Download - 05. Rests & Rest Seats
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
Fractured abutment, no rest seat
Major connector imbeds into tissueMajor 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 Occlusal Rest SeatsSeats 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 rest
seat if pulledproximallly
Explorer WILLslip off rest seat
if 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 Adjacent teeth, the form is also modifiedmodified
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 typical cingulum rest contraindicatedcontraindicated Large restorationLarge restoration Lack of clearance with the Lack of clearance with the opposing teethopposing teeth
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