"Peroperative estimation of bone quality and primary dental implant stability"

Dental implants are widely used to restore function and appearance. It may be essential to choose the appropriate drilling protocol and implant design in order to optimise primary stability. This could be achieved based on an assessment of the implantation site with respect to bone quality and objective biomechanical descriptors such as stiffness and strength of the bone-implant system. The aim of this ex vivo study is to relate these descriptors with bone quality, with a pre-implantation indicator of implant stability: pilot-hole drilling force (F_drilling), and with two post-implantation indicators: maximal implantation torque (T_implantation) and resonance frequency analysis (RFA).

Eighty trabecular bone specimens were cored from human vertebrae and bovine tibiae. Bone volume fraction (BV/TV), a representative for bone quality, was obtained through micro-computed tomography scans. Implants were kept in controlled laboratory conditions following standard surgical procedures. Forces and torques were recorded and RFA was assessed after implantation. Off-axis compression tests were conducted on the implants until failure. Implant stability was identified by stiffness and ultimate force (F_ultimate). The relationships between BV/TV, Stiffness, F_ultimate and F_drilling, T_implantation, RFA were established.

F_drilling correlated well with BV/TV of the implantation site (r² = 0.81), stiffness (r² = 0.75) and F_ultimate (r² = 0.80). T_implantation correlated better with stiffness (r² = 0.86) and F_ultimate (r² = 0.94) than RFA (r² = 0.77 and r² = 0.74, respectively).

Our results indicate that BV/TV and bone-implant stability can be directly estimated by the force needed for the pilot drilling that occurs during the site preparation before implantation. Moreover, implantation torque outperforms RFA for evaluating the mechanical competence of the bone-implant system.