Rest And Rest Seat in Preclinical Prosthodontics

Rest And Rest Seat Introduction

Rest is part of the partial denture framework and the rest seat is prepared on the tooth surface to accommodate rest. If the abutment tooth is restored then the rest seat can be prepared for restoration. This chapter briefly describes the rest and rest seat.

Rest And Rest Seat Definition

Rest:

Part of removable partial denture which transfers forces along the long axis of abutment teeth.

Rest Seat:

The prepared recess in a tooth or restoration is created to receive the occlusal, incisal, cingulum, or lingual rest.

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Functions Of Rest

• It transfers the masticatory load to the abutment teeth.
• It provides a definite vertical stop to the partial denture.
• It prevents the impingement of soft tissue.
• Maintain the clasp in the proper position.
• To prevent extrusion of abutment teeth.
• To provide positive reference seats in rebasing and/or impression procedures.

Types Of Rest

Primary Rest:

It is part of direct retainer assembly. It provides a definite vertical stop to the prosthesis and prevents its displacement toward the tissue. It also transfers lateral and horizontal forces applied on the partial denture to the abutment tooth. This load can be absorbed by the fibers of the periodontal ligaments without damaging the ligaments or bone.

Read and Learn  More: Preclinical Prosthodontics Notes

Auxiliary Rest:

It is used for indirect retention in distal extension cases (class I and class II). It is also called secondary rest. It prevents the movement of partial dentures around the fulcrum.

Rest And Rest Seat Form

Occlusal Rest:

• The outline of an occlusal rest seat is a rounded triangular shape.
• The apex of rest is located toward the center of the tooth.
• The base of the triangular shape is at the marginal ridge.
• Rest should be approximately one-third the buccolingual width of the tooth.
• The marginal ridge must be lowered and rounded to permit a sufficient bulk of metal to prevent fracture of the rest from the minor connector (1–1.5 mm).
• The occlusal rest seat should be shallow and saucer-shaped. The floor of the rest seat should be inclined toward the center of the tooth, and should be less than 90°. This helps to direct the occlusal forces along the long axis of the tooth.

Cingulum or Lingual Rest:

• Used primarily on maxillary canines.
• If in the canine is missing then multiple incisors are used to receive cingulum rest.
• It is more esthetical than incisal rest.
• Less chances of breakage and distortion.

Incisal Rest:

• Commonly used on mandibular canines.
• Positioned near the incisal edge of the abutment tooth.
• For aesthetic reasons, it is placed on the distal surface of the tooth.