Digital evaluation of the accuracy of impressiontechniques and materials in angulated implants

Sevcan Kurtulmus-Yilmaz a,*, Oguz Ozan a, Tuncer Burak Ozcelik b,Ayberk Yagiz c

aDepartment of Prosthodontics, Faculty of Dentistry, Near East University, Mersin 10, TurkeybDepartment of Prosthodontics, Faculty of Dentistry, Baskent University, Adana, TurkeycAy Tasarim Ltd., Ankara, Turkey

j o u r n a l o f d e n t i s t r y 4 2 ( 2 0 1 4 ) 1 5 5 1 – 1 5 5 9

a r t i c l e i n f o

Article history:

Received 4 August 2014

Received in revised form

11 October 2014

Accepted 14 October 2014

Keywords:

Implant angulation

Splinted direct technique

Indirect technique

Vinyl polysiloxane

Polyether

Vinyl polyether silicone

a b s t r a c t

Objectives: The aim of this study was to investigate the accuracy of 2 different impression

techniques and 3 different impression materials in models simulating parallel and angu-

lated implants.

Methods: Three master models simulating partial edentulous mandible with 2 implants at

the sites of second premolars (parallel) and second molars with different angulations

(parallel, 108 or 208 angulated) were fabricated. Two different impression techniques

[splinted direct (D), indirect (I)] and 3 different monophase impression materials [polyether

(PE), vinyl polysiloxane (VPS), vinyl polyether silicone (VPES)] were used for each master

model and a total of 180 impressions were made (n = 10). Master model and casts were

scanned by a modified laser scanner and data were transferred to VRMesh software. Master

model and duplicate cast scans were digitally aligned observing the superposition of

anatomic markers. Angular and coronal deviations between master and duplicated copings

were calculated and data were statistically analyzed.

Results: Mean angular and coronal deviations were in a range of 0.205–0.3598 and 22.56-

33.33 mm, respectively. Statistical analysis revealed that the angulation of implant affected

both coronal and angular deviations of the impression copings (P < 0.05). According to

statistical analyses, for parallel implants, the accuracy of impression materials and tech-

niques were ranging as VPS-D = PE-D > VPS-I = PE-I > VPES-D > VPES-I from most accurate

to the least. For 108 and 208 angulated implants the most accurate material and technique

was VPS-D whereas the least accurate combination was VPES-I (P < 0.05).

Conclusion: Angulation, impression technique and material were found to be effective on the

accuracy of implant impressions.

Clinical significance: Clinicians may prefer VPS impression material and splinted direct

technique for impressions of both parallel and up to 208 angulated implants.

# 2014 Elsevier Ltd. All rights reserved.

* Corresponding author at: Near East University, Faculty of Dentistry, Department of Prosthodontics, Lefkosa, Mersin 10, Turkey.Tel.: +90 392 6802030; fax: +90 392 6802025.

E-mail address: sevcankurtulmusyilmaz@gmail.com (S. Kurtulmus-Yilmaz).

Available online at www.sciencedirect.com

ScienceDirect

journal homepage: www.intl.elsevierhealth.com/journals/jden

http://dx.doi.org/10.1016/j.jdent.2014.10.0080300-5712/# 2014 Elsevier Ltd. All rights reserved.

j o u r n a l o f d e n t i s t r y 4 2 ( 2 0 1 4 ) 1 5 5 1 – 1 5 5 91552

1. Introduction

The passive fit of implant-supported prosthesis is critical for

long term clinical success.1 Any misfit between the prosthesis

and implant may lead to complications, such as screw

loosening, screw fracture, occlusal discrepancies, increased

plaque accumulation caused by misfit components and even

loss of osseointegration and implant fracture.1–4 Impression is

one of the most important steps for a passive fit and transfer of

the precise position of implant to definitive cast with an

accurate impression is essential.5 Impression technique,

type of impression material,6 splinting or non-splinting

impression copings, type of splinting material, number

and angulation of implants7 are the factors that affect the

accuracy of impression.

