Test One: Acrylic Resins

Question 0

Vinyl resins

Answer 0

Vinyl refers to having a carbon double bond. These compounds are used when there is an acrylic allergy

Question 1

Resin vs plastic

Answer 1

Resins are natural or synthetic substances that form plastic materials. Resins are polymers in an unpolymerized state. Plastic means moldable.

Question 2

Acrylic resins

Answer 2

Compounds derived from acrylic acid–Has an ester group coming off the vinyl.

Question 3

Methacrylic resins

Answer 3

Substituting a hydrogen from the acrylic acid for a methyl group.

Question 4

What materials are used for temp crown and bridge resins and how do they compare to methyl methacrylate?

Answer 4

ethyl methacrylate or butyl methacrylate. They have low heats of polymerization (low exothermic values on curing) and low polymerization shrinkage values

Question 5

What precautions are needed for protection from contact sensitization of a methyl methacrylate monomer?

Answer 5

boiling point 100.3° C
flammability potential high
need to use in a well ventilated area
penetrates latex gloves easily, use only rubber gloves to provide a barrier to skin and systemic absorption

Question 6

What wavelength can polymerize pure methyl methacrylate without an activator?

Answer 6

280-320 nm harsh uv light

Question 7

How does an acrylic monomer undergo spontaneous polymerization?

Answer 7

Random collisions will form free radicals which will react with other molecules and begin the polymerization process

Question 8

How can free radicals be created from benzoyl peroxide?

Answer 8

Heat, uv light, tertiary amines

Question 9

What are the steps for vinyl, free radical polymerization?

Answer 9

Initiation- the free radical forms a complex with the monomer
Propagation- this new complex will seek out other monomers to react with which will extend the polymer chain
Termination- two free radical complexes collide with each other or the material has become too viscous for movement

Question 10

How does cross-linking occur?

Answer 10

when the monomer has more than one vinyl group such as ethylene glycol dimethacrylate, it can form a bond at each double bond

Question 11

What is a pendent methacrylate group?

Answer 11

A pendent group results from a crosslinker monomer that has an unreacted vinyl group that remains part of the polymer

Question 12

How much polymerization shrinkage is to be expected and how is this affected by monomer size?

Answer 12

For every mole of methacrylate groups there is approximately 23 cc of volumetric shrinkage. Larger molecules can be used to reduce the amount of methacrylate and therefore reduce shrinkage.

Question 13

What monomers are commonly used for resin based restorative materials?

Answer 13

BisGMA- very viscous fluid that needs to be diluted in order to be used
TegDMA- co monomer that dilutes bisGMA and increases crosslinking/ flexibility of the polymer
Ethoxylated BIS-GMA- less hydrophilic than bisGMA therefor less sticky and prone to water sorption
Urethane monomers-enhanced photopolymerization with uv energy

Question 14

What can affect the shelf life of a resin?

Answer 14

• Heat increases the amount of spontaneous free radical formation
• methylether of hydroquinone (MEHQ), BHT, and eugenol are inhibitors that reduce the free radicals and transfer the electrons to a benzene ring
• Retarders can also be added to a chemical to react with the free radicals and delay polymerization until they’re all used
• UV stabilizers like PABA can be used to absorb some of the uv light that can cause polymerization

Question 15

Oxygen inhibition

Answer 15

Free radicals will preferentially react with dissolved oxygen in resins. This can form a sticky outer layer that is uncured resin if no matrix strip is used

Question 16

How can fillers help with the oxygen inhibited layer?

Answer 16

Fillers can increase viscosity thus limiting the depth that the oxygen can diffuse and inhibit polymerization