Composite ResinsComposite Resins

Dr.Shahbaz Ahmed

BDS, MSc (UK), FCPS (Pak)

Assistant Professor

Department of Operative Dentistry

DIKIOHS

Overview

• Direct restoratives– Composition– Classification– Performance factors

• Forms

- Flowable

- Packables

Composite• Material with two or more distinct substances

– metals, ceramics, or polymers

• Dental resin composite– soft organic-resin matrix

• polymer

– hard, inorganic-filler particles• glass particles

• Most frequently used– esthetic-restorative material

History

• 1871 – silicate cements – alumina-silica glass &

phosphoric acid– very soluble– poor mechanical properties

• 1948 – acrylic resins – polymethylmethacrylate– high polymerization shrinkage– Known as ‘Unfilled acrylics’

History(cont.)

• 1962 – Bis-GMA– stronger resin

• 1969 – filled composite resin– improved mechanical properties

– less shrinkage

– paste/paste system

• 1970’s – acid etching and microfills• 1980’s – light curing and hybrids• 1990’s – flowables and packables• 2000’s – nanofills

Indications

• Anterior restorations

• Posterior restorations– preventive resin– conservative class 1 or 2– cuspal coverage– core Build up- materials

Contraindications

• Large posterior restorations

• Bruxism

• Poor isolation

Advantages

• Esthetics

• Conservation of tooth structure

• Adhesion to tooth structure

• Low thermal conductivity

• Alternative to amalgam

Disadvantages

• Technique sensitivity

• Polymerization shrinkage – marginal leakage– secondary caries– postoperative sensitivity

• Decreased wear resistance

Composition• Resin matrix

– Monomer – initiator– inhibitors– pigments

• Inorganic filler– glass– quartz– colloidal silica

• Coupling Agent - Silane agent

OCH2CHCH2O-C-C=CH2CH2=C-C-O-CH2CH-CH2O -C-

CH3 CH3

CH3

CH3OH OH

O O

Bis-GMA

Monomers• Binds filler particles together• Provides “workability”• Typical monomers

– Bisphenol A glycidyl methacrylate (Bis-GMA)

– Urethane dimethacrylate (UEDMA)

– Triethylene glycol dimethacrylate (TEGMA) Lower viscosity Diluent

CH2=C-C-O-CH2CH2-O-C-NHCH2CH2CHCH2-C-CH2-NH-C-

CH3

CH3

OCH2CH2O-C-C=CH2

CH3

O OOO

CH3

CH3

OCH2CHCH2O-C-C=CH2CH2=C-C-O-CH2CH-CH2O -C-

CH3 CH3

CH3

CH3OH OH

O O

CH2=C-C-O-CH2CH2-OCH2CH2

CH3

OCH2CH2O-C-C=CH2

CH3

O O

Monomers• Bis-GMA

– extremely viscous– lowered by adding TEGDMA

• freely movable

• increases polymer conversion• increases crosslinking• increases shrinkage

CH2=C-C-O-CH2CH-CH2O -C- OCH2CHCH2O-C-C=CH2

CH3 CH3

CH3

CH3OH OH

O O

Monomers

• Shrinkage– 2 – 7 %– marginal gap

formation

Filler Particles

• Crystalline quartz– larger particles– not polishable

• Silica glass– barium

– strontium– Lithium

- Polishable

Filler Particles

• Increase fillers, increase mechanical properties– strength

– abrasion resistance

– esthetics

– handling

0

0.5

1

1.5

2

Fra

ctur

e T

ough

ness

0 28 37 48 53 62

% Filler Volume

Coupling Agent

• Chemical bond– filler particle - resin matrix

• Organosilane (bifunctional molecule)– siloxane end bonds to hydroxyl groups on filler– methacrylate end polymerizes with resin

CH3-C-C-O-CH2-CH2-CH2-Si-OH

CH2

O OH

OH

Bonds with filler

Silane

Bis-GMABonds with resin

Inhibitors

• Prevents spontaneous polymer formation

• Extends shelf life

• Butylated Hydroxytoluene

Pigments and UV Absorbers

• Pigments– metal oxides

• provide shading and opacity

• titanium and aluminum oxides

• UV absorbers– prevent discoloration– acts like a “sunscreen”

