Restorative resins Restorative resins By Bibinbhaskaran
Index Aesthetic restorative materials Composite restorative materials Curing of resin-based composites Classification of resin based composites Composites for posterior restorations Use of composite for resin veneers Finishing of composites Biocompatibility of composites Repair of composites Survival 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 manipulation Excessive thermal expansion and contraction –stresses develop Problem solved by addition of quartz Early composites based on PMMA not sucessful A major advancement made after introduction of bis-GMA by Dr ray l. bowen in 19 50,s
Composite restorative materials Uses-
Restoration of anterior and posterior teeth
To veneer metal crowns and bridges
To bulid up cores
Cementation of orthodontic brackets,marylandbridges,ceramiccrowns,inlays ,onlays,laminates
Pit and fissure sealants
Repair of chipped porcelain restorations
Types Based on curing mechanism- Chemically activated Light activated Based on size of filler particles- Conventional 8-12 um Small particle 1-5 um Microfilled 0.04-0.4 um Hybrid 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 matrix Filler particles Coupling agent An 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 added Size of particles and distribution Index of refraction Radiopacity Hardness
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 resin Glasses of ceramic containing heavy metals Radiopacity Barium
Coupling agent Bond 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
Inhibitors Inhibitors are added to the resin to minimise or prevent spontaneous or accidental polymerization of monomers A typical inhibitor is butylatedhydroxytoluene (BHT) used in concentration of 0.01 wt%
Optical modifiers Dental composites must have visual shading and transluscency for a natural appearance. Shading is achieved by adding pigments usually metal oxide particles All 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.
Chemically activated composite system Two paste system Base paste – benzoyl peroxide initiator Catalyst paste– tertiary amine activator (N,N-dimethyl-p-toludine)
Light activated composite resins— Earliest system---Uv light activated system Limitations – Limited penetration of light into resin Lack of penetration through tooth structure
Visible light activated system--- Single paste system Photoinitiator – Camphoroquinone Amine accelerator – diethyl-amino-ethyl-methacrylate
Types of lamps used for curing LED 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 time Light absorption and scattering in resin composites reduces the power density and degree of conversion (DC) with depth of penetration Intensity 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- 3mm Light attenuation vary from one type of composite to other depending on opacity,fillersize,filler concentration and pigment shade
Darker shades require long curing time When polymerising resin through tooth structure exposure time should be increased by a factor of 2 – 3 to compensate for reduction in light intensity For 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 tip Despite 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 curing One 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 resins Extra-oral heat or light can be used to promote a higher level of cure For 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 conversion DC is a measure of percentage of carbon-carbon double bonds that have been converted to single bonds to form polymeric resin The higher the DC the better the strength,wear,resistance Conversion 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 system Clinical techniques designed to offset the effects of polymerisation shrinkage
Incremental buildup and cavity configuration One technique is the attempt to reduce the so called C-factor(configuration factor) which is related to the cavity preparation geometry A 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 curing Variations 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.
Based on indications and use
Conventional / traditional /macrofilled composite Composition- Ground quartz most commonly used filler Average size : 8- 12 µm Filler loading - 70-80 weight % or 50 – 60 vol %
Properties Compressive 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 resins Coefficient 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 stain Radiopacity – Composites using quartz as filler are radioluscent Radiopacity less than dentin
Polishing was difficult
Poor resistance to occlusal wear
Tendency to discolor
Rough surface tends to stain
Inferior for posterior restorations
Microfilled composites Developed to overcome surface roughness of conventional composites Composition- 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 composites 40 – 80 % of the restorative material is made up of resin Increased surface smoothness Areas of proximal contact- Tooth drifting .
Clinical considerations Choice of restoration for anterior teeth. Greater potential for fracture in class 4 and class 2 restorations. Chipping occurs at margins.
