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141 Cards in this Set

  • Front
  • Back
what creates an accurate negative reproduction of the pts oral structure(soft and hard tissues)
what is the positive pour into an impression called
model- dimensionally accurate reproduction of hard and soft tissues used primarily for observations and records

cast- a repro of the oral tissues used as a working model

die- a working reprod of a single tooth or several teeth on which a prostheses is constructed
What will a model or cast be used for
Bridges crowns, make dentures(c and p), make framework for implants(not breasts), study models for restorative and ortho procedures
What is the ANSI/ADA spec for gypsum products
No. 25
What is ADA type I(impression plaster) used for
impressions of edentulous arch
NOTE rarely used in dentistry and is a plaster paris material
What is a ADA type II(model plaster) gypsum used for
study casts and record purposes
What group do ADA types III, IV and V gypsum fall into
dental stone

NOTE I and II are considered plaster paris
WHat is ADA type III dental stone(model stone) used for
full arch casts, investing dentures
Whats is ADA type IV dental stone(Die stone) used for
dies for high noble and noble casting alloys
What is ADA type V dental stone(high expansion stone) used for
dies for base-metal casting alloys

NOTE the base-metal contracts and the High expansion stone compensates for this
Which type of material(guess its a stone) doesnt fall into one of the five classes of gypsum products under ADA Spec 25
Investment material
What factors should be taken into consideration when selecting a stone
Dimensional stability
ease of trimming
resistance to abrasion
ability to reproduce fine detail
Should a cast or model have a stone that is greater in accuracy and dimensional stability
A cast

Models dont need as high a strength as casts and dies either
What is CaSO4 - 1/2H2O
Calcium Sulfate Hemihydrate
what type of hemihydrate is in dental plasters
how is beta hemihydrate(dental plaster) produced
heating gypsum in open air at 115 deg C

Note beta hemihydrate is porous, irregularly shaped crystals which requires a water powder ratio of 50ml/100g
how is alpha-hemihydrate(dental stone) made
autoclaved under pressure at 125 deg C

NOTE it is less porous, uniform shaped crystals which requires less water than b-hemihydrate. Water ratio of alpha is 30ml/100g
how is alpha modified hemihydrate(high strength dental stone) made
boiling gypsum in 30% aqueous solution of CaCl2 and MgCl2(calcining process)
What is calciing
addition of CaCl2 and MgCl2 to gypsum to make alpha modified hemihydrate
What are some other manuf steps used in gypsum product production and what do they do
the hemihydrate particles are ground to emliminate needlelike particles which improves particles

surface-active materials(gum arabic with Ca Carbonate) are added to reduce water requirements
What is the manufacture reactions for gypsum products
CaSO4-2H2O --heat--> CaSO4-1/2H2O + 3/2H2O

NOTE the starting material is gypsum and the end product is plaster or stone. this plaster or stone is what goes into the setting reaction
What is the setting rxn of gypsum
CaSO4-1/2H2O + 3/2H2O ----> CaSO4-2H2O + heat

NOTE Plaster or stone from manuf rxn is used to start the setting rxn and ends up as gypsum. This is an exothermic reaction.
Dont forget the review article and Tylka's handout for impression class
Dont forget it man!!!
Why do we do impressions
to allow us to study the piehole when the pt is not present and to make restorations on and then place them in the piehole
What factors affect accuracy of an impression material
Type of setting rxn
evaporation of volatile components
continued settingafter removal from the mouth
Describe the ideal impression material
fluid enough to adapt to oral tissue but viscous enough to stay in tray
transform to rubbery solid in reasonable time
should not tear or distort upon removal
should be dimensionally stable
have good shelf life
be biocompatible
materials, equipment and time should be cost-effective
know the classification table on 1st page of Impr Materials handout
for a chemical setting rxn with an inelastic recovery zinc oxide eugenol, impression plaster. For elastic its alginate non aqueous elastomers

