impression materials new era

PRESENTED BY Dr. KUMAR .A I st Yr PG orthodontics, Guided by Dr.Rajasigamani MDS., vice principal, RMDCH

& H.O.D Department of orthodontics

Impression Materials and Orthodontic Cements

Impression Materials used in orthodontics.

Contents

Definitions

Objectives

Ideal requirements

Classification of impression materials

Compositions and Reactions of Elastomeric materials.

Properties of Elastomeric materials.

Disinfection Of impressions.

Failures In impressions Making.

Conclusion

References

Impression

Definition :-

1) A negative likeness or copy in reverse of the surface or object.

2) An imprint of the teeth and adjacent structures for use in dentistry

Impression

Definition :

Impressions are negative reproduction of oral structures.

Impression material

Impression material:- Any substance or combination of

substances used for making an impression or negative reproduction.

Impression technique:- A method and manner used in

making a negative likeness.

Objectives

Provide general review of types of dental impression materials.

Provide general information on the physical and handling properties and indications for use of various types of impression materials.

Objectives of impression making

To provide

a. support , b. retention, c. stability, d. foundation of improved appearance of lips, e. maintain the health of tissues.

The impression should record all the potential denture-bearing surfaces available

The Ideal Impression Material

Easy to mix and handle.

Suitable working time.

Suitable setting time.

Compatible with die and stone

Not toxic or allergenic to the patient.

Dimensionally stable on setting.

Accurate to record the fine details of the prepared tooth

Has acceptable odor and taste.

Adequate strength.

Adequate shelf life.

The Ideal Impression Material cont.

Economical

Ready to disinfected without loss of accuracy.

Fluid or plastic when inserted into the mouth.

It must be an exact record of all the aspects of the prepared tooth and sufficient unprepared tooth structure immediately adjacent to margins, to allow the dentist and the technician to be certain of the location and configuration of the finish line.

Other teeth and tissue surrounding the abutment tooth must be accurately reproduced to permit proper articulation of the cast and contouring of the restoration.

It must be free from air bubbles especially in the finish line area.

• High accuracy Biocompatibility(very small contraction <0.5%)

• High dimensional stability Compatibility to stone

• High elastic recovery High tear strength• Ease of use Long shelf life• Hydrophilic Pleasant color &taste

and Hydrophobic• Proper setting time Cost

Classification of impression materialsImpression materials

Non elastic elastic

Hydrocolloids Synthetic elastomers

Reversible Irreversible Polysulphide

Polyether

Silicones

Addition silicone Condensation silicone

Zinc oxide eugenolZinc oxide eugenol

Impression CompoundImpression Compound

PlasterPlaster

Impression waxImpression wax

NonelasticNonelastic

Properties: Reaction: Set:Rigid:1. Impression Plaster Rigid Irrev (Chem)2. Impression Compound Rigid Rev (Phys)3. Zinc Oxide/ Eugenol Rigid Irrev (Chem)

CLASSIFICATION SYSTEMBased on Properties of Set Materials

Water-Based Gel:4. Alginate (Irreversible Hydrocolloid) Flexible Irrev (Chem)5. Agar-Agar (Reversible Hydrocolloid) FlexibleRev (Phys)

Elastomers:6. Polysulfide (Rubber Base, Thiokol) Flexible Irrev (Chem)7. Silicone (Conventional, Condensation) Flexible Irrev (Chem)8. Polyether Flexible Irrev (Chem)9. Polyvinyl Siloxane (Addition Silicone) Flexible Irrev (Chem)

Introduction

Elasto mers refer to a group of rubbery polymers, which are

chemically or physically cross-linked. They can be easily stretched and rapidly recover their original dimensions when applied stress is released.

