Rests and Rest Seats

Question 1

Rest

Answer 1

A rigid extension of a fixed or
removable partial denture that
transmits functional forces to
the teeth
and prevents
movement
toward the
mucosa.

Question 2

Rest Seat

Answer 2

The portion of a natural tooth
or cast restoration prepared
to receive an occlusal, incisal,
lingual, internal, or
semi-precision rest

Question 3

Functions of Rests:
(5)

Answer 3

• 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

Question 4

Prevent cervical movement of the RPD
If this is not accomplished,

Answer 4

the underlying hard and soft tissues may be damaged.

Question 5

Guiding Principles of
Rest Seat Preparation:
• Evaluate inter-occlusal/inter-incisal
relationships in both

Answer 5

static & excursive
movements

Question 6

Types of Rests:
(5)

Answer 6

Occlusal
Embrasure
Cingulum
Hooded
Incisal

Question 7

Location of Occlusal Rests:
(2)

Answer 7

Mesial/distal pits of premolars and
molars
Centered over the marginal ridge
whenever possible

Question 8

hape of Occlusal Rest Seats:
(3)

Answer 8

• Concave, “saucer”, “spoon”-shaped
• “Ball and socket” analogy
• Triangular in shape

Question 9

• “Ball and socket” analogy

Answer 9

• Less than half of a sphere

Question 10

• Triangular in shape

Answer 10

• Base of triangle over
marginal ridge

Question 11

Width of Occlusal Rest Seats:
(3)

Answer 11

• One-third the
buccolingual width
• One-half the width
between the cusp
tips
• Do not undermine
the triangular
ridges

Question 12

Depth of Occlusal Rest Seats:
(3)

Answer 12

• 1.0-1.5 mm reduction
over marginal ridge
• 1.5-2.0 mm reduction
at deepest portion
• Deepest portion
located in pit area

Question 13

The floor of rest seat
should incline towards
the axial center, forming
an angle less than —

Answer 13

90

Question 14

Preparation should be

Answer 14

wide and shallow (spoon
shaped/rounded),
rather than narrow and
deep

Question 15

The angle formed by
the occlusal rest and
the vertical minor
connector should be

Answer 15

less than 90 degrees.

Question 16

Extended Occlusal Rest
Designed to ensure

Answer 16

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

Question 17

Location of Embrasure
Rest Seats:
(2)

Answer 17

• Two adjacent posterior teeth
• Often used when no posterior
modification space is present

Question 18

Form of Embrasure Rest Seats
(5)

Answer 18

• 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

Question 19

Embrasure Occlusal Rest
Requires

Answer 19

additional marginal ridge preparation
U-shaped trough to accommodate clasp
assembly
adjacent marginal ridges.
Depth: ~1mm, Width: ~2mm

Question 20

Embrasure Rest Seats
Occlusal clearance is
evaluated by

Answer 20

placing two
pieces of 18-gauge wire
across the preparation.

Question 21

Indications for Lingual
Rest Seats:
(3)

Answer 21

• 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

Question 22

Location & Type of Cingulum Rest
Seats:
(3)

Answer 22

• Thick well-defined cingulum enamel
• Maxillary - cut into enamel
• Mandibular - composite resin

Question 23

Form of Cingulum Rest Seats:
• Proximal view
(2)

Answer 23

• Floor 1 mm wide
• Extends from marginal ridge to marginal
ridge

Question 24

Form of Cingulum Rest Seats:
Incisal view
(2)

Answer 24

• “Crescent”-shaped
• Widest portion at the center

Question 25

Form of Cingulum Rest Seats:
Lingual view
(1)

Answer 25

• Inverted “V”, chevron-shaped

Question 26

Placement of rests on
inclined surfaces
displaces the —
and destroys —.

Answer 26

tooth
bone

Question 27

maxillary cingulum rest seats
avoid

Answer 27

opposing occlusion

Question 28

Lingual Cingulum Rest
 Primarily

Answer 28

maxillary canines

Question 29

Lingual Cingulum Rest
shape

Answer 29

chevron V shaped

Question 30

Lingual Cingulum Rest
Rest seat slopes — slightly

Answer 30

downward
– <90 degree angle with path of insertion

Question 31

Lingual Cingulum Rest
Width of floor:

Answer 31

0.75-2.0 mm

Question 32

Lingual Cingulum Rest
Iniciso-apical depth:

Answer 32

1.0-1.5 mm

Question 33

— does not
exhibit a sufficient thickness
of lingual enamel.

Answer 33

Mandibular canine

Question 34

Lingual Resin-bonded Cingulum
Rest Seat
(4)

Answer 34

 Alternative Mandibular Canine Lingual
Rest
 Lingual cingulum area roughened with
diamond & acid-etch
 Composite resin placed & shaped to
resemble chevron rest seat
 Clinical studies report long-term
success

Question 35

Indications for
Hooded Rests:
(3)

Answer 35

• Mandibular first premolars only
• To provide for increased occlusal support
• Decreases torque by lowering the center
of rotation

Question 36

Hooded Rests:
Not on

Answer 36

distal abutment of
distal extensions

Question 37

Shape of Hooded Rest
Seats:
(2)

Answer 37

• 1.0 - 1.5 mm
reduction
• Extends from
marginal ridge to
marginal ridge

Question 38

Shape of Hooded Rest
Seats:
(2)

Answer 38

• 1.0 - 1.5 mm
reduction
• Extends from
marginal ridge to
marginal ridge

Question 39

Least desirable of all rests

Answer 39

Incisal Rest

Question 40

Indications for Incisal Rest:
• Least desirable of all rests
(3)

Answer 40

• poor esthetics
• occlusal interference
• Increased torquing forces

Question 41

Indications for Incisal Rest:
Primarily used on

Answer 41

mandibular canines

Question 42

Incisal Rests
•Primarily used as an

Answer 42

indirect retainer
and/or auxiliary rest

Question 43

An incisal rest seat should
appear as a

Answer 43

small, V-shaped
notch located 1.5 to 2.0 mm
from the proximal-incisal angle
of the tooth.

Question 44

Rest Fracture (2)

Answer 44

 Under preparation of rest seat-
Minimum of 1 mm reduction is
needed.
 Inadequate thickness of metal