Rests & Rest Seats

Rest Rigid component resting in a recessed preparation on the occlusal, lingual or incisal surface Provides vertical support

Rest Seat Portion of a tooth prepared to receive a rest

Functions SUPPORT - prevents denture base from moving cervically & impinging gingiva Slides down incline Fractured abutment, no rest seat

Major connector imbeds into tissue

Functions Direct forces along long axis of abutment

Functions Maintain a clasp -tooth relationship

Functions Prevent extrusion of abutments Provide reference for relines or impressions

Functions Act as indirect retainer Prevents rotation (Class I or II RPD’s only)

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

Preparation of Rest Seats Keep in enamel No anesthesia

Preparation of Rest Seats Occlusal Rest Seats Diamonds 8801- 014 38006 -135 8801- 014

Rest Seat Form Smooth flowing outline form (no sharp angles)

Occlusal Rest Seat Form Rounded triangular shape Apex near center of tooth

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

Occlusal Rest Seat Form Marginal ridge must be lowered and rounded 1-1.5mm Bulk of metal to prevent fracture

Occlusal Rest Seat Form Begin preparation middle of marginal ridge,1-1.5mm Depth gauge is single width of bur, 1-1.5 mm deep from marginal ridge on either side of bur

Occlusal Rest Seat Form If plan to refine external line angle reduce 1mm Refinement and rounding will deepen Minimizes chance of excessive depth

Occlusal Rest Seat Form After depth gauge preparation widen bucco-lingually 1/3 occlusal width at proximal surface

Avoid Undercuts All axial walls must draw Round burs are good for depth cuts, but leave undercuts unless the operator pulls the bur away from the tooth at widest part of the preparation

Avoid Undercuts Mushroom shaped burs leave slightly divergent walls which minimizes chance of undercuts

Must Draw with Path of Insertion Rest is rigid and framework will not seat if rest seat preparation is undercut with path of insertion Axial walls draw with each other and also with the path of insertion Axial walls do NOT draw with each other NOR with the path of insertion Axial walls draw with each other and with the long axis of the tooth but NOT with the path of insertion

Occlusal Rest Seat Form Floor inclined towards the center Angle formed by rest and minor connector should be less than 900

Occlusal Rest Seat Form Deepest portion is central

Occlusal Rest Seat Form Floor should be concave or spoon shaped ball-&-socket joint Minimizes horizontal stresses & torque

Occlusal Rest Seat Form Directs occlusal forces along long axis Minimizes orthodontic movement

“Positive” Rest Seats Explorer will not slide off rest seat

Occlusal Rest Seat Video

Occlusal Rest Seat Form Conventional Form

Occlusal Rest Seat Form Adjacent Tooth Preparation does not involve proximal contact for facial line angle Lingual flared more - space for minor connector

Double Embrasure Rest Seat Form Adjacent teeth, the form is also modified Flared more on facial & lingual line angles

Double Embrasure Rest Seat Form Provides space for the retentive & bracing arms Ensure all line angles are smoothed

Lingual Rest Seats Usually the canine, due to well-developed cingulum When canine can not be used, incisor may be used

Cingulum Rest Seat Form Inverted “V” < 900

Cingulum Rest Seat Form Slightly rounded to avoid sharp line angles Test as ‘positive’ with explorer tip 1mm depth, 1.5 mm clearance

Correct Preparation

Correct Preparation

Preparation Too High

Preparation Too Low

Preparation of Rest Seats 8837K-014 Cingulum Rest Seats & Guiding Planes Long, medium diameter cylindrical diamond 8837K-014

Cingulum Rest Preparation Do not create an enamel undercut Cylindrical bur from incisal approach

Cingulum Rest Preparation Ensure middle of preparation is full 1-1.5mm Bring bur past midline to ensure middle of rest seat is sufficiently repaired

Cingulum Rest Seat Video

Cingulum Rest Seat Placement Place in sound tooth structure or restorations Not on amalgam restorations If not prominent or large pulp Use different tooth Bonded rest seat Onlay or crown

Maxillary Cingulum Rest Seats Avoid opposing occlusion Minimum of 1.5mm clearance in centric and excurions

Maxillary Cingulum Rest Seats 1.5 mm minimum clearance for metal Check with articulated models when possible

Bonded Cingulum Rests Flat emergence profile Pumice, rinse, etch, bond using rubber dam Ensure cervical composite well adapted

Composite Bonded Rest Seat Form Correct Overcontoured Overcontoured Open margin

Bonded Rest Seat Video

Round Lingual Rest Seat Form Mesial of the canine teeth when typical cingulum rest contraindicated: Lack of clearance with the opposing teeth Poor cingulum Large restoration

Round Lingual Rest Seat Form Spoon shaped, similar to occlusal rest seat More difficult due to incline of lingual surface Easily incorporated into crowns

Incisal Rests Inferior mechanically & esthetically Lingual rest is nearer to the center of rotation Less torquing potential

Bring to Seminar Rooms: Ball burnisher if you have one Box of casts with preparations on them Any typodonts for checking of guiding plane preparations (Surveyor needed for checking)