Elastomeric Impression Materials

Question 1

What is the composition (base and accelerator pastes) of polyether?

Answer 1

Base paste:

1. Low MW polyether with azridine rings
2. Colloidal silica
3. Cross-linking agent: Glycolether phthalate
4. Triglycerides

Accelerator paste:

1. Catalyst: Dichlorobenzene sulfonate
2. Colloidal silica
3. Cross-linking agent: Glycolether phthalate

Question 2

What is the composition (base and accelerator pastes) of polysulfide?

Answer 2

Base paste:

1. Polysulfide polymer
2. Titanium oxide, zinc
3. Sulfate, silica, copper carbonate

Accelerator paste:

1. Lead oxide
2. Sulfur
3. Dibutyl phthalate
4. Other additives: Magnesium stearate, deoderants, oxidising agents

Question 3

What is the composition (base and accelerator pastes) of CPS?

Answer 3

Base paste:

1. Silicone polymer
2. Colloidal silica

Accelerator paste:

1. Alkyl silicate
2. Stannous octoate

Question 4

What is the composition (base and accelerator pastes) of APS?

Answer 4

Base paste:

1. Low MW silicone with terminal silane hydrogen
2. Reinforcing filler

Accelerator paste:

1. Low MW polymer with vinyl terminal groups
2. Reinforcing filler
3. Catalyst: Chloroplatinic acid
4. Palladium black

Question 5

Which is the only elastomeric impression material that is hydrophilic? (polysulfide, CPS, APS, polyether?)

Answer 5

Polyether

Question 6

What are the respective setting times of polyether, CPS, APS and polysulfide?

Answer 6

Polyether: 3-6min
APS: 3-7min
CPS: 6-10min
Polysulfide: 10-16min

Question 7

What is the setting reaction of polyether?

Answer 7

Polyether sets by an exothermic, addition polymerisation reaction.

Dichlorobenzene sulfonate in the accelerator paste catalyses the reaction by opening up the azridine rings in polyether. Cross-linking occurs between aromatic alkyl sulfonate and azridine rings.

Question 8

What is the setting reaction of polysulfide?

Answer 8

Polysulfide sets by an exothermic, condensation polymerisation reaction. Condensation occurs between -SH groups in polysulfide polymer and lead oxide and sulfur, to produce disulfide links and water as a by product.

The reaction occurs in 2 steps.

1. Chain lengthening confers viscosity to the set material
2. Cross-linking confers elasticity to the set material

Question 9

What is the setting reaction of CPS?

Answer 9

CPS sets by an exothermic, condensation polymerisation reaction. Condensation between terminal groups of silicone polymer and alkyl silicate in the presence of stannous octoate to form a 3D network. Ethyl alcohol is formed as a by-product, which evaporates and causes shrinkage to the material.

Question 10

What is the setting reaction of APS?

Answer 10

APS sets by addition polymerisation. Cross-linking occurs between the terminal silane hydrogen groups and vinyl double bonds. If -OH groups are present, a secondary reaction occurs producing hydrogen gas.