Is insertion torque (IT) correlated to bone-implant contact percentage (BIC) in the early healing period? A histological and histomorphometrical evaluation of 17 human retrieved dental implants.

OBJECTIVE: A precise and scientifically established method for the evaluation of the bone quality/primary stability is the measure of the insertion torque (IT). The aim of this study was a comparison between the IT values and the bone-implant contact percentage (BIC) of human implants retrieved after a 4/8-week healing period. MATERIALS: Seventeen implants, all with a sandblasted and acid-etched surface, were evaluated in the present study. METHODS: The implants had been retrieved for different causes, after 4/8 weeks, with a 5 mm trephine bur, and immersed in 10% buffered formalin to be processed for histology. RESULTS: A not statistically significant correlation was found between IT and BIC (P<or=0.892). CONCLUSIONS: In the present study on human-retrieved implants, no statistically significant correlation was found between the IT values and BIC. These results could be due to a lack of relationship between bone structure and IT, or to the fact that primary stability may not only be influenced by bone volumetrical density and/or bone trabecular connectivity but also by the thickness and density of the cortical layer. Moreover, the present knowledge of the bone microstructure is not enough to explain the relationship of bone quality and primary implant stability.