Imp

ress

ion

M

ate

rials

Non-elastic

Elastic

Aqueous Hydrocolloids

Non-aqueous Elastomers

Polysulfide

Silicones

Polyether

Condensation

Addition

Agar (reversible)

Alginate (irreversible)

Plaster

Compound

ZnO - Eugenol

Waxes

O’Brien, Dental Materials & their Selection 1997


Colloidal suspensions chains align to form fibrils traps water in interstices

Two forms sol

viscous liquid gel

elastic solid Placed intra-orally as sol

converts to gel thermal or chemical process

Phillip’s Science of Dental Materials 1996


Semi-permeable membranes poor dimensional stability

Evaporation Syneresis

fibril cross linking continues contracts with time exudes water

Imbibition water absorption

swells


Hydrocolloids

Reversible and Irreversible

Introduced by Sears 1939 First elastic

Hydrocolloid impression materials

Reversible Agar Sets by cooling.

Irreversible Alginate Sets by chemical

reaction.

Elastic



Polysulfide

Silicones

Polyether

Condensation

Addition

Agar (reversible)


O’Brien, Dental Materials & their Selection 1997

Irreversible Hydrocolloid (Alginate) Most widely used

impression material Indications

study models removable fixed partial dentures

framework Examples

Jeltrate (Dentsply/Caulk) Coe Alginate (GC America)


Irreversible Hydrocolloid

Material that cannot return to a solution state after it becomes a gel.

Alginate is the irreversible hydrocolloid most widely used for preliminary impressions.

Alginate

Alginic acid;

Alginic acid, also called algin or alginate, is an anionic polysaccharide distributed widely in the cell walls of brown algae, where it, through binding water, forms a viscous gum.

In extracted form it absorbs water quickly; it is capable of absorbing 200-300 times

its own weight in water. Its colour ranges from white to yellowish-

brown. It is sold in filamentous, granular or

powdered forms.

http://en.wikipedia.org/wiki/Anionic

http://en.wikipedia.org/wiki/Polysaccharide

http://en.wikipedia.org/wiki/Cell_wall

http://en.wikipedia.org/wiki/Brown_algae

http://en.wikipedia.org/wiki/Natural_gum

http://en.wikipedia.org/wiki/Filament

Makeup of Alginate

Potassium alginate (Alginic Acid) (12-15%)Comes from seaweed; is also used in foods

such as ice cream as a thickening agent. Calcium sulfate (8-12%)

Reacts with the potassium alginate to form the gel.

Trisodium phosphateAdded to slow down the reaction time for

mixing.

Composition

Sodium alginate salt of alginic

acid mucous

extraction of seaweed (algae)

Calcium sulfate reactor

Sodium phosphate retarder

Filler Potassium

fluoride improves

gypsum surface2 Na3PO4 + 3 CaSO4 Ca3(PO4)2 + 3 Na2SO4

Na alginate + CaSO4 Ca alginate + Na2SO4

(powder) (gel)

H2O

O’Brien Dental Materials & their Selection 1997

Makeup of Alginate- cont’d

Diatomaceous earth (70%)A filler that adds bulk to the material. Controls the stiffness of the set gel

Zinc oxideAdds bulk to the material.

Potassium titanium fluoride (~10%)Added so as not to interfere with the setting and

surface strength. Sodium Phosphate (retarder) (2%)

Coloring and flavouring agents (traces)

Physical Phases of Alginate

The first phase is a sol (as in solution). In the sol phase, the material is in a liquid or semiliquid form. (sol: resembles a solution, but is made up of colloidal particles dispersed in a liquid)

The second phase is a gel. In the gel phase, the material is semisolid, similar to a gelatin dessert.

“gel” entangled framework of solid colloidal particles in which liquid is trapped in the interstices and held by capillary forces (Jello)

Fig. 46-7 Examples of packaging for alginate.

Packaging and Storing of AlginateContainers about the size of a coffee

can are the most commonly used form of packaging.

Shelf life of alginate is approximately 1 year.

Manipulation

Weigh powder Powder added to water

rubber bowl vacuum mixer

Mixed for 45 sec to 1 min Place tray Remove 2 to 3 minutes

after gelation (loss of tackiness)

Caswell JADA 1986

Fig. 46-8 Scoop and water measure for alginate.

