A rest is a metal part of a partial denture that ensures stability by distributing chewing forces.
Key Terms:
Rest Prep: The process of preparing the tooth to create a rest seat.
The process of preparing the tooth to create a rest seat.
Involves shaping the tooth to accommodate the rest.
Ensures the partial denture sits properly and provides optimal function.
Rest Seat: Tooth preparation to accommodate the rest.
A prepared area or divot in the tooth where the rest sits.
Created during the rest prep process.
Ensures the rest fits flush and stable in the mouth.
Rest: Metal component of a partial denture for support.
A metal extension of a partial denture.
Fits into the rest seat to provide support by transferring chewing forces to the teeth.
Types include occlusal, lingual, and incisal rests.
 | The deepest part of an occlusal rest preparation should be inside the lowered marginal ridge at X. The marginal ridge is lowered to provide bulk and to accommodate the origin of the occlusal rest with the least occlusal interference. |
 | Occlusal rest seat preparation on molar. The preparation is rounded, and the triangular concavity has smooth margins on the occlusal surface and a lowered, rounded marginal ridge. |
 | The occlusal rest should be spoon shaped and slightly inclined apically from the marginal ridge. The rest should restore the occlusal morphology of the tooth that existed before preparation of the rest seat. |
 | The floor of the occlusal rest seat should be inclined apically from the lowered marginal ridge. Any angle less than 90 degrees is acceptable as long as the preparation of the proximal surface and lowering and rounding of the marginal ridge precede completion of the rest seat itself. |
| The result of force applied to an inclined plane when the floor of the occlusal rest preparation inclines apically toward the marginal ridge of the abutment tooth. F, Occlusal force applied to the abutment tooth. AB, Relationship of the occlusal rest to the abutment tooth when the angle is greater than 90 degrees. ABC, Removable partial denture framework. ABD, Abutment tooth. |
Types of Rests:
Occlusal Rest: Positioned on the chewing surface of a tooth.
Lingual Rest: Located on the tongue side of a tooth.
Incisal Rest: Placed on the biting edge of an anterior tooth.
Occlusal Rest Seats
Occlusal rest seats are prepared next to an edentulous space the morphology follows conventional form
Single occlusal rest seat is prepared next to an adjacent tooth
Lingual line angle is flared more dramatically to provide additional space for the minor connector
Embrasure occlusal rest seats
Additional tooth structure is removed in the marginal areas to provide at least 1.5 mm of room for the embrasure clasps.
The rest seats are flared more dramatically to the facial and the lingual line angles to provide additional space for the retentive arms and minor connector.
The floor of the rest seat should be inclined towards the centre of the tooth, so that the angle formed by the rest and the minor connector should be less than 90 degrees. This helps to direct the occlusal forces along the long axis of the tooth.
The floor of the rest seat should be concave or spoon shaped to create a ball-and-socket type of joint. This will prevent horizontal stresses and torque on the abutment tooth.
Lingual Rest Seats
An incisal rest seat is usually placed on the mesio- or disto-incisal angle of the incisor teeth with the deepest portion towards the center of the tooth. It is predominantly used as an auxiliary rest or an
indirect retainer.It is usually used on the mandibular incisor where the lower lip can cover, as much as possible, the metal of the rest that shows at the incisal edge.
Preparation Too High: Unnecessary Reduction
Preparation Too Low: Excessive Cingulum Reduction
Composite bonded cingulum rests
correct
incorrect
over-contoured
open margin
Incisal Rest Seats
Lingual view: Forms of a broad inverted "V' maintaining the natural contour often seen in the canine cingulum.
Incisal view: The rest seat is broadest at the central aspect of the canine (approximately 1 mm).
Proximal view: Angulation of the floor of the rest seat (< 90°).
The borders of the rest seat are slightly rounded to avoid sharp line angles in its preparation.