Restorative resins

Restorative resinsRestorative resinsByBibinbhaskaran

Index Aesthetic restorative materialsComposite restorative materialsCuring of resin-based compositesClassification of resin based compositesComposites for posterior restorationsUse of composite for resin veneersFinishing of compositesBiocompatibility of compositesRepair of compositesSurvival probability of composites

History 20th century-silicates only tooth-colored aesthetic material.Acrylic resins replaced silicates in1940’s because of their aesthetics insolubility in oral fluids low cost and ease of manipulationExcessive thermal expansion and contraction –stresses developProblem solved by addition of quartzEarly composites based on PMMA not sucessfulA major advancement made after introduction of bis-GMA by Dr ray l. bowen in 19 50,s

Composite restorative materialsUses-Restoration of anterior and posterior teeth

To veneer metal crowns and bridges

Cementation of orthodontic brackets,marylandbridges,ceramiccrowns,inlays ,onlays,laminates

Repair of chipped porcelain restorationsTypes Based on curing mechanism-Chemically activatedLight activated Based on size of filler particles-Conventional 8-12 umSmall particle 1-5 umMicrofilled 0.04-0.4 umHybrid 0.6-1.0 um

Dental composites Dental composites - They are highly crosslinked polymeric materials reinforced by a dispersion of glass,crystalline or resin filler particles or short fibres bound to the matrix by silane coupling agents Composition -Resin matrixFiller particlesCoupling agentAn activator-initiator system required to convert resin to soft moldable filling material to hard durable restoration

Resin matrix- mostly blend of aromatic/aliphatic dimethacrylate monomers such as BISGMA,TEGDMA,UDMA. Fillers – Based on the type of filler particles composites are currently classified as microhybridand microfilledproducts.

Benefits of fillers- (1) reinforcement of the matrix resin, resulting in increased hardness, strength, and decreased wear (2) reduction in polymerization shrinkage (3) reduction in thermal expansion and contraction(4) improved workability by increasing viscosity(5) reduction in water sorption, softening, and staining (6) increased radiopacity

Important factors with regard to fillers that determine the properties and clinical application-Amount of filler addedSize of particles and distributionIndex of refractionRadiopacityHardness

Types of fillers used-Ground quartz- Makes restoration difficult to polish and cause abrasion of opposing teeth and restorations Colloidal silica— Used in microfilled composites Thicken the resinGlasses of ceramic containing heavy metalsRadiopacity Barium

Coupling agentBond filler particles to resin.Allows for transfer of stresses to stiffer filler particles.FUNCTIONS---Improve physical and mechanical properties.Prevent water from penetrating the resin-filler surface. 3-methoxy-propyl-trimethoxy silane most commonly used

InhibitorsInhibitors are added to the resin to minimise or prevent spontaneous or accidental polymerization of monomersA typical inhibitor is butylatedhydroxytoluene (BHT) used in concentration of 0.01 wt%

Optical modifiersDental composites must have visual shading and transluscency for a natural appearance.Shading is achieved by adding pigments usually metal oxide particlesAll optical modifiers affect light transmission through a composite. Darker shades and greater opacities have a decreased depth of light curing ability.titanium dioxide and aluminium oxide most commonly used.

Polymerisation mechanism2 types Chemically activated Light-activated

Chemically activated composite system Two paste systemBase paste – benzoyl peroxide initiatorCatalyst paste– tertiary amine activator (N,N-dimethyl-p-toludine)

Light activated composite resins—Earliest system---Uv light activated systemLimitations – Limited penetration of light into resin Lack of penetration through tooth structure

Visible light activated system---Single paste systemPhotoinitiator – CamphoroquinoneAmine accelerator – diethyl-amino-ethyl-methacrylate

Types of lamps used for curingLED lamps. Using a solid-state, electronic process, these light sources emit radiation only in the blue part of the visible spectrum between 440 and 480 nm QTH lamps. QTH lamps have a quartz bulb with a tungsten filament that irradiates both LTV and white light that must be filtered to remove heat and all wavelengths except those in the violet-blue range (400 to 500 nm).

PAC lamps. PAC lamps use a xenon gas that is ionized to produce a plasma. The high-intensity white light is filtered to remove heat and to allow blue light (400 to 500 nm) to be emitted. Argon laser lamps- have the highest intensity and emit at a single wave length.lamps currently avaialble emit 490 nm

Depth of cure and exposure timeLight absorption and scattering in resin composites reduces the power density and degree of conversion (DC) with depth of penetrationIntensity can be reduced by a factor of 10 to 100 in a 2-mm thick layer of composite which reduces monomer conversion to an accceptable level.The practical consequence is that curing depth is limited to 2- 3mmLight attenuation vary from one type of composite to other depending on opacity,fillersize,filler concentration and pigment shade

Darker shades require long curing timeWhen polymerising resin through tooth structure exposure time should be increased by a factor of 2 – 3 to compensate for reduction in light intensityFor halogen lamps light intensity can decrease depending on quality and age of light source,orientation of light tip,distance between light tip and restoration and presence of contamination,such as composite residue on light tipDespite the many advantages of light cured resins,there is still need for chemically cured composites for egchemicaly cured materials can be used with reliable results as luting agent under metallic restorations.

