rest and rest seats Flashcards
rigid extension of a fixed or removable partial denture that transmits functional forces to the teeth and prevents movement toward the mucosa
rest
portion of a natural tooth or cast restoration prepared to receive an occlusal, incisal, lingual ,internal, or semi-precision rest
rest seat
what are the functions of rests
*direct forces down the long axis of teeth
-prevent cervical movement of RPD
-limit lateral movement of RPD
-maintain retentive arm in proper vertical relation
-improve occlusal plane
if preventing cervical movement of RPD is not accomplished by rest,
underlying hard and soft tissues may be damaged
guiding principles of rest seat preparation:
evaulate inter-occlusal/inter-incisal relationships in both static and excursive movements
what are the 5 types of rests
occlusal
embrasure
cingulum
hooded
incisal
location of occlusal rests
-mesial/distal pits of premolars and molars
-centered over marginal ridge whenever possible
shape of occlusal rest seats:
-concave “saucer” “spoon shaped”
-ball and socket
-triangular in shape
width of occlusal rest seats
- one-third the buccolingual width
- one-half the width between the cusp tups
-do not undermine the triangular ridges
depth of occlusal rest seats
-1-1.5mm reduction over marginal ridge
-1.5-2mm reduction at deepest portion
-deepest portion located in pit area
the floor of rest seat should incline towards the axial center, forming an angle
less than 90 degrees
rest seat preparation should be (wide/narrow) and (shallow/deep)
wide and shallow
designed to ensure max bracing from the tooth. this rest would ensure that the forces are directed down the long axis of abutment and therefore the disto-occlusal rest would not have been needed
extended occlusal rest
location of embrasure rest seats:
used when:
-two adjacent posterior teeth
-often used when no posterior modification space is present
the embrasure rest seat follows the form of
of occlusal rest
where are the occlusal rests are placed on
adjacent posterior teeth
adequate tooth reduction for embrasure rest seats
1mm
-prepare “sluiceway” of around 2mm
what requires additional marginal ridge preparation u-shaped trough to accomodate clasp assembly
depth: 1mm
width:
embrasure occlusal rest
depth 1mm
width: 2mm
how is the occlusal clearance evaluated for embrasure rest seats
by placing two pieces of 18-gauge wire across the preparation
indications for lingual rest seats
- can be prepared in canines having gradual lingual slop
- can be prepared in canines using composite resin
- may be used on most anterior teeth if placed in cast restorations
location and type of cingulum rest seats
- thick well- defined cingulum enamel
- maxillary- cut into enamel
- mandibular- composite resin
form of cingulum rest seats proximal view
-floor 1mm wide
-extends from marginal ridge to marginal ridge
form of cingulum rest seats incisal view
“crescent” shaped
widest portion at the center
form of cingulum rest seats lingual view
inverted V, chevron-shaped
if rest is placed on inclined surfaces, what happens
displaces tooth and destroys bone
with maxillary cingulum rest seats, what do you want to avoid
avoid opposing occlusion
where are lingual cingulum rests primarily on
maxillary canines
shape of lingual cingulum rests
chevron V shape
lingual cingulum rest measurements
-rest seat slopes downward slightly: 90 degree angle with path of insertion
-width of floor: 0.75-2.0mm
-inciso-apical depth: 1.0-1.5mm
mandibular canine does not exhibit a sufficient thickness of lingual enamel, so
must use lingual resin-bonded cingulum rest seat
how is lingual resin-bonded cingulum rest seat made
-lingual cingulum area roughened with diamond and acid-etch
-composite resin placed and shaped to resemble chevron rest seat
-clinical studies report long-term success
indications for hooded rests:
- mandibular first premolars only
- to provide for increased occlusal support
- decreases torque(twisting) by lowering the center
where are hooded rests not on with mand first premolars
not on distal abutment of distal extensions
shape of hooded rest seats
1-1.5mm reduction
extends from marginal ridge to marginal ridge
least desirable of all rests
-poor esthetics
-occlusal interferences
-increased torquing forces
incisal rests
where are incisal rests primarily used on
mandibular canines
what rest is primarily used an indirect retainer and/or auxillary rest
incisal rests
how should incisal rest seat
appear as small, V-shaped notch located 1.5-2.0mm from the proximal-incisal angle of the tooth
under preparation of rest seat, minimum of what reduction is needed to prevent rest fracture
1mm
