Construct idea (25%)



Analysis (25%)





Supervision (50%)


Funding (100%)


Supervision (50%)

10. Ha WN. Registrant of GMDN Term ‘Hydraulic dental cement’, (now Hygroscopic

dental cement), Term P60510. Available from https://www.gmdnagency.org/

Incorporated in the Appendix


William Ha (Candidate) Application and submission (100%)

xvi

Contributions by others to the thesis

No contributions by others.

Statement of parts of the thesis submitted to qualify for the award of another degree

None.

xvii

Acknowledgements

I would also like to acknowledge the assistance, collaboration and advice of the following:

o Prof Laurence Walsh, Professor of Dental Science, School of Dentistry - UQ, for his

assistance in everything dental and research related;

o Associate Prof Bill Kahler, Honorary Associate Professor of Endodontics, School of

Dentistry - UQ, for his specialist knowledge in endodontics and dental materials;

o Dr Tim Nicholson, Senior Researcher, School of Chemical Engineering - UQ, for his

help in rheology;

o Dr Mingyuan Lu, Post-doc, School of Mechanical & Mining Engineering - UQ, for

her assistance in indentation setting time testing, compressive strength testing and

flexural strength testing;

o Dr Fardad Shakibaie, Post-doc, School of Dentistry - UQ, for his assistance in

mathematical deconvolution;

o Dale Bentz, Chemical Engineer, Materials and Structural Systems Division -

National Institute of Standards and Testing (USA) for collaborating research;

o Adjunct Associate Professor Peter Duckmanton - University of Sydney for the

opportunity to present to ASE-NSW and undertake collaborative research;

o Michael Archer, General Manager, Si Powders Pty Ltd for cement samples, particle

size testing and technical advice;

o Shane Shipperley, Lab manager, Cement Australia for assistance with particle size

testing;

o Bobbie Jennings, Corporate Services, School of Dentistry - UQ, for organising

payments of grant monies;

o Dr Lei Chai, Postdoc, School of Dentistry - UQ, for SEM images of MTA;

o Queensland University of Technology - for preparing MTA for SEM imaging;

o ATA Scientific - for use of their scanning electron microscopes;

o the Australian Dental Research Foundation - for the Early Career Researcher Grant

2012;

o the Australian Society of Endodontology - for the Endodontic Research Grants 2014

and 2016;

o the members of the Australian Society of Endodontology – for completing a survey

on MTA usage;

o the International Association of Dental Research - for a travel grant to Bangkok,

Thailand, to present my research;

xviii

o the Japanese Association for Dental Research - for the travel grant to Fukuoka,

Japan, to present my research;

o the members of the Australian and New Zealand Society of Paediatric Dentistry - for

completing a survey on MTA usage; and

o Dentsply, Gunz, Angelus, Septodont, Henry Schein Halas, Maruchi, Micromega,

BioMTA, Bisco and VladMiVa - for providing samples of dental materials.

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Keywords

Particle size analysis, International Organization for Standardization, elastic modulus,

compressive strength, indentation tests, Portland cement, calcium silicate, bismuth oxide,

setting time, laser diffraction.

Australian and New Zealand Standard Research Classifications (ANZSRC)

ANZSRC code 110503, Endodontics, 60%

ANZSRC code 090301, Biomaterials, 30%

ANZSRC code 110507, Paedodontics, 10%

Fields of Research (FoR) Classification

FoR code 1105, Dentistry, 60%

FoR code 0903, Biomedical Engineering, 30%

FoR code 0912, Materials engineering, 10%

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Dedication

To my friends, particularly those who laugh that I’d become twice the doctor, but not a

medical doctor.

To my family, who never understood my research, but supported me anyway.

And, to my field, which has given me the opportunity to continually challenge my hands

and my brain.

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Table of Contents

Abstract ........................................................................................................................ ii

Declaration by author......................................................................................................... v

Publications during candidature ...................................................................................... viPeer-reviewed papers ...................................................................................................................... viDatabase publication ........................................................................................................................ vi

Conference proceedings .................................................................................................................. viiConference abstracts ....................................................................................................................... vii

Publications included in this thesis .............................................................................. viii

Contributions by others to the thesis ............................................................................ xvi

Statement of parts of the thesis submitted to qualify for the award of another degree

..................................................................................................................... xvi

Acknowledgements ........................................................................................................ xvii

Keywords ..................................................................................................................... xix

Australian and New Zealand Standard Research Classifications (ANZSRC) ............ xix

Dedication ...................................................................................................................... xx

Table of Contents ............................................................................................................ xxi

List of Figures ................................................................................................................ xxvi

List of Tables ................................................................................................................ xxvii

List of Equations ........................................................................................................... xxix

Appendices ................................................................................................................... xxix

List of Symbols and Abbreviations .............................................................................. xxx

List of dental materials described in the thesis ....................................................... xxxiii

Introduction ........................................................................................................................ 1

Chapter 1 Literature Review .......................................................................................... 61.1 Introduction ............................................................................................................................ 61.2 A review of hygroscopic dental cements – MTA, bioceramics and calcium silicate cements10

1.2.1 Introduction .................................................................................................................. 10

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1.2.2 Methods ....................................................................................................................... 11

1.2.3 Review ......................................................................................................................... 111.2.4 Clinical and research consequences ........................................................................... 231.2.5 Conclusions ................................................................................................................. 23

1.3 Review of the placement of cements in the construction industry ....................................... 251.3.1 Introduction .................................................................................................................. 25

1.3.2 Water and the setting reaction ..................................................................................... 251.3.3 Exposure of the set material to acids ........................................................................... 26

1.3.4 Acids present at the time of mixing .............................................................................. 261.3.5 Interactions with EDTA ................................................................................................ 271.3.6 Interactions with phosphoric acid ................................................................................. 28

1.3.7 Presence of contaminants such as blood .................................................................... 281.3.8 Variations in the liquid component of MTA .................................................................. 29

1.3.9 Curing of the cement ................................................................................................... 291.3.10 Storage of MTA ............................................................................................................ 301.3.11 Summary ..................................................................................................................... 31

1.4 The properties of MTA and how it can be manipulated ....................................................... 321.4.1 Aims ............................................................................................................................. 32

1.4.2 MTA formulation .......................................................................................................... 321.4.3 CH & MTA .................................................................................................................... 341.4.4 pH and Calcium hydroxide release .............................................................................. 35

1.4.5 Clinical properties ........................................................................................................ 361.4.6 Commercial brands of MTA ......................................................................................... 37

1.4.7 Clinical uses ................................................................................................................. 451.4.8 Handling MTA .............................................................................................................. 481.4.9 Conclusions ................................................................................................................. 50

1.5 Review of properties and testing methodologies ................................................................. 511.5.1 Introduction .................................................................................................................. 51

1.5.2 Aims ............................................................................................................................. 52

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1.5.3 Methods and materials ................................................................................................ 53

1.5.4 Results ......................................................................................................................... 541.5.5 Discussion ................................................................................................................... 621.5.6 Conclusion ................................................................................................................... 68

Chapter 2 How do paediatric dentists use MTA? ...................................................... 692.1 Introduction .......................................................................................................................... 69

2.2 Methods ............................................................................................................................... 702.3 Results ................................................................................................................................. 71

2.3.1 Respondent characteristics ......................................................................................... 71

2.3.2 MTA Usage .................................................................................................................. 712.3.3 Education regarding MTA usage ................................................................................. 73

2.3.4 IPCs ............................................................................................................................. 752.3.5 DPCs ........................................................................................................................... 762.3.6 Pulpotomies ................................................................................................................. 76

2.4 Discussion ........................................................................................................................... 772.5 Conclusions ......................................................................................................................... 80

Chapter 3 How do endodontists use MTA? ............................................................... 813.1 Introduction .......................................................................................................................... 813.2 Methods ............................................................................................................................... 82

3.3 Results ................................................................................................................................. 833.3.1 Membership ................................................................................................................. 833.3.2 Education on MTA use ................................................................................................ 85

3.3.3 MTA Usage .................................................................................................................. 853.4 Discussion ........................................................................................................................... 90

3.5 Conclusions ......................................................................................................................... 92

Chapter 4 What is the particle size of MTA? .............................................................. 934.1 Introduction .......................................................................................................................... 93

4.2 Materials and methods ........................................................................................................ 954.3 Results ................................................................................................................................. 96

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4.4 Discussion ........................................................................................................................... 98

4.5 Conclusion ......................................................................................................................... 100

Chapter 5 What constitutes the particle size of MTA? ............................................ 1015.1 Introduction ........................................................................................................................ 101

5.2 Materials and methods ...................................................................................................... 1025.2.1 Particle size assessment ........................................................................................... 102

5.2.2 Statistical analysis ..................................................................................................... 1025.2.3 SEM ........................................................................................................................... 103

5.3 Results ............................................................................................................................... 103

5.3.1 Backscatter SEM ....................................................................................................... 1065.3.2 Energy dispersive X-ray spectroscopy ...................................................................... 106

5.4 Discussion ......................................................................................................................... 107

Chapter 6 How does the particle size correlate with the setting time of MTA and

PC? .................................................................................................................... 1096.1 Introduction ........................................................................................................................ 109

6.2 Materials and Methods ...................................................................................................... 1146.2.1 PSD ........................................................................................................................... 114

6.2.2 Materials .................................................................................................................... 1146.2.3 Heat of hydration ....................................................................................................... 117

6.3 Results ............................................................................................................................... 1176.4 Discussion ......................................................................................................................... 120

Chapter 7 What are the strength implications for set MTA if the particle size was

changed? .................................................................................................................... 1227.1 Introduction ........................................................................................................................ 1227.2 Material and Methods: ....................................................................................................... 123

7.2.1 Sample Preparation ................................................................................................... 1237.2.2 PSD ........................................................................................................................... 1237.2.3 Curing conditions and CS .......................................................................................... 124

7.2.4 Curing conditions and FS .......................................................................................... 125

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7.2.5 Particle size effects on CS ......................................................................................... 126

7.2.6 Particle size effects on FS ......................................................................................... 1267.2.7 Statistical analysis ..................................................................................................... 126

7.3 Results ............................................................................................................................... 126

7.3.1 PSD ........................................................................................................................... 1267.3.2 Effect of curing and testing conditions on CS ............................................................ 127

7.3.3 Effect of curing and testing conditions on FS ............................................................ 1297.3.4 Effect of particle size on CS ....................................................................................... 131

7.3.5 Effects of particle size on FS ..................................................................................... 1327.4 Discussion ......................................................................................................................... 132

Chapter 8 How is the setting time measured? What if the particle size was

changed to hasten the setting time? ............................................................................ 1358.1 Introduction ........................................................................................................................ 1358.2 Material and methods: ....................................................................................................... 137

8.2.1 Determination of PSD ................................................................................................ 1388.2.2 Indentation testing ..................................................................................................... 1388.2.3 Rheology testing ........................................................................................................ 138

8.3 Results ............................................................................................................................... 1398.3.1 PSDs: ......................................................................................................................... 139

8.3.2 Indentation setting times ............................................................................................ 1408.3.3 Rheological testing .................................................................................................... 140

8.4 Discussion ......................................................................................................................... 142

8.5 Conclusion ......................................................................................................................... 143

Chapter 9 Can the rheological method of setting time assessment be used for

other cements? ............................................................................................................... 1459.1 Introduction ........................................................................................................................ 1459.2 Materials and methods ...................................................................................................... 148

9.2.1 Sample Preparation ................................................................................................... 1489.2.2 Rheological testing .................................................................................................... 148

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9.3 Results ............................................................................................................................... 149

9.4 Discussion ......................................................................................................................... 1529.5 Conclusions ....................................................................................................................... 154

Chapter 10 General Discussion ................................................................................... 156

Chapter 11 Clinical Implication Summary .................................................................. 16211.1 Chapter 1 Literature Review .............................................................................................. 16211.2 Chapter 2 Use of MTA in paediatric dentistry .................................................................... 163

11.3 Chapter 3 Use of MTA in endodontics ............................................................................... 16311.4 Chapter 4 Particle size of MTA .......................................................................................... 163

11.5 Chapter 5 What constitutes the PSD of MTA .................................................................... 16311.6 Chapter 6 Correlation of particle size with setting time ..................................................... 16311.7 Chapter 7 Strength and particle size ................................................................................. 163

11.8 Chapter 8 How is the setting time measured? ................................................................... 16411.9 Rheology for other cements ............................................................................................... 164

Chapter 12 Conclusions ............................................................................................... 164

Chapter 13 References ................................................................................................. 167

Chapter 14 Appendix .................................................................................................... 209

List of Figures

Figure 1 Flow of literature review and surveys with corresponding chapters .................................... 3Figure 2 Flow of experiments and corresponding chapters .............................................................. 5Figure 1-1 pH of setting MTA .......................................................................................................... 36

Figure 1-2 Applications of MTA ....................................................................................................... 45Figure 2-1 Proportions of clinicians who perform IPC ..................................................................... 73

Figure 2-2 Proportions of clinicians who perform DPC ................................................................... 74Figure 2-3 Proportions of clinicians who perform DPCs .................................................................. 74

xxvii

Figure 4-1 PSD of MTA-P (above) and MTA-A (below) when fresh and 2 y after having the

packaging opened ................................................................................................................... 97Figure 4-2 BSE imaging of MTA-P. ................................................................................................. 98Figure 5-1 Normalised PSD for BO and three PC samples of differing size ................................. 104

Figure 5-2 PSD of MTA-P (upper) and MTA-A (lower) and the associated deconvoluted

components ........................................................................................................................... 105

Figure 5-3 SEM of MTA-P (left) and MTA-A (right) ....................................................................... 106Figure 6-1 Setting time versus D90 of MTA .................................................................................. 118

Figure 6-2 Setting times and cumulative heat release versus particle size of PC ......................... 119Figure 7-1 Effect of curing conditions on the physical properties on MTA .................................... 128Figure 7-2 Influence of particle size and time on the physical properties of MTA, when stored in

PBS ....................................................................................................................................... 130Figure 8-1 G', G" and their ratio (tan_delta) .................................................................................. 141

Figure 9-1 G' of tested dental cements ......................................................................................... 150Figure 10-1 Summary of literature review ..................................................................................... 156Figure 10-2 Summary of surveys on MTA usage .......................................................................... 157

Figure 10-3 Summary of PSD of MTA studies .............................................................................. 159

List of Tables

Table 1-1 PubMed keyword search results and comparisons with this thesis - reviews ................... 6

Table 1-2 PubMed keyword search results and comparisons with this thesis - surveys ................... 7Table 1-3 PubMed keyword search results and comparisons with this thesis – particle size ........... 8

Table 1-4 PubMed keyword search results and comparisons with this thesis - rheology ................. 9Table 1-5 Examples of reactions of various HDCs with water

72 ...................................................... 15

Table 1-6 Commercial packable HDCs - permanent restoratives (Part 1, A-I) ............................... 16

Table 1-7 Commercial packable HDCs - permanent restoratives (Part 2, I-T) ................................ 17Table 1-8 Commercial packable HDCs - intermediate restoratives ................................................ 19

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Table 1-9 Possible categorisation of obturation to supersede 'Endodontic filling / sealing material'.

................................................................................................................................................. 19Table 1-10 Commercial HDCs - endodontic sealers ....................................................................... 20Table 1-11 Clinical Techniques that influence MTA's properties ..................................................... 31

Table 1-12 Radiopacity of ProRoot MTA and dental structures ...................................................... 32Table 1-13 Radiopacity of MTAs with different radiopacifiers (20% w/w) ....................................... 33

Table 1-14 A comparison of MTA with CH products ....................................................................... 35Table 1-15 Comparison of MTA-P with Biodentine ......................................................................... 38

Table 1-16 Comparison of MTA-P with iRoot BP ............................................................................ 39Table 1-17 Comparison of BioRoot RCS with AH Plus ................................................................... 40Table 1-18 Comparison of AH Plus and TotalFill Sealer ................................................................. 41

Table 1-19 Comparison of AH Plus and ProRoot MTA ES ............................................................. 41Table 1-20 Comparison of AH Plus and MTA Fillapex .................................................................... 42

Table 1-21 Comparative summary of popular MTA and 'MTA-like' products .................................. 43Table 1-22 Comparison of MTA-P with Bioaggregate / DiaRoot ..................................................... 44Table 1-23 Properties of root-end fillings ........................................................................................ 47

Table 1-24 Properties of MTA restoratives and sealers after mixing .............................................. 56Table 1-25 Non-biological properties of MTA restoratives and sealers after setting ....................... 59

Table 2-1 MTA usage and training patterns of respondents ........................................................... 72Table 2-2 Preferred materials for IPCs ............................................................................................ 75Table 2-3 Preferred materials for direct pulp capping (DPCs) ........................................................ 76

Table 2-4 Preferred materials for pulpotomies ................................................................................ 77Table 3-1 MTA usage, training and perforation repairs by GD and ED ........................................... 84

Table 3-2 Apical barrier procedures by GD and ED ........................................................................ 88Table 3-3 MTA root-end fillings and regenerative endodontics by GD and ED ............................... 90Table 4-1 PSD of MTA .................................................................................................................... 96

Table 5-1 PSD of PC and BO libraries, MTA-P and MTA-A .......................................................... 104Table 5-2 Energy dispersive X-ray spectroscopy of points in Figure 7-3 ...................................... 106

Table 6-1 Comparison and composition of MTA brands ............................................................... 110

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Table 6-2 Summary of setting time standards commonly encountered in dentistry and for PC .... 112

Table 6-3 Summary of PSDs of PC, MTA, their setting times and cumulative heat release ......... 116Table 7-1 PSDs of experimental cements and their constituents .................................................. 127Table 8-1 PSDs of PC, experimental MTA and bismuth oxide used to produce MTA .................. 139

Table 8-2 Indentation testing initial and final setting times ............................................................ 140Table 8-3 Plateau G’ and the time to reach 95% .......................................................................... 141

Table 9-1 Plateau G’ of various dental cements (in MPa) ............................................................. 151Table 9-2 Time to reach 90% of plateau G’ (in minutes) ............................................................... 151

Table 9-3 Comparison of marketed setting times against setting times using the time to reach 90%

of the plateau G’ .................................................................................................................... 152

List of Equations

Equation 4-1 Degree of Hydration ................................................................................................... 94

Equation 5-1 Normalised frequency at a given particle size ......................................................... 102Equation 6-1 Function of setting time with D90 ............................................................................. 117

Equation 6-2 Function of initial setting time with D90 .................................................................... 118Equation 6-3 Function of final setting time with D90 ..................................................................... 118Equation 6-4 Function of cumulative heat with D90 ...................................................................... 118

Equation 5 Formula for compressive strength ............................................................................... 125Equation 6 Formula for flexural strength ....................................................................................... 125

Appendices

Appendix 1 GMDN Registration for Hygroscopic Dental Cement ................................................. 209Appendix 2 Dental material choices for pulp therapy by ANZSPD members ................................ 210

xxx

List of Symbols and Abbreviations

a Degree of hydration

°C Degrees Celsius

μm Micrometres

AAE American Association of Endodontists

ADA 57 American Dental Association’s specification 57 for endodontic filling

materials

ADRF Australian Dental Research Foundation

ANOVA Analysis of Variance

ANZSPD Australian and New Zealand Society of Paediatric Dentistry

ASE Australian Society of Endodontology

ASTM American Society for Testing and Materials

ASTM C 191 ASTM test method for time of setting of hydraulic cement (Vicat needle)

ASTM C 266 ASTM test method for time of setting of hydraulic cement (Gillmore

needle)

ASTM C 1608 ASTM test method for chemical shrinkage of hydraulic cement

BC Bioceramic

BO Bismuth oxide

BSE Scanning electron microscopy with backscatter imaging

CH Calcium hydroxide

CHC Calcium hydroxide cement

CHX Aqueous solution containing chlorhexidine gluconate

CHP Calcium hydroxide paste

CPD Continuing professional development

CS Compressive strength

CSH Calcium silicate hydrate

D10 Particle size at the 10th percentile (smaller size)

D50 Particle size at the 50th percentile (median size)

D90 Particle size at the 90th percentile (larger size)

DPC Direct pulp cap

ED Endodontist

EDX Energy dispersive X-ray spectroscopy

EDTA Aqueous solution containing Ethylenediaminetetraacetic acid

F Normalised frequency

FeSO4 Ferric sulphate

xxxi

FC Formocresol

FS Flexural Strength

G’ Elastic modulus

G” Viscous modulus

g/L Grammes per litre

GD General dentist

GIC Glass ionomer cement

GMDN Global Medical Device Nomenclature

GP Gutta Percha

h Hour

h (J/g) Heat (Joules per gramme)

HDC Hygroscopic dental cement

Hz Hertz

IPC Indirect pulp cap

ISO International Organization for Standardization

ISO 4049 ISO for testing polymer based restorative materials

ISO 6876 ISO for testing root canal sealing materials

ISO 9917-1 ISO for testing water-based cements

ISO 13320 ISO for Particle size analysis (Laser diffraction)

ISO 15223 ISO for symbols for medical devices

k Rate constant

kg Kilogramme

kV Kilovolts

LDA Laser diffraction analysis

m Metres

M1 Experimental MTA 1 (Smaller sized particles)

M2 Experimental MTA 2 (Standard sized particles)

mm Millimetres

MPa Megapascals

MTA Mineral Trioxide Aggregate

MTA-A MTA Angelus

MTA-P ProRoot MTA

NaOCl Aqueous solution containing sodium hypochlorite

P P-value

P1 Experimental PC 1 (Smaller sized particles)

xxxii

P2 Experimental PC 2 (Standard sized particles)

PBS Phosphate buffered saline

PC Portland cement

PC1 Reference Portland cement 1



PD Paediatric dentist

PSD Particle size distribution

r Pearson’s product-moment correlation coefficient

r Radius of the particle

rad/s Radians per second

RI Refractive index

RMGIC Resin-modified glass ionomer cement

SEM Scanning Electron Microscopy

t (h) Setting time (hours)

UQ University of Queensland

UK United Kingdom

USA United States of America

w/w Percentage by mass (“weight-weight percentage”)

ZO Zirconium oxide

ZOE Zinc oxide eugenol cement

xxxiii

List of dental materials described in the thesis

Hygroscopic Dental Cements

Product (Supplier, City, Country) Page

Apatite Root Sealer I (Dentsply Sirona, York, USA) 20

Apatite Root Sealer II (Dentsply Sirona, York, USA) 20

Apatite Root Sealer III (Dentsply Sirona, York, USA) 20

iRoot® BP (Innovative Bioceramix Inc. Vancouver, Canada) 16

EndoSequence® RRM (Putty) see iRoot BP

EndoSequence® RRM Fast Set (Syringe Putty) see iRoot FS

TotalFill® RRM (Putty) see iRoot BP

TotalFill® RRM Fast Set (Syringe Putty) see iRoot FS

BioAggregate® (Innovative Bioceramix Inc, Vancouver, Canada) 16

Biodentine® (Septodont, Saint-Maur-des-Fossés, France) 16

BioRootTM

(Septodont, Saint-Maur-des-Fossés, France) 20

CEM Cement® (BioniqueDent, Tehran, Iran) 16

CavitTM

(3M, St Paul, USA) 19

CavitTM

G (3M, St Paul, USA) 19

CavitTM

W (3M, St Paul, USA) 19

Coltosol® F (Coltene, Altstätten, Switzerland) 19

DiaRoot® BioAggregate see BioAggregate

DuoTEMP® (Coltene, Altstätten, Switzerland) 19

Endobinder® (Binderware, São Carlos, Brazil) 12

Endocem MTA (Maruchi, Wonju-si, South Korea) 16

Endocem Zr (Maruchi, Wonju-si, South Korea) 16

EndoCPM Sealer (EGEO Dental, Buenos Aires, Argentina) 20

Endoseal (Maruchi, Wonju-si, South Korea) 20

EndoSeal MTA (Maruchi, Wonju-si, South Korea) 20

EndoSequence® BC RRMTM

see iRoot BP

EndoSequence® BC RRM Fast Set PuttyTM

see iRoot FS

EndoSequence® BC SealerTM

see iRoot SP

Grey MTA Plus® (Avalon Biomed, Houston, USA) 16

Harvard MTA Universal OptiCaps® (Harvard Dental International GmbH, Hoppergarten,

Germany) 16

Harvard MTA XR Fast OptiCaps® (Harvard Dental International GmbH, Hoppergarten,

Germany) 16

xxxiv

Harvard MTA XR Flow EWT OptiCaps® Harvard Dental International GmbH,

Hoppergarten, Germany) 16

Harvard MTA XR Flow Fast OptiCaps® (Harvard Dental International GmbH,

Hoppergarten, Germany) 16

iRoot® BP (Innovative BioCeramix Inc, Vancouver, Canada) 16

iRoot® FS (Innovative BioCeramix Inc, Vancouver, Canada) 16

iRoot® SP (Innovative BioCeramix Inc, Vancouver, Canada) 20

MM-MTATM

(Micro-Mega, Besançon, France) 17

MTA Angelus® (Angelus, Londrina, Brazil) see MTA Angelus

ChannelsTM

MTA see MTA Angelus

MTA* Caps (Acteon, Merignac, France) 17

MTA PlusTM

(Prevest Denpro Ltd, Jammu, India) 17

MTA Repair HP (Angelus, Londrina, Brazil) 17

NeoMTA PlusTM

(Avalon Biomed, Houston, USA) 17

NuSmile® NeoMTA® See NeoMTA Plus

Ortho MTA (BioMTA, Seoul, South Korea) 17

ProRoot® ES Endo Root Canal Sealer (Dentsply Sirona, Tulsa, USA) 20

ProRoot® MTA (Dentsply Sirona, Tulsa, USA) 17

Retro MTA® (BioMTA, Seoul, South Korea) 17

Root MTA (Lotfi Research Group, Tabriz, Iran) 17

TechBioSealer Apex (Isasan, Rovello Porro, Italy) 17

TechBioSealer Endo (Isasan, Rovello Porro, Italy) 17

TechBioSealer Root End (Isasan, Rovello Porro, Italy) 17

TechBioSealer Capping (Isasan, Rovello Porro, Italy) 17

TotalFill® RRMTM

see iRoot BP

TotalFill® RRMTM

Fast Set Putty see iRoot FS

TotalFill® BC SealerTM

see iRoot SP

Trioxident (VladMiVa, Belgorod, Russia) 17

Other restoratives

Fuji VII® (GC Corporation, Tokyo, Japan) 148

Fuji VII® EP (GC Corporation, Tokyo, Japan) 148

Fuji IX® (GC Corporation, Tokyo, Japan) 148

Super EBA (Harry J Bosworth Co, Skokie, USA) 89

TheraCal LC® (Bisco, Schaumburg, USA) 12

xxxv

Other endodontic sealers

AH 26® (Dentsply DeTrey, Konstanz, Germany) 145

AH Plus JetTM

(Dentsply DeTrey, Konstanz, Germany) 145

MTA Fillapex® (Angelus, Londrina, Brazil) 12

RealSeal SE (SybronEndo, Amersfoort, Netherlands) 145

1

Introduction

MTA is an important cement that is used in endodontics and paediatric dentistry. MTA has

a prolonged setting time, which is often viewed as an undesirable but fundamental

property of the material. Hence the question can be raised, “How can the prolonged

setting time of MTA be overcome?”

This question can be answered through a series of smaller questions:

• what is MTA and why does it have a long setting time?

• what is known about the properties of MTA and how does it correlate to the clinic?

• based on the scientific information regarding its composition, how should clinicians

use MTA to optimize its handling and physical properties?

• how do clinicians (such as general dentists (GDs), paediatric dentists (PDs) and

endodontists (EDs) use MTA?

• what is the particle size of MTA, and what factors influence this?

• how does particle size influence the setting time of MTA?

• how is setting time measured? Are these methods relevant to its clinical use?

• can a rheological method of assessing setting time provide information on the

product and other dental cements? And

• what are the implications of changing particle size in terms of the physical

properties of the set cement?

The properties of MTA were first assessed through a literature review, which explored the

composition and properties of the cement with those of similar cements. From this, it was

evident that components found commonly in industrial cements, i.e. calcium silicates and

calcium aluminates from Portland cement (PC), had a dominant influence on its properties.

In attempts to provide dentists with quicker setting MTA cements, variations on this

material have emerged that claim to be light-cured MTA, but are in fact resins with

superfluous inclusions of MTA. Furthermore, injectable and packable cements have

appeared, which are cements mixed with thickening agents.

A review of the published literature on the properties of MTA and MTA variants was

undertaken, and methods used to test their properties. Most of these methods are based

on tests for GICs or endodontic sealers. Many of the tests in the literature have been

2

modified from the standard tests stipulated by the International Organization for

Standardization (ISO). The tests results obtained for MTA and some MTA variants are

inconsistent, even within studies. This has complicated meaningful comparison of how the

properties differ between products.

Two reviews were performed on the handling features and properties of MTA, exploring

how various clinical procedures and manipulations influence the setting of MTA.

Contamination from acids, medicaments and blood can retard the setting of MTA, which

then raises various methods to mitigate these issues. MTA can, in fact, be ‘wet’ cured,

where a glass ionomer cement (GIC) or resin is carefully placed within 10 minutes above

MTA, enabling the tooth to be restored in one visit. The minimum time period of time of 10

minutes is a parameter that was examined in subsequent studies.

Surveys of dental specialists (PDs and EDs) were performed. These showed which

procedures MTA was the material of choice for root-end fillings, apical barrier placement,

perforation repair and pulp regeneration. Although many PDs use MTA, this material is

often restricted to pulpotomies. It was evident in both specialist cohorts that most

specialists learnt how to handle MTA through continuing education development courses,

yet they wish for more practical education focused on its clinical handling.

The figure below illustrates the logical flow for the chapters relating to the general

literature, and how these are linked to the surveys of MTA usage in clinical practice.

3

Figure 1 Flow of literature review and surveys with corresponding chapters

In a series of laboratory studies, the correlations between indentation-based setting time

and MTA particle size were determined. This involved comparing the marketed indentation

setting times of various commercial MTA products against results from analysis of the

particle size using LDA. Of note, the largest particles of the cement (D90) were found to

have the greatest influence on the setting time, and reductions in this size parameter have

accelerated setting reactions. The D90 value for PC showed a stronger correlation to

particle size than did the D90 value for MTA, indicating that commercial MTA cements

contain other ingredients that influence the setting time.

The PSDs within MTA were further analysed via mathematical deconvolution of PSD,

using the non-linear least-squares fit method. This also established the PSDs and

contributions of the respective ingredients of 80% PC and 20% BO. These respective

distributions are important as there is a dynamic relationship between the setting of the PC

4

in the hydration of MTA, and in the impediment of setting from the radiopaque filler

particles of BO. The slowed setting rate involving interactions of PC and BO was studied

further through the use of setting time tests, using indentation and rheology. This involved

testing the setting of samples of PC and comparing these against samples of PC mixed

with BO. It was found that smaller PSDs of PC resulted in faster setting reactions.

However, the inclusion of BO slowed the setting time.

The use of rheology illustrated that accelerated setting is expected via the quicker growth

of the elastic modulus (G’). However, smaller particle sizes did not result in significant

increases in the final G’. A similar finding was found with the testing of the CS of MTA,

whereby the final strengths were not significantly different between samples with finer

versus larger particles.

The use of rheology to test the setting time of other dental cements has been explored in

this thesis because there is a gap in the literature assessing the change of the flow

properties of a material over time as a means to express its setting rate. The results

illustrate the differences in setting time of MTA against other endodontic and restorative

cements. This method provides greater meaning to the understanding of setting reactions

than traditional indentation tests that are based on arbitrary weights. Current tests are

somewhat arbitrary with little clinical correlation to the properties of the material. Future

studies will enable clinicians to have a better understanding of setting times and rates.

The figure below illustrates the logical flow of the chapters relating to MTA particle size:

5

Figure 2 Flow of experiments and corresponding chapters

Although MTA has a prolonged setting time, various clinical procedures can be considered

and utilised to optimise its properties to overcome the difficulties associated with a delayed

setting process. Chemical additives have been considered. However, using these may

compromise the performance of the material. A reduction of particle size, particularly of its

90th percentile (i.e., the larger sizes) will result in an accelerated set. However, this does

not give any long-term advantages or disadvantages in terms of physical properties.

Future research on modifying the radiopaque agent would be of value to improve the

mechanical properties of the set MTA cement.

6

Chapter 1 Literature Review

1.1 Introduction

Chapter 1 of this thesis incorporates several published articles, each of which reviews

the existing literature on a specific aspect of MTA in detail.

The tables below summarise the PubMed findings of relevant terms

and the gaps in the literature. These gaps are addressed in chapters that have been

cross-referenced.

“Mineral trioxide aggregate” AND “Nomenclature”

Findings: No relevant publications with these two terms.

Comments: Although literature exists suggesting particular terms that could supersede ‘MTA’, and

some have tried to list ingredients of commercial products, none have tried to objectively compare

multiple cements by their compositions.

*Refer to Subchapter 1.2 on page 6 for further detail.

“Mineral trioxide aggregate” AND “clinical” AND “manipulation” AND “Review”

Findings: Rao1 reviewed MTA with a focus on manipulation of MTA for paediatric usage.

Comments: While there has been one review on how MTA is handled in paediatric dentistry, there have

been no reviews on the clinical use of MTA in general dentistry and endodontic practice.

*Refer to Subchapter 1.3 on page 25 and Subchapter 1.4 on page 32 for further detail.

“Mineral trioxide aggregate” AND “flow” OR “working time” OR “setting time” OR “film

thickness” OR “dimensional change” OR “solubility” OR “radiopacity” OR “compressive

strength” OR “acid erosion” OR “arsenic” OR “lead” OR “genotoxicity” OR “cytotoxicity” OR

implantation”.

Comments: There are multiples studies that report testing the properties of MTA. These studies

typically utilise ISO 9917.1,2 ISO 6876

3 and ISO 10993.

4 Many of these tests are benchtop tests which

have poor correlation to the clinical situation.

*Refer to Subchapter 1.5 on page 51 for further detail.

Table 1-1 PubMed keyword search results and comparisons with this thesis - reviews

7

“Mineral trioxide aggregate” AND “survey” and “paediatric

Findings: Walker5 surveyed the use of MTA, FC and FS in postgraduate programmes. Kathariya

6

surveyed the use of NiTi and endodontic microscopes in paediatric dentistry. Foley7 surveyed the

usage of MTA by postgraduate paediatric dentistry students for various procedures. Pitt Ford8 surveyed

undergraduate departments on which faculty members taught the use of MTA.

Comments: These surveys examined the use of MTA within university programmes. No surveys have

assessed the use of these materials outside the university setting.

*Refer to Chapter 2 on page 69.

“Mineral trioxide aggregate” AND “survey” AND “endodontics

Findings: The study of Kathariya 6 is summarised above. Asgary

9 reported the growth in the number of

articles on MTA over time. Tanalp10

reported that MTA is not used commonly by undergraduate

students. Casella11

reviewed the properties and usage of MTA.

Comments: As with the previous point, no prior surveys have assessed the use of these materials

outside of the university setting.

*Refer to Chapter 3 on page 81 for further detail.

Table 1-2 PubMed keyword search results and comparisons with this thesis - surveys

8

“Mineral trioxide aggregate” AND “particle size”

Findings: McMichael12

showed that various MTA based sealers can penetrate into dentinal tubules.

Khan13

compared MTA-P against two experimental MTAs. Silva14

illustrated that nanoparticles of

niobium pentoxide can be used as an alternative to BO as a radiopaque agent. Saghiri showed that

smaller particle sizes of MTA increase calcium ion release. 15

Furthermore, the use of nano-sized BO

improved both the pushout and CS of MTA.16

Greater bone regeneration appears to occur with nano-

sized MTA.17

Komabayashi18

showed that MTA particles enter dentinal tubules. Particle size can be

assessed with a flow particle image analyser, with 88% of particles between 0.5 and 3 μm. MTA-P has

more smaller particles than MTA-A.19

Viapiana20

illustrated that radiopacifier particle size has a limited

effect on sealer microstructure and chemical properties. Camilleri21

showed that MTA and Biodentine

have slightly different hydration structures. Alternative radiopacifiers (silver/tin alloy and gold) can be

used to achieve high radiopacity. 22

Hwang23

showed that PC combined with BO resembles commercial

MTA cements. Asgary24

reported that white MTA-P has smaller particles than grey MTA-P.

