Removable partial denture Rests & Rest Seat

Rest A rigid component resting in a recessed preparation on the occlusal, lingual or incisal surface

Rest Seat Portion of a tooth prepared to receive a rest

1.provide vertical support (direct force along long axis of abutment). Functions: 1.provide vertical support (direct force along long axis of abutment).

2 SUPPORT - prevents denture base from moving cervically & impinging gingiva Fractured abutment, no rest seat

3 Maintain a clasp -tooth relationship

4 Act as indirect retainer Prevents rotation (Class I or II RPD only)

Types of the rests: A. Occlusal Rest: 1. Occlusal Rest (Conventional) 2.Extended Occlusal Rest 3. interproximal Occlusal Rest 4. Internal Occlusal Rest B. lingual Rest (Cingulum Rest) C. Incisal Rest D. implants as Rest

1. Occlusal rest: Is a rigid extension of partial denture which is located on occlusal surface of the molars and premolars teeth to provide vertical support for the R.P.D.

Form and location: 1. The outline form of an occlusal rest seat should be a rounded triangular shape with apex toward the center of the occlusal surface

Form and location: 2. It should be as long as it is wide, and the base of the triangular shape (at the marginal ridge) should be at least (2.5 mm) for both molars and pre molars.

Form and location: 3. The marginal ridge of the abutment tooth at the site of the rest seat must be lowered to permit a sufficient bulk of metal for strength and rigidity of the rest and minor connector (the reduction of the marginal ridge of approximately 1.5mm.

Form and location: 4. The floor of the occlusal rest seat should be apical to the marginal ridge and the occlusal surface should be concave, or spoon shape.

Form and location: 5. The angle formed by the occlusal rest and the vertical minor connector form which it originate should be less than 90 degree.

Occlusal rest Note: only in this way can the occlusal forces be directed along axis of the abutment tooth.an angle greater than 90 degree fails to transmit occlusal forces along the supporting vertical axis of the abutment, this also permits slippage of the prosthesis away from the abutment, which can results in orthodontic like movement of the tooth.

2. Lingual rest and rest seat: Is rigid extension on the canine and incisors teeth.

Lingual rest and rest seat Note: lingual rest is preferable to an incisal rest because: . More esthetically acceptable than incisal rests.

Lingual rest and rest seat Note: lingual rest is preferred on maxillary anterior teeth especially in the canine than mandibular anterior teeth because: Smaller bulk of the tooth (lack of enamel thickness).

Lingual rest and rest seat

3. Incisal rest and rest seat: The incisal rest are placed at the incisal angles of the anterior teeth and on the prepared rest seat, they are generally placed on enamel.

Incisal rest and rest seat -incisal rests may be used on a canine abutment in both arch and it is more used for mandibular canine.

Form and location: -Incisal rest seat should be approximately (2.5mm) wide and (1.5mm) deep so that the rest will be strong without having to exceed the natural contour of the incisal edge.

Incisal rest and rest seat

D. implant as a rest Implants can also be considered to serve as a rest when one takes advantage of the vertical stiffness characteristic they possess. In this application, they can serve to resist tissue ward movement alone and may be considered useful for retentive needs as well. When implant used as a rest, implants can serve to efficiently resist vertical movement and provide positive support. This use allows a low profile connection (i.e., close to the ridge),