To date, several implant impression techniques have been

introduced and evaluated for accuracy. Two basic impression

techniques are commonly used in implant dentistry: the

indirect (transfer, closed tray) and the direct (pick-up, open

tray) technique. In indirect technique, the copings are

connected to the implant and after the removal of the

impression they are retained on the implants. The copings

are then removed from implant, attached to the implant

analogues and reinserted in the impression. In direct

technique, an open tray that exposes coronal ends of the

impression coping screws is used. Screws of the copings are

loosened when the impression material is set and impression

is removed from the mouth with impression copings retained

in the impression. The implant analogues are connected to the

copings using the same screw.5,8

The accuracy of direct and indirect techniques were

compared in many studies.9–24 However the results are still

contradictory. In a systematic review, Lee et al.5 investigated

the published researches regarding the accuracy of implant

impressions and concluded that there was no difference

between direct and indirect techniques if there were 3 or fewer

implants.

Accuracy of various implant impression materials were

investigated in numerous studies and more accurate impres-

sions were obtained with polyether (PE) and vinyl polysiloxane

(VPS) in comparison to condensation silicone, polysulfide,

reversible hydrocolloid, irreversible hydrocolloid and plas-

ter.6,13,25–27 Wetting behaviour is an important physiochemical

property of elastomeric impression materials that affects the

accuracy of the material. Hydrophilicity provides detailed

reproduction of wet oral surfaces and increased wettability

with gypsum slurry.28 Hydrophobic or hydrophilic character of

materials can be attributed to their chemical structure. VPS

has hydrophobic aliphatic hydrocarbon groups which sur-

round the siloxane bond. However, PE contains functional

groups that attract and interact with water molecules, making

this material hydrophilic.29 To improve the wettability of VPS,

manufacturers added extrinsic surfactants and labelled these

as hydrophilic VPS materials. Recent studies reported that

hydrophilized VPS has similar hydrophilicity to PE.28,30 Many

studies showed that there was no difference in the accuracy of

PE and VPS6,13,25,26,31–36 and both of the materials are

recommended for implant impressions. Vinyl polyether

silicone (VPES) (EXA’lence, GC America Inc., Alsip, IL, USA),

a combination of VPS and PE was introduced a few years ago.

According to the manufacturer, VPES has intrinsic hydrophi-

licity and high dimensional stability. However, the data

regarding the accuracy of VPES is very limited.37–39 In a recent

study, Schaefer et al.39 evaluated the accuracy and repro-

ducibility of VPES, VPS and PE impression materials by a 3-D

analysis. They reported that there was no significant

difference among the materials in terms of spatial deviation

and all of the materials demonstrated high accuracy and

reproducibility.39

Parallel placement of implants is not always possible due to

the anatomical limitations and angulations may occur in

implant positions. The effect of angulation of implants on the

accuracy of impression has been evaluated in previous studies

and researches reported that angulated implants caused less

accurate impressions in comparison to parallel implants when

there were 4–6 implants.8,25,40,41 However, the studies that

used 2 or 3 implants did not report any difference between

angulated and parallel implants in terms of impression

accuracy.42–44 There is limited data regarding the accuracy

of impression materials in case of implant angulation. The

results of previous studies40,41,45 investigating the accuracy of

impression materials for angulated implants showed incon-

sistency. Sorrentino et al.41 found VPS more accurate than PE

whereas Akalın et al.40 obtained more accurate impressions

with PE. On the other hand, Reddy et al.45 reported that there

was no significant difference in accuracy of VPS and PE for

angulated implants. To the best of authors’ knowledge, the

accuracy of VPES impression material with angulated

implants has not been investigated.

The aim of the present study was to investigate the

accuracy of 2 different impression techniques (splinted direct

and indirect) and 3 different impression materials (PE, VPS,

VPES) in models simulating parallel and angulated (108, 208)

implants.

2. Materials and methods

2.1. Fabrication of master models

Three autopolymerizing transparent acrylic resin (Pegasus

Plus Repair Acrylic, Davis Schottlander & Davis Ltd., Hertford-

shire, England) master models simulating partial edentulous

mandible were fabricated. Two implants (T4 3810, NucleOSS,

Sanlilar Tibbi Cihazlar Medikal Kimya San Tic Ltd. Sti, Izmir,

Turkey) were placed at the sites of the right second premolar

(implant 1) and right second molar (implant 2) of each model

with different angulations (parallel, 108 or 208 angulated)

(Fig. 1).