Dammaschke25

illustrated that MTA-P and PC are not identical with regards to surface characterization.

Comments: The work of Komabayashi is the only prior research that has attempted to assess the PSD

of MTA. However, the method of assessment used was not appropriate to the range of particle sizes

found in MTA. None of the articles listed above consider the bimodal effect of having two separate

powders combined with different PSDs for each (namely of PC and BO). No past work has used

particle size analysis to explore how humidity can change the particle size of MTA.

This is reviewed in greater detail in Chapter 4 on page 93 and Chapter 5 on page 101

Although it is logical that smaller particle sizes correlates with faster setting times, this has not yet been

explored for MTA. As the particles within both MTA and PC powder have a range of particle sizes, no

past work has attempted to correlate setting time with particle size. Possible setting time parameters to

consider are the 10th percentile particle size, the median particle size and the 90

th percentile particle

size.

Refer to Chapter 6 on page 109 for greater detail.

Lastly, there is no prior research on how curing conditions, testing conditions and particle size could

alter the physical properties of MTA. This aspect has implications for how the properties of MTA are

tested.

Refer to Chapter 7 on page 122 for greater detail.

Table 1-3 PubMed keyword search results and comparisons with this thesis – particle size

9

“Mineral trioxide aggregate” AND “Rheology”

Natu26

showed that adding propylene glycol to MTA increased the setting time, flow and calcium

release, but lowered the hardness and caused greater porosity. The work of Komabayashi18

has

already been summarised above. Setbon27

showed that various MTA cements and MTA-like materials

vary in their composition. Setting time was defined as the time required to reach a CS of 8x108 Pa.

Vitti28

showed that MTA Fillapex has reduced flow, shortened working and setting times than AH Plus.

Silva29

showed that MTA Fillapex is more cytotoxic than AH Plus but has more flow. Duarte30

added

propylene glycol to MTA-A, which increased the setting time, flow, pH and calcium ion release.

Wongkornchaowalit31

showed that the addition of a polycarboxylate superplasticiser reduced the setting

time and increased the flow of MTA. Camilleri32

showed that MTA is more soluble in water than PC.

The addition of a water-soluble polymer may be required for MTA to conform to the ISO standards for

sealers.33

Bernardes34

used ADA Specification 57 to show that Sealer 26, AH Plus and MTA Obtura

(Fillapex) had flow rates greater than the specified minimum value. De Bruyne showed that all sealers

are prone to leakage. However, the seal from MTA and from gutta percha (GP) improves with time.35

Furthermore, under laboratory conditions the seal of Fuji IX GIC was superior to MTA-P.36

De-Deus37

illustrated that all hygroscopic cements allow fluid movement when assessed using a fluid filtration

leakage model. Asgary38

reported on a new endodontic cement with characteristics similar to MTA.

John39

reported similar leakage rates for Fuji Triage and MTA-P. Martin40

demonstrated that MTA

reacts with phosphate buffers to form apatites. Yatsushiro41

reported that MTA provided a superior seal

to dental amalgam.

Comments: Although there have been several studies of ‘flow’, these relate mainly to how it influences

leakage. The change in flow of a material can be used to determine the setting time of a material such

as MTA and this has not been reported previously.

Refer to Chapter 8 on page 135 and Chapter 9 on page 145 for greater detail.

Table 1-4 PubMed keyword search results and comparisons with this thesis - rheology

10

1.2 A review of hygroscopic dental cements – MTA, bioceramics and calcium

silicate cements

This subchapter is in press:

Ha WN, Kahler B, Walsh LJ. Classification and nomenclature of commercial hygroscopic

dental cements. Euro Endod J. In press 2017 (accepted 9 Sep 2017).

1.2.1 Introduction

A range of cements are used in clinical dental practice, including zinc oxide eugenol

cements (ZOE), zinc phosphate cements, polycarboxylate cements, glass ionomer

cements (GIC), and mineral trioxide aggregate (MTA) cements. The latter was introduced

by Torabinejad in the early 1990s.42

There are now many types of cement on the market

that, like MTA, use water as a major reagent in a setting process involving hydration

reactions. Such cements differ from products where water-based solutions contain ions or

compounds that react in the setting process, rather than the water itself.

The Global Medical Device Nomenclature (GMDN) is a system of internationally agreed

terms for identifying and categorising medical devices that is used by regulators,

manufacturers and healthcare systems to objectively categorise data relating to market

surveillance, adverse event reporting and other management activities.43

Under the

GMDN, the newly introduced term “hygroscopic dental cement” (HDC) refers to “a non-

sterile substance intended for professional use as a dental cement (e.g., luting agent, liner,

base, pulp-capping material) and/or direct dental restorative material whereby the majority

of the setting reaction is based on the hardening reaction of a hygroscopic inorganic

compound(s) [e.g., calcium silicates, calcium aluminates, zinc sulphate, calcium sulphate]

with water (hydration). It is available as a powder intended to be either mixed water prior to

application or react with dentinal fluid in situ. After application, this device cannot be

reused.”43

Despite increasing interest in the use of HDCs in clinical practice, many practitioners are

unsure of how the various products differ one from another. Because there is no

standardised nomenclature for describing these products, clinicians can easily become

confused. Using the term “bioceramics” for some HDCs that require water to set into a

solid form is confusing as this term also includes metal oxides and glasses used in fixed

prosthodontics.44

11

The aim of this subchapter is to review recent advancements in HDC materials to propose

an appropriate nomenclature to facilitate a better understanding of the similarities and

differences between materials. This new classification scheme describes existing products

on the global market, and can be expanded to new types of hydraulic or alkaline cements

developed. The chemical additives used to modify the cements are discussed since such

modifications have clinical implications.

1.2.2 Methods

Commercial manufacturers of HDCs were contacted requesting detailed information on the

compositions of products. Manufacturers that were unknown by the authors, unable to be

contacted, or wished to be excluded in this paper, were not included. Of these products,

their chemical compositions were searched in the PubMed search engine and compared

with information provided by the manufacturer.

1.2.3 Review

1.2.3.1 Currenttermsintheliterature

1.2.3.1.1 MTA

While the term mineral trioxide aggregate (MTA) is in common use, it has been argued by

Darvell that this has ‘no chemically-meaningful sense’.45

The origin of the term MTA is

found in the early research of Torabinejad, who invented MTA,46

rather than from the

original patent, which described “a cement composition in which, in a preferred

embodiment, the principal composition is Portland cement’ together with ‘an additive…to

render the overall cement composition radiopaque’.47

European Standard EN 197-1 defines Portland cement as consisting of “at least two-thirds

by mass of calcium silicates (3CaO·SiO2 and 2CaO·SiO2), with the remainder consisting of

aluminium- and iron-containing clinker phases and other compounds. The ratio of CaO to

SiO2 shall not be less than 2.0. The magnesium oxide content (MgO) shall not exceed

5.0% by mass.”48

Thus, combining the patent with the original research articles on MTA one could define

MTA as “Portland cement with a radiopacifier.” Under such a definition, materials such as

BiodentineTM

(Septodont, Saint Maur des Fossés, France) and BioAggregate® (Innovative

BioCeramix, Vancouver, Canada) could be included within the grouping of MTA as their

12

composition of includes calcium silicates within the range found in Portland cement as well

as radiopacifiers.49, 50

Nevertheless, there are other products that likewise contain a high

percentage of calcium silicates but are not commonly referred as MTA and indeed, show

significant differences in their properties.50

1.2.3.1.2 Bioceramics

The term “bioceramic” appears to be first mentioned when describing a related product,

BioAggregate, produced by the same manufacturer (Innovative BioCeramix).51

The term is

used on all their products and often is used to collectively refer to MTA and other HDCs,52

which is problematic. As ceramics are non-metallic inorganic materials,53

the term

ceramics encompasses practically all of the powdered components of MTA, zinc

phosphate, zinc oxide eugenol and GICs. The term ‘bioceramics’ in a dental setting refers

to prosthetic restorative materials as opposed to HDCs.53

1.2.3.1.3 Hydraulic silicate cements, calcium silicate cements, hydraulic calcium silicate

cements

There is a history of use in the literature for ‘hydraulic silicate cement’ ,54

‘calcium silicate

cement’55

and ‘hydraulic calcium silicate cement’.56

The term ‘hydraulic cement’ is a term

which originates in the engineering literature and refers to materials which reacts “under

water”, which can be extended to include GICs and related glass-based cements that set

using acid-base aqueous reactions.57

As GICs contain calcium aluminium fluorosilicate,

any of the terms ‘hydraulic silicate cement’, ‘calcium silicate cement’ or ‘hydraulic silicate

cement’ could include GICs. Changing the descriptor from ‘hydraulic’ dental cement to

‘hygroscopic’ dental cement would clarify that the material reacts with water, which would

then exclude GICs.

An excessive emphasis on calcium silicates excludes other HDCs that react directly with

water, particularly those that include calcium sulphate or calcium phosphate.

1.2.3.2 Confusionintheliterature

The ‘ideal formulation’ described within a patent is not necessarily the composition of a

final commercialised product, as ongoing research and development since the patent was

awarded may have revealed that a different composition may be preferred. Furthermore,

the protection afforded by a patent is limited to the countries where the patent has been

applied for and granted. Therefore, a product with a patent can have “copycat” products

appear in other countries where protection was not applied.

13

An example of confusion in the literature is TheraCal LC® (Bisco, Schaumburg, USA).

TheraCal LC is a cement-modified resin composite and has been referred to as a ‘light-

curable MTA cement’, when in fact, there is no light-initiated setting of the Portland

cement.58

Rather, only the resin component (polyethylene glycol dimethacrylate)

undergoes photopolymerization.59

The material is supplied as a single component, which

is applied to the tooth, in the same manner as a flowable resin. The setting reaction is

based on light-initiated cross-linking of the polyethylene glycol dimethacrylate, which is a

slightly water-soluble di-functional methacrylic monomer.58

Thus, the setting reaction

depends upon polymerization of the resin component, rather than a reaction with water,

thus excluding this material from the classification of HDCs.

Another example is MTA Fillapex® (Angelus, Londrina, Brazil) which is a two-paste

system, within one paste contains salicylate resin, fumed silica, and bismuth trioxide (as

the radiopaque agent), while the second paste contains MTA (40%), fumed silica, titanium

dioxide, and 1,3-butylene glycol disalicylate resin.60

In the setting reaction, this resin reacts

with calcium hydroxide released from the MTA. This same calcium hydroxide-based

reaction occurs in Dycal Radiopaque Calcium Hydroxide (Dentsply Sirona, USA).60, 61

Therefore, MTA Fillapex contains a HDC but its setting reaction is not specifically based

only on a reaction with water, which excludes it from being included within the HDC

grouping.

1.2.3.3 Confirmationofcompositions

Multiple studies exist assessing the compositions of HDCs. Commonly used methods are

energy dispersive x-ray spectroscopy, (EDX) X-ray powder diffraction (XRD), X-ray

fluorescence (XRF),50, 62

X-ray photoelectron spectroscopy (XPS)63

and inductively

coupled plasma-atomic emission spectroscopy (ICP-AES).27

All methods involve

measuring interactions with electromagnetic radiation, which is dependent on the elements

that are present.

The atomic composition of BioAggregate when assessed using XRF,50

, was found to be

primarily the elements oxygen, calcium, silicon, tantalum and phosphorus. Likewise, the

composition of Biodentine assessed using XRF,62

XPS,63

EDX, and ICP-AES27

all

revealed that the cement is primarily the elements oxygen, calcium, silicon, and zirconium.

Using EDX, EndoCem MTA was found to contain oxygen, calcium, silicon, aluminium and

14

bismuth.64

Likewise, using EDX EndoCem Zr was found to contain oxygen, calcium silicon,

aluminium and zirconium.64

An EDX assessment of grey MTA Plus found this to be

composed primarily of oxygen, calcium, silicon and bismuth.65

MM MTA, when assessed

using EDX66

and ICP-AES,27

was found to contain primarily oxygen, calcium, silicon,

bismuth and aluminium.

The composition of MTA Angelus has been examined using XRF,50, 62

EDX66

67

and ICP-

AES27

all of which show that the major elements present are oxygen, calcium, silicon,

bismuth and aluminium. Comparable studies of MTA Cap using EDX and ICP-AES27

found

oxygen, calcium, silicon, tungsten and aluminium as major component elements. Likewise,

studies of Neo MTA Plus using EDX also revealed oxygen, calcium, silicon and tantalum.65

Finally, the composition of ProRoot MTA, when assessed using EDX,64, 66, 68

XRD,13

XPS63

and ICP-AES27

has been found to be primarily the elements oxygen, calcium silicon,

aluminium and bismuth, while BioRoot RCS, when examined using EDX,69

was found to

contain primarily calcium, silicon and zirconium.

For the above analyses, it must be emphasized that the all listed elements are present as

compounds, rather than as the pure element. Calcium is generally present as calcium

silicates, aluminium as calcium aluminate, bismuth as bismuth oxide, zirconia as zirconium

oxide, tantalum as tantalum oxide, and tungsten as calcium tungstate. This has been

confirmed by communications with the manufacturers. Furthermore, XRD studies have

revealed the presence of different types of calcium silicates, aluminates and

radiopacifiers.13, 21, 27, 50, 66-68, 70

One study has utilised Rietveld refinement to determine

the quantities of these components.71

Moreover, some cements contain organic additives,

such as polycarboxylic acid in Biodentine. Such organic additives can be identified with

XPS, but their precise composition cannot be identified.63

For many commercial HDCs, there is no published literature on their composition. For

products where there is some published data, not all components have been recorded or

their presence verified. This is particularly the case when organic additives are present.

15

1.2.3.4 Hygroscopicdentalcementclassifications

The definition of HDCs includes both products with calcium silicates as well as others

where components react with water to produce crystalline solid structures, ‘hydrates’.

Some examples of components in HDCs are given in Table 1-5.

HDC reactants Products

Calcium silicates

2(CaO)3SiO2 + 7H2O

2(CaO)2SiO2 +5H2O

(CaO)3(SiO2)2•4H2O + 3Ca(OH)2

(CaO)3(SiO2)2•4H2O + Ca(OH)2

Calcium aluminate

2(CaO)3Al2O3 + 21H2O

2(CaO)3Al2O3•6(H2O) + 9H2O

Calcium phosphates

3Ca4•(PO4)2•O + 2H2O

Ca10•(PO4)6•(OH)2 + Ca(OH)2

Calcium sulphates

CaSO4•1/2H2O +

3/2H2O

CaSO4•2H2O

Zinc sulphate & Zinc

oxide

ZnSO4•H2O+ZnO

ZnSO4+ZnO+H2O

Zn2(OH)2SO4

Zn2(OH)2SO4

Table 1-5 Examples of reactions of various HDCs with water72

*This list details the most common HDC reactions. However, there are other reactions. Furthermore, when

multiple HDC ingredients are present in a material, reactions may occur between the HDCs and not just with

the water.

Table 1-6 and Table 1-7 summarises confirmed compositions of commercially available

packable hygroscopic dental cements that are likely to be included under the GMDN term

for HDCs. Grey and white formulations within brands are not listed as separate entities as

their compositions are generally the same, albeit with different levels of iron and

aluminium.68

16

Table 1-6 Commercial packable HDCs - permanent restoratives (Part 1, A-I)

? The manufacturer withheld information, as it was commercial-in-confidence.

Other additives may be present but may not be included here if the manufacturer withheld information, or if

no other product featured the same additive.

17

Table 1-7 Commercial packable HDCs - permanent restoratives (Part 2, I-T)

? The manufacturer withheld information, as it was commercial-in-confidence.

Other additives may be present but may not be included here if the manufacturer withheld information, or if

no other product featured the same additive.

18

Most current HDCs are hybrid materials. For example, for MTA cements, the Portland

cement component, which constitutes 80% of the material, contains both calcium silicate

and calcium aluminate.42

Most hybrid cements are often predominately one particular type

of HDC, particularly calcium silicate cements.54

Calcium sulphate, in the form of

CaSO4•1/2H2O (gypsum), although a commonly used a cement in the form of dental

plaster, is found mixed within other HDCs. This is illustrated in Table 1-6 and Table 1-7.

Table 1-6 and Table 1-7 list the commercial packable HDC permanent restoratives. It is

evident that the commercial products contain calcium silicates. However, this does not

mean that calcium silicate is a mandatory ingredient. For example, calcium sulphate

cements that are used for bone augmentation procedures can also be used for pulp

therapy.72

These products have not been included here as the use of a bone graft material

for pulp therapy is ‘off-label’ and further research is required. Also, EndoBinder®

(Binderware, São Carlos, Brazil) is a calcium aluminate cement with no calcium silicates,

and is a permanent restorative HDC but has not yet been commercialised.73

Table 1-8 lists the commercial packable HDC intermediate restoratives. These cements

comprised of mixtures of zinc oxide and zinc sulphate.

The GMDN currently has dental restorative materials divided into subcategories based on

their setting reactions. Examples include HDCs, composite resins and GICs. However, all

endodontic obturants are encompassed under one category of ‘Endodontic filling/sealing

material,’ which includes obturation cones, thermoplastic obturation materials, endodontic

sealers and root-end filling materials.

19

CommercialBrands Manufacturer CementtypeRadio-opacifier Mixingsolution

Calciumsulphates

Zincsulphate&Zincoxide

Premixedwithnon-aqueousliquid

Methacrylateresin

Coltosol®F Coltene(Altstätten,Switzerland) • • ZnO •

DuoTEMP® Coltene(Altstätten,Switzerland) • • ZnO • •

CavitTM 3MESPE(StPaul,USA) • • BaSO4 •

CavitTMG 3MESPE(StPaul,USA) • • BaSO4 •

CavitTMW 3MESPE(StPaul,USA) • • BaSO4 •

Table 1-8 Commercial packable HDCs - intermediate restoratives

Other additives may be present but may not be included here if the manufacturer withheld information or if

there was no other product featuring the same additive.

A material that falls under two GMDN codes, one of composition and one of clinical

indication, is not ideal as medical devices should only have one identifier.43

This is the

case for root-end fillings where amalgam, ethoxy benzoic acid cement, and HDC each

have their own separate GMDN term but could also fall under the descriptor for endodontic

filling/sealing materials.43

The existing GMDN term ‘Endodontic filling/sealing material’ could be replaced by

categories for dental materials based on their composition and include possible usage in

endodontics. Table 1-9 illustrates a scheme for the GMDN term ‘Endodontic filling/sealing

material’ to categorise various obturation materials. Table 1-10 lists the HDC sealers that

are commercially available.

GP (cold or thermoplasticised)

Resin obturation points

Epoxy resin sealers

Diketone resin sealers

Methacrylate sealers

CH or calcium oxide with salicylate ester sealers

HDC based sealers (see Table 6)

ZOE

GIC

Silicone (polydimethylsiloxane)

Table 1-9 Possible categorisation of obturation to supersede 'Endodontic filling / sealing material'.

20

Table 1-10 Commercial HDCs - endodontic sealers

D Discontinued, *MTA Fillapex is not viewed as a HDC but is listed here as it contains HDC components.

Other additives may be present but may not be included here if information was withheld by the

manufacturer or if there was no other product featuring the same additive.

21

1.2.3.4.1 Property modifiers

As well as differences in the composition between various subgroups of HDCs, other

modifications influence their properties. These include:

• changing the particle size distribution of the reactant powder;

• altering the radiopacifier;

• presence of chemical accelerators;

• inclusion of supplementary cementitious materials (SCMs);

• inclusion of rheological modifiers and

• the absence of mixing water.

1.2.3.4.2 PSD

Altering the particle size distribution influences handling properties and the setting time.74

The smaller the particles, the greater the surface area and thus the faster the rate of

reaction.75

More water is needed to adequately wet smaller particles.76

Altering the particle

size also influences the flow properties of the material when it is being inserted into the

tooth.77

1.2.3.4.3 Radiopacifier

Although radiopacifiers are not reagents of the hydration setting reaction, they can change

or impede the setting reaction leading to some changes to the physical properties of the

set cement.78-80

The choice of radiopacifier has other implications, including whether the

cement darkens over time or causes darkening of adjacent tooth structure, e.g. when

bismuth oxide is used.81

Different radiopacifiers provide different levels of radiopacity and

therefore radiopacity is expected to vary between products.82, 83

1.2.3.4.4 Accelerators

With MTA cements, the most common accelerant is calcium chloride, which when used at

levels up to 10% can effectively halve the initial and final setting times.84

The addition of

calcium chloride increases calcium concentration available to react to form the calcium-

silicate-hydrate structures.85

However, how the chloride ions interacts with calcium-silicate-

hydrate structures is not universally agreed.85

22

1.2.3.4.5 Supplementary cementitious materials (SCMs)

SCMs are mineral admixtures which do not in themselves react with water.86

However,

when combined with a HDC, particularly those based on Portland cement, can react with

aqueous calcium hydroxide to form compounds that will be incorporated within the hydrate

structures of the HDC.86

The reaction of the aqueous calcium hydroxide from the pores of

Portland cement results in lower porosity and higher strengths.86

SCMs are often rich in

silica and include slag, fly ash and natural pozzolans.86

Using this approach, EndoCem

MTA has achieved a faster setting time than ProRoot MTA (Dentsply Sirona, York, USA),

but with similar handling characteristics to the latter.87

1.2.3.4.6 Aqueous Gels / Rheological modifiers

Plasticisers, also known as water reducing agents, work by bonding to the cement

particles, and applying their negative charge to the cement particles. 88

This causes the

particles to spread out more evenly when mixed with water, and as a result less water is

required to mix the cement.88

As less water is required to mix the material with water, the

set product has greater compressive strength.89

A plasticiser has been included in

Biodentine. This agent may also improve bonding to dentine and thereby increase the

resistance of the material to dislodging forces.45

Thickeners can be added to HDCs for several purposes. Adding a thickener to a cement

powder can produce a paste (e.g. for use as an endodontic sealer) or a putty (e.g. for a

restoration).90

Thickeners are typically added to the water component of the HDC, where

they alter the flow of the material when it is mixed.90

Examples of this include ProRoot

Endosealer® (Dentsply Sirona, York, USA) and EndoCPM® (EGEO Dental, Buenos Aires,

Argentina). ProRoot Endosealer powder has the same ingredients as conventional MTA,

but the water component is enriched with a water-soluble polymer.91

EndoCPM contains

Portland cement, propylene glycol alginate, propylene glycol, sodium citrate and calcium

chloride.92

In this product, the propylene glycol serves as the thickening agent because of

its ability to form intermolecular links that create a scaffold,93

while the calcium chloride

accelerates the setting reaction.84

1.2.3.4.7 Absence of mixing water

Some HDCs are supplied as a single component injectable paste with no water, and the

setting reaction requires water from the dentine to diffuse through the material to enable

the cement to set.94

Because the paste is water-free, a thickening agent is used to create

a gel-like consistency. iRoot® SP (Innovative BioCeramix, Vancouver, Canada), is

23

supplied as a single component injectable paste, which does not contain any water. A

thickening agent is used to create a gel-like consistency for the paste.94

The manufacturer

claims that the typical setting time is 4 hours, but this will extend to over 10 hours when the

material is placed in dry canals.95

Likewise, iRoot® BP (Innovative BioCeramix,

Vancouver, Canada) is the packable version and is placed without any water to then rely

upon water from an outside source (such as tooth structure surrounding the cavity

preparation) to cause the material to set.96

The current GMDN term states that the HDCs are “available as a powder intended to be

either mixed water prior to application or react with dentinal fluid in situ”. Some HDCs are

commercially available as water-free pastes that then react with the water present in

dentinal fluid once placed into the tooth. Therefore, the GMDN term should be updated to

reflect these products.

1.2.4 Clinicalandresearchconsequences

There are commercial products that are more like resins than HDCs, as well as HDCs that

are placed without first mixing them with water. Without a functional classification of these

products, clinicians would assume that all these HDCs perform identically. More research

is needed to compare the subtypes of HDCs, particularly resin and HDCs that are placed

without water.

The terms ‘bioceramic’, ‘MTA’ and ‘calcium silicate cement’ can be misleading as not all

properties are shared amongst such materials. Clinicians should be aware of the differing

compositions of cements as these differences result in variations in performance.

Differences in the choice of radiopacifer and its percentage composition can result in

significant differences in radiopacity.

1.2.5 Conclusions

HDCs, particularly those involving calcium silicates, have become an integral part of

clinical practice, including endodontics and restorative dentistry. Some HDCs have then

been modified to create variants, which are either flowable, for use as an endodontic

sealer or highly viscous and putty-like for packing into defects.

While there is a growing body of evidence supporting the use of HDCs, much of the

existing literature relates to the original ProRoot MTA composition, and the data from this

cannot simply be extrapolated to all HDCs, because of the influence of changes in

24

composition. One cannot simply assume equivalence even between HDCs of the same

type (such as MTA) because of variations in particle size distribution, thickeners,

accelerants and other components that can affect handling properties and setting

reactions.

There is a growing body of evidence supporting the use of HDC. However, most of this

relates to the original ProRoot MTA composition. As some HDCs can be more different

than others, care should be considered when assuming equivalence between products.

Unlike the restorative cements, the existing GMDN scheme groups all endodontic

obturation materials under the same term. The creation of separate terms based on

material composition will improve the understanding of products that have similar

compositions and uses, and better distinguish these from those with contrasting

compositions.

25

1.3 Review of the placement of cements in the construction industry

This subchapter has been published as:

Ha WN, Kahler B, Walsh LJ. Clinical manipulation of mineral trioxide aggregate: Lessons

from the construction industry and their relevance to clinical practice. J Can Dent Assoc

2015;81:f4.

1.3.1 Introduction

The use of MTA as a dental material has become popular, despite its high cost. A typical

MTA cement contains 80% PC, to which is added 20% BO to make the material

radiopaque so it can easily be identified on dental radiographs. Although MTA has become

a well-recognised material in endodontics, restorative dentistry and paediatric dentistry,

training in its use is not common outside postgraduate continuing education courses and

endodontic specialist training programmes. Despite the accepted indications for its use in

the primary dentition, MTA techniques are not taught universally at dental schools, with the

greatest barrier being its high cost.10, 97

Thus, information on handling and use is limited to

the supplied instructions for use prepared by the manufacturer and to various published

case reports.8

Although case reports and clinical trials guide clinicians as to where MTA can be used,

they do not provide practical information on the rationale for the individual steps used to

manipulate the material and how these steps affect clinical success. Because MTA is

primarily PC, it is insightful to assess literature related to the use of PC in the construction

industry to identify key factors that relate to performance to draw parallels between them

and clinical practice.

1.3.2 Waterandthesettingreaction

In the construction industry, PC is commonly combined with sand or gravel and water to

produce concrete. The sand or gravel filler, which is termed aggregate, provides additional

strength to the final set product, making it better suited to situations where heavy loads will

be applied, such as in buildings, roads and bridges. During setting, PC reacts with the

water to form calcium silicate/aluminate hydrates (such as (CaO)3•(Al2O3)•6H2O,

(CaO)3(SiO2)2•4H2O), and CH water.

The final set cement is a crystalline structure with voids containing water and CH. Despite

appearances, the set material is not fully solid; rather there is an associated fluid state,

much like water held within in a wet sponge.98

During the setting reaction, needle-like

26

crystalline hydrates form a framework connecting all the particles together and, effectively,

turning the original powder–liquid mixture into a solid-like colloidal gel.98

If water is lost to

the atmosphere during the setting reaction, this will significantly weaken the set material.

Hence, loss of moisture while MTA is setting must be avoided.99

1.3.3 Exposureofthesetmaterialtoacids

When set cement is exposed to acids, the saturation of its contained fluids with CH is lost,

as hydroxide ions are consumed in acid–base reactions.100

This leads to loss of some of

the hydrate structure, creating a surface etching effect. A single treatment with

hydrochloric acid can be used both to clean and etch concrete, exposing the aggregate as

well as the matrix.101

Any other exposure of concrete to acidic environments is avoided.101

Likewise, exposure of MTA to strong acids will cause surface etching resulting from the

loss of CH from the set cement, as hydroxyl ions react with the acid, and consequent

dissolution of calcium silicate hydrates (CSHs).101

Fluids from the surrounding environment

may enter the cement to replace the lost CH or hydrates, depending on the ions present in

those fluids.102

1.3.4 Acidspresentatthetimeofmixing

In the construction industry, acidic water is never used in mixing concrete, because it will

cause the formation of intermediate compounds that retard hydration of the cement and

limit the production of CH.103, 104

Furthermore, acids will decompose both CSH structures

and CH. In the presence of acids, the compounds that form during setting are likely to be

more soluble; this disrupts the formation of the mesh of interlocking crystals and also

causes them to leach out of the set material.105

Before concrete is poured onto acidic soil,

a process known as chemical stabilization or soil conditioning is performed.105

The soil is

mixed with an alkaline material (such as calcium oxide or CH) and allowed to reach a

neutral pH before placement of cement.

The dental parallels to acidic soil are the presence of deep caries (indicating organic acids

in the dentine), bacteria in large numbers, such as in infected root canals (accompanied by

acidic waste products and metabolites) and inflammation, such as in periapical regions. An

acidic pH can be expected at sites of necrosis and inflammation.106

As in construction, the presence of acids in the environment where MTA is to be placed

will adversely affect the setting reaction. As the environmental pH falls from 7.4 to 4.4,

27

greater leakage can be expected at the margins of the set MTA, and its adhesion to the

tooth structure will decrease.107, 108

The micro-hardness of the set MTA is reduced and its

microstructure changes from cubic and needle-like crystals to eroded cubic crystal

structures.109

Thus, pH should be increased back to physiological normal before placing MTA. For

example, dressing the root canal of an abscessed tooth with CH for 1–2 weeks before

MTA placement will improve the properties of the set MTA.110

Moreover, in a vital tooth

undergoing apexification, a short treatment with CH can stimulate repair at the apex of the

tooth, as well as help to disinfect the canal.111, 112

It has been suggested that pretreatment with CH paste may adversely affect the sealing

ability of MTA, as it may be difficult to remove and, thus, remnants might act as a barrier to

the adaptation of MTA to the root canal walls or become involved in the MTA setting

reaction.113

The latter point is at odds with the literature from the construction industry that

advocates the use of CH to condition acidic soil. However, CH dressings used in dentistry

may contain various additives, such as methylcellulose and carboxymethylcellulose, which

are known to retard the setting of PC.114, 115

Therefore, if a dressing of CH paste is used,

extensive irrigation should be carried out to ensure that no remaining dressing material is

present, as remnants of the cellulose thickener will retard the setting of MTA.

Similarly, acidic irrigants, etching solutions and conditioners must be washed away before

MTA placement. Sodium hypochlorite (NaOCl) irrigants, which have pH values above 11,

should neutralise any remaining acids when used to rinse root canals.116

As discussed

earlier, the presence of acids can modify the hydration of MTA, resulting in the formation of

new compounds within the matrix structure that may inhibit the hydration reactions.117-119

NaOCl reacts with BO that turns the yellow powder a dark brown; therefore, the

preparation should be adequately irrigated with saline to avoid unnecessary darkening of

the MTA.81

As darkening of MTA may be expected, Belobrov and Parashos suggest that

white MTA should not be used in the aesthetic zone, rather, CH should be considered for

Cvek pulpotomies.120

1.3.5 InteractionswithEDTA

Some common irrigating solutions are not acidic (e.g., disodium edetate has a pH of 7.0–

7.4; and tetrasodium edetate has a pH up to 11.3). The issue with

28

ethylenediaminetetraacetic acid (EDTA) is not primarily the pH, but rather chelation. EDTA

has 6 potential sites for binding positively charged ions, such as metal ions. Calcium ions

are important reactants in the setting of PC and MTA. If EDTA solutions used to remove

the smear layer in endodontics are not rinsed away properly, residual EDTA will chelate

calcium ions and disturb the precipitation of hydration products during the setting

reaction.121

This explains the finding of Lee121

who found that MTA stored in EDTA

solution had no crystalline structure and a low Ca:Si molar ratio. Furthermore, EDTA-

treated MTA has been shown to have reduced micro-hardness and to be less

biocompatible, as gauged by reduced adhesion of fibroblasts, compared with MTA that

has not been treated with EDTA.121

1.3.6 Interactionswithphosphoricacid

From the above discussion, it follows that phosphoric acid used for etching should be

washed away thoroughly before MTA is placed. This situation is particularly relevant in a

deep cavity or pulp capping application, where other acids, such as organic acids from

bacteria, are also likely present. Even in small amounts, phosphoric acid will alter the MTA

setting reaction and reduce the micro-hardness of the set material.122

Thus, acid etchant

should be washed from the walls of the cavity preparation with water before MTA

placement in a deep cavity. Alternatively, MTA can be covered with a GIC before etching

of the cavity margins in the final phases of restoration placement.123

In many cases, the

easiest way to address the influence of both acid etchants and EDTA will be to irrigate or

rinse the area with water before placement of MTA.124

1.3.7 Presenceofcontaminantssuchasblood

A general principle in the construction literature is that the higher the level of chemical

impurities in the mixing water, the greater the likelihood that one or more of these

impurities will interfere with the PC setting reaction, resulting in reduced CS.125

MTA set in

the presence of blood has inferior physical properties, i.e., reduced CS, reduced micro-

hardness and less resistance to displacement.126-128

Likewise, in the presence of serum,

the MTA setting process is altered with a changed surface morphology, reduced micro-

hardness and the reaction may be retarded.129

Although MTA is often described or marketed as being able to set in a wet and possibly

bloody environment, it is important to minimise the ingress of any tissue fluids or blood into

MTA during placement or as it is setting. This is particularly important along the margins of

the preparation where leakage would occur if the MTA sets with inferior properties.

29

Clinicians should minimise a haemorrhagic contamination, as excessive blood will not only

impair vision and access but will also affect the setting reaction and the quality of the end

product. Contamination with blood has particular implications when MTA is used as a root-

end filling.

1.3.8 VariationsintheliquidcomponentofMTA

In concrete, various additives and impurities in the mixing water are known to alter the

setting reaction and affect the end product. Sodium chloride (as found in saline) and many

other inorganic and organic materials will likely result in slower setting due to the formation

of alternative products.130

Manufacturers' instructions for use of MTA typically recommend sterile or distilled water as

the liquid to be mixed with the MTA powder. For both quality control and convenience, this

is often included with the MTA powder. Although MTA powder will set if mixed with local

anaesthetic solutions, the reaction is slower and the set material has less CS.131, 132

NaOCl solutions will allow MTA to set faster than distilled water, but once again at the

expense of CS.131, 133

However, in a confined situation where the cement is placed in a

non-loading area, this would not be an issue. In many cases, the benefits of an

accelerated setting reaction, i.e., less opportunity for dislodgement and disintegration of

the restoration being placed, must be balanced carefully against reduced physical

properties.131, 133, 134

Chlorhexidine gluconate (CHX) as an alternative to sterile water is not suitable because it

completely inhibits the setting reaction of MTA.133

1.3.9 Curingofthecement

The reaction of PC with water is dynamic, and water must be retained within the cement

during curing to maintain the structure and ensure the strength of the final product. If water

is lost to evaporation, the strength of the set cement will be reduced. In the construction

industry, a range of methods are used to minimise water loss during curing, including wet

curing (e.g., sprinkling water on the cement to replace water that has evaporated) and

membrane curing (e.g., covering the cement with a water-tight membrane to prevent

evaporation).

