Volumetric determination of the amount of misfit in CAD/CAM and cast implant frameworks: a multicenter laboratory study.

PURPOSE The purposes of this study were (1) to evaluate the fit between implant frameworks and implants fabricated with two types of implant framework fabrication techniques: computer-aided design/computer-assisted machining (CAD/CAM) and conventional casting with the lost wax technique; and (2) to describe a digital measurement system consisting of tactile scanning and computer software programs that measured the volumetric differences between implant-supported frameworks and implant restorative platforms fabricated with these technologies. MATERIALS AND METHODS This laboratory study used acrylic resin models with five interforaminal implants. The models were scanned; implant-level impressions and verification indexes were then made to construct master casts. First, a cast gold alloy framework and a titanium milled bar fabricated with CAD/CAM technology were made to clarify the construction processes of each. After this pilot study was completed, five cast and five CAD/CAM frameworks were made at each of three dental schools (15 milled and 15 cast bars). Each framework was made on a master cast from individual impressions. The implant restorative interfaces of the frameworks were scanned, and the data were entered into a computer software program. The virtual representations of the frameworks were fit onto digitized scans of the implant restorative platforms and used for virtual one-screw tests on both sides of the arch. Volumetric differences between the implant restorative platforms of the implant-supported frameworks and the model implants were measured to determine the amount of misfit between the frameworks and the model implants. RESULTS Implant-supported frameworks made with the CAD/CAM technology fit significantly better onto the implants than the cast implant frameworks. There was a significant difference between the right and left one-screw tests; there were no significant differences among the three university sites. CONCLUSIONS The CAD/CAM frameworks featured in this study were significantly more accurate than cast frameworks made with the lost-wax technique.