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Indian Dental Academy: will be one of the most relevant and exciting training center with best faculty and flexible training programs for dental professionals who wish to advance in their dental practice,Offers certified courses in Dental implants,Orthodontics,Endodontics,Cosmetic Dentistry, Prosthetic Dentistry, Periodontics and General Dentistry.

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Resins/ academy general dentistry Resins/ academy general dentistry Presentation Transcript

  • www.indiandentalacademy.comwww.indiandentalacademy.com
  • ChemistryChemistry ofof The Synthetic ResinsThe Synthetic Resins INDIAN DENTAL ACADEMY Leader in continuing dental education www.indiandentalacademy.com www.indiandentalacademy.comwww.indiandentalacademy.com
  •  INTRODUCTIONINTRODUCTION  HISTORYHISTORY  REQUISITES FOR DENTAL RESINSREQUISITES FOR DENTAL RESINS  BASIC NATURE OF POLYMERSBASIC NATURE OF POLYMERS  PHYSICAL PROPERTIEPHYSICAL PROPERTIEss  THERMAL PROPERTIESTHERMAL PROPERTIES  CHEMISTRY OF POLYMERIZATIONCHEMISTRY OF POLYMERIZATION  CONCLUSIONCONCLUSION    www.indiandentalacademy.comwww.indiandentalacademy.com View slide
  • Introduction: Polymers have been of importance for 60 years or more  and find use in almost every sphere of modern life.  It continues to be the material of choice for fabricating  many denture prosthesis because of its ease of processing  and generally favorable physical and mechanical properties www.indiandentalacademy.comwww.indiandentalacademy.com View slide
  • History: The loss of teeth by accident or disease has plagued mankind  throughout the ages. In ancient times the materials available were  simple in nature, few in number and with much disappointment often  with the final results.  Among the more valuable developments in very recent years has been  the synthetic resins that now are so important to prosthetic and  restorative dentistry.  Materials between 1840 and 1940: It was about 1855 that vulcanized hard rubber was discovered  and introduced as a denture base material with such names applied as  ebonite or vulcanite. During the following 75 years the use of vulcanized rubber was to remain. From  the time it was introduced until about 1930 and 1940 vulcanite was the best  denture base material that science and industry could produce. The principal  disadvantage was the poor overall esthetic quality. www.indiandentalacademy.comwww.indiandentalacademy.com
  • Celluloid, Bakelite, and other resins:Celluloid, Bakelite, and other resins: In 1868 John Wesley Hyatt is credited with preparing the first organic In 1868 John Wesley Hyatt is credited with preparing the first organic  plastic molding compound, which was cellulose nitrate, then popularly known plastic molding compound, which was cellulose nitrate, then popularly known  asas “celluloid“celluloid”.”.    Cellulose nitrate was produced in pink tissue colors that were more pleasing Cellulose nitrate was produced in pink tissue colors that were more pleasing  thanthan  vulcanitevulcanite.The presence of camphor (as a plasticizer), produced an .The presence of camphor (as a plasticizer), produced an  unpleasant taste and odor. unpleasant taste and odor.  During the years to about 1930, various modifications of cellulose were used. During the years to about 1930, various modifications of cellulose were used.  Not until 1909 was phenol formaldehyde resin was discovered by Not until 1909 was phenol formaldehyde resin was discovered by Dr. LeoDr. Leo   BakelandBakeland and known as  and known as Bakelite.Bakelite. Products were available in the form of sheets, cakes, and powder. Products were available in the form of sheets, cakes, and powder.  The physical qualities of the final denture depended to a large degree on the The physical qualities of the final denture depended to a large degree on the  processing conditionsprocessing conditions..   www.indiandentalacademy.comwww.indiandentalacademy.com
  • This lack of uniformity and control of qualities were the principal This lack of uniformity and control of qualities were the principal  disadvantage of this material. disadvantage of this material.  The period from 1930 to 1940 was one of the rapid expansion in the The period from 1930 to 1940 was one of the rapid expansion in the  resin industry.resin industry. The introduction of a more satisfactory plastic denture base material The introduction of a more satisfactory plastic denture base material  occurred in 1937 when occurred in 1937 when Dr. Walter WrightDr. Walter Wright described the results of  described the results of  his clinical evaluation of his clinical evaluation of methyl methacrylate resin.methyl methacrylate resin. Vulcanite, celluloid, bakelite were rapidly displaced from dental Vulcanite, celluloid, bakelite were rapidly displaced from dental  practice. practice.  An ADA specification number 12 has been developed for acrylic An ADA specification number 12 has been developed for acrylic  denture base material.denture base material. Dental resin since 1940Dental resin since 1940 During the past 65 years since acrylic resins were introduced, the During the past 65 years since acrylic resins were introduced, the  quality of resins has been more refined and improved.quality of resins has been more refined and improved. The methylmethacrylate polymers and copolymers continue to be The methylmethacrylate polymers and copolymers continue to be  the most popular resin. the most popular resin.  www.indiandentalacademy.comwww.indiandentalacademy.com
  • CLASSIFICATION;CLASSIFICATION; BASED ON THE THERMAL BEHAVIOURBASED ON THE THERMAL BEHAVIOUR 1 THERMOPLASTIC1 THERMOPLASTIC 2 THERMOSETTING2 THERMOSETTING poly(methyl methacrylate)poly(methyl methacrylate) polyethylenepolyethylene polystyrene.polystyrene. e.g.: cross linked poly(methyl methacrylate)e.g.: cross linked poly(methyl methacrylate) SiliconSilicon BASED ON THE SPATIAL STRUCTUREBASED ON THE SPATIAL STRUCTURE A) LINEARA) LINEAR Random copolymer of the linear type.Random copolymer of the linear type. Linear block copolymerLinear block copolymer B) BRANCHEDB) BRANCHED Branched homopolymerBranched homopolymer Graft branchedGraft branched C) CROSS LINKEDC) CROSS LINKED www.indiandentalacademy.comwww.indiandentalacademy.com
  •  ““REQUISITES FOR DENTAL RESINSREQUISITES FOR DENTAL RESINS”.”.  Biological compatibilityBiological compatibility  →→ the resin should be tasteless, odorless,  the resin should be tasteless, odorless,  non toxic, non irritating, and otherwise not harmful to the oral non toxic, non irritating, and otherwise not harmful to the oral  tissues. tissues.         →→  It should be It should be completely insoluble in salivacompletely insoluble in saliva or in any fluids  or in any fluids  taken into the mouth. taken into the mouth.   It should be impermeable to oral fluids to the extent that the resin It should be impermeable to oral fluids to the extent that the resin  does not become does not become unsanitary or disagreeableunsanitary or disagreeable in taste or odor.  in taste or odor.   Physical propertiesPhysical properties →→ Should possess adequate strength and  Should possess adequate strength and  resilience, as well as resistance to biting, chewing forces, impact resilience, as well as resistance to biting, chewing forces, impact  forces, and excessive wear. forces, and excessive wear.   The material should be The material should be dimensionally stabledimensionally stable under all  under all  conditions. conditions.   The resin should have aThe resin should have a low specific gravitylow specific gravity when used for  when used for  maxillary denturesmaxillary dentures. .  www.indiandentalacademy.comwww.indiandentalacademy.com
