Part II - Impression Materials

Gypsum bonded Setting Time:

- longer spatulation, increase water temperature, use of slurry water, less water: powder ratio = greater expansion, shorter setting time - older investment = decrease expansion - Increasing water: powder ratio - decrease expansion, longer setting time ^opposite of alginate

Tolerates moisture the most - A. hydrocolloid, B. polyether, C. addition silicone, D. polysulfide

hydrocolloid

Increased trituration time will increase/decrease compressive strength and increase/decrease setting expansion

increase compressive strength decrease setting expansion

Gypsum: If you have decrease spatula/mixing, you decrease expansion. If you have increase spatula/mixing, you

increase expansion

Decrease setting time of gypsum by - increase/decrease spatulation time, increase/decrease water temperature, increase/decreases water: powder ratio use of _ water

increase spatulation time increase water temperature decrease water:powder ratio use slurry water

increasing water:powder ratio for alginate impressions does what?

increases setting time & decreases expansion

mixing alginate faster does what?

increases water temperature and decreases setting time

C1 inhibitors are used in angioedema to

inhibit the complement system

alginate is what type of impression material

irreversible hydrocolloid

What is the most inaccurate impression material?

irreversible hydrocolloid (alginate)

When compared to other materials, which of the following is the main disadvantage of using polyether elastomeric impression materials:

is much stiffer

Catalyst of POLYSULFIDE impression material-

lead dioxide

Imbibition of alginate causes what?

more water absorbed into alginate resulting in alginate expansion

If you decrease water temp (colder), you have more/less working time for an irreversible hydrocollod?

more working time

Which material cannot be used to get cast impression? o Reversible hydrocolloid o Irreversible hydrocolloid o Polysulfide o PVS

o Irreversible hydrocolloid

What material would you not use for a single crown: a) polyether b) polysulfide c) PVS

polysulfide

Which of the following is the best for tear strength

polysulfide

Most stability: 1. hydrocolloid reversible 2. hydrocolloid irreversible 3. polysulfide (polyvinyl sulfide, the smelly one)

polysulfide (polyvinyl sulfide, the smelly one) - PVS and polyether were not option

Condensation silicone sets via _ and gives off what byproduct?

sets via cross-linking polymerization reaction byproduct: ethanol

Alginate impression in 100% humidity, why will shrinkage occur?

shrinkage occurs b/c of syneresis tricky question b/c the LEAST amount of shrinkage occurs when alginate is stored in 100% humidity, but they can still lose moisture (syneresis)

Polyether, disadvantage compared to other elastomeric? A. sticks to teeth/hard to remove from teeth, B. longer working time, C. less accuracy

sticks to teeth/hard to remove from teeth

Polysulfide gives out?

water

PVS is also known as?

Addition silicone

Which impression material is least distorted by water?

Addition silicone (Condensation silicone better ans if available)

Polysulfide advantages (2) Polysulfide disadvantages (3)

Advantages: 1. long working time 2. flexible and tear resistant Disadvantages: 1. long setting time 2. very unpleasant odor and taste 3. highest permanent deformation

Why elastomer is not a good interocclusal record?

Rebound when mounting

Imbibition and syneresis affect which one the most a. reversible hydrocolloid b. impression compound c. polysulfide d. silicone

Reversible hydrocolloid. Irreversible was not an option

When pouring gypsum material into an impression, which material will cause the least amount of bubbles?

Silicone

polysulfide (rubber base) is an ____ impression material

Elastomer

Condensation silicone is an _ impression material.

Elastomeric

Polysulfide has an _ setting reaction with _ as a byproduct

Polysulfide has an exothermic setting reaction with water as a byproduct.

Condensation silicone release

ethyl alcohol as by product

What is syneresis of alginate?

exudation of liquid component of a gel leads to alginate shrinkage

What decreases setting time of Gypsum:

Decrease water: powder ratio

Addition silicones (PVS) releases?

H2 (as secondary reaction) —> should wait an hour before pouring casts

Which one most likely to get stuck in mouth?

Polyether

Condensation silicone disadvantages (4)

1. must be poured immediately 2. poor dimensional stability due to evaporation of ethanol 3. hydrophobic 4. low tear strength

What happens when you take an impression & lip immediately swells?

Angioedema (allergy reaction)

Which of the following systems is thought to malfunction in the hereditary form of angioneurotic edema? A. C-1 esterase B. C-1q inhibitor C. CH50 consumption D. Serine phosphatase E. Complement synthetase

C-1 esterase

Impressions, what's wrong with polyether?

It's hard & engages undercuts.

What happens if you increase water in gypsum stone?

Less expansion and strength (b/c particles are farther apart)

Property of interocclusal recording material?

Low resistance to jaw closure

What impression material gets affected by latex?

PVS Sulfur in latex gloves retards the setting of PVS

What is PVS's byproduct?

PVS doesn't have byproducts compared to condensation silicones

Most rigid impression material:

Polyether

Which is hardest one to remove from the oral cavity (STIFFEST)?

Polyether

The most stable elastic impression in moisture environment? a. polyether b. additional silicone c. condensation silicone d. polysulfide

additional silicone

Most stable impression material that provides best dimensional quality?

additional silicones (PVS)

PVS advantages (3) PVS disadvantages (2)

advantages: 1. excellent dimensional stability (2 weeks) 2. excellent surface detail 3. low permanent deformation disadvantages: 1. hydrophobic 2. temperature sensitive

Gypsum: If you increase water to powder ratio, you have

decrease expansion

What happens when you increase the water:powder ratio of gypsum?

decreases thermal expansion

Which is not recommended for final FPD cast impression? • irreversible hydrocolloid • reversible hydrocolloid • PVS • Polyether

• irreversible hydrocolloid