Incisal rests are seated on the incisal edges/angles of anterior teeth, most frequently used on mandibular canines, but may be used on maxillary canines.
Indications
Incisal rests are less desirable than lingual rests for anterior teeth, not indicated on incisors except under exceptional circumstances.
- May be used successfully if abutments are sound and cast restorations are not indicated.
- Predominantly used as auxiliary rests or as indirect retainers.
- If stabilisation of incisors is indicated and placement of a fixed restoration is not warranted, incisal rest may be incorporated into a lingual plate to support these teeth.
Design Considerations
Incisor rests should be positioned near the incisal angles of abutment teeth and depending on the prescribed clasping system, they can be designed for mesioincisal or disto-incisal angles.
- Incisal rest seat: Prepared as a small, V-shaped notch located approximately 1.5 to 2.0 mm from the proximal-incisal angle of the tooth (at the incisal angle of canine or on the incisal edge of incisor).
- Dimensions: 2.5mm wide and 1.5mm deep.
- The deepest part of the preparation should be toward the center of the tooth mesiodistally, apical to the incisal edge.
- The notch should be rounded (beveled both labially and lingually) and should extend slightly onto the facial surface to provide a positive seat for the rest.
- Lingual surface: The enamel should be prepared as a shallow depression to accommodate the minor connector and avoid annoying the tongue. Because of the greater length of this minor connector, care must be taken to ensure its rigidity.
- If an individual tooth is not to be clasped, yet requires an incisal rest, the rest should be placed where it will exert the least impact upon esthetics (mostly, at the distoincisal surface of the abutment).
- The incisal rest should be overcontoured slightly to allow for labial and incisal finishing to the adjoining enamel (similar to finishing done in three-quarter crown or inlay).
Points to Note
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If a cast restoration is planned for an anterior abutment, an incisal rest is never indicated. A lingual rest should be incorporated into the restoration instead.
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Incisal rests are preferred on mandibular canines as this provides definite support with relatively less loss of tooth structure and little display of material.
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Multiple mandibular incisal rests: In case tooth morphology does not permit other designs, use can be justified by following factors,
- May take advantage of natural incisal faceting.
- Can restore defective or abraded tooth anatomy.
- Provide stabilisation.
- Full incisal rests may restore or provide anterior guidance.
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Patient should be thoroughly informed regarding location, form and impact on esthetic, in case of full incisal rests.
References
- Stewart’s Clinical Removable Partial Prosthodontics (4th edition), Rodney D. Phoenix, David R. Cagna, Charles F. DeFreest, Quintessence Books.
- McCracken’s Removable Partial Prosthodontics (13th edition), Alan B. Carr DMD MS, David T. Brown DDS MS, Elsevier.
- The image used is in public domain (Source : Wikimedia Commons).
*This article is an excerpt from the above mentioned books and Medical Sutras does not make any ownership and affiliation claims.