Passive fit and trueness of complete-arch implant-supported cobalt chromium frameworks manufactured using different digital techniques: a laboratory study

Abstract

BACKGROUND: Passive fit and trueness are keys to the success of complete-arch implant-supported cobalt chromium frameworks, so this study aimed to assess and compare the passive fit and trueness of cobalt chromium (Co-Cr) complete-arch implant-supported frameworks fabricated using milling and three-dimensional (3D) printing technologies with those produced using the conventional lost wax technique. METHODS: A maxillary typodont with 5 implant digital analogs was scanned using a desktop scanner, a complete-arch implant-supported framework was designed, and the design's standard tessellation language (STL) file was designated as the reference file. A total of 24 frameworks were fabricated. In the first group, the frameworks were initially milled from wax blanks and subsequently processed using the conventional lost wax technique. In the second group, frameworks were milled from Co-Cr blanks, while in the third group, frameworks were 3D printed utilizing the selective laser melting technique from Co-Cr powder. Frameworks were scanned, and corresponding STL files were imported into a surface-matching software program to assess trueness. Passive fit was evaluated using a one-screw test and a handheld digital microscope. Statistical analysis was performed using one-way and two-way ANOVA followed by the Tukey post hoc test (α = 0.05) for pairwise comparison. RESULTS: Significant differences were found among fabrication techniques for both passive fit and trueness. The milled group demonstrated the lowest mean of vertical gap during passive fit assessment, while the conventional lost wax group exhibited the highest mean. Correspondingly, trueness values were lowest for the milled frameworks, intermediate for 3D-printed frameworks, and highest for conventional lost-wax. CONCLUSIONS: Digital fabrication techniques, particularly CAD-CAM milling, provided superior fit and trueness compared to conventional casting of Co-Cr complete-arch implant frameworks.