Dual curing and extra oral curingOne way to overcome problems associated with light curing is to combine chemical curing and light curing components in same resin.Air inhibition and porosity are problems associated with dual-cure resinsExtra-oral heat or light can be used to promote a higher level of cureFor eg light cured or chemical cured composite for inlay can be cured directly within the tooth or die and then transferred to oven to receive additional heat or light curing

Degree of conversionDC is a measure of percentage of carbon-carbon double bonds that have been converted to single bonds to form polymeric resinThe higher the DC the better the strength,wear,resistanceConversion values of 50%-70% are achieved at room temperature for both types of curing system

Reduction of residual stresses 2 approaches-Reduction in volume contraction by altering the chemistry of resin systemClinical techniques designed to offset the effects of polymerisation shrinkage

Incremental buildup and cavity configurationOne technique is the attempt to reduce the so called C-factor(configuration factor) which is related to the cavity preparation geometryA layering technique in which restoration is built up in increments,reducespolymerisation stress by minimising the Cfactor.Incremental technique overcomes both limited depth of cure and residual stress concentration.

Soft started,ramped curing and delayed curingVariations on this technique include ramping and delayed cure.In ramping the intensity is gradually increased or ramped up during the exposure which consists of either step wise,linear or exponential modes.In delayed curing restoration is initialy cured at low intensity and after contouring the resin to correct occlusion second exposure for final cure is done.The longer the time available for relaxation,lower the residual stress

High intensity curing High intensity lamps could provide savings in chair time. However high intensity, short exposure times cause accelerated rates of curing, which leads to substantial residual stress build up.

Conventional / traditional /macrofilled compositeComposition- Ground quartz most commonly used filler Average size : 8- 12 µm Filler loading - 70-80 weight % or 50 – 60 vol %

PropertiesCompressive strength- Four to five times greater than that of unfilled resins ( 250-300 Mpa)Tensile strength- Double than of unfilled acrylic resins (50 – 65 Mpa)Elastic modulus- Four to six times greater (8-15 Gpa)Hardness – Considerably greater (55 KHN) than that of unfilled resinsCoefficient of thermal expansion- High filler –resin ratio reduces the CTE significantly.

Esthetics – Polishing result in rough surface Selective wear of softer resin matrix Tendency to stainRadiopacity – Composites using quartz as filler are radioluscentRadiopacity less than dentin

Clinical considerations- Polishing was difficult

Poor resistance to occlusal wear

Inferior for posterior restorations Microfilled composites Developed to overcome surface roughness of conventional compositesComposition- Smoother surface is due to the incorporation of microfillers. Colloidal silica is used as the microfiller 200—300 times smaller than the average particle in traditional composites Filler particles consists of pulverised composite filler particles

Properties Inferior physical and mechanical properties to those of traditional composites40 – 80 % of the restorative material is made up of resinIncreased surface smoothnessAreas of proximal contact- Tooth drifting.

Compressive strength- 250- 350 Mpa.Tensile strength- 30- 50 Mpa. Lowest among compositesHardness – 25- 30 KHN.Thermal Expansion Coefficient- highest among composite resins

Clinical considerationsChoice of restoration for anterior teeth.Greater potential for fracture in class 4 and class 2 restorations.Chipping occurs at margins.

Small particle compositeIntroduced in an attempt to have good surface smoothness and to improve physical and mechanical properties of conventional composites.Composition – Smaller size fillers used- Colloidal silica - present in small amounts ( 5 wt % ) to adjust paste viscosity Heavy metal glasses . Ground quartz also usedFiller content 65 – 70 vol % or 80 – 90 %

Properties Due to higher filler content the best physical and mechanical properties are observedCompressive strength- Highest compressive strength (350 – 400 Mpa )Tensile strength- Double that of microfilled and 1.5 times greater than that of traditional composites ( 75- 90 Mpa )

Hardness – Similar to conventional composites ( 50 – 60 KHN)Thermal expansion coefficient- Twice that of tooth structureEsthetics – Better surface smoothness than conventional because of small and highly packed fillersRadiopacity – Composites containing heavy metal glasses as fillers are radio-opaque which is an important property in restoration of posterior teeth

Clinical considerationsIn stress bearing areas such as class 4 and class 2 restorationsResin of choice for aesthetic restoration of anterior teethFor restoring sub gingival areas

Hybrid compositeDeveloped in an effort to obtain even better surface smoothness than that provided by the small particle composite.Composition – 2 kinds of fillers- Colloidal silica – present in higher concentrations 10 – 20 wt % Heavy metal glasses – Constituting 75 % Average particle size 0.4 – 1.0 µm