Model 1: Implant 1 and implant 2 were positioned parallel to

each other and long axes of neighbouring teeth; perpendicular

to the horizontal plane.

Model 2: Implant 1 was positioned parallel to the long axis of

neighbouring tooth and perpendicular to the horizontal plane;

implant 2 was placed with 108 mesial angulation with respect

to the long axis of implant 1.

Model 3: Implant 1 was positioned parallel to the long axis of

neighbouring tooth and perpendicular to the horizontal plane;

Fig. 2 – The alignment of the master model and duplicate

cast scan by superpositioning of the anatomic markers.

Fig. 1 – Master models with parallel, 108 and 208 angulated implants.

j o u r n a l o f d e n t i s t r y 4 2 ( 2 0 1 4 ) 1 5 5 1 – 1 5 5 9 1553

implant 2 was placed with 208 mesial angulation with respect

to the long axis of implant 1.

2.2. Fabrication of custom trays

Ninety custom trays with 3 mm relief and 2 guide stops on the

occlusal surface of neighbouring teeth were made for each

impression technique (totally 180 trays) with light polymeriz-

ing resin (Plaque Photo, W + P Dental, Hamburg, Germany) and

polymerized (Tray Lux, Ampac Dental, Rockdale, Australia).

For direct impression technique, a hole was made on the trays

to access to the coronal ends of the impression copings.

2.3. Impression procedures

A total of 180 impressions were made with 2 different

impression techniques (splinted direct and indirect) and 3

different impression materials (PE, VPS, VPES) from each

master model (n = 10).

Indirect technique (I): Impression copings (T4 4040, NucleOSS)

were screwed into the implants and tray with impression

material was placed on the model. After the impression

material set, the tray was removed from the model. The

copings were unscrewed from the model and screwed to the

implant analogues (T4 4020, NucleOSS) and they were

repositioned in the impression.

Splinted direct technique (D): Impression copings were

screwed on implants and the copings were splinted with

dental floss and autopolymerizing acrylic resin (Pattern Resin

LS, GC America Inc., Alsip, IL, USA). Splint was sectioned after

17 min of application and reconnected with an autopolymer-

izing acrylic resin. Open tray with impression material was

placed on the model and a syringe was used to inject the

impression material around the exposed surfaces of

the impression copings. After the impression material set,

the screws of the copings were loosened and the impression

was separated from the model. Implant analogues were

screwed to the impression copings that fixed in the impression.

PE (Impregum Penta Soft, 3M ESPE AG, Seefeld, Germany),

VPS (Hydrorise Maxi Monophase, Zhermack, Badia Polesine,

Italy) and VPES (EXA’lence 370 Monophase, GC America Inc,

Alsip, IL, USA) impression materials were used for both

impression techniques. Before making the impression, cus-

tom trays were coated with tray adhesives recommended by

the manufacturer. All impression materials used in this study

were monophase and prepared straight from the polyester bag

using the automated mixing device (Pentamix 2, 3M ESPE,

Seefeld, Germany). The mixed impression materials were both

syringed around the impression copings and loaded in the

custom tray. The custom tray was seated over the guide stops

with finger pressure and tray was removed after the material

set. All the impressions were taken by a single operator.

All impressions were poured with a type IV dental stone

(Hinriplast N, Ernst Hinrichs GmbH, Goslar, Germany) follow-

ing the manufacturer’s instructions. The stone was left for 1 h

and then the casts were gently separated from the impression.

2.4. Measurement procedures

After the impression procedure, impression copings were

screwed to the implants on the master models. Master models

and duplicate casts were scanned by an optical scanner

(Activity 880, Smart Optics Sensortechnik GmbH, Bochum,

Germany) within 10 mm accuracy ratio.46 To avoid glossy

surface reflections, a single layer of powder was applied on the

surface of master models with handy pushbutton powder

brush pen (NextEngine Inc., CA, USA). Master model and

duplicate cast scans were aligned observing the superposition

of anatomic markers using software (VRMesh Studio, Virtual-

Grid Inc., Bellevue City, WA, USA) (Figs. 2 and 3). Two points

were located (x-, y-, z-coordinates) on the long axes of each

master and duplicate impression copings of implant 2 and the

copings were converted into cylinders. The first point was

located at the centre of the bottom of impression coping

whereas the second point was located at the centre of the top

of impression coping (Fig. 4). The linear differences between

the centres of the master and duplicate copings for bottom

point (coronal deviation) and the angles occurred between the

Fig. 3 – The alignment of the impression copings of the master model and duplicate cast.

