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Rests & Rest SeatsRests & Rest Seats
RestRest• A rigid component resting in a recessed A rigid component resting in a recessed
preparation on the occlusal, lingual or preparation on the occlusal, lingual or incisal surfaceincisal surface
• Provides vertical supportProvides vertical support
Rest SeatRest Seat
• Portion of a tooth prepared to receive a Portion of a tooth prepared to receive a restrest
FunctionsFunctions
• Direct forces along long axis of abutmentDirect forces along long axis of abutment
FunctionsFunctions• SUPPORT - prevents denture base from SUPPORT - prevents denture base from
moving cervically & impinging gingivamoving cervically & impinging gingivaSlides down inclineSlides down incline
Fractured abutment, no rest seat
Major connector imbeds into tissue
FunctionsFunctions
• Maintain a clasp -tooth relationshipMaintain a clasp -tooth relationship
FunctionsFunctions
• Prevent extrusion of abutmentsPrevent extrusion of abutments• Provide reference for relines or Provide reference for relines or
impressionsimpressions
FunctionsFunctions
• Act as indirect retainerAct as indirect retainer− Prevents rotation (Class I or II RPD’s Prevents rotation (Class I or II RPD’s
only)only)
Preparation of Rest SeatsPreparation of Rest Seats
• Light pressure Light pressure • High-speed handpieceHigh-speed handpiece• +/- Waterspray+/- Waterspray• Minimal heat is generatedMinimal heat is generated
Preparation of Rest SeatsPreparation of Rest Seats
• Keep in enamelKeep in enamel• No anesthesiaNo anesthesia
Preparation of Rest SeatsPreparation of Rest Seats
• Occlusal Rest SeatsOcclusal Rest Seats− Diamonds Diamonds
• 8801- 0148801- 014• 38006 -13538006 -135
− Medium round Medium round carbide burs carbide burs • #2, #2, #4#4
8801- 0148801- 014
Preparation of Rest SeatsPreparation of Rest Seats
• Cingulum Rest Seats & Cingulum Rest Seats & Guiding PlanesGuiding Planes− Long, medium Long, medium
diameter cylindrical diameter cylindrical bur or diamond (e.g. bur or diamond (e.g. #57L; #57L; 8837K-0148837K-014))
8837K-0148837K-014
Rest Seat FormRest Seat Form
• Smooth flowing outline form (i.e. no Smooth flowing outline form (i.e. no sharp line angles)sharp line angles)
Occlusal Rest Seat FormOcclusal Rest Seat Form
• Rounded triangular shape Rounded triangular shape − Apex near center of toothApex near center of tooth
Occlusal Rest Seat FormOcclusal Rest Seat Form
• Base of triangle should be one third the Base of triangle should be one third the bucco-lingual width of the toothbucco-lingual width of the tooth
Occlusal Rest Seat FormOcclusal Rest Seat Form
• Marginal ridge must be lowered and Marginal ridge must be lowered and rounded 1-1.5mmrounded 1-1.5mm− Bulk of metal to prevent fractureBulk of metal to prevent fracture
Occlusal Rest Seat FormOcclusal Rest Seat Form
• Floor inclined towards the center Floor inclined towards the center • Angle formed by rest and minor Angle formed by rest and minor
connector should be less than 90connector should be less than 9000
Occlusal Rest Seat FormOcclusal Rest Seat Form
• Deepest portion is centralDeepest portion is central
Occlusal Rest Seat FormOcclusal Rest Seat Form
• Floor should be concave or spoon shaped Floor should be concave or spoon shaped ball-&-socket jointball-&-socket joint
• Prevents horizontal stresses & torquePrevents horizontal stresses & torque
Occlusal Rest Seat FormOcclusal Rest Seat Form
• Directs the occlusal forces along the long Directs the occlusal forces along the long axis of the toothaxis of the tooth
• Prevent orthodontic movementPrevent orthodontic movement
““Positive” Rest SeatsPositive” Rest Seats
• An explorer tip will not slide off the rest An explorer tip will not slide off the rest seatseat
a