• Benzophenone

Visible-Light Activation• Camphorquinone

– most common photoinitiator• absorbs blue light

– 400 – 500 nm range

• Initiator reacts with amine activator

• Forms free radicals

• Initiates addition polymerization

OCH2CHCH2O-C-C=CH2CH2=C-C-O-CH2CH-CH2O -C-

CH3 CH3

CH3

CH3OH OH

O O

Bis-GMA

Polymerization

• Initiation– production of reactive free radicals

• typically with light for restorative materials

• Propagation– hundreds of monomer units– polymer network

• Termination

Classification System

• Matrix composition

• Method of cure

• Filler content

• Filler particle size– traditional ( macrofilled)– microfilled– small particle – hybrid

Newer Classification System

• Based on particle size– megafill

• 0.5–2 millimeters– macrofill

• 10–100 microns– midifill

• 1–10 microns– minifill

• 0.1–1 microns– microfill

• 0.01–0.1 microns– nanofill

• 0.005–0.01 microns

• Most new systems– minifillers

• Newest trend – nanofillers

Nanofilled Composite

• Filtek Supreme (3M ESPE)

• Filler particles– filled: 78% wgt– nanomers

• 0.02 – 0.07 microns

– nanocluster• act as single unit

– 0.6 – 1.4 microns

Performance Factors

• Material factors– biocompatibility– polymerization shrinkage– wear resistance– polish mechanisms– placement types – mechanical & physical properties

Biocompatibility

• Tolerated by pulp– with good seal

• Rare allergic reactions– HEMA

• Cytotoxicity– short lived

• Degree of cure important– decrease free monomer

Systemic• Estrogenic effects seen in cell cultures

– impurities in Bis-GMA-based resins• Bis-phenol A in sealants

– Olea, EHP 1996

– however, insignificant short-term risk

• literature review– Soderholm, JADA 1999

Polymerization Shrinkage• Significant role in restoration failure

– gap formation• secondary caries formation

• marginal leakage

• post-operative sensitivity

• Counteract– lower shrinkage composites– incremental placement

Composite Wear• Less wear

– small particle size• less abrasion

– heavier filled• less attrition

– non-contact areas• 3 - 5 times less

– less surface area– anterior location

• premolars vs. molars

Polish Mechanisms

• Acquired polish– clinician induced

• Inherent polish– ultimate surface

Composite Selection

• Anterior/stress (Class 4)– hybrid

• mini- or midi-fill

– hybrid/microfill

• Anterior/non-stress (Class 3 or 5)– hybrid

• mini-fill

– microfill

Composite Selection

• Posterior composites– hybrid

• mini- or midi-fill

– reinforced microfill

Composite Variants

• Packable

• Flowable

Packable Composites

• Marketed for posterior use– increase in viscosity

• better proximal contacts • handle like amalgam?

• Subtle alteration of filler– shape– size– particle distribution

Flowable Composites

• Marketed – class 1, 3, 5– liner

• Particle size similar to hybrid composites• Reduced filler content

– reduces viscosity

Flowable Composites

• Clinical applications– preventive resin restorations– small Class 5– provisional repair– composite repair– Liners ??

Future Composites

• Low-shrinking monomers

• Self-adhesive ?

Composite Curing

• Original composites (Chemical cured)

• UV- Light curing

• Visible light curing

- “ Dual curing”

Light curing

• Quartz- Tungsten Halogen (QTH)

• Light- emitting diode (LED)

• Plasma Arc

• Laser

Light Curing variables

Curing equipment factors

• Bulb degradation

• Light reflector degradation

• Optical filter degradation

• Light guide fracture

• Tip contamination

• Sterilization problems ?