The mix of an alginate impression material is made by a vigorous stropping of the material against the side of the mixing bowl

Water-to-Powder Ratio

An adult mandibular impression generally requires two scoops of powder and two measures of water.

An adult maxillary impression generally requires three scoops of powder and three measures of water.

Manipulation

Weigh powder Powder added to water

rubber bowl vacuum mixer

Mixed for 45 sec to 1 min Place tray Remove 2 to 3 minutes

after gelation (loss of tackiness)

Caswell JADA 1986

Altering the Setting Times of AlginateCooler water can increase the setting

time if additional time is needed for the procedure.

Warmer water can reduce or shorten the setting time of the procedure.

Taking an Alginate Impression

Explain the procedure to the patient:The material will feel cold, there is no unpleasant

taste, and the material will set quickly.Breathe deeply through your nose to help you

relax and be more comfortable.Use hand signals to communicate any

discomfort.

Rinse and dry the patient's teeth, If teeth are too dry,

alginate will stick

An Acceptable Alginate Impression The impression tray is centered over the central and

lateral incisors. There is a complete "peripheral roll," which includes all

of the vestibular areas. The tray is not "overseated," which would result in

exposure of areas of the impression tray.The impression is free from tears or voids.There is sharp anatomic detail of all teeth and soft

tissues.The retromolar area, lingual frenum, tongue space,

and mylohyoid ridge are reproduced in the mandibular impression.

The hard palate and tuberosities are recorded in the maxillary impression.

Advantages

Inexpensive Easy to use Hydrophilic

displace moisture, blood, fluids Stock trays


Disadvantages

Tears easily Dimensionally unstable

immediate pour single cast

Lower detail reproduction unacceptable for fixed pros

High permanent deformation Difficult to disinfect


Uses of alginate impression and its applications

Irreversible hydrocolloid (alginate) : Alginate is the most widely used impression

material in dentistry. They are used to take impressions for:1. Diagnostic casts.2. Partial dentures with clasps.3. Preliminary impressions for CD.4. Occlusal analysis

5. Orthodontic treatment planning & ort. retainers 6. Crown, bridge and implant planning 7. Mouthguards 8. Occlusal splints 9. Inlays & onlaysslide 42

Elastic



Polysulfide

Silicones

Polyether

Condensation

Addition

Agar (reversible)


Condensation Silicone

Indications complete dentures crown and bridge

Examples Speedex (Coltene/Whaledent) Primasil (TISS Dental)

Composition

Base poly(dimethylsiloxane) tetraethylorthosilicate filler

Catalyst metal organic ester

By-product ethyl alcohol

Phillip’s 1996

Manipulation

Mix thoroughly paste - paste paste - liquid

Putty-wash technique reduces effect of polymerization shrinkage stock tray

putty placed thin plastic sheet spacer preliminary impression

intraoral custom tray inject wash material

Advantages

Better elastic properties Clean, pleasant Stock tray

putty-wash Good working and setting time

Disadvantages

Poor dimensional stability high shrinkage

polymerization evaporation of ethanol

pour immediately within 30 minutes

Hydrophobic poor wettability

Elastic



Polysulfide

Silicones

Polyether

Condensation

Addition

Agar (reversible)


Addition Silicones

AKA: Vinyl polysiloxane Indications

crown and bridge denture bite registration

Examples Extrude (Kerr) Express (3M/ESPE) Aquasil (Dentsply Caulk) Genie (Sultan Chemists) Virtual (Ivoclar Vivadent)

Composition

Improvement over condensation silicones no by-product

First paste vinyl poly(dimethylsiloxane)

prepolymer Second paste

siloxane prepolymer Catalyst

chloroplatinic acidPhillip’s 1996


Manipulation

Adhesive to tray Double mix

custom tray heavy-body

light-body to prep Putty-wash

stock tray

Craig Adv Dent Res 1988

Advantages

Highly accurate High dimensional stability

pour up to one week Stock or custom trays Multiple casts Easy to mix Pleasant odor


