rests & rest seats. rest a rigid component resting in a recessed preparation on the occlusal,...

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 seatFractured abutment, no rest seat

Major connector imbeds into tissueMajor 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 RPDPrevents rotation (Class I or II RPD’’s 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

8801- 0148801- 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

““PositivePositive”” Rest Seats Rest Seats

Explorer tip will not slide off the rest seatExplorer tip will not slide off the rest seat

Avoid UndercutsAvoid Undercuts

Must draw along path of insertionMust draw along path of insertion

Occlusal Rest Seat MovieOcclusal Rest Seat Movie

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 Inverted ““VV ”” < 90< 9000

Cingulum Rest Seat FormCingulum Rest Seat Form

Slightly rounded to avoid sharp line Slightly rounded to avoid sharp line anglesangles

Test as Test as ‘‘positivepositive’’ with explorer tip with explorer tip 1mm depth1mm depth

Correct PreparationCorrect Preparation

Preparation Too HighPreparation Too High

Preparation Too LowPreparation Too Low

Preparation of Rest SeatsPreparation of Rest Seats

Cingulum Rest Seats & Cingulum Rest Seats & Guiding PlanesGuiding Planes Long, medium Long, medium

diameter cylindrical diameter cylindrical diamond diamond 8837K-0148837K-014

8837K-0148837K-014

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 MovieCingulum Rest Seat Movie

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

Bonded Rest Seat MovieBonded Rest Seat Movie

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 teethLack of clearance with the opposing teeth 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

Bring to Seminar Rooms:Bring to Seminar Rooms:

Ball burnisher if you have oneBall burnisher if you have one Boxof casts with prepartions on themBoxof casts with prepartions on them Any typodonts for checking of guiding Any typodonts for checking of guiding

plane preparations (Surveyor needed for plane preparations (Surveyor needed for checking)checking)