比較自然牙與牙科植體受力後力學行為之異同:動物實驗

Abstract

牙周膜韌帶(periodontal ligament) 主要連結牙根和齒槽骨壁，是一種軟的結締組織、富含微血管網。牙周膜韌帶的平均厚度約為0.2~0.4 mm。目前所提出過的牙周支撐理論有：簡單張力理論（simple tension theory），受壓理論（compression theory），流體靜力理論（hydrodynamic damping theory）觸變性理論（thixotropic theory）及黏彈理論（The viscoelasticity Theory）。 牙周膜韌帶的力學行為在牙科不論補綴、植體、牙齒斷裂、及矯正等的探討上是不能忽略的，且其所表現出來的行為皆不同。但是目前仍然未有明確的定論。牙科植體應用於全口或部分缺牙牙病人已經有近五十年的歷史，目前植牙病人也與日俱增，而近年來與植體相關的後遺症包括周圍齒槽骨喪失，植體螺絲或上方的贗復鬆動或斷裂，都與植體受力後的力學分佈有關，但相關植體力學的研究卻依舊缺乏。由於人類身上實驗之架設不易，變因較不易控制，本研究中我們針對動物體內的單牙根與植體做研究，以了解牙周膜韌帶及植體的受力機轉。 本實驗的主要目的在比較單牙根與植體生物力學行為的不同，實驗以兩隻米格犬進行進行相關測試，以自行設計的測量儀器得到自然牙與植體潛變，應力鬆弛，遲滯現象等的曲線，由實驗中可以了解自然牙牙周膜韌帶具有潛變，應力鬆弛，遲滯現象，而植體骨整合受力後潛變現象不明顯，惟仍有應力鬆弛及遲滯現象，進一步的結果需要更多的實驗來進行。此研究成果提供初步了解自然牙與植體力學行為模式。

The periodontal ligament (PDL) is a soft connective tissue which joins the tooth root to the alveolus and thus provides for anchorage of the tooth in the alveolar bone. Understanding how the PDL functions is important and still lacking in dental biomechanics research. Although many experimental techniques and theroretical analyses have been employed in understanding the PDL, experiments concerning the PDL are especially difficult due to its complex structure, and testing device should be very accurate. The goal of our study was to investigate the creep source , stress relaxation and hysteresis properties of PDL and the dental implant by using animal study. Two beagle dogs were used in this study, and modified occlusal splints were made. After three month extraction of lower right premolars, Straumann 3.3mm x 8mm implant was placed . Two displacement sensors and the force actuator loading device were inserted to this occlusal splint and anchored with posterior teeth. In vivo experimental tests were carried out on the mandibular incisor’s PDL and the implant to obtain creep , stress-relaxation and hystrersis curves. It was found that the creep , stress relaxation and hysteresis properties of the PDL was defined. From the implant test , slight stress relaxation and hysteresis phenomenon was detected but the creep properties wasn’t clear.