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Dental polymers


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Dental polymers

  2. 2. CONTENTS Resins used in Dentistry Classification of Resins Polymerization Classification of Polymers Stages of Polymerization Inhibition of Polymerization Physical properties of polymers
  3. 3. RESINS USED IN DENTISTRY Resins are hard, brittle glassy polymers. Principal polymers- Vulcanized rubber for denture bases. Later- Acrylic resins. Polymers in dentistry are: Vinyl acrylics- relining material. Epoxy resins- die material. Polyether- impression material. Polysulphide - “ “ Silicone “ “ Polycarbonates- temporary crown material Polyacrylic acid- denture base material Polystyrene, Polyethylene, Poly vinyl acetate
  5. 5. THERMOPLASTIC THERMOSET Resins are softened &  Final product cannot molded under heat & softened by reheating. pressure.  Set by chemical reaction. No chemical change.  Insoluble in organic solvents Soluble in organic solvents & infusible. & fusible.  Superior abration Eg: Acrylic resin resistence. Impression comp. Plastics in dentistry
  6. 6. CLASSIFICATION OF RESINS Based upon their origin. Natural resin - e.g : Gum Synthetic resin Thermoplastic Thermoset Synthetic elastomers Based on Thermal Behaviour. Thermoplastic Thermoset
  7. 7. Based on structural units. Vinyl Resins Polystyrene Acrylic Resins Epoxy “ Multifuctional acrylate resins
  8. 8. APPLICATIONS IN DENTISTRY Dentures (bases, liners, artificial teeth). Cavity filling materials ( “Composites” ). Sealants. Impression materials. Cements (resin based). Orthodontics (elastics). Equipments (mixing bowl)
  9. 9. POLYMERIZATION Chemical reaction in which monomers of a low molecular weight are converted into chains of polymers with a high molecular weight. Monomer molecules are bonded by covalent bonds. It is an ongoing reaction, never fully complete. Average degree of polymerization= no. of structural units/ total no. of units.
  11. 11. CLASSIFICATION OF POLYMERS Based on Nature of monomer.1) Homopolymer :Same chemical composition.2) Copolymer : Different chemical composition. Based on Spatial Arrangement : 1) Linear 2) Branched
  12. 12. Based on Type of Poymerization. Addition Polymerization Condensation “Based on Type of Copolymerization. Random copolymerization Graft type “ Block type “
  13. 13. Polymerization unit
  14. 14. ADDITION POLYMERIZATION Reaction between two molecules to form a larger molecule by addition reaction without the formation of byproducts. Formed polymers have better dimensional stability. 3 types : Free- radical polymerization. Ring- opening “ Ionic “
  15. 15. Free- radical polymerization Initiatorreleases free- radicals which bring about the Polymerization reaction. Eg : Benzoyl peroxide releases free- radicals to bring polymerization in acrylic resins.
  16. 16. Ring- opening poymerization Ring structure in the polymer chain is opened & crossing- linking occurs. Eg : Epoxy resin, Polyether impression material.Ionic polymerization : Catalyst bring about exchange of ions resulting in cross- linked polymer. Eg : Addition silicones
  17. 17. CONDENSATION POLYMERIZATION[ Step- growth ] Reaction b/w 2 molecules to form a larger molecule with elimination of a small molecule As the rtns proceed, longer chains including trimers, tetramers form through other estrification rtns until the rctn contain a mixture of polymer chains of large m.wt. Thus, formation of polymers by this process is slow due to step – growth.
  18. 18. 2 types a) Condensation rctn where it gives a byproduct Eg : Condensation silicone impression material.Gives ethyl alcohol as byproduct. Byproduct may evaporate & affect the dimensional stability. b) Condensation rctn which occurs by the additon of a reactive part & the elimination of a byproduct. Eg ; Polyurethane
  19. 19. COPOLYMERIZATION Polymer chain contains 2 or more chemically different types of monomer units. 3 types 1) Random copolymerization 2) Graft type “ 3) Block type “
  21. 21. Random copolymerization Different monomer units are randomly distributed. They could be either Linear or Branched.Block Copolymerization When specific number of monomer units are repeated together in a particular pattern.
  22. 22. Graft copolymerization Ifthe same occurs in a branched polymer it is called Graft copolymer.Requirements of Polymerization 1) Momomer (reactive gp) with functional gp C=C. 2)Side gp on polymer determines the physical properties of resulting polymer. Side group is usually pendent group.
  23. 23. STAGES OF POLYMERIZATION 1) Initiation 2) Propagation 3) Termination 4) Chain transfer
  24. 24. 1) Initiation First step involves formation of free- radical. An initiator is converted to a free- radical by the action of heat / chemical rctns. This free- radical initiates polymerization rctn Eg : Conversion of benzoyl peroxide into free- radical initiates polymerization in acrylic resins. Activation by heat or chemical rctns.
  25. 25. Second step is rctn of free-radical &monomer. Free- radical converts monomer into polymer The electrons from lower energy levels pair with electrons of higher energy levels resulting in atomic bonding. Results in repeated linking of monomer units to form polymer
  26. 26. Egs : In Heat cure acrylic resins, Initiator : Benzoyl peroxide Activator : Heat In chemical activated resins, Initiator : Benzoyl peroxide Activator : Tertiary amine In light activated resins, Initiator : Camphoroquinone Activator : Visible light
  27. 27. 2) Propagation Initiation followed by propagation & linking more monomer units to form polymer units. Increase in polymer chain requires energy. The process continues with considerable velocity, is accompanied with evolution of heat. If ideal conditions is there,propagation continue untill all monomer get changed to polymer. Usually this never happens.
  28. 28. 3) Termination Polymerization rctn can be controlled by termination. This can be either by direct coupling or by exchage of H2 atom from the growing chain to another.
  29. 29. 4) Chain transfer Termination can occur due to chain transfer. The activated radical is converted into an inactive molecule. A new nucleus growth is created.
  30. 30. INHIBITION OF POLYMERIZATION Inhibitedby impurities. These react with activated free- radical or any activated nucleus or with an activated growing chain to prevent further growth. Eg: Hydroquinone Presence of O2
  31. 31. PHYSICAL PROPERTIES OFPOLYMERS.1) Deformation & Recovery Applied forces within polymers produces’ a) Plastic deformation- Permanent change b) Elastic “ - Reversible “ c) Viscoelastic “ - Combination of both In viscoelastic, recovery occurs over time.
  32. 32. 2)Rheometric properties The rheometry, or flow behaviour, of solid polymers involves a combination of elastic & plastic deformation (viscous flow) & elastic recovery when stresses are eliminated.
  33. 33. 3)Solvation properties Polymers are usually slow to dissolve. Solvation charecteristics are sensitive to Mw,Mw/Mn (piolydispersty), cross-linking, crystallinity & chain branching. Longer chain- polymer dissolve slowly. Highly cross-linked – not dissolve. Polymers absorb a solvent, swell, &soften, rather than dissolve.
  34. 34. 4) Thermal properties Higher the temperature, softer & weaker the polymer .
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