A novel in vitro approach to assess the fit of implant frameworks.

OBJECTIVE

To introduce a new strain gauge approach to assess the fit of fixed implant frameworks.

MATERIALS AND METHODS

A partially edentulous epoxy resin mandible model received two Straumann implants in the area of the lower left second premolar and second molar. The model was used to fabricate four zirconia and four identical cobalt-chromium alloy frameworks using a laboratory computer-aided design/computer-aided manufacturing (CAD/CAM) system. A total of four linear strain gauges were then bonded around each implant on the peri-implant structure (mesial, distal, buccal, and lingual). The experimental part was composed of two phases: qualitative and quantitative. For the qualitative assessment, the model was verified by recording the response of each strain gauge while applying a near-constant force of known directions on each implant. For the quantitative phase, the frameworks were attached on the implants and the screws were torqued to 15 N cm.

RESULTS

In the qualitative phase, the strain gauge response to every force direction was recorded. After attaching the frameworks, all frameworks produced measurable strains, but with different strain patterns. Upon correlating the two phases, the zirconia frameworks were found to be slightly smaller than the inter-implant distance, whereas the cobalt-chromium alloy frameworks tended to be slightly larger than the inter-implant distance.

CONCLUSIONS

The proposed technique is not only valid for detecting implant framework misfit but also for determining the form of inaccuracies. Model verification is an essential informative step to aid the interpretation of the pattern of framework distortion.