j o u r n a l o f d e n t i s t r y 4 2 ( 2 0 1 4 ) 1 5 5 1 – 1 5 5 91554

long axes of master and duplicate copings in x-, y-, z-axes

(angular deviation) (Fig. 5) were measured by cartesian

multiplication of the analytical coordinates of the points by

a single observer.47,48

2.5. Sample size calculation

A minimum significant difference in deviation of 0.05 mm was

determined from available literature on accuracy of implant

impressions.25 The power analysis was conducted based on

this minimum significant difference in deviation, using alpha

Fig. 4 – Two points were located at the centre of the bottom

and top areas of the master and duplicate impression

copings and the copings were converted into cylinders.

Green colour indicates master cylinder and blue colour

indicates duplicate cylinder. (For interpretation of the

references to colour in this figure legend, the reader is

referred to the web version of this article.)

at level 0.05, at 80% power and a s of 0.048 according to our

preliminary study. On the basis of these data, the number of

samples required to be enrolled to conduct this study has been

calculated as 10.

2.6. Statistical analysis

Shapiro–Wilks test was used to confirm that the data were

normally distributed. Data were analyzed by three-way

analysis of variance (ANOVA). The considered variables were

impression technique (splinted direct, indirect), impression

material (PE, VPS, VPES) and implant angulation (parallel, 108,

208). Post hoc comparisons were performed using the

Bonferroni test when significance was detected. Values of

P < 0.05 were accepted as statistically significant.

3. Results

Mean values and standard deviations of angular and coronal

deviations of the copings are shown in Tables 1 and 2,

respectively. Mean angular and coronal deviations were in a

range of 0.205–0.3598 and 22.56-33.33 mm, respectively. Three-

way ANOVA revealed that impression technique, impression

material and the implant angulation had significant effects on

both angular (Table 3) and coronal (Table 4) deviations

(P < 0.0001).

According to statistical analysis, direct splinted technique

showed higher accuracy in comparison to indirect technique

for all impression materials and angulations (P < 0.05).

Angular and coronal deviations increased with the increase

in angulation of implants for all impression techniques and

materials. For parallel positioned implants, significantly

lowest angular and coronal deviations were observed in

splinted direct group (P < 0.05) and there was no statistically

significant difference between PE and VPS (P > 0.05). In 108 and

208 angulated implants, significantly low deviations were

detected in splinted direct technique with VPS impression

material. For all angulations, regardless of the impression

Fig. 5 – Matching procedure between master and duplicate

impression copings. ‘‘A’’ is the distance between master

and duplicate impression copings at the bottom that

represents coronal deviation. ‘‘B’’ represents the angular

deviation between master and duplicate impression

copings.

j o u r n a l o f d e n t i s t r y 4 2 ( 2 0 1 4 ) 1 5 5 1 – 1 5 5 9 1555

technique, VPES showed the highest deviations (P = 0.0001)

(Tables 1 and 2).

4. Discussion

An impression that precisely records the exact 3-dimensional

positions of implants is paramount in order to achieve a

passively fitting prosthesis.1,5 Therefore, in implant dentistry,

comparative accuracy of impression techniques and materials

becomes an important issue in consideration of passive fit.49

In the present study, accuracy of 2 different impression

techniques and 3 different impression materials were com-

pared and the effect of implant angulation on the accuracy of

impression was evaluated. Statistical analysis revealed that

impression technique, impression material and implant

angulation had a significant effect on the accuracy of

impressions. Among the evaluated parameters, for both

angular and coronal deviations, impression material was

found to be the most significant factor and it was followed by

impression technique and implant angulation (Tables 3 and 4).

