Finite element analysis of four thread-form configurations in a stepped screw implant.

The purpose of this study was to determine the optimal thread form configuration for an experimental stepped screw implant. Two-dimensional finite element analysis was applied to model the experimental stepped screw implant in a standard cross-section of the posterior human mandible digitized from a CT-generated patient data set. Four different thread form configurations: v-thread (V), thin-thread (T), and two square-thread forms of 0.24 mm (S1) and 0.36 mm (S2) thread width were compared under oblique load in normal cortical bone condition. The support-type constraint position changed from middle to the base of the bone segment. In middle support-type constraint position only the thin-thread (T) model demonstrated significantly different stress distribution from the other three models, however, in base support-type constraint position T and S1 models demonstrated significantly different stress distribution from the other two models. The results implies that v-thread (V) or large square-thread (S2) are optimal thread form for the experimental stepped screw implant. While, minimal support constraints allow clearer differentiation of the stress picture between the different stepped screw types at the trabecular bone-implant interface.