6. Rests and Rest Seats Flashcards
Rests and Rest Seats
Rest:
“a rigid extension of a PRDP which contacts a remaining tooth in a prepared rest seat to transmit ____ and horizontal forces”
Rest Seat:
“the prepared ____ in a tooth or restoration created to receive the occlusal, incisal, cingulum, or lingual rest” (GPT, 1999)
vertical
recess
Primary rest
Component of ____
retainer unit
Secondary rest
Additional rests used for ____ retention or extra support
Used in ____ extension PRDP
direct
indirect
distal
Rests: Primary Purpose
To provide ____ support for the PRDP
Directs and distributes occlusal loads apically down the ____ of the abutment teeth (absorbed by PDL fibers)
vertical stop: prevents ____ and over-displacement of underlying soft tissue
maintains retentive ____ in proper position
vertical
long axis
injury
clasp
Three Forms Of Rests Occlusal Rest -- \_\_\_\_ -- \_\_\_\_ -- \_\_\_\_
conventional
extended
overlay
Three Forms of Rests
Lingual Rest
– ____
– ____
____ Rest
cingulum
ball
incisal
Occlusal Rests “\_\_\_\_” triangular outline form with apex toward \_\_\_\_ of the occlusal surface It should be as \_\_\_\_ as it is wide Premolars: # \_\_\_\_ round bur Large molars: Can use #\_\_\_\_ round bur
rounded center long 6 8
Occlusal Rest Seat Size Guidelines
Size varies from ____ the M-D diameter
____ the cusp tip to cusp tip distance or ____ the B-L width of tooth
1/3 to 1/2
1/2
1/3
Occlusal Rest Seats
The floor of the rest seat
– apical to the ____
– ____ with no sharp edges or line-angles
The angle formed by the rest and the vertical minor connector from which it originates should be ____ than 90°
marginal floor
concave
less
Occlusal Rest Seat Preparation
• ____-shaped rest seat preparation
• The angle formed by the rest and the minor connector from should
be ____ than 90°
• The deepest part of the rest seat should be in ____ of prep
spoon
less
center
1.5 mm Thickness
• At least ____mm thick at thinnest point
• ____mm thick where it crosses the marginal ridge otherwise a potential for fracture of the rest exists as well as the resulting destructive settling of the PRDP into the gingival tissues
- 5
1. 5
Embrasure Clasp Rest Seat Preparation
Two adjacent occlusal rests for ____ clasps
Note: adequate tooth ____ to allow sufficient thickness for rests, ____ connectors and clasp arms
embrasure
reduction
minor
Occlusal Rest Seats
in Metal not Porcelain
Metal ceramic restorations for abutment teeth
Note: ____ preferred in force-bearing areas such as rest seats
metal
Extended Occlusal Rest Seat Preparation Indicated in \_\_\_\_ teeth Splinting Tipped abutments to prevent further tipping Increased support and bracing
> ____ the M-D width of tooth
____ mm in depth
posterior
1/2
1.5 to 2
Extended Occlusal Rest
Extended rest on mandibular molar promotes ____ force direction
axial
CONVENTIONAL PRDP DESIGN
Path of insertion ____ to occlusal plane
– To create favorable ____
– Easy to prepare guide planes
– ____
– Patients often seat PRDP using occlusal force
All rests seat ____
perpendicular
undercuts
repeatable
simultaneously
Guiding Plane Path of Placement
Rests Seat ____
simultaneously
ROTATIONAL PATH PRDP When conventional PRDP will not work Compensate for lack of ideal tooth \_\_\_\_ or contours \_\_\_\_ tipped molar
position
mesially
ADVANTAGES OF ROTATIONAL PATH PRDP Minimal use of \_\_\_\_ Reduced \_\_\_\_ accumulation Reduced number of \_\_\_\_ clasp arms -- Reduced chance of \_\_\_\_ Less tooth \_\_\_\_ than if utilizing precision attachments Improved esthetics
clasps plaque flexible distortion reduction
DISADVANTAGES OF ROTATIONAL PATH PRDP
Technique sensitive
Lab technician must understand the design principles
Rest design may require ____ treatment prior to final prep
Difficult to improve deficient ____
Requires excellent ____ since blockout areas can be fairly large
Requires manual dexterity
restorative
retention
oral hygiene
DUAL PATH PRDP DESIGN
Gordon King, 1978
First path:
- - Approach of the framework to the teeth
- - To gain access to ____
Second path:
– ____ to seated position
Framework cannot be removed without ____ out of undercuts
Only ____ portion of framework required for retention
- - Elimination of some clasp arms
- - Improves cleansibility
- - Improves esthetics
undercuts
rotated
rotating
small
ROTATIONAL PATH DESIGN
Rigid component of the framework acts as retentive component
– ____ connector
– proximal ____
Contacts proximal tooth surface intimately below survey line at ____° tilt
Must gain access by ____ into place
A specially designed ____ is needed
minor
plate
0
rotating
rest
Rotational Path of Placement
Extended Rest on Molar Seated ____
A true rotational path PRDP cannot be seated along a ____ path
first
straight
Overlay Rest and Rest Seat
Restoration of occlusal surface of abutment teeth by the PRDP framework
Indications: Restoration of the occlusal plane \_\_\_\_-erupted teeth Loss of \_\_\_\_ Resistance to further \_\_\_\_ of tooth
Rest seat is ____ to prevent further tipping
Occlusal contacts established with opposing ____
infra OVD tipping beveled dentition
Cingulum Rest
Indications: maxillary ____ and mandibular ____ teeth
Only indicated on incisors when ____ are missing
Preferred to an ____ rest on an anterior tooth
Rest seat is in form of an inverted ____ shaped notch
anterior
incisors
incisal
U or V
Cingulum Rest Seat
Inverted “____” shaped rest prepared with a cylindrical bur; all internal line angles are ____
V
rounded
Cingulum Rest and Rest Seat
Cingulum rest should be placed in a ____ rest seat that prevents gingival movement of the rest thereby causing labial movement of the tooth
positive
Cingulum Rest Seat in Partially-veneered Cast Crown
B-L: ____ “U” or “V”
M-D: ____ “U” or “V”
concave
inverted
Ball Rest and Rest Seat
Indications: ____ teeth
Ball shaped rest resembles small occlusal rest seat
– Allows ____ movements during function of distal extension PRDP
Placed on the ____ half of a tooth at junction of ____ 1/3s
____ reduction required
• If dentin is exposed, preparation may be modified to accept an ____ or composite resin restoration
anterior rotational M or D middle and gingival marginal ridge amalgam
Ball Rest Seat
____ inclined
____ internal form
Prepared with # ____ round bur
apically
rounded
4 or 6
Incisal Rests and Rests Seats
Most frequently indicated on mandibular ____ teeth
Successful if sound abutment tooth and a cast restoration is not ____
Near ____ angles of abutment teeth
Disadvantages:
____ forces generated against abutment teeth (least ____ of rests for anterior teeth)
Unfavorable esthetics
anterior
indicated
incisal
tipping
Incisal Rest Seat Preparation
A small ____-shaped notch approximately ____mm from the proximal-incisal angle of the tooth
Notch is ____ and extends slightly unto facial surface
M-D: ____
B-L: ____
v
1.5 to 2.0
concave
convex
Rests Are Good
Do not ____ the occlusion
Be aware of ____ contacts
Occlusion may affect choice of direct retainer and rest placement
Evaluate occlusion before preparing all rests
destabilize
centric
