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.