  •  ManipulationManipulation →→ The resin should not produce The resin should not produce toxic fumes or dusttoxic fumes or dust   during handling and manipulation. during handling and manipulation.   It should be easy to mix, insert, shape, and cure. It should be easy to mix, insert, shape, and cure.   The final product should be easy to polish, and in case of unavoidable The final product should be easy to polish, and in case of unavoidable  breakage it  should be possible to repair the resin easily and efficiently. breakage it  should be possible to repair the resin easily and efficiently.   Aesthetic propertiesAesthetic properties →→ The material  The material  should exhibit sufficient should exhibit sufficient  translucency or transparencytranslucency or transparency so that it can be made to match the  so that it can be made to match the  appearance of the oral tissues it replaces. appearance of the oral tissues it replaces.   The resin should be capable of being The resin should be capable of being tinted or pigmentedtinted or pigmented, but there , but there  should be no change in color or appearance of the material subsequent to should be no change in color or appearance of the material subsequent to  its fabrication. its fabrication.  www.indiandentalacademy.comwww.indiandentalacademy.com
  •  Economic considerationsEconomic considerations →→ The cost of the resin and its  The cost of the resin and its  processing method should be relatively low, without requiring any processing method should be relatively low, without requiring any  expensive equipment.expensive equipment.    Chemical stabilityChemical stability →→ The conditions in the mouth are highly  The conditions in the mouth are highly  demanding, and only  the most chemically stable and inert materials demanding, and only  the most chemically stable and inert materials  can withstand such conditions without deterioration. can withstand such conditions without deterioration.  www.indiandentalacademy.comwww.indiandentalacademy.com
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  •  BASIC NATURE OF POLYMERS:BASIC NATURE OF POLYMERS: Chemical compositionChemical composition →→ TheThe term polymer denotes a molecule that is made up of  term polymer denotes a molecule that is made up of  manymany(Poly) parts (mer).(Poly) parts (mer). The mer ending represents the simplest repeating chemical The mer ending represents the simplest repeating chemical  structural unit from which the polymer is composed. structural unit from which the polymer is composed.  Thus Thus poly (methyl methacrylatepoly (methyl methacrylate..) ) is a polymer having chemical structural  units is a polymer having chemical structural  units  derived from methyl methacrylate. derived from methyl methacrylate.  Copolymer structures – polymers that have only one type of repeating unit (mer) are Copolymer structures – polymers that have only one type of repeating unit (mer) are  homopolymers. homopolymers.  Those with two or more types of mer units are known as copolymers. Those with two or more types of mer units are known as copolymers.  There are 3 different types of copolymers. There are 3 different types of copolymers.  - Random co-polymer – no sequential order exists between the two (or more) mer units - Random co-polymer – no sequential order exists between the two (or more) mer units  along the polymer chain. along the polymer chain.  ……. ABBABABAAABAAAABABBBB….. ABBABABAAABAAAABABBBB…. -- www.indiandentalacademy.comwww.indiandentalacademy.com
  • Block  copolymerBlock  copolymer  –  identical  monomer  units  occur  in  relatively  long   –  identical  monomer  units  occur  in  relatively  long  sequences along the main polymer. sequences along the main polymer.  … … AAAAABBBBBBAAAABBBBBBBAAABBB….AAAAABBBBBBAAAABBBBBBBAAABBB…. -- Graft or branched copolymerGraft or branched copolymer – Sequences of one type of mer unit are  – Sequences of one type of mer unit are  attached as a graft onto a backbone of a second type of mer unit. attached as a graft onto a backbone of a second type of mer unit.  BB BB BB BB BB BB AAAAAAAAAA……AAAAAAAAAA……    www.indiandentalacademy.comwww.indiandentalacademy.com
  •  Molecular weightMolecular weight :: The molecular weight of the polymer molecule whichThe molecular weight of the polymer molecule which equals the molecular weight of the various mers multiplied by the number of mers Itequals the molecular weight of the various mers multiplied by the number of mers It may range from thousands to millions of molecular weight units, depending on themay range from thousands to millions of molecular weight units, depending on the preparation conditions.preparation conditions.  The higher the molecular weight of the polymer made from a single monomer, theThe higher the molecular weight of the polymer made from a single monomer, the higher the degree of polymerization.higher the degree of polymerization.  TheThe degree of polymerizationdegree of polymerization is defined as the total number of mers in a polymeris defined as the total number of mers in a polymer molecule.molecule.  Two poly (methyl methacrylate) samples can have the same chemical compositionTwo poly (methyl methacrylate) samples can have the same chemical composition but greatly differ in physical properties because one of the samples has a highbut greatly differ in physical properties because one of the samples has a high percentage of low-mol weight molecules, whereas the other has a high % of high-percentage of low-mol weight molecules, whereas the other has a high % of high- molecular weight molecules.molecular weight molecules. The higher the mol weight,The higher the mol weight, the higher the softeningthe higher the softening and melting points and the stiffer the plastic.and melting points and the stiffer the plastic. www.indiandentalacademy.comwww.indiandentalacademy.com
  •  The longer the polymer chainThe longer the polymer chain – the more difficult it is to distort the– the more difficult it is to distort the polymer material.polymer material.  The strength, rigidity, melting temperature increases with theThe strength, rigidity, melting temperature increases with the increasing chain length.increasing chain length.  Synthetic resins polymerize randomlySynthetic resins polymerize randomly from local sites that havefrom local sites that have been activated. Thus, depending on the ability of the chains to growbeen activated. Thus, depending on the ability of the chains to grow from their local activation sites, the chain varies in length.from their local activation sites, the chain varies in length.  The average molecular weight for various commercial denture baseThe average molecular weight for various commercial denture base polymers varies frompolymers varies from 8,000 to 39,000.8,000 to 39,000.  Two types of averages are commonly used The number averageTwo types of averages are commonly used The number average based on the average number of mer repeating units in a chain, andbased on the average number of mer repeating units in a chain, and the weight average based on the molecular weight of the averagethe weight average based on the molecular weight of the average chain. The residual monomer also has a pronounced effect on thechain. The residual monomer also has a pronounced effect on the molecular weight – for ex- 0.9% of residual monomer in a polymer,molecular weight – for ex- 0.9% of residual monomer in a polymer, with a theoretical number average molecular weight of 22, 400, ifwith a theoretical number average molecular weight of 22, 400, if completely cured will reduce the molecular weight of the polymer tocompletely cured will reduce the molecular weight of the polymer to 7,300.7,300. www.indiandentalacademy.comwww.indiandentalacademy.com
