In-vitro Evaluation of Accuracy of Conventional and CAD/CAM Removable Partial Denture Frameworks

Purpose: Computer-aided design/computer-aided manufacturing (CAD/CAM) technology is gaining popularity in dentistry, and more recently, to fabricate removable partial dentures (RPD). The purpose of this study was 1) to evaluate the overall accuracy and fit of conventional versus CAD/CAM fabricated printed RPD frameworks based on STL data analysis, and 2) to evaluate the accuracy and fit of each component of the RPD framework. Materials and Methods: A maxillary metal framework was designed for a Kennedy class III modification I situation. The master model was scanned and used to compare the fit and accuracy of the RPD frameworks. A total of 40 impressions (conventional and digital) of the master cast were made and divided into 4 groups based on fabrication method: Group I, conventional method (Lost-wax technique); group II, CAD-rapid prototyping (CAD-RP); group III, CAD-rapid prototyping from stone model (CAD-RPS); and group IV, Lost-wax technique from resin model (LWTR). RPD frameworks were fabricated in cobaltchromium alloy. All frameworks were scanned and the gap distance to the original master model in 8 different locations were measured, as well as color mapping with a comprehensive metrology software. Data were statistically analyzed using the Kruskall- Wallis analysis of variance and post hoc comparisons, followed by the Bonferroni method

for pairwise comparisons (α = 0.05). Results: Color mapping revealed distinct discrepancies in major connectors amongst the groups. When compared to 3D printed frameworks, conventional cast frameworks fabricated either from dental stone or 3D printed resin models revealed significantly better fit (P<0.05) with the major connectors and guide plates. The biggest gap (>0.3mm) was observed with the anterior strap of the major connector with the printed frameworks (groups II and III). The method of fabrication did not affect the adaptation of the rests or reciprocation plates. Conclusions: Within the limitations of this study, although both methods revealed clinically acceptable adaptation, the conventional processed RPD groups revealed better overall fit and accuracy.