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141 Cards in this Set
- Front
- Back
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what creates an accurate negative reproduction of the pts oral structure(soft and hard tissues)
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impression
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what is the positive pour into an impression called
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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 |
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What will a model or cast be used for
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Bridges crowns, make dentures(c and p), make framework for implants(not breasts), study models for restorative and ortho procedures
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What is the ANSI/ADA spec for gypsum products
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No. 25
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What is ADA type I(impression plaster) used for
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impressions of edentulous arch
NOTE rarely used in dentistry and is a plaster paris material |
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What is a ADA type II(model plaster) gypsum used for
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study casts and record purposes
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What group do ADA types III, IV and V gypsum fall into
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dental stone
NOTE I and II are considered plaster paris |
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WHat is ADA type III dental stone(model stone) used for
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full arch casts, investing dentures
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Whats is ADA type IV dental stone(Die stone) used for
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dies for high noble and noble casting alloys
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What is ADA type V dental stone(high expansion stone) used for
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dies for base-metal casting alloys
NOTE the base-metal contracts and the High expansion stone compensates for this |
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Which type of material(guess its a stone) doesnt fall into one of the five classes of gypsum products under ADA Spec 25
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Investment material
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What factors should be taken into consideration when selecting a stone
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Dimensional stability
cost strength ease of trimming resistance to abrasion ability to reproduce fine detail |
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Should a cast or model have a stone that is greater in accuracy and dimensional stability
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A cast
Models dont need as high a strength as casts and dies either |
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What is CaSO4 - 1/2H2O
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Calcium Sulfate Hemihydrate
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what type of hemihydrate is in dental plasters
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beta-hemihydrate
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how is beta hemihydrate(dental plaster) produced
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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 |
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how is alpha-hemihydrate(dental stone) made
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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 |
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how is alpha modified hemihydrate(high strength dental stone) made
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boiling gypsum in 30% aqueous solution of CaCl2 and MgCl2(calcining process)
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What is calciing
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addition of CaCl2 and MgCl2 to gypsum to make alpha modified hemihydrate
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What are some other manuf steps used in gypsum product production and what do they do
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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 |
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What is the manufacture reactions for gypsum products
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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 |
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What is the setting rxn of gypsum
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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. |
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Dont forget the review article and Tylka's handout for impression class
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Dont forget it man!!!
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Why do we do impressions
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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
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What factors affect accuracy of an impression material
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Type of setting rxn
evaporation of volatile components continued settingafter removal from the mouth |
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Describe the ideal impression material
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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 |
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know the classification table on 1st page of Impr Materials handout
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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 |
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what are the chemical setting reaction materials used in dentistry
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Alginate hydrocolloid
Nonaqueous elastomeric materials like polysulfides, silicones and poly ethers Zinc oxide-eugenol(ZOE) impression plaster |
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What are the thermal setting reaction materials used in dentistry
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Agar hydrocolloid
impression compound |
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What does colloid mean
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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
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which hydrocolloid material is a reversible hydrocolloid
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Agar Hydrocolloid
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What makes up agar hydrocolloid
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long strands of polysaccharide sugars molecules
major component is water, rest is agar(polysach). |
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What gives agar hydrocolloid its body and strength and retards setting of the stone
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Borax
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What material in agar counteracts borax and accelerates the setting of stone
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Potassium Sulfate
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True of False, agar hydrocolloid does not contain wax fillers and thixotropic materials
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False it does contain these
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Is agar hydrocolloid a thermoplastic materials
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Yes, remember that thermoplastic means its moldable with application of heat
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What type of setting reaction does agar hydrocolloid set by
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reversible, it sets by change in temps
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What is the solid form of a agar hydrocolloid called
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gel
gel --heat--> sol (Solation) |
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What is the liquid form of agar hydrocolloid called
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Sol
sol -----> gel precipitate (gelation) |
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What are the important temps for agar hydrocolloid
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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 |
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The difference in temps at which the hydrocolloid sols and at which it returns back to the gel form is called
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Hysteresis
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Water being squeezed out of the impression when it sets results in impression shrinkage and deformation
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Syneresis
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water coming into set impression results in swelling and distortion is called
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imbibition
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Why do you remove agar impression from mouth quickly
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to increase tear resistance and minimize permanent deformation
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What characteristic of agar allows you to take impressions in presence of blood and saliva
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its naturally hydrophilic
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What limits agars use in supragingival areaas
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its low tear strength
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Why should you pour model quickly when using agar
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material distorts easily from water gain or loss
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the addition of K2SO4 on agar impression is for what reason
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to increase stone hardness and reduce inhibitory effect of colloid on stone setting
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What are the uses of agar impressions
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preps for crowns, bridges, inlays and onlays
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How should you disinfect an agar impression
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spray 1:10 hypochlorite solution and leave in bag for 10-15 mins