for thermal setting rxn inelastic its impression compound and for elastic its agar
what are the chemical setting reaction materials used in dentistry
Alginate hydrocolloid
Nonaqueous elastomeric materials like polysulfides, silicones and poly ethers
Zinc oxide-eugenol(ZOE)
impression plaster
What are the thermal setting reaction materials used in dentistry
Agar hydrocolloid
impression compound
What does colloid mean
A colloid is a solid, liquid or gas made up of finely sized particles(<0.5 micrometers) that are suspended in solution. The particle doesnt settle to the bottom over time
which hydrocolloid material is a reversible hydrocolloid
Agar Hydrocolloid
What makes up agar hydrocolloid
long strands of polysaccharide sugars molecules

major component is water, rest is agar(polysach).
What gives agar hydrocolloid its body and strength and retards setting of the stone
What material in agar counteracts borax and accelerates the setting of stone
Potassium Sulfate
True of False, agar hydrocolloid does not contain wax fillers and thixotropic materials
False it does contain these
Is agar hydrocolloid a thermoplastic materials
Yes, remember that thermoplastic means its moldable with application of heat
What type of setting reaction does agar hydrocolloid set by
reversible, it sets by change in temps
What is the solid form of a agar hydrocolloid called

gel --heat--> sol (Solation)
What is the liquid form of agar hydrocolloid called

sol -----> gel precipitate (gelation)
What are the important temps for agar hydrocolloid
liquify at 100C for 10 min
stored at 65C
tempered at 45C
cooled in mouth at 35 C for 3-5 min
Water in tray at 18-21C for 3-5 min
The difference in temps at which the hydrocolloid sols and at which it returns back to the gel form is called
Water being squeezed out of the impression when it sets results in impression shrinkage and deformation
water coming into set impression results in swelling and distortion is called
Why do you remove agar impression from mouth quickly
to increase tear resistance and minimize permanent deformation
What characteristic of agar allows you to take impressions in presence of blood and saliva
its naturally hydrophilic
What limits agars use in supragingival areaas
its low tear strength
Why should you pour model quickly when using agar
material distorts easily from water gain or loss
the addition of K2SO4 on agar impression is for what reason
to increase stone hardness and reduce inhibitory effect of colloid on stone setting
What are the uses of agar impressions
preps for crowns, bridges, inlays and onlays
How should you disinfect an agar impression
spray 1:10 hypochlorite solution and leave in bag for 10-15 mins
What type of irreversible hydrocolloids do we use in dentistry
Alginate hydrocolloid

H2O + CaSO4-2H2O(gypsum) --->Ca2+

Ca2+ + NaPO4 ---> Ca3(PO4)2

Ca2+ + Na-Alginate ---> set material(calcium alginate)
What is the composition of alglinate hydrocolloid
Powder of 18% Na or K alginate salt that functions to react and hold everything together
14 % gypsum that provides Ca ions to react with alginate
10% K2SO4 which functions to counteract inhibitingeffect of hydrocolloid on stone
2% Na3PO4 that acts as inhibitor and gives working time
56% diatomaceous earth which is an unreactive filler to give body
Which type 1 or 2 is the fast setting alginate
Type 1 is fast set

setting time depends on how much retarder manuf puts in
T or F warm water lengthens the setting reaction and cold water shortens the setting reaction time for an alginate impression material
F Warm water makes it set quicker

NOTE the warm water will make a gypsum product set more slowly, which is exact opposite of warm waters effect on alginate impression material
What type of dental procedure should alginate impressions not be used
things like crown preps cause its not as accurate
why should the cast/die combo be separate shortly after the casting material is cooled down in an alginate/stone pour
if you wait to long the cast will dry out and get weakened
When are inelastic impression materials used
when there are no undercuts present
What type of impression materials will not spring back to their original positions if distorted
non elastic impression materials
What is the ZOE impression material setting rxn
ZnO + H2O ---> Zn(OH)2
Zn(OH)2 + 2HE ---> ZnE2 + 2H2O

base(paste 1) - Zn(OH)2
Acid(paste 2) - 2HE
zinc eugenolate salt - ZnE2 + 2H2O
how does ZOE impression material set(chemically or thermally)
whats one things pts seem to dislike about ZOE impression
very messy and eugenol has burning effect
what are the thin layers in a ZOE impression called
"wash impressions" or "mucostatic impressions"