  • Spatial structure:Spatial structure: There are 3 basic types of structures – linear, branched, and cross-linked.There are 3 basic types of structures – linear, branched, and cross-linked. www.indiandentalacademy.comwww.indiandentalacademy.com
  • The linearThe linear homopolymer has mer units of the same type.homopolymer has mer units of the same type. And theAnd the random polymerrandom polymer of the linear type has the two mer units randomlyof the linear type has the two mer units randomly distributed along the chain.distributed along the chain. TheThe linear block copolymerlinear block copolymer has segments or blocks along the chain where thehas segments or blocks along the chain where the mer units are the same.mer units are the same. www.indiandentalacademy.comwww.indiandentalacademy.com
  •  TheThe branched homopolymerbranched homopolymer consists of the same mer units,consists of the same mer units,  whereas thewhereas the graft branched copolymergraft branched copolymer consists of one type of mer unit onconsists of one type of mer unit on the main chain and another mer for the branches.the main chain and another mer for the branches. www.indiandentalacademy.comwww.indiandentalacademy.com
  •  PHYSICAL PROPERTIES OF POLYMERSPHYSICAL PROPERTIES OF POLYMERS ::  Deformation and RecoveryDeformation and Recovery:: Applied forces produce stresses within theApplied forces produce stresses within the polymers that can causepolymers that can cause elastic strain, plastic strain, or a combination ofelastic strain, plastic strain, or a combination of elastic plus plastic strain.elastic plus plastic strain.  - Plastic deformation is- Plastic deformation is irreversibleirreversible and results in a new permanent shape.and results in a new permanent shape.  - Elastic deformation is- Elastic deformation is reversiblereversible and will be completely recovered whenand will be completely recovered when the stress is eliminated.the stress is eliminated.  Viscoelastic deformationViscoelastic deformation results in a combination of elastic and plasticresults in a combination of elastic and plastic strain, however once the stress is eliminated, the process of recoverystrain, however once the stress is eliminated, the process of recovery occurs over time.occurs over time. www.indiandentalacademy.comwww.indiandentalacademy.com
  •  Rheometric propertiesRheometric properties :: The rheometry, or flow behavior of solid polymersThe rheometry, or flow behavior of solid polymers involves a combination of elastic and plastic deformation and elastic recoveryinvolves a combination of elastic and plastic deformation and elastic recovery when stresses are eliminated.when stresses are eliminated. This combination of elastic and plastic changes is termed viscoelasticity. The chain length, number of cross links, temperature, and rate of force application determine with type of behavior dominates. - Plastic flow – Irreversible strain behavior that occurs when polymer chains slide over one another and become relocated within the material resulting in permanent deformation. www.indiandentalacademy.comwww.indiandentalacademy.com
  • -- Elastic recoveryElastic recovery – reversible strain behavior that occurs– reversible strain behavior that occurs in the amorphous regions of polymers when thein the amorphous regions of polymers when the randomly coiled chains straighten and then recoilrandomly coiled chains straighten and then recoil without sliding past one another when an applied force iswithout sliding past one another when an applied force is removed.removed.  - The actual dental polymers are deformed by a- The actual dental polymers are deformed by a combination of elastic plus plastic strain processes.combination of elastic plus plastic strain processes. Plastics exhibit a high level of plastic deformation, butPlastics exhibit a high level of plastic deformation, but they also have at least some small degree of elasticthey also have at least some small degree of elastic recovery. This phenomenon is called Viscoelasticrecovery. This phenomenon is called Viscoelastic recovery.recovery. www.indiandentalacademy.comwww.indiandentalacademy.com
  •  Solvation propertiesSolvation properties :: Polymers are usually slow to dissolve, are seldomPolymers are usually slow to dissolve, are seldom clearly either soluble or insoluble in any given liquid, and their solvationclearly either soluble or insoluble in any given liquid, and their solvation characteristics are very sensitive to molecular weight, cross-linking,characteristics are very sensitive to molecular weight, cross-linking, crystallinity, chain branching.crystallinity, chain branching.  -- The longer the chains the more slowly a polymer dissolves.The longer the chains the more slowly a polymer dissolves.  - Polymers tend to absorb a solvent, swell, and soften, rather than- Polymers tend to absorb a solvent, swell, and soften, rather than dissolve.dissolve.  -- Cross-linking preventsCross-linking prevents complete chain separation and retardscomplete chain separation and retards dissolution.dissolution.  -- Highly cross-linked polymers cannot be dissolvedHighly cross-linked polymers cannot be dissolved..  - Elastomers swell more than plastic.- Elastomers swell more than plastic.  - A small amount of swelling of dental polymeric devices can have- A small amount of swelling of dental polymeric devices can have undesirable results on the fit of prosthesis.undesirable results on the fit of prosthesis. www.indiandentalacademy.comwww.indiandentalacademy.com
  •  -- Absorbed molecules spread polymer chains apart, facilitate slipAbsorbed molecules spread polymer chains apart, facilitate slip between chains. This effect is calledbetween chains. This effect is called PLASTICIZATION.PLASTICIZATION. Cross linkageCross linkage provides sufficient number of bridges between linear macromolecules toprovides sufficient number of bridges between linear macromolecules to form a 3-dimensional network, that decreases water sorption, solubility andform a 3-dimensional network, that decreases water sorption, solubility and increases strength and rigidity of the resin.increases strength and rigidity of the resin.  - Plasticizers are often added to resins to reduce their- Plasticizers are often added to resins to reduce their softeningsoftening oror fusion temperatures.fusion temperatures. A plasticizer acts to partially neutralize secondaryA plasticizer acts to partially neutralize secondary bonds or intermolecular forces that normally prevent the resin moleculesbonds or intermolecular forces that normally prevent the resin molecules from slipping past one another when the material is stressed. In some casesfrom slipping past one another when the material is stressed. In some cases the action is analogous to that of a solvent, with the plasticizing agentthe action is analogous to that of a solvent, with the plasticizing agent  increases theincreases the intermolecular spacingintermolecular spacing. This type of plasticizer is referred to. This type of plasticizer is referred to as anas an external plasticizer.external plasticizer.  Plasticizing can also be accomplished by copolymerization with a suitablePlasticizing can also be accomplished by copolymerization with a suitable comonomer. In this case the plasticizing agent becomes part of the polymercomonomer. In this case the plasticizing agent becomes part of the polymer and thus acts as anand thus acts as an Internal plasticizer.Internal plasticizer.  For ex. When butyl methacrylate is added to methyl methacrylateFor ex. When butyl methacrylate is added to methyl methacrylate before polymerization, the action of the butyl methacrylate is to increasebefore polymerization, the action of the butyl methacrylate is to increase intermolecular spacing via pendant groups.intermolecular spacing via pendant groups.www.indiandentalacademy.comwww.indiandentalacademy.com
