| dc.description.abstract | In clinical application, although bone screws became the general parts in the orthodontic and orthopaedic domains, the cases of screw failure were emerged in endlessly. When screw fractured or loosened, it would cause surgery fail, secondary operation, and delayed union. Current researches considered that the initial primary stability during inserted process was correlated to insertion torque; the enough torque can provide higher stability. However, some researches also pointed out the excessive insertion torque might cause fracture of implants, bionecrosis of bone tissue, and delayed union. The influence of factors on insertion torque were geometry of screw、strength of bone and the diameter of pilot hole.
This study improved a mathematical model of the engineering self-tapping screw fastening process in previous research, so that it could be used in dental implants to estimate the influence of difference on thread profile、taper of screw and pilot-hole on insertion torque. The two behaviors of removal and friction in bone was probe by concept of mechanics of materials.To confirm the accuracy of the model, four dental implants were used in this research. Besides, experimental results for torque tester and predictions of the mathematical model were compared. The results appeared high accuracy in thread shape test. However, the results in the taper of screw test showed low accuracy. The author suggested that stress on the surface of thread and coefficient of friction be considered carefully.
The results of this research provided the influence of geometry of bone screws on insertion torque in the fundamental of mechanics and materials, and assist design engineers in developing new bone screws.
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