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

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

Read And Learn More: Dental Materials Question and Answers

Polymer And Monomer In Dentistry

Dental Polymers Long Essays

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

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 by bonds
• It is a repetitive intermolecular reaction

Polymerization 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 the chain continues
• There is no change in chemical composition and no by-products are formed

Inhibition of Polymerization:

Polymerization is inhibited by

Polymer And Monomer In Dentistry

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

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 increase 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. Thus it is an exothermic reaction
• The growth of the polymer chain stops if the reactive center 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

Polymer And Monomer In Dentistry

4. Termination

It occurs through two processes

• Direct coupling of two free radical end chains
  • The two molecules combine and become deactivated by the formation of a covalent bond

• 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:

Copolymerization

• 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

Polymer And Monomer In Dentistry

1. Random type
2. Graft type
3. Block type

Importance of Copolymerisation:

It is used to improve the physical properties of resins