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What type of irreversible hydrocolloids do we use in dentistry
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Alginate hydrocolloid
H2O + CaSO4-2H2O(gypsum) --->Ca2+ Ca2+ + NaPO4 ---> Ca3(PO4)2 Ca2+ + Na-Alginate ---> set material(calcium alginate) |
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What is the composition of alglinate hydrocolloid
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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 |
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Which type 1 or 2 is the fast setting alginate
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Type 1 is fast set
setting time depends on how much retarder manuf puts in |
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T or F warm water lengthens the setting reaction and cold water shortens the setting reaction time for an alginate impression material
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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 |
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What type of dental procedure should alginate impressions not be used
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things like crown preps cause its not as accurate
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why should the cast/die combo be separate shortly after the casting material is cooled down in an alginate/stone pour
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if you wait to long the cast will dry out and get weakened
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When are inelastic impression materials used
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when there are no undercuts present
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What type of impression materials will not spring back to their original positions if distorted
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non elastic impression materials
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What is the ZOE impression material setting rxn
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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 |
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how does ZOE impression material set(chemically or thermally)
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chemically
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whats one things pts seem to dislike about ZOE impression
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very messy and eugenol has burning effect
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what are the thin layers in a ZOE impression called
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"wash impressions" or "mucostatic impressions"
these are very fluid and capture oral tissue in undisturbed state |
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What is the initial setting time for a ZOE impression
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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
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what are some other dental uses of ZOE
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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 |
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T or F eugenol is not known to cause GI disturbance
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F it does cause GI disturbance
also stings or burns soft tissue |
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what is a mixture that can be made that can be used in place of eugenol
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orthoethoxy benzoic acid(EBA) combined with ZnO in an insoluble soap(saponification)
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What kind of setting rxn does tray compound undergo
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thermoplastic(setting involves cooling the heated material)
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What spec covers tray compound
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ADA/ANSI spec # 3
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what is the characteristics of tray compound
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comes in sticks or cakes and is made up of resins, waxes, organic acids and fillers
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What is a use of tray compound
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obtaining a primary impression to make a tray that supports a more accurate secondary impression material
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How is tray compound used
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it is heated over flame or tempered in hot water
BE CAREFUL NOT TO OVERHEAT OR GET ON PATIENTS SKIN IF IT IS TOO HOT |
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what type of settin rxn is impression compound
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thermoplastic(setting involves cooling the heated material)
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what is a base
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component forming main structure of the set material
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what is accelerator
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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
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what is an elastomer
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lightly crosslinked material having elastic behavior after settin
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what does monophase mean
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a single component material that is viscous enough to serve as a tray material yet serveds as a syringe material after shear-thinning
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What is a thixotropic
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its a time dependent pseudoplastic behavior of materials charaterized by the gradual decrease of viscosity under a constant applied shear rate
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what is working time
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time from start of mixing until just before elastic properties have developed
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what is setting time
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time from start of mixing until material can resist permanent deformation
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what is viscoelastic behavior
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characteristic behavior that behaves intermediate to an elastic solid(spring) and a viscous fluid(dashpot)
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what ADA spec deals with nonaqueous elastomeric materials
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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 |
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what are the 4 classes of nonaqueous elastomeric materials different viscosity names
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low viscosity
medium viscosity high viscoity puddy |
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What are the 4 types of elastoemr chemical compositions
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Polysulfide
condensation silicone addition silicone polyether materials |
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What are elastomers usually used for
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obtaining highly accurate impressions for indirectly making restorations
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how do you keep polym shrinkage occuring in proper direction(towards tray)
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used tray adhesive
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what characteristic of elastomeric impression materials makes them able to reduce distortion and increase tear resistance if a rapid removal technique is properly used
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Fast Strain Rate
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How do elastomeric impression materials set
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they are cross-linked polymeric two pasted materials that set by irreversible chemical rxn
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What is the one exception to the elastomeric materials that must not be removed by a rapid removal technique
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polysulfide
it has the highest tera resistance of all impression materials and is slow setting, must be left in mouth from 10 min |
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what is the setting rxn for a polysulfide elastomeric material
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[polymer + filler] + [lead dioxide] ----> set material + H2O
the polymer + filler is the white paste and the lead dioxide is the brown reactor/accel paste |
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what are the SH groups in a polysulfide elastomeric material crosslinked with in the set reaction
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the lead dioxide
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What is in the base layer of a polysulfide elastomeric material
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linear polyfunctional mercaptan or polysulfide(charateristic odor)
lithophone or TiO2 filler, dibutyl phthalate plasticizer, 0.5% sulfur |
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what does the reactor paste of a polysulfide elastomeric material have in it
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lead dioxide, filler, plasticizer and oleic/stearic acid retarders
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the chain lengthening and formation of crosslinked disulfide bonds that occurs in a polysulfide elastomeric setting rxn is known as
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vulcanization
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What aspect of polysulfide elastomeric materials allows it to easily trap air bubbles
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the fact that its hydrophobic
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how much time do you have after making a polysulfide impression and making your cast
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30 min but should be done faster to reduce shrinkage by H2O
polysulfides also require a custom tray to do the impression |
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What are the uses of polysulfide impressions
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use on teeth preped for crowns, bridges, inlays and onlays
also use on edentulous ridges for denture fabric. |
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How do you disinfect a polysulfide impression
