Research of PDL Damage after Extraction for Cryopreservation
[[abstract]]牙齒再植與自體牙齒移植手術於臨床上發展多年，技術成熟，文獻上均有超過90%的成功率，為台灣健保制度之给付項目。齒顎矯正病患常為了將牙齒排列整齊而必須被拔除健康完好的小臼齒或其他牙齒，當成醫療廢棄物丟棄實在可惜。「北醫牙齒銀行」的設立，可以將沒有嚴重齲齒與牙周病的健康完好牙齒進行短期或長期的冷凍保存，以便未來缺牙時，能將健康的牙齒解凍後植回自體口腔中。然而拔牙時若無法保存足夠的牙周韌帶組織(簡稱PDL)，上述美意與成果都將大打折扣。同時自體牙齒移植的窩洞(socket)癒合亦決定在PDL組織於拔牙時損傷的程度，亦即牙根表面PDL組織的殘留量決定了自體牙齒移植的成效。本研究目的是改良傳統拔牙方法期能將牙齒以保留最多PDL組織方式拔出，再利用新型微米磁振造影來掃描拔出之牙齒，逐步建立拔牙後殘存之PDL體積以及於牙根部位覆蓋面積之資料庫。利用台北醫學大學附設醫院口腔顎面外科拔牙病人，選取齒顎矯正病患欲拔除的下顎第一小臼齒，以傳統拔牙方法，將傳統拔牙鉗夾到琺瑯質牙骨質交界(cemento-enamel junction 簡稱 CEJ)以下，亦即拔牙鉗必須侵入齒槽骨內;以及新式拔牙鉗(鉗口內有加工之防滑粗操面)搭配改良式拔牙方法，亦即拔牙鉗只夾到琺瑯質牙骨質交界以上，且不侵入齒槽骨內。以此兩種拔牙方法分別進行，牙齒拔出後以生理食鹽水保存後，再利用微米磁振造影掃描後來比較拔牙後的殘存在牙根表面牙周韌帶的體積多寡，以及牙根部位牙周韌帶覆蓋面積之百分比。傳統拔牙組總共有六顆下顎第一小臼齒接受微米磁振造影掃描，其中有兩顆牙齒PDL嚴重損傷，無法判讀，僅四顆牙齒得到可比較結果；而改良式拔牙組則有三顆接受掃描，但其中也有一顆牙齒無法判讀，所以得到的比較結果只有兩組。傳統拔牙法組的牙周韌帶體積平均為 5.64 mm³，其覆蓋牙根面積平均為21.25%；而改良拔牙組，牙周韌帶體積平均為5.79 mm³，其覆蓋面積平均為20.5%。與文獻比較，突顯幾點意義，第一，在牙根覆蓋面積比例上，與Haas發表過的研究約50%殘存率，有著較低的百分比，顯示過可能過去高估了拔牙後殘存於牙根的牙周韌帶組織。第二，Andreasen曾指出，當牙周韌帶損傷面積超過16 mm²，就會降低牙齒再植成功率，而本研究顯示，拔牙對於牙周韌帶的損傷平均值160 mm²`,是遠超過這個面積的，但對照現今牙齒再植成功率卻是遠超過90%，顯示先前研究似乎低估了即使是少量PDL在齒槽骨中修復的能力。第三，微米磁振造影精確地描繪牙周韌帶在拔牙後於牙根之分布，在傳統拔牙組，對於正頰側和舌側之牙周韌帶易造成嚴重損傷，而遠心側以及近心側甚至於根尖處的牙周韌帶的損傷就較小。反之，改良式拔牙組在根尖部位的牙周韌帶的損傷較為嚴重，而在靠近齒頸部位，尤其是正頰側和舌側的牙周韌帶其損傷就較小。回顧文獻，從未有牙科研究可以清楚描繪拔牙後牙周韌帶在牙根上的分布與面積，甚至量化殘存的體積，利用微米磁振造影作為研究工具，牙齒接受掃描並3D重組後可以建立拔牙後牙周韌帶組織的體積與殘存面積資料庫，並發展出較優良的拔牙方法，顯示本研究在牙科領域利用微米磁振造影掃描具有里程碑意義。 The tooth bank can store healthy permanent teeth, such as wisdom teeth and premolars, that are removed for better alignment for orthodontic treatment. The teeth can be stored for use later in life, such as when a patient has a missing tooth and needs to undergo a tooth implant. Natural tooth transplantation is putting a patient’s own previously stored tooth into the missing tooth area, and has a very high success rate(more than 90% in many reviews). At the sane time, a natural transplant can improve integration with the jawbone, shorten recovery time and lower costs. The key to the high success rate of auto-transplantation is to preserve the residual PDL(periodontal ligament) covered root surface as much as possible. Because of the PDL with many mesenchymal cells or progenitor cells for osteoblasts and cementoblast, they are important cells for the success of the auto-transplantation or replantation. Even in socket healing, if PDL is damaged largely during tooth extraction, the tooth bank should not store the damaged tooth. My research was to find the modified extraction method with the expectation to preserve more residual PDL tissue. Using the Micro-MRI scanning instrument to scan the teeth, I compare the PDL covering surface area and volume of the teeth extracted by different methods. Then I recorded the data of the PDL volume and covered surface after extraction, and developed the methods or instruments of extraction to provide a PDL-harmless extraction for tooth bank storage. Because the premolars are the most commonly stored teeth in tooth bank, I chose patients who planned to have mandibular first premolars extracted for orthodontic treatment. Then I extracted the teeth using different extraction instruments and methods. The conventional extraction method used conventional extraction forceps No.151, with beaks invading beneath the Cemento-enamel junction(CEJ) into the socket. The modified extraction method use the modified No.151 forceps with a rough carbide coating surface inside the beak. During extraction the beaks should not invade into the socket. After extraction, all teeth are sent to Functionl & Micro-Magnetic Resonance Imaging Center of Academia Sinica to be scanned and compared the PDL volume and area of covered surface. There were four teeth removed using the conventional extraction method and two teeth removed using the modified extraction method. These were scanned and calculated the PDL volume and root covered surface area. For the teeth using conventional extraction method, the mean PDL volume was5.64 mm³, the mean PDL/ root surface ratio was 21.25%. For the modified extraction teeth, the mean PDL volume was 5.79 mm³, the mean PDL/root surface ratio was 20.5%. There were 3 different results compared with the previous researches. First, Haas’s research reported the PDL/ root surface ratio was about 50 %, which was much higher ratio than my result. It could be resulted from over-estimated residual PDL tissue volume in the previous research. Second, Andreasen reported PDL damaged more than 16 mm² area would decrease the success rate of replantation. In my research, the mean damaged PDL area was 160 mm², which showed much severer damaged than Andreasen’s. The great repairing by small volume of PDL tissue could explain the high success rate of contemporary replantation. Last, micro-MRI clearly recorded the distribution of the residual PDL. PDL was damaged over the buccal and lingual root area mostly in the conventional extraction teeth; and PDL was damaged over apex and line angle area of a root in the modified extraction teeth. In a review of the dental research articles, no any articles about dental research using micro-MRI as a researching instrument were found. Using micro-MRI as scanning instrument to measure the PDL tissues after extraction, then developing a new and better extraction method is a milestone in dental research.
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