Disadvantages

Expensive Sulfur inhibits set

latex gloves ferric and Al sulfate

retraction solution Pumice teeth before

impressing Short working time Lower tear strength Possible hydrogen gas release

bubbles on die palladium added to absorb

Manikos Aust Dent J 1998

Addition Silicones

Surfactants added reduce contact angle improved

castability gypsum

wettability?? still need dry field clinically

Elastic



Polysulfide

Silicones

Polyether

Condensation

Addition

Agar (reversible)


Composition

Base difunctional epimine-terminated prepolymer fillers plasticizers

Catalyst aromatic sulfonic acid ester fillers

Cationic polymerization ring opening and chain extension

Manipulation

Adhesive to tray stock or custom tray

very stiff Paste-paste mix Auto-mixing

hand-held low viscosity

mechanical dispenser high viscosity

Advantages

Highly accurate Good dimensional stability Stock or dual-arch trays Good surface detail Pour within one week

kept dry Multiple casts Good wettability

Disadvantages

Expensive Short working time Rigid

difficult to remove from undercuts Bitter taste Low tear strength Absorbs water

changes dimension


Impression Material Usage*Civilian General Dentists

Crown & Bridge vinylpolysiloxane 81% alginate 38% polyether 28%

Inlays and Onlays vinylpolysiloxane 71% polyether 22% alginate 20%

*Multiple responses DPR 2001

Handling Properties

Agar Alginate Polysulfide Condensation Silicone

Addition Silicone

Polyether

PreparationBoil,

temper, store

Powder, water

2 pastes 2 pastes or paste/liquid

2 pastes 2 pastes

Ease of Use Technique sensitive

Good Fair Fair Excellent Good

Patient Reaction

Thermal Shock

Pleasant, clean

Unpleasant, stains

Pleasant, clean Pleasant

Unpleasant clean

Ease of removal

Very easy

Very easy

Easy Moderate Moderate Moderate to difficult

Disinfection Poor Poor Fair Fair Excellent Fair

Handling Properties

Agar Alginate Polysulfide Condensation Silicone

Addition Silicone

Polyether

Working Time (min) 7 – 15 2.5 5 – 7 3 2 –4.5 2.5

Setting Time(min)

5 3.5 8 – 12 6 – 8 3 – 7 4.5

Stability 1 hour 100% RH

Immediate pour 1 hour

Immediate pour 1 week

1 week kept dry

Wettability and

castabilityExcellent Excellent Fair Fair Fair to

goodGood

Cost Low Very low Low Moderate High to very high

Very high

Comparison of Properties

Working time longest to shortest

agar > polysulfide > silicones > alginate = polyether

Setting time shortest to longest

alginate < polyether < agar < silicones < polysulfide

Comparison of Properties

Stiffness most to least

polyether > addition silicone > condensation silicone > polysulfide = hydrocolloids

Tear strength greatest to least

polysulfide > addition silicone > polyether > condensation silicone >> hydrocolloids

Summary

Study models Alginate most widely used

inexpensive displaces moisture lower detail reproduction dimensionally unstable

Impression

Impression Tray

IMPRESSION MATERIALSKey Properties

Accuracy

a. Accuracy = ability to replicate the intraoral surface details.

DimensionalStability

b. Dimensional Stability = ability to retain its absolute dimensional size over time.

TearResistance

c. Tear Resistance = ability to resist tearing in thin sections (such as through the feather-edged material within the gingival sulcus.

