General Classes of Dental Materials (Polymer) PDF

Polymer Shimaa Abdallah El-saady Assistant professor of Dental Biomaterials Faculty of Dentistry Aqaba Medical Sciences University Definition Polymer: it is a high molecular weight molecule that is composed of many repeating units. (poly=many, mer=units Definition Monomer: It is t...

Polymer Shimaa Abdallah El-saady Assistant professor of Dental Biomaterials Faculty of Dentistry Aqaba Medical Sciences University Definition Polymer: it is a high molecular weight molecule that is composed of many repeating units. (poly=many, mer=units Definition Monomer: It is the smallest repeating building unit of the polymer chain (mono=single).  Definition Polymerization reaction: It is the reaction by which the monomer from the polymeric chain.  Classification of polymers: 1.According to origin: a) Natural polymer: Synthesized by living cells, eg: proteins, starch and polysaccharides (agar & alginate).  Classification of polymers: 1.According to origin: b) synthetic polymer: Synthesized by chemical reaction inside the laboratory. e.g; Acrylic resin  Classification of polymers: 2. According to arrangement in space (spatial configuration): a) linear polymer: The polymer molecule forms a thread without any branches.  Classification of polymers: b) Branched polymer: In the polymer molecule, a shorter side chains are attached to the main backbone chain.  Classification of polymers: c) Cross-linked Polymer: The main polymer chain are bonded by covalent bond.  Classification of polymers: 3. According to thermal behavior: a) Thermoplastic Polymer. b) Thermoset Polymer. Classification of polymers: Classification of polymers:  Classification of polymers: 4. According to mechanical properties: a) Elastomers (Elastic Polymer) They have wide range of elastic deformation & low modulus of elasticity. e.g: rubber base impression materials..  Classification of polymers: 4. According to mechanical properties: b) Plastic Polymers: They have moderate range of elastic deformation & moderate modulus of elasticity. e.g: Acrylic resin..  Classification of polymers: 4. According to mechanical properties: c) Brittle Polymers: They have small range of elastic deformation & high modulus of elasticity..  Classification of polymers: 4. According to mechanical properties:  Classification of polymers: 5. According to chemical composition of monomers: b) Homo-Polymers: It is a polymer consists of single type of monomers..  Classification of polymers: 5. According to chemical composition of monomers: b) Co-Polymers: It is a polymer consists of two or three different types of monomers They could be:. Classification of polymers:  Classification of polymers: 5. According to chemical composition of monomers: b) Co-Polymers: 1) Alternating copolymers: Different monomers are arranged regularly in an alternative pattern..  Classification of polymers: 5. According to chemical composition of monomers: b) Co-Polymers: 2) Random copolymers: Different monomers are arranged randomly..  Classification of polymers: 5. According to chemical composition of monomers: b) Co-Polymers: 3) Block copolymers: Each monomer forms a cluster. The clusters are arranged alternatively..  Classification of polymers: 5. According to chemical composition of monomers: b) Co-Polymers: 4) Graft copolymers: One polymer forms a backbone. The other monomer is attached as side chains to the backbone.  Classification of polymers: 6. According to Polymerization Reaction: a) Addition Polymerization reaction. b) Addition Polymerization reaction: i. Free radical. ii. Ring opening..  Classification of polymers: 6. According to Polymerization Reaction: a) Condensation Polymerization reaction The monomers react together to form the polymer chains with elimination of a small molecule called by- product. e.g: water, gas,....etc.  Classification of polymers: 6. According to Polymerization Reaction: a) Addition Polymerization reaction The monomers react together to form the polymer chains without elimination of by-product. e.g: water, gas,....etc.  Classification of polymers: 6. According to Polymerization Reaction: a) Addition Polymerization reaction The addition Polymerization reaction gives more accurate polymers than the condensation type as there is no elimination of by-product.. Stages of Polymerization reaction: 1. Activation. 2. Initiation. 3. Propagation 4.Termination.  Stages of Polymerization reaction: 1.Activation: It is the process of production of free radicals. Free radicals are the active form of the initiators. Free radicals is highly reactive compound due to presence of unpaired electrons.  Stages of Polymerization reaction: 1.Activation: Initiator can be activated by: a. Heat. b. Light. c. Chemical compound.  Stages of Polymerization reaction: 2. Initiation: It is the reaction of free radicals with the first monomer. The free radical braks the double bond of the monomer (C=C) & react with one carbon atom.  Stages of Polymerization Reaction: 2. Initiation: The other carbon atom contains the unpaired electron making it very reactive. i.e The reactivity of the free radical is transferred to the monomer (activated monomer).  Stages of Polymerization reaction: 3. Propagation: It is the process of addition of the monomers to the growing chains. each activated monomer attacks C=C of unreacted monomers transferring the active part to it.  Stages of Polymerization Reaction: 4. Termination: The termination process stops the growth chaina either by: i. Direct Coupling ii. Hydrogen atom transfer.  Stages of Polymerization reaction: 4. Termination: i. Direct Coupling Two growing chains reacts together to give one long stable chain.  