assay exam questions & answers (sample 8)：实验试题及答案（8例）

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1、AssayExamquestions&answers(Sample8):§HowtoincreaseretentionandresistanceofFPD?Retention:Resistancetodislodgementofthecrownintheocclusaldirection1)walltaper:6degrees(3degreesperwall):Jorgensen1955-idealtaper2-6.5degrees;Shillingburg'sowntaperis14.3degree

2、s;Mack(1984)-need12degreetapersothatyoucanseedownwallswith1eye2)taperhasexponentialrelationshiptoretention,surfaceareahasdirectrelationship3)areaundershear:toutilizeshearstrengthofcement,musthaveopposingwalls;reducepathofremovaltoonedirection4)surfacero

3、ughness:mechanicalinterlockingofcement:Felton&Kanoy(1987)diamonds-31%increasedretentionovercarbidesResistance:-oppositiontodislodgementofthecrowninallnon-occlusaldirection-rotationaboutcrownmargins-groovesshortentheradiusaboutthemarginfulcrumpoint1)leve

4、rage-tangentpoint2)preplength3)toothwidth-thenarrowerthetooththegreateritcanresisttippingcomparedtowidertooth4)taper:Parker(1988)-conceptoflimitingtaper;resistiveandnon-resistiveportionofpreparation;someprepswithtaperof0degarenon-resistivewhilesomewith4

5、5degtaperareresistiveOcclusalreduction:Au-1.5mmworkingcusp,I.0mmnon-workingcuspsPFM-2.0mmworkingcusps,1.5mmnon-workingcusps§Howdosemetalbondtoporcelain?1.Mechanicalretention-airabrasioneliminatessurfaceirregularities(stresses);increasessurfacearea2.Vand

6、erWaalsforces(weak)-mattefinishwithaluminumoxide,airabrasioninc.wettingbyporcelain3.Compressionbonding-porcelainstrongestundercompression;CTEmetal>CTEporcelain4.Chemicalbonding(mostimportant)-convalentandionicbonds;usesoxidelayer§Writeanassayaboutcastin

7、gInvestments.BeautyCast-CalciumSulfatebondedinvestmentSettingExpansion0.35%>HygroscopicExpansion1.50%>ThermalExpansion(900'F)0.55%>compensatefor1.25-1.7%coldshrinkageThermalExpansion(1200-1300'F)1.20%>CompressiveStrength:wet-500psi,dry-1000psiComponents

8、:Binder:Gypsum25-45%Refractory:Silica65-75%(regulatesthermalexpansion)Modifiers:BoricAcid/NaCl5%(regulatesettingexp&settingtime)ADASpec#2Type11investment:hygroscopicexpansionmin1.2%/max2.2%increaseW/P:lessHSEshortermixing:lessHSE