these are very fluid and capture oral tissue in undisturbed state
What is the initial setting time for a ZOE impression
3-6 minutes final sets in 10 min for type I(hardset) and 15 min for type II(soft set)ADA spec #16 covers ZOE Materials
what are some other dental uses of ZOE
cementing material
surgical paste(perio pack)
it has a sedative/pallative effect on pulpal tissues and soft tissue
bite registration paste
root canal filling material
temporary filling material
temporary denture base liner
T or F eugenol is not known to cause GI disturbance
F it does cause GI disturbance

also stings or burns soft tissue
what is a mixture that can be made that can be used in place of eugenol
orthoethoxy benzoic acid(EBA) combined with ZnO in an insoluble soap(saponification)
What kind of setting rxn does tray compound undergo
thermoplastic(setting involves cooling the heated material)
What spec covers tray compound
ADA/ANSI spec # 3
what is the characteristics of tray compound
comes in sticks or cakes and is made up of resins, waxes, organic acids and fillers
What is a use of tray compound
obtaining a primary impression to make a tray that supports a more accurate secondary impression material
How is tray compound used
it is heated over flame or tempered in hot water

what type of settin rxn is impression compound
thermoplastic(setting involves cooling the heated material)
what is a base
component forming main structure of the set material
what is accelerator
speeds up reaction and is similar to catalyst but unlike the catylys the accelerator is used up in the reaction and becomes part of the final product
what is an elastomer
lightly crosslinked material having elastic behavior after settin
what does monophase mean
a single component material that is viscous enough to serve as a tray material yet serveds as a syringe material after shear-thinning
What is a thixotropic
its a time dependent pseudoplastic behavior of materials charaterized by the gradual decrease of viscosity under a constant applied shear rate
what is working time
time from start of mixing until just before elastic properties have developed
what is setting time
time from start of mixing until material can resist permanent deformation
what is viscoelastic behavior
characteristic behavior that behaves intermediate to an elastic solid(spring) and a viscous fluid(dashpot)
what ADA spec deals with nonaqueous elastomeric materials
ADA/ANSI spec # 19

divides elastomeric materials into 3 types based on selected elastic properties and dimensional change. There are then 4 classes in each type that are based on viscosity
what are the 4 classes of nonaqueous elastomeric materials different viscosity names
low viscosity
medium viscosity
high viscoity
What are the 4 types of elastoemr chemical compositions
condensation silicone
addition silicone
polyether materials
What are elastomers usually used for
obtaining highly accurate impressions for indirectly making restorations
how do you keep polym shrinkage occuring in proper direction(towards tray)
used tray adhesive
what characteristic of elastomeric impression materials makes them able to reduce distortion and increase tear resistance if a rapid removal technique is properly used
Fast Strain Rate
How do elastomeric impression materials set
they are cross-linked polymeric two pasted materials that set by irreversible chemical rxn
What is the one exception to the elastomeric materials that must not be removed by a rapid removal technique

it has the highest tera resistance of all impression materials and is slow setting, must be left in mouth from 10 min
what is the setting rxn for a polysulfide elastomeric material
[polymer + filler] + [lead dioxide] ----> set material + H2O

the polymer + filler is the white paste and the lead dioxide is the brown reactor/accel paste
what are the SH groups in a polysulfide elastomeric material crosslinked with in the set reaction
the lead dioxide
What is in the base layer of a polysulfide elastomeric material
linear polyfunctional mercaptan or polysulfide(charateristic odor)
lithophone or TiO2 filler, dibutyl phthalate plasticizer, 0.5% sulfur
what does the reactor paste of a polysulfide elastomeric material have in it
lead dioxide, filler, plasticizer and oleic/stearic acid retarders
the chain lengthening and formation of crosslinked disulfide bonds that occurs in a polysulfide elastomeric setting rxn is known as
What aspect of polysulfide elastomeric materials allows it to easily trap air bubbles
the fact that its hydrophobic
how much time do you have after making a polysulfide impression and making your cast
30 min but should be done faster to reduce shrinkage by H2O

