Evaluation of alternative approaches in designing CAD/CAM frameworks for fixed partial dentures

Background: The need for proper framework support for the veneer porcelain in fixed partial dentures (FPDs) has been well documented. The aim of this study was to compare the variations of the support provided by frameworks designed directly on the computer, or indirectly through scanning a wax pattern. Materials and Methods: For each of the six upper anterior FPDs that were involved in the study, prior to milling one framework was designed conventionally in wax and scanned and another one was directly digitally designed. The restorations consisted of full coverage retainers and pontics on natural abutment teeth and implant abutments at random. The produced frameworks were evaluated regarding the incisal support they would provide to the veneer material, as this was revealed by a silicon key representing the outer labial contour of the provisional restoration. The distances between the distal and mesial incisaledges and the corresponding negative incisal contour of the key were measured with a digital caliper. Statistical analysis was performed by linear regression with the design method, abutment type and pontic type as independent parameters (a = 0.05). Results: The values recorded were: means ± SD: 3.3 ± (direct CAD), 2.6 ± mm (indirect CAD) 2.7 ± mm (for retainers on natural teeth) 2.7 (on implant abutments), and 3.3 mm (for pontics). Linear regression analysis showed that the indirect technique provided more intimate incisal support for the ceramic veneer on a statistically significant level and even more so in the pontic areas.