牙齒DNA之人別鑑定

Abstract

牙齒可以作為人類遺骸基因組DNA的可靠來源。使用牙齒組織作為個體識別的 DNA 來源來自於其抵抗環境攻擊的特徵，例如焚燒、浸泡、創傷和肢解。從牙齒中提取 DNA 的傳統方法需要對牙齒進行完全機械破壞。雖然這方法簡單可靠，但對於希望進一步證據目的或人類學研究來說並不理想。牙齒細胞豐富的區域是牙髓 (pulp)和牙骨質(cementum)。 本研究分別採用牙髓和牙骨質樣本兩種對牙齒破壞最小的方法提取DNA進行個體鑑定。牙髓取樣是用牙科手機在牙齒的咬合面鑽孔，然後用牙銼取出牙髓和成牙本質細胞，然後用複合樹脂將孔回填。牙骨質取樣是用刀片刮牙根外表面的牙骨質。牙骨質的損失非常小，幾乎無法發現 本研究測試了 58 個埋藏和未埋藏的脫落牙齒樣本，以及 4 個法醫牙齒樣本。 將 DNA 產量和 STR 成功率與這兩種採樣方法進行了比較。 結果表明，牙骨質取樣在 DNA 質量和效率方面優於牙髓取樣。 這說明微生物在降解核DNA和降低 DNA 產量方面有至關重要的影響。門齒、小臼齒和大臼齒之間的STR基因分型成功率表明多牙根比單牙根提供更好的DNA數量和質量。在牙髓採集的樣本中，有蛀牙的牙齒的 DNA 產量非常少，而在牙骨質採集的樣本中則不然。如果牙齒型態保存是重中之重，那牙骨質取樣是一種理想的 DNA 提取方法。如果對病原菌 DNA 感興趣的話，從咬合方向鑽孔取牙髓可能是一種很好的替代方法，這兩種方法都可以在不破壞牙齒結構的情況下製備 DNA。

The teeth could serve as a reliable source of genomic DNA of human remains. Using dental tissues as a DNA source of individual identification is due to its particular character of resistance to environmental assaults such as incineration, immersion, trauma, mutilation and decomposition. The traditional method to extract DNA from teeth requires mechanical crush of the entire tooth. Although this is easy and reliable, it is not ideal for further evidence purpose or anthropological study. Cell-abundant areas of the tooth are pulp and cementum. Two methods of minimum destruction on tooth for pulp and cementum samplings respectively were used in this study to extract DNA for individual identification. About the pulp sampling, a dental handpiece was used to drill a hole on occlusal surface of the tooth, and then dental files were used to retrieve pulp and odontoblasts, after that the hole was filled back with composite resin. As for the cementum sampling, blades were used to scrape cementum which is on the outer surface of the root . The loss of cementum was so small that could hardly be found. Fifty-eight fallen tooth samples were buried and unburied, and 4 forensic tooth samples were tested in this study. DNA yields and STR success rates were compared with these two sampling methods. It showed that cementum sampling outperformed pulp sampling in DNA quality and efficiency. It indicated that microbes played an imperative role in degrading the nuclear material and reduced DNA yields. The success rates of STR genotyping among incisors, premolars, and molars showed multirooted teeth provided better DNA quantity and quality than single-root teeth. The DNA quantity of teeth with cavities were seriously affected in pulp samples, while the cementum was not observed in this matter. Cementum sampling is an ideal method for DNA extraction if tooth morphological preservation is the highest priority. If pathogen DNA is of interest, occlusal approach to retrieve pulp may serve as a good alternative to prepare DNA without destruction of the tooth structure.