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  •  Impact strength:Impact strength:  Impact strength is a measure of the energyImpact strength is a measure of the energy absorbed by a material when a sudden blow breaks it.absorbed by a material when a sudden blow breaks it.  The impact strength of polyvinyl acrylics is aboutThe impact strength of polyvinyl acrylics is about twice that of poly (methyl methacrylate).twice that of poly (methyl methacrylate).  Although the addition ofAlthough the addition of plasticizer may increase theplasticizer may increase the impact strength, the increase is accompanied by aimpact strength, the increase is accompanied by a decrease in hardness, proportionate limit, elasticdecrease in hardness, proportionate limit, elastic modulus, and compressive strengthmodulus, and compressive strength..  When surface defects are present the impactWhen surface defects are present the impact strength is significantly reduced.strength is significantly reduced. www.indiandentalacademy.comwww.indiandentalacademy.com
  •  Hardness:Hardness:  TheThe low knoop hardness numberlow knoop hardness number of the denture baseof the denture base plastic indicates these materials may be scratched and abradedplastic indicates these materials may be scratched and abraded easilyeasily..  Cross-linked poly (methyl methacrylate) is only slightly harderCross-linked poly (methyl methacrylate) is only slightly harder than regular poly (methyl methacrylate). The incorporation of fillersthan regular poly (methyl methacrylate). The incorporation of fillers in plastics may alter the resistance to abrasion, but the hardness ofin plastics may alter the resistance to abrasion, but the hardness of the plastic matrix remains unchanged. Polishing, shell blasting,the plastic matrix remains unchanged. Polishing, shell blasting, cleaning denture bases by brushes should be carried out with this incleaning denture bases by brushes should be carried out with this in mind.mind. www.indiandentalacademy.comwww.indiandentalacademy.com
  •  THERMAL PROPERTIES:THERMAL PROPERTIES:  The physical properties of a polymer are influenced byThe physical properties of a polymer are influenced by changes in temperature and environment and by the composition,changes in temperature and environment and by the composition, structure, and molecular weight of the polymer.structure, and molecular weight of the polymer.  Thermoplastic polymersThermoplastic polymers –– Are made of linear and / orAre made of linear and / or branched chains. They soften when heated above the glassbranched chains. They soften when heated above the glass transition temperature (Tg), at which molecular motion begins totransition temperature (Tg), at which molecular motion begins to force the chains apart. The resin can then be shaped and moldedforce the chains apart. The resin can then be shaped and molded and upon cooling will harden in this form. However on reheatingand upon cooling will harden in this form. However on reheating again they soften and can be reshaped if required before hardening.again they soften and can be reshaped if required before hardening. This cycle can be carried out repeatedly. Thermoplastic resins areThis cycle can be carried out repeatedly. Thermoplastic resins are fusible and they are usually soluble in organic solventsfusible and they are usually soluble in organic solvents www.indiandentalacademy.comwww.indiandentalacademy.com
  •  Thermosetting polymersThermosetting polymers:: Undergo a chemical change andUndergo a chemical change and become permanently hard when heated above the temperature at whichbecome permanently hard when heated above the temperature at which they begin to polymerize, and do not soften again an reheating to the samethey begin to polymerize, and do not soften again an reheating to the same temperature. They are usually cross linked at this state and, thus, aretemperature. They are usually cross linked at this state and, thus, are insoluble and infusible, decomposing instead.insoluble and infusible, decomposing instead.  Thermosetting plastics generally haveThermosetting plastics generally have superior abrasion resistancesuperior abrasion resistance andand dimensional stability compareddimensional stability compared with thermoplastic resins, which havewith thermoplastic resins, which have better flexural and impact properties.better flexural and impact properties. www.indiandentalacademy.comwww.indiandentalacademy.com
  •  Glass Transition temperature: (Glass Transition temperature: (Tg) :Tg) :  Along each single polymer chain, valence electrons continuously moveAlong each single polymer chain, valence electrons continuously move back and forth. Because of these electron movements, varying electronback and forth. Because of these electron movements, varying electron densities exist along the chain at different times and locations. Because ofdensities exist along the chain at different times and locations. Because of these interactions, interatomic induction forces (Van der Walls and Londonthese interactions, interatomic induction forces (Van der Walls and London forces) are developed between the chains.forces) are developed between the chains.  These forces, as well as hydrogen bonding, form polar bonds betweenThese forces, as well as hydrogen bonding, form polar bonds between the polymer chains, bonds that are much weaker than the primary bondsthe polymer chains, bonds that are much weaker than the primary bonds along the polymer chain. When a polymer is heated to its Tg or to a higheralong the polymer chain. When a polymer is heated to its Tg or to a higher temperature, the weak polar bonds are broken and the polymer moleculartemperature, the weak polar bonds are broken and the polymer molecular chains can move freely relative to each other.chains can move freely relative to each other.  The increased mobility has a strong impact on many physicalThe increased mobility has a strong impact on many physical properties such as strength, modulus of elasticity thermal expansion.properties such as strength, modulus of elasticity thermal expansion.  Strength and elastic modulus decrease as the temperatureStrength and elastic modulus decrease as the temperature approaches Tg, whereas thermal expansion increases.approaches Tg, whereas thermal expansion increases. www.indiandentalacademy.comwww.indiandentalacademy.com
  •  Polymer chains with the higher molecular weight will also have aPolymer chains with the higher molecular weight will also have a higher Tg. If the straight-polymer chain length is increased, thehigher Tg. If the straight-polymer chain length is increased, the number of polar bond sites increases along that chain.number of polar bond sites increases along that chain.  The longer chain length increases the chance for chainThe longer chain length increases the chance for chain entanglements.entanglements.  From a mechanical point of view, chain slippage alsoFrom a mechanical point of view, chain slippage also decreases as the chain length increases.decreases as the chain length increases.  As the temperature increases the rotation of polymer segmentsAs the temperature increases the rotation of polymer segments increases. These rotations, coupled with thermal expansionincreases. These rotations, coupled with thermal expansion increase chain separation, break polar bonds, facilitate chainincrease chain separation, break polar bonds, facilitate chain disentanglement. These factors in turn facilitate chain slippage anddisentanglement. These factors in turn facilitate chain slippage and explain the thermoplastic behavior of the resin when it reaches Tg.explain the thermoplastic behavior of the resin when it reaches Tg.  If cross-linkages exist, slippage cannot occur and the materialIf cross-linkages exist, slippage cannot occur and the material becomes more difficult to soften.becomes more difficult to soften.www.indiandentalacademy.comwww.indiandentalacademy.com