30

In clinical practice, the technique corresponding to wet curing is to place a damp cotton

pellet on the MTA as it begins to set and leave it in place. However, if the cotton pellet is

too dry, water will be drawn out of the cement, weakening it; if the pellet is too wet and is

placed too soon, this will also weaken the cement. Using a cotton pellet also delays

completing the clinical procedure and may compromise the quality of the seal.135

Following the industry approach of membrane curing, a material, such as GIC or resin-

modified GIC (RMGIC) liner, can be placed over the MTA. Once this has been placed, the

MTA is stable in terms of water loss or gain from the surface, and the clinician can proceed

to restore the tooth or obturate the canal. This concept has been tested with white MTA-P

(Dentsply, Johnson City, USA), which has an initial setting time of 45 minutes. GIC placed

over the MTA after 45 minutes gives a shear bond strength to dentine that is the same as

waiting 72 hours.123

Therefore, there appears to be no advantage in leaving MTA to set

over a period of a few days compared to a one-visit restoration. However, there do not

appear to be any adequate studies that assess the implications of waiting less than 45

minutes before placing GIC onto MTA.

An alternative to covering MTA with GIC is to use a self-etching bonding agent system as

a waterproof layer above the material. In one study,136

after allowing 10 minutes for the

MTA to set, a bonding agent was placed without significantly affecting the final Vickers

micro-hardness or distance between the MTA and the bonding agent, compared with

waiting 1 day or 7 days before placing the bonding agent. Again, this illustrates that a

single-visit restoration with composite resin can be placed over MTA.136

1.3.10 StorageofMTA

Both PC and MTA powders are highly hygroscopic and, when exposed to the atmosphere,

will absorb moisture and begin to hydrate. Although PC can be packaged in airtight bags

and containers of appropriate size, the issue of packaging arises with MTA, as some

products are sold in multiple-use bottles. Recent research has shown that opening the

container causes changes in the particle size of the remaining MTA, which likely has

implications in terms of delayed setting and inferior resulting material. Single-use

packaging is ideal. Alternatively, airtight jars allow fewer changes in stored material.40

31

The PC setting reaction is retarded in cold temperatures. Likewise, MTA that has been

refrigerated shows a significant reduction in surface hardness, greater porosity and

leakage; therefore, refrigeration of MTA should be avoided.137, 138

1.3.11 Summary

This analysis of certain aspects of industrial concrete provides insight into and sound

principles for the clinical manipulation of MTA. The practical points from this discussion are

summarised in Table 1-11.

Clinical situation Recommendation

Infected (acidic) radicular structures Neutralise with CH paste and/or NaOCl

irrigation.

Restoration in the aesthetic zone Consider other materials and procedural

alternatives; e.g., CH Cvek pulpotomy in

traumatised exposures.

Endodontic medicaments present in

canal

Remove with NaOCl or saline irrigation.

Etchant, conditioners and chelating

irrigants

Neutralise with NaOCl irrigation.

Haemorrhage into prepared cavity Minimise haemorrhage.

Use of local anaesthetic solution, CHX

or saline water to mix MTA

Use distilled water.

Wet cure MTA using a damp cotton

pellet

Single-visit membrane cure using:

- GIC/RMGIC liner, but allow MTA to set for

45 minutes before application.

- Self-etching bonding agent, but allow MTA

to set for 10 minutes before application.

Storage of MTA Do not refrigerate.

Once opened, place material to be re-used in

an airtight container.

Keep sealed when not in use.

Table 1-11 Clinical Techniques that influence MTA's properties

32

1.4 The properties of MTA and how it can be manipulated

This part of the literature review explores how MTA should be used. Parts of this chapter

were published as conference proceedings for ASE-NSW, ASE-VIC and ANZCVS

seminars.

1.4.1 Aims

This subchapter aims to discuss the clinical properties of commercial brands of MTA,

specifically:

• how MTA is made and the relevance of calcium hydroxide release;

• the properties relating to antimicrobial activity, leakage and porosity, marginal

adaptation;

• an overview of the brands;

• the uses of MTA; and

• the handling of MTA.

The subsequent subchapter 1.5 on page 51 will discuss the properties of MTA as related

to standard tests found in ISO 6876 and ISO 9917.1.

1.4.2 MTAformulation

Many MTA cements are fundamentally the same, being a cement powder based on PC

that is mixed with water, and likewise their clinical outcomes are similar.74

Different

products vary in terms of particle sizes and additives, causing them to handle slightly

differently. Some cements contain zirconium compounds as radiopaque agents rather than

BO, which is expected to have a lower radiopacity since zirconium has a lower atomic

number than bismuth. Table 1-12 illustrates the difference in radiopacity of normal PC,

ProRoot MTA, dental structures as well as the international standard for radiopacity for

endodontic sealers.

Materials Radiopacity (in mm Al)

Enamel139

1.8-2.0

Dentine139

0.9-1.0

Portland cement23

0.96

International Standard for endodontic sealers (minimum)3 3.00

ProRoot MTA23

6.53

Table 1-12 Radiopacity of ProRoot MTA and dental structures

33

MTA is made by mixing two powders, 80% PC (w/w) and 20% BO (w/w). To achieve a

similar level of radiopacity using powders that may not darken as much as BO, the

following percentages of radiopacifiers can be used to replace the 20% BO: 30% ZrO2,

30% ZnO, 30% BaSO4, 10% Au or 10%Ag-Sn alloy.22, 140

Hygroscopic cements such as PC that do not have radiopacificers show a radiopacity less

than dentine.83

The addition of radiopacifiers in MTA is essential for creating a radiopacity

greater than dentine. Radiopacifiers are based on either:

• radiodensity. This is proportional to the density of the material; and

• percentage of radiopacifier powder added to the cement.

Table 1-13 illustrates the differences in radiopacity when 20% (w/w) radiopacifier is

combined to PC to produce MTA.

Substance Density

(mg/cm3)

Radiopacity

(mm Al)141

Radiopacity

(mm Al)82

Radiopacity

(mm Al)83

100% PC 3.15 0.75 1.69 1.01

ProRoot MTA 3.65 5.72

Radiopacifier When 20% radiopacifier is combined with

80% PC

Bismuth oxide 8.90 3.71 5.88 5.93

Tantalum oxide 8.20 2.78

Bismuth

carbonate

6.86 3.25

Calcium

tungstate

6.06 3.11

Zirconium oxide 5.68 3.87 3.41

Zinc oxide 5.61 2.65

Barium sulphate 4.50 1.48 2.35 2.80

Iodoform 4.02 3.50 4.24

Table 1-13 Radiopacity of MTAs with different radiopacifiers (20% w/w)

The findings of one study of radiopacity cannot be reliably compared with another study,

as the method of mixing, properties of the aluminium step wedge, exposure settings and

assessment of radiopacity can influence the results. Nevertheless, there is a general trend

that the higher the density of a material, the higher the radiopacity. In the case of MTA-P,

radiopacity can vary from 2.5142

to 6.523

mm Al. This can be due to the differences in how

studies place the MTA, i.e. packing123

and the water-powder ratio.143

34

Radiopacifiers are not directly involved in the setting reaction. However, their inclusion can

be described as a steric hindrance. Therefore, their inclusion results in detriment to the

CS, prolongs setting time and increases solubility.79, 80, 144, 145

HDCs that opt to use alternative radiopacifiers to BO may either have a substantially

higher proportion of radiopacifier in their efforts to be as radiopaque as MTA-P, or may not

be as radiopaque as MTA-P.

While it may be said that MTA could be substituted with Portland cement,146

clinicians

should be wary about such comparisons as they imply that industrial concrete can be used

in teeth. In Australia, chemicals that are supplied for use in the prevention and treatment of

diseases must be registered by the Therapeutic Good Administration, which has functions

that parallel those of the United States Food and Drug Administration. There are studies in

both animals and humans illustrating comparative positive results for MTA and PC when

used for dental treatment.147, 148

Despite these findings, health care device regulations will

not allow an industrial product that contains a variable number and amount of heavy metal

contaminants to be used for medical purposes. Furthermore, PC is not radiopaque and

therefore fails radiopacity standards for dental restorative materials.

1.4.3 CH&MTA

CH paste (CHP) is a “gold standard” material for endodontic antibacterial medication. Its

main antibacterial effects are due to its alkaline pH. It takes 7 days for CHP, supplied at a

pH 12, to elevate the pH in the surrounding dentine from neutral to a pH of 9, a point

where the growth of some bacteria is inhibited.149

CH resin-cements (CHC) do not release CH,60

rather they consume it in their setting

reaction. Their pH when set is therefore less than the other CH products that do not

consume CH in their setting reaction.150

Table 1-14 compares MTA with CHP and CHC.

35

Properties CHP151

CHC61, 152

MTA122, 153

Brands Calcipulp, Pulpdent,

Calyxl

Dycal, MTA

Fillapex, Life

ProRoot MTA, MTA

Angelus

Key / Majority

Reactants:

As below Butylene glycol

disalicylate(l) +

Ca(OH)2(s)

2(CaO)3(SiO2) (s) +

2(CaO)2(SiO2) (s)

+12H2O(l)

Key / Majority

Products:

Ca+

(aq) + 2OH-(aq) +

Gel-like thickening

agent

(e.g. methylcellulose)

Calcium

disalicylate(S) +

2H2O(l)

2[(CaO)3(SiO2)2•4H2O]

(s) + 4Ca+

(aq) + 8OH-(aq)

State &

Handling

Paste Thick paste that

solidifies into

flaky cement

Hard paste that

solidifies into rock-like

cement

Immediate pH: 12.5 9-10 12.5

Antibacterial

effect

Strong Mild Strong

Long term

state:

Soluble Semi-soluble Insoluble

Clinical

indication

Therapeutic dressing Liner Permanent restoration

Table 1-14 A comparison of MTA with CH products

1.4.4 pHandCalciumhydroxiderelease

The alkalinity of MTA when mixed, and hence Ca2+

and OH- release, is notable over 1-2

days.154

After this time period, the alkalinity is below antimicrobial effects and also

corresponds to its increase in cytotoxicity.155, 156

This change in pH is illustrated in Figure

1-1.

36

Figure 1-1 pH of setting MTA

1.4.5 Clinicalproperties

1.4.5.1 Marginaladaptation

A study by Shokouhinejad on the marginal adaptation of ProRoot MTA, iRoot BP and

iRoot FS in simulated root end fillings illustrated that, longitudinally, the iRoot FS had

larger gaps.157

The authors of this study believe that difference lies in the fact that iRoot

BP and MTA can be gently compacted to reduce voids while the iRoot FS cannot be

compacted as it’s applied by a syringe.157

1.4.5.2 Bacterialleakagestudy

The bacterial leakage model appears to be the most clinically relevant method of

assessing the quality of the seal.158

A study by Hirschberg compared MTA and bioceramic

putty as root-end fillings in extracted teeth with no orthograde obturation.159

After 28 days

from exposure to introduced E faecalis culture, 20% of MTA samples permitted bacterial

leakage past the apex while 93% of bioceramic putty samples permitted bacterial leakage

past the apex.159

MTA has a median leakage time of 90 days.160

This study by Hirschberg159

is notable when comparing with studies that illustrate no

difference as other studies include greater setting times for iRoot BP and the placement of

gutta percha coronal to the root end filling.161, 162

The greater setting time will improve the

37

setting and hence the seal of the iRoot BP. The placement of gutta percha in a leakage

study can also improve the overall seal. Therefore, these two changes will increase the

likelihood that an overall difference will not be found between MTA and iRoot BP.

1.4.5.3 Antimicrobialeffects

For a material to provide such biological effects normally requires something be released

from the material. For example, if CH is being released, then the cement should be losing

mass over time. This could result in a compromised seal. The exception is that some

materials (e.g. MTA) may also absorb ions and hence their overall mass is not reduced.163

Against E. faecalis, when immediately placed, MTA and the iRoot BP had similar

antibacterial activity.155

As the material is given time to set, the antimicrobial activity

reduces and begins to match the negative control.

This is similar with Candida albicans, albeit with milder activity.155

This corresponds to the

setting time and cytotoxicity of the cements. If a material has set, there should be no

appreciable calcium hydroxide release and therefore no antibacterial nor cytotoxic effects.

1.4.6 CommercialbrandsofMTA

1.4.6.1 MTA-P

MTA-P is provided as sachets that are intended to be single-use only. However, many

clinicians use the one sachet multiple times to lower the cost-per-use. This practice is

against the manufacturer’s instructions. The advertised setting time of 4 hours for this

material is based on a test where needle indentation by a force of 5 MPa is resisted.74

However, clinicians can carefully place other restorative materials above this MTA after

only 10 minutes, since at this time the MTA has reached a sufficient hardness.136

1.4.6.2 MTA-A

MTA-A is supplied in a re-sealable jar, which is easier to store for re-use than MTA-P. The

advertised setting time of 15 minutes is based on a test that involves resisting needle

indentation by a light force of only 0.3 MPa.74

It is not possible to directly compare this

setting time with that of MTA-P.

38

1.4.6.3 EndoCemMTA

EndoCem MTA is a relatively new product and studies on its performance are lacking. Its

composition is similar to MTA-P with the difference being the inclusion of pozzolans that

react with CH in the setting structure. Although this may assist in the faster setting of

EndoCem, it also results in less calcium release and less apatite formation.64

MTA-P could

be more biocompatible, while EndoCem MTA may have a shorter setting time.164

EndoCem Zr is likely to behave similarly to EndoCem MTA with the key difference of a

change in radiopacifier from BO to ZO. Therefore, less staining is expected.

1.4.6.4 Biodentine

Biodentine is supplied as a powder in a capsule with an aqueous solution that must be

poured into the capsule prior to mixing. This material sets faster than conventional MTA

cements. However, it is not hard enough to be a conventional bulk restorative material,

unlike GIC. Table 1-15 compares MTA-P with Biodentine.

ProRoot MTA Biodentine Superiority?

75% calcium silicates and

aluminates

85% calcium silicates ProRoot MTA is less

soluble49

5% gypsum 10% calcium carbonate Biodentine sets faster.49

20% bismuth oxide 5% zirconium oxide ProRoot MTA is more

radiopaque49

100% distilled water Water with 15% calcium chloride and

polycarboxylate

Biodentine has a greater

hardness49

Table 1-15 Comparison of MTA-P with Biodentine

1.4.6.5 iRootBP(TotalFillRRM)andiRootFS(TotalFillRRMFastSet))

Table 1-16 compares MTA-P with iRoot BP and iRoot FS.

39

Property MTA iRoot BP

(Putty)

iRoot FS

(Syringe)

Radiopacity Good Good* Good*

Setting time in blood165

Good Bad No studies

Cytotoxicity166

Good Good Not as good

1-3-week Skin implantation167

Good Best Worst

6-week skin implantation168

Good Good Worst

Bone implantation169

Good No studies No studies

Antimicrobial effects155

Some Some Some

Marginal adaptation157

Good Good Worst

Bacterial leakage159

Good Bad No studies

Solubility32


Dimensional change32


2-year clinical performance170

Good Good No studies

5-year clinical performance171


Table 1-16 Comparison of MTA-P with iRoot BP

*Stated by manufacturer to be comparable to ProRoot MTA and appears to seem clinically suitable

1.4.6.6 Settingtimeofpremixedputties

The premixed (waterless) putties are advertised as having faster setting times than MTA

cements that are mixed with water. This is because the putty structure provides

indentation resistance and hence the material can appear to have set earlier. However,

the putty requires diffusion of water through the apical tissues as well as the dentinal

tubules to set the putty and therefore, the setting time can be variable. Furthermore, the

more blood present, the more prolonged the setting time, which can increase the risk of

leakage.165

1.4.6.7 Stainingofpremixedputties

There are inconsistent reported findings regarding which products stain. The original grey

MTA-P was known to darken, hence the development of white, ‘tooth-coloured’ MTA-P.

This material was also found to darken somewhat over time. Caution is needed regarding

claims of products being non-staining.

Studies involving the application of sunlight and heat show that MTA-P will darken, while

Biodentine, Total Fill Sealer, Total Fill Putty and AH Plus will not.172

A likely reason why

MTA-P stains while Biodentine does not is the difference in radiopacifiers. MTA-P contains

40

bismuth oxide while Biodentine contains ZO. When radiopacifiers are excluded, PC

appears to be colour stable. However, in the presence of blood, PC will stain.173

Therefore,

it is expected that all HDCs used for root-end fillings will exhibit some level of darkening

over time.

1.4.6.8 PropertiesofHDCSealers

To turn a HDC package cement into a sealer there are two options:

• adding more mixing water; and

• having no mixing water.

Adding greater amounts of mixing water to MTA results in lower CS,174

increased

solubility, increased porosity,175

lower radiopacity and longer setting time.143

Alternatively, waterless gels can be used to turn the cement into a paste, similar to the

putties discussed in the section 1.2.3.4.7 on page 22.

1.4.6.9 BioRootRCS

BioRoot RCS is a new endodontic sealer from Septodont that uses a similar composition

to Biodentine, with modifications to enable higher flow for use as a sealer. Table 1-17

compares BioRoot RCS with AH Plus.

Property BioRoot RCS AH Plus

Voids176

More Less

Solubility177

More Less

Setting time177

324 min 612 min

Flow and film

thickness178

Less flow and thicker

consistency

Complies with ISO 6876

Table 1-17 Comparison of BioRoot RCS with AH Plus

1.4.6.10 iRootSP

iRoot SP is also known as Endosequence BC Sealer and Total Fill Sealer. The

manufacturer’s directions advise that the typical setting time is 4 hours, but this will extend

to over 10 hours when the material is placed in dry canals.179

Table 1-18 compares

TotalFill Sealer with AH Plus.

41

Property AH Plus iRoot SP

Clinical Success Commonly used in endodontic literature Case Reports

Radiopacity Better Worse180

Sealing Tests Better Worse181

Bacteriostatic Similar Similar182

Push-out Strength Better Worse183

Solubility Better

(Less soluble)

Worse184

(More soluble)

Table 1-18 Comparison of AH Plus and TotalFill Sealer

1.4.6.11 ProRootMTAES(ProRootEndoSealer)

Unfortunately, there is little other published research available for ProRoot MTA ES.

ProRoot MTA ES is mixed with water and therefore its properties may be similar to

BioRoot RCS. (Table 1-19).

Property ProRoot MTA ES AH Plus

Seal91

Similar Similar

Table 1-19 Comparison of AH Plus and ProRoot MTA ES

1.4.6.12 MTAFillapex

MTA Fillapex is essentially Dycal™ mixed with MTA powder. It is a flowable endodontic

sealer, and should not be used for endodontic repairs of teeth or for pulp therapy. It

requires water to diffuse from the dentine to cause the setting reaction, and therefore the

setting time is uncertain. Furthermore, it has higher solubility and greater cytotoxicity than

other endodontic sealers (such as AH Plus) while the long-term seal achieved can be

inferior.184-187

42

Property AH Plus MTA Fillapex

Clinical Success Many and long

studies

Lab studies and

pulp caps studies

Radiopacity Better Worse188

Film Thickness Better Worse189

Cytotoxicity Better Worse29

Bond strength Better Worse190

Antibacterial

activity

Worse Better191

Solubility Better

(Less soluble)

Worse185

(More Soluble)

Table 1-20 Comparison of AH Plus and MTA Fillapex

1.4.6.13 TheraCalLC

TheraCal LC has been marketed as having high calcium ion release and as being able to

create an alkaline pH.58, 192

However, the assays used involved placing the material into

water and measuring changes over only a few days. TheraCal LC is not mixed with water

on placement and therefore it cannot be expected to perform clinically as well as when

tested in water immersion under laboratory conditions. Compared to Vitrebond and

Ultrablend Plus, TheraCal LC has less cytotoxicity.193

However, there have been no

comparative studies on this aspect with MTA.193

43

1.4.6.14 DifferencesbetweenMTAbrandsand“MTABrands”

ProRoot

MTA

MTA Angelus Biodentine MTA

Fillapex

TheraCal

LC

What is it

really?

Portland

cement &

bismuth

oxide

Portland

cement &

bismuth oxide

Modified

PC & ZrO

Dycal &

MTA

Flowable

resin & PC

Clinical

Uses

Endodontic

repair

Endodontic

repair

Endodontic

repair

Endodontic

Sealer

Pulp caps

only

Packaging One-use

only sachets

Re-sealable jar Manually

combined,

capsule

mixed

Two-part

mixing paste

syringe

Single one

component

syringe

Setting

speed*

4 hours 15 Minutes 12 Minutes 2 hours Light Cured

Evidence

base

Very

extensive

studies

Extensive

studies.

Chemically

almost

identical to

ProRoot MTA

Mostly

small trials

and case

reports.

Promising

results

Performance

equal to or

less than

AH26

Mainly

anecdotal

and lab

studies

Cost to

buy

2 grammes

(4 sachets)

$370.51

1gramme jars

for $123

5 capsules

$92.40

Cost per

use

$92.63 for

one-use only

$26.47 for

re-using

packet

$17.57 per use $18.48 per

use

Supplier Dentsply Gunz Halas Gunz Erskine

Dental &

Amalgadent

Table 1-21 Comparative summary of popular MTA and 'MTA-like' products

Prices are in Australian Dollars.

44

1.4.6.15 Variationbetweenbrands

Many MTA cements are fundamentally the same, being a cement powder based on PC

that is mixed with water, and likewise their clinical outcomes are similar.74

Different

products vary in terms of particle sizes and additives, causing them to handle slightly

differently. Some cements contain zirconium compounds as radiopaque agents rather than

BO, which is expected to have a lower radiopacity since zirconium has a lower atomic

number than bismuth.

Changes in the composition of HDCs away from MTA can result in differences of

performance. BioAggregate, which is a HDC with compositional differences to MTA

illustrated in Table 1-6, is compared against MTA-P in Table 1-22.

Property ProRoot MTA BioAggregate / DiaRoot

Clinical Success Many and long studies Lab studies and pulp cap studies

Strength Better Worse194

Radiopacity Good No studies

Setting Time 4 hours 4 hours

Sealing Tests Good Good195

pH / Ca(OH)2 Better Worse

Solubility Better

(Less Soluble)

Worse196

(More Soluble)

Table 1-22 Comparison of MTA-P with Bioaggregate / DiaRoot

45

1.4.7 Clinicaluses

1.4.7.1 Clinicalapplications

Figure 1-2 Applications of MTA

1.4.7.2 SuccessRates

The reported success rates for MTA are 97.6% in pulp capping, 79% in pulpotomy in

permanent teeth and >95% in pulpotomy in primary teeth.197

In apical barriers the success

rate can be expected to be over 90%.198

1.4.7.3 MTAusedforpulpcapping

Pulp capping is performed for exposures of the dental pulp where the pulp is vital and not

irreversibly inflamed. Aseptic technique is mandatory and any burs used should be water-

cooled to prevent over heating of the pulp. Once the pulp is exposed using burs in a dental

handpiece, haemostasis of the pulp is achieved via a sterile cotton pellet soaked in

NaOCl. If haemostasis cannot be achieved it is likely that the area of the pulp is inflamed

and the preparation should be extended until all inflamed areas of the pulp are removed,

leading to a pulpotomy or a pulpectomy. Once this is done, MTA or CH can then be

placed.

CH has been the gold standard for pulp capping. However, this suffers from certain

problems. CH when applied in a water-based paste is soluble in oral fluids and can wash

out. It does not adhere to tooth structure and dislodges easily after placement. MTA has a

higher success rate with less pulpal inflammation and more predictable hard dentine

bridge formation than CH.199

Instead of CH, MTA can be placed, followed by a layer of

46

RMGIC over the MTA to protect it. The tooth is then etched, washed, primed, treated with

adhesive and restored with a composite resin restoration.200

1.4.7.4 MTApulpotomy

Pulpotomies are performed for deep carious exposures or exposures of the pulp where the

pulp is vital and not irreversibly inflamed. The clinical procedure is the same as that for

pulp capping, with the key difference being the removal of all tissues in the pulp

chamber.201

1.4.7.5 MTAapexificationandapicalbarrier

The larger the apex the greater the chance that the apical region of the tooth will be poorly

obturated and the more difficult it is for the clinician to length control the obturation

material. In the past, multiple appointments to dress the canals with CH were utilised,

while with MTA, this can be done in one visit.

As set MTA exerts antibacterial actions and promotes bone growth, clinicians can place

MTA at the apex of a tooth with confidence the area will be well sealed. In teeth with

apices wider than a 55 K-file (0.55 mm), and/or in situations when apical patency becomes

difficult to achieve, MTA may be used to create an apical plug of 3-5 mm thickness, before

restoring the remainder of the canal with GP or more MTA.202

1.4.7.6 MTAroot-endfillings

Apical infections that do not respond to conventional and adequate root canal therapy can

respond to apicoectomy. In this procedure, the last 3 mm of the tooth is removed along

with any pathological material, and the end of the root canal is sealed with MTA. In this

procedure, MTA is used because it has excellent sealing properties and will encourage

healing of the cementum repair around it, unlike the historical alternative of dental

amalgam.

In a survey of EDs in Australia on what was their preferred material for root-end fillings,

85.3% use MTA and 8.0% use Super EBA. Of those who use MTA, 81.5% use MTA-P and

17.3% use MTA-A. This is explained further in Chapter 3 on page 81.

1.4.7.7 Primaryidealpropertiesofroot-endfillings

The properties of a desirable root-end filling are compared in Table 1-23.

47

Material MTA IRM SuperEBA Amalgam

Success Rate ~90%203-205

~90%203

~90%204

~50%205

Biocompatibility* Best206

Mid-range206

Mid-range206

Worst206

Radiopacity as per

ISO standard3

Passable142

Passable142

Passable142

Best

Staining Darkens root120

but not likely to

stain soft tissue

Nil noted Nil noted Corrosion

products darken

oral soft tissues

Table 1-23 Properties of root-end fillings

MTA, IRM and SuperEBA have had comparable clinical success in the literature, with the

bulk of MTA clinical evidence involving MTA-P.203-205

Nevertheless, there is a preference

for MTA in root-end fillings.207

This could be attributed to its better biological properties that

would instill greater confidence with clinicians for its use.206

As already mentioned, radiopacity is an important feature of dental materials as it enables

identification of its placement and marginal integrity. This is of particular importance in

root-end filling, where cases with good radiographic density have significant higher healing

rates than those with poor density.208

1.4.7.8 Clinicaltrialsofrootendfillings

1.4.7.9 MTAvsbioceramics:

There are two randomized controlled trials comparing MTA versus bioceramic putty.

A prospective randomized controlled study illustrated that at 12 months, MTA and

bioceramic putty had statistically similar success rates, 93.1% and 94.4% respectively.209

Success rate was defined as incomplete or complete healing on PAs.

A similar study, albeit over 24 months illustrated that MTA had a success rate (incomplete

or complete healing) of 95.6% on PAs, 89.3% on CBVTs while bioceramic putties had a

success rate of 95.8% on PAs, 88.7% on CBVTs.170

MTA has shown similar success rates when the review period is extended to 3

years(88.8%)210

and 5 years (92.55%171

and 91%204

). Of interest, of the 92.55%

successful cases at 5 years, 88.1% illustrated complete healing.171

48

There are studies on the success rates of bioceramic putty past two years and no studies

on bioceramic flowable putty.

1.4.7.10 TrendsinAustralia

MTA-P is the most common MTA used in Australia, followed by MTA-A.207

Almost all EDs

in Australia use MTA, while less than half of GDs in the Australian Society of

Endodontology (ASE) use MTA.207

MTA is the material of choice used by EDs for

perforations, apexification, apicoectomy and regenerative endodontics.207

For apexifications, ED generally perform a single visit MTA barrier placement, while GDs

typically use multiple visits placing CH.207

Most EDs prefer to use NaOCl as their final irrigant prior to MTA placement.207

1.4.7.11 StainingandMTA

NaOCl will react with BO to produce a dark brown precipitate. Therefore, if MTA is used in

aesthetically important areas, the tooth should be adequately irrigated with saline to

remove any NaOCl residues, so that darkening of MTA is reduced.22

Regardless of NaOCl

use, darkening of the MTA can still be expected. Therefore, CH should be considered in

aesthetic regions where darkening of the tooth would not be acceptable.120

Furthermore,

MTA will darken in the presence of blood,211

which is expected for root-end fillings.

1.4.8 HandlingMTA

1.4.8.1 Workingtime

As MTA is mixed, water starts to evaporate from the reacting mass as well as being

consumed by the setting MTA. Therefore, the workability dramatically changes in a short

amount of time. The typical working time is 6 minutes.212

A method that extends the

working time is to cover the MTA with wet gauze so that less water will evaporate from the

setting MTA.

1.4.8.2 Mixingtechniques

Most instructions for use for these products stipulate use of 3 parts powder to 1 part water

by weight. After mixing, if the working time has elapsed, extra water can be added to make

49

the MTA workable again. MTA can be mixed on a glass slab or on a paper mixing pad.

However, paper mixing pads are flimsy, and thus spillage of the mix is more likely to occur.

To adjust the wetness of the MTA mix, two sterile cotton rolls can be kept at hand, one dry

and one wet. If the mix is dry, squeezing the wet cotton roll will gently release water into

the MTA. Alternatively, a small pipette can be used to add droplets of water. If the mixture

is too wet, the dry cotton roll can be used to soak up excess water. In an ideal mixture,

parts of the mix collected on a flat plastic instrument neither drip off nor crumble away.

1.4.8.3 MTAcarriers

Amalgam carriers and normal hand instruments can be used for placing MTA for large

restorations. Damp cotton pellets held by tweezers are easier to use for compacting MTA

than traditional condensing instruments. For smaller restorations, MTA carriers can be

used, such as the MTA Carrier, MAP MTA Carrier, or the Dovgan carrier. If excess mixed

MTA is left within a carrier at the end of an appointment, the tip is likely to become clogged

and unusable. If this occurs, the carrier can be submerged in vinegar (dilute acetic acid) to

soften the cement. Sharp-tipped instruments such as probes and K-files can be used to

remove the cement from the carrier.

1.4.8.4 Leeblock(Alsoknownas“MTAPelletFormingBlock”)

Many clinicians prefer to insert MTA into a defect in the form of blocks or pillars. One

simple way to shape MTA into such ideal pillars is to use a “Lee Block”.213

This plastic

block has bur-sized grooves. Freshly mixed MTA is placed into the grooves, and pillars of

MTA can then be lifted out from the base of each groove using a half Hollenback carver or

a spoon excavator, for insertion into the tooth. Such blocks can be purchased or self-made

using a fissure bur to create the channels. If several grooves are made and loaded with

mixed MTA the clinician can quickly insert several pillars into the tooth without interruption.

1.4.8.5 CompactingMTAintoacanal

Some clinicians use ultrasonic instruments to compress and compact MTA.214

However, if

ultrasonic instrument tips are applied for more than 2 seconds, the effect of such vibrations

may introduce porosities and disrupt the setting structure, reducing the hardness of the set

cement.215

50

1.4.8.6 Syringingbioceramicflowableputty

iRoot FS is packaged in a luer-lock syringe. The plastic syringe tip may not reach into

cavity preparations. However, the metal tips commonly used for dispensing etch can be

used and custom bent216

As the flowable putty has low viscosity, there’s a risk that it may

flow out with blood or irrigation and therefore Nasseh advocates a “lid” of normal putty

placed on top of the flowable putty.216

The lid technique, advocated by Nasseh, claims that the flowable putty and a similarly

packaged sealer are interchangeable.216

However, BC sealer (Total FillBC Sealer, iRoot

SP, Endosequence BC Sealer) is more soluble than AH Plus.184

There is no clinical

evidence to support the use of either BC flowable putty or BC sealer as a root end filling.

The syringe nature of the flowable putty has handling advantages in difficult areas.

Clinicians who don’t want to rely on the having a cavity mostly filled with flowable putty

may use a method similar to the double mix method of crown impressions. The walls and

deepest areas are lined with flowable putty. Normal putty is then placed on top, pushing

out excess flowable putty. This method can hypothetically reduce the chance of voids.

However, there is no evidence of this having a clinical advantage over the use of normal

putty or MTA.

1.4.8.7 RemovingMTAfromtoothwalls

Unset MTA can be removed from tooth cavity walls by gentle brushing using cotton pellets

or micro-brushes, by gentle irrigation with water, or by using ultrasonic instruments with

water spray. Another method is to fabricate a long absorbent brush by twisting a K-file

through a cotton roll.

1.4.9 Conclusions

The release of calcium hydroxide from MTA as the material sets contributes to the

biological properties of MTA. However, because the rate of release diminishes as the

setting reaction ends any properties relating to alkalinity are likely to diminish. Variants

from the original MTA composition have different properties. The handing of MTA is unique

amongst dental materials.

51

1.5 Review of properties and testing methodologies

This subchapter is in press:

Ha WN, Nicholson T, Kahler B, Walsh LJ. Mineral trioxide aggregate – a review of

properties and testing methodologies. Materials. In press 2017 (accepted 26 Sep 2017).

1.5.1 Introduction

Mineral Trioxide Aggregate (MTA) was first described in 1993 as a cement used for its use

in repairing lateral root perforations.217

Its composition was described as being primarily a

mixture of calcium silicates comprised of calcium oxide (CaO) (50-75% w/w) and silicon

dioxide (SiO2) (15-25% w/w).42

Calcium silicates are not particularly radiopaque, and thus

a radiopaque agent such as bismuth oxide was then added.42

Since its invention, MTA has

been tested under laboratory conditions, then in animal studies and in clinical trials.122, 153,

218 The positive results of these investigations have resulted in MTA becoming a

commonly used material in pediatric dentistry and in endodontics.207, 219

1.5.1.1 Terminology

As well as the term MTA, other words have been used to describe these types of

materials. The term ‘bioceramics’, which was originally used for a material known as

BioAggregate® (Innovative Bioceramix, Vancouver, BC, Canada) has been used for MTA-

like cements.51

Despite the differences in terminology, these cements are similar in their

elemental compositions.50, 62, 64

BioAggregate contains 38.5% calcium, 11.5% silicon and

10.6% tantalum.50

When converted to their oxide forms using element to stoichiometric

oxide conversion, the respective weights of calcium oxide and silicon dioxide would be

53.9% and 24.60%. If tantalum was removed in its oxide form from the whole sample (i.e.

12.9% of Ta2O5, leaving 87.1%), the remaining percentages would be 61.8% CaO and

28.3% SiO2. These values place the material well within the definition of MTA.

Another product that is not marketed as MTA but is chemically similar is BiodentineTM

(Septodont, Saint Maur des Fosses, France). The elemental composition in 46.3%

calcium, 9.8% silicon and 2.7% zirconium. If a similar element to stoichiometric oxide

conversion is performed, the remaining cement percentages once the radiopacifier is

removed are 67.2% CaO and 21.8% SiO2, values which again place the material within the

definition of MTA.

If one defines bioceramics as “non-metallic inorganic materials”,53

then this encompasses

the powdered components of MTA, as well as zinc phosphate, zinc oxide eugenol and

52

glass ionomer dental cements, materials which do not share many similarities at the

chemical level. Hence, this definition of bioceramics has little functional purpose and

should not be used. Nevertheless, products which claim to be either MTA or bioceramic

sealers have appeared.

MTA Fillapex® (Angelus, Londrina, Brazil) is a two-paste system. One paste contains

salicylate resin, fumed silica, and bismuth trioxide (as the radiopaque agent), while the

second paste contains MTA (40%), fumed silica, titanium dioxide, and 1,3-butylene glycol

disalicylate resin.60

Therefore, the composition is predominately salicylate resin, but with

some MTA included as an additive. It is not primarily an MTA cement. Likewise, iRoot® SP

(Innovative BioCeramix, Vancouver, Canada), is a single component injectable paste that

does not contain any water but uses a thickening agent to create a gel-like paste.94

The

lack of water for setting reaction puts this material outside the definition of MTA.

