Effect of Finishing and Polishing Techniques on the Fit Accuracy and Dimensions of Conventional and CAD-CAM Removable Partial Denture Frameworks

Abstract

Rapid advancements in computer-aided design and computer-aided manufacturing (CAD- CAM) in removable dental prosthodontics have offered new modalities for fabrication of removable partial denture frameworks. The standard tessellation language (STL) files of the scans are used to digitally design the removable partial denture (RPD) framework, which are then printed in cobalt-chromium (Co-Cr) alloy and finished and polished according to manufacturers’ recommendations. There are few studies compare the fit accuracy of the cast DPD framework versus the CAD CAM RPD frameworks which found that CAD-RP frameworks exhibited the highest discrepancies, using different methods of evaluation. Good fit between the denture base and the supporting tissue, the intimate contacts between the teeth and framework components improve support, stability and retention and are critical to the satisfactory outcome for the RPD patient. Currently, no study has evaluated the fit accuracy of 3D printed removable partial dentures (RPD) after finishing and polishing techniques based on the manufacturer’s protocol.

Purpose: The purpose of this study was to: 1) Compare the effects of finishing and polishing techniques on the overall fit accuracy and dimension of conventional versus CAD-CAM fabricated RPD frameworks. 2) Evaluate the loss of metal from various components of the RPD framework after finishing and polishing. Material and methods: A maxillary arch 3D printed model with a Kennedy class III modification I situation was fabricated as a master cast. The master model was scanned and used to compare the fit and accuracy of the RPD frameworks. The master cast were made and divided into 4 groups based on fabrication method: group I, lost-wax technique (conventional technique), group II, CAD-printing, group III, CAD-printing from stone cast, and group IV, lost-wax technique from resin-printed model. RPD frameworks were fabricated in cobalt-chromium alloy. The finishing and polishing techniques of the RPD frameworks using different methods were performed based on manufacturers’ recommendation. All RPD frameworks were scanned, and accuracy of fitting and metal thickness loss of various components of the RPD framework were evaluated. All RPD frameworks were evaluated the surface roughness based on SEM analysis. Results: All RPD frameworks were evaluated before and after finishing and polishing techniques based on manufacturers’ recommendation. Color mapping revealed state statistically significant between cast RPD framework versus 3D printed frameworks major

connectors, reciprocal and retentive arms among the groups after finishing and polishing techniques based on manufacture’s recommendation (P < 0.05). There was statistically significant difference between the conventionally cast framework groups (LWT versus LWTR) compared to the 3D-printed framework groups (CAD-RP versus CAD-RPS) (P < 0.001). The biggest gap (0.33 mm ± 0.20 mm) was observed with the guide plates with the printed frameworks (groups II and III). The overall metal loss after using different finishing and polishing techniques revealed statistically significant differences in metal loss between the conventional polishing and finishing technique of cast RPD frameworks (P < 0.001) compared to the D-Lyte polishing and finishing technique of 3D printed frameworks particularly in the occlusal rest and the junction with the proximal plate. The conventional finishing and polishing technique showed more surface roughness than D- lyte finishing and polishing technique based on scanning electron microscope (SEM) analysis. Conclusion: Within the limitations of the present study, although both conventional cast RPD and 3D printed frameworks were found to be clinically acceptable, the conventionally processed RPD groups revealed better overall fit and accuracy after finishing and polishing. The conventional cast RPD frameworks showed more metal loss than 3D printed RPD frameworks after finishing and polishing technique and more surface roughness based on SEM analysis.