An accuracy evaluation of four removable die systems

The advent of implant dentistry has redefined the need for accuracy of working cast models. Die stone expansion and errors introduced by removable die casts may exceed the accuracy required for the passive fit of implant prostheses.

Several removable die systems claim improved accuracy because of their design and/or technical advancements. This study evaluated the 3-dimensional accuracy of 4 removable die systems. All 4 systems tested use either 1 or 2 pins as the repositioning device.

Four removable die systems were evaluated (Belle de St. Claire, Pindex, DVA, and conventional brass dowel system). Master model impressions were made with polyvinyl siloxane material and were later cast with type IV die stone material. Comparative dimensional analysis between the master model and the solid and sectioned casts was made by placing the cast in a standardized position and fabricating an individual custom base for each cast. Landmarks were measured with a traveling microscope, and by mathematically rotating the casts. Discrepancies beyond that of stone expansion or residual stress release at the time of die separation were due to the inability to precisely reposition the removable die of the sectioned cast. Data were analyzed with multivariate analysis of variance and paired t tests at alpha = .05 (n = 10).

Significant differences were found among die systems tested (P = .005). When sectioned dies were compared with the master model, the accuracy of all 4 die systems was within 0.055 mm of the master model. Once sectioned, the Pindex system had the least linear expansion in the y dimension, and the brass dowel system demonstrated the least reseating discrepancy in the z (occlusogingival) dimension.

All 4 die systems provided a similar degree of dimensional accuracy, although Pindex showed the least horizontal movement and the brass dowel system produced the least occlusogingival reseating discrepancy.