Influence of Vertical Misfit of Titanium and Zirconia Frameworks on Peri-Implant Strain

Purpose: To assess the influence of misfit of implant titanium and zirconia frameworks on peri-implant strains. Materials and Methods: Two Brånemark implants were inserted in the areas of the mandibular left second premolar and second molar of an artificial epoxy resin mandible. From this model, five titanium and five zirconia frameworks of similar design were fabricated by means of computer numeric controlled milling. Strain gauges were mounted around each implant to assess strain development as a result of framework fit/misfit. In addition, the vertical gap at the framework-implant interface was measured using an optical microscope when only one screw was tightened (one-screw test) and when both screws were tightened (two-screw test). The vertical fit of the frameworks was altered by introducing one to three nominally 30-µm steel shims on one of the implants. The data were analyzed statistically using one-way analysis of variance and the Mann-Whitney test. Results: For each condition, a measurable amount of strain was recorded. As more vertical misfit was introduced, a linear increase in peri-implant strains was observed. The two framework materials generated similar amounts of strain. A direct relationship was observed between strain and the vertical gap. Conclusions: The magnitude of peri-implant strain is primarily affected by the fit of the framework rather than the material. Titanium and zirconia frameworks showed a similar outcome in relation to fit and strain development. Keywords: computer-aided design/computer-assisted manufacture, computer numeric controlled milling, distortion, framework fit, strain gauge