Accuracy and surface roughness of Co-Cr partial denture frameworks with different digital fabrication methods.

STATEMENT OF PROBLEM: Traditional removable partial denture (RPD) manufacture is being phased out in favor of computer-aided design and computer-aided manufacturing (CAD-CAM) techniques and rapid prototyping (RP), which provide more efficient methods of producing RPD frameworks. However, studies comparing the accuracy and surface roughness of these approaches on RPD frameworks are still scarce. PURPOSE: The purpose of this in vitro study was to evaluate the accuracy and surface roughness of class I cobalt chromium (Co-Cr) removable partial denture frameworks digitally constructed using 2 different CAD-CAM technologies: direct milling (DM) and selective laser melting (SLM). MATERIAL AND METHODS: An educational maxillary stone cast was scanned to create a resin model after rest seat preparation. The resin model was scanned, and an RPD framework was digitally designed. Sixteen frameworks were constructed (n=8). Two groups were defined. In the direct milling (DM) group, the standard tessellation language (STL) file of the RPD framework was used to mill the design from a Co-Cr blank directly. In the selective laser melting (SLM) group, the STL file of the RPD framework was used to print the design from Co-Cr powder using the selective laser melting technique. Geomagic Control X software program was used to measure the accuracy of the fabricated frameworks. Surface roughness was tested using optical profilometry. An unpaired t test was used to compare the 2 groups (α=.05). RESULTS: The DM group showed significantly higher mean ±standard deviation accuracy (189 ±9 µm) (P<.001) compared with the SLM group (456 ±122 µm). Regarding the surface roughness, the DM group (0.157 ±0.001 mm) showed significantly lower surface roughness (P<.001) compared with the SLM group (0.256 ±0.001 mm). CONCLUSIONS: The direct milling fabrication technique enabled the fabrication of Co-Cr RPD frameworks with higher accuracy and less surface roughness when compared with the 3-dimensionally printed SLM technique.

Evaluation of the Accuracy and Adaptation of BioHPP Removable Partial Denture Frameworks Constructed by Milling vs the Pressing Technique.

PURPOSE: To evaluate the accuracy and adaptation of BioHPP removable partial denture frameworks constructed from milling vs the pressing technique. MATERIALS AND METHODS: This in vitro study was applied on an educational maxillary stone model with bilateral bounded saddles. Two different manufacturing techniques were used, and thus two groups were defined: (1) the pressed group, in which 20 BioHPP frameworks were constructed by milling a castable resin that was pressed into BioHPP using the lost wax technique; and (2) the milled group, in which 20 BioHPP frameworks were constructed directly by milling the BioHPP blanks. The accuracy of the frameworks was evaluated using Geomagic Control X software, and the gap distance was captured using a stereomicroscope. RESULTS: The milled group showed higher values of accuracy than the pressed group in the x, y, and z axes, and according to Student t test, this difference was statistically significant in the x and z axes. Regarding the adaptation of the frameworks, the milled group showed lower adaptation values than the pressed group. Student t test showed that this difference was statistically significant regarding adaptation of the major connector. However, there was no statistically significant difference concerning adaptation of the denture bases between the two groups. CONCLUSION: Within the limitations of this study, it could be concluded that: (1) the milling technique could be used to fabricate BioHPP RPD frameworks with higher accuracy than the pressing technique; and (2) the pressing technique showed less gap distance (ie, better adaptation) at the area of the major connector.