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2% gluteraldehyde or EPA approved disinfectant for 10-15 min
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what are the two types of silicone impression materials
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condensation - reinforcing agents(silica) are used. These usually form ethanol as harmful byprodut
addition - no volatile by products but early versions released Hydrogen |
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What is the setting rxn for a condensation silicone
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Polymer + crosslinking agent ---> set material + ethanol
ethanol is a volatile byproduct |
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what is the polymer used in condensation silicone materials
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alpha-w-hydroxy-terminated polydimethyl siloxane that reacts with tri- or tetra functional alkyl silicates in the presence of stannous octoate
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what kind of filler does a condensation silicone material have
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colloidal silica or metal oxide
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describe the condensation silicone impression materials setting reaction
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room temp condensation polymerization rxn with cross linking between silicone polymers and alkyl silicates with ethanol formed as a byproduct
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describe the "putty wash technique" used for doing condensation silicone impressions
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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
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what is the typical shrinkage seen in a condensation silicone rxn
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0.03 - 0.06% (number lower if putty wash tech is used)
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what are the implications of condensation silicones very hydrophobic nature
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you need a dry field for impression
difficult to pour cast without getting bubbles in stone |
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how much time do you have to pour stone into a condensation silicone impression
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within 30 minutes but not until all the ethanol has evaporated
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What are some characteristics concerning working with condensation silicone impressions
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adequate working time, pleasant odor and has low tear strength
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what are condensation silicones used for
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teeth prepped for C&B, inlays onlays
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Why are condensation silicones not used as often as addition silicones today
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condensations dont have as good a dimensional stability
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what are some of the other names for polysulfide materials
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rubber base, mercaptan, thiokol
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What are some of the other names for addition silicone materials
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polyvinyl siloxane, vinyl polysiloxane
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what is the setting rxn of addition silicone materials
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polymer + Pt salt with prepolymer ----> set material
polymer is the base Pt salt is catylyst |
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what is in the base and catalyst of an addition silicond material
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base - polymethyl hydrogen siloxane
catalyst - divinyl polydimethyl siloxane Addition polymerization with crosslinking of vinyl silicone groups to hydride groups activated by catalyst |
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What is a main advantage of addition silicones
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no volatile byproduct but H2 may be released when moisture and hydrides combined
Pt/Pd is added to help prevent H2 formation |
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What are some other advantages of addition silicones
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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 |
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what are some disadvantages of addition silicones
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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 |
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what are some uses for addition silicones
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teeth prepped for C&B, inlays, onlays
also edentulous ridge impressions for dentures |
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what is an ether
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has a C-O-C bond and usually has aromatic odor
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what is the composition of a polyether material
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base - polyether pre polymer, colloidal silica filler, glycolether or phthalate plasicizer
accelerator - sulfonate ester initiator, imine catalyst(may be skin sensitizer) |
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what are the characteristics of a polyether material
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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 |
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Which nonaqueous elastomer is the least hydrophobic
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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
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what are the uses of polyethers
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teeth prepped for C&B, inlays, onlays
edentulous ridges for denture impressions(IF NO UNDERCUTS) |
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what are some clinical implications of polyethers
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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 DONT USE FOR IMPRESSION OF SUBGINGIVAL REGION |
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Know relative ranking of these properties for Elastomeric Impression materials
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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 |
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describe the setting reaction of a gypsum stone
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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
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What is the initial setting time(working time) of gypsum stone
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approx 3 minutes clinically its when you get "loss of gloss"
finaly setting time is approx 15 minutes |
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What are the factors that atler setting time of gypsum stone
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W/P ratio - as w/p increases setting time increases while strength and setting expansion decrease
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What is the correlation between W/P ratio and initial setting times
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as W/P goes down the setting time gets less
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what are some factors that can alter setting time of gypsum stone products
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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. |
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what does normal setting expansion of a gypsum stone product in air depend on
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W/P ratio
spatulation rate and duration type of gypsum product |
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Which gypsum product experiences the least amount of expansion upon settin
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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%) |
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what is hygroscopic setting expansion when related to gypsum stone
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setting under water at a higher temp. Results in more than twice the normal setting expansion
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Is dry strength of gypsum more or less than wet(green) strength after 1 hour of set material
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Its more, 2 or more times
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What does strength of gypsum depend upon
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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) |
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Reproduction of the cast surface detail
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# air bubbles correlated with wettability of impression material
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What is abrasion resistance and surface hardness of a gypsum stone proportional to
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compressive strength
they are improved by addition of gypsum hardners |
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What is the effect of the W/P ratio on wet and dry compressive strengths
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as the W/P ratio gets smaller the wet compressive strengths increase. the dry strengths dont change appreciably
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what is the tendency of a material to absorb water from the air called
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hydroscopic property
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What is a method used to sterilize gypsum casts of a patient with a known infection
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Overnight gas sterilization
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what do you use to disinfect gypsum casts
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iodophors or 1:10 Na Hypochlorite or use a gypsum product containing disinfectant(will cause slight deterioration in properties)
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What are some of the special gypsum products
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Orthodontic plaster, mounting plaster and mounting stone
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