  •  Thermal conductivityThermal conductivity:: Resins are poor thermal andResins are poor thermal and electrical conductors, compared with gold, cobalt alloys or evenelectrical conductors, compared with gold, cobalt alloys or even human dentine. Low thermal conductivity allows plastic denturehuman dentine. Low thermal conductivity allows plastic denture bases to serve as an insulator between the oral tissues and hot orbases to serve as an insulator between the oral tissues and hot or cold materials placed in the mouth.cold materials placed in the mouth. www.indiandentalacademy.comwww.indiandentalacademy.com
  • Polymerization shrinkage:Polymerization shrinkage: The density of methylmethacrylate monomer is only 0.945 g / cm3 atThe density of methylmethacrylate monomer is only 0.945 g / cm3 at 200C compared with 1.16 to 1.18 g / cm3 for poly200C compared with 1.16 to 1.18 g / cm3 for poly (methylmethacrylate).(methylmethacrylate). This decrease in density is mainly accounted for by an approximateThis decrease in density is mainly accounted for by an approximate 21%21% decrease in vol of monomer during polymerization.decrease in vol of monomer during polymerization. Because the ratio of polymer to monomer isBecause the ratio of polymer to monomer is 3:13:1, the free volumetric, the free volumetric shrinkage amounts to approximately 6%. The light activated dentureshrinkage amounts to approximately 6%. The light activated denture base material has low polymerization shrinkage of 3% because ofbase material has low polymerization shrinkage of 3% because of higher molecularhigher molecular weight oligomersweight oligomers used.used. However it should be noted that the linear shrinkage values, reported inHowever it should be noted that the linear shrinkage values, reported in the literature are generally much less than would be expected onthe literature are generally much less than would be expected on the basis of free volumetric shrinkage, because a portion ofthe basis of free volumetric shrinkage, because a portion of polymerization takes place after the plastic has attained a solidpolymerization takes place after the plastic has attained a solid condition, resulting in residual stresses in the plastic rather thancondition, resulting in residual stresses in the plastic rather than addition shrinkage, but thermal dimensional change would still resultaddition shrinkage, but thermal dimensional change would still result from cooling the plastic from molding temperature to roomfrom cooling the plastic from molding temperature to room temperature,temperature, www.indiandentalacademy.comwww.indiandentalacademy.com
  • Dimensional stabilityDimensional stability:: -- If the denture is properly processes, theIf the denture is properly processes, the original fit and the dimensional stability of the various denture baseoriginal fit and the dimensional stability of the various denture base plastics are good.plastics are good. However excess heat generated during finishing of the denture canHowever excess heat generated during finishing of the denture can easily distort a denture base by releasing residual stresses.easily distort a denture base by releasing residual stresses. It has been shown that chemically activated denture basesIt has been shown that chemically activated denture bases processed by dough molding with a dimensional accuracy of – 0.1%processed by dough molding with a dimensional accuracy of – 0.1% were more accurate than heat- activated denture based to 0.4%.were more accurate than heat- activated denture based to 0.4%. Water sorption and solubility: -Water sorption and solubility: - The sorption of water alters the dimensions of acrylic dentures, polyThe sorption of water alters the dimensions of acrylic dentures, poly (methyl methacrylate) have relatively high water sorption (0.69mg /(methyl methacrylate) have relatively high water sorption (0.69mg / m2m2)) polyvinyl acrylicspolyvinyl acrylics→→ 0.26 mg / cm2.0.26 mg / cm2. Adhesion propertiesAdhesion properties:: The adhesion to untreated porcelain or metalsThe adhesion to untreated porcelain or metals is generally poor. As a result, porcelain teeth or combined metal andis generally poor. As a result, porcelain teeth or combined metal and plastic bases should be designed so that the porcelain or metal isplastic bases should be designed so that the porcelain or metal is held by mechanical retention.held by mechanical retention. The silane coupling agent,The silane coupling agent, →→ γγ - methacryloxypropyltrime- methacryloxypropyltrime thoxysilane provides a bond between the porcelain and the plasticthoxysilane provides a bond between the porcelain and the plastic surface.surface. www.indiandentalacademy.comwww.indiandentalacademy.com
  • EstheticsEsthetics ::esthetic qualities induce properties such as colorability,esthetic qualities induce properties such as colorability, color stability, taste, odor, the ability of the plastics to be colored andcolor stability, taste, odor, the ability of the plastics to be colored and their compatibility with dyed synthetic fibers for characterization aretheir compatibility with dyed synthetic fibers for characterization are both good.both good. Tissue compatibilityTissue compatibility →→ It can be said that the completely polymerizedIt can be said that the completely polymerized poly (methyl methacrylate) or polyvinyl acrylics rarely cause allergicpoly (methyl methacrylate) or polyvinyl acrylics rarely cause allergic reactions but that methyl / methacrylate monomer or other tracereactions but that methyl / methacrylate monomer or other trace components in the monomer may produce an allergic reaction.components in the monomer may produce an allergic reaction. Residual monomer is considered the allergen, and strict adherenceResidual monomer is considered the allergen, and strict adherence to processing instructions recommended by the manufacturer canto processing instructions recommended by the manufacturer can keep the residual monomer to minimum.keep the residual monomer to minimum. When patients are known to have suffered from an allergic reaction,When patients are known to have suffered from an allergic reaction, processing the denture for extended periods (such as 24 versus 8)processing the denture for extended periods (such as 24 versus 8) may be helpful.may be helpful. Residual monomer levels can also be reduced dramatically byResidual monomer levels can also be reduced dramatically by processing heat polymerized poly (methyl methacrylate) in a waterprocessing heat polymerized poly (methyl methacrylate) in a water bath for 7 hrs at 700C followed by boiling for 1 hr .bath for 7 hrs at 700C followed by boiling for 1 hr . www.indiandentalacademy.comwww.indiandentalacademy.com
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  • Chemistry of polymerizationChemistry of polymerization :: Monomers may be joined via one of two types of reactionMonomers may be joined via one of two types of reaction Addition polymerizationAddition polymerization Step-growth or condensation polymerizationStep-growth or condensation polymerization Addition polymerizationAddition polymerization →→ AdditionAddition polymerization starts from an active center, adding one monomer atpolymerization starts from an active center, adding one monomer at a time to rapidly form a chain. The process is simple but not easy toa time to rapidly form a chain. The process is simple but not easy to control.control. StagesStages -activation-activation -- initiationinitiation www.indiandentalacademy.comwww.indiandentalacademy.com