polysulfides also require a custom tray to do the impression
What are the uses of polysulfide impressions
use on teeth preped for crowns, bridges, inlays and onlays

also use on edentulous ridges for denture fabric.
How do you disinfect a polysulfide impression
2% gluteraldehyde or EPA approved disinfectant for 10-15 min
what are the two types of silicone impression materials
condensation - reinforcing agents(silica) are used. These usually form ethanol as harmful byprodut

addition - no volatile by products but early versions released Hydrogen
What is the setting rxn for a condensation silicone
Polymer + crosslinking agent ---> set material + ethanol

ethanol is a volatile byproduct
what is the polymer used in condensation silicone materials
alpha-w-hydroxy-terminated polydimethyl siloxane that reacts with tri- or tetra functional alkyl silicates in the presence of stannous octoate
what kind of filler does a condensation silicone material have
colloidal silica or metal oxide
describe the condensation silicone impression materials setting reaction
room temp condensation polymerization rxn with cross linking between silicone polymers and alkyl silicates with ethanol formed as a byproduct
describe the "putty wash technique" used for doing condensation silicone impressions
no custom trays are needed they just need to be metal. To compensate for large polym shrinkage characteristic of condensation silicone materials, a highly filled, high vicosity putty is used in conjunction with a low viscosity material
what is the typical shrinkage seen in a condensation silicone rxn
0.03 - 0.06% (number lower if putty wash tech is used)
what are the implications of condensation silicones very hydrophobic nature
you need a dry field for impression
difficult to pour cast without getting bubbles in stone
how much time do you have to pour stone into a condensation silicone impression
within 30 minutes but not until all the ethanol has evaporated
What are some characteristics concerning working with condensation silicone impressions
adequate working time, pleasant odor and has low tear strength
what are condensation silicones used for
teeth prepped for C&B, inlays onlays
Why are condensation silicones not used as often as addition silicones today
condensations dont have as good a dimensional stability
what are some of the other names for polysulfide materials
rubber base, mercaptan, thiokol
What are some of the other names for addition silicone materials
polyvinyl siloxane, vinyl polysiloxane
what is the setting rxn of addition silicone materials
polymer + Pt salt with prepolymer ----> set material

polymer is the base
Pt salt is catylyst
what is in the base and catalyst of an addition silicond material
base - polymethyl hydrogen siloxane

catalyst - divinyl polydimethyl siloxane

Addition polymerization with crosslinking of vinyl silicone groups to hydride groups activated by catalyst
What is a main advantage of addition silicones
no volatile byproduct but H2 may be released when moisture and hydrides combined

Pt/Pd is added to help prevent H2 formation
What are some other advantages of addition silicones
shrinkage on curing is 0.05 - 0.16%
best dimensional stability
pour can be delayed and repeated
with putty wash technique no custom tray needed
what are some disadvantages of addition silicones
naturally hydrophobic but some have added surfactant to maker their surface more hydrophilic
wait before pouring to permit release of H2 gas from some brands
sulfur in latex and vinyl gloves inhibits setting
what are some uses for addition silicones
teeth prepped for C&B, inlays, onlays
also edentulous ridge impressions for dentures
what is an ether
has a C-O-C bond and usually has aromatic odor
what is the composition of a polyether material
base - polyether pre polymer, colloidal silica filler, glycolether or phthalate plasicizer