Trouble Shooting

Inadequate working or setting time:

temperature of the water, incomplete spatulation W/P too low improper storage of alginate powder

Distortion: Tray movement during gelation or removed from mouth prematurely weight of tray compressing or distorting alginate

impression not poured up immediately

Tearing: removing impression from mouth before adequately set thin mixes (high W/P ratio) presence of undercuts (blocking out these areas before an impression may help) inadequate amount of impression material in tray (avoided by minimum 3 mm of

impression material between tray and oral tissues)

• Loss of detail: removed from mouth prematurely

Consistency: preset mix is too thin or thick The W/P ratio is incorrect (avoid by fluffing powder before measuring; do not

overfill powder dispenser) inadequate mixing (avoided by vigorous spatulation and mixing for recommended

time) using hot water: grainy and prematurely thick mix

• Dimensional change: delay in pouring alginate impression stored in air: results in distorted, undersized cast due to

alginate impressions losing water when stored in air

Porosity: whipping air into the mix during spatulation (proper mixing: after initial wetting of powder by the water, mix alginate so as to squeeze the material

between the spatula blade and the side of the rubber bowl)

• Poor stone surface (of cast) set gypsum remaining in contact with the alginate for too long a period of time

Disinfection of Impression Materials

Irreversible Hydrocolloids (Alginate) Diagnostic Casts:

Soak 10 min in Gluteraldehyde

Final Impressions: Dip in Gluteraldehyde ,rinse in sterile water, dip again let stand under

damp gauze 10 min Spray with Sodium Hypochlorite rinse, spray again & let stand under

damp gauze 10 min

Reversible Hydrocolloid Dip in Gluteraldehyde ,rinse in sterile water, dip again let stand under

damp gauze 10 min Spray with Sodium Hypochlorite rinse, spray again & let stand under

damp gauze 10 min

Addition –reaction Silicones In Gluteraldehyde 1 hr., Rinse sterile water Soak in fresh solution Gluteraldehyde 10 min

Disinfection for impression materials

Formulated with isopropyl alcohol, Septodont's Dimenol isdesigned specifically to disinfect impression materials – alginates and silicones – to protect patients, practice professionals,laboratory professionals and the prosthesis itself.

Spray sufficient bactericidal, fungicidal and virucidalDimenol evenly onto the impression materials to moisten, leave for 15 minutes and rinse carefully to effectively decontaminatethe blood, saliva and proteins that can harbor pathogens. Supplied in 200ml spray bottles,

Dimenol disinfects without altering the surface accuracy and without producing any dimensional variation

References

Phillips’ Science of Dental Materials, edited by K Anusavice, 11th ed., 2008, Saunders Publishing.

RG Craig, Review of Impression Materials, Advance in Dental Research, Aug 1988, 2,51-64.

ORTHODONTICCEMENTS

CONTENTS

INTRODUCTION CLASSIFICATION OF CEMENTS ZINC PHOSPHATE CEMENT ZINC POLYCARBOXYLATE CEMENT GLASS IONOMER CEMENT RESIN IONOMER HYBRID CEMENTS IN BANDING CEMENTS IN BONDING NEWER PRODUCTS

INTRODUCTION Cements are routinely used for orthodontic purposes.

Proper cementation of the bands and bonding of the brackets plays an important role for the betterment of treatment and for reducing the duration.

Problems like failure of the bands and brackets and demineralisation were often faced by the practitioner.

These problems can be due to poor seal between

cement ,bracket or band material and enamel surface; inadequate structural and bonding strength;solubility of cements in oral fluids and so on.

What are cements? In the Oxford dictionary

A material which ”glues“ various things together e.g.

embedded particles in minerals are glued in a compact

body sand, particles of rocks are ”glued“ using Portland cement in a concrete

2007/2008

Powder + Liquid

Pastelike or flowable material

Hardens to a rigid solid

In dentistry

Materials used for: Luting, fixation, cementation - i.e. luting

inlays crowns, bridges, veneers on the prepared tooth To protect pulp from heat (”thermal

insulation“) and from chemical irritation (liners and bases) - to stimulate secondary dentin formation Temporary filling material

2007/2008

Applications of Dental Cements:

Cementing agent for permanent restorations.

Temporary restorations. Liners and bases. Cementing agents for orthodontic

appliances. Periodontal dressing. Root canal fillers and sealers. Pulp capping agents. Anterior restorations.

2007/2008

Requirement of Dental Cements Adequate mechanical properties. Non-irritating & non-toxic. Insoluble. Insulating the pulp from thermal,

electrical and chemical irritants. Adhesive properties. Esthetic properties. Easy to manipulate.

