Accurate planning for the framework design of removable partial dentures requires careful analysis of the diagnostic cast with a dental surveyor to determine the optimal path of placement. Some techniques described in the literature are helpful in reorienting the same cast on the surveyor, including the tripod marking method; however, there is a possibility of introducing human errors during marking and repositioning of the tripod points on to the different casts at the same location. Other techniques, which do not require markings on the cast to reorient different casts of the same patient, need specific devices or trays. This article suggests the direct use of a putty-elastomeric orientation index that can be preserved and used multiple times while reorienting different casts of the same patients at various laboratory steps. A putty elastomeric impression material is mixed and adapted on to the diagnostic cast, covering key teeth areas of the cast and incorporating the analyzing rod of the surveyor. Thus there is no need to use a special device or the tray to reorient different casts.
The marginal fit of crowns is a concern for clinicians, and there is no conclusive evidence of any one margin configuration yielding better results than others in terms of marginal fit.
Standardized digital images of maxillary dental casts of 47 subjects were analyzed using MATLAB software whereby the two hamular notches and the incisive papilla defines the Cartesian vertical and horizontal axes, as well as the origin. The angle and length of the midpoints of the anterior teeth, mesiobuccal and distobuccal cusp of the posterior teeth were measured from the origin and denoted as θ(1), …, θ(18) and l(1), …, l(18) respectively. These values were collectively used to represent the shape of each dental cast. Clustering and principal component analyses were employed to find possible groups of dental arches using the above measure of shape. The main result of this study is that the 3 groups of dental arch shape may be represented by the novel feature vector v(k) = (θ(k)(1), l(k)(1), θ(k)(3), l(k)(3), θ(k)(5), l(k)(5), θ(k)(13), l(k)(13)), k = 1, 2, 3. Knowledge of v(k) implies three impression trays should be sufficient in a particular prosthetic dentistry application for Malaysian patients. Further, given that v(k) are accurately measured they may be potential candidates as evidence in specific application of forensic dentistry.