Abstract
A screw-retained prosthesis on an osseointegrated implant requires high accuracy, through so-called “ passive fit.” Two tests are proposed to evaluate the fit of an abutment/superstructure joint:the one-screw test (Sheffield's test), and the angular change with tightening the screw. The purpose of this study was to experimentally reconsider both passive fit tests.
1. The required force was measured when waxes prepared were pressed down on the digital force gauge. Influence of the manufacture and shape of wax, and room temperature at measurement,on the force was examined. The results suggest that pressing of wax is an unstable procedure to make a 200-g load, and the load was influenced by the manufacture and shape of wax,and room temperature.
2. The influence of the 200-g load of the Sheffield's test on the stress distribution of the implant and bone was evaluated by a three-dimensional liner static stress analysis. A 25-mm cantilever model was constructed for a 3-dimensional finite element model, and the apex of the cantilever was loaded in 200 gf. The maximum equivalence stress of 4 MPa was observed at the implant.
3. A custom-designed apparatus was constructed to measure the torque and angular change with the screw tightening. The relationship between required torque and angular change with the screwing was examined. The PME and conical abutment of a Steri-oss implant system were used for the sample materials. The results suggest that measuring the angular change with the screw tightening is useful for the fit test, and the angular change is different in each abutment.