  • A sourceA source of free radicals,of free radicals, RR••is required.is required. Free radicals can beFree radicals can be generated by activation of radicals producinggenerated by activation of radicals producing molecules using amolecules using a second chemical, heat, visible light, ultraviolet light, or energysecond chemical, heat, visible light, ultraviolet light, or energy transfer from another compound that acts as free radicals.transfer from another compound that acts as free radicals. Heat, chemical agents, visible lights are most often used inHeat, chemical agents, visible lights are most often used in dentistry.dentistry. R – R+ external energy = 2RR – R+ external energy = 2R••.. One of the requisites of on addition polymerizable compound is theOne of the requisites of on addition polymerizable compound is the presence of an unsaturated group that is, a double bond as well aspresence of an unsaturated group that is, a double bond as well as a source of fee radicals.a source of fee radicals. Free radicalsFree radicals is an atom or groups of atoms possessing anis an atom or groups of atoms possessing an unpaired electron (unpaired electron (••). When the free radical and its unpaired). When the free radical and its unpaired electron approach a monomer with its high electron – an electron iselectron approach a monomer with its high electron – an electron is extracted and it pairs with the Rextracted and it pairs with the R•• electron to form a bond betweenelectron to form a bond between the radical and the monomer, leaving the other electron of thethe radical and the monomer, leaving the other electron of the double bond unpaired.double bond unpaired. www.indiandentalacademy.comwww.indiandentalacademy.com
  • The free radical forming chemical used to start the polymerization isThe free radical forming chemical used to start the polymerization is not a catalyst, because it enters into the chemical reaction andnot a catalyst, because it enters into the chemical reaction and becomes part of the final chemical compound. It is more accuratelybecomes part of the final chemical compound. It is more accurately called on initiator, because it is used to start the reaction.called on initiator, because it is used to start the reaction. The most commonly used initiator isThe most commonly used initiator is benzoly peroxidebenzoly peroxide, which is, which is activated rapidly between 500 and 1000C to release two freeactivated rapidly between 500 and 1000C to release two free radicals per benzoyl peroxide molecule.radicals per benzoyl peroxide molecule. InductionInduction is the period during which initiator molecules becomeis the period during which initiator molecules become energized and breaks down into free radicals, followed by theseenergized and breaks down into free radicals, followed by these radicals reacting with monomer molecules to initiate chain grown.radicals reacting with monomer molecules to initiate chain grown. This period is greatly influenced byThis period is greatly influenced by the purity of the monomerthe purity of the monomer. Any. Any impurities present can decrease the length of this period byimpurities present can decrease the length of this period by consuming the activated initiator.consuming the activated initiator. www.indiandentalacademy.comwww.indiandentalacademy.com
  • However,However, the higher the temperature, the more rapid the formation ofthe higher the temperature, the more rapid the formation of free radicals and consequently the shorter the induction period.free radicals and consequently the shorter the induction period. A second type of induction system is chemically activatedA second type of induction system is chemically activated atat ambient oral temperature. Such a system consists of at least twoambient oral temperature. Such a system consists of at least two reactions that, when mixed together undergo a chemical reactionreactions that, when mixed together undergo a chemical reaction that generates free radicals.that generates free radicals. Ex: - is the tertiary amine (the activator) and benzoyl peroxideEx: - is the tertiary amine (the activator) and benzoyl peroxide (initiator) which are mixed together to initiate the polymerization of(initiator) which are mixed together to initiate the polymerization of so-called “Self-cured: resins at room temperature .This in fact is aso-called “Self-cured: resins at room temperature .This in fact is a special case of heat activation, because of the presence of thespecial case of heat activation, because of the presence of the amine, reduces the thermal energy required to break the initiatoramine, reduces the thermal energy required to break the initiator into free radicals at ambient temperature. The amine form ainto free radicals at ambient temperature. The amine form a complex with benzoyl peroxide, which reduces the thermal energy,complex with benzoyl peroxide, which reduces the thermal energy, needed to split it into two free radicals.needed to split it into two free radicals. A third type of reaction system ie light activated. In this photons fromA third type of reaction system ie light activated. In this photons from a light source activate the initiator to generate free radicals that ina light source activate the initiator to generate free radicals that in turn, can initiate the polymerization process.turn, can initiate the polymerization process. In the visible light-cured dental restoratives,In the visible light-cured dental restoratives, camphorquinone andcamphorquinone and organic amine generate free radicals when irradiated by light in theorganic amine generate free radicals when irradiated by light in the blue to violet region.blue to violet region. Light with a wavelength of aboutLight with a wavelength of about 470 mm470 mm is needed to trigger thisis needed to trigger this reaction.reaction. However, factors such asHowever, factors such as light intensity, angle of illuminationlight intensity, angle of illumination,, distance of resin from the light sourcedistance of resin from the light source can significantly affect thecan significantly affect the number of free radicals that are formed, thereby making thisnumber of free radicals that are formed, thereby making this technique sensitive.technique sensitive. www.indiandentalacademy.comwww.indiandentalacademy.com
  •  PropagationPropagation:: The resulting free radical monomer complexThe resulting free radical monomer complex than acts as a new free radical center when it approaches anotherthan acts as a new free radical center when it approaches another monomer to form a dim er, with also becomes a free radical.monomer to form a dim er, with also becomes a free radical.  Because little energy is required once chain growth begins, theBecause little energy is required once chain growth begins, the process continues with evolution of heat and leads to large polymerprocess continues with evolution of heat and leads to large polymer molecules within seconds.molecules within seconds.  Theoretically, the chain reactions should continue until all ofTheoretically, the chain reactions should continue until all of the monomer has been converted to a polymer between the initialthe monomer has been converted to a polymer between the initial set and the final set.set and the final set.  However, theHowever, the polymerization reaction is never quite completedpolymerization reaction is never quite completed.. The growth of the polymer chain ceases when the reaction center isThe growth of the polymer chain ceases when the reaction center is destroyed by one of a number of possible termination reactions. Thedestroyed by one of a number of possible termination reactions. The reaction is exothermic and considerable heat is evolved.reaction is exothermic and considerable heat is evolved. www.indiandentalacademy.comwww.indiandentalacademy.com
