Scanning Electron Microscope Evaluation of Vertical and Horizontal Discrepancy in Cast Copings for Single-Tooth Implant-Supported Prostheses

Abstract

Despite careful attention to waxing, investing, and casting, marginal discrepancies are inevitable. Vertical and horizontal discrepancies can result in crestal bone resorption, peri-implantitis, and loss of osseointegration. The aim of this study was to evaluate marginal gap and overhang in 3 casting techniques for implant framework fabrication. A total of 24 frameworks, 8 each with the Burn-out Cap (ITI; Straumann) (group BC), with Impression Cap (ITI; Straumann) (group IC), and with conventional wax-up technique (group WX) were fabricated. All specimens were waxed on the analog abutments and cast with Type IV gold alloy. All castings were fixed on the analog abutments with cyanoacrylate and embedded in acrylic resin. Specimens were sectioned and prepared for scanning electron microscope evaluation. Frameworks were analyzed for vertical and horizontal discrepancies with x200 magnification (scanning electron microscopy). Data were analyzed statistically by multivariate analysis and the post hoc tests (alpha = 0.05). The vertical discrepancy measurements for the 3 groups showed mean values of 53.74 +/- 11.0 mum, 63.6 +/- 13.2 mum, and 50.1 +/- 17.3 mum, respectively. The interfacial gap differences were not statistically significant in all groups (P > 0.05). Waxing the frameworks with impression caps significantly increased the horizontal discrepancy at the interfaces (P < 0.001). Within the limitations of this experiment, it was demonstrated that the vertical discrepancy of the frameworks made with the 3 techniques were comparable in lack of accuracy with each other. Although conventional waxing produced the least horizontal discrepancy, the difference with burn-out cap group was not statistically different.