Theoretical considerations: implant positional index design.

Rotational freedom of implant positional indices in two-piece implants was investigated. The aim of the study was to determine, analytically, the rotational freedom of three different positional index designs, based on the hypothesis that it is not influenced by their geometric principle. Regular polygonal, polygon profile, and cam-groove patterns were analyzed. Schematic descriptions were made and idealized equations developed. Parameters influencing the extent of rotational freedom were identified for the different positional index designs. A general equation that describes the rotational freedom of differently designed indices was also formulated. The present analysis showed that the rotational freedom of positional indices can be analytically calculated and is influenced by different parameters. The rotational freedom of the positional index of commonly used implant-abutment connections depends on their geometric design and size.