1.5.1.2 Performancetesting

A range of techniques have been used to assess the performance of MTA. The purpose of

this paper is to explore the published literature on the testing of MTA and therefore identify

key aspects of the testing methodologies used, what insights they reveal as to the

behaviour of the material, and what the limitations are of widely used international testing

standards and how these relate to clinical performance. Because the performance of MTA

is affected by the conditions used in the testing environment, significant concerns arise

when standardized testing does not represent physiological or clinical conditions.

Typical international standards (ISO) that have been used to assess the properties of MTA

comprise:

• ISO 6876, which tests the physical properties of endodontic sealers;3

• ISO 9917-1, which tests the physical properties of restorative cements;2 and

• ISO 10993 which tests the biocompatibility of medical devices.4

1.5.2 Aims

This review aims to:

• Describe the commonly used ISO tests for MTA;

• List findings from the literature on MTA using these tests;

• Identify problems with the methods used for testing MTA; and

• Suggest alternative testing methods.

53

1.5.3 Methodsandmaterials

A PubMed search was undertaken using ‘Mineral Trioxide Aggregate’ combined with the

following terms:

From testing methods for ISO 6876:

• flow;

• working time;

• setting time;

• film thickness;

• dimensional change,2 which has been removed in the latest version;

• solubility; and

• radiopacity.3

From testing methods for ISO 9917-1:

• setting time;

• compressive strength;

• acid erosion;

• acid-soluble arsenic and lead contents; and

• radiopacity.2

From testing methods for ISO 10993:

• genotoxicity, carcinogenicity and reproductive toxicity (ISO 10993-3);220

• cytotoxicity (ISO 10993-5);221

and

• local effects after implantation (ISO 10993-6).222

From the results, when multiple studies were found, studies which compared MTA

products against Super EBA (Harry J Bosworth Co, Skokie, USA), glass ionomer cement,

‘bioceramics’ or AH Plus® (Dentsply DeTrey, Konstanz, Germany) were prioritized. This

was done to enable meaningful comparison of MTA against its contemporary alternatives.

The results of each search term were reviewed, and the methodologies were considered in

light of the known properties of MTA. These properties were grouped as follows:

Properties after mixing:

• flow (ISO 6876);

• working time (ISO 6876);

• setting time (ISO 6876 and 9917-1); and

54

• film thickness (ISO 6876).

• Properties after setting:

• flow (ISO 6876);

• dimensional change (ISO 6876);

• solubility (ISO 6876); and

• radiopacity (ISO 6876 and 9917-1)

• compressive strength (ISO 9917-1);

• acid erosion (ISO 9917-1); and

• acid-soluble arsenic and lead contents (ISO 9917-1).

• genotoxicity, carcinogenicity and reproductive toxicity (ISO 10993-3);

• cytotoxicity (ISO 10993-5); and

• local effects after implantation (ISO 10993-6).

1.5.4 Results

Many of the materials that have been tested using ISO 6876 for endodontic sealers have

been indicated for use as an endodontic sealer. These products are henceforth called

‘MTA sealers’, irrespective of whether the material is marketed as an MTA or as a

bioceramic. Similarly, many materials that have been tested using ISO 9917.1 for

restorative cements are described as ‘MTA restoratives’, irrespective of whether the

material is marketed as an MTA or a bioceramic.

1.5.4.1 Propertiesaftermixing

The results of tests on MTA restoratives and MTA sealers involving properties after mixing

are summarised in Table 1-24.

1.5.4.1.1 Flow

This test involves placing sealer on the centre of a glass plate. After waiting for 180 s, a

glass plate of placed on top of the dispensed sealer. After 10 min, the diameter of the

sealer is to be measured. If the diameter is less than 17 mm, the material does not comply

with the standard.3

1.5.4.1.2 Film thickness

Sealer is placed on a glass plate. After 180 s, another glass plate is placed on top of the

sealer, with a load of 150 N.3 The load needs to compress the sealer such that it

55

completely fills the area between the glass plates. After 10 min, the distance between the

two plates is determined, to measure the thickness of the film of sealer.3

1.5.4.1.3 Working time

This test is similar to the flow test ISO 6876. Instead of delaying the compression by the

glass plates by 180 s, the cement is tested at longer time points, until the specimen

diameter is 10% less than the tested diameter at 180 s.3

1.5.4.1.4 Setting time

For MTA restoratives, cements are mixed and placed into a mould. An indentation needle

with a diameter of 1 mm and a mass of 400 g is placed gently onto the setting cement at

progressive time points. If a full circular indentation appears upon placement of the needle,

the cement is unset. If the indentation is incomplete, it is deemed as set.2

For MTA sealers, sealers are placed into ring-shaped moulds. Sealers that require

moisture to set are placed into a dental plaster mold. The mould is pre-treated by storing it

in 95% humidity for 24 h prior to placing the sealer. Sealers that do not require moisture to

set are placed into a metal mould.3

Of note, the ANSI/ADA standards for initial and final setting times resemble the ISO 6876

values for initial setting time and ISO 9917.1 for final setting time.2, 3, 74

56

Commercial

products

ISO 6876

flow (mm)

ISO 6876 film

thickness (µm)

ISO 6876

working time

(min)

ISO 6876

setting

time (min)

ISO 9917.1

setting

time (min)

MTA restoratives

BioAggregate 1260 223

Biodentine 6.5 224*

6.5 225

45-85.7

49,

223

EndoCem MTA 4 87

78 87

MTA Angelus 6.3-13.6

224,

226§ 101

226† 8.5-24.3

225, 227, 228

171-175

227, 228

ProRoot MTA 14.2 212* 6

212

2.5-165 87,

212, 229

140-284 49,

87, 229, 230

MTA sealers

BioRoot RCS 16 178* 52

178†

EndoSeal MTA 20.2 231

iRoot SP 23.1 232

22 232

>1440 232

162 232‡

or

4320-6480

233§

10080-

14400

233§

MTA Fillapex 24.9 232

23.9 232

45 232

66 232

Epoxy resin control

AH Plus 17-21.2

178,

232

15-16 178, 232

240 232

690 232

Table 1-24 Properties of MTA restoratives and sealers after mixing

* Fails ISO 6876 standard for a minimum of 17 mm;

3

† Fails ISO 6876 standard for a minimum of no greater than 50µm;

3

‡ Performed using accelerated setting conditions;

232

§ As greater amounts of water (0-9%) are provided for the setting of iRoot SP, the initial setting time

increases from 72 h to 108 h, while the final setting time decreases from 168 h to 240 h.233

1.5.4.2 Propertiesaftersetting

The results of non-biological tests on MTA restoratives and MTA sealers involving

properties after setting are summarised in Table 1-25. The results for acid erosion and

acid soluble arsenic and lead contents are not included in Table 1-25 as the studies are

few and results are highly variable. The results of non-biological results are not

summarised in a table like Table 1-25 because biological tests do not standardize precise

cell lines, location for implantation or animals tested.

1.5.4.2.1 Dimensional change (ISO 6876)

Materials are mixed and placed in polyethylene molds. Once set, they are removed from

the mold and the length measured. After storage in distilled water for 30 days at room

57

temperature, the length is re-measured. To conform with the standard, samples should not

exceed 0.1% in shrinkage or 0.1% in expansion.2

Samples that require moisture to set are mixed with 0.02 mL of water per 2 g of material

prior to placement into the mold.2 This is a ratio of 0.01 g water: 1 g powder, which does

not align with the manufacturer’s recommended ratio of 0.33 g water to 1 g powder.

Therefore, MTA cements that are placed into the mold without mixing water will be too dry.

To overcome this problem of inadequate water, in one study iRoot SP was tested by being

held between two pieces of wet cloth, located between the mold and the glass plates, prior

to immersing the mold into water.232

There are no known published results using the ISO 6876 test for dimensional change for

MTA restoratives.

As iRoot SP is highly soluble,232

the results for dimensional change are difficult to interpret

in terms of what may have happened if the cement was not given added water prior to

placement in the mold.

1.5.4.2.2 Solubility (ISO 6876)

Solubility tests for MTA are performed by placing set samples into distilled water for 24 h

to room temperature. Any residue that enters the water is then measured. To conform to

the standard, sealers should not be more soluble by more than 3% by mass.3

1.5.4.2.3 Radiopacity (ISO 6876 and ISO 9917-1)

A one mm thick sample of MTA placed beside an aluminum step wedge of steps of 0.5 or

1 mm is exposed to X-rays at 65 kV. The radiopacity of the sample is compared to the step

wedge, and the equivalent mm thickness of aluminum (mm Al) determined.2, 3

ISO 6876 specifies that sealers must be a minimum of 3 mm Al.3 ISO 9917:2007 requires

samples to be stored for no more than seven days before testing.2

1.5.4.2.4 Compressive strength (9917-1)

This test involves placing samples within moulds for only one hour prior to testing.2

However, as MTA cements take longer than one hour to set, some consider curing MTA

for 24 hours.2, 47

58

This test does not have a method (such as a gypsum mould) which requires diffused

ambient water to aid in the setting reaction.2 Therefore, MTA cements that lack mixing

water need the intentional addition of water, or otherwise they will not solidify and hence

will have no compressive strength.234

Dry-stored and dry-tested ProRoot MTA has a compressive strength of 27 MPa,235

while

the reported compressive strengths of MTA cements stored in water have reached 86.2

MPa,236

iRoot FS and iRoot BP, when stored using an accelerated setting method in a hot

water bath, have produced compressive strengths of 96 MPa and 177 MPa,

respectively.234

There are no known published results using the ISO 9917.1 test for MTA sealers.

1.5.4.2.5 Acid erosion (9917-1)

Lactic acid and sodium lactate are added to water to create a demineralizing solution with

pH of 2.74. Samples are placed into specimen holders and given 24 hr to set, then

removed and immersed in the acidic solution for 24 h. The depth of erosion is the

measured.2

There are no known published results using the ISO 9917 test for acid erosion for either

MTA restoratives or MTA sealers.

1.5.4.2.6 Acid soluble arsenic and lead contents (ISO 9917-1)

Cements are mixed and set for 24 h, then crushed into a powder. Two grams of the

powdered cement is then added to 50 mL of HCl, and allowed to stand for 16 h. The

solution is then measured for the amount of free arsenic and lead. The maximum

permitted content for arsenic and lead is 2 mg/kg and 100 mg/kg, respectively.2

One study found that both ProRoot MTA and MTA Angelus had levels of arsenic levels

higher than the safe limit specified by ISO 9917.237

This result was in contrast to another

study that reported both cements as having safe limits of arsenic.238

Yet another study

found that both ProRoot MTA and Ortho MTA (BioMTA, Seoul, Republic of Korea) had

59

safe levels of arsenic.239

Several studies have reported safe levels of lead in MTA

cements.237, 239

There are no known published results for MTA sealers.

Commercial

products

ISO 6876

dimensional

change (%)

ISO 6876

solubility

(%)

Radiopacifier(s)

ISO 6876 and

ISO 9917.1

radiopacity in

mm Al

ISO 991.1

compressive

strength

(MPa)

MTA restoratives

Bioaggregate Ta2O5 5.0-5.7 223§

16.34-29.07

223, 236

Biodentine 4.61 492

ZrO2 1.5-2.8

49, 240||,

3.3-4.1 223§

67.18-170.8

223, 225

MTA Angelus 0.82-3.7

32,

227, 228†

Bi2O3 4.5-5.96 226-228, 240

19.63-41.51

225, 227

NeoMTA Ta2O5 3.8 65

ProRoot MTA 0.30 229

1.1-1.5

32,

49, 229

Bi2O3 6.4-8.5 49, 229, 241

27 229

65-86.23 144,

236, 242¶

iRoot BP 177 234#

iRoot FS 96 234#

MTA sealers

BioRoot RCS ZrO2 8.3 178

EndoSeal MTA 0.21 231

ZrO2 9.50 231

iRoot SP 0.087 232*

2.9

232‡

20.64 184†

ZrO2 3.0-6.68

180, 231

MTA Fillapex -0.67 232

1.1 232‡

5.65-14.89

184, 226†

Bi2O3 6.5-9.4 226, 243

Epoxy resin

control

AH Plus -0.034 232

0.06-

0.28184, 232

CaWO4, ZrO2

6.9-18.4 178, 180,

231, 243

22 244

Table 1-25 Non-biological properties of MTA restoratives and sealers after setting

* In this study, the ISO test was modified to provide extra water to enable a complete set of iRoot SP.

232

† Fails ISO 6876 standard of a maximum of 3%.

3

‡ The solubility test was modified by submerging the molds into heated water, hence providing more water to

enable the complete setting.

§ Radiopacity was tested at day 1 and day 28 of immersion in Hank’s balanced salt solution;

223

|| Fails ISO 6876 standard of a minimum of 3 mm Al;

3

¶ These samples were cured in wet conditions rather than dry conditions;

144, 236, 242

# In this study, the ISO test was modified using an accelerated setting method in a hot water bath.

234

60

1.5.4.2.7 Genotoxicity and carcinogenicity (ISO 10993-3)

Genotoxicity testing is a series of in vitro and, under some circumstances, in vivo tests

involving assessment of gene mutations in bacteria, chromosomal damage in mammalian

cells, the mouse lymphoma tk assay and the mammalian cell micronucleus test for

chromosomal damage. In vivo tests can include analysis of bone marrow cells or

micronuclei in bone marrow or peripheral blood erythrocytes. For carcinogenicity, materials

are implanted into tissues and assessed for tumour development.220

Numerous tests unanimously show that ProRoot MTA and MTA Angelus cause little or no

DNA damage.245-247

MTA Fillapex has shown greater genotoxicity than MTA Angelus.248

MTA sealers have been modified from the original formulation to alter their handling

properties, by adding in various organic (carbon-based) substances. Therefore, MTA

sealers should not be assumed to give identical biological responses to the original

formulation of MTA.

1.5.4.2.8 Cytotoxicity (ISO 10993-3)

The agar diffusion test is a qualitative assessment of cytotoxicity involving culture medium

containing serum with melted agar that is compatible with mammalian cells. The specimen

is then placed in contact with one-tenth of the cell layer surface, and cytotoxicity is

determined from the cellular response after 24-72 hours.

A study by Miranda249

using a 5-point cytotoxicity grading system found that ProRoot MTA

and Angelus WMTA received grade 1 (slight cytotoxicity).

Colorimetric assays measure the activity of enzymes that reduce MTT or similar dyes

(XTT, MTS, WSTs) to formazan dyes, giving a purple colour. These assays allow

assessment of cell viability and proliferation in cell culture assays, which provide

information on whether a material is cytotoxic. Cell viability can be compared against a

negative control (a material which does not produce a cytotoxic response).

ProRoot MTA that has been freshly mixed i.e. mixed within 1-12 hours, shows cytotoxicity

(~50% cell survival)156, 250

while samples of ProRoot MTA and MTA Angelus that have set

for 1 day or longer consistently show near 100% cell survival.166, 246, 251-254

61

Samples of iRoot FS and iRoot BP Plus, when given 1 week to set166, 251, 255

, or even 1 day

to set,256

show negligible cytotoxicity, and in this regard, are equivalent to ProRoot MTA.

However, fresh samples of iRoot FS show significantly more cytotoxicity than iRoot BP

Plus and ProRoot MTA.166

Furthermore, if iRoot BP Plus is compared against ProRoot

MTA in an immediate placement model, iRoot BP Plus gives greater cytotoxicity.257

MTA sealers show greater toxicity than AH Plus.258

. In a four-week study, MTA Fillapex

showed continual cytotoxicity.29, 259

Similarly, iRoot SP showed continual cytotoxicity in a

six-week study.233

Both MTA sealers were more cytotoxic than AH Plus over the same

testing period.29, 233

1.5.4.2.9 Implantation in subcutaneous and intraosseous tissues (ISO 10993-3)

Implantation studies involve placing materials under the skin of rats and in their jaws and

then assessing histologically the appearance of the tissues around the material at different

points in time.222

ProRoot MTA and MTA Angelus cause initial inflammation, which then subsides over a 30

to 90-day period.260-263

iRoot FS implanted into subcutaneous tissues is more irritating than

ProRoot MTA at 1 week and at 3 weeks.167

In contrast, iRoot BP Plus is less inflammatory

than ProRoot MTA.168

For MTA sealers, there is no significant difference between iRoot SP and AH Plus.264

iRoot

SP causes less severe subcutaneous connective tissue reactions than MTA Fillapex, but

more than a conventional MTA cement.187, 265

The MTA sealer Endo CPM Sealer (EGEO

SRL, Buenos Aires, Argentina) causes similar reactions to AH Plus, and similar reactions

to MTA cements.262

When placed into bone, the initial inflammation elicited by MTA decreases over time.261,

266-271 The trend seen in studies of this type is that there is moderate inflammation at 7

days, mild inflammation at 30 days, and no inflammation from 60 days onward.

For placement into bone, the MTA sealers MTA Fillapex showed comparable reactions to

AH Plus over 28 days.272

Reactions to iRoot SP were not significantly different to MTA and

AH Plus over 60 days.264

62

1.5.5 Discussion

1.5.5.1 Propertiesaftermixing

1.5.5.1.1 Flow (ISO 6876)

For the ISO test to have an acceptable result, the glass plate above the sealer needs to

apply force evenly so that the material shape remains a circle. The operator performing the

test is required to balance the glass plate so that the flowing material remains in a circle.

The test result is therefore directly affected by the skill and experience of the operator and

is subject to bias.

The purpose of the delay of 180 s is possibly an attempt to match the time between when

the sealer is mixed and used in clinical practice, where the sealer is dispensed upon a

mixing pad and then used to coat gutta percha points. However, some sealers are now

dispensed using a syringe, the tip of which can be applied within the root canal, which

removes any delay. Some newer sealers are water-based, and exposure to air can cause

desiccation, resulting in a reduced flow. With such materials, a delay of 180 s is not

appropriate.

In clinical practice, sealers can be applied in a multitude of ways, including injection by

syringe as mentioned above, direct application into the root canal using spiral rotary

instruments, and by the manual manipulation of gutta percha points on the bench.273

Each

method applies different types and amounts of stress on the sealer which, in turn, alters its

viscosity. Sealers are often shear thinning (pseudo-plastic), and show reduced viscosity

and increased flow when the shear rate (i.e. the velocity of the sealer against substrates)

is increased.232

Rather than measuring how far a material flows under constant pressure over many

minutes, changes in its viscosity can be measured with rheometers that apply specific

shear forces to the material. This method has greater precision than the ISO flow test and

thus is more likely to identify significant differences between samples.232

Furthermore, the

application of different shear rates which affects the viscosities has clinical implications.

Higher shear rates will lead to lower viscosity of a material and hence increase its ability

adapt into voids. However, a low viscosity may also increase the likelihood of periapical

63

extrusion. In this case, rapid placement under excessive pressure would increase the

probability of periapical extrusion.232

When viscosity has been measured at three different shear strains, under all three testing

conditions AH Plus had a lower viscosity than MTA Fillapex, which in turn had a lower

viscosity than iRoot SP.232

The advantage of using a rheometer to assess endodontic

sealers is that this instrument can measure the viscosity of the material as well as its other

important properties such as elastic modulus and storage modulus, recording how these

change over time.274

Furthermore, a strong negative correlation exists between flow using

the glass plate press method, and viscosity, whereby the greater the flow, the lower the

viscosity.274

This is typical of shear thinning behaviour.

1.5.5.1.2 Film thickness (ISO 6876)

The ISO test implies that under a particular load, the material should flow in a certain way

to produce a specific thickness. However, it does not give guidance as to how a material

flows under different loads. This is relevant to endodontics as shear thinning (pseudo-

plastic) materials will become less viscous under increasing loads, while shear thickening

(dilatant) materials will show an increase in viscosity under increasing loads. Endodontic

sealers typically exhibit pseudo-plastic properties.232

Therefore, clinicians can apply

excess pressure to intentionally force the material to flow into areas that are more difficult

to reach. However, Portland cement, and hence MTA cements in general, typically exhibit

shear thickening behavior unless substantial admixtures are present.275

MTA cements

without such additives will not reliably flow these limited access areas when increased

pressure is applied.90

Measuring the shear strain rate versus shear stress can identify whether a material has

pseudo-plastic, dilatant, plastic or Newtonian properties. This provides greater clinical

information as to which materials flow better when extra pressure is applied.232

As

discussed above, using rheology the viscosity and elastic modulus can be measured,

particularly as functions of time and temperature.274

1.5.5.1.3 Working time (ISO 6876)

The reduction in flow to within 10% of its value does not necessarily correlate with clinical

usage of the material, nor does it provide any objective data to assess the handling of the

material under clinically relevant conditions of temperature and humidity.

64

Rheological studies can measure viscosity, elastic modulus and storage modulus over

time. However, further research is required to determine which points in the elastic

modulus curve could best be defined as the working time.274

1.5.5.2 Propertiesaftersetting

1.5.5.2.1 Dimensional change (ISO 6876)

Although iRoot SP is a hygroscopic cement and will require water for its setting reaction,

varying the test methods used with iRoot SP when it is compared to other cements

reduces the validity of the results. Both MTA Fillapex and AH Plus absorb some water.28

If

these were tested in the same modified way as iRoot SP, their values for dimensional

change would likely change. When MTA cements absorb water, they expand.276

When

samples are tested, they should not be submerged in water but rather in a buffered saline

solution so that there are physiological concentrations of ions, and the testing conditions

are more aligned to clinical conditions.32

1.5.5.2.2 Solubility (ISO 6876)

MTA is more soluble in distilled water than in isotonic solutions. The ISO test uses

hypotonic solutions, which increases the solubility far beyond that in the clinical situation.

When MTA is tested in physiological solution, Hank’s balanced salt solution and

phosphate buffered solution, BioAggregate, Biodentine and ProRoot illustrated negative

values indicating that they had absorbed ions from the environment, rather than an overall

loss of mass.49, 223

Hence, the clinical relevance of this method of testing is

questionable.277

The test also involves giving cements the opportunity to set for a period of 50% longer

than the setting time stated by the manufacturer. Those setting times often utilize ISO

6876, and thus may not reflect whether this material has reached its final hardness. As an

example, ProRoot MTA when tested under ISO 6876 has a setting time of 78 min, but

when tested under ISO 9917.1 has a setting time of 4 h.87, 230

Allowing a period of 50%

may be insufficient if the goal is to test completely set samples.

Once fully set, MTA contains calcium hydroxide and can produce some alkalinity after 28

days.154

On this basis, it could be argued that if a completely set material is desired,

65

testing the cement should occur after it has aged at least 28 days. For clinical relevance,

solubility should be tested immediately after placement. This could involve a slow

submergence, at some arbitrary rate, preferably into a physiological solution or into blood.

1.5.5.2.3 Radiopacity (ISO 6876 and 9917-1)

There is a wide range of reported values for radiopacity within various cements and some

issues around the details of the method for determining radiopacity.278

Minor variations in

exposure time, or in target distance within the allowed range of 300-400 mm do not

significantly influence the results.279

One could expect minor variations according to the

level of curing between samples280

and the type of imaging system used.281

The ISO standards describe the use of an optical density instruments on exposed films.2, 3

Digital imaging enables objective quantification with greater specificity, through the use of

grayscale histogram analysis, of greyscales of radiopacity.282, 283

Regardless of the methods used, it seems the most meaningful comparisons are tests that

involve several cements within the one study so that direct comparisons can be made

between materials, rather than comparisons between studies where more variables are at

play.282

Alternatively, a clinically relevant test based on the clinical appearance and usage of MTA

in radiographs could be considered,283

possibly in a tissue simulator model with teeth and

bone.284

Solubility affects radiopacity with more soluble MTAs illustrating greater loss of

radiopacity over time.223

Future studies should assess changes in radiopacity as

dissolution occurs.

1.5.5.2.4 Compressive strength (ISO 9917-1)

MTA will expand when stored fully immersed in physiological solutions but will shrink when

stored in a humid chamber.32

Therefore, it is important to know whether samples are

stored dry, stored in a humid chamber, or immersed completely in water or other fluids.235,

285

For assessing compressive strength, most studies in the literature test samples of MTA

once the cement has been allowed to age for 21-28 days prior to testing,144, 234, 242

which is

a major difference from what is allowed in ISO 9917.2

66

Ideally, MTA should be wet cured, i.e. submerged in a physiological buffer solution, to

prevent desiccation of samples, and tested in physiological solution (e.g. phosphate

buffered saline), to replicate physiological conditions.79

While there is logic in testing

samples that have aged for 304 weeks, there is also value in testing samples at earlier

points in time, e.g. 1 day, 1 week and 3 weeks, to track how compressive strength

develops over time. At any given point in time after mixing, if a cement has not set, it will

have no compressive strength. This information is of value to the clinician. A further point

of clinical relevance is exposure to blood. MTA that has been cured in the presence of

blood has reduced compressive strength.127

1.5.5.2.5 Acid erosion (ISO 9917-1)

This test is suitable for dental restoratives which are exposed to the acids in the oral

environment. MTA, whether it be used as a restorative material or as a sealer, is typically

located under coronal restorations, and not exposed to the oral environment. The risk of

acid erosion from exposure to lactic acid produced by dental plaque biofilm is not a

clinically relevant risk.

Set MTA has increased solubility in acidic environments, and these conditions may occur

wherever inflammation is present.286

As with solubility studies, a more clinically relevant

method would be to test samples that have been exposed to weak acids immediately after

mixing, rather testing the material once it has cured fully under neutral pH conditions.

1.5.5.2.6 Acid soluble arsenic and lead contents (ISO 9917-1)

The results of the ISO test for acid soluble arsenic and lead content show inconsistent

patterns of results. This may be due to differences in types of acids and concentrations

used, as well as variations in exposure time to those acids.239

Variations in the results can

also be caused by how the samples are prepared by grinding them into powder using a

mortar and pestle. Materials of different hardness will be ground to different fineness, and

hence will have a different surface area. This will affect how much heavy metals can be

leached out from exposure to acid. The clinical relevance of this test is questionable since

MTA is not exposed to the occlusion where it can undergo attrition, or be exposed to

strong acids. Biological response tests, such as implantation studies, are of greater clinical

relevance. There is no direct relationship between the concentration of arsenic found in

MTA and the associated inflammatory response in the tissues.287

67

1.5.5.2.7 Genotoxicity and carcinogenicity (ISO 10993-1)

The current panel of tests which use bacterial and mammalian cells in culture may not

represent what happens in human tissues. Implantation tests in animals are more relevant,

but may not be practicable for assessing long term safety issues such as carcinogenicity.

1.5.5.2.8 Cytotoxicity (ISO 10993-5)

The cytotoxicity of MTA cement is affected by several variables, including storage time and

storage media. The key consideration is the release of calcium hydroxide from the cement

as it is setting. Initially, the speed of the setting reaction is high, and cytotoxic effects are

seen from released calcium hydroxide. As the material reaches its final set, much of the

alkalinity is lost and hence there is less cytotoxicity.154

Therefore, any test method where

the MTA sample is fully set and then is placed into a culture or against tissues is not

reflective of the clinical use of the material. On the other hand, putting freshly mixed MTA

cement directly into a cell culture well will likely result in the disintegration of the material,

giving greater alkaline effects from the calcium oxide components of the Portland cement.

Similar considerations would apply to sealers, but with the caveat that the viscosity

modifiers used in these could also affect cell viability.259

An alternative method would be to

place freshly mixed MTA immediately into a simulated root-end filling that is then exposed

to the testing culture.257

This prevents the disintegration of the MTA.

Cytotoxicity tests employ short testing periods of typically 1-3 days. This will not identify

concerns of sustained toxicity due to slow dissolution or degradation over time. This is

especially important for MTA sealers which have high solubility.259

These materials should

be tested over longer periods of time. Samples can be prepared, placed into a simulated

root-end filling, allowed to cure in water for 1, 2 or 3 weeks, and then placed into cell

culture.

1.5.5.2.9 Implantation in subcutaneous tissues and intraosseous tissues (ISO 10993-6)

Results from subcutaneous implantation are considered of less relevance than those from

intraosseous implantation since the clinical usage of MTA is within osseous structures.

When interpreting the results of inflammation in implantation studies, it is important to

understand that, as stated by Sumer,260

“when assessing the biocompatibility of a material,

later harmful effects are considered to be more important than its initial effects.” The initial

inflammation is partly due to the trauma of the surgical procedure to implant the material,

68

and partly due to the material itself. Review periods should account for this, and use

longer intervals such as 7 days, 30 and 60 days.

Although animal biocompatibility studies are considered superior to cell culture studies, it

must be remembered that a material which appears to be well tolerated and which does

not elicit intense inflammation may have inferior physical properties, such as high solubility

or shrinkage, which compromise its performance.

Studies using larger animals, e.g. beagle dogs, where MTA is placed into root-end fillings

in a location where apical periodontitis has been induced, provide a method of assessing

osseous healing. This is an important consideration as it goes beyond the inflammatory

response. Furthermore, the use of larger animals in this manner enables not only

histological assessment as per ISO 10993-6 but also the radiographic assessment of

healing. However, large animal welfare can prohibit such studies being undertaken.288

1.5.6 Conclusion

MTAs can be separated into two main types, MTA restoratives and MTA sealers, and

feature products which are often marketed as bioceramics. These endodontic bioceramics,

as with MTA, fall under the categories of MTA restoratives and MTA sealers.

The results for ISO tests used for testing MTA can be biased by curing method of the

MTA. MTA should be cured in a way that represents the clinical usage of the material. This

typically involves immediate placement and immediate testing of samples rather than

curing the cement outside of testing conditions.

69

Chapter 2 How do paediatric dentists use MTA?

This chapter presents a survey of MTA usage by PDs and GD members of the ANZSPD.

Although there is literature supporting the use of MTA in pulp capping and pulpotomy,

within paediatric dentistry MTA is used predominately for primary molar pulpotomies.

Alternative dental materials are chosen for other clinical scenarios. Although cost may

contribute to the selection of alternative materials, it is known that MTA stains anterior

teeth, a point that may lead clinicians to prefer alternatives such as CH.

This chapter has been published as:

Ha WN, Kahler B, Walsh LJ. Dental material choices for pulp therapy in paediatric

dentistry. Eur Endod J; 2017, 2017; 2:1-7.

2.1 Introduction

MTA has been advocated for various paediatric dental indications such as vital pulp

therapy and pulpotomy in primary and permanent teeth.153

When MTA is used in

permanent teeth, there is a 97.6% success rate for DPCs,289

and a 79% success rate for

pulpotomies.290

In primary teeth, the corresponding success rates are 100% for DPCs291

and 97% for pulpotomies.292

Despite these high success rates, MTA is not widely used.

The high cost of the material is considered to be the major barrier to its use in clinical

practice.97

However, it is also possible that lack of knowledge regarding how to use MTA

could be another significant issue.

The extent of teaching on the use of MTA has been limited. In 2009, across the UK and

Ireland, only 2 of 14 postgraduate paediatric dentistry departments taught the use of MTA

for pulp therapy in primary molars.293

A similar study in the UK in 2005 of 13 dental schools

reported that CH was used routinely for pulp capping, and FeSO4 for pulpotomy, with only

one school teaching the use of MTA as an alternative material.8 In Europe, use of MTA is

becoming more widespread as training in the use of the material has extended further. A

2013 survey of 29 postgraduate departments in Europe reported that 6 used MTA for pulp

capping and 17 used MTA for pulpotomy.7

There is no published data on the use of MTA in paediatric dentistry in Australia or New

Zealand. Accordingly, the aim of the present study was to assess the use of MTA by

members of the Australian and New Zealand Society of Paediatric Dentistry (ANZSPD).

This society is composed of both GDs with an interest in paediatric dentistry as well as

70

PDs. The study examined the choices of clinicians and assessed how well patterns of

clinical use of MTA aligned with the scientific literature, focusing on pulp capping and

pulpotomy, grouping both partial and complete pulpotomy into the one category.

2.2 Methods

The national office of the ANZSPD distributed information regarding a survey to all society

members on November 28th of 2014 and this was followed by a reminder email sent on

April 15th April 2015. The survey was conducted online using www.surveymonkey.com.

The final response was received on the 21st of May 2015.

The survey sought information from respondents on:

• whether the respondent was a GD, PD, or a dentist undergoing speciality training in

paediatric dentistry;

• material handling and placement preferences;

• education and training received on MTA; and

• preferences for materials used for IPCs, DPCs and pulpotomy in anterior and

posterior primary and permanent teeth.

For each survey question, respondents were supplied with a menu of options, including an

“other” option to enable short written responses. If the “other” was a listing of single

responses, the first single response replaced their response. If their “other” response was

equivalent to another single response, their answer was grouped with that single

response. The least popular responses (i.e. <10% of respondents or single unique

responses) were grouped together under “other”.

For the purpose of the study, responses indicating the use of Biodentine or various

commercial MTA products were all grouped under the classification of MTA. A typical MTA

cement contains PC with a radiopaque additive, with the major ingredients of the PC being

calcium silicates and calcium aluminates.294

The composition of MTA has many similarities

to the composition of Biodentine, which is primarily calcium silicates with a radiopacifier.294

Differences in the patterns of responses between GD and PD were assessed according to

their frequency distribution using Fisher’s exact test, with GraphPad™ statistical software

(http://graphpad.com/quickcalcs/catMenu/). P values of less than 0.05 were regarded as

significant.

71

2.3 Results

2.3.1 Respondentcharacteristics

A total of 103 of the 280 members of the ANZSPD completed the survey, giving an overall

response rate of 37%. As the respondents included 17 dental therapists, but none of these

used MTA, there was no further analysis undertaken for this group. Responses from

dentists undergoing speciality training in paediatric dentistry were grouped with those for

PDs, giving 31 GD and 55 PD.

Overall, MTA was used by more PD than GD (69% vs. 35%). This difference was

statistically significant (P<0.05). The choice of MTA product brand was similar for GD

(64% MTA-P, 36% MTA-A) and PD (70% MTA-P, 27% MTA-A).

2.3.2 MTAUsage

As illustrated in Table 2-1, most GD and PD preferred to permanently restore teeth

immediately after MTA placement, while others waited an arbitrary period of time. A

minority placed a temporary restoration after MTA placement and then returned to

permanently restore the tooth in a subsequent appointment.

Some respondents stored their MTA in the refrigerator, and some used single-use satchels

of MTA-P for multiple applications. Both these actions are against the manufacturer’s

instructions. Although minor differences existed between GD and PD for these aspects

these were not statistically significant.

72

GD PD

N % n %

Do you use MTA or MTA like cements?

Yes (*) 11 35% 37 69%

No 20 65% 17 31%

Which MTA do you use?

MTA-P 7 64% 26 70%

MTA-A 4 36% 10 27%

Other 0 0% 1 >1%

After placing MTA how long do you wait before permanently restoring the

tooth?

Don’t wait 1 20% 8 47%

5 minutes 2 40% 6 35%

15 minutes 0 0% 1 6%

Temporise the tooth and restore another day 2 40% 2 12%

Where do you store your MTA? In the

refrigerator?

In the refrigerator 0 0% 3 19%

In the drawer 5 100% 13 81%

If you use MTA-P, do you use the satchels for multiple applications?

Yes 2 50% 5 71%

No 2 50% 2 29%

Where did you learn to use MTA?

Training as a GD 2 13% 2 5%

Training as a specialist PD (*) 0 0% 19 44%

Continuing education lectures (*) 13 87% 15 35%

Other 0 0% 7 16%

Did this education include a hands-on component with MTA or PC

Yes (*) 3 20% 24 57%

No 12 80% 18 43%

Would you be interested in sitting hands on MTA courses?

Yes 18 86% 32 65%

No 3 14% 17 35%

Table 2-1 MTA usage and training patterns of respondents

* Statistically significant difference between GDs and PDs, p < 0.05.

