Polymers used in Dentistry Question and Answers

Polymers used in Dentistry

Polymers used in Dentistry Question and Answers Dental Polymers Important Notes 1. Types of polymerization Condensation polymerization  Involves combining two dissimilar molecules into a third entirely different product  Ex: phenol and formaldehyde to form Bakelite  Addition polymerization  When similar molecules are combined the reaction is called an addition reaction  In it, the monomer is repeated many times to form a polymer  No by-products are formed  Example: polymethylmethacrylate 2. Stages of polymerization 

Initiation  Propagation  Termination  Chain transfer 3. Copolymerization 

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Resin formed by two or more chemically different monomers is called copolymer The process of formation is called copolymerization

Dental Polymers Long Essays

Question 1. Describe polymerization mechanisms. Add a note on stages in addition to polymerization. Answer:

Polymers used in Dentistry Polymerization: It is the chemical reaction in which monomers of low molecular weight are converted into chains of polymers with a high molecular weight  Monomer + Monomer + Monomer+ → Polymer  These monomers are connected to each other by bonds  It is a repetitive intermolecular reaction Types: 

1. Condensation polymerization It is divided into two groups  Those in which polymerization occurs along with the repeated elimination of small molecules  Those in which functional groups like amide, and ester are repeated 2. Addition polymerization 

In this type of polymerization, monomers are repeated and every time one molecule is added and the chain continues  There is no change in chemical composition and no by-products are formed Inhibition of Polymerization: 

Polymerization is inhibited by 1. Impurities Any impurity in the monomer that can react with free radicals inhibits or retards the polymerization  It occurs during storage  Example: The addition of a small amount of hydro-quinone inhibits polymerization 2. Oxygen 

It reacts rapidly with free radicals and retards polymerization Stages of Addition Polymerization: There are four stages of addition polymerization

Polymers used in Dentistry 1. Induction      

It is the time during which the molecules of the initiator become activated It is the activation of free radicals which in turn initiate growing polymer chains Thus, this stage is controlled by activation and initiation Any impurities present increases the length of the induction period It is useful for dental resins These resins are activated by heat, chemicals, and light

Example: Amine acts as an activator and benzoyl peroxide as an initiator for dental resins 2. Propagation 

It is a stage of polymerization during which polymer chains continue to grow to high molecular weights  It is accompanied by the liberation of heat t Thus it is an exothermic reaction  The growth of the polymer chain stops if the reactive centre is destroyed by the termination reaction 3. Chain transfer 

During this stage, the growing end of a chain is transferred to another molecule and initiates further chain growth  Here the active state is transferred from active radical to inactive molecule 4. Termination 

It occurs through two processes

Polymers used in Dentistry Direct coupling of two free radical end chains  The two molecules combine and become deactivated by the formation of a covalent bond Read And Learn More: Dental Materials Question and Answers 

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Exchange of hydrogen atom  The hydrogen atom is transferred from one growing chain to another  A double bond is produced between them

Dental Polymers Short Question And Answers Question 1. Copolymerization Answer:

It is the process of polymerization where two or more chemically different monomers combine to form polymers called copolymers.  There are three different types of copolymers 1. Random type 2. Graft type 3. Block type Importance of Copolymerisation: 

It is used to improve the physical properties of resins