Explorer willNOT slip off restseat if pulledproximallly Explorer WILLslip off rest seatif pulledproximallly‘Positive’ Rest Seat(< 90°) Rest Seat not ‘Positive’(>90°)
Occlusal Rest Seat FormOcclusal Rest Seat Form
• Conventional FormConventional Form
Occlusal Rest Seat FormOcclusal Rest Seat Form
• Adjacent ToothAdjacent Tooth− Rest not flared to facial line angleRest not flared to facial line angle− Lingual flared more - space for minor Lingual flared more - space for minor
connectorconnector
Double Embrasure Rest Seat Double Embrasure Rest Seat FormForm• Adjacent teeth, the form is also modifiedAdjacent teeth, the form is also modified• Flared more dramatically on facial and Flared more dramatically on facial and
lingual line angleslingual line angles
Double Embrasure Rest Seat Double Embrasure Rest Seat FormForm• Provides space for the retentive & Provides space for the retentive &
bracing armsbracing arms• Ensure all line angles are smoothedEnsure all line angles are smoothed
Lingual Rest SeatsLingual Rest Seats
• Usually the canine, due to its well-Usually the canine, due to its well-developed cingulumdeveloped cingulum
• When canine is not available, an incisor When canine is not available, an incisor may be usedmay be used
Cingulum Rest Seat FormCingulum Rest Seat Form
• Inverted “V”Inverted “V”• < 90< 9000
Cingulum Rest Seat FormCingulum Rest Seat Form
• Slightly rounded to avoid sharp line Slightly rounded to avoid sharp line anglesangles
• Test as ‘positive’ with explorer tipTest as ‘positive’ with explorer tip• 1mm depth1mm depth
Correct PreparationCorrect Preparation
Preparation Too HighPreparation Too High
Preparation Too LowPreparation Too Low
Cingulum Rest PreparationCingulum Rest Preparation
• Do not create an enamel undercutDo not create an enamel undercut• Cylindrical bur along the long axis of the Cylindrical bur along the long axis of the
toothtooth
Cingulum Rest Seat PlacementCingulum Rest Seat Placement
• Place in sound tooth structure or Place in sound tooth structure or restorationsrestorations
• Not on amalgam restorationsNot on amalgam restorations• If not prominent or large pulpIf not prominent or large pulp
− Use different toothUse different tooth− Bonded rest seatBonded rest seat− Onlay or crownOnlay or crown
Maxillary Cingulum Rest SeatsMaxillary Cingulum Rest Seats
• Avoid opposing occlusionAvoid opposing occlusion
Maxillary Cingulum Rest SeatsMaxillary Cingulum Rest Seats
• 1.5 - 2.0 mm clearance for metal1.5 - 2.0 mm clearance for metal• Check with articulated modelsCheck with articulated models
Bonded Cingulum RestsBonded Cingulum Rests
• Flat emergence profileFlat emergence profile• Pumice, rinse, etch, bond using rubber Pumice, rinse, etch, bond using rubber
damdam• Ensure cervical composite well adaptedEnsure cervical composite well adapted
Composite Bonded Rest Seat FormComposite Bonded Rest Seat Form
CorrectCorrect OvercontouredOvercontoured OvercontouredOvercontouredOpen marginOpen margin
Round Lingual Rest Seat FormRound Lingual Rest Seat Form
• Mesial of the canine teeth when typical Mesial of the canine teeth when typical cingulum rest contraindicatedcingulum rest contraindicated− Large restorationLarge restoration− Lack of clearance with the opposing Lack of clearance with the opposing
teethteeth− Poor cingulumPoor cingulum
Round Lingual Rest Seat FormRound Lingual Rest Seat Form
• Spoon shaped, similar to occlusal rest seatSpoon shaped, similar to occlusal rest seat• More difficult due to the incline of the More difficult due to the incline of the
lingual surface lingual surface • Easily incorporated into crownsEasily incorporated into crowns
Incisal Rests Incisal Rests • Inferior mechanically & estheticallyInferior mechanically & esthetically• Lingual rest is nearer to the center of Lingual rest is nearer to the center of
rotationrotation− Less torquing potentialLess torquing potential