In most of the studies, direct technique was reported to be

more precise and predictable in comparison to indirect

technique using repositionable copings.9,12,50,51 However,

the studies evaluating non-splinted direct and indirect

techniques demonstrated none of the two procedures to be

superior.10,17,32,44,51 Splinting of impression copings has been

suggested as an important factor for increasing the precision

of the impressions.15,17,19,20,27,52–54 Therefore in the present

study, accuracies of splinted direct and indirect techniques

were compared. In splinted direct technique, autopolymeriz-

ing acrylic resin was used and to reduce the effects of

polymerizing shrinkage it was separated and reconnected

after 17 min of application.55 According to the results of this

study, regardless of the impression material, splinted direct

technique had a greater accuracy than indirect technique for

both parallel and angulated implants.

Angulated implants are common clinical situation due to

the anatomic and aesthetic limitations. It has been reported

that the increased angulation of the implants tended to

increase the distortion of the impression material and

decrease the impression accuracy56 since higher strength is

needed for the removal of the impression.41 In the present

study, angular and coronal deviation of the both 108 and 208

angulated copings were significantly higher than the parallel

copings. Contradictory, in previous studies, angulation was

not found to be effective on the accuracy of impressions for 3

or fewer nonparallel implants with up to 158 of angulation.42–44

However, in these studies42–44 master models were block

shaped and had flat impression surfaces which may not

simulate the deformation of the impression material upon

removal. In this study, partial mandible models with an

anatomical shape and neighbouring teeth were used to better

simulate the clinical conditions. On the other hand, the

methodology for the assessment of the impression accuracy

showed differences among the studies. In aforementioned

studies, the positional changes of the analogues were

evaluated by measuring inter-implant distances either with

coordinate measuring machine44 or measuring microscope43;

or evaluating the stress in the metal framework with strain

gauges.42 In this study, a digital method was used for the

evaluation of deviations which may provide more precise

results.

PEs and VPSs have been suggested as the materials of

choice for implant impressions due to the superior chemical

and physical properties.6,8,12,13,15,33 For direct impression

technique, impression material should show sufficient rigidity

to hold the coping in its position and prevent any displace-

ment during the removal of the impression.41 Therefore, the

Table 1 – Mean and standard deviation (SD) values of angular deviations of the copings. Same capital letters in the samecolumn and same lower cases in the same row show no statistically significance according to 3-way ANOVA.

Material–technique 08 108 208

Mean SD Sig. Mean SD Sig. Mean SD Sig.

PE-I 0.235 0.005 B,a 0.245 0.005 F,G,b 0.292 0.003 L,c

PE-D 0.204 0.007 A,d 0.233 0.007 F,e 0.252 0.006 K,f

VPS-I 0.229 0.005 B,g 0.247 0.006 G,H,h 0.254 0.004 K,i

VPS-D 0.205 0.009 A,j 0.216 0.016 E,k 0.227 0.018 J,l

VPES-I 0.266 0.007 D,m 0.276 0.008 I,n 0.359 0.046 M,o

VPES-D 0.250 0.006 C,p 0.259 0.005 H,r 0.305 0.005 L,s

Table 2 – Mean and standard deviation (SD) values of coronal deviations of the copings. Same capital letters in the samecolumn and same lower cases in the same row show no statistically significance according to 3-way ANOVA.

Material–technique 08 108 208

Mean SD Sig. Mean SD Sig. Mean SD Sig.

PE-I 26.33 1.11 B,a 27.34 1.13 F,b 28.83 1.39 I,c

PE-D 22.56 0.67 A,d 25.66 1.83 E,F,f 28.53 1.62 I,g

VPS-I 25.88 1.36 B,h 27.19 1.65 F,i 28.69 1.34 I,j

VPS-D 22.74 1.74 A,k 23.54 0.68 E,l 25.18 1.43 H,m

VPES-I 30.24 1.17 D,n 31.86 1.75 G,o 33.33 1.71 J,p

VPES-D 28.28 1.44 C,r 29.67 1.29 F,s 31.74 1.81 J,t

Table 3 – Results of 3-way ANOVA for angular deviations.

Source Tests of between-subjects effects

Type III sum of squares df Mean square F Sig.

Corrected model 0.251a 17 0.015 85.755 0.000

Intercept 11.455 1 11.455 66,432.772 0.000

Technique 0.038 1 0.038 221.664 0.000

Material 0.108 2 0.054 311.851 0.000

Angulation 0.073 2 0.036 210.741 0.000

Technique � material 0.000 2 0.000 0.996 0.372

Technique � angulation 0.005 2 0.003 15.861 0.000

Material � angulation 0.024 4 0.006 35.077 0.000

Technique � material � angulation 0.003 4 0.001 4.239 0.003

Error 0.028 162 0.000

Total 11.735 180

Corrected total 0.279 179

a R2 = 0.900 (adjusted R2 = 0.889).