73

2.3.3 EducationregardingMTAusage

Attendance at continuing professional development (CPD) lectures was the major way in

which GD had learnt how to use MTA (87%). This differed significantly from PD, for whom

nearly half (44%) learnt how to use MTA during their specialist training, and only one-third

(35%) from CPD. The courses attended by GD rarely included hands-on training in the use

of MTA (20%) while the specialist training of PD often included hands-on training in the

use of MTA (57%). The majority of respondents in both groups wanted to attend hands-on

courses in using MTA (GD: 86%; PD: 65%).

The types of clinical procedures undertaken by respondents are shown in Figure 2-1,

showing IPC, Figure 2-2 showing DPC and Figure 2-3 showing pulpotomy.

Figure 2-1 Proportions of clinicians who perform IPC

Red segments show proportions of those who do not perform these procedures.

74

Figure 2-2 Proportions of clinicians who perform DPC


Figure 2-3 Proportions of clinicians who perform DPCs


75

2.3.4 IPCs

2.3.4.1 Primaryteeth

Popular choices for IPC were CH cements (CHC) (GD: 45%; PD: 18%) and either GICs or

RMGIC (GD: 45%; PD: 58%).

In posterior teeth, many clinicians preferred GIC/RMGIC (GD 50%; PD 65%) or CH

cements (GD: 42%; PD 9%), rather than MTA. Detailed results are presented in Table 2-2

2.3.4.2 Permanentteeth

In anterior teeth, popular choices for IPC were CHC (GD: 40%; PD 34%), GIC/RMGIC

(GD: 30%; PD: 47%) and CH pastes (CHP) (GD: 20%; PD: 9%), rather than MTA.

Likewise, in posterior teeth, popular choices for IPC were CHC (GD: 42%; PD: 29%) and

GIC/RMGIC (GD: 26%; PD 38%), followed by MTA (GD: 16%; PD: 15%) (Table 2-2).

GD PD

N % n %

For IPCs in anterior primary teeth, what is your preferred material?

GIC/RMGIC 5 45% 19 58%

CHC 5 45% 6 18%

Other 1 9% 8 24%

For IPCs in posterior primary teeth, what is your preferred material?

GIC/RMGIC 6 50% 28 65%

CHC(*) 5 42% 4 9%

Other 1 8% 11 26%

For IPCs in anterior permanent teeth, what is your preferred material?

GIC/RMGIC 6 30% 22 47%

CHC 8 40% 16 34%

CHP 4 20% 4 9%

Other 2 10% 5 11%

For IPCs in posterior permanent teeth, what is your preferred material?

CHC 8 42% 14 29%

GIC/RMGIC 5 26% 18 38%

MTA 3 16% 7 15%

Other 3 16% 9 19%

Table 2-2 Preferred materials for IPCs

* Statistically significant difference between GDs and PDs, p < 0.05

76

2.3.5 DPCs


In anterior teeth, the most common choice for DPC was MTA (GD: 50%; PD: 42%), and

the same occurred for DPC in posterior teeth (GD: 50%; PD: 43%) (Table 3).


Popular choices for DPC in anterior teeth were CHC (GD: 44%; PD 23%) and CHP (GD:

33%, PD: 51%), followed by MTA (GD: 17%; PD: 18%). In contrast, in posterior teeth the

preferred materials were CHC (GD: 44%; PD 16%) followed by MTA (GD: 31%; PD 44%)

and then CHP (GD 25%; PD: 31%) (Table 3).

GD PD

N % n %

For DPCs in anterior primary teeth, what is your preferred material?

MTA 2 50% 5 42%

Other 2 50% 7 58%

For DPCs in posterior primary teeth, what is your preferred material?

MTA 2 50% 6 43%

Other 2 50% 8 57%

For DPCs in anterior permanent teeth, what is your preferred material?

CHP 6 33% 20 51%

CHC 8 44% 9 23%

MTA 3 17% 7 18%

Other 1 6% 3 8%

For DPCs in posterior permanent teeth, what is your preferred material?

MTA 5 31% 14 44%

CHP 4 25% 10 31%

CHC 7 44% 5 16%

Other 0 0% 3 9%

Table 2-3 Preferred materials for direct pulp capping (DPCs)

2.3.6 Pulpotomies


For pulpotomy in anterior teeth, the most popular material was FeSO4 (GD: 33%; PD:

45%) followed by MTA (GD: 33%; 26%), diathermy (GD: 11%; PD: 13%) and then FC

(GD: 11%, PD: 10%).

77

For pulpotomy in posterior teeth, the most popular material was again FeSO4 (GD: 61%;

PD: 36%) followed by MTA (GD: 11%; PD 40%) and then FC (GD: 11%; PD: 11%) (Table

2-4).


For pulpotomy in anterior permanent teeth, the most popular choice was CHP (GD: 57%;

PD: 54%) followed by CHC (GD: 21%; PD 18%) and then MTA (GD: 14%; PD:18%). In

contrast, for pulpotomy in posterior permanent teeth, MTA was the most popular material

(GD: 21%; PD: 41%) followed by CHP (GD: 43%; PD: 18%) (Table 2-4).

GD PD

N % n %

For pulpotomies in anterior primary teeth, what is your preferred material?

MTA 3 33% 8 26%

FeSO4 3 33% 14 45%

FC 1 11% 3 10%

Diathermy 1 11% 4 13%

Other 1 11% 2 6%

For pulpotomies in posterior primary teeth, what is your preferred material?

MTA (*) 2 11% 18 40%

FeSO4 11 61% 16 36%

FC 2 11% 5 11%

Diathermy 1 6% 4 9%

Other 2 11% 2 4%

For pulpotomies in anterior permanent teeth, what is your preferred material?

MTA 2 14% 7 18%

CHP 8 57% 21 54%

CHC 3 21% 7 18%

Other 1 7% 4 10%

For pulpotomies in posterior permanent teeth, what is your preferred material?

MTA 3 21% 16 41%

CHP 6 43% 7 18%

Other 1 7% 8 21%

Table 2-4 Preferred materials for pulpotomies

* Statistically significant difference between GDs and PDs, p < 0.05

2.4 Discussion

Although there is literature that shows that MTA is successful when used in various

scenarios in restorative dentistry and endodontics,197

in Australia and New Zealand this

material is not used frequently in clinical practice. The results of the present study show

that clinicians working with paediatric dental patients use a range of materials for pulp

78

capping and pulpotomy procedures, with MTA not being used frequently for pulp capping

and pulpotomy, despite its suitability for this. Of note, all the GD respondents in the

present study are members of the ANZSPD and therefore have a special interest in

paediatric dentistry. However, they may not be completely representative of the wider

population of GDs in Australia and New Zealand.

The literature often cites the high cost of MTA being a major barrier to its use in clinical

practice.7, 295, 296

despite a widely held view that for procedures such as DPC that it is the

material of choice.296-298

The mismatch between the evidence from the literature and the

patterns of clinical practice suggests that there may be factors other than cost that

influence the materials selection of GDs and PDs. A recent survey of GDs and EDs in

Australia and New Zealand showed that a lack of education on the use of MTA was more

of a barrier than its cost.207

This aligns with the present study, where education on MTA

was desired by a majority of respondents. A further point supporting this is the product

brand selection. In the dental market in Australia and New Zealand, there is a limited

range of MTA products available, yet clinicians most often used MTA-P, which is the most

expensive brand and argues against cost being the strongest influence. A preference to

use MTA-P has also been noted in other surveys of MTA product usage.7, 207

In the present study, CHC and GICs were preferred over MTA for IPC in both primary

teeth and permanent teeth, which is in line with evidence for effectiveness.137, 138

In

contrast, for DPC in primary teeth, MTA was the most popular material choice, even

though this procedure was not undertaken commonly, even by specialists. The use of MTA

for DPC is supported by clinical studies that show success after 2 to 9 years of follow-

up.289, 291

For DPC in permanent teeth, clinicians used MTA, CHP or CHC. When considering clinical

studies with a follow-up of at least 5 years as being sufficient to cover eventual pulpal

necrosis.299

the selection of both MTA and CHP are supported in the literature.289

There is,

on the other hand, evidence for failure if CHC are used for DPC in permanent teeth.300

A

study by Barthel et al. reported a 44.5% failure rate at 5 years and a 79.7% failure rate at

10 years.301

These results stand in contrast to those for MTA in the same clinical situation,

with 98% success at 9 years.289

Although studies that compare directly long term clinical

outcomes of DPC with MTA versus CHC are lacking, one study of 2 years duration

reported 31.5% failure with CHC and only 19.7% with MTA.302

79

In the present study, when DPC with MTA was undertaken in permanent teeth, there was

a clear preference for MTA to be used less often in anterior teeth. This likely reflects

concerns of tooth discolouration, as discolouration is problematic for teeth in the aesthetic

zone. Instead, clinicians were choosing CHP, which avoids long term staining problems.

As yet, there is limited data on outcomes from CHP versus MTA over the long term.120

For pulpotomies in primary teeth, the clinicians in this survey preferred either FeSO4 or

MTA. This finding agrees with a recent Cochrane Review illustrating similar successful

clinical outcomes at 6 and 12 months for both materials, with a trend for better outcomes

for MTA at two years, although the difference was not statistically significant.303

It was

surprising to find that some clinicians were still using FC for pulpotomies in primary teeth,

as this has become a very difficult dental material to obtain.

The need to use MTA in IPC when managing vital teeth with deep carious lesions is limited

because of the widespread use of alternatives such as GIC. Selective caries excavation

and a focus on sealing the margins are designed to reduce iatrogenic pulpal exposure

during caries removal. Some infected carious dentine may intentionally be left, and this is

then entombed using a well-sealed restoration.296

In the Hall technique, preformed metal

crowns filled with viscous GIC are placed onto teeth without local anaesthesia and without

caries removal or approximal enamel preparation.

In cases where the vitality of the coronal pulp is in question because of irreversible pulpitis,

options include pulpotomy and pulpectomy, which can give respectable clinical success

rates for pulpotomy.304

In the present study, for pulpotomy of permanent anterior teeth,

CHC and pastes were the most popular products, while MTA was more popular for

posterior teeth followed by CHP. This pattern of use aligns with evidence that supports the

use of CHP for partial pulpotomies in permanent teeth, with reported success rates of

93.5% over 4 years.305

There are similar reported success rates for CHP and MTA for

partial pulpotomies,306, 307

although the situation is less clear for complete pulpotomies as

many studies do not clarify the type of CH used.303

In the present study, the preference of

CHP over MTA for pulpotomy in anterior teeth and the corresponding preference for MTA

for pulpotomy in posterior teeth most likely reflect concerns regarding discolouration of

treated teeth rather than concerns regarding effectiveness.120

80

2.5 Conclusions

The choices to use MTA and other dental materials were similar between GD and PD.

There were situations where MTA was not being used despite strong clinical evidence in

the literature. This reflects several factors including training, concerns regarding

discolouration, and relative cost. The expressed desire of clinicians to attend further

training in the use and handling of MTA suggests that a lack of education and awareness

remain the major obstacles to its wider use. This same lack of knowledge explains why

some clinicians store MTA in an incorrect way.

81

Chapter 3 How do endodontists use MTA?

This chapter discusses a survey of MTA usage by endodontists (EDs) and GD members of

the ASE. It applies a similar approach to that used in the previous chapter for PDs. The

most common procedures for MTA use by both groups are apexification and perforation

repair. Electing to barrier-cure (placing a restoration on MTA) is common illustrating that

the prolonged setting time is not an issue to some. Nevertheless, some members are

choosing to wet-cure MTA (i.e. using a damp cotton pellet).


Ha WN, Duckmanton P, Kahler B, Walsh LJ. A survey of various endodontic procedures

related to MTA usage by members of the Australian Society of Endodontology. Aust

Endod J; 2016; 42; 132-138.

3.1 Introduction

Important endodontic applications for MTA are the creation of an apical barrier,198

perforation repair308

and for root-end fillings.309

A study in the United Kingdom (UK)

revealed that MTA usage is common within postgraduate endodontic training programmes

and that its high cost was perceived as being the major barrier to its use.97

Nearly half the

respondents in the UK survey were interested in further education on the use of MTA in

clinical practice.97

A similar study conducted of postgraduates in paediatric dentistry in

Europe likewise found that cost was an issue limiting the use of MTA, and that almost all

respondents were interested in further educational opportunities in material use.7 Surveys

of consultant PDs have shown that the majority of PDs do not use MTA due to cost.5

There do not appear to be studies assessing usage patterns of MTA amongst EDs and

GD.

An interest in receiving further education on the usage of MTA is possibly related to the

scarcity of information on handling, which is limited to the manufacturer’s instructions for

use as well as to various published case reports.8, 310

Furthermore, there is no literature

surveying the procedural steps involving MTA.

The aim of this study was to establish the level of MTA usage amongst members of the

ASE, the preferred handling methods for MTA by clinicians, the perceived need of ASE

members for receiving further training in the manipulation and clinical applications of MTA.

82

Although MTA has illustrated popularity in pulp capping (10), it has not been assessed in

this study as EDs are not likely to perform pulp caps. A similar study is currently underway

by the authors assessing the use of MTA in pulp therapy by members of the ANZSPD.298

3.2 Methods

The federal body of the ASE was contacted, and permission obtained to distribute a

survey on MTA to all society members. Invitations to participate were sent out from the 8th

of December 2014 onwards. A reminder email was sent to all members who did not reply.

The survey was conducted online using www.surveymonkey.com. The final response was

received on the 19th of March 2015.

The survey sought information on:

• whether the respondent was a GD, ED, or a dentist undergoing speciality training in

endodontics;

• what procedures the respondents used MTA for;

• reasons for not using MTA in clinical practice;

• education and training received on MTA; and

• techniques used when placing MTA and other endodontic materials.

Results were assessed using Fisher’s exact test to compare the GD and ED populations

for significant differences utilising the two-sided p-value using the method of summing

small p-values. Calculations were performed using GraphPad.

(http://graphpad.com/quickcalcs/catMenu/).

In this study, responses from EDs and postgraduate endodontic students were grouped

together. The questionnaire was a single-response questionnaire with the option to enter

alternatives answers under ‘others’. If respondents answered more than one response as

their answer, their first answer in the response was taken as their single-response answer.

P-values of less than 0.05 were described as significant.

MTA is found in Australia as MTA-P and MTA-A. The patent for MTA describes within its

summary that MTA is a cement comprised of PC with a radiopaque additive.153

The patent

then describes the key role that calcium silicates play in the setting reaction. 153

PC is

typically calcium silicates with a minority component of calcium aluminate while

BiodentineTM

(Septodont, Saint-Maur-des-Fossés, France) has calcium silicates without

83

calcium aluminates.294

Therefore, as the differences are tenuous, Biodentine has been

grouped with MTA for the purpose of this study.294

The questionnaire offered several multiple-choice answers with an option for the

respondent to type their own answer (in “Other”) should they differ to the options provided.

If the respondent decided to answer multiple answers in the “Other” section, their first

answer was given precedence and their response was hence grouped with that first

answer.

Responses that were not popular or common with many respondents were grouped under

the answer “Others”, which is illustrated in the results of this study.

3.3 Results

3.3.1 Membership

From 499 members of the ASE, 208 completed the survey, giving an overall response rate

of 41.7%. Of the respondents, some 60.1% were GD, 35.6% were ED and 3.8% were

undertaking endodontic speciality training programmes. The geographic base spread of

responses was as follows: 55 from New South Wales (26.4%), 49 from Queensland

(23.6%), 47 from Victoria (22.6%), 26 from South Australia (12.5%), 24 from Western

Australia (11.5%), 2 from Tasmania (1.0%), 1 from the Northern Territory (0.5%), and 4

from overseas locations (1.9%).

Overall, MTA was used by 63.0% of the ASE members who responded to the survey. The

rate of usage of MTA was much higher in ED (97.6%) than in GD (40.0%), with a

significant difference (P<0.0001). Of those who used MTA, the most popular MTA brand

was MTA-P (ED: 83.8%, GD 60.8%), followed by MTA-A (ED: 40.0%, GD: 25.5%). Some

members used Biodentine (ED: 12.5%, GD: 17.6%). These results are found in Table 3-1.

84

Table 3-1 MTA usage, training and perforation repairs by GD and ED

GD ED Fisher’s

exact test n % n % P-value

Do you use MTA? yes 50 40.0% 81 97.6% <0.0001 ***

no 75 60.0% 2 2.4%

What is your preferred brand?

ProRoot MTA yes 31 60.8% 66 81.5% 0.0144 *

no 20 39.2% 15 18.5%

MTA Angelus yes 11 21.6% 14 17.3% 0.6491 Ns

no 38 74.5% 48 60.0%

Biodentine yes 7 13.7% 0 0% 0.001 **

no 44 86.3% 81 100%

What is your main reason for not using MTA?

No experience yes 37 48.7% 1 25.0% 0.6173 Ns

no 39 51.3% 3 75.0%

High cost yes 24 31.6% 2 50.0% 0.5922 Ns

no 53 69.7% 2 50.0%

Difficult handling Yes 3 3.9% 1 25.0% 0.1888 Ns

No 73 96.1% 3 75.0%

Where did you learn how to use MTA?

Continuing professional development lectures yes 29 58.0% 17 21.0% <0.0001 ***

no 21 42.0% 64 79.0%

Endodontic speciality training yes 0 0.0% 49 60.5% <0.0001 ***

no 50 100.0% 32 39.5%

Of users of MTA, have you attended hands-

on MTA courses?

yes 15 32.6% 55 67.9% 0.0002 ***

no 31 67.4% 26 32.1%

Of all respondents, are you interested in

hands-on MTA courses?

yes 104 82.5% 21 25.6% <0.0001 ***

no 22 17.5% 61 74.4%

Do you restore perforations? yes 49 39.8% 79 98.8% <0.0001 ***

no 74 60.2% 1 1.3%

What do you use to restore perforations?

MTA yes 43 87.8% 77 97.5% 0.0534 Ns

no 6 12.2% 2 2.5%

Biodentine yes 3 6.1% 0 0.0% 0.0540 Ns

no 46 93.9% 79 100.0%

If radiolucency is present how do you

manage the radiolucency?

Will use a CH dressing first yes 27 58.7% 41 51.9% 0.5767 Ns

no 19 41.3% 38 48.1%

Will restore the tooth immediately yes 15 32.6% 32 40.5% 0.4458 Ns

no 31 67.4% 47 59.5%

Final irrigant for perforation repair

NaOCl yes 19 35.8% 52 64.2% 0.0015 **

no 34 64.2% 29 35.8%

EDTA yes 11 20.8% 16 19.8% 1.0000 Ns

no 42 79.2% 65 80.2%

CHX yes 6 11.3% 3 3.7% 0.1543 Ns

no 47 88.7% 78 96.3%

What is your order of restoring perforations?

Perforation first, obturate rest of tooth in a yes 25 54.3% 35 44.3% 0.3536 Ns

subsequent appointment no 21 45.7% 44 55.7%

Perforation first, obturate rest of canals in the

ointment

yes 15 32.6% 11 13.9% 0.0211 *

same appointment no 31 67.4% 68 86.1%

Obturate canals first and then perforation in

the appointment

yes 2 4.3% 22 27.8% 0.0009 ***

same appointment no 44 95.7% 57 72.2%

85

3.3.2 EducationonMTAuse

The major reasons for GD not using MTA were no experience with the material (48.7%)

and high cost (31.6%). Of those who used MTA, 58.0% GD learnt how to use MTA via

continuing professional development (CPD) lectures while 60.5% ED learnt how to use

MTA from their training to become a specialist with 21.0% learning how to use MTA via

CPD lectures.

Of all respondents, 82.5% of GD and 26.5% of ED are interested in taking hands-on MTA

courses. These results are found in Table 3-1.

3.3.3 MTAUsage

3.3.3.1 Perforationrepair

These results are found in Table 3-1. When a perforation occurs, 39.8% of GD will

personally repair the perforation while 98.8% ED will restore perforations. This difference

was statistically significant (P<0.0001).

When repairing the perforation, 87.8% preferred MTA, followed by 6.1% Biodentine. For

ED, 97.5% preferred MTA. Of those who would restore perforations, if a radiolucency was

present around a perforation, 58.7% of GD and 51.9% of ED would utilise a CH dressing.

Otherwise, 32.6% of GD would restore the tooth immediately and 40.5% of ED would

restore the tooth immediately. These differences were not statistically significant.

When placing MTA for perforation repairs, the most common final irrigant solution used

prior to placing the material was NaOCl, at 53.0% (35.8% GD, 64.2% ED). This difference

was statistically significant (p=0.0015). Less popular irrigants were EDTA, at 20.1%

(20.8% GD, 19.8% ED), followed by CHX, at 6.7% (11.3% GD, 3.7% ED). These were not

statistically significant.

Some 48% (54.3% GD, 44.3% ED) of respondents restored perforations with MTA and

then obturated the tooth in a subsequent appointment, with no significant differences

between GD and ED. Only 20.8% (32.6% GD, 13.3% ED) would restore the perforation

first and then obturate the canals in the same appointment. Some 19.2% (4.3% GD,

27.8% ED) obturate the canals first and then restore the perforation in the same

86

appointment. Of these two latter options, significant differences were found between the

two cohorts (respectively p=0.0211 and 0.0009).

3.3.3.2 Apicalbarrier

These results are found in Table 3-2. Some 63.9% respondents perform apical barrier

procedures (42.7% GD, 96.3% ED) and then complete the treatment using MTA (28.3%

GD, 80.2% ED) or using GP (69.8% GD, 14.8% ED) after apical closure. Significant

differences existed between the two cohorts (all with P<0.0001).

If a periapical radiolucency was present, 82.1% (94.7% GD, 78.5% ED) of those who use

MTA would dress the tooth with a CH medicament paste first. The remainder would

restore the tooth immediately. If blood was actively flowing into the chamber during

preparation, 57.1% (47.4% GD, 60.0% ED), would dress the canal and return to complete

the treatment in a subsequent visit, while 19% (26.3% GD, 16.9% ED) would wait

passively for bleeding to stop, and 13.1% (10.6% GD, 13.90% ED) % would apply a

haemostatic agent. No significance was found between the two cohorts.

The term ‘one-visit’ apical barrier has not been used because there could be ambiguity to

some readers as to whether one visit includes the procedures of temporary dressing with

CH prior to MTA apical barrier placement or temporary restoration with Cavit (3M ESPE

Dental AG, Seefeld, Germany) and a damp cotton pellet.

When placing MTA in apical barrier cases, the final irrigant used before MTA placement

was NaOCl (61.9%: 31.6% GD, 70.8% ED), followed by EDTA (21.4%: 31.6% GD, 18.5%

ED), saline (10.7%, 21.10% GD, 7.7% ED), and CHX (4.8%: 15.8% GD, 1.6% ED).

Extremely significant differences existed between GD and ED for the use of NaOCl and

CHX (respectively p=0.0030 and p=0.0347).

Once MTA had been placed, the most popular ways of obturating the root canal were via

gutta percha injection technique (5.6% GD, 53.1% ED) followed by vertical compaction of

GP (22.2% GD, 14.1% ED). There was an extremely significant difference for the use of

injection technique (p=0.0003) although no significance existed for vertical compaction.

87

Some 79.3% (55.6% GD, 85.9% ED) of respondents chose to immediately obturate the

canals after MTA placement, while 20.7% (44.4% GD, 14.1% ED) chose to obturate at a

subsequent appointment. This difference was significant (p=0.0089).

For those who chose to immediately obturate after placing MTA, 68.7% used GP (54.5%

GD, 71.4% ED). Some 16.4% (18.2% GD, 16.1% ED) would place a GIC or RMGIC over

the MTA. Of those who chose to obturate at a subsequent appointment, 94.1% (87.5%

GD, 100% ED) would place a damp cotton pellet in contact with the MTA and then place

Cavit. The differences between the cohorts were not statistically significant.

88

Table 3-2 Apical barrier procedures by GD and ED

GD ED Fisher’s


Do you perform apical barrier procedures? yes 53 42.7% 78 96.3% <0.0001 ***

no 71 57.3% 3 3.7%

What material do you prefer to use for apical

barrier?

MTA yes 15 28.3% 65 83.3% <0.0001 ***

no 38 71.7% 13 16.7%

GP after apical closure with CH dressing yes 37 69.8% 12 15.4% <0.0001 ***

no 16 30.2% 66 84.6%

If a radicular radiolucency is present, would you

prefer?

An interim CH dressing yes 18 94.7% 51 82.3% 0.2768 Ns

no 1 5.3% 11 17.7%

To restore the tooth immediately yes 1 5.3% 11 17.7% 0.2768 Ns

no 18 94.7% 51 82.3%

If there is blood in chamber, how do you manage the haemorrhage?

Dress the canal and complete the treatment in a

subsequent visit

yes 9 47.4% 39 60.0% 0.4306 Ns

no 10 52.6% 26 40.0%

Wait passively for bleeding to stop yes 5 26.3% 11 16.9% 0.3432 Ns

no 14 73.7% 54 83.1%

Apply haemostatic agent yes 2 10.5% 9 13.8% 1.0000 Ns

no 17 89.5% 56 86.2%

What is your final irrigant prior to placing MTA?

NaOCl yes 6 31.6% 46 70.8% 0.0030 **

no 13 68.4% 19 29.2%

EDTA yes 6 31.6% 12 18.5% 0.2228 Ns

no 13 68.4% 53 81.5%

CHX yes 3 15.8% 1 1.5% 0.0347 *

no 16 84.2% 64 98.5%

Do you immediately obturate canals after MTA

placement?

yes 10 55.6% 55 85.9% 0.0089 **

no 8 44.4% 9 14.1%

What is your method of obturation after MTA

placement?

Injection technique yes 1 5.6% 34 53.1% 0.0003 ***

no 17 94.4% 30 46.9%

Vertical compaction yes 4 22.2% 9 14.1% 0.4679 Ns

no 14 77.8% 55 85.9%

If you restored the tooth in the same appointment, what material do you place above the MTA?

GP yes 6 54.5% 40 71.4% 0.3006 Ns

no 5 45.5% 16 28.6%

GIC/RMGIC yes 2 18.2% 9 16.1% 1.0000 Ns

no 9 81.8% 47 83.9%

If you permanently restore the tooth in a subsequent appointment, how do you temporise the tooth?

Damp cotton pellet followed by Cavit (3M ESPE) yes 7 87.5% 9 100.0% 0.4706 Ns

no 1 12.5% 0 0.0%

89

3.3.3.3 Root-endfillings

These results are found in Table 3-3. Only 45.5% of respondents perform root-end fillings

(13.8% GD, 94.9% ED). The majority of those undertaking this procedure used MTA

(78.3%: 47.1% GD, 85.4% ED). The differences were significant (respectively P<0.0001

and 0.0016). The remainder (3.5%) used Super EBA (Harry J Bosworth Co, Skokie, USA)

(5.8% GD, 7.6% ED). If there is blood actively flowing into the cavity preparation, 30.8%

(8.3% GD, 34.8% ED) would wash the surgical site with a haemostatic liquid, 28.2%

(33.3% GD, 27.3% ED) would use a haemostatic putty or solid, while 9.0% (8.34% GD,

9.1% ED) would wait passively for bleeding to stop. These differences between the GD

and ED cohorts were not significant.

3.3.3.4 Regenerativeendodontics

These results are found in Table 3-3. Of the total respondents, only 37.3% (11.5% GD,

77.2% ED) perform regenerative endodontics. The differences were significant

(P<0.0001). The most common material used was MTA (82.7%: 71.3% GD, 85.2% ED),

followed by Biodentine (6.7%: 14.8% GD, 4.9% ED) and GIC (4%: 7.0% GD, 3.2% ED).

The differences between the cohorts in material choices were not significant.

The most popular medicament pastes used in regenerative endodontic cases were CH

pastes (41.6%: 20.0% GD, 41.6% ED), followed by antibiotic-steroid combinations (24.7%:

33.3% GD, 22.6% ED), and tri-antibiotic pastes (19.5%: 13.3% GD, 21.0% ED).

90

Table 3-3 MTA root-end fillings and regenerative endodontics by GD and ED

3.4 Discussion

Although much literature from the UK, Europe and the USA describes the high cost of

MTA as being the main barrier to its widespread clinical use,5, 7, 10, 295, 296

the results of this study show that in the Australian context, the main factor that restricts

the use of MTA is a lack of formal training in how to use the material appropriately. It is

noteworthy that the majority of GD members of the ASE expressed a need to undertake

hands-on training in the use of MTA.

Although comparisons between the GD and ED respondents were made, the GD

respondents in this survey are members of the ASE and therefore have a special interest

GD ED Fisher’s


Do you preform root-end fillings? yes 17 13.8% 75 94.9% <0.0001 ***

no 106 86.2% 4 5.1%

What material do you prefer to use in root-end

fillings?

MTA yes 8 47.1% 64 85.3% 0.0016 **

no 9 52.9% 11 14.7%

SuperEBA (Harry J Bosworth Co) yes 1 5.9% 6 8.0% 1.0000 Ns

no 16 94.1% 69 92.0%

If there is blood in the cavity, how do you manage the haemorrhage?

Use haemostatic liquid yes 1 8.3% 23 34.8% 0.0922 Ns

no 11 91.7% 43 65.2%

Use haemostatic putty or solid yes 4 33.3% 18 27.3% 0.7314 Ns

no 8 66.7% 48 72.7%

Would wait passively for the bleeding to stop yes 5 41.7% 14 21.2% 0.1519 Ns

no 7 58.3% 52 78.8%

Do you perform regenerative endodontics? yes 14 11.5% 61 77.2% <0.0001 ***

no 108 88.5% 18 22.8%

What material do you prefer to use in

regenerative endodontics?

MTA yes 10 71.4% 52 85.2% 0.2476 Ns

no 4 28.6% 9 14.8%

Biodentine yes 2 14.3% 3 4.9% 0.2320 Ns

no 12 85.7% 58 95.1%

GIC yes 1 7.1% 2 3.3% 0.4670 Ns

no 13 92.9% 59 96.7%

What is your preferred Inter-appointment medicament for regenerative

endodontics?

CH yes 3 20.0% 29 46.8% 0.0811 Ns

no 12 80.0% 33 53.2%

Antibiotic and steroid paste combination yes 5 33.3% 14 22.6% 0.5049 Ns

no 10 66.7% 48 77.4%

Tri-antibiotic pastes yes 2 13.3% 13 21.0% 0.7214 Ns

no 13 86.7% 49 79.0%

91

in endodontics. Therefore, the GD that completed the survey may not be representative of

non-ASE member GD from Australia due to their special interest in endodontics.

The survey results indicate that MTA is the most popular material used for the creation of

an apical barrier, root-end fillings, perforation repair and regenerative endodontics. These

procedures are performed mostly by ED. Current 3-year specialist endodontic training

programmes in endodontics include the use of MTA as a component of specialist training.

MTA’s popularity in the Australian setting is resonated in international studies of PDs when

asked about the material of choice for apical barrier placement.295

Since acidic environments are unfavourable for MTA placement, it is encouraging to see

that for both perforation repairs and apexification cases, the most popular irrigant used

was NaOCl, which is an alkaline agent.310

The use of CHX as the final irrigant was less

popular than EDTA and NaOCl, which could be due to findings by Ng et al. that abstaining

from CHX use improves periapical healing.311

The concerns with CHX relate to its

interaction with NaOCl to form the cytotoxic and carcinogenic para-chloroaniline.312

Furthermore, CHX’s use with MTA can result in the retardation of the setting of MTA.133

The differences between GD and ED may be a reflection on the educational CPD

available on the handling and properties of MTA.

Most respondents to the survey opt to restore apical barrier cases with MTA immediately

with GP, instead of temporisation. For those who chose to obturate the remaining tooth

structure in a subsequent appointment, the common practice is to utilise a wet cotton pellet

followed by Cavit.313

The obvious rationale for immediate restoration is to reduce chairside

time. However, there is emerging literature supporting immediate restoration, albeit with

composite or GIC.123, 136

This difference between the GD and ED groups may also be a

reflection on the educational CPD available on the handling and properties of MTA.

Although it was common for almost all EDs to perform root-end fillings, apical barrier

placement and perforation repairs, fewer EDs performed regenerative endodontics. This is

possibly a reflection of the concerns that the procedure is less predictable than apical

barrier placement,314

or that treating anterior teeth with MTA can lead to substantial

darkening.120

The American Association of Endodontists (AAE) has published guidelines

on their recommended considerations when performing regenerative endodontics.

92

Australian GD and ED differ from the guidelines with combination antibiotic-corticosteroid

pastes as an alternative choice from CH or triple or dual antibiotic pastes. MTA is the

popular choice in Australia, which is in line to the AAE guidelines recommending the use

of MTA for regenerative endodontics.315

Most procedures in this survey were performed by over 94% of ED, the exception was

regenerative endodontics, which was performed by 77.2% of ED. Some ED who did not

perform regenerative endodontics commented that they did feel the treatment was

predictable or that it was an inferior treatment option to apical barrier placement. This is

comparable to a survey of the 2008 Endodontic Board of Diplomats 2008 Summer

Conference where the option of MTA apical plugs was preferred over regenerative

endodontics for treatment of necrotic immature teeth.316

In the United States of America (USA), a 2012 survey of endodontic postgraduate

residents illustrated that despite 96.8% were willing to receive training in regenerative

endodontics, 55.1% were unsure whether regenerative procedures would be

successful.317

Therefore, it is of interest that in 2015, 77.2% of Australian ED had

embraced regenerative endodontic treatments.

3.5 Conclusions

Significant differences exist between GD and ED, particularly on the percentages who use

MTA and the perceived need for continuing education on the use of MTA. This may be a

reflection on the educational CPD available on the handling and properties of MTA

contributing to the differences in technical procedures. Experience in handling MTA is a

larger barrier to its widespread use in endodontics than its cost.

93

Chapter 4 What is the particle size of MTA?

This chapter describes a study that assessed the particle size of two commercial brands of

MTA, MTA-P and MTA-A. While performing this test, opened package samples were also

tested. The study demonstrated that changes of particle size occur over time once the

packaging has been opened.


Ha WN, Kahler B, Walsh LJ. Particle size changes in unsealed mineral trioxide aggregate

powder. J Endod 2014;40:423-426.

4.1 Introduction

The original patent for MTA describes its ideal composition as 1 part BO and 4 parts PC.42

The latter component is hygroscopic and can absorb atmospheric moisture. 122

MTA-P is

supplied in 1-gramme packets, with the instructions “1 gramme - 1 treatment.” Therefore,

the packet should not be opened until its use, and any powder not dispensed for the

patient should not be reused. Nevertheless, a search of the term “MTA Uses” on a popular

internet discussion forum, “Dentaltown”,318

revealed numerous postings from clinicians

who are using MTA-P packets for multiple applications in order to lower the cost per

application. The high cost influences its clinical use. A recent survey has shown that, if

cost was not an issue some 85% of PDs and EDs would use it over FC.296

Furthermore,

cost has limited the uptake of MTA by educational institutions.10, 97

Whereas opened packets of MTA-P cannot easily be resealed, the container for white

MTA-A (Angelus Soluções Odontológicas, Londrina, Brazil) has a resealable lid. The

packaging is marked with the international standard symbol for “Do not reuse, Single use

only, Use only once”.319, 320

However, it is marketed as providing 7 applications for 1

gramme.

The existing literature does not address whether multiple uses of MTA from the same

container affects its properties. It can be expected that because MTA powder is

hygroscopic when it is left exposed to atmospheric moisture, it will react in a similar way as

MTA powder mixed with water.122

The particles will begin to hydrate and agglomerate with

neighbouring particles into larger structures. Therefore, MTA powder that has had

significant exposure to moisture should show an increased particle size. A larger particle

94

would have a lower surface area than that of the particles from which it was formed and

thus be less reactive. This could have implications for setting time, CS, and alkalinity.

