rests & rest seats

8/13/2019 Rests & Rest Seats

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Rests & Rest Seats


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Rest

A rigid component resting in a recessed

preparation on the occlusal, lingual or

incisal surface

Provides vertical support


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Rest Seat

Portion of a tooth prepared to receive a

rest


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Functions

Direct forces along long axis of abutment


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Functions SUPPORT - prevents denture base from

moving cervically & impinging gingiva

Slides down incline

Fractured abutment, no

rest seat


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Major connector imbeds into tissue


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Functions

Maintain a clasp -tooth relationship


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Functions

Prevent extrusion of abutments

Provide reference for relines or

impressions


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Functions

Act as indirect retainer

Prevents rotation (Class I or II RPDs

only)


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Preparation of Rest Seats

Light pressure

High-speed handpiece

+/- Waterspray

Minimal heat is generated


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Keep in enamel

No anesthesia


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Occlusal Rest Seats

Diamonds

8801- 014

38006 -135

Medium roundcarbide burs

#2, #4

8801- 014


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Cingulum Rest Seats &

Guiding Planes

Long, medium

diameter cylindrical

bur or diamond (e.g.

#57L; 8837K-014)

8837K-014


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Rest Seat Form

Smooth flowing outline form (i.e. no

sharp line angles)


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Occlusal Rest Seat Form

Rounded triangular shape

Apex near center of tooth


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Base of triangle should be one third the

bucco-lingual width of the tooth


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Marginal ridge must be lowered and

rounded 1-1.5mm

Bulk of metal to prevent fracture


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Floor inclined towards the center

Angle formed by rest and minor

connector should be less than 900


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Deepest portion is central


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Floor should be concave or spoon shaped

ball-&-socket joint

Prevents horizontal stresses & torque


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Directs the occlusal forces along the long

axis of the tooth

Prevent orthodontic movement


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Positive Rest Seats

An explorer tip will not slide off the rest

seat


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Conventional Form


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Adjacent Tooth

Rest not flared to facial line angle

Lingual flared more - space for minor

connector


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Double Embrasure Rest Seat

Form Adjacent teeth, the form is also modified

Flared more dramatically on facial and

lingual line angles


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Double Embrasure Rest Seat

Form Provides space for the retentive &

bracing arms

Ensure all line angles are smoothed


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Lingual Rest Seats

Usually the canine, due to its well-

developed cingulum

When canine is not available, an incisormay be used


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Cingulum Rest Seat Form

Inverted V

< 900


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Cingulum Rest Seat Form

Slightly rounded to avoid sharp line

angles

Test as positive with explorer tip

1mm depth


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Correct Preparation


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Preparation Too High


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Preparation Too Low


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Cingulum Rest Preparation

Do not create an enamel undercut

Cylindrical bur along the long axis of the

tooth


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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


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Maxillary Cingulum Rest Seats

Avoid opposing occlusion


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Maxillary Cingulum Rest Seats

1.5 - 2.0 mm clearance for metal

Check with articulated models


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Bonded Cingulum Rests

Flat emergence profile

Pumice, rinse, etch, bond using rubber

dam

Ensure cervical composite well adapted


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Composite Bonded Rest Seat Form

Correct Overcontoured Overcontoured

Open margin


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Round Lingual Rest Seat Form

Mesial of the canine teeth when typical

cingulum rest contraindicated

Large restoration

Lack of clearance with the opposing

teeth

Poor cingulum


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Incisal Rests

Inferior mechanically & esthetically Lingual rest is nearer to the center of

rotation

Less torquing potential

rests & rest seats

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