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    Restorative resins Restorative resins Presentation Transcript

    • 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.
    • Polymerisation mechanism
      2 types
      Chemically activated
      Light-activated
    • 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
    • Clinical considerations-
      • 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
      .
    • Compressive strength-
      250- 350 Mpa.
      Tensile strength-
      30- 50 Mpa.
      Lowest among composites
      Hardness –
      25- 30 KHN.
      Thermal Expansion Coefficient-
      highest among composite resins
    • 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.