Evaluation of Occlusal Rests of Metal Based Removable Partial Dentures

Occlusal rests provide vertical support for removable partial dentures (RPDs). RPDs without occlusal rests are “gum strippers” that adversely affect the gingival margins of teeth. Objective: To evaluate occlusal rest seats for metal based removable partial dentures (MBRPD) prepared by dental students at the UWC Oral Health Centres. Materials and methods: Twenty stone models and the corresponding metal frameworks of MBRPD were examined for the depth, width and length of occlusal rest preparations and the metal thickness of the rests. Models were surveyed for the maximum bucco-lingual (B-L) width of the tooth. The mesio-distal (M-D) length was obtained from the marginal ridges of the tooth. Measurements were made with a modified Digital Calliper, under magnification of 1.5X, by a pre-calibrated observer. The B-L width and M-D length of the rest preparation was compared to the recommended one third B-L width and one third M-D length of the tooth, respectively. The depth of the rest preparation was compared to the minimum recommended depth (1 mm) and the thickness of the metal rest. Data was analysed using a pair-wise comparison (Wilcoxon signed-rank test) at p<0.05. Results: The occlusal rest preparations (B-L width, M-D length and depth) were significantly different (p<0.05) from the recommended preparation dimensions. However, there was no significant difference between the minimum recommended thickness (1 mm) and the actual metal rest thickness. Conclusions: Within the limitations of this study, dental students tend to be conservative when preparing occlusal rests for MBRPD. However, the fabricated metal rests were thicker than the depth of the preparations, suggesting overcompensation by the technicians. Rests less than 1 mm in thickness may fracture, resulting in a lack of support for the MBRPD.