Tikrit University – College of Dentistry Dr. Reem Ahmed Sh. – 3th class
cden.tu.edu.iq
RESTANDRESTSEAT
REST:-arigidextensionofpartialdenturewhichrestonocclusal,incisal,andlingualsurfacesofatoothandtousedtodissipatetheforcesthatappliedontheprosthesis.
RESTSEAT:-isthatportionofthetooththathavebeenselectedandpreparedtoreceivearest.
Typesofrest:
1-occlusalrest
2-lingualrest
3-incisalrest
FUNCTIONsOFREST
1- directforcesalongthelongaxisofabutment.2- Verticalstop:-preventsdenturebasefrommovingcervicallyand
impinginggingival.3- maintainaclasp-toothrelationship4- preventextrusionofabutment5- actasindirectretainerpreventrotationincase(CLI&CLII)REQUIREMENTSOFAREST1-shouldhavesufficientthicknessofmetaltopreventbreakageespeciallyoverthemarginalridge.2-Itshouldfittherestseataccuratelywithbeveledmargins,properlycontoured,thuspreventingfoodstagnationorimpaction
Tikrit University – College of Dentistry Dr. Reem Ahmed Sh. – 3th class
cden.tu.edu.iq
OCCLUSALRESTSANDRESTSEATItisessentialthatarestseatbepreparedintheocclusalsurfaceofeachtooththatreceiveocclusalrest1- Itshouldneverbeplacedonatooththathasnotbeen
adequatelyprepared.2- theoutlineformshouldberoughlytriangle,withthebaseof
thetrianglelocatedatthemarginalridgeandtheroundedapexdirectedtowardthecenterofthetooth.
3- itshouldbe(smoothgentlecurve).Sharpangles,walls,and
ledgesmustbeavoided.
4-restseatshouldoccupyonethirdtoonehalfofthemesiodistaldiameterofthetoothandapproximatelyonehalfthebuccolingualwidthofthetoothmeasuredfromcusptiptocusptip.
4- theflooroftherestseatshouldinclinedtowardthecenterofthetooth.
5- theflooroftherestseatshouldbelessthan900sothetransmittedforcescandirectedalongthelongaxisofthetooth.ananglegreaterthan900willcauseslippageoftheprosthesisandorthodonticmovementofabutmenttooth.
Tikrit University – College of Dentistry Dr. Reem Ahmed Sh. – 3th class
cden.tu.edu.iq
6- thedeepestpartshouldlocatednearthecenterofthetooth.7- itshould1-1.5mmthicknessofrest.
OCCLUSALRESTONAMULGUMRESTORATION
Placingocclusalrestsonlargeamalgamrestorationishazardousatbest.Theprimaryreasonforattemptingthisiseconomic,sinceanamalgamrestorationcostslessthanacompletecoveragerestoration(crown).Theunfavourableflowpropertiesandpoortensilecharacteristicsofamalgamincreasetheprobabilityofrestorationfailure.Thepatientshouldinformedoftreatmentoptionsandtheircomplications.
ifwehavetwoocclusalrestoneonthedistalsideofonetoothandanotheronmesialsideonanothertoothiscalled(doubleembrasurerest).
Tikrit University – College of Dentistry Dr. Reem Ahmed Sh. – 3th class
cden.tu.edu.iq
Lingualorcingulumrestandrestseat
usedprimarilyonmaxillarycanines.Thenormalmorphologyofamaxillarycaninepermitspreparationofasatisfactoryrestseatwithminimaltoothreduction.Thethicknessofenamelonthelingualsurfaceofmandibularcaninerarelyallowsalingualresttobeused.Whencanineisnotavailable,anincisorsmaybeused
1- lingualrestseatshouldbepreparedonenamelandithasinvertedVshapeatthejunctionofthegingivalandmiddlethirdofthetoothandtheapexdirectedincisally.
2- donnotcreateanenamelundercut.3- placeonsoundtoothorcastrestoration(crown)4- weshouldnotplaceonamalgamrestoration5- ifwehadprominentpulpwedoingeither
a- onlayorcrownb- usedifferenttooth
6- avoidapposingocclusion
Tikrit University – College of Dentistry Dr. Reem Ahmed Sh. – 3th class
cden.tu.edu.iq
Incisalrestandrestseat
inferiormechanicallyandesthetically,usedfrequentlyonmandibularcanine,theymayusedsuccessfullyifabutmentsaresoundandcastrestorationarenotindicated.
1- incisalrestsshouldbepositionedneartheincisalanglesofabutmentteeth,whatevertheyaredesignedformesioincisalordistoincisalanglesdependsontheprescribedclaspingsystem.
2- appearasasmallVshapenotchlocatedapproximately1.5-2mmfromtheproximal-incisalangleofthetooth.Thedeepestpartofthepreparationshouldbetowardthecenterofthetoothmesio-distaly.Thenotchshouldprovidepositiveseatfortherest.
3- Theenamelonthelingualsurfaceshouldbepreparedasashallowdepressiontoaccommodatetheminorconnectorandavoidannoyingthetongue.