Table 4 – Results of 3-way ANOVA for coronal deviations.

Source Tests of between-subjects effects

Type III sum of squares df Mean square F Sig.

Corrected model 1562.303a 17 91.900 39.759 0.000

Intercept 133,380.178 1 133,380.178 57,703.952 0.000

Technique 278.656 1 278.656 120.554 0.000

Material 1010.211 2 505.105 218.523 0.000

Angulation 172.624 2 86.312 37.341 0.000

Technique � material 19.233 2 9.617 4.160 0.017

Technique � angulation 8.768 2 4.381 1.895 0.154

Material � angulation 57.458 4 14.365 6.215 0.000

Technique � material � angulation 15.358 4 3.839 1.661 0.162

Error 374.456 162 2.311

Total 135,356.937 180

Corrected total 1936.759 179

a R2 = 0.807 (adjusted R2 = 0.786).

j o u r n a l o f d e n t i s t r y 4 2 ( 2 0 1 4 ) 1 5 5 1 – 1 5 5 91556

j o u r n a l o f d e n t i s t r y 4 2 ( 2 0 1 4 ) 1 5 5 1 – 1 5 5 9 1557

use of PE is recommended for fully edentulous and multi-

implant cases.41 On the other hand, elastic recovery is a

significant factor in determining the accuracy of an impres-

sion material.57 The use of a more elastic material may reduce

the permanent distortion caused by the stress between

copings and the implant impression material.19 Thus, VPS

could be considered as a feasible option especially when

nonparallel implants are present.41 In the present study,

accuracies of 3 monophase elastomeric impression materials

with medium-consistency were assessed. Regardless of the

impression technique, no significant difference was detected

between the accuracies of PE and VPS for parallel implants,

whereas VPS provided statistically the most accurate impres-

sions for 108 and 208 angulated implants. This may be

explained by the higher elastic recovery of VPS in comparison

to PE. The highest angular and coronal deviations of the

copings were detected in the casts obtained with VPES. VPES is

a relatively new material and there is limited data regarding

the accuracy and rigidity of this material. Further studies are

needed for evaluation of its chemical and physical properties.

According to the results of the present study, the best

combination of impression material and technique for

angulated implants were VPS and splinted direct technique.

Although significant differences were detected among the

accuracies of the materials and techniques tested in this study,

the mean deviations were in a range of 22.56-33.33 mm.

Assuncao et al.25 stated that in a good impression, a discrepancy

of 50 mm may be found in any axis. The discrepancies are not

only caused by the accuracy of impression techniques and

materials but also by the machining tolerances between

implant and the impression coping, and abutments. Ma58

reported machining tolerances between implant components

ranging from 22 to 100 mm. When interpreting the results of the

studies regarding the accuracy of implant impressions, ma-

chining tolerance should also be considered.5

This in vitro study has several limitations. The hardness,

structure and wettability of acrylic resin surface of the master

models are different from oral tissues. Also all impressions

were taken under ideal conditions without the presence of soft

tissues, blood, saliva and sulcular fluid which may affect the

accuracy of the impressions. Another possible limitation of

the study was that the axial rotation of the implant

components caused by the impression technique and material

were not detected. Furthermore, the results are limited to two

internal connection implants and may not be relevant with

higher number of implants and different connection geome-

tries. Further studies testing more implants, different angula-

tions and connection geometry are needed to evaluate the

accuracy of implant impressions.

5. Conclusions

Within the limitations of this study, the following conclusions

can be drawn:

1. Angulation, impression technique and impression material

were found to be effective on the accuracy of implant

impressions.

2. For parallel implants, more accurate impressions were

obtained with splinted direct technique and there was no

significant difference between PE and VPS. However VPES

showed higher deviations.

3. In the presence of angulated implants the most accurate

impression material was VPS and the most accurate

technique was splinted direct technique.

Conflict of interest

The authors declare no potential conflicts of interest with

respect to the authorship and/or publication of this article.

This study was self-funded by the authors.

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