Rests & Rest SeatsRests & Rest Seats

RestRest A rigid component resting in a A rigid component resting in a recessed preparation on the recessed preparation on the occlusal, lingual or incisal surfaceocclusal, lingual or incisal surface

Provides vertical supportProvides vertical support

Rest SeatRest Seat Portion of a tooth prepared Portion of a tooth prepared to receive a restto receive a rest

FunctionsFunctions Direct forces along long axis Direct forces along long axis of abutmentof abutment

FunctionsFunctions SUPPORT - prevents denture base from SUPPORT - prevents denture base from moving cervically & impinging gingivamoving cervically & impinging gingiva

Slides down Slides down inclineincline

Fractured abutment, no rest seat

Major connector imbeds into tissue

FunctionsFunctions Maintain a clasp -tooth Maintain a clasp -tooth relationshiprelationship

FunctionsFunctions Prevent extrusion of abutmentsPrevent extrusion of abutments Provide reference for relines Provide reference for relines or impressionsor impressions

FunctionsFunctions Act as indirect retainerAct as indirect retainer

Prevents rotation (Class I Prevents rotation (Class I or II RPD’s only)or II RPD’s only)

Preparation of Rest Preparation of Rest SeatsSeats Light pressure Light pressure High-speed handpieceHigh-speed handpiece +/- Waterspray+/- Waterspray Minimal heat is generatedMinimal heat is generated

Preparation of Rest Preparation of Rest SeatsSeats Keep in enamelKeep in enamel No anesthesiaNo anesthesia

Preparation of Rest Preparation of Rest SeatsSeats 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 Preparation of Rest SeatsSeats Cingulum Rest Cingulum Rest Seats & Guiding Seats & Guiding PlanesPlanes Long, medium Long, medium diameter diameter cylindrical bur cylindrical bur or diamond (e.g. or diamond (e.g. #57L; #57L; 8837K-0148837K-014))

8837K-8837K-014014

Rest Seat FormRest Seat Form Smooth flowing outline form Smooth flowing outline form (i.e. no sharp line angles)(i.e. no sharp line angles)

Occlusal Rest Seat Occlusal Rest Seat FormForm Rounded triangular shape Rounded triangular shape

Apex near center of toothApex near center of tooth

Occlusal Rest Seat Occlusal Rest Seat FormForm Base of triangle should be Base of triangle should be one third the bucco-lingual one third the bucco-lingual width of the toothwidth of the tooth

Occlusal Rest Seat Occlusal Rest Seat FormForm Marginal ridge must be Marginal ridge must be lowered and rounded 1-1.5mmlowered and rounded 1-1.5mm Bulk of metal to prevent Bulk of metal to prevent fracturefracture

Occlusal Rest Seat Occlusal Rest Seat FormForm 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 Occlusal Rest Seat FormForm Deepest portion is centralDeepest portion is central

Occlusal Rest Seat Occlusal Rest Seat FormForm Floor should be concave or Floor should be concave or spoon shaped ball-&-socket spoon shaped ball-&-socket jointjoint

Prevents horizontal stresses Prevents horizontal stresses & torque& torque

Occlusal Rest Seat Occlusal Rest Seat FormForm Directs the occlusal forces along Directs the occlusal forces along the long axis of the tooththe long axis of the tooth

Prevent orthodontic movementPrevent orthodontic movement

““Positive” Rest SeatsPositive” Rest Seats An explorer tip will not An explorer tip will not slide off the rest seatslide off the rest seat

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 Occlusal Rest Seat FormForm Conventional FormConventional Form

Occlusal Rest Seat Occlusal Rest Seat FormForm Adjacent ToothAdjacent Tooth

Rest not flared to facial Rest not flared to facial line angleline angle

Lingual flared more - space Lingual flared more - space for minor connectorfor minor connector

Double Embrasure Rest Double Embrasure Rest Seat FormSeat Form 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 Double Embrasure Rest Seat FormSeat Form 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 Usually the canine, due to its well-developed cingulumits well-developed cingulum

When canine is not available, When canine is not available, an incisor may be usedan incisor may be used

Cingulum Rest Seat Cingulum Rest Seat FormForm Inverted “V”Inverted “V” < 90< 9000

Cingulum Rest Seat Cingulum Rest Seat FormForm Slightly rounded to avoid Slightly rounded to avoid sharp line anglessharp line angles

Test as ‘positive’ with Test as ‘positive’ with explorer tipexplorer tip

1mm depth1mm depth

Correct PreparationCorrect Preparation

Preparation Too HighPreparation Too High

Preparation Too LowPreparation Too Low

Cingulum Rest Cingulum Rest PreparationPreparation Do not create an enamel Do not create an enamel undercutundercut

Cylindrical bur along the Cylindrical bur along the long axis of the toothlong axis of the tooth

Cingulum Rest Seat Cingulum Rest Seat PlacementPlacement Place in sound tooth structure Place in sound tooth structure or restorationsor restorations

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 Maxillary Cingulum Rest SeatsRest Seats Avoid opposing occlusionAvoid opposing occlusion

Maxillary Cingulum Maxillary Cingulum Rest SeatsRest Seats 1.5 - 2.0 mm clearance for 1.5 - 2.0 mm clearance for metalmetal

Check with articulated modelsCheck with articulated models

Bonded Cingulum RestsBonded Cingulum Rests Flat emergence profileFlat emergence profile Pumice, rinse, etch, bond using Pumice, rinse, etch, bond using rubber damrubber dam

Ensure cervical composite well Ensure cervical composite well adaptedadapted

Composite Bonded Rest Seat Composite Bonded Rest Seat FormForm

CorrectCorrect OvercontouredOvercontoured OvercontouredOvercontouredOpen marginOpen margin

Round Lingual Rest Round Lingual Rest Seat FormSeat Form Mesial of the canine teeth when Mesial of the canine teeth when typical cingulum rest contraindicatedtypical cingulum 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 Round Lingual Rest Seat FormForm

Spoon shaped, similar to Spoon shaped, similar to occlusal rest seatocclusal rest seat

More difficult due to the More difficult due to the incline of the lingual surface incline of the lingual surface

Easily incorporated into crownsEasily incorporated into crowns

Incisal Rests Incisal Rests Inferior mechanically & Inferior mechanically & estheticallyesthetically

Lingual rest is nearer to the Lingual rest is nearer to the center of rotationcenter of rotation Less torquing potentialLess torquing potential