Define and describe resistance form and identify the specific features, with criteria, that address it in the class I occlusal cavity preparation. (pp. 304-306)
- Resistance form refers to the ability of the filled prepation to withstand the occlusal force associated with mastication and normal use.
- The criteria are listed as follows.
- (a) A pulpal wall depth of 1.5-1.9 mm. (for adequate thickness given compressive and tensile properties of restorative material)
- (b) Pulpal wall (or floor) parallel to occlusal surface (may be tilted in some premolars)
- (c) The pulpal floor should be smooth, flat and even throughout the prep – this helps the tooth resist occlusal loading by virtue of being at right angles to those forces of mastication.
- (d) Resist the extension of the external walls (keep as small as possible) to allow strong cusp and ridge areas to remain with sufficient dentin support.
- (e) The dovetail segments should be divergent to eliminate the possibility of undermined enamel
- (f) Dovetail placement should be at least 1 mm from edge of marginal ridge in order to not undermine the integrity of this ridge
- (g) To have slight rounding of internal line angles to reduce stress concentrations in the tooth structure.