骨螺絲在牙科與骨科領域中已成為臨床相當普遍的零件，儘管如此，骨螺絲失效的案例依然層出不窮。當骨螺絲發生斷裂或鬆脫時將導致手術失敗、二次手術與延遲癒合等問題。現今研究認為鎖入力矩與骨螺絲鎖入的初始穩定度相關，足夠的鎖入力矩可以提供較高的穩定度。然而，也有研究指出過高的鎖入力矩可能導致骨螺絲斷裂、骨頭壞死與延遲癒合。影響鎖入力矩的因素有螺絲幾何參數、骨頭強度以及預鑽孔的大小。 本研究目的在於將過去應用於工程自鑽螺絲之數學模型，修改至適用齒科螺絲，並評估不同牙型、螺絲錐度與預鑽孔對鎖入力矩的影響。藉由材料力學觀點來探討螺絲在骨頭中攻牙與摩擦過程的兩種行為。為了驗證理論推導模型的正確性，利用四支齒科螺絲的理論預測與實際測詴結果進行比對，結果顯示牙型有較高的準確性，然而，螺絲錐度在不同預鑽孔的準確性較低。作者認為螺絲錐度與預鑽孔在理論模型中應仔細考慮螺牙表面應力與摩擦係數。 本論文之研究成果在機械力學與材料力學基礎下提供了骨螺絲幾何參數對鎖入力矩之影響的數學模型。給予工程領域的設計人員在研發新型骨螺絲的依據。 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.