Small particle composite Introduced 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 used Filler content 65 – 70 vol % or 80 – 90 %
Properties Due to higher filler content the best physical and mechanical properties are observed Compressive 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 structure Esthetics – Better surface smoothness than conventional because of small and highly packed fillers Radiopacity – Composites containing heavy metal glasses as fillers are radio-opaque which is an important property in restoration of posterior teeth
Clinical considerations In stress bearing areas such as class 4 and class 2 restorations Resin of choice for aesthetic restoration of anterior teeth For restoring sub gingival areas
Hybrid composite Developed 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 particle Superior to microfilled composites Compressive 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 restoration Radiopacity – Presence of heavy metal glasses makes the hybrid more radio-opaque than enamel
Clinical considerations Used for anterior restorations including class 4 because of its smooth surface and good strength Widely employed for stress bearing restorations
Flowable composites Modification of SPF and Hybrid composites. Reduced filler level Clinical considerations- Class 1 restorations in gingival areas. Class 2 posterior restorations where acess is difficult. Fissure sealants.
Composites for posterior restorations Amalgam choice of restoration for posterior teeth Mercury toxicity and increased esthetic demand. All types of composites except flowable composites Conservative cavity preparation Meticulous manipulation technique.
Packable composites 1990s Elongated fibrous,filler particles of about 100µm Time consuming Inferior in stength when compared to amalgam
Problems in use of composites for posterior restoration In class 5 restoration where gingival margin is located in cementum or dentin. Marginal leakage Time consuming Composites wear faster than amalgam
Indications – Esthetics Allergic to mercury To minimse thermal conduction
Indirect posterior composites Introduced to overcome wear and leakage. Polymerised outside the oral cavity and luted with resin cement For fabrication of inlays and onlays. Different approaches for resin inlay constuction- Use of both direct and indirect fabrication systems Application of heat,light,pressure or combination Combined use of hybrid and microfilled composites
Uses of composites for Resin veneers These 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 fabrication Predictable intra-oral reparability Less wear of opposing teeth or restorations Disadvantages – Leakage of oral fluids Staining below veneers Susceptible to wear during tooth brushing
Techniques of insertion Chemically activated resins— Correct proportions dispensed Rapid spatulation with plastic instrument for 30 sec Avoid metal instruments Inserted with syringe or plastic instrument Cavity slightly overfilled Matrix strip placed to apply pressure and to avoid air inhibition
Light activated resins- Single component pastes Working time under control of operator Hardens rapidly once exposed to curing lights Limited depth of cure Incremental build up High intensity light used Exposure time not less than 40 – 60 sec Resin thickness not greater than 2.0-2.5mm Caution – 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 enamel Etching increases surface area Etched enamel allow resin to wet the tooth surface better When 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.
Cores If 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 stable Greater microleakage
Finishing and polishing Started 5 min after curing Initial contouring with knife or diamond stone Final finishing with rubber impregnated abrasives or aluminum oxide discs Best finish obtained on setting against matrix strip
Biocompatibility Relatively biocompatible. Inadequately cured composites serve as reservoir that can induce pulpal inflammation Shrinkage of composite leading to marginal leakage and secondary caries Bisphenol A precursor of bis-GMA – Xenoestrogen – Reproductive anomalies
Survival probability of composites Judged on longterm clinical trials Survival rates of composites after 7yrs was 67.4% Amalgam 94.5% Glass ionomer was 64% after 5 yrs. Glass ionomer/composites avoided in class II restorations
Recent Advancements Nano-Composites The decreasing of filler particles size from micronlevel to nanometer level leads to the change of- Distribution of filler particles in a matrix. Charge carriers transport between particles. Conductivity of filler particles themselves.
Advantages – High adhesion of nanoparticles to polymer matrix result in the enhanced strength of nanocomposites Small size of nanoparticles ensures small size of pores in the case of exfoliation of a matrix from filler particles which resulted in increased strength Introduction of small amount of nanoparticles to polymer significantly enhance the adhesion of polymer to different substrates. Optically more transparent in comparison to conventional composites
Summary Amalgam continues to be the best posterior restorative material :-- Ease of use. Low cost. Wear resistance. Freedom from shrinkage during setting. High survival probabilities
References Anusavice K.J Phillips’science of dental materials ,11th Edition Saunders publication. Craig.R.G, Dental Materials, 8th edition, Elsevier publications. O’Brien.W.J, Dental materials and their selection, 3rd edition, Quintessence publications. Smith.B.G Clinical Handling Of Dental Materials , 2 nd edition,Heinemann publications.