Rest Seats

Question 1

What is a 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

What is a 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

What are the 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

What can happen if rests do not prevent cervical movement of the RPD?

Answer 4

the underlying hard and soft tissues may be damaged

Question 5

What is the guiding principle of rest seat preparation?

Answer 5

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

Question 6

What are the different types of rests?

Answer 6

Occlusal
Embrasure
Cingulum
Hooded
Incisal
Ball

Question 7

Where are the occlusal rests located?

Answer 7

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

Question 8

What are the different shapes of the occlusal rest seats?

Answer 8

• concave/”spoon” shaped
• “ball and socket”
• triangular

Question 9

If an occlusal rest seat is a “ball and socket” type what type of sphere is it?

Answer 9

less than half of a sphere

Question 10

If an occlusal rest seat is triangular in shape, the base of the triangle is…

Answer 10

over the marginal ridge

Question 10

What should the width be of an occlusal rest seat?

Answer 10

• 1/3 of the buccolingual width
• 1/2 the width between cusp tips

Question 10

What should the depth be of an occlusal rest seat over the marginal ridge?

Answer 10

1.0-1.5 mm

Question 11

What should the dpeth be of an occlusal rest seat at the deepest portion?

Answer 11

1.5-2.0 mm

Question 12

Where is the deepest portion of an occlusal rest seat?

Answer 12

pit area of the tooth

Question 13

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

Answer 13

90 degrees

Question 14

Preparation on the tooth for an occlusal rest seat should be…

wide and shallow
or
deep and narrow

Answer 14

wide and shallow

Question 15

What is the purpose of an extended occlusal rest?

Answer 15

• 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

Question 16

Where are embrasure rest seats located?

Answer 16

• two adjacent posterior teeth
  (used when no posterior modification space is present)

Question 17

What is the form of an embrasure rest seat?

Answer 17

• Allow adequate tooth
  reduction: approximately 1 mm
• Prepare “sluiceway” of around 2 mm

Question 18

What does an embrasure occlusal rest require for additional marginal ridge preparation?

Answer 18

U-shaped trough to accommodate clasp assembly adjacent marginal ridges

Question 19

What is the depth and width of the marginal ridge preparation for an embrasure occlusal rest?

Answer 19

Depth: ~1mm
Width: ~2mm

Question 20

How do you determine occlusal clearance for an embrasure rest seat?

Answer 20

placing two pieces of 18-gauge wire across the preparation

Question 21

What are the indications for lingual rest seats?

Answer 21

• canines having a gradual lingual slope
• canines using composite resin
• most anterior teeth if placed in cast restorations

Question 22

Where is a cingulum rest seat located?

Answer 22

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

Question 23

What is the form of cingulum rest seat from the proximal view?

Answer 23

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

Question 24

What is the form of cingulum rest seat from the incisal view?

Answer 24

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

Question 25

What is the form of cingulum rest seat from the lingual view?

Answer 25

• Inverted “V”, chevron-shaped

Question 26

What happens if you place cingulum rests on inclined surfaces?

Answer 26

displaces tooth and destroys bone

Question 27

What is the shape of a lingual cingulum rest?

Answer 27

Chevron “V” shaped

Question 28

Where are lingual cingulum rests usually located?

Answer 28

mostly maxillary canines

Question 29

What is the angle of a lingual cingulum rest seat?

Answer 29

slopes downward slightly
– <90 degree angle with path of insertion

Question 30

What is the width of a lingual cingulum rest?

Answer 30

0.75-2.0 mm

Question 31

What is the iniciso-apical depth of a lingual cingulum rest?

Answer 31

1.0-1.5 mm

Question 32

Why do you sometimes do a lingual resin-bonded cingulum rest seat?

Answer 32

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

Question 33

What is the process of making a lingual resin-bonded cingulum rest seat?

Answer 33

• Lingual cingulum area roughened with diamond & acid-etch
• Composite resin placed & shaped to resemble chevron rest seat

Question 34

Why are incisal rests not used very often?

Answer 34

• poor esthetics
• occlusal interference
• Increased torquing forces

Question 35

Where are incisal rests usually used?

Answer 35

Primarily used on mandibular canines

Question 36

An incisal rest seat should appear as a small, V-shaped notch located __________ from the proximal-incisal angle of the tooth

Answer 36

1.5 to 2.0 mm

Question 37

Minimum of ______ reduction is needed to prevent rest fracture

Answer 37

1 mm