Stages of Polymerization reaction: 4. Termination: ii. Hydrogen atom transfer: The hydrogen atom transfers from the active chain to another active chain to give two stable chains.  Stages of Polymerization reaction: 4. Termination: ii. Hydrogen atom transfer:  Stages of Polymerization reaction: 4. Termination: ii. Hydrogen atom transfer:  Stages of Polymerization reaction: 4. Termination: ii. Hydrogen atom transfer:  Chain Transfer Chain transfer is a transfer reactivity from active chain to inactive chain  Termination The termination process occurs under normal conditions. This results in incompletion of the polymerization reaction & presence of residual monomers.  Ring Opening Polymerization Reaction The terminal group of the monomer is a ring.  Ring Opening Polymerization Reaction Advantages: 1.Less polymerization shrinkage. 2.Less heat evolution.  Inhibition & Retardation 1.Inhibition....stopping. 2.Retardation....lowering the rate.  Inhibition & Retardation 1.Hydroquinone are added to the monomers to inhibit the premature polymerization reaction of the monomers during storage or accidental exposure to heat or light.  Inhibition & Retardation 2. Eugenol inhibits the polymerization reaction of resin composite. So bases containing eugenol should not be used as a base under composite resin restorations.  Inhibition & Retardation 3. Oxygen inhibits the polymerization reaction of resin composite. So the surfaces of the restorations (in contact with oxygen during polymerization) should be polished to remove the unreacted surface layer or covered by a matrix band.  Factors associated with polymerization reaction: 1.Evolution of heat due to the breaking of the monomers. 2.Reduction in the volume (Polymerization shrinkage). 3.Presence of residual monomers (because not all the monomers participate in the reaction).  General properties of the polymers 1.Polymers are molecular solids. 2.Polymers are amorphous solids. Factors affecting the properties of the polymers  Factors affecting the properties of the polymers 1.Molecular weight (M.W) & degree of polymerization (DP): M.W of polymer molecule = Weight of mers X Number of mers. The higher the M.W, the higher the degree of polymerization.  Factors affecting the properties of the polymers 1.Molecular weight (M.W) & degree of polymerization (DP): Degree of conversion (Degree of polymerization): is the total number of monomer in the polymer chain. D.P = Mw of Polymer / Mw of mer  Factors affecting the properties of the polymers 1.Molecular weight (M.W) & degree of polymerization (DP): Effect on properties: The longer the polymer chain.....the more the entanglement between chains occurs....more secondary bonds.  Factors affecting the properties of the polymers 2. Copolymerization Copolymer is a polymer consists of two or more different types of monomers.  Factors affecting the properties of the polymers 2. Copolymerization Effects on properties: Copolymerization allows the chemists to synthetize a polymer with desired properties (Tailor-make effect).  Factors affecting the properties of the polymers 2. Copolymerization  Factors affecting the properties of the polymers 3. Cross-linking It is the bonding of the polymer chains with primary covalent bond. This leads to forming a network structure.  Factors affecting the properties of the polymers 3. Cross-linking Effect on properties: a) Small degree of cross linking: It limits the movement of the polymer chains past over each other.  Factors affecting the properties of the polymers 3. Cross-linking Effect on properties: b) Extensive cross linking: It leads to brittleness of the polymer.  Factors affecting the properties of the polymers 4. Plasticizer: It is the partially neutralization of the secondary van der waal forces between the polymer chains.  Factors affecting the properties of the polymers 4. Plasticizer: Types of plasticizers: a) Internal plasticizers. b) External plasticizers.  Factors affecting the properties of the polymers 4. Plasticizer: a) Internal plasticizers. Incorporated by copolymerization. It is a part of the polymer.  Factors affecting the properties of the polymers 4. Plasticizer: b) External plasticizers. It is a compound added to the polymer. It penetrates between the polymer chains partially neutralize the secondary forces between the chains.  Factors affecting the properties of the polymers 4. Plasticizer: Effect on properties: It partially neutralizes the secondary forces between polymers.  Factors affecting the properties of the polymers 4. Plasticizer: Effect on properties:  Factors affecting the properties of the polymers 5. Addition of inorganic fillers: Like composite resin Effect on properties: The fillers improve the properties.  Factors affecting the properties of the polymers 5. Addition of inorganic fillers:  Factors affecting the properties of the polymers 6. Rate of loading: Polymers are viscoelastic materials...sensitive t rate of loading: At slow rate of loading... behave in a ductile manner. At high rate of loading... behave in a brittle manner.  Factors affecting the properties of the polymers 7. Degree of crystallinity: Polymers are generally amorphous solids. In certain polymers, the chain can be aligned to form different degree of ordered crystalline structure.  Factors affecting the properties of the polymers 8. Spatial configuration:  Factors affecting the properties of the polymers 9. Temperature: Polymers softens when they heated near their glass transition temperature. Uses of polymers in dentistry:  Uses of polymers in dentistry: Denture base materials. Artificial teeth. Teeth restorative materials. Dental cements. Temporary crowns. Endodontic filling &sealers. Maxillo-facial prosthesis. Impression materials. Thank you