Accuracy of CAD-CAM-fabricated removable partial dentures

Statement of problem. The conventional fabrication of removable partial dentures (RPDs) is a complex, error-prone, time-consuming, and expensive process. The use of computer-aided design and computer-aided manufacturing (CAD-CAM) techniques, especially rapid prototyping, promises a more effective method for fabricating RPD frameworks. Purpose. The purpose of this in vitro study was to evaluate the fit of RPD clasps fabricated by means of 4 different CAD-CAM-systems and to compare those fittings with that of the conventional lost-wax casting technique (LWT). Material and methods. A master model of a partially edentulous maxilla with the canines and second molars as the remaining teeth was fabricated. After the model was optically scanned, we designed a quadrangularly supported RPD with 4 clasps and a palatal strap major connector. A standard tessellation language data set was used to fabricate 12 identical RPDs by using 4 different CAD-CAM techniques: indirect rapid prototyping (wax inject printing combined with LWT), direct rapid prototyping (selective laser melting), indirect milling (wax milling with LWT), and direct milling (resin milling [polyetheretherketond. Three conventionally cast RPDs (LWT) served as the control group. The fit accuracy of the clasps (n=12 for each group) was determined in both the horizontal and vertical dimensions by using light microscopy. Results. Indirectly milled RPDs (117 +/- 34 mu m horizontal and 45 +/- 21 mu m vertical) and directly milled RPDs (43 +/- 23 mu m horizontal, and 38 +/- 21 mu m vertical) showed significantly better (P<.05) fit than did conventionally fabricated LWT RPDs (133 +/- 591.1 mu m horizontal; 73 +/- 25 mu m vertical). The worst fit was found for RPDs fabricated using indirect rapid prototyping (323 +/- 188 mu m horizontal and 112 +/- 60 mu m vertical) or direct rapid prototyping (365 +/- 205 mu m horizontal and 363 +/- 133 mu m vertical), which were unstable on the master model, making them unsuitable for clinical use. Most RPDs exhibited smaller vertical measuring distances. Conclusions. Compared with the LWT, milling techniques enabled fabrication of RPDs with comparable or better fit. However, RPDs fabricated with rapid prototyping techniques showed distinct fitting irregularities.