  •  Chain transferChain transfer: -: - In this process the active free radical ofIn this process the active free radical of a growing chain is transferred to another molecule and a new freea growing chain is transferred to another molecule and a new free radical for further growth is created for ex:- a monomer moleculeradical for further growth is created for ex:- a monomer molecule may be activated by a growing macromolecule in such a mannermay be activated by a growing macromolecule in such a manner that termination occurs in the latter. Thus a new nucleus of growththat termination occurs in the latter. Thus a new nucleus of growth occurs.occurs.  Termination:Termination: -- Addition polymerization reaction are mostAddition polymerization reaction are most often terminated either by direct coupling of two free radical chain oroften terminated either by direct coupling of two free radical chain or by the exchange of a hydrogen atom from one growing chain toby the exchange of a hydrogen atom from one growing chain to anotheranother www.indiandentalacademy.comwww.indiandentalacademy.com
  •  Inhibition of addition polymerization:Inhibition of addition polymerization: -- AnyAny impurity in the monomer that can react with the activated initiator or with animpurity in the monomer that can react with the activated initiator or with an activated growing chain to prevent further growth.activated growing chain to prevent further growth.  For ex: addition of a initiator such as hydroquinone inhibits spontaneousFor ex: addition of a initiator such as hydroquinone inhibits spontaneous polymerization if no initiator is present and retards the polymerizations in thepolymerization if no initiator is present and retards the polymerizations in the presence of an initiator. Thus commercial dental resins contain a smallpresence of an initiator. Thus commercial dental resins contain a small amount of an inhibitor such as methyl ether of hydroquinone to aid in theamount of an inhibitor such as methyl ether of hydroquinone to aid in the prevention of polymerization during storage and in case of self cure resinsprevention of polymerization during storage and in case of self cure resins to provide adequate time for mixing and placement.to provide adequate time for mixing and placement.  Oxygen reacts rapidly with the free radicals and its presence retardsOxygen reacts rapidly with the free radicals and its presence retards the polymerization reaction.the polymerization reaction. www.indiandentalacademy.comwww.indiandentalacademy.com
  •  Step growth polymerization:Step growth polymerization:  The primary compounds reacts, often with the formation of a by-productThe primary compounds reacts, often with the formation of a by-product such as water, alcohols, halogen acids, ammonia. The formation of these bysuch as water, alcohols, halogen acids, ammonia. The formation of these by products is the reason step-growth polymerization is often called asproducts is the reason step-growth polymerization is often called as condensation polymerization.condensation polymerization.  A linear chain of repeating mer units is obtained by the stepwise interA linear chain of repeating mer units is obtained by the stepwise inter molecular condensation or addition of the reactive groups in whichmolecular condensation or addition of the reactive groups in which bifunctional or trifunctional monomers are all simultaneously activated, asbifunctional or trifunctional monomers are all simultaneously activated, as opposed to the activation of one monomer at a time in additionopposed to the activation of one monomer at a time in addition polymerization.polymerization.  Step – growth polymerization resins are those in which polymerization isStep – growth polymerization resins are those in which polymerization is accompanied by repeated elimination of small molecules.accompanied by repeated elimination of small molecules.  The formation of polymers is slow because the reaction proceeds in aThe formation of polymers is slow because the reaction proceeds in a stepwise to fashion from monomer to dimmer to trimer until large polymerstepwise to fashion from monomer to dimmer to trimer until large polymer molecules containing many monomer moleculesmolecules containing many monomer molecules www.indiandentalacademy.comwww.indiandentalacademy.com
  • Copolymerization :Copolymerization : Two or more chemically different monomer each with some desirableTwo or more chemically different monomer each with some desirable property can be combined to yield specific physical properties of a polymer.property can be combined to yield specific physical properties of a polymer. The polymer formed is a copolymer, the process of formation is known asThe polymer formed is a copolymer, the process of formation is known as co polymerization.co polymerization. Acrylic resins :Acrylic resins : The acrylic resins are derivatives of ethylene and contain vinyl (-C=C-)The acrylic resins are derivatives of ethylene and contain vinyl (-C=C-) group. There are at least two acrylic resins series.group. There are at least two acrylic resins series. Acrylic acidAcrylic acid Methacrylic acidMethacrylic acid Methyl methacrylateMethyl methacrylate – the monomer is mixed with the polymer which is supplied– the monomer is mixed with the polymer which is supplied in the powdered form. The monomer partially dissolves the polymer to formin the powdered form. The monomer partially dissolves the polymer to form a plastic dough. This dough is packed into the mold, and the monomer isa plastic dough. This dough is packed into the mold, and the monomer is polymerized. Methyl methacrylate is a transparent liquid at roompolymerized. Methyl methacrylate is a transparent liquid at room temperature.temperature. www.indiandentalacademy.comwww.indiandentalacademy.com
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  •  Molecular weight - 100Molecular weight - 100  Melting point – 480CMelting point – 480C  Boiling point – 100.80C.Boiling point – 100.80C.  Density – 0.945 g/ml at 200CDensity – 0.945 g/ml at 200C  Heat of polymerization – 12.9 K cal / molHeat of polymerization – 12.9 K cal / mol  A volume shrinkage of 21% occurs duringA volume shrinkage of 21% occurs during the polymerization of the purethe polymerization of the pure methylmethacrylate monomer.methylmethacrylate monomer. www.indiandentalacademy.comwww.indiandentalacademy.com
  •  Poly methyl methacrylate:Poly methyl methacrylate:  Transparent resin of remarkable clarity.Transparent resin of remarkable clarity.  Density – 1.19 g / cm3.Density – 1.19 g / cm3.  Tensile strength – 60 MpaTensile strength – 60 Mpa  knoop hardness number of 18 to 20.knoop hardness number of 18 to 20.  Modulus of elasticity – 2.4 Gpa.Modulus of elasticity – 2.4 Gpa.  Chemically stable to heatChemically stable to heat  Softens at 1250CSoftens at 1250C  Between 1250 and 2000C depolymerizationBetween 1250 and 2000C depolymerization takes placetakes place  At appear - 4500C, 90% of the polymerAt appear - 4500C, 90% of the polymer depolymerizes to from the monomer.depolymerizes to from the monomer. www.indiandentalacademy.comwww.indiandentalacademy.com
  •  HEAT – ACTIVATED DENTURE BASE RESINSHEAT – ACTIVATED DENTURE BASE RESINS::  The thermal energy required for polymerization of such materialThe thermal energy required for polymerization of such material may be provided using a water bath or microwave oven.may be provided using a water bath or microwave oven.  Composition :Composition :  POWDERPOWDERa) Poly (methyl methacrylate) b) Benzoyl peroxide –a) Poly (methyl methacrylate) b) Benzoyl peroxide – initiatorinitiator  LIQUIDLIQUID a) Methyl methacrylate b) Hydroquinone acts as inhibitor.a) Methyl methacrylate b) Hydroquinone acts as inhibitor. c) a cross linking agent such as glycol dimethacrylate can also bec) a cross linking agent such as glycol dimethacrylate can also be adder. They are incorporated at a concentration of 1% to 2% byadder. They are incorporated at a concentration of 1% to 2% by volumevolume www.indiandentalacademy.comwww.indiandentalacademy.com