2007/2008

CLASSIFICATION OF DENTAL CEMENTS

The cements may be classified by composition into four categories

a. Phosphates; which includes the zinc phosphate and silicophosphate cement.

b. Phenolates; which includes the zinc oxide eugenol and calcium hydroxide cements

c. Polycarboxylate; which includes the zinc polycarboxylate and glass ionomer cements.

d.Resin cements.

Types of Dental Cements:

1- Cements based on Zinc Oxide. 2- Cements based on Alumino Silicate

Glasses ( Ion leachable glasses ). 3- Other cements:

Resin cements. Calcium – Hydroxide cements. Cavity liners and Varnishes.

2007/2008

1- Cements based on Zinc Oxide

2007/2008

Zinc Oxide

Eugenol Phosphoric acid Polyacrylic acid

Zinc oxide eugenol cement

Zinc phosphate cement

Zinc polycarboxylatecement

2- Cements based on Alumino Silicate Glasses.

2007/2008

Phosphoric acid Polyacrylic acid

Alumino-Slicate Glass

Slicate cements Glass-ionomer cements

GLASS IONOMER CEMENTS HISTORY

Development of glass ionomer cements was first announced by Wilson and kent in 1972.

It is referred to as polyalkenoate cement.

The first commercial glass ionomer was made by the De Trey company and distributed by the amalgamated Dental company in England and by Caulk in the United States.

Known as ASPA(Alumino-silicate poly acrylate) it consisted of an ion leachable alumino silicate glass and an aqueous solution of a copolymer of acrylic acid.

Glass ionomers are hybrids of silicate cements and polycarboxylate cements.

The intention was to produce a cement with characteristics of both the silicate cements (flouride release and translucency) with those of the polycarboxylate cements(ability to chemically bond to tooth structure and kindness to pulp).

Glass ionomer cement was introduced to orthodontics in 1986.

Glass Ionomer Cement

2007/2008

Composition

Powder Liquid

-Calcium fluoroalumino silicate glass .

-Barium glass or zinc oxide.

-Polyacrylic acid copolymer with itaconic, maleic, or tricarboxylic acid.

- Tartaric acid.

Setting Reaction of Glass Ionomer Cement:

2007/2008

Dissolution .

Gelation

Hydration

SETTING REACTION AND STRUCTURE The setting reaction of conventional glass ionomer

cement can be represented as an acid base reaction leading to the formation of polycarboxylate salts that comprise the cement matrix.

Dissolution : The carboxyl(COOH)groups are dissociated to carboxylate groups(COO-)and hydrogen(H+)ions.

The positively charged hydrogen ions attack the surface layer of glass particles,releasing calcium and aluminium ions in the form of flouride complexes.

The calcium ion concentration rises more rapidly.As the ionisation reaction continues, the polyacrylic chains assume a more linear format, allowing the commencement of gelation.

Gelation : The more readily available calcium ions are complexed with the carboxyl groups and a weak ionic cross linking is formed,which corresponds to the initial setting of the cement that is observed.

Final Hardening : As the setting reaction continues,Al3+ ions are increasingly deposited in the matrix,leading to calcium-aluminium carboxylate gel that corresponds to the final stage of cement hardening.

2007/2008

Unreacted glass particles.

Silica hydrogel sheath .

Amorphous matrix of cross- Linked polysalt hydrogel of Ca++&Al+++.

The structure of the set GIC

TYPES OF GIC

Type-I Luting applicationsType-II Restorative materialType-III Liner or Base Type-IV Pit and Fissure SealantType-V Orthodontic BracketType-VI Core build up

Manipulation:

The proper powder/liquid ratio is dispensed onto paper pad or glass slab,mixed for30-60 sec.

Encapsulated products are mixed for 10 sec.in mechanical mixer.

An extension of the working time to 9 minutes can be achieved by mixing on a cold slab.

The cement should not be used once a “skin” forms on the surface or when the viscosity increases noticeably.