Although the thermodynamic process involved in cement hydration is not completely

understood,321

a simplified mathematical model to understand the relationship between

particle size and the degree of hydration is the following:322

€

α(r) =1− 1− ktr

$

% &

'

( )

$

% &

'

( )

3

Equation 4-1 Degree of Hydration

Alpha (a) is the degree of hydration, t is the time, k is the rate constant and r is the radius

of the particle. From this formula, there is an exponential increase in the degree of

hydration as the particle size is reduced. This also suggests any differences in PSD

between MTA-P and MTA-A may also alter the degree of hydration.

Studies on the PSD of MTA are few.19, 323, 324

The patent for white MTA describes the PC

component as having 90% of the particles finer than 25 μm, 50% of the particles finer than

9 μm, and 10% of the particles finer than 3 μm.325

BO powder is supplied in various PSDs

and the patent does not discuss the resultant PSD once BO has been added. Scanning

electron microscope (SEM) examination of MTA indicates that particles range from < 1 µm

to as large as 50 µm.24, 326

The distribution of MTA particle size has been determined by using a flow particle

analyser. 24, 326

However, this method cannot accurately measure particles that are less

than 1.5 μm or greater than 40 μm.24, 326

An alternative method for assessing PSD is LDA,

which measures the size of particles through the scattering of the laser beam through a

dispersed particulate sample. The MicroPlus™ analyser (Malvern Instruments,

Worcestershire, UK) can accurately measure particles from 0.05-550 µm and is widely

used in the cement industry for quality control of PC.327

This study was undertaken to evaluate changes in the particle size of MTA over time that

result from atmospheric exposure during storage. It sets the groundwork for future work to

explore concerns with MTA properties when taken from multiple-use containers.

95

4.2 Materials and methods

This study replicated the methods of an investigation of fly ash, an industrial cementitious

product similar to MTA.328, 329

For LDA, the refractive index (RI) used for MTA was 1.842,

which was calculated as a weighted average from the RI of 20% BO and 80% PC.

A packet of MTA-P (lot no. 09001921) was opened, folded on itself, and kept within closed

boxed packaging for 2 years under normal room conditions. Another unopened packet of

the same lot served as the control. A jar of MTA-A (lot no. 12862) was opened once,

reclosed, and then kept for 2 years. For comparison, an unopened jar of fresh material (lot

no. 21381) was tested soon after receipt from the supplier. The manufacturer's instructions

for MTA-P suggest storing MTA between 10°C and 25°C. All containers were kept at room

temperature in a cabinet away from sunlight, in accordance with the manufacturer's

instructions for storage, for a period of 2 years. This duration was based on the expiration

date being 3 years from manufacture (S. Freeman, personal communication). The study

was performed in Brisbane, a city with a subtropical climate, with a mean maximum

temperature of 25.3°C and a mean minimum temperature of 15.5°C.330

One gramme of each MTA sample was placed into 1 L distilled water within a Malvern

MicroPlus Analyzer, with analysis taking 4 seconds. The water dispersant was under

continuous ultrasonic agitation to prevent agglomerated cement sinking to the bottom of

the beaker and to prevent re-agglomeration. The water was supplemented with 1 g/L

sodium hexametaphosphate (Calgon) to prevent the MTA powder floating on the surface

of the water and also to prevent hydration of the cement during the analysis. The period

from placing the powder into the dispersant until analysis was less than 10 seconds.

Spherical latex beads of 5 known sizes (0.8–20 μm) (lot no. 011899; ProSciTech Pty Ltd,

Kirwan, Australia) served as controls for instrument calibration. Particle area was

estimated by using spherical and cubic particle models with mean particle size as the

diameter.

Samples of fresh and 2-year-aged MTA-P were examined by using SEM with backscatter

imaging. Powder was sprinkled onto carbon tape and left uncoated. Images were taken at

15.0 kV with final magnification of ×1200 under low vacuum conditions by using an FEI

200 SEM (Quanta, Hillsboro, USA).

96

4.3 Results

Results from LDA are presented in Table 4-1 and Figure 4-1. MTA-P underwent a 6.5-fold

increase in median particle size from 1.99 to 12.87 μm, whereas MTA-A showed a 2-fold

increase in its D10 and D50, although its D90 remain relatively unchanged.

Cement Type D10 (10% of

particles are

below this size)

D50 (Median

particle size)

D90 (90% of

particles are

below this size)

ProRoot MTA,

freshly opened

1.13 μm 1.99 μm 4.30 μm

ProRoot MTA.

aged 2 years

4.37 μm 12.87 μm 34.67 μm

MTA Angelus,

freshly opened

4.15 μm 12.72 μm 42.66 μm

MTA Angelus,

aged 2 years

8.32 μm 23.79 μm 47.91 μm

Latex 0.8 μm 0.69 μm 0.77 μm 0.86 μm

Latex 1 μm 0.81 μm 0.91 μm 1.03 μm

Latex 3 μm 2.73 μm 2.88 μm 3.06 μm

Latex 5 μm 4.66 μm 5.59 μm 8.18 μm

Latex 20 μm 15.22 μm 18.55 μm 21.05 μm

Table 4-1 PSD of MTA

97

Figure 4-1 PSD of MTA-P (above) and MTA-A (below) when fresh and 2 y after having the packaging

opened

In terms of particle surface area, for MTA-P the increase in particle size from fresh to aged

product was from 15.2 to 725.4 square microns, a 47.7-fold change in the available

surface area. For MTA-A, the surface area change was from 936.5 to 1882.6 square

microns, a 2-fold change. When particles were modelled as being perfectly cubic, the

surface area reduction was 6.9-fold for MTA-P and 1.4-fold for MTA-A.

98

Backscattered SEM images of MTA revealed the agglomeration of particles (Figure 4-2).

In these images, BO appears as bright white particles (approximately 1–4 μm), which

corresponds to the first modal peak of 3–4 μm seen in the PSD for MTA-P.

Figure 4-2 BSE imaging of MTA-P.

BO appears as white particles because of the higher atomic number of the bismuth. Left: Fresh MTA. Right:

MTA after 2 years after opening packaging.

4.4 Discussion

This study has identified differences in PSD between MTA-P, MTA-A and between fresh

and aged samples. The instrumentation used had superior measurement abilities

compared with that used in previous studies,19, 323

and its accuracy was verified by using

latex spheres. Changes over time with the 2 different MTA products likely reflect

differences in their particle size (as per Equation 4-1) and their packaging systems, with

MTA-P having smaller particles at baseline and thus greater surface area, as well as being

stored in a non-resealable packet. The combination of these factors results in MTA-P

particles showing more dramatic agglomeration over time.

A potential technical limitation of the study relates to the dispersal method used for

samples. Ethanol is generally preferred over water as the dispersant for cements because

it eliminates the confounding effect of reactions with water. Samples were dispersed in

water rather than ethanol for occupational health and safety reasons, and sodium

hexametaphosphate was included to retard hydration, an approach that is accepted in the

cement industry for particle analysis.331

(B. Collins, e-mail to William Ha, December 12,

99

2012). The Malvern Analyzer takes only 4 seconds to analyse the whole 1-g amount of the

sample, a time period during which only limited setting would occur, even if sodium

hexametaphosphate was not used.332

(B. Collins, e-mail to William Ha, December 12,

2012). An additional limitation is that the test and control samples of MTA-A were not from

the same batch, which relates to how the material was supplied at the time the study was

commenced.

The increase in MTA particle size during storage alters the PSDs, with the smaller

particles being the most reactive. For example, with MTA-A, changes in D50 and D10 are

more prominent than D90, which would be predicted from Equation 4-1. Any MTA product

with an even smaller median particle size than MTA-P would be even more prone to

effects of atmospheric moisture during packaging and storage. This would require

heightened attention to the single-use principle as well as to the quality of the seal during

storage and may warrant the inclusion of a desiccant to ensure the shelf life of a sealed

container remains adequate.

A concern with partial or pre-hydration of particles is that larger particles of reacted cement

impair mixing333

and would likely retard the setting of the PC component as well as

decrease its CS once set.333, 334

Previous studies have revealed that pre-hydration of MTA

can cause the material to fail to set.335

The PSD graphs show a bimodal distribution, which results from the combination of

Gaussian distributions of the smaller BO powder particles (3.5 μm in MTA-P and 8 μm in

MTA-A) with PC particles that are much larger. BO powder is insoluble in water and is

believed to be chemically inert.175

There was no evidence of the BO particles reacting with

moisture over time in the study.

In terms of clinical implications, MTA-A in a bottle was better able to resist pre-hydration

than MTA-P in a packet when opened once during the 2-year period. MTA-A product

advertising states that 1 g is sufficient for 7 applications. If an MTA-A bottle was opened 7

times, one would expect much greater changes than observed in the study. It is suggested

that MTA packaging where multiple uses are promoted should feature a desiccant. An

example of this is MTA Plus (Avalon Biomed, Bradenton, USA), which is packaged as 8 g

MTA powder in a desiccant-lined container. There is as yet no published evidence to

illustrate that a desiccant can maintain the stability of MTA over multiple-use conditions.

100

Placing cement that has pre-hydrated because of exposure to atmospheric moisture in a

drying environment will not return the cement to the same state before pre-hydration.334

Therefore, any product that is not single-use has the potential for hydration on every

instance when exposed to the atmosphere.

4.5 Conclusion

MTA undergoes an increase in particle size once the manufactured seal has been broken.

The increase in particle size from exposure to atmospheric moisture differs between

brands and may affect the handling and subsequent clinical performance of the material, a

point that requires further investigation. In the absence of this information, the material

should be handled as a one-use application as recommended by the manufacturers.

101

Chapter 5 What constitutes the particle size of MTA?

This chapter describes a method of deconvoluting the particle size distribution (PSD) curve

of commercial brands of MTA to its core ingredients of PC and BO. The PSD curves of PC

and BO found in MTA-P and MTA-A are significantly different and contributes to their

different setting times.


Ha WN, Shakibaie F, Kahler B, Walsh LJ. Deconvolution of the particle size distribution of

ProRoot MTA and MTA Angelus. Acta Biomater Odontol Scand 2016;2:7-11.

5.1 Introduction

A typical MTA cement contains one part BO and four parts PC.16, 47

While essential for

radiographic identification of the material, the inclusion of BO extends the setting time67,

144, 336-338 and influences the physical properties of the set cement, altering its

microhardness,67

CS,338-340

porosity,339

biocompatibility341

and the speed of formation of

reaction products such as CSH.55

The particle sizes of both the BO and PC components can vary widely and has

implications for the performance of the cement. For example, cements with smaller

particles of PC will be more likely to penetrate into dentinal tubules, set quickly and give

greater initial release of CH.76, 322

There are also effects of the particle size of BO on the

cement, with nano-sized BO particles contributing positively to the properties of the set

cement, and BO particle sizes of 10 μm or more having the opposite effect.16

In previous studies, the PSD of common MTA cements have been examined using laser

diffraction analysis (LDA), a rapid, accurate and reproducible measurement method that is

used widely to assess the PSD of materials with fine particles, including industrial PC.342

In

this technique, as individual particles pass through a laser beam they scatter light at

angles that are inversely related to their size.343

A recent study of the particle size of MTA-

P revealed a bimodal distribution with 10% of particles below (D10) 1.13 μm, 50% of

particles below (D50) 1.99 μm, and 90% of particles below (D90) 4.30 μm. By comparison,

MTA-A showed a bimodal distribution with much larger particle sizes overall, with the D10

at 4.15 μm, D50 at 12.72 μm, and D90 at 42.66 μm.342

102

Given that a bimodal distribution implies the presence of at least two components of

differing particle size, it was of interest to determine the respective contributions of PC and

BO to the PSDs of the two commercial MTA cements, MTA-P and MTA-A.


5.2.1 Particlesizeassessment

Particle size analysis of MTA-P, MTA-A, PC and BO was performed using LDA, as

described in Ha et al,342

using a MicroPlus Analyser (Malvern Instruments, Worcestershire,

UK). This instrument can measure the size of particles from 0.05 to 500 µm in diameter.344

For MTA, the RI used was 1.844 and was calculated as the weighted mean of 80% PC (RI

= 1.68) and 20% BO (RI = 2.5). The Mie model was used for calculating particle size.345

The particle absorption index used was 0.1. One litre distilled water was used to disperse

1 gramme of particles from each material. Agglomeration of particles during testing was

prevented by the combination of sodium hexametaphosphate in the water (1g/L) together

with continuous ultrasonic agitation.

MTA-P (lot no. 09001921), MTA-A (lot no. 21381) and BO samples (lot no. F02U033, Alfa

Aesar®, MA, USA) were analysed, together with three samples of PC. PC1 (lot no.

SI0702, SiPowders, Toowoomba, Australia) was unmodified and was representative of

common general-purpose PC. PC2 (lot no. UFGP1707, SiPowders, Toowoomba,

Australia) was derived from PC1 and had undergone jet milling to reduce the mean particle

size to <14µm. PC3 (lot no. UFGP2307, SiPowders, Toowoomba, Australia) in turn was

derived from PC2 using selective particle filtration, and had a mean particle size <8 µm.

5.2.2 Statisticalanalysis

Data from PC1, PC2, PC3 and BO served as a reference for the deconvolution of the PSD

curves of MTA-A and MTA-P using a non-linear least-squares fit method. For both MTA-A

and MTA-P, the normalised frequency (F) at a given particle size was defined as:

F = (A×PC1) + (B×PC2) + (C×PC3) + (D×BO)

Equation 5-1 Normalised frequency at a given particle size

Where A, B, C and D are all constant coefficients for either MTA-A or MTA-P.

Equation 5-1 was solved to minimise the sum of squared residuals between actual and

predicted values, using values for A-D that were either positive or zero (component not

103

present). The results were then used to determine the number of components present

within MTA-P and MTA-A.

5.2.3 SEM

Dry MTA-P (lot no. 201404-01) and MTA-A (lot no. 21934) powders were lightly poured

onto carbon adhesive discs on SEM specimen stubs and left uncoated. Excess powder

was removed using compressed air. Samples were placed into a Phenom ProX (Malvern

Instruments, Worcestershire, UK) with images taken at 10 kV with a magnification of

1900� under vacuum conditions. Energy dispersive X-ray spectroscopy (EDX) was

performed on the same field of view to determine the elements present in the MTA

powder.

5.3 Results

All pure materials (BO, PC1, PC2 and PC3) showed a near Gaussian distribution for

particle size, with mode distribution peaks at 10.48, 19.31, 6.64 and 4.88 μm, respectively

(Figure 5-1). In order from largest to smallest, the three PC materials followed the

expected trend. BO particles were on average smaller than PC1 but larger than PC2 and

PC3. Table 5-1 shows PSD for BO and the three PC samples summarised according to

the D10, D50 and D90.

104

Figure 5-1 Normalised PSD for BO and three PC samples of differing size

Sample D10 (µm) D50 (µm) D90 (µm)

BO 4.26 10.34 20.92

PC1 (Raw PC) 0.22 9.44 94.38

PC2 (Sub-14 µm) 0.21 3.02 13.56

PC3 (Sub-8 µm) 0.19 1.73 7.69

ProRoot MTA 1.23 1.99 4.32

MTA Angelus 4.15 12.76 42.84

Table 5-1 PSD of PC and BO libraries, MTA-P and MTA-A

D10 = 10% of particles are below this size. D50 = median particle size. D90 = 90% of particles are below this

size.

The PSD for MTA-P had six peaks (0.42, 3.09, 5.69, 12.21, 22.49 and 41.43 µm). These

correspond well to PC3, BO and PC1 as its components (Figure 5-2). In contrast, the PSD

for MTA-A had only two maxima (9.0 and 30.53 µm) and corresponded to BO and PC1 as

its two components (Figure 5-2).

105

Figure 5-2 PSD of MTA-P (upper) and MTA-A (lower) and the associated deconvoluted components

106

5.3.1 BackscatterSEM

Backscattered SEM with EDX images of MTA-P and MTA-A revealed two predominant

crystalline structures in both powders. For both MTA-P and MTA-A, one component of the

powder was bright indicating a high atomic number, and displayed a different morphology.

5.3.2 EnergydispersiveX-rayspectroscopy

Energy dispersive X-ray spectroscopy (EDX) was performed on both powders on the SEM

field of view (Figure 5-3 and Table 5-2). This established that the strongly bright high

atomic number component contained bismuth and oxygen (thus BO) while the other

powder component contained calcium and silicon (thus PC). Thus, MTA-P illustrated

smaller BO and smaller PC particles than MTA-A. This corresponds to the deconvolution

results.

Figure 5-3 SEM of MTA-P (left) and MTA-A (right)

Bismuth oxide (white) and PC particles (grey) particles can be seen. Refer to Table 7-2 for EDX of four

points from each image.

Image ProRoot MTA MTA Angelus

Point 1 2 3 4 1 2 3 4

Element % % % % % % % %

Bi 77.5 - 80.8 - 86.2 90.2 - 87.2

O 10.0 27.6 7.9 43.3 2.8 2.5 33.5 5.2

C* 7.2 17.2 7.1 13.3 6.1 6.2 10.4 6.3

Ca 4.2 39.2 3.4 25.4 1.3 1.1 35.6 6.3

Si 1.1 9.8 0.9 7.5 - - 11.2 -

Table 5-2 Energy dispersive X-ray spectroscopy of points in Figure 7-3

* The presence of carbon is due to the conductive carbon adhesive tape

107

5.4 Discussion

An understanding of the particle size of MTA is fundamental to appreciating the influence

of this parameter on its setting reactions, physical properties when mixed and after setting,

and extent of penetration into dentine tubules. The results of this study show that there is a

bimodal distribution for both MTA-P and MTA-A. For MTA-P, both fine and larger particles

of PC are present, and BO is intermediate in size by comparison. In contrast, MTA-A is

simpler in composition, with finer BO particles and larger PC particles.

The findings that MTA-A had larger particles than MTA-P are similar to another LDA study.

19 However, our results differ as Komabayashi reports that MTA-A also has a high number

of small particles.19

This difference could be attributed the methods of testing as flow

particle analysis data have been presented in high power and low power fields. Neither of

these are able to completely assess the full range of the PSD found in MTA and PC.

The findings that MTA-A had larger particles than MTA-P are similar to another LDA

study.74

However, differences in PSD between MTA-A and MTA-P are more marked in this

study. The variance between studies could be attributed to the use of water as the testing

medium instead of alcohol as well as differences between testing batches.

The present findings provide insight into variations in performance between different MTA

products. Particles of MTA can penetrate into and obstruct dentinal tubules, which explains

the ability of MTA to provide an effective seal.346

MTA-P is more resistant to bacterial

leakage than vertically condensed GP and sealer,347

a fact that could be due in part to its

smaller PC particles that can penetrate further into dentinal tubules.

As with many other dental materials, the handling properties of PC varies according to

particle size and particle shape.76

Particle size modification is a common method to

accelerate setting reactions through increased surface area.74

For MTA, only the PC

particles contribute to the setting reaction, since BO is an inert filler. Adding BO to PC

separates the PC particles by diffusion and prolongs the setting reaction, with the material

taking longer to reach its final set. Increasing BO enhances radiopacity but at the expense

of slower setting,337, 340

reduced CS and increased water uptake.340

The same will be true

if other radiopaque agents are substituted for BO.348, 349

108

The PSD of MTA-P and MTA-A can be compared against Biodentine illustrating that its

largest and median particles are smaller than MTA-P and MTA-A.74

From communications

with the manufacturer, the composition of Biodentine features the replacement PC with

calcium silicate powder, various additives and ZO instead of BO as its radiopaque agent.

Although the smaller PSD of Biodentine may account for a faster setting time than MTA,

the ingredients are different and therefore comparisons relating to the PSD of the products

are speculative.74

It is recommended that any advertising by manufacturers around the topic of particle size

should state as a minimum the D10, D50 and D90 parameters of the product as well as

the particle size of the radiopaque agent used. This would avoid simplistic interpretations

of one product being superior on the basis of having a lower mean particle size (which

would infer faster setting), since the smaller particles could well be the radiopaque agent

rather than the PC, as is the case for MTA-A. This point could well become more important

in the future with the possible inclusion of nano-sized fillers rather than micro-sized fillers

to enhance the physical properties of MTA.16

109

Chapter 6 How does the particle size correlate with the setting time of MTA and

PC?

This chapter presents a study that assesses the correlation of setting time and particle size

of MTA and PC. The largest particles (D90) of a sample of PC strongly correlate with the

setting time of PC. The largest particles of a sample of MTA correlate less strongly with the

setting time suggesting that bismuth oxide and its particle size also contributes to the

setting time of MTA. Samples that had the smaller largest particles generally set faster

than samples with larger largest particles.

This chapter has been published as

Ha WN, Bentz DP, Kahler B, Walsh LJ. D90: The strongest contributor to setting time in

mineral trioxide aggregate and Portland cement. J Endod 2015;41:1146-1150. An abstract

from this also appeared in the Australian Dental Journal Research Supplement 2015; S11-

12.

6.1 Introduction

According to the relevant patent, MTA-P contains 80% PC and 20% BO by mass.42

Variants in composition exist for other MTA cements, namely 70% PC with 30% ZO.140, 350

BO or ZO is included to make the set material radiopaque, with a greater proportion of ZO

required to attain radiopacity in comparison with the original version that used BO.140, 350

There are minor variations in composition among MTA cements, such as the inclusion in

some products of calcium chloride, calcium carbonate, silicon dioxide, or the removal of

calcium sulphate, all of which accelerate the setting of PC.351-353

Rheologic modifiers serve

to improve the flow and handling characteristics of MTA. However, their compositions have

not been divulged to the authors because they are proprietary. The variation in the

compositions of the MTA cements examined in this study is shown in Table 6-1.

110

Ca

lciu

m s

ilic

ate

s

Ca

lciu

m a

lum

ina

tes

Ca

lciu

m s

ulp

ha

te

Bis

mu

th o

xid

e

Zir

co

niu

m o

xid

e

Ca

lciu

m c

arb

on

ate

Sil

ico

n d

iox

ide

Ph

yll

os

ilic

ate

s

Rh

eo

log

ica

l

mo

dif

ier

Ca

lciu

m c

hlo

rid

e

Biodentine y y y y y

EndoCem

MTA

y y y y y

EndoCem Zr y y y y y

EndoSeal y y y y y

MM MTA y y y y y y

MTA Angelus y y y

MTA Plus y y y y y

Ortho MTA y y y

ProRoot MTA y y y y

Retro MTA y y y

Trioxident y y y y y

Table 6-1 Comparison and composition of MTA brands

The advertised setting times of commercial MTA cements range from 2.3 minutes with

EndoCem Zr (Maruchi, Wonju, South Korea) to 4 hours with Trioxident (VladMiVa,

Belgorod, Russia). The range of new products can be confusing to the clinicians,

particularly as to why such a large range exists within products, despite all falling under the

general term of MTA. These differences may be attributed to their compositions, their

PSDs, and the methodology used to determine the setting time.

Two international standards are used to measure the setting time of MTA, ISO 6876 for

endodontic sealers 3 is more commonly used even though MTA is not used as a traditional

endodontic sealer in combination with GP points. The second international standard is ISO

9917-1, which is designed for cements that set with an acid-base reaction and is more

tailored to GIC-type cement-based materials.2

Although manufacturers have a vested interest in the marketing information to claim their

products are superior to others, their statements on setting time have greater reliability

because the statements of conformity to an ISO standard when registering to therapeutic

111

bodies such as the Food and Drug Administration and Conformité Européenne require

consistently repeatable results over different production batches.

MTA-P's advertised set time is 4 hours, which corresponds with 2 articles that describe its

“final set time” as 4 hours.87, 230

This shows the likely methodology that is advertised in

MTA-P's marketing is from ISO 9917-1. Endocem Zr's advertised setting time corresponds

with the “initial set time” or ISO 6876.87

Similarly, MTA-A advertises a set time of 15

minutes that is consistent with an article testing the “final set time,” which was defined by

the American Dental Association's specification 57 for setting times using American

Society for Testing and Materials (ASTM) C 266 at 18.33 minutes.67

Variations between the literature and the manufacturers' testing results may exist because

of the differences in the methodology as well as how the samples are processed.

Furthermore, the composition of dental materials is subject to change at the discretion of

the manufacturer.

Standard test method ASTM C 191 is commonly used for testing the initial and final setting

time of PC pastes using a Vicat needle.354

The differences between this Vicat needle test

and the Gillmore needle test (ASTM C 266) are compared in Table 6-2 below. The 2 ISO

standards are somewhat similar to ASTM C 266 (Gillmore needle); ISO 9917-1 uses

parameters similar to the defined initial setting time of ASTM C 266, and the parameters

used in ISO 6876 are similar to the defined final setting time of ASTM C 266. The

American Dental Association's specification 57 for setting time uses ASTM C 266 but with

the key difference of the temperature requirement being 37°C.

112

Standard Setting

time

term

Mass

(kg)

Diameter

(m)

Indentation

pressure:

(MPa)

Indentation

requirement as

‘set’

Test

temp.

(° C)

Needle

type

ISO 9917-

1

Net 0.4 0.001 4.99 No visible

penetration

37 Gillmore

ISO 6876 Setting

Time

0.1 0.002 0.312 No visible

penetration

37 Gillmore

ASTM C

266

Initial 0.1134 0.00212 0.315 No visible

penetration

23 Gillmore

ASTM C

266

Final 0.4536 0.00106 5.037 No visible

penetration

23 Gillmore

ASTM C

191

Initial 0.3 0.001 3.132 Less than 25mm

penetration

23 Vicat

ASTM C

191

Final 0.3 0.001 3.132 No visible

penetration

23 Vicat

Table 6-2 Summary of setting time standards commonly encountered in dentistry and for PC

Another way to assess the ongoing reactions within a material that contribute to the setting

is to measure their cumulative heat release whereby the thermal energy released by a

sample is measured over an arbitrary period of time. In this study, isothermal calorimetry

was applied to the PCs to assess their cumulative heat release during the first 4 hours of

hydration. For a given set of reactions occurring in the same proportions, the sample with

the most energy released on a per mass basis shows the greatest amount of reaction.

A fundamental concept in reaction kinetics is that any reduction of particle size of a powder

reactant will result in a higher surface area per unit mass and, therefore, is generally

expected to increase the rate of reaction. This increased rate of reaction with a reduced

particle size has been observed with PC when used in industrial applications.76

Therefore,

an MTA cement with a lower (average) particle size is anticipated to have an accelerated

reaction and a reduced setting time. Particle sizes within a given sample of PC typically

vary over 3 orders of magnitude,342

and the PSD is typically described using 3 reference

points: the 10th percentile (D10), 10% of the estimated particle diameters fall under this

size; the median (D50), 50% of the particles fall under this size; and the 90th percentile

(D90), 90% of the particles fall under this size.

113

The PSD of MTA has been assessed in studies by Komabayashi and Spangberg19, 323

and

Ha et al.342

The studies by Komabayashi and Spangberg used flow particle image analysis

in which MTA particles flow past a camera that rapidly determines the characteristics of

the particles. Within 1 study, Komabayashi and Spangberg19

used 2 flow particle methods

to analyse the PSD, with a lower-power field showing half or more of the particles being

between 6 and 10 μm, whereas another method using a high-power field showed three-

quarters of the particles to be within 1.5 and 3 μm.19

Within this study, these 2 methods

appear to provide results that are at odds with each other. However, the 2 methods are

restricted by the limitations of the machine. A low-power field can only effectively assess 6-

to 160-μm particles. However, it is evident through the results of this study that there are

MTA particles that are unable to be measured because their sizes are smaller than 6 μm

and larger than 40 μm. Similarly, a high-power field can only measure particles between

1.5 and 40 μm.19

The subsequent study by Ha et al, 342

using LDA for particle analysis on

a machine that can effectively measure between 0.05 and 550 μm, showed that MTA-P

has 80% of its particles falling between 1.13 and 4.30 μm, which matches the high-power

field findings of Komabayashi and Spangberg. MTA-A exhibited 80% of its particles falling

between 4.15 and 42.55 μm. However, the study by Ha et al used water as the

dispersant,342

which can react with MTA, resulting in the dissolution of some larger

particles into smaller particles as well as the formation of CSH structures forming larger

particles.

Laser diffraction involves the cement sample passing through a laser light source whereby

the scattering of the beam, the angular dependence, and the intensity of the light are

measured by detectors.345

The particle size, shape, and optical properties of the particles

influence the scattering of the beam, requiring the use of mathematical models to estimate

the PSD.345

The 2 most common mathematical methods used are the Mie and Fraunhofer

models, with little difference between them when particle sizes are above 50 μm; the Mie

model is recommended for particles below 50 μm in size.

Clinicians are now seeing multiple variations of MTA that set faster than the original

formulations, with their respective marketing attributing their properties to unique

differences in their formulations. This study explores whether a correlation exists between

the setting time of MTA and some measure of the powder’s PSD, irrespective of the

formulation. The inclusion of PC in this study serves to confirm whether any trends

114

identified with MTA are replicable with PC, particularly when the cements all originate from

the same clinker, albeit ground to different particle sizes.

6.2 Materials and Methods

6.2.1 PSD

The standard method of LDA was used to measure the PSD of MTA cement powders, as

performed by Ha et al,342

with a difference being that methanol was used as the solvent

instead of water to prevent hydration of the particles during analysis. One gramme of each

MTA sample was suspended in 1 L methanol within a Mastersizer 2000 (Malvern

Instruments, Worcestershire, UK), with the analysis being completed within 4 seconds.

The Mastersizer 2000 can assess particle sizes from 0.02–2000 μm.

The methanol solution was under continuous ultrasonic agitation to prevent particle

agglomeration. Based on the equipment manufacturer's recommendations, the RI used for

MTA cements nominally containing 80% PC and 20% BO was 1.844 (calculated from the

weighted average of the 2 components, respectively [1.68 and 2.5]). Likewise, the RI used

for MTA products nominally containing 70% PC and 30% ZO was 1.82 (calculated from

the weighted average of the 2 components, respectively [1.68 and 2.25]). For both

variants, the particle absorption index used was 0.1. The ability to classify each of the 11

materials used according to their composition was based on data provided by the

manufacturers although exact compositions were not disclosed to the investigators.

6.2.2 Materials

The commercial MTA products that were analysed using an RI of 1.842 were EndoCem

MTA (lot no. C2304160610; Maruchi, Wonju, Republic of Korea), MM MTA (lot no.

7302238; MicroMega, Besancon, France), MTA-A (lot no. 21934), MTA Plus (lot no.

85001), OrthoMTA (lot no. OM1305D02; BioMTA, Seoul, Republic of Korea), MTA-P (lot

no. 9001766), and Trioxident (lot no. 0509; VladMiVa, Belgorod, Russia). The commercial

brands of MTA or related HDCs that were analysed using an RI of 1.82 were Biodentine

(lot no. B01564), EndoCem Zr (lot no. ZC2403120516), EndoSeal MTA (lot no.

SC402080525, Maruchi), and RetroMTA (lot no. RM1304D05, BioMTA).

Three cements, having different fineness but manufactured from the same cement clinker,

were supplied by Lehigh Cement Corporation (Redding, USA). These 3 cements from fine

to coarse are classified according to ASTM C150 as being type III, type II/V, and type I/II

115

PC. From these 3 cements, 3 more cements of intermediate levels of fineness were

created by blending the coarsest and finest cements at 3 different ratios as seen in Table

6-3. Similar to the determination of MTA's PSDs, the PC was also assessed using wet

LDA, as described by Bentz.355

116

Types of PC D10

(µm)

D50

(µm)

D90 (µm) Initial

setting

time (h)

Final

setting

time (h)

4 h heat

release

(J/g cem)

Type III PC 0.975 6.768 17.441 1.92 2.67 36.56

Type II/V PC 1.245 11.24 32.912 2.17 3.18 33.03

25:75 blend of Type I/II and III PC 1.079 7.875 24.180 2.89 3.70 29.44



Type I/II coarse PC 1.850 17.78 49.870 3.76 4.97 20.71

Correlation with initial setting time r= 0.748 0.674 0.804

Correlation with final setting Time r= 0.837 0.781 0.873

Correlation with 4 h heat release r= -0.835 -0.769 -0.901

Brand of MTA D10

(µm)

D50

(µm)

D90

(µm)

Setting

time (h)

Biodentine 1.170 3.481 7.510 0.20

EndoCem MTA 1.086 3.247 8.328 0.08

EndoCem Zr 0.967 2.490 6.035 0.04

EndoSeal MTA 0.838 2.060 5.394 0.10

MM MTA 1.844 7.286 16.511 0.33

MTA Angelus 2.606 8.493 23.739 0.25

MTA Plus 1.259 4.740 10.267 1.25

OrthoMTA 0.966 3.384 21.117 5.50

ProRoot MTA 0.980 5.070 19.386 4.00

RetroMTA 1.225 8.218 24.948 0.04

Trioxident 2.969

12.789

32.259 4.00

Correlation with setting time: r = 0.110 0.212 0.538

Table 6-3 Summary of PSDs of PC, MTA, their setting times and cumulative heat release

Data for the setting time of MTA were compiled through direct contact with the

manufacturers. With 2 exceptions, all confirmed the testing methodology used was ISO

6876. The manufacturers of Biodentine used ISO 9917-1, whereas the manufacturers of

MTA-P did not divulge their methodology. The correlation of D10, D50, and D90 of the

PSD with the setting time was assessed for strength of correlation via determination of r,

the Pearson correlation coefficient.

117

The initial and final setting times of PC were determined using a Vicat needle as described

in ASTM C 191354

for pastes with a water-to-cement mass ratio of 0.40 prepared in a high

shear blender.355

6.2.3 Heatofhydration

Heat of hydration was measured over a period of 4 hours using isothermal calorimetry of

sealed 5 g samples of premixed pastes of cement and water (same water-to-cement mass

ratio of 0.4 as the setting time specimens).355

6.3 Results

The PSDs of MTA products are summarised in Table 6-3. When data from all 11 materials

were combined, the highest positive correlation with setting times was found for D90,

which gave a positive Pearson correlation of r = 0.538. This is illustrated in Figure 6-1. In

contrast, the correlations for D50 and D10 were significantly less (i.e. 0.212 and 0.110,

respectively). The equation describing the correlation for setting time (t) to D90 was as

follows:

t (h) = 0.1188×(D90)-0.4932

Equation 6-1 Function of setting time with D90

The plot of Equation 6-1 with the actual results is shown in Figure 6-1 in which a modest fit

of the experimental data to this function can be seen. Some of the MTA cements are likely

to contain chemical accelerators or are based on different chemistries, confounding the

observed relationship with particle size.

118

Figure 6-1 Setting time versus D90 of MTA

A summary of the PSD characteristics of the PCs and their measured setting times and

heat release is provided in Table 6-3, whereas the results are shown graphically in Figure

6-2.76

For the initial setting time, positive correlations exist with D10 (r = 0.748) and d50 (r

= 0.674), but the highest correlation exists with D90 (r = 0.804). The final setting time is

positively correlated with D50 (r = 0.781) and is more strongly correlated with D10 and

D90 although the D90 strengths of correlation (r = 0.872) are greater than that of D10 (r =

0.837). Heat release is negatively correlated with all 3 PSD parameters, with once again

the highest magnitude correlation being found for D90 (r = −0.901). The equations

describing the correlation for the initial setting time (it), final setting time (ft), and cumulative

heat (h) to D90 were as follows:

it (h) = 0.0507×(D90 )+1.276

Equation 6-2 Function of initial setting time with D90

ft(h) = 0.0615×(D90 )+1.8428

Equation 6-3 Function of final setting time with D90

h (J/g) = -0.4906×(D90)+44.264

Equation 6-4 Function of cumulative heat with D90

119

Figure 6-2 Setting times and cumulative heat release versus particle size of PC

120

The heat released after 4 hours is greatest for samples with the smaller particle sizes,

illustrating a greater exothermic reaction has occurred within that timeframe. This shows

smaller particles result in a greater exothermic reaction within that period of time, which

produces a quicker setting time.