  •  Polymer To Monomer Ratio :Polymer To Monomer Ratio :  The polymerization of denture base resin results in volumetric and linearThe polymerization of denture base resin results in volumetric and linear shrinkage.shrinkage.  If we imagine two methyl methacrylate molecules, each molecule possessesIf we imagine two methyl methacrylate molecules, each molecule possesses an electrical field that repels nearby molecules, consequently the distancean electrical field that repels nearby molecules, consequently the distance between molecules is significantly greater than the length of a carbon tobetween molecules is significantly greater than the length of a carbon to carbon bond.carbon bond.  When the methyl methacrylate molecules are chemical bonded, a newWhen the methyl methacrylate molecules are chemical bonded, a new carbon – to – carbon linkage is formed. This produces a net decrease in thecarbon – to – carbon linkage is formed. This produces a net decrease in the space occupies.space occupies.  Research indicates that there isResearch indicates that there is 21% decrease in the volume of material21% decrease in the volume of material..  To minimize dimensional changes manufactures prepolymerize significantTo minimize dimensional changes manufactures prepolymerize significant fraction of the denture base material that may be thought as “preshrinking”.fraction of the denture base material that may be thought as “preshrinking”.  The accepted polymer to monomer ratio is 3:1 by volume.The accepted polymer to monomer ratio is 3:1 by volume.  Using 3:1 ratio the volumetric shrinkage may be limited to approximately 6%Using 3:1 ratio the volumetric shrinkage may be limited to approximately 6% (0.5% linear shrinkage.)(0.5% linear shrinkage.) www.indiandentalacademy.comwww.indiandentalacademy.com
  •  Chemically activated denture baseChemically activated denture base ::  In most cases chemical activation is accomplished through theIn most cases chemical activation is accomplished through the addition of a tertiary amine such as dimethyl – para toludine.addition of a tertiary amine such as dimethyl – para toludine.  Upon mixing the tertiary amine cause decomposition ofUpon mixing the tertiary amine cause decomposition of benzoyl peroxide – consequently free radicals are produced andbenzoyl peroxide – consequently free radicals are produced and polymerization is initiated.polymerization is initiated.  As a general rule, the degree of polymerization achieved usingAs a general rule, the degree of polymerization achieved using chemically activated resins is not as complete as that achievedchemically activated resins is not as complete as that achieved using heat-activated resins – this indicates there is a greater amountusing heat-activated resins – this indicates there is a greater amount of unreacted monomer –of unreacted monomer – this unreacted monomer causes two majorthis unreacted monomer causes two major difficulties- first – it as a plasticizer that results in decreaseddifficulties- first – it as a plasticizer that results in decreased transverse strength of the denture resin second – serves as atransverse strength of the denture resin second – serves as a potential tissue irritant.potential tissue irritant.  But from a physical stand point – chemically activated resinBut from a physical stand point – chemically activated resin display slightly less shrinkage hence imparts greater dimensionaldisplay slightly less shrinkage hence imparts greater dimensional accuracy.accuracy.  The color stability of chemically activated resins is poorThe color stability of chemically activated resins is poor – this is– this is related to the presencerelated to the presence of tertiary aminesof tertiary amines →→ such amines aresuch amines are susceptible to oxidation. Discoloration may be minimized via thesusceptible to oxidation. Discoloration may be minimized via the addition of stabilizing agents that prevent such oxidation.addition of stabilizing agents that prevent such oxidation. www.indiandentalacademy.comwww.indiandentalacademy.com
  •  Modified acrylic materialsModified acrylic materials ::  The impact strength of acrylic polymers can be improved significantlyThe impact strength of acrylic polymers can be improved significantly by incorporation of elastomers.by incorporation of elastomers.  The elastomer is able to absorb energy on impact and thus protect theThe elastomer is able to absorb energy on impact and thus protect the acrylic resin from fracture.acrylic resin from fracture.  An alternative to the direct addition of elastomers is the use of acrylicAn alternative to the direct addition of elastomers is the use of acrylic elastomer copolymer. These are typically, methylmethacrylate butadiene-elastomer copolymer. These are typically, methylmethacrylate butadiene- styrene copolymers.styrene copolymers.  Attempts to improve the fatigue resistance of acrylic denture polymersAttempts to improve the fatigue resistance of acrylic denture polymers has involved the use of carbon fiber inserts. They stiffen the denture,has involved the use of carbon fiber inserts. They stiffen the denture, reducing the degree of flexing and the possibility of fatigue fracture.reducing the degree of flexing and the possibility of fatigue fracture. However bonding between the fibers and the acrylic resin may be difficult toHowever bonding between the fibers and the acrylic resin may be difficult to achieve and it bonding is not achieved the fibers may weaken the denture.achieve and it bonding is not achieved the fibers may weaken the denture. Other reinforcing fibers, including Kevlar and ultra high modulusOther reinforcing fibers, including Kevlar and ultra high modulus polyethylene are currently under investigation.polyethylene are currently under investigation. www.indiandentalacademy.comwww.indiandentalacademy.com
  •  Alternative polymers :Alternative polymers :  The major alternatives to acrylic polymer or modified acrylic areThe major alternatives to acrylic polymer or modified acrylic are the polycarbonates and certain vinyl polymers. These may bethe polycarbonates and certain vinyl polymers. These may be considered when the patient has proven allergy to acrylic resin orconsidered when the patient has proven allergy to acrylic resin or when greater impact strength is required.when greater impact strength is required.  The other alternative to acrylic resin is vulcanite.The other alternative to acrylic resin is vulcanite.  The equipment required to process vulcanite denture is now aThe equipment required to process vulcanite denture is now a rarity however and the material can no longer be considered as ararity however and the material can no longer be considered as a serious alternative.serious alternative. www.indiandentalacademy.comwww.indiandentalacademy.com
  • Conclusion:Conclusion: In the development of any biomaterial oneIn the development of any biomaterial one must consider not only the strength,must consider not only the strength, esthetics or functional aspect of theesthetics or functional aspect of the material, but, its biocompatibility as well.material, but, its biocompatibility as well. The dentist should have a throughThe dentist should have a through knowledge of the material that he is usingknowledge of the material that he is using to make a successful prosthesis.to make a successful prosthesis. www.indiandentalacademy.comwww.indiandentalacademy.com
  • Thank you For more details please visit www.indiandentalacademy.com www.indiandentalacademy.comwww.indiandentalacademy.com