Midterm Content Flashcards by Justyus Jackson

Gypsum is a sulfate mineral composed of..

Calcium sulfate dihydrate

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Direct retortive procedures include…

amalgum and composite

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Indirect restorative procedures include

crowns and bridges

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Natural gypsum rock is found in what form?

Dihydrate form

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Heat removes water and converts dihydrate to…

hemihydrate

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What happens when 11/2 water molecules are added to hemi hydrate?

reverse reaction; dihydrate product

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Heating gypsum under stem pressure in an autoclave at 120-150 produces…

dental stone

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Boiling gypsum in a 30% aqueous calcium and magnesium chloride solution produces…

high strength die stone

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Gypsum mineral heated in an open kettle/vessel at temperatures above 110-120 produces…

Dental plaster (weak gypsum product)

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What are the two forms of hemihydrate?

alpha and beta

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alpha-hemihydrate is characterized by crystals that are…

more dense and prismatic

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which hemihydrate is stronger and harder?

alpha

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What is another name for beta hemihydrate?

plaster of Paris

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beta-hemihydrate is characterized by crystals that are…

spongy and irregular shape

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The most important and well-recognized theory for the mechanism of setting is the …

crystalline theory

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The reverse reaction back to dihydrate form is due to…

addition of water; the difference in solubility between the two components

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Type II gypsum

Dental plaster

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Type III gypsum

Dental stone

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Type IV gypsum

dental stone; low expansion

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Type V gypsum

dental stone; high expansion

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Mineral gypsum undergoes the dehydration process to become…

plaster of Paris, hydrocal, or densite

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Plaster of Paris has what type of density?

porous

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What are the production steps for the plaster of Paris?

Heat to 115 C in AIR

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what are dental products produced with plaster of Paris?

Plaster and impression material

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If too much water is added to the powder, the final product will be...

weaker

Vertical pressure applied to stone until it breaks is known as...

compressive strength

An object's ability to bend without obtaining any major deformities is...

flexural strength

What common dental product does NOT have good flexural strength?

Gypsum

A tooth snapping off an impression when separated from the impression material is an example of...

low flexural strength

Mixing time (Gypsum) is...

the time from adding power to water until it is done being mixed

How long does mechanical mixing take for gypsum?

20-30s

How long does mixing by hand take for gypsum?

2 minutes

Working time (Gypsum) is...

time available to get a workable mix

Setting time (Gypsum) is...

time that goes by from beginning of mixing until stone is hard

Vigorous vibrations can cause what reaction between the water and the crystals?

phase separation

The remaining gypsum particles shorten the setting time because of the increase in potential nuclei of crystallization is called...

Impurities

The finer the particle size of the hemihydrate, the faster the mix hardens is...

Fineness

A gradual retardation will occur if...

water temp > 50 cent.

What are common accelerators?

Potassium sulfate or set gypsum (slurry water)

What are common retarders?

blood, saliva, alginate, sodium citrate

Hydrophillic

Water loving

Hydrophobic

water hating

Tear strength

amount of resistance material has to tearing

Dimensional stability

degree which set material remains dimensions under different temps and humidity

Elasticity

ability for a material to go back to its original shape after deformation

What are the 3 types of non-elastic impression materials?

1. plaster 2. Impression compound 3. ZOE

Mucostatic impression

flabby ridges; the material does NOT displace mucosa; complete dentures

Mucocompressive impression

material DOES displace mucosa; records tissue in a functional, loaded state

What are the two types of elastic impression materials?

Hydrocolloids and synthetic elastomers

What are the two hypes of hydrocolloids?

Reversible (agar) and irreversible (alginate)

What is the most commonly used impression material in dentistry?

alginate

For alginate, adding powder and mix results in a...

sol

For alginate, too much water can lead to...

bubbles and reduced strength

For alginate, too litter water can lead to...

loss of surface detail

For alginate, when selecting a tray, you should look for...

3-5mm clearance and perforated trays (non-perforated can use an adhesive)

For alginate, what should be done when the material is set?

rinse with cold water and wrap in a damp paper towel

This process occurs when the impression absorbs water, which expands the dimensions of the impressions.

Imbibition

This process occurs with the exudation or loss of water from the impression causing it to shrink

Syneresis

What are the 4 synthetic elastomers?

polyether, polysulfides, PVS, and condensation silicone

What are the advantages of synthetic elastomers?

can undergo deformation and recover; used for undercuts

What is the most HYDROPHILLIC synthetic elastic impression material?

Polyether

What elastic material is used for crowns?

polyether

What is a disadvantage when using polyethers?

is very ridged when set = avoid deep undercuts (do NOT use a metal tray) and it absorbs water (do NOT store with alginate)

Which impression material has an Ethyl Alcohol by-product that results in shrinkage of the material?

Condensation Silicon

Which impression material can be removed from an undercut without permanent damage?

Condensation Silicon

What impression material can be used on patients with deep undercuts?

Condensation Silicon

Is condensation silicon hydrophobic or hydrophilic?

hydroPHOBIC

What is the most widely used impression material in dentistry for fixed prosthodontics?

PVS

PVS, undergoes an addition polymerization reaction that has...

no by-products

For PVS, the lack of by-products...

increases dimensional stability and accuracy; remains unchanged for a long time

What is added to the PVS base-catalyst reaction to remove hydrogen gas produced during the reaction?

Platinum or palladium

Which impression material has great detail reproduction and great dimensional stability with fast setting?

PVS

is PVS hydrophilic or hydrophobic?

hydrophobic

What are the disadvantages of PVS?

cannot use powdered gloves and no metal trays

What are the criteria for selecting a tray for PVS?

4-6mm thickness of impression material, plastic tray w/ PVS tray adhesive

Inadequate margins with PVs can be caused by...

bad tissue management and wash material

Midterm Content Flashcards

Terminology, Impression Materials, and Gypsum (77 cards)