Chapter 17: Polymers for Prosthetic Dentistry

Chapter 17: Polymers for Prosthetic Dentistry

 

Complete Chapter Questions With Answers

 

Sample Questions Are Posted Below

 

MULTIPLE CHOICE

 

1. Which of the following is true regarding addition polymerization?

a.	It occurs in three stages: initiation, margination, and condensation.
b.	Monomers have a core of two silicon atoms joined by a double bond.
c.	One carbon atom has two hydrogen atoms attached, and the other carbon atom has attached to it one hydrogen atom and one reactive group called a free radical.
d.	The reaction produces by-products such as water, hydrogen gas, or alcohol that may compromise the physical properties or handling characteristics.

 

 

ANS:  C

One carbon atom has two hydrogen atoms attached, and the other carbon atom has attached to it one hydrogen atom and one reactive group called a free radical. Addition polymerization occurs in three stages: initiation, propagation, and termination. Monomers have a core unit of two carbon atoms joined by a double bond. The condensation polymerization reaction produces by-products such as water, hydrogen gas, or alcohol that may compromise the physical properties or handling characteristics.

 

REF:   p. 301             TOP:   Review of Polymer Formation (Addition Polymerization)

 

2. In an addition polymerization reaction, the free radical initiates what reaction?

a.	Opening the bond between the two carbon atoms of the monomer
b.	Reversing the polarity of the monomer chain
c.	Creating a bend in the carbon atom
d.	Excluding divalent cations

 

 

ANS:  A

In an addition polymerization reaction, the free radical initiates the reaction by opening the bond between the two carbon atoms of the monomer. The broken bond causes the monomer molecule to bond to another monomer. Each linkage leaves a free radical available for further reaction.

 

REF:   p. 301             TOP:   Review of Polymer Formation (Addition Polymerization)

 

3. The monomer will _____ if the temperature becomes too great during the polymerization process.

a.	vaporize and produce porosity
b.	cause crazing of the material
c.	bleach the denture white
d.	warp the prosthesis

 

 

ANS:  A

The monomer will vaporize and produce porosity if the temperature becomes too great during the polymerization process. Porosity weakens the material, causes it to discolor as stains are absorbed into the pores, and can lead to retention and growth of oral microorganisms.

 

REF:   p. 301             TOP:   Review of Polymer Formation (Curing Methods)

 

4. What is the polymerized acrylic resin formed when a liquid monomer is mixed with a powder of small polymer beads?

a.	BIS-GMA
b.	Benzoyl peroxide
c.	Poly (ethyl methacrylate)
d.	Poly (methyl methacrylate)

 

 

ANS:  D

The polymerized acrylic resin formed when a liquid monomer is mixed with a powder of small polymer beads is poly (methyl methacrylate). It is composed of numerous methyl methacrylate (MMA) monomer units linked together to form a long-chain polymer.

 

REF:   p. 302             TOP:   Acrylic Resins (Plastics)

 

5. Which of the following is true regarding the properties of acrylic resins used in dentistry?

a.	Denture bases conduct temperature very well.
b.	Heat-cured acrylic resins shrink about 0.6% by volume.
c.	The strength of acrylic resins is comparable with dental amalgam.
d.	The coefficient of thermal expansion of acrylic resins is more than twice that of composite resins.

 

 

ANS:  C

The coefficient of thermal expansion of acrylic resins is more than twice that of composite resins. Heat-cured acrylic resins shrink about 6% by volume and about 0.2% to 0.5% linearly. The strength of acrylic resins is fairly low, with a compressive strength of approximately 11,000 psi and a tensile strength of 8000 psi. By comparison, amalgam has a compressive strength of about 60,000 psi. Denture bases do not conduct temperature well.

 

REF:   p. 302             TOP:   Acrylic Resins (Plastics)   (Properties)