An In Vitro Investigation of Accuracy and Fit of Conventional and CAD/CAM Removable Partial Denture Frameworks

Abstract

Purpose: To evaluate the overall accuracy and fit of conventional versus computeraided design/computer-aided manufactured (CAD/CAM) removable partial denture (RPD) frameworks based on standard tessellation language (STL) data analysis, and 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 arch. The master model was scanned and used to compare the fit and accuracy of RPD frameworks. Forty impressions (conventional and digital) of 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. All frameworks were scanned, and the gap distance between the framework and scanned master model was measured at 8 locations. Color mapping was conducted using comprehensive metrology software. Data were statistically analyzed using the Kruskall-Wallis test, followed by the Bonferroni method for pairwise comparisons (α = 0.05). Results: Color mapping revealed distinct discrepancies in major connectors among the groups. When compared to 3D-printed frameworks, conventional cast frameworks fabricated using dental stone or printed resin models revealed significantly better fit (p < 0.05) particularly in the major connectors and guide plates. The biggest gap (0.33 mm ± 0.20 mm) 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: Although both conventional and 3D-printing methods of framework fabrication revealed clinically acceptable adaptation, the conventional cast RPD groups revealed better overall fit and accuracy.

Virtual Evaluation of the Accuracy of Fit and Trueness in Maxillary Poly(etheretherketone) Removable Partial Denture Frameworks Fabricated by Direct and Indirect CAD/CAM Techniques

“…Gowri et al found a misfit of 0.16 mm at the anterior border of the palatal strap major connector, similar to the direct technique results from this study. The indirect technique results of this study were in opposition to other studies, which showed the greatest misfit occurred at the anterior strap area of the indirect RP techniques. They reported that some structural flaws might occur during the manufacturing process or that scanning errors were behind this misfit.…”

“…The results in the posterior strap area of the indirect technique were similar to the results found by Soltanzadeh et al . Concerning the guiding planes and the A‐P strap areas, the mean distance measured for the direct technique was considered as acceptable clinical fit (<0.31 mm); however, it was considered as close contact (<0.05 mm) for the indirect technique, consistent with the finding of Soltanzadeh et al . The results in the A‐P strap areas were also consistent with Gan et al's results that the adaptation of major connectors was better at the two sides of the palatal vault than at the midline palatine suture.…”

“…The results in the posterior strap area of the indirect technique were similar to the results found by Soltanzadeh et al . Concerning the guiding planes and the A‐P strap areas, the mean distance measured for the direct technique was considered as acceptable clinical fit (<0.31 mm); however, it was considered as close contact (<0.05 mm) for the indirect technique, consistent with the finding of Soltanzadeh et al .…”

“…Scientific evidence related to the accuracy of fit and the trueness of the RPD framework fabricated by the CAD/CAM techniques is scarce. Only three studies have digitally evaluated the fit accuracy of the RPD frameworks manufactured by different techniques in contrast to CAD/CAM milling or prototyping and found an adequate to an acceptable fit …”

“…Recently, digital methods were developed to evaluate the fit of a removable prosthesis to the cast by scanning the prosthesis and the cast after saving the scan into a standard tessellation language (STL) file format and superimposing the two STL files of each scan using surface matching software. Then, the distance between framework and the cast is measured . Recent advances in CAD software also allow the evaluation of trueness (deviations of the fabricated prosthesis from the virtually designed prosthesis) using a special type of superimposing software …”