2007/2008

Manipulation:

Once the cement has achieved its initial set (about 7 minutes), the cement should be coated with the coating agent supplied with the cement.

2007/2008

Working time-range is 3-5 min Setting time- 5-9 min Manipulation- The powder is introduced into the

liquid in large increments and spatulated rapidly for 30 to 45 seconds

Recommended P:L ratio is 1.25 to 1.5 g of powder per 1ml of liquid

Glass Ionomer Cement

Adhesion to tooth structure.

Biocompatibility. High compressive

strength. Low solubility.

Technique sensetive

Moisture sensitivity.

Short working time and long setting time.

Low abrasion resistance.

Brittlness. 2007/2008

Advantages Disadvantages

Modification of GIC :

A. Metal Reinforced GIC .1. Silver alloy admix.2. Cermet cement.

B. Hybrid Ionomer (Resin-Modified GIC)

Dual cure . Tricure .

C. Compomer (Polyacid modified resin composite materials ).

2007/2008

RESIN MODIFIED GLASS IONOMERS

COMPOSITION

The powder of resin modified glass ionomer cements,consists of either the glass composition used for conventional glass ionomer cements or strontiumaluminoflourosilicate glass; a barium aluminosilicate glass is also incorporated in some products.

Significant alteration have been made in the liquid component of RMGIC's.

Applications of Resin-Modified GIC :

1) Restoration.2) Liners and bases.3) Fissure sealants.4) Core buld up.5) Cementation of orthodontic

brackets.6) Retrograde root filling material.

2007/2008

CEMENTS IN BONDING When used for bonding GIC requires no more etching

other than cleaning with pumice and moderate drying with a cotton roll.

The absolute dryness required for composites have been found to be unnecessary and even harmful for GIC bonding.

It acts as a reservoir of fluoride ions preventing decalcification that occurs around brackets.Also it offers a longer working time.

Light forces must be used first,because gelation continues and full bond strength is not reached for 24 hours.

However, the bond strength of GIC to enamel(2 to 6 MPa) is approximately one-half that of Composite resin(5 to 25 MPa) bonding after etching.No enamel is damaged during debonding.

Compomers in Bonding

Robert A.Miller describes a compomer (Dyract Ortho) that consists of a radiopaque flourosilicate glass in a matrix of acid polymerisable monomers and other light cured polymers.

It is dispersed in single unit 'no mix'capsules.

The 'no mix' feature is made possible by an acid polymerisable monomer that cross links after exposure to light and cross links further after uptake from saliva.

This saves time when bonding in difficult,wet fields,or with impacted canines or second molars.

Although Dyract is self adhesive,it is most retentive to enamel when used after Prime&Bond, a light cured, single component direct bonding agent.

Prime&Bond provides an active adhesion monomer that forms ionic interactions with the inorganic portions of the enamel.

This yields a bond strength that is adequate for brackets and other attachments under wet conditions in most impaction cases.

The impacted tooth is pumiced shortly after surgical exposure.

Prime&Bond is applied followed by Dyract to bracket base and placed firmly to remove excess adhesive since this material is considerably viscous.

Composite resin cement Composite :

Resin matrix + inorganic filler

Silane coated

Composition

Filler Silica

Matrix Bis-GMA (polymer)

The fillers binds with matrix by

silane coupling agent

Setting reaction

Polymerization Chemical activation Light activation Dual activation [chemical and light]

Preparations

Powder / liquid Chemical, light, or dual cure

2 paste system [base / catalyst]Chemical, light, or dual cure

Single paste

Light cure

Bonding system

Bond with the tooth surface by enamel an dentine bonding system.

Bond with metal by using metal primer.

Bond with ceramic restoration by treating the surface of porcelain with silane coupling agent

Properties

Very good bond strength High compressive strength Water sensitive Might irritate pulpal tissues

Applications

Tooth color filling materials Luting cements

References

Textbooks Kenneth J. Anusavice

Phillips’ science of dental materials 11th edition W.B. Saunders company 2003

Thanks

impression materials new era

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