6.4 Discussion

Equation 6-1 describes a modest trend line with 4 notable outliers, OrthoMTA, MTA-P,

MTA-A, and RetroMTA. If the assumption is made that MTA-P's advertised set time is the

“final set time” of ASTM C 266 or ISO 9917-1, then the preferred value to include within

this study is the initial set time, or ISO 6876, which would be approximately 78 minutes,87

with the setting time of MTA-P falling much closer to the trend line. MTA-A and RetroMTA

both have setting times substantially quicker than the trend line, with both MTA products

not including calcium sulphate, a common setting retarder found in PC.

The highest correlation indicated by this study is the setting time to the D90 reference

point in particle size. This correlation was observed in both PC and MTA materials,

although the magnitude of the correlation in the MTA studies was smaller, perhaps due to

the presence of accelerants or other modifiers in some of those formulations.

The highest correlation indicated by this study is between the setting time and the D90

reference point in particle size. This correlation was observed in both PC and MTA

materials although the magnitude of the correlation in the MTA studies was smaller,

perhaps because of the presence of accelerants or other modifiers in some of those

formulations.

The largest particles play a significant role in setting because they typically react the

slowest because they provide less surface area per unit volume, slowing the nucleation

and growth of hydration products.356

In other words, the testing method for setting reflects

the characteristics and proportions of the largest-sized particles that are consumed at a

slower rate, not those of the smallest particles that are consumed in less time. Setting

requires the formation of a percolated framework (scaffolding) of connected partially

hydrated cement particles. Some of the smallest particles (eg, 1 μm or less in diameter)

will dissolve quickly in the mix water and therefore will not be available to participate in the

construction of this percolated particle network. This will not be the case for the larger

particles that only partially hydrate, even after a curing duration of several days, and can,

therefore, contribute to the connected structure that will produce a set cement paste.

121

Aside from using indentation tests, such as the Gillmore and Vicat needles, there are other

ways to infer the setting during hydration of cement. This study features the use of

isothermal calorimetry where it is shown that smaller particle sizes result in greater heat

release over a period of 4 hours. In the case of PC, halving the D90 size almost doubled

the heat release. Because the D90 of the different brands of MTAs range from 7.5–32.3

μm, it is possible that the heat release between 2 different samples could almost be

several times different. Further research is required to determine if this could potentially

affect pulpal repair and osteogenesis.

Many manufacturers alter the setting time of MTA by adjusting PSD. There are limits to

this approach because smaller particles of PC may produce hydration products with

greater porosity (because of increased water demand), an elevated risk of cracking, or

greater shrinkage during setting.76

An accelerated setting time can lead to potential clinical

advantages such as reduced washout and a lower possibility of blood or serum

contamination during setting.357

. More research is required to determine if such practical

advantages outweigh possible long-term structural concerns when the material sets too

quickly.

122

Chapter 7 What are the strength implications for set MTA if the particle size was

changed?

To overcome the prolonged setting time of MTA, the cement powder can be made finer

which would accelerate the setting time. This chapter assesses the changes in physical

strength of an experimental MTA and PC when the particle size is reduced. It found that

initial CS was stronger for finer cements. However, over the long term, no advantage was

seen.

This chapter is published as

Ha WN, Kahler B, Walsh LJ. The influence of particle size and curing conditions on testing

Mineral Trioxide Aggregate cement. Acta Biomater Odontol Scand 2016;2:130-137.

7.1 Introduction

MTA is typically comprised of 80% PC and 20% BO. Particles of BO make the cement

radiopaque,47

but they are insoluble in water and do not make a significant contribution to

the setting reaction.175

However, BO physically separates particles of PC during the setting

reaction, which then influences the properties of the set cement.22, 144, 356

The PSD is known to influence the setting time of both PC and MTA since cements with

smaller particle sizes achieve earlier resistance to indentation and take less time to reach

95% of the plateau value for the elastic modulus (G’) plateau.74, 80

It is not yet known how

changing the particle size affects the CS and FS of the set cement.

Assessment of PSD is performed using LDA as it can account for the three dimensionality

of particles and accounts for a large range of particle sizes.358

The use of SEM sampling

was not used because the method involves assessing individual particles and hence

would lead to an unrepresentative result.358

The international standard for testing the CS of water-based cements involves removing

samples from their setting moulds after only one hour.2 However, as MTA cements

typically take several hours to set, it is prudent to keep the samples within their moulds for

a wet curing period of 24 hours.2, 47

The international standard does not describe how to store samples of cement after the

initial 24-hour period, prior to testing. A range of storage methods have been used,

123

including dry storage, storage in air with 95% or 100% humidity, and complete immersion

in water.235, 285

MTA cement will expand when stored in physiological solutions and

therefore is expected to desiccate if stored dry in room air,276

which could result in lower

strengths. Aggarwal et al. assessed the FS of set MTA when exposed to various irrigation

solutions including 5.25% NaOCl, 2% CHX, 17% EDTA, BioPure MTAD and distilled

water,124

but their study did not assess the influence of pH per se.

It can be anticipated that storage parameters such as moisture and pH in the laboratory

have parallels to clinical conditions where set MTA is in contact with tooth structure. Given

the likely influence of environmental conditions on the physical properties of MTA, the aim

of this study was to assess the impact of curing conditions on the mechanical properties of

MTA (i.e. CS and FS), particularly variables that could contribute to differences in

laboratory studies of MTA. Likewise, this study also examined the effect of PC particle size

on these same parameters, since alterations in particle size could give improved

properties to the set MTA cement.

7.2 Material and Methods:

7.2.1 SamplePreparation

Two experimental MTA cements were created by combining PC (Si Powders Pty Ltd,

Toowoomba, Australia, lot no. UFGP0907/MilledGP) and BO (Alfa Aesar, Ward Hill, USA,

lot no. E11Y009). Regular PC (P2) was created by routine milling processes to create PC.

A finer powder (P1) was produced by jet-milling the PC which abrades the larger particles

into smaller particles while selectively collecting particles of lower mass and size. P2 and

P1 was and then mixed with BO powder at a 4:1 ratio, thus producing two MTA cements of

differing particle size (M2 > M1).

7.2.2 PSD

Laser diffraction particle size analysis was performed in accordance with ISO 13320 as

described previously,345

using a Mastersizer 2000 Analyser (Malvern Instruments,

Worcestershire, UK). The Mastersizer 2000 Analyser can measure particles from 0.02μm

to 2000μm with accuracy of +/- 1%.359

One gramme of each powder dispersed into 1 L of methylated spirits as the diluent.74, 342,

360 Methylated spirits was used as it produces similar results to isopropyl alcohol when

assessing small particles.358

Ultrasonic energy was applied to disperse agglomerated

124

particles with samples tested within 5 seconds on the application of the samples to diluent.

This short period of ultrasonication is not expected to significantly alter the PSD of the

sample and is commonly applied in industries assessing PC.332

The particle absorption index used was 0.1. The RI of heterogeneous materials was

calculated using weighted averages. For methylated spirits, the calculated RI was 1.36

(5% of methanol RI 1.327 and 95% of ethanol RI 1.362).361

Likewise, the calculated RI for

MTA was 1.844 (80% of PC RI 1.68 and 20% of BO RI 2.5).362, 363

The Mie theory for

calculating particle size was applied, as it is the preferred method for samples with

particles below 50μm.345

7.2.3 CuringconditionsandCS

To prepare samples for testing CS and FS, powders were mixed with water at a powder-

to-water ratio of 3:1 (by mass), as suggested by the original MTA patent,47

using mixing

capsules with 30 seconds agitation at 4600 oscillations per minute within an amalgamator

(Ultramat 2 SDI Ltd, Bayswater, Australia).

To assess the effects of storage on physical properties, cement M2 was chosen. CS was

assessed using the method of ISO 9917-1 at 1 week.2 M2 cement was prepared and

placed into split moulds (internal dimensions 4 mm diameter and 6 mm height) and the

material allowed to set for 1 day.

ISO 9917-1 involves setting cements in moulds for 1 hour followed by storage of the

cement in Grade 3* water at 37±1°C for 23±0.5 h. However, as MTA takes several hours to

set,47

the following alterations to ISO 9917-1 were performed:

1. Rather than setting the cement for 1 hour prior to removing the cement from the moulds,

the cements were allowed to set for 1 day. This was to accommodate the prolonged

setting time of MTA as ISO 9917-1 is more appropriate for fast setting cements such as

GIC.2

2. Rather than storing the cement in Grade 3 water, the cement was stored under four

conditions, namely dry, in pH 5 Grade 3 water, in pH 7.5 Grade 3 water and in 0.15

mmol/L phosphate buffered saline (PBS) (Sigma-Aldrich, St. Louis, USA), at pH 7.2. The

* Grade 3 water as defined by ISO 3696:1987

125

purpose of using PBS compared against the other conditions was to see if physiological

conditions differ from anticipated typical laboratory conditions. The purpose of the two

types of Grade 3 water is to assess whether Grade 3 water can produce variable results.

3. Samples were then tested with one of two CS assessments. The first used an Instron

5543 Testing Machine (High Wycombe, UK), which was used in a dry room (24°C). The

second used an Instron 5848 Testing Machine (High Wycombe, UK), in which the samples

were submerged in PBS at 37°C in an Instron BioPuls bath (High Wycombe, UK). The

loading rate for both machines was 50 N/min. Six replicates were used for each sample

group instead of five. The purpose was to again, consider the differences between testing

in a dry environment against testing submerged in PBS to replicate physiological

conditions.

CS was calculated using the formula:

CS 4p

πd2

Equation 5 Formula for compressive strength

Where p is the maximum force applied (N);

d is the measured diameter of the specimen (mm).

7.2.4 CuringconditionsandFS

Samples of M2 cement were cured, stored and tested in various environmental conditions

as described above. The split moulds had internal dimensions of 25 mm length, 2 mm

height, and 2 mm width, as per ISO 4049.364

Eight replicates were used for each sample

group. ISO 4049 is typically for composite resins and hence the curing conditions

described above for CS were utilised.364

FS was calculated with the formula:

FS 3Fl

2bh2

Equation 6 Formula for flexural strength

Where F is the maximum load (N) exerted on the specimen;

l is the distance (mm) between the supports;

b is the width (mm) at the centre of the specimen;

h is the height (mm) at the centre of the specimen.

126

7.2.5 ParticlesizeeffectsonCS

Samples of P1, P2, M1 and M2 cements were prepared, using split moulds with internal

dimensions of 6 mm height and 4 mm diameter. The samples were allowed to set for 1 day

submerged in PBS solution at 37°C, and then allowed to cure for a further 1 day, 1 week

or 3 weeks, all in PBS at 37°C. This protocol was chosen based on the optimal results

obtained for M2 cement in the previous part of the study. CS was assessed as per ISO

9917-1,2 using an Instron 5848 Testing Machine (High Wycombe, UK) with the samples

submerged in PBS at 37°C as described above. The loading rate was 50 N/min. Nine

replicates were used for each sample group, which was different to the suggested five

replicates in ISO 9917-1.

7.2.6 ParticlesizeeffectsonFS

Samples of P1, P2, M1 and M2 cements were prepared, using split moulds which had

internal dimensions of 25 mm length, 2 mm height, and 2 mm width, as per ISO 4049.364

The samples were allowed to set for 1 day submerged in PBS solution at 37°C, and then

allowed to cure for a further 1 day, 1 week or 3 weeks, all in PBS at 37°C. FS was

assessed as described above for M2 cement. Ten replicates were used for each sample

group.

7.2.7 Statisticalanalysis

Data sets were tested for normality followed by ANOVA with post-hoc tests. Those that did

not pass normality tests were assessed using the Mann-Whitney or Kruskal-Wallis test to

determine differences between groups, with Dunn’s multiple comparison post-hoc tests.

Data sets that did pass normality tests were assessed using analysis of variance, with

Bonferroni post-hoc tests.

7.3 Results

7.3.1 PSD

Data for PSD is summarised in Table 7-1. P2 and M2 had larger particle sizes, while P1

and M1 had smaller particles.

127

Description D10 (μm) D50 (μm) D90 (μm)

100% BO 4.6 8.8 16.4

P2 (100% PC) 2.2 12.5 29.1

P1 (100% PC) 1.8 6.1 15.2

M2 (80% P2 / 20% BO)

2.7 13.0 37.1

M1 (80% P1 / 20% BO) 1.8 6.5 16.5

Table 7-1 PSDs of experimental cements and their constituents

D10 = 10% of particles below this size; D50 = median particle size; D90 = 90% of particles below this size

7.3.2 EffectofcuringandtestingconditionsonCS

As shown in Figure 7-1, M2 cement, in a PBS was significantly greater in CS than dry

storage when tested in dry conditions (P<0.01) with all other samples that were tested in

dry conditions illustrating no significant differences. However, when comparing samples

that were all tested in PBS, there was no significance between the groups.

When comparing dry versus submersion in PBS testing conditions, there was a twofold

increase in the means from a sample that was stored dry and tested dry, to a sample that

was stored dry and tested in PBS. However, there was no significant difference between

the groups.

128

Figure 7-1 Effect of curing conditions on the physical properties on MTA

Bars show means and errors bars indicate 95% confidence intervals. Differences between groups were

calculated with the Kruskal-Wallis test, with post-hoc Dunn's multiple comparison tests. Error bars are 95%

confidence intervals. Bars indicated with the same letters are significantly different. S: Storage conditions for

1 week. T: Testing conditions.

129

7.3.3 EffectofcuringandtestingconditionsonFS

As shown in Figure 7-2, M2 that were stored in PBS and tested in dry conditions illustrated

significantly greater FS than samples that were stored dry and tested in dry conditions

(P<0.05). However, there were no differences among the remainder of the samples under

dry conditions.

For samples that were tested in PBS, there was a significant difference between samples

that were stored dry and samples that were stored in pH5 (P<0.05). However, there was

no difference between the other groups.

130

Figure 7-2 Influence of particle size and time on the physical properties of MTA, when stored in PBS

Bars show means and errors bars indicate 95% confidence intervals. Differences between groups were

calculated with parametric ANOVA with post-hoc Bonferroni's multiple comparison tests. Bars indicated with

the same letters are significantly different. 1d, 1w, 3w: Stored in PBS for 1 day, 1 week and 3 weeks,

respectively.

131

7.3.4 EffectofparticlesizeonCS

Results for CS over time in the 4 different cements during storage in PBS are summarised

in Figure 7-2. At day 1, the cements with smaller particle sizes (M1 and P1) had greater

CS than those with larger particle sizes (M2 and P2). Comparing similar products, there

was a significant difference between M1 and M2 (P<0.001), and between P1 and P2

(P<0.01). Also, there was significance between P1 and M2, (P<0.001) and P2 and M1

(P<0.05).

By one week of curing, there was no significance difference between the cements.

After 3 weeks, P2 showed a significantly higher CS than the other three cements

(P<0.001) while the other cements had no differences between each other.

P1 had a significant drop from 1 day to 1 week (P<0.05). However, there was no

significant difference between the other time periods. P2 had significant increase in CS

over those time periods (P<0.05/3). There was no difference in M1 over the time periods of

1 day, 1 week and 3 weeks. M2 had a significant increase (P<0.001) from 1 day to 1 week

and from 1 day to 3 weeks. However, the differences between the other time periods were

not significant.

132

7.3.5 EffectsofparticlesizeonFS

Changes in FS over time are summarised in Figure 7-2. At day 1, P1 had a significantly

greater FS than P2 and M2 (P<0.05 and <0.001, respectively). There were no significant

differences between the other groups.

By one week of curing, M2 had a significantly greater FS than P2 (P<0.05). However,

there were no significant differences between the other groups.

By three weeks of curing, M2 was significantly lower than the other cements (P<0.05) with

the other cements having no difference between each other.

Comparing the same cement tested over different time periods, P1 and M1 had no

significant difference over the time periods. P2 at 1 week was significantly lower (P<0.01)

than the other time periods of 1 day and 3 weeks. However, 1 day and 3 weeks were not

different from each other. M2 is significantly improved from 1 day to 1 week (P<0.01) and

there was a significant, albeit small, drop from 1 week to 3 weeks (P<0.01) but there were

no significant differences between 1 day to 3 weeks.

7.4 Discussion

This study utilised the mechanical mixing of encapsulated MTA to eliminate operator-

induced variability on mixing and consistent mixing of optimum water-to-powder

proportions, a method applied by other studies.174, 365

Samples that were stored in PBS, when tested in dry conditions, had better CS and FS

than samples that were stored dry and tested dry. This illustrates the importance of

submerged MTA in PBS when storing samples as dry storage of MTA would desiccate the

MTA resulting in weaker CS. The average value of 26.5 MPa obtained for dry-stored and

dry-tested MTA is comparable to the findings of Porter (27 MPa),235

while the 66 MPa

value obtained for PBS-stored and wet-tested MTA is comparable to that of Camilleri

(above 65 MPa)144

and Torabinejad et al (67MPa).242

A trend was seen for lower CS under acidic conditions. This aligns with results of previous

studies that reported environmental acids causing MTA to deteriorate.107, 108, 366

This point

is also relevant to sites of dental caries or acute inflammation where a lower pH will be

133

found. Despite the trend of lower CS for acidic conditions, the differences were not

statistically significant with PBS and slightly alkaline mixing water.

Interestingly, the CS of dry-stored MTA tested in PBS was comparable to samples cured in

aqueous conditions, suggesting that MTA once rehydrated shows improved CS but not

improved FS.

In this study, the number of samples assessed in each group varied slightly due to some

samples becoming locked into the split moulds or being damaged upon removal, and thus

excluded. This problem could be overcome if the stainless-steel moulds specified in the

ISO standard were replaced with single-use or re-useable soft bendable moulds, to

facilitate sample removal. One study has employed single-use moulds that are cut to

preserve the integrity of the set samples, and reported that the CS of such MTA samples

when cured in the presence of air, albeit, with a nearby wet cotton pellet were higher than

similarly dry stored samples in other studies.127

After placing MTA, clinicians can place a wet cotton pellet, dry cotton pellet,367

or a

restorative material above the newly placed MTA.368

The results of the present study

illustrates that using a dry cotton pellet could be detrimental to the strength of the MTA.

Although curing MTA in a wet environment is better than curing in a dry environment, the

current results do not suggest that placing a wet cotton pellet is superior to placing a

restoration directly above the MTA.

In the cements tested in the present study, smaller particle sizes gave significantly greater

initial CS at 1 day. However, over periods of 1 to 3 weeks, this advantage became less

apparent. The results show a trend where MTA generally had weaker initial strengths than

its counterpart in PC, which replicates the findings of Islam and colleagues.229

However, a

significant difference was not found in this study, likely due to the smaller sample sizes.

The other trend demonstrated that was that cements with larger particle sizes have weaker

initial strengths than their counterparts with smaller particles. This trend is comparable to a

rheological study that illustrated that both MTA and PC with smaller sizes had faster

setting times.80

M2 was used in this study as its PSD is similar to commonly acquirable PC enabling

greater reproducibility of similar studies. Although M1 has faster setting times, its long-term

134

properties showed no advantages over M2. In fact, the fast setting time of ultrafine PCs

can result in thermal cracking as well as chemical shrinkage.76

Ultrafine PCs also require a

greater water-to-cement mixing ratio, or alternatively, will become a difficult to handle

material (i.e. crumbly).369

A possible risk is utilising greater amounts of mixing water will

increase the solubility of MTA, which is a clinically undesirable property.143

Although the use of finer cements can reduce the setting time of PC and MTA,

consideration of chemical additives is required to overcome the other properties that

accompany the reduction in PSD.74

An interesting finding was that the D90 for the experimental MTAs was greater than the

D90 of the PCs and BO when it should be less. The use of a weighted average RI is

appropriate for D10 and D50. However, this approach becomes less accurate for the

larger D90 particles. A possible method that could be employed in future studies

measuring the PSD of MTA would be to use centrifugal separation, as the density of the

BO radiopacifier particles is far greater than those of the PC particles, and to then perform

LDA of the separated mixtures. Alternatively, a study could be performed using various PC

and BO products with a range of PSDs that are then combined to create experimental

MTA cements to determine an ideal RI for MTA.

In summary, when MTA is assessed in vitro, it should be wet-cured, i.e. submerged in

water, to prevent desiccation of the samples. Testing should also be performed in

physiological conditions. Reducing the particle size provides initial advantages in CS and

FS as well as reported acceleration in setting time.74

However, this advantage is lost over

time and other methods to improve the properties of MTA should be considered.

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Chapter 8 How is the setting time measured? What if the particle size was

changed to hasten the setting time?

This chapter utilises the historical indentation method for assessing setting time, and offers

an alternative method to assessing setting time, based on rheology. Both methods are

used on PC and experimental MTA cements to illustrate the influence of particle size of the

PC upon the setting time, as well as the slowing effect of bismuth oxide on the setting

reaction. As with the previous chapter, it is noted that the cements with smaller particle

sizes had faster setting times. Rheological methods provide a better insight as to

progression of the hydration reaction of MTA than indentation tests.

This chapter is published as

Ha WN, Nicholson T, Kahler B, Walsh LJ. Methodologies for measuring the setting times

of mineral trioxide aggregate and Portland cement products used in dentistry. Acta

Biomater Odontol Scand 2016;2:25-30.

8.1 Introduction

MTA is an important dental cement with multiple uses in both endodontics and paediatric

dentistry.122, 153, 218

Its handling has been viewed as difficult, and its setting reaction is

known to be slow.370

There have been numerous attempts to improve the handling

properties and to accelerate the setting reaction of MTA cements.

Indentation tests are commonly used for analysing setting characteristics. These tests

assess the point when the setting material has sufficient resistance to indentation from a

standardised weight. The ISO methods used currently for assessing the setting time of

MTA, namely, ISO 6876 and 9917-1 are designed for testing endodontic sealers and

dental restorative materials, respectively. Both ISO tests involve indenting the cement, with

resistance to indentation illustrating the final set.2, 3

ASTM C 266, also known as the

Gillmore needle test, defines initial set using a similar indentation pressure to ISO 6876,

and final set with a similar indentation pressure to ISO 9917-1.371

Applying different

indentation tests can produce quite different outcomes. For example, MTA-P has a setting

time of 32 min according to ISO 6876,372

but 3.8 h according to ISO 9917-1.353

Despite the convenience and simplicity of indentation testing for MTA cements, the validity

of this approach is questionable. The ability of a cement to resist indentation from an

arbitrary weight has limited relevance to whether the material is nearing the end of its

136

setting reaction. From a clinical point of view, indentation from a small area point load is

not reflective of the forces applied to the material when placed within the tooth. This is

particularly the case in endodontics where occlusal load should not appreciably affect a

material placed in a perforation repair or other radicular location. Furthermore, indentations

tests do not provide insight into the kinetics of the setting reaction of MTA.

An alternative method of measuring setting time is by utilising rheometric measurements.

Rheometry has been used previously to assess the flow properties of endodontic sealers

through narrow capillaries (as a model of flow into root canals)373

and the setting of GICs

using either a “displacement rheometer”, which measures the developing elastic recovery

of the sample as it cures373

or a cone/plate rheometer in steady shear mode.374, 375

To

date, the use of rheology to characterise MTA cements has been limited to one

investigation,376

which compared MTA to Biodentine and Fuji IX® (GC, Tokyo, Japan). The

initial setting point was arbitrarily set at a G’ of 10 MPa and 100 MPa as final set. Based on

this, the MTA cement evaluated had an initial setting time of 70 min, and a final setting

time of 175 min. These long time periods conflict with clinical evidence that MTA is

restorable after 45 min using GIC placed above the MTA,123

and after 10 min with

composite resin placed above the MTA.136

Thus, the MTA had reached a restorable

condition despite not reaching either the traditional definitions of setting based on

indentation tests, or when applying the arbitrary G’ values of 10 and 100 MPa to indicate

initial and final setting, respectively.

Within rheology, the parameter of G’ is of particular interest, since it measures resistance

to elastic (temporary) deformation under a force. Tracking changes in G’ over time can

document the change in a material from a liquid-like state (with less resistance) to a solid-

like state (with greater resistance). The G’ will asymptotically approach a plateau value at

long time periods when the material is fully set. Therefore, rather than a fixed modulus

being chosen for the initial setting point, a better choice would be to use a certain

percentage of the final modulus. One study proposed a setting time based on the

accumulation of 95% of deformation recovery.373

While the choice of a percentage is

arbitrary, the results must match the clinical properties of the material.

The setting properties of MTA cement are influenced by the particle size of the PC.

Commercial brands of MTA have different particle sizes, but many have smaller particle

sizes than MTA-P, the original MTA product. Products with smaller particle sizes set more

137

rapidly when the setting is evaluated using indentation tests.342

. A typical MTA cement is

four parts PC and one part BO.42

The latter is insoluble in water and does not contribute to

the setting reaction.175

Adding the BO makes the cement radiopaque, but it also alters the

water-powder ratio, with more water required to hydrate the combined powder compared

to PC powder alone.356

Moreover, adding BO or other radiopaque agents to the PC

powder dilutes the system and physically separates the PC particles, which then changes

the flow, workability and setting time of the cement.22, 144, 356

The current literature on the particle size of MTA describes particle size distributions that

represent the combined distributions of PC and BO. This overlooks the properties and

influences of the particle sizes of PC and BO on the properties of MTA. Accordingly, this

study was undertaken to assess the changes in rheological setting properties that occur in

experimental MTA from the inclusion of BO, and as PC particle size is reduced. The study

compared the setting time using traditional indentation testing with that from “95% of

plateau G’” as a definition of the setting time for MTA. The choice of 95% reflects a close

alignment with the observed clinical handling of the material, i.e. MTA-P can be restored at

10 min.136

Therefore, the chosen parameter within the setting properties should be close to

10 min since the feature of considerable relevance to the clinician is the property of

restorability.

8.2 Material and methods:

Two PC powders of different fineness but manufactured from the same cement clinker,

were supplied by Si Powders Pty Ltd (Toowoomba, Australia, lot no. UFGP0907/MilledGP;

UFGP0907/TS8GP). The regular powder (P2) was created by routine milling processes to

create PC. The finer powder (P1) was produced using by jet-milling the regular powder,

which abrades the larger particles into smaller particles while selectively collecting

particles of lower mass and size.

From these PC powders, experimental MTA cements were created by the addition of BO

(Alfa Aesar®, MA, lot no. E11Y009) to a final level of 20%. This approach generated a

regular (P2) and fine (P1) PC, and a regular (M2) and a fine (M1) experimental MTA, from

the same original clinker. All four prepared powders were then mixed at powder to water

ratio of 3:1 by mass, as recommended in the original MTA patent.42

138

8.2.1 DeterminationofPSD

Laser diffraction was used to measure the PSD of the cement powders, as employed in

previous studies.342

One gramme of each cement was suspended in 1 L of methylated

spirits as the dispersion liquid. The sample within the dispersion liquid was collected by the

Mastersizer 2000 analyser (Malvern Instruments, Worcestershire, UK). Analysis by the

Mastersizer was completed within four seconds. This instrument can measure particles

within the range of 0.02–2000 μm.

Mie theory was applied as it is the preferred method when there are particles below 50 μm,

with testing performed in accordance with ISO 13320:2009.345

The particle absorption

index used was 0.1. The RI of a heterogeneous material was calculated using weighted

averages, based on the equipment manufacturer’s recommendations. The dispersant,

methylated spirits, had a RI of 1.36 (5% methanol at a RI of 1.327 and 95% ethanol at a RI

of 1.362).361

The RI for PC was 1.68362

and the RI for MTA was 1.844 (80% of PC at RI

1.68 and 20% of BO at RI 2.5).363

The particle absorption index used was 0.1. A sample of

MTA-P powder (lot no. 9001766) was also assessed using a RI of 1.844.

8.2.2 Indentationtesting

PC and experimental MTA powders were mixed with water at a powder-to-water ratio of

3:1 (by mass) using mixing capsules for a period of 30 s, within a dental amalgamator. The

mixed samples were placed into metal moulds with internal dimensions of 5 mm depth,

10 mm length and 8 mm width, and the surface flattened. The samples were incubated at

37 °C and 95% humidity, as per ISO 9917-1.2 Indentation tests were used to determine the

initial and final setting times, following ASTM C 266–08.371

The initial setting time was

based on the sample resisting a load of 113.4 g applied using a needle diameter of

2.11 mm. The duration from the time of mixing and the point in time where the 113.4 g

needle did not mark the surface with a complete circular indentation was deemed as the

initial set time. The final set time was performed using the same method, but using a load

of 453.6 g and a needle diameter of 1.06 mm. There were seven replicates used to assess

initial and final setting time measurements for each of the cements.

8.2.3 Rheologytesting

The G’ and G” of the setting cements were tested following a method similar to that from a

previous study,376

using an ARES strain-controlled rheometer (Advanced Rheometric

Expansion System, TA Instruments, New Castle, USA). The mixed samples were placed

between two parallel plates covered in emery paper, 25 mm in diameter with a 0.6–0.7 mm

139

gap. The lower plate was maintained at a temperature of 38 °C, and a closed chamber

was used to maintain a constant temperature and 100% relative humidity, to prevent

desiccation. The rheometer was operating in an oscillatory (sinusoidal) mode with an

oscillation frequency of 0.159 Hz and an applied strain of 0.01%. Under these conditions,

the applied strain was less than that required to alter the structure of the material,

approximately 0.05%, established from performing a strain sweep on the cements using

the rheometer, the changes in elastic shear modulus over a period of 30 min were

measured.

Using rheometry, the “setting time” was defined as the point in time when the material

reached 95% of its plateau G’. In all cases a plateauing of the G’ was seen within the

30 min of data collection so the value of the modulus at 30 min was taken as the ultimate

modulus.

8.3 Results

8.3.1 PSDs:

The PSDs of the P1, P2, M1, M2 cements, BO and MTA-P are summarised in Table 8-1.

Description D10 (μm) D50 (μm) D90 (μm)

BO (100% Bi2O3) 4.6 8.8 16.4

P2 cement (100% PC) 2.2 12.5 29.1

P1 cement (100% PC) 1.8 6.1 15.2

M2 MTA (80% P2 / 20% BO) 2.7 13.0 37.1

M1 MTA (80% P1 / 20% BO) 1.8 6.5 16.5

ProRoot MTA 1.0 5.1 19.4

Table 8-1 PSDs of PC, experimental MTA and bismuth oxide used to produce MTA

D10 = 10% of particles below this size; D50 = median particle size; D90 = 90% of particles below this size

The BO used to create the experimental MTA cements had a median size of 6.5 μm, and

90% of particles (D90) were below 16.4 μm. This was similar to the D90 value for the finer

powder used (Table 8-1). As expected, P2 cement and M2 MTA (P2 with BO) had larger

particles and were similar in particle size, while P1 and M1 were also similar but had finer

particles (Table 8-1).

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8.3.2 Indentationsettingtimes

Data for setting times using indentation testing are shown in Table 8-2. For experimental

MTA, initial setting times, finer particle size samples had a faster initial setting time than

those with larger particle sizes. The fine powder MTA set the fastest, while the large

particle size MTA set the slowest. Comparing the groups, M1<P1<P2<M2 with all

differences between groups being statistically significant (P<0.05).

Cement Initial Set (minutes) Final Set (minutes)

P2 cement (100% PC) 144.7 ± 24.4 300.3 ± 12.8

P1 cement (100% PC) 79.0 ± 9.2 225.2 ± 35.7

M2 MTA (80%P2 /20% BO) 169.1 ± 29.0 419.3 ± 50.4

M1 MTA (80%P1 /20% BO) 68.67 ± 24.8 243.0 ± 39.1

MTA-P 87

78 ± 5 261 ± 21

Table 8-2 Indentation testing initial and final setting times

Values shown are means and standard deviations. Data listed for MTA-P are taken from Choi.87

In terms of final setting, the inclusion of BO delayed the setting reaction, with PC showing

a faster final setting time than the experimental MTA of the same particle size. As was

seen for initial setting times, finer particle size samples had a faster final setting time than

those with larger particle sizes. Comparing the groups, P1<M1<P2<M2, with all

differences between groups being statistically significant (P<0.05).

8.3.3 Rheologicaltesting

For the G’ plateau, the differences between experimental MTA and the corresponding PC

(i.e. P1 versus M1 and P2 versus M2) were small and did not reach statistical significance.

The finer particle powders showed a reduced time to reach the 95% maximal value for G’

compared to the larger particle powders. As before, finer particle samples had lower final

setting times than larger particle samples, and PC had a faster setting time than

experimental MTA samples made from powders of the same particle size

(P1 < M1 < P2 < M2). The faster setting time corresponded with a greater G’ plateau

(P1 > M1 > P2 > M2) Table 8-3.

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Cement N G’ Plateau (MPa) Time to reach 95% of

Plateau G’ (minutes)

P2 (100% PC) 4 1.9±0.2ab

13±3ab

P1 (100% PC) 3 2.7±0.6a 7±2

b

M2 (80% P2 / 20% BO) 4 1.5±0.6b 19±6

a

M1 (80% P1 / 20% BO) 3 2.4±0.4a 10±5

b

Table 8-3 Plateau G’ and the time to reach 95%

Values shown are means and standard deviations. Different superscript letters indicate statistically

significant differences between groups by Fishers exact test (P < 0.05)

Figure 8-1 shows the transition of the G’ and G″ over time for M1. The horizontal dotted

line shows 95% of the plateau modulus. These trends are representative of the materials

tested since in all cases (P1, P2, M1, M2) the G″ value increased initially and then fell. The

material is initially visco-elastic at the point where G’ and G″ are similar in magnitude,

albeit at low values. At this point, during initial stages of the setting process, the

interlocking of crystals begins to occur and both the G’ and G” will rise. At this stage, the

cement mix is becoming progressively thicker and is less able to flow. At later times, as

crystallite interlocking becomes more complete, the viscous modulus (G″) falls. The value

for tan delta (the ratio G″/G’) tracks the transition from viscoelasticity to elasticity.

Figure 8-1 G', G" and their ratio (tan_delta)

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8.4 Discussion

The results of this study provide several useful insights into testing the setting process of

PC and materials such as MTA that are based on PC. The first point is that reducing the

particle size of the powder accelerates the setting reaction. For both PC and the

experimental MTA, the finer particle cements had faster setting times, regardless of

whether the testing method was indentation or rheology. Of note, the fine powder used in

the study had a median particle size half that of the standard PC powder, and the

corresponding reduction of setting time using the plateau G’ method was also halved, for

both PC and experimental MTA. However, the extent of acceleration seen using

indentation testing for assessing final setting was much less marked.

The second key point is that the inclusion of BO slows the setting reaction, and this effect

is seen more so with indentation testing than with rheometry. There are several

explanations that can be offered, and these are not exclusive. First, the addition of the BO

radiopaquer dilutes the PC powder. Second, BO particles may impair the extension of

crystallites during the hydration phase. Finally, BO may act as a barrier between the PC

particles and the water during the initial hydration stage.

Previous work using rheology arbitrarily set an G’ of 10 MPa as the initial set and 100 MPa

as the final set. For MTA, this would correspond to times of 70 and 175 min,

respectively.376

Neither of the 10 or 100 MPa values correspond to realistic loads that the

material would be expected to be subjected to during its setting.

This study utilised an experimental MTA, M1, which had a comparable PSD, initial

indentation set time, and, final setting time to MTA-P. For this experimental material, the

time to reach 95% of the plateau for G’ was 9.3 min. This time point at which the material

had become significantly more resistant to deformation is similar to the time point at which

MTA-P is ready to be overlaid with a permanent restoration, which is 10 min.136

For

example, in paediatric dentistry, when MTA is placed during a pulpotomy, it is then

overlaid with a permanent restorative material in the same appointment.377-380

Likewise,

when MTA is used in endodontics, it will be overlaid with a conventional restorative

material. These additional restoratives alter the distribution of forces through the tooth and

reduce the load that reaches the MTA during its curing phase.

