Accuracy of CAD-CAM-fabricated removable partial dentures.

ABSTRACT

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 [polyetheretherketone]). 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 µm horizontal and 45 ±21 µm vertical) and directly milled RPDs (43 ±23 µm horizontal, and 38 ±21 µm vertical) showed significantly better (P<.05) fit than did conventionally fabricated LWT RPDs (133 ±59 µm horizontal; 73 ±25 µm vertical). The worst fit was found for RPDs fabricated using indirect rapid prototyping (323 ±188 µm horizontal and 112 ±60 µm vertical) or direct rapid prototyping (365 ±205 µm horizontal and 363 ±133 µm 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.