School of Dentistry, The University of Manchester, Manchester, UK.
Int Endod J. 2010 May;43(5):424-9. doi: 10.1111/j.1365-2591.2010.01698.x.
To investigate ex vivo root resistance to vertical fracture after fractured instruments were ultrasonically removed from different locations in the root canal.
Fifty-three canine roots were weighed and divided into four groups. Eight roots served as a control group in which canals were instrumented to a size F5-ProTaper instrument. In the experimental groups, F5-ProTaper fragments were fractured in the coronal, middle and apical one-thirds, and then removed ultrasonically. The time required for removal was recorded. Roots were reweighed, and canals were shaped to a size F5-ProTaper and filled with GuttaFlow. After incubation, roots underwent a vertical fracture test in which the force at fracture was recorded. The difference in root mass before and after treatment (fractured file removal or canal preparation) was calculated. Data were analysed using the Kruskal-Wallis, Mann-Whitney post-hoc and regression tests at P < 0.05.
The highest root-mass loss was recorded when fragments were removed from the apical one-third (46.04 mg) followed by the middle and coronal (27.7 and 13.5 mg, respectively); these differences were significant (P < 0.05). There were significant differences in the force required for vertical fracture amongst the experimental groups (P < 0.05) with the lowest mean force recorded in the apical-third group (107.1 N) followed by the middle and coronal (152.6 and 283.3 N, respectively). The highest mean force was recorded in the control group (301.5 N) which was not significantly different from that in the coronal group (P = 1.00). A negative exponential correlation (r = 0.669) existed between the root-mass loss and the force required to fracture the roots.
Whilst removal of fractured instruments from the coronal one-third of the root canal can be considered as a safe procedure, removal from deeper locations renders the root less resistant to vertical fracture.
研究从根管不同部位超声取出折断器械后，离体牙根对垂直断裂的阻力。
对 53 个犬牙根称重并分为四组。8 个牙根作为对照组，根管用 F5-ProTaper 器械扩大至 F5 号。实验组中，F5-ProTaper 器械折断于根管冠 1/3、中 1/3 和根尖 1/3，然后超声取出。记录取出所需的时间。再次称重牙根，根管用 F5-ProTaper 器械扩大并填充 GuttaFlow。孵育后，牙根进行垂直断裂测试，记录断裂时的力。计算治疗前后（折断器械取出或根管预备）根质量的差异。使用 Kruskal-Wallis、Mann-Whitney 事后检验和回归检验，P＜0.05 为差异有统计学意义。
当从根尖 1/3 取出碎片时，根质量损失最大（46.04mg），其次是中 1/3 和冠 1/3（分别为 27.7 和 13.5mg）；这些差异有统计学意义（P＜0.05）。实验组间垂直断裂所需的力有显著差异（P＜0.05），根尖 1/3 组记录的平均力最低（107.1N），中 1/3 和冠 1/3 组分别为 152.6N 和 283.3N。对照组（301.5N）记录的平均力最高，但与冠 1/3 组无显著差异（P=1.00）。根质量损失与断裂根所需力之间存在负指数相关性（r=0.669）。
虽然从根管冠 1/3 部位取出折断器械可以认为是安全的，但从更深部位取出会使牙根对垂直断裂的抵抗力降低。