– Infection control barriers

Procedural factors

• Light tip direction - adjacent to the surface

• Access to restoration – light transmitting wedges

• Distance from surface – 1-2mm ideally

• Size of tip

• Tip movement• Time of exposure – minimum of 20 secs

Restoration factors

• Restoration thickness – 1.5 to 2mm incrementally

• Cavity design – C Factor

• Filler amount – scatter light

• Restoration shade – darker shades decrease depth of cure – 1mm increment, Increase curing time

__ “ Post Curing”

Curing methods

• Stepped or Soft start

- Start at low intensity 2-10 seconds

and later increase intensity

- Decreases stress, marginal leakage

and fewer gaps

- Increases mechanical properties

- Controversial ?

• Pulse delay technique

• Used with final increment

• Waiting period between exposures – shape occlusal surface

• Improved physical properties?

C- Factor – Cavity Configuration

C=C=BONDED WALLSBONDED WALLS

C-FACTORC-FACTOR

UNBONDED WALLS

Smooth surface restoration

C=C= 1155

C-FACTORC-FACTOR 0.20.2

BondedBonded

UnbondedUnbonded

Two walled cavity

C=C= 2244

C-FACTORC-FACTOR 0.50.5

CAVITY CLASSCAVITY CLASS IVIV

BondedBonded

UnbondedUnbonded

Three walled cavity

C=C= 3333

C-FACTORC-FACTOR 11

CAVITY CLASSCAVITY CLASS IIIIII

BondedBonded

UnbondedUnbonded

Four walled cavity

C=C= 4422

C-FACTORC-FACTOR 22

CAVITY CLASSCAVITY CLASS IIII

BondedBonded

UnbondedUnbonded

Five walled cavity

C=C= 5511

C-FACTORC-FACTOR 55

CAVITY CLASSCAVITY CLASS V & I V & I

BondedBonded

UnbondedUnbonded

C-Factor

• Increasing C-Factor increases the shrinkage stress loading on the tooth-resin interface leading to de-bonding

• Once failure occurs, post insertion sensitivity and recurrent caries can become a problem

• C-Factor problem is a consequence of resin chemistry

Possible solutions

• Don’t cut G.V.Black style cavity preps

• Bonded base or Sandwich techniqueBonded base or Sandwich technique

• Incremental placementIncremental placement

• Restoration sectioningRestoration sectioning

Acid Etching / ConditioningAcid Etching / Conditioning

History

Buonocore 1955, applied acid to teeth

‘ Render the tooth surface more

receptive to adhesion’

Theories of Adhesion

• Mechanical

• micromechanical interlocking

• Adsorption - chemical bonds

• Primary - ionic and covalent

• Secondary - hydrogen, van der Waals

Acid Etchants / Conditioners

• Citric acid

• lactic acid

• Maleic acid

• EDTA• Phosphoric acid - a strong inorganic acid

(30% - 50%) most commonly used for etching

Conditioning Enamel

• Removes 10 microns of surface and creates microporous layer

• Three etching patterns

- Type I – Core etching

- Type II – Periphery etching

- Type III – Mixed patterns

• Resin tags

- Macrotags

- Microtags

Etched Enamel

Important considerations

• Type of acid• Acid Concentration• Etching time• Form of etchant• Enamel instrumented prior• Condition of enamel• Primary or permanent enamel• Prism or prismless enamel

Conditioning Dentine

• Chemical alteration of dentine

• Objective is to remove the smear layer

• Demineralizing the dentine to expose a microporous scaffold of collagen fibrils

(Hybrid layer)

Conditioned Dentine

Important considerations

• Kind of acid

• Application time

• Acid concentration and pH

• Distance between tubules

• Type of dentine

Acid Etching

• Enamel• Selective Demineralization• Increases surface area• Increases life of composite• Decreases marginal staining• Decreases secondary caries• Decreases post-operative

sensitivity• Permits efficient wetting by

hydrophobic resin• Tag formation in

microporosities

• Dentine• Demineralizes dentine

surface• Opens dentinal tubules• Exposes collagen

• Conditions dentine for better wetting of the primer

Thank You