rests & rest seats
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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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Preparation of Rest Seats
Keep in enamel
No anesthesia
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Preparation of Rest Seats
Occlusal Rest Seats
Diamonds
8801- 014
38006 -135
Medium roundcarbide burs
#2, #4
8801- 014
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Preparation of Rest Seats
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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Occlusal Rest Seat Form
Base of triangle should be one third the
bucco-lingual width of the tooth
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Occlusal Rest Seat Form
Marginal ridge must be lowered and
rounded 1-1.5mm
Bulk of metal to prevent fracture
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Occlusal Rest Seat Form
Floor inclined towards the center
Angle formed by rest and minor
connector should be less than 900
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Occlusal Rest Seat Form
Deepest portion is central
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Occlusal Rest Seat Form
Floor should be concave or spoon shaped
ball-&-socket joint
Prevents horizontal stresses & torque
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Occlusal Rest Seat Form
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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Occlusal Rest Seat Form
Conventional Form
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Occlusal Rest Seat Form
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
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