Rests and Rest Seats Flashcards
Rest
A rigid extension of a fixed or
removable partial denture that
transmits functional forces to
the teeth
and prevents
movement
toward the
mucosa.
Rest Seat
The portion of a natural tooth
or cast restoration prepared
to receive an occlusal, incisal,
lingual, internal, or
semi-precision rest
Functions of Rests:
(5)
• Direct forces down the long axis of
teeth
• Prevent cervical movement of the RPD
• Limit lateral movement of the RPD
• Maintain retentive arm in proper
vertical relation
• Improve the occlusal plane
Prevent cervical movement of the RPD
If this is not accomplished,
the underlying hard and soft tissues may be damaged.
Guiding Principles of
Rest Seat Preparation:
• Evaluate inter-occlusal/inter-incisal
relationships in both
static & excursive
movements
Types of Rests:
(5)
Occlusal
Embrasure
Cingulum
Hooded
Incisal
Location of Occlusal Rests:
(2)
Mesial/distal pits of premolars and
molars
Centered over the marginal ridge
whenever possible
hape of Occlusal Rest Seats:
(3)
• Concave, “saucer”, “spoon”-shaped
• “Ball and socket” analogy
• Triangular in shape
• “Ball and socket” analogy
• Less than half of a sphere
• Triangular in shape
• Base of triangle over
marginal ridge
Width of Occlusal Rest Seats:
(3)
• One-third the
buccolingual width
• One-half the width
between the cusp
tips
• Do not undermine
the triangular
ridges
Depth of Occlusal Rest Seats:
(3)
• 1.0-1.5 mm reduction
over marginal ridge
• 1.5-2.0 mm 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
Preparation should be
wide and shallow (spoon
shaped/rounded),
rather than narrow and
deep
The angle formed by
the occlusal rest and
the vertical minor
connector should be
less than 90 degrees.
Extended Occlusal Rest
Designed to ensure
maximum bracing from
the tooth. The extended rest would ensure that the
forces are directed down the long axis of the abutment,
and therefore the disto-occlusal rest would not have
been needed
Location of Embrasure
Rest Seats:
(2)
• Two adjacent posterior teeth
• Often used when no posterior
modification space is present
Form of Embrasure Rest Seats
(5)
• Follows form of occlusal rest
• Occlusal rests are placed on
adjacent posterior teeth
• Avoid eliminating the contact
point
• Allow adequate tooth
reduction:
approximately 1 mm
• Prepare “sluiceway”
of around 2 mm
Embrasure Occlusal Rest
Requires
additional marginal ridge preparation
U-shaped trough to accommodate clasp
assembly
adjacent marginal ridges.
Depth: ~1mm, Width: ~2mm
Embrasure Rest Seats
Occlusal clearance is
evaluated by
placing two
pieces of 18-gauge wire
across the preparation.
Indications for Lingual
Rest Seats:
(3)
• Can be prepared in canines
having a gradual lingual slope
• Can be prepared in canines using
composite resin
• May be used on most anterior
teeth if placed in cast
restorations
Location & Type of Cingulum Rest
Seats:
(3)
• Thick well-defined cingulum enamel
• Maxillary - cut into enamel
• Mandibular - composite resin
Form of Cingulum Rest Seats:
• Proximal view
(2)
• Floor 1 mm wide
• Extends from marginal ridge to marginal
ridge
Form of Cingulum Rest Seats:
Incisal view
(2)
• “Crescent”-shaped
• Widest portion at the center
