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:

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

failure to prevent cervical RPD movement

Answer 4

If this is not accomplished, the underlying hard and soft tissues may be damaged.

Question 5

Guiding Principles of Rest Seat Preparation:

Answer 5

• Evaluate inter-occlusal/inter-incisal relationships in both static & excursive movements

Question 6

Types of Rests:

Answer 6

Occlusal
Embrasure
Cingulum
Hooded
Incisal

Question 7

Location of Occlusal Rests:

Answer 7

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

Question 8

deepest portion of posterior occlusal rest seat

Answer 8

pit area

Question 9

shape of occlusal rest seats

Answer 9

• Concave, “saucer”, “spoon”-shaped
• “Ball and socket” analogy
• Less than half of a sphere
• Triangular in shape
• Base of triangle over marginal ridge

Question 10

Width of Occlusal Rest Seats: undermine?

Answer 10

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

Question 11

Depth of Occlusal Rest Seats:

Answer 11

• 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 12

the floor of occlusal rest seat prep angle

Answer 12

The floor of rest seat should incline towards the axial center, forming an angle less than 90

Question 13

occlusal line angles of rest preps shape

Answer 13

rounded

Question 14

should occlusal rest seats be deep and narrow

Answer 14

no, shallow and wide

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

Answer 16

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
diverge walls for placement

Question 17

Location of Embrasure Rest Seats:
used when?

Answer 17

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

Question 18

Form of Embrasure Rest Seats

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

additional prep of embrasure occlusal rests

Answer 19

Requires 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 evaluation

Answer 20

Embrasure Rest Seats
Occlusal clearance is
evaluated by placing two
pieces of 18-gauge wire
across the preparation.

Question 21

Indications for Lingual
Rest Seats:

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:

Answer 22

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

Question 23

Form of Cingulum Rest Seats: proximal, lingual and incisal views

Answer 23

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

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

• Lingual view
• Inverted “V”, chevron-shaped

Question 24

placement of cingulum rest on an inclined surface? (ie no seat)

Answer 24

Placement of rests on inclined surfaces displaces the tooth and destroys bone.

Question 25

what should be avoided with cingulum rest seats

Answer 25

the opposing occlusion

Question 26

Lingual Cingulum Rest of Primarily maxillary canines form

Answer 26

 Chevron “V” shaped
 Rest seat slopes downward slightly– <90 degree angle with path of insertion
 Width of floor: 0.75-2.0 mm
 Iniciso-apical depth: 1.0-1.5 mm

Question 27

Lingual Resin-bonded Cingulum Rest Seat when/why?

Answer 27

Mandibular canine does not
exhibit a sufficient thickness
of lingual enamel.

Question 28

Lingual Resin-bonded Cingulum Rest Seat procedure

Answer 28

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

Question 29

Indications for Hooded Rests:
when not used?

Answer 29

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

Not on distal abutment of distal extensions

Question 30

Shape of Hooded Rest
Seats:

Answer 30

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

Question 31

Indications for Incisal Rest and cons
desireable?
esthetics?
occlusion?
torque?
used on which teeth most commonly?

Answer 31

• Least desirable of all rests
• poor esthetics
• occlusal interference
• Increased torquing forces
• Primarily used on mandibular canines

Question 32

Incisal Rests Primarily used as

Answer 32

an indirect retainer and/or auxiliary rest

Question 33

incisal rest seat form

Answer 33

An incisal rest seat should appear as a small, V-shaped notch located 1.5 to 2.0 mm from the proximal-incisal angle of the tooth.

Question 34

Rest Fracture

Answer 34

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