accelerator - sulfonate ester initiator, imine catalyst(may be skin sensitizer)
what are the characteristics of a polyether material
high mod of elasticity(very rigid) May remover perio involved tooth upon impression removal
shrinkage on curing is 0.15%(can delay pour)
working and setting time short which is good for gagger but not good for multiple preps
tear strength is low
easier to get good impressions in wet field
easier to pour without bubbles
Which nonaqueous elastomer is the least hydrophobic
of the non modified materials Polyether is the least hydrophobic, however when modifying addition and condensation silicones with surfactant they become less hydrophilic than polyethers
what are the uses of polyethers
teeth prepped for C&B, inlays, onlays
edentulous ridges for denture impressions(IF NO UNDERCUTS)
what are some clinical implications of polyethers
difficult to remove from mouth(NEVER DO A FULL ARCH IMPRESSION)
Wait 10 minutes before pouring to allow it to recover from being distorted upon removal from mouth
Know relative ranking of these properties for Elastomeric Impression materials
working and setting times(long to short) - polysulfide, condensation, polyether, addition
Dimensional stability(most stable to least)- addition, polyether, poly sulfide, condensation
tear strenth(lowest to highest) - hydrocolloids(agar and alginate), silicones(addition and condensation), polyether, polysulfide
Biocompatibilty - polysulfide kills least cells while polyether kills most cells
Rheological - Polysulfide has lowest viscosity, addition silicone and polyether are psuedoplastic
describe the setting reaction of a gypsum stone
when hemihydrate mixes with H2O a suspension is formed, the hemihydrate dissolves until it forms a saturated solution. Saturated hemihydrate solution ppts out dihydrate since the solution is supersaturated in dihydrate. Since the solution is then not saturated in hemihydrate it continues to dissolve. Dissolution of hemihydrate and pptation of dihydrate contitinues until no more dihydrate pptates out of solution
What is the initial setting time(working time) of gypsum stone
approx 3 minutes clinically its when you get "loss of gloss"

finaly setting time is approx 15 minutes
What are the factors that atler setting time of gypsum stone
W/P ratio - as w/p increases setting time increases while strength and setting expansion decrease
What is the correlation between W/P ratio and initial setting times
as W/P goes down the setting time gets less
what are some factors that can alter setting time of gypsum stone products
Accelerators - increase rate of chemical rxn and shorten work time (K2SO4, NaCl(>20%), gypsum particles(<20%) or gypsum slurry

retarders -decrease rate of chemical rxn and lengthen working time(borax, colloidal systems(ie blood, saliva, agar), NaCl(28%), glue, gelatin, potassium citrate(K3C6H5O7))

temp and humidity - EXACT OPPOSITE OF ALGINATE EFFECTS increased water temp >50C retards set time but >100C no rxn at all

Rate and duration of spatulation - longer adn faster spatulation shortens set time because gypsum crystals formed are broken up and form satellite nucleis of crystallization

Particle size - smaller particle size mixes hard faster especially if particles were ground during manuf.
what does normal setting expansion of a gypsum stone product in air depend on
W/P ratio
spatulation rate and duration
type of gypsum product
Which gypsum product experiences the least amount of expansion upon settin
Improved stone

from most to least it goes
Dental Plaster(0.2 - 0.3 Spec max of 0.3%)
Dental Stone(0.08-0.10% spec max 0.2%)
Improved Stone(0.05-0.07% spec max 0.1%)
what is hygroscopic setting expansion when related to gypsum stone
setting under water at a higher temp. Results in more than twice the normal setting expansion
Is dry strength of gypsum more or less than wet(green) strength after 1 hour of set material
Its more, 2 or more times
What does strength of gypsum depend upon
W/P ratio(higher the W/P ratio lower the wet compressive strength, however dry compressive strenght is not affected by W/P ratio very significantly)
Spatulation time(notes not clear on whether it decreases or increases strenght)
Addition of accelerator or retarder(lowers strength, im thinking both lower strength but not 100% sure)
Reproduction of the cast surface detail
# air bubbles correlated with wettability of impression material
What is abrasion resistance and surface hardness of a gypsum stone proportional to
compressive strength

they are improved by addition of gypsum hardners
What is the effect of the W/P ratio on wet and dry compressive strengths
as the W/P ratio gets smaller the wet compressive strengths increase. the dry strengths dont change appreciably
what is the tendency of a material to absorb water from the air called
hydroscopic property
What is a method used to sterilize gypsum casts of a patient with a known infection
Overnight gas sterilization
what do you use to disinfect gypsum casts
iodophors or 1:10 Na Hypochlorite or use a gypsum product containing disinfectant(will cause slight deterioration in properties)
What are some of the special gypsum products
Orthodontic plaster, mounting plaster and mounting stone