Effect of vertical misfit on strain within screw-retained implant titanium and zirconia frameworks

To assess the implication of vertical misfit on strain within implant frameworks manufactured in titanium or zirconia.

A master model was fabricated by inserting a Brånemark implant in left side of a mandibular model in the area of the first premolar and the first molar. This model was used to fabricate identical frameworks, five in titanium and five in zirconia. A single strain gauge was mounted on the occlusal surface of each framework to assess strain development as a result of framework fitting. In addition, the peak-to-peak strain amplitude was measured for each framework to determine the strain pattern fluctuation. The vertical gap of the framework-implant interface was measured using a measuring microscope, when only one screw was tightened (1-screw test) and when both screws were tightened (2-screw test). The vertical fit of the frameworks was altered by adding one to three layers of 30 μm steel shims on one of the implants.

For all fitting conditions, measurable amount of strains were recorded, however, as the vertical misfit was introduced, linear increase in framework strain was detected. The titanium and zirconia frameworks exhibited similar strain activities. A direct relationship was observed between the framework strain and vertical gap.

Framework misfit clearly influenced the framework strain magnitude and pattern. The framework material did not affect the framework strain for a similar level of misfit.