根管治療最重要的目的就是要將根管系統中細菌和牙本質殘屑的數量降至最低甚至沒有，以預防
或治癒根尖牙周炎的病況。如何達到良好的清潔與成功的修形，一直是根管治療醫師所努力的方向。
本研究之目的在於探討使用相同錐度的鎳-鈦旋轉器械初步修形後，進而選用不同徑輻（diameter）的器械作根尖部的深度修形，然後觀察根管壁清創完的境況，以及評估根尖修形是否切削過大或不足。本實驗包括四個實驗組，利用ProTaperTM鎳-鈦旋轉根管銼（ProTaperTM rotary file）配合冠端向下法（crown- down technique）加以修形。A組之最終修形號數為
Finishing File No.3，B組修形至F3/＃30，C組修形至F3/＃35，而D組則修形至F3/＃40。之後將牙根縱劈觀察。結果顯示，在根尖部之殘屑殘留為最多。且不同尺寸的根尖修形之比較，發現各組其殘屑在冠部和中央部無顯著差異；而分析所得之結果，顯示根管位置及根尖修形尺寸都與殘屑殘留有顯著影響。
結論：根管修形時，不論根尖修形至何種尺寸大小，根尖部之清潔率皆為整個根管之中最差者。在根尖錐度為.09的條件下，若增加根尖修形的尺寸，便可以提高根管清潔率及沖洗效益；就根尖部殘屑移除之成效而言，至少需修形至＃35 K型根管銼。

The most important objective of root canal therapy is to minimize the number of microorganisms and pathologic debris in root canal system to prevent or treat apical periodontitis. It depends on how to clean and shape the root canal system to achieve the objective. The purpose of this study was to compare the cleanliness of the root canal wall in different levels after preparation with the same tapering Ni-Ti rotary instruments and apical preparation with different hand file. ProTaperTM Rotary Files were used to prepare the root canals with crown – down technique. The four different canal groups were used the same final ProTaperTM Rotary Files, and prepared apically without and with hand file in different sizes,
which were group A（without hand file preparation）, group B（＃30 K file）, group C（＃35 K file）, group D（＃40 K file）respectively. ANOVA and MANOVA were used to analyze the differences in the amounts of debris among four groups and three positions. The highest scores of debris was found in the apical level. There was no significant difference in the coronal and middle levels between all groups. In the apical level, group A left significantly more debris compared with group C and group D；group B left significantly more debris compared with group C and group D. The two-way ANOVA showed that the canal position and the size of apical preparation were both significant risky factors for debris scores.
In conclusion, the apical third cleanliness was worse than the other positions. The cleaning efficiency of debris could be improved by increasing the apical preparation size to ＃35 K file.