The relation between surface roughness and interfacial shear strength for bone-anchored implants. A mathematical model.

A rough bone implant surface was conceptualized as being built up of pits of different sizes and of different shapes. Hypotheses were formulated regarding the mechanical strength of the interfacial bone based upon the present knowledge of the character of the tissues adjacent to endosseous implants and the mechanical characteristics of different bone constituents. A surface roughness parameter was derived, the pit effectivity factor (fpe), which describes how effective the individual pits of the rough surface are as retention elements with regard to shear. Another surface roughness parameter was defined, the pit density factor (fpd), the value of which depends upon how densely packed the pits are. The interfacial shear strength of a rough implant surface with known microgeometry can be estimated by means of these two surface roughness parameters. The effectiveness of pits of different sizes and of different shapes was investigated using this model.