Influence of Misfit on the Occurrence of Porcelain Veneer Fractures in Implant-Supported Metal-Ceramic Fixed Dental Prostheses. Part 2: A Three-Dimensional Finite Element Analysis.

PURPOSE: To investigate the impact of different extents of misfit between a restoration and the supporting implant on veneer fractures in screw-retained implant-supported metal-ceramic fixed dental prostheses (FDPs). MATERIALS AND METHODS: A finite element analysis (FEA) model of a five-unit screw-retained metal-ceramic FDP supported by three implants was constructed, replicating a previous in vitro study. Eight different gap configurations at the single terminal implant, ranging from 0 to 150 mum, were tested. All setups were tested after clamping and with a load of 200 N applied. Maximum stress within the FDP was calculated. RESULTS: The stress increased with each increase in misfit size above 30 mum, with the relationship between gap size and stress being linear up to 100-mum misfit. Above 100 mum, the stress increase accelerated. The stress pattern within the FDP changed with increasing gap size, confirming the findings of a previously conducted in vitro experiment for a misfit of 150 mum. CONCLUSION: The results of the FEA were in agreement with in vitro observations, validating the predictive value of FEA for technical complications. A misfit between an FDP and a supporting implant implies an increased risk of veneer fracture. Above a misfit of 30 mum, the stress levels are likely to be high enough to cause veneer fracture, and the risk increases disproportionately for misfit above 100 mum.