143

This study illustrates that the time taken to reach 95% of the plateau value for the G’ is the

most useful parameter since it aligns to attributes of the set material that have meaning to

clinicians. In contrast, indentation tests do not relate to how MTA is used clinically in

dentistry, despite their obvious utility and relevance for assessing concrete used in

construction or civil engineering projects, where resistance to point loads is important.

Thus, clinicians should consider, when using MTA-P, to wait 10 min prior to placing

another direct restoration over the MTA as this time period enables MTA to reach its peak

physical properties within clinically viable time frames.

Clinicians should consider, when using MTA-P, to wait 10 minutes before placing another

direct restoration over the MTA as this time period enables MTA to reach its peak physical

properties within clinically viable time frames.

Rheology as a method of assessing setting time provides several advantages over

indentation testing. First, rheometers apply pressures onto the cement that are controlled

by a machine while indentation relies upon the tester to use human judgment to drop a

weighted needle at a minimised distance from the cement without touching the cement

prior to its release. Second, rheometers use a small chamber that is part of the rheometer

with controlled temperature and humidity to match physiological conditions. Indentation

testing is not typically performed with controlled humidity. Third, rheometric findings can be

plotted over time to assess progressive changes in a setting material. These changes

relate to the progressive setting and hardening of a material that enables quantitative

assessment. Indentation testing is a nominal descriptor with the defining point illustrating

no known clinical applicability. Furthermore, indentation testing relies upon the subjective

visual assessment of whether a material has a full indentation.

The final positive point regarding rheology is that when cement sets, a superficial water

layer forms on top of the cement. Rheometer plates can use graded plates that engage

into the cement to ensure the rheometer is assessing the properties of the cement instead

of the water.381

The subjective visual assessment of indentations in indentation testing is

confounded when testing MTA by a watery layer that forms over setting cement.

8.5 Conclusion

As both PC and its dental cement derivatives such as MTA set slowly, the tests used to

confirm that final set has been achieved should have meaning clinically, and be

informative to clinicians when they are comparing various products. The time taken for the

144

setting cement to reach 95% of the plateau value for the G’ is suggested as a better and

more useful parameter to express the dynamics of the setting reaction of these materials

than the currently used indentation tests.

145

Chapter 9 Can the rheological method of setting time assessment be used for

other cements?

In the previous chapter, the results produced from use of rheology to assess the setting

time of MTA and PC correlated well with the appropriate time to restore MTA. This chapter

explores whether this same rheological method can be applied for other endodontic and

restorative cements.

This chapter is intended to be submitted to the journal “Materials”.

Ha WN, Nicholson T, Kahler B, Walsh LJ. Rheology as an alternative method to

indentation for determining the setting time of restorative and endodontic cements.

9.1 Introduction

The Academy of Prosthodontics defines dental cements as “binding elements or agents

used to make objects adhere to each other, or something serving to firmly unite”, i.e. a

luting agent,382

while the international standard for dental vocabulary defines dental

cements as materials for “luting of dental prostheses and lining or base filling of prepared

teeth, or, the substitution of missing parts of teeth”.383

Furthermore, the AAE defines a

“root canal sealer” as “a radiopaque dental cement used, usually in combination with a

solid or semi-solid core material, to fill voids and to seal root canals during obturation;

included are bioceramics, resins, CH, ZOE, GICs and others”.384

There does not appear to be any formally accepted definition for dental cements that

encompasses luting agents, liners, bases, restorative cements and endodontic sealers,

although from a clinical end user perspective they all could be grouped under a definition

such as “any material that requires mixing of components resulting in a hardening colloid

that progressively sets to become a solid.”

Of the two commonly referenced testing methods for testing dental cements, ISO 9917-1

details methods for testing the properties of zinc phosphate, zinc polycarboxylate, and

GICs, while ISO 9917-2 describes the same approach for resin-modified cements and ISO

6876 details methods for testing the properties of endodontic sealing materials.2, 3

The

method used to assess setting time in both sets of standards involves placing a weighted

circular needle (Gillmore needle) perpendicularly onto the setting cement. If the needle

leaves a circular indentation, the cement is deemed to be unset. If the needle does not

leave a circular indentation, then the cement is deemed to be set. In ISO 9917-1, the

146

Gillmore needle has a mass of 0.4 kg and a diameter of 1 mm and applies a force of 4.99

MPa.2 In ISO 6876, the Gillmore needle has a mass of only 0.1 kg, a diameter of 2 mm

and so applies a force of only 0.312 MPa.3 The logic that underpins the 16-fold difference

in the pressures applied between the two standards appears to be that restorative

cements are expected to sustain greater loading under function.

A key issue when interpreting indentation setting times is that the outcomes at any one

point in time are dichotomous, since the material is defined as either ‘unset’ or ‘set’. The

indentation approach gives no insight into the progression of the setting reaction. It is

possible that the definition of ‘set” could erroneously be interpreted as meaning

‘completely reacted’ when in fact the setting reactions of the cement have not yet reached

completion.80

A different approach to determining the setting time is described in ISO 4049 for resin

dental materials and specifically refers to changes in temperature over time that reflect the

exothermic nature of the setting reaction which, when graphed, resembles a sigmoid

curve. Setting time is determined by extending a horizontal line from the plateau to meet

an extension of the straight line along the temperature increase.364

This point of

intersection occurs just before the temperature reaches a plateau.

A third approach to measuring setting times is to track changes in the rheological

properties of materials over time. This has been used to measure the flow properties of

endodontic sealers373

and for testing the properties of GICs.374, 375, 385

An advantage of this

approach is that the clinical handling and setting properties relate strongly to the flow of

the material. Past rheological studies of GIC have used either a displacement rheometer,

which measures the developing elastic recovery of the sample as it cures or a cone/plate

rheometer in steady shear mode.374, 375, 385

A study of an experimental MTA cement used a

strain-controlled rheometer with two parallel plates to measure the changes in G’.80

There

have also been reports of the flow properties of endodontic sealers.274

When assessing rheological properties, the parameter of G’ is of most interest, since this

represents resistance to elastic (temporary) deformation under force. Tracking the G’ over

time can document the progression of a mixture from a liquid-like state (with less

resistance) to a solid-like state (with greater resistance).80

As time progresses and the

material sets the G’ will asymptotically approach a plateau value. One could then set a

147

threshold such as 90 or 95% of the final modulus to define an endpoint,80

although the

selection between such specific threshold values is arbitrary. Logically the definition of

when the material sets should correspond closely with its clinical manipulation.

MTA is typically a mixture of 80% PC with 20% bismuth oxide.47

The principal setting

reaction occurs between tricalcium silicate, dicalcium silicate and water, producing various

CSHs.47

Under ISO 9917-1, which is named “water-based cements”, the indentation

needle approach gives a setting time of 4 hours, which does not align with its clinical use

since in most cases MTA is overlaid with a permanent material within the same

appointment.80, 87, 136, 230

A similar situation exists for Biodentine, a material that has setting

reactions that are broadly similar to MTA but with a shorter setting time.360

The setting reaction of GIC involves aluminosilicate glass particles reacting with

polycarboxylic acid, producing a gel within which polyacid chains cross-link to produce the

set material.45

Under ISO 9917-1, GIC luting agents are expected to set under 8 min, while

GIC used as bases, liners and bulk restoratives are expected to set under 6 min. The

setting reaction of GIC continues long after the indentation-designated setting time and is

described as ‘maturation’.386

AH 26® (Dentsply DeTrey, Konstanz, Germany) is an epoxy resin cement supplied as a

powder that is mixed with a liquid (bisphenol diglycidyl ether). The powder contains

bismuth oxide (as the radiopaque agent) and hexamethylenetetramine (HMT), which

serves as the hardener. When mixed, the HMT crosslinks the bisphenol diglycidyl ether to

produce a three-dimensional network and hence making the material set into a hard

mass.387

A related epoxy resin cement is AH Plus JetTM

(Dentsply DeTrey, Konstanz, Germany),

which is supplied as a dual paste system. The epoxy resin component is diepoxide, while

the hardener component is a polyfunctional amine mixed with silicon oil. Both components

also contain fumed silica as an inert thickener.388

Another endodontic sealer is RealSeal SETM

(SybronEndo, Amersfoort, Netherlands),

which is a fourth generation methacrylate resin sealer, specifically, 4-methacryloxyethyl

trimellitic anhydride.389

148

The aim of the present study was to assess changes in G’ over time for a range of dental

materials (MTA, Biodentine, two GICs, two epoxy resin sealers and one methacrylate resin

sealer), using the time to reach 90% of the plateau G’ as the setting time.


9.2.1 SamplePreparation

MTA-P (lot no. 13102907) was mixed with distilled water to a ratio of 0.40 by weight. This

mixing ratio was based upon a compromise between the water:powder ratio of 0.33, as

recommended in the patent47

and the ideal water:powder ratio of 0.42 required when

mixing water with PC to achieve complete hydration without supplying extra water.390

This

ratio of 0.40 for mixing water with MTA powder has been used by other studies.391, 392

The

powder and water mix was placed into a capsule that was agitated in an amalgamator for

30 seconds at 4600 oscillations per minute. The use of a capsule to mix the cement aligns

with previous studies.79, 80

In a similar manner, Biodentine® powder (lot no. B05594) in

capsules was mixed with the provided liquid in an amalgamator for 30 seconds at 4600

oscillations per minute.

AH 26 ® (lot no. 1406001107) was mixed by combining 2 volumes of powder with 1

volume of resin (paste), while AH Plus Jet (lot no. 1406000958) was prepared from the two

component pastes using the supplied automatic mixing tips to provide the correct ratio.

Likewise, RealSeal SE (lot no. 4971883) was prepared using the supplied automatic

mixing tips.

Fuji VII® (GC Corporation, Tokyo, Japan, lot no. 1303041), Fuji VII® EP (lot no. 1108031)

and Fuji IX® GP Extra (GC Corporation, Tokyo, Japan, lot no. 1111261) were supplied in

capsules that were mixed in an amalgamator for 10 seconds at 4600 oscillations per

minute.

9.2.2 Rheologicaltesting

The measurement of elastic modulus (G’), viscous modulus (G”) and their respective ratio

(tan delta) for various dental cements during the setting process followed the protocol

used in a previous study.80

In brief, testing was performed using an ARES strain-controlled

rheometer (Advanced Rheometric Expansion System, TA Instruments, New Castle, USA),

within which freshly mixed cements were placed between two parallel 25 mm diameter

circular plates separated by a 0.6-0.7 mm gap. Each plate was covered with emery paper.

149

The lower plate was maintained at 38oC, and an enclosed chamber was used to maintain

this constant temperature as well as 100% relative humidity to prevent desiccation. The

rheometer conditions were an applied strain of 0.01% with a 1 radians per second

oscillation frequency. These conditions apply less strain than would alter the structure of

the material, approximately 0.05%, a threshold established by performing a strain on the

cements. Each material was tested in triplicate.

A minor difference between this study and previous investigations was that the rheological

setting time was defined as the point in time when the material reached 90% of its plateau

G’, while in past work the rheological setting time was defined as the point where the

cement reached 95% of the plateau G’.80

9.3 Results

Representative rheological data are presented in Figure 9-1, while data for plateau G’ (in

MPa) are given in Table 9-1. The calculated setting times based on the time to reach 90%

of the plateau G’ are given in Table 9-2.

In increasing order, the setting times were as follows: Fuji VII EP: 3.3 min, Fuji VII: 3.6 min,

Fuji IX GP Extra: 3.7 min, Biodentine: 15.9 min, RealSeal SE 22.2 min. These values

illustrated margins of error below 5%. However, the remaining setting times of AH Plus Jet:

5933.3 min, AH 26: 5066.7 min and ProRoot MTA: 5.1 illustrated larger margins of error.

Figure 9-1 illustrated that ProRoot MTA samples did not illustrate the same pattern of

gradual elastic modulus increases seen in other samples. This is likely due to loss of

structural integrity of the material.

A comparison of marketed setting times against proposed setting times using the time to

reach 90% of the plateau elastic modulus is given in Table 9-2.

150

Figure 9-1 G' of tested dental cements

151

n Mean

(min)

SD

(min) SE

Margin of

Error1

(min)

Upper

Bound

(min)

Lower

Bound

(min)

Max

(min) Min (min)

Range

(min)

Fuji IX GP

Extra 3 1.7E+08 1.5E+07 8.8E+06 1.73E+07 1.84E+08 1.49E+08 1.80E+08 1.50E+08 3.00E+07

Fuji VII 3 1.5E+08 1.7E+07 1.0E+07 1.96E+07 1.70E+08 1.30E+08 1.70E+08 1.40E+08 3.00E+07

Fuji VII EP 3 1.4E+08 3.2E+07 1.9E+07 3.64E+07 1.73E+08 1.00E+08 1.60E+08 1.00E+08 6.00E+07

Biodentine 3 1.1E+08 5.8E+06 3.3E+06 6.53E+06 1.20E+08 1.07E+08 1.20E+08 1.10E+08 1.00E+07

ProRoot

MTA 3 6.4E+07 5.6E+07 3.2E+07 6.33E+07 1.27E+08 7.20E+05 1.20E+08 8.10E+06 1.12E+08

RealSeal

SE 3 9.6E+07 5.0E+07 2.9E+07 5.65E+07 1.53E+08 3.99E+07 1.30E+08 3.90E+07 9.10E+07

AH 26 3 4.3E+07 7.5E+07 4.3E+07 8.48E+07 1.28E+08

-

4.13E+07 1.30E+08 1.80E+05 1.30E+08

AH Plus 3 7.5E+07 6.4E+07 3.7E+07 7.19E+07 1.47E+08 2.72E+06 1.40E+08 1.30E+07 1.27E+08

Table 9-1 Plateau G’ of various dental cements (in MPa)

1 - Confidence coefficient is set at 1.96.

n Mean

(min)

SD

(min) SE

Margin

of Error1

(min)

Upper

Bound

(min)

Lower

Bound

(min)

Max

(min)

Min

(min)

Range

(min)

Fuji IX GP Extra 3 3.7 0.1 0.0 0.1 3.8 3.7 3.8 3.7 0.1

Fuji VII 3 3.6 0.2 0.1 0.2 3.8 3.4 3.8 3.5 0.3

Fuji VII EP 3 3.3 0.3 0.2 0.3 3.6 3.0 3.5 3.0 0.5

Biodentine 3 15.9 2.8 1.6 3.1 19.0 12.7 18.5 13.0 5.5

ProRoot MTA 3 5.1 2.8 1.6 3.2 8.3 1.9 7.6 2.0 5.6

RealSeal SE 3 22.2 3.6 2.1 4.1 26.3 18.2 24.4 18.1 6.3

AH 26 3 5066.7 1674.3 966.7 1894.7 6961.3 3172.0 7000.0 4100.0 2900.0

AH Plus 3 5933.3 1686.2 973.5 1908.1 7841.5 4025.2 7100.0 4000.0 3100.0

Table 9-2 Time to reach 90% of plateau G’ (in minutes)

1 - Confidence coefficient is set at 1.96.

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Dental Materials

Clinical usage Average time to

90% plateau G’ Testing method

1

Setting time1

(min)

Fuji IX GP Extra Restorative 3.7 ISO 9917-1 2.0

Fuji VII Restorative 3.6 ISO 9917-1 2.5

Fuji VII EP Restorative 3.3 ISO 9917-1 2.5

Biodentine Root repair 15.9 Not stated 12.0

ProRoot MTA Root repair 5.1 Not stated 240.0

(4 hours)

RealSeal SE Endodontic sealer 22.2 6876 45.0

AH 26 Endodontic sealer 5933.3

(4 days)

6876 540.0 to 900.0

(9-15 hours)

AH Plus Endodontic sealer 5066.7

(3.5 days)

6876 Minimum 480.0

(8 hours)

Table 9-3 Comparison of marketed setting times against setting times using the time to reach 90% of

the plateau G’

1 According to manufacturer’s product information.

9.4 Discussion

The current common definitions for dental cements are based on their clinical uses rather

than their chemical properties. As many materials can have multiple clinical uses, the term

“dental cement” should be defined by the setting properties as primarily chemical in nature

and becomes progressively more rigid over time.

The ISO 9917-1 standard “Dentistry - water based cements” specifies methods for testing

the properties of zinc phosphate, zinc polycarboxylate, and glass polyalkenoate cements.2

It does not include in its scope MTA or any ‘bioceramics’. The major differences between

the materials listed in this ISO standard and MTA or ‘bioceramics’ are that the materials

specified in the standard react with aqueous fluids of various types containing components

such as phosphoric acid or polyacrylic acid, while with MTA and bioceramics, the powder

reacts with pure water. ISO 9917.1 assumes that the setting reaction has completed after

one hour and at this point in time the material is ready for compressive strength testing.

Because the ISO standard does not consider ‘wet curing’, testing of MTA and bioceramics

can yield unexpected or inferior results.79

Changes in temperature can be used to determine how a setting reaction is progressing,

and this parameter is used for following polymerization of dental resin cements 364

. In

comparison, rheological studies can measure the elastic modulus and therefore measure

both the working time and the setting time. However, further research is required to

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determine which points in the elastic modulus curve could best be defined as the working

time.274

In this study, the rheological setting times of the tested glass ionomer cements, defined by

the time required to reach 90% of the plateau elastic modulus, are similar to the

indentation setting times marketed by the manufacturer for Fuji VII and Fuji IX. In contrast,

the rheological setting time for Biodentine was longer than the advertised setting time.

Other studies have reported that the setting time for Biodentine longer than the advertised

setting time.49, 223

In the present study, ProRoot MTA was mixed in a method similar to that used with

Biodentine. One sample showed progressive increases in elastic modulus, to give a

rheological setting time of 7 minutes. Compared to the marketed setting time of 4 hours,

the time period of 7 minutes is far closer to the time after mixing when the material can be

overlaid in the clinical setting. As an example, bonding resin being placed onto MTA at 10

minutes after mixing has been proposed by Tsujimoto.136

Likewise, placing GIC over MTA

after 45 minutes has been suggested by Yeilyurt.123

Factors related to handling materials which could be responsible for observed variability in

the results. The use of capsules with pre-dispensed amounts of powder and liquid

eliminates variations in setting time due to inherent variations in dispensing. In the present

study, materials which were dispensed and mixed by hand displayed greater variation in

their setting properties than those dispensed in capsules. Both ProRoot MTA and AH 26

were mixed after manual dispensing of powder and liquid components, while Fuji VII, Fuji

IX, and Biodentine were delivered using capsules, and RealSeal SE and AH Plus Jet used

dual barrelled mixing tips to give the correct paste to paste ratios. Taking this into account,

manufacturers of hand mixed materials should state the setting time as a range rather than

as a precise value. The wide range in setting times for AH Plus Jet could be attributed to

changes in the effect of changes in application pressure and the rheological properties of

the epoxy resin and medium that enables it to be dispensed through a dual barreled

mixing tip. As the applied pressure changes between uses, the relative quantities of epoxy

resin to medium dispensed may change and hence the differences in the setting times.

Alternatively, the stability of samples may be highly variable after opening. Nevertheless,

this variability in setting time should be further researched as it could impact the clinical

performance.

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For hand-mixed materials in the present study, both water and powder components were

weighed using digital scales. The use of an amalgamator for mixing will give greater

consistency than hand mixing. Nevertheless, some variations in rheological setting times

could be due to loss of water by evaporation of water as materials are mixed and then

loaded into the rheometer. In the case of ProRoot MTA, the instructions for use do not

specify a particular water to powder ratio but instead suggest adding water to the powder

until a thick creamy consistency is achieved. It must therefore be stated that the setting

time of ProRoot MTA in clinical practice will be vary according to the water to powder ratio

chosen by the clinical end user.

The present results for endodontic sealers show values for rheological setting time that are

substantially longer than those that are advertised. Such differences may have

implications for clinical practice, for example when sealer that has not yet fully set could be

displaced, compromising the seal. This could occur if post space preparation is undertaken

immediately after obturation of the root canal.

The rheological method of measuring setting time provides several advantages over the

traditional method of indentation testing. Indentation testing relies upon human judgment

to determine whether or not a material has set, while the rheological method is objective

and does not require human judgment. The use of a closed chamber enables control of

humidity and temperature, and removes variability due to oxygen inhibition of resin

polymerization, or desiccation of water-based cements during setting. While the testing

environment of the rheometer is closer to clinical conditions in terms of humidity and

temperature than testing on the bench, it cannot replicate all clinical variables that could

potentially influence setting reactions when a material is placed into the tooth. Such factors

include the presence of other fluids such as endodontic irrigants, dentinal fluid, and blood,

which influence the setting reaction of MTA.393

9.5 Conclusions

Rheology provides a means to assess setting time which has greater relevance to the

clinical situation than indentation. The time to reach the 90% plateau elastic modulus

aligns with the transition from being liquid-like to illustrating some rigidity. The setting time

is more consistent with materials which mixed automatically from single-use packing.

Materials that provide multiple uses illustrate greater variability and hence manufacturers

155

should provide a range of setting times to reflect the variability that may occur under

clinical conditions.

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Chapter 10 General Discussion

In addressing the question, “How can the prolonged setting time of MTA be overcome?” a

series of smaller questions were considered producing a series of unique studies that

addressed different gaps in the knowledge of MTA.

Figure 10-1 summaries the literature review.

Figure 10-1 Summary of literature review

Prior to this research, there were no published reviews in the literature that subcategorised

HDCs or reviewed the additives that change the handling properties of HDCs. The review

in this thesis shows there are commercial products that are more-like resins than HDCs,

as well as HDCs that are placed without first mixing them with water. Without a functional

classification of these products, clinicians would assume that all these HDCs perform

identically. More research is needed to compare the subtypes of HDCs, particularly resin

and HDCs that are placed without water.

The review on the properties of MTA illustrated that the literature on PC can give guidance

for areas where there is an absence of knowledge for MTA since there are analogous

157

situations between environmental conditions and clinical conditions. The review of relevant

PC literature provided a foundation in the knowledge of PC prior to performing laboratory

tests on MTA. Future studies in MTA should not limit their literature searches to studies of

MTA but should also consider the literature on PC for similar or relevant studies.

A review of commercial MTA products and other HDCs illustrated that the modified MTAs

and other HDCs have inferior physical properties compared to conventional MTA and AH

Plus, a point that is yet to be considered in detail in the literature. Therefore, clinicians

should be wary of extrapolating the success of one product to products that could be

marketed as being equivalent. The published research supporting the use of modified

MTAs and other HDCs is often limited to laboratory studies and isolated case reports.

Further research is required to assess the clinical outcomes when modified MTAs and

HDCs are used.

The published research on MTA products and other HDCs often involves using tests that

are not reflective of how HDCs are used in the clinical setting or how they are expected to

perform under physiological conditions. This can confound meaningful comparisons

between HDC materials and between HDCs and other materials. Future tests on HDCs

should use physiological conditions that simulate the clinical environment.

To place the literature review of MTA cements into an end-user perspective, as part of the

work done for this thesis, surveys of GDs, EDs and PDs were conducted. Figure 10-2

summarises the surveys on MTA.

Figure 10-2 Summary of surveys on MTA usage

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Past literature on pulp therapy for paediatric dentistry has focused on the expense of MTA

as being a major barrier to its use. In contrast, the results of the survey of clinicians

working in paediatric dentistry indicate that the larger barrier to MTA use is a lack of

knowledge on how to handle the material, than its high cost. The finding that some

clinicians are mishandling and inappropriately storing MTA is important since it reveals that

some of the reported problems with the handling properties of MTA could reflect a lack of

knowledge of the clinician, rather than being a fundamental problem with the material.

A similar survey on MTA usage conducted with ED and GD illustrated that practically all

ED used MTA, while GD used alternative materials. GD also expressed a desire to learn

how to better use MTA in clinical practice. Thus, the differences between MTA use of ED

and GD may be a reflection of the educational programmes available. An interesting

finding was that regenerative endodontics was not performed by all EDs, which could be a

reflection of their concerns regarding the predictability of the procedure, with apexification

serving as an alternative procedure.

The surveys undertaken all reveal that a lack of education on the use of MTA is the largest

barrier to use. Nevertheless, the handling of MTA, specifically the setting time, is often

mentioned as a problem of MTA. The reduction of the particle size to accelerate the setting

time and the related implications of this change are summarised in Figure 10-3.

159

Figure 10-3 Summary of PSD of MTA studies

In Chapter 4 LDA was used for PSD analyses of commercial MTA. This is the first time this

analytical approach has been used. Since some clinicians were known to be using packets

of MTA-P for multiple uses, this part of the thesis documented how this would lead to

changes in the particle size of the material. Although future studies on the implications of

re-use of 1 gramme packets of material (such as those used with MTA-P) could be

considered, it is noteworthy that manufacturers have noticed the publication of this study

and have now opted to provide smaller packet quantities that are better suited to single-

use.

The work described in Chapter 4 was the first to consider the separate PSDs of PC and

BO found within MTA. Following on from this, the study described in Chapter 5

deconvoluted the PSDs into the separate PSDs of PC and BO. Future studies that

compare the properties of particular MTA products against PC or other MTA products

should likewise consider that the composition of the material is determined not only by the

particles of PC but also those of the radiopaque agent used.

160

The work described in Chapter 6 showed a strong correlation between the D90 parameter

and the setting time of PC. From this, one could predict with confidence that a substantial

reduction in D90 would accelerate the setting time of PC. The correlation for the D90 for

MTA cements was not as strong as that for PC, which likely reflects the inclusion of

radiopaque agents as well as other additives found in commercial MTA products. Further

studies are needed to assess how changes in the PSD of PC or the accompanying

radiopaque agent could change the properties of MTA.

The reported variance in the literature in the properties of MTA can be attributed to the

differences in laboratory conditions for testing. This point is shown by the work described

in Chapter 7. The conditions used for laboratory tests of the properties of MTA should

replicate, as closely as possible, physiological conditions. Cements with smaller particles

set faster, but their better short-term properties did not carry through to the set cement.

Future studies on HDCs should be conducted with testing under physiological conditions

to provide appropriate comparisons between dental materials.

The use of indentation needle weights to test the progress of the setting reaction, even

though a simple and popular approach, has no clinical relevance to the time that MTA can

be restored. This method does not give any insight into the progression of the setting

reactions over time. In Chapter 8, a rheological method of determining the time to reach

95% of the plateau G’ used was described. This method, when used with an experimental

MTA material, gave similar setting time trends to the indentation method. However, the

rheological setting time was more clinically appropriate and more informative. This thread

of research was continued in Chapter 9 which adopted the same methodology to the

testing of commercial MTA cements and other dental products.

Based on the results presented in Chapter 9, the time required for commercial cements to

reach the 90% G’ threshold showed some correlation with the marketed indentation setting

times. However, the rheological setting time of MTA-P was found to be substantially

shorter than the indentation setting time. This illustrates that indentation-based tests of

setting times are not clinically appropriate. In the case of epoxy resin sealers, the setting

time assessed using rheology was substantially longer than the indentation setting time.

This discrepancy can have implications for the timing of procedures that involve revisiting

161

the obturation i.e. post space preparation. The rheological method of testing would need to

be modified to test ‘bioceramics’ that require diffusion of water to set the material.

162

Chapter 11 Clinical Implication Summary

11.1 Chapter 1 Literature Review

The terms ‘bioceramic’, ‘MTA’ and ‘calcium silicate cement’ can be misleading as not all

properties are shared amongst such materials. Clinicians should be aware of the differing

compositions of cements as these differences result in variations in performance. For

example, differences in the choice of radiopacifer and its percentage composition can

result in significant differences in radiopacity.

Acids, EDTA, CHX and blood contaminants have been shown to be detrimental to the

setting reaction of MTA, resulting in either retardation of the setting process and/or

reduction of strength of the set material. Contact between these and freshly placed MTA

should be avoided. Instead, NaOCl irrigation and Ca(OH)2 dressings should be considered

to neutralise any acids before MTA is placed.

When being dispensed in the clinic, MTA containers should be used once only, and they

should not be refrigerated because moisture effects the particle size and setting

behaviour.

MTA can be cured using ‘membrane curing’ whereby a permanent restorative can be

placed immediately on MTA rather than placing a temporary restorative above the cement.

This helps retain moisture in the cement.

MTA and HDCs are expected to stain when they are placed in the presence of blood.

Alternative materials and treatments should be considered when restoring a tooth in the

aesthetic zone.

The interpretation of the results of studies of the properties of HDCs (e.g. setting time,

solubility) must done with considerable caution, since the tests results may be biased

when the test conditions do not reflect normal clinical handling or physiological conditions.

Clinicians should not simply choose a product for patient-use based on assumed

superiority, but rather should take into account the limitations of the testing methods.

163

11.2 Chapter 2 Use of MTA in paediatric dentistry

For IPC, the materials used may include CHC cement, GIC/RMGIC, CHP and MTA, while

MTA, CHP and CHC are used for DPC. MTA can be used in pulpotomy cases, as an

alternative to materials and techniques such as CHC, FeSO4, FC and diathermy. Most

dentists can readily learn how to use MTA, and hands-on courses are better suited for that

purpose than lecture-only courses, because the former provides hands-on experience.

Gaining such education should overcome a major barrier to the use of MTA.

11.3 Chapter 3 Use of MTA in endodontics

MTA is used widely for perforation repairs and for apical barrier procedures. For EDs, it is

the material of choice for pulp regeneration procedures and root-end fillings. Significant

differences exist in how MTA is used between GDs and EDs. A lack of experience in

handling MTA is a larger barrier to its widespread use in EDs than its cost.

11.4 Chapter 4 Particle size of MTA

If stored incorrectly, MTA reacts with atmospheric moisture, causing an increase in particle

size that may adversely affect the properties and shelf life of the material. Smaller particles

have a greater predisposition to absorb moisture because of their larger surface area.

Single-use dispensing systems are advised.

11.5 Chapter 5 What constitutes the PSD of MTA

Manufacturers should disclose particle size information for the PC component and for the

radiopaque agents used in commercial MTA cements. The availability of this information

would prevent simplistic conclusions being drawn from statements of “average” particle

size for MTA materials.

11.6 Chapter 6 Correlation of particle size with setting time

Smaller particle sizes give faster setting times, with the D90 parameter (the largest

particles) being most closely correlated with setting time.

11.7 Chapter 7 Strength and particle size

Cements with smaller particle sizes give greater CS and FS after 1 day than those with

larger particle sizes. However, this advantage is transient and is over the following 1-3

weeks. Experiments that test the properties of MTA should cure the MTA under wet

conditions and at physiological pH, for reasons of consistency and clinical relevance.

164

11.8 Chapter 8 How is the setting time measured?

The time for a setting MTA cement to reach the 95% elastic modulus plateau corresponds

to the clinical time point when the material can be overlaid with another restorative material

to give a final restoration. The 95% plateau value for elastic modulus is a useful parameter

for determining how the setting reaction of PC and MTA cements progress over time.

11.9 Rheology for other cements

The time to reach the 90% plateau G’ correlates well with the setting time of GICs and the

time required to restore MTA and Biodentine. Using this approach gives much longer

setting times for endodontic sealers than previously recognised.

Chapter 12 Conclusions

MTA has often been criticised for its handling properties, particularly its prolonged setting

time. There are many commercial products of “MTA” and MTA-like products, often termed

‘bio-ceramics’, within which the manufacturers have attempted to address some of the

perceived problems in handling the material.

From a review of these cements, a family of related materials, the HDCs, can be identified,

all of which react directly with water to chemically set. These materials differ from other

dental cements that use aqueous solutions where water is the solvent medium but is not a

reactant.

There has been growth in the number of modified HDCs in the market. These are attempts

to leverage the beneficial properties of MTA while imitating the handling properties of more

familiar contemporary endodontic sealers, flowable resin and putties. Some commercial

HDCs that seem to have attempted to overcome the handling issues of MTA are either

hybrids with resins or are placed within a waterless mix using rheological modifiers with no

mixing water. Therefore, the HDC component requires water to infiltrate via dentinal fluid

or a degree of leakage to introduce water to enable setting to occur.

Hybrids of HDC such as endodontic sealers often show inferior properties to common

resin-based endodontic sealers. Therefore, modified HDCs should not be assumed to

have similar properties to MTA. Indeed, their physical properties may be significantly

compromised.

165

Despite concerns over handling, MTA is used widely in specialist endodontic practice,

while GD and PD are far less likely to use MTA. ED have been trained to use MTA, while

GD and PD have had far less training in the use of MTA, which explains in part their

reluctance to use the material. This appears to be a more important factor than the cost of

the material or its handling properties.

The historic use of MTA in perforation repair and apical barrier placement involves

delaying restoration of the tooth. Clinicians place a damp cotton pellet and Cavit above the

MTA and then return to restore the tooth on the subsequent day. Because this is a

clinically unfavourable situation, many clinicians are now restoring the tooth at the same

appointment as placing MTA. This behaviour illustrates how the advertised setting time of

the material does not correlate with the time when clinicians will permanently restore the

tooth.

The work presented in this thesis shows that the setting time of MTA determined from

indentation tests using the Gillmore needle method over-estimates the clinical setting time.

In contrast, the rheological method of determining the time to reach 95% of the plateau

elastic modulus appears to align better to the point in the clinic when freshly placed MTA

can be overlaid (approximately 10 minutes).

The setting of MTA is longer than pure PC, as MTA is only 80% PC. The setting time of

MTA correlates strongly with the D90 of the PC component. Taken together, these points

reveal that the setting reaction in MTA is slowed by the presence of ingredients such as

the radiopaque agent or other additives. On the other hand, reducing the particle size will

make MTA set faster. While the cement will reach a greater hardness in a shorter period of

time, it is not stronger over the long term. The consideration of long-term strength is of

limited relevance in many MTA applications since the material will be overlaid with another

stronger material. Thus, there is not a great requirement for structural strength.

There may be benefits in reducing the PSD of MTA to achieve a setting time that is

comparable to GIC since this would mean that clinicians would need to wait only 3 minutes

rather than 10 minutes before overlaying the MTA with another material. Whether any

such improvement in MTA would change the behaviour of clinicians is an entirely separate

question. It appears that EDs who are well-educated in the use of MTA will not use

166

alternatives to MTA, while those who are untrained in using MTA use alternatives and may

well choose to continue doing so.

Moreover, even when there has been an acceleration of the setting reactions of MTA, the

final set cement is unlikely to mirror the physical properties of GIC, meaning that even a

rapidly setting MTA would not be used as a general-purpose bulk restorative.

In answering the question, “how can the prolonged setting time of MTA be overcome?” the

following key points arise:

• inappropriate handling of MTA can prolong setting time (e.g. blood contamination);

• the setting time can be reduced by using smaller particles and by including

chemical additives;

• some variants of MTA include chemical additives and claim to be faster setting, but

do not show a considerably faster setting time;

• a definition of setting time based on indentation tests is flawed as it does not

correlate with how MTA is used;

• rheological tests for setting time show that MTA progressively develops rigidity over

a 10-minute period; and

• MTA restorations can be placed and then overlaid within an acceptable clinical time

frame.

Therefore, when formulated and used properly, and handled under optimum conditions,

MTA does not have a prolonged setting time.

167

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Chapter 14 Appendix

The definition has been updated on the 23rd

of September 2016 to:

P60510 Hygroscopic dental cement

Modified Term Definition: A non-sterile substance intended for professional use as a dental

cement (e.g., luting agent, liner, base, pulp-capping material) and/or direct dental

restorative material whereby the majority of the setting reaction is based on the hardening

reaction of a hygroscopic inorganic compound(s) [e.g., calcium silicates, calcium

aluminates, zinc sulfate, calcium sulfate] with water (hydration). It is available as a powder

intended to be either mixed water prior to application or react with dentinal fluid in situ. After

application, this device cannot be reused.

Appendix 1 GMDN Registration for Hygroscopic Dental Cement

210

Appendix 2 Dental material choices for pulp therapy by ANZSPD members

mineral trioxide aggregate: a review of clinical usage and ...689794/s... · school of dentistry ....

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