Properties Range between conventional and small particleSuperior to microfilled compositesCompressive strength- Slightly less than that of small particle composite(300 – 350 Mpa )Tensile strength- Comparable to small particle (70 – 90 Mpa )Hardness – Similar to small particle ( 50 – 60 KHN )

Esthetics – Competitive with microfilled composite for anterior restorationRadiopacity – Presence of heavy metal glasses makes the hybrid more radio-opaque than enamel

Clinical considerationsUsed for anterior restorations including class 4 because of its smooth surface and good strengthWidely employed for stress bearing restorations

Flowable compositesModification of SPF and Hybrid composites.Reduced filler levelClinical considerations-Class 1 restorations in gingival areas. Class 2 posterior restorations where acess is difficult. Fissure sealants.

Composites for posterior restorationsAmalgam choice of restoration for posterior teethMercury toxicity and increased esthetic demand.All types of composites except flowable compositesConservative cavity preparationMeticulous manipulation technique.

Packable composites1990sElongated fibrous,filler particles of about 100µmTime consumingInferior in stength when compared to amalgam

Problems in use of composites for posterior restorationIn class 5 restoration where gingival margin is located in cementum or dentin.Marginal leakageTime consuming Composites wear faster than amalgam

Indications –Esthetics Allergic to mercury To minimse thermal conduction

Indirect posterior compositesIntroduced to overcome wear and leakage.Polymerised outside the oral cavity and luted with resin cementFor fabrication of inlays and onlays.Different approaches for resin inlay constuction-Use of both direct and indirect fabrication systemsApplication of heat,light,pressure or combination Combined use of hybrid and microfilled composites

Uses of composites for Resin veneersThese resins are polymerized by visible light in violet –blue range or by combination of heat and pressure.Uses – Veneers for masking tooth discoloration Used as performed laminate veneers

Advantages –Ease of fabricationPredictable intra-oral reparabilityLess wear of opposing teeth or restorationsDisadvantages –Leakage of oral fluidsStaining below veneersSusceptible to wear during tooth brushing

Techniques of insertionChemically activated resins—Correct proportions dispensed Rapid spatulation with plastic instrument for 30 secAvoid metal instrumentsInserted with syringe or plastic instrumentCavity slightly overfilledMatrix strip placed to apply pressure and to avoid air inhibition

Light activated resins-Single component pastesWorking time under control of operatorHardens rapidly once exposed to curing lightsLimited depth of cureIncremental build upHigh intensity light usedExposure time not less than 40 – 60 secResin thickness not greater than 2.0-2.5mmCaution – High intensity light causes retinal damage

Acid etch technique Most effective way of improving marginal seal between resin and enamel Mode of action-Creates microporosities by discrete etching of enamelEtching increases surface areaEtched enamel allow resin to wet the tooth surface betterWhen polymerised forms resin tags Acid used-37% phosphoric acid

Dentin bonding agents Supplied as - kit containing primers/conditioners and the bonding liquid. Primers/conditioners-Remove the smear layer and provides opening of dentinal tubules.Provides modest etching of inter-tubular dentin.

Classification First generation –Use glycerophosphoric acid dimethacrylate.Main disadvantage-low bond strenghth. Second generation –Developed as adhesive agents for composites.Bond strength 3 times more.Disadvantage – short term adhesion. bond hydrolysed eventually.EgPrisma,Universalbond,Miragebond.

Third generation – Had bond strengths comparable to that of resin to etched enamel.Complex use-requires 2-3 application steps.EgTenure,Scotch Bond 2,Prisma. Fourth generation –All bond – 2 systems.Consists of 2 primers (NPG-GMA and BPDM).An unfilled resin adhesive(40%BIS-GMA,30%UDMA,30%HEMA). Bonds composite not oly to dentin but to most surfaces like enamel,castingalloys,amalgam,porcelain and composite.

Fifth generation – Most recent product.More simple to use.Only single step application.Eg 3M Single Bond,Prime and Bond(Dentsply).

Indications for use For bonding composite to tooth structure.Bonding composite to porcelain and various metals like amalgam,base metal and noble metal alloys.Desensitization of exposed dentin or root surfaces.Bonding of porcelain veneers.

Sandwich Technique Composite does not bond adequately to dentin.Bond to dentin improved by placing GIC liner between composite and dentin. Indications Lesions where one or more margins are in dentin. eg cervical lesions.Class II composite restorations.

CoresIf half or more of clinical crown is destroyed.Must be anchored firmly to tooth.Pin-retained cores mostly used.Amalgam and composite resins .Composited more favored.

Advantages- Easily molded into large cavities.Polymerise quickly.Crown preparation done at same appointment. Disadvantage –Dimensionaly not stableGreater microleakage

Restorative resins

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