Department of Endodontology, Faculty of Dentistry, Hacettepe University, Ankara, Turkey.
Int Endod J. 2018 May;51(5):529-540. doi: 10.1111/iej.12770. Epub 2017 Apr 28.
To evaluate the effect of three nickel-titanium (Ni-Ti) rotary systems with varying tapers on stress distribution and to analyse potential fracture patterns as well as the volume of fracture-susceptible regions in two-rooted maxillary premolars.
The root canals of three single-rooted premolars were prepared with either HeroShaper (Micro-Mega, Besançon, France) to (size 30, .04 taper), Revo-S (Micro-Mega) to AS30 (size 30, .06 taper) or ProTaper Universal (Dentsply Maillefer, Ballaigues, Switzerland) to F3 (size 30, .09 taper) Ni-Ti files. The three root canals were scanned using micro-computed tomography (μCT) (Skyscan 1174, Skyscan, Kontich, Belgium) and modelled according to the μCT data. An intact tooth model with a root length of 16 mm was also constructed based on μCT images of an extracted maxillary premolar with two roots. New models were constructed by replacing both of the original canals of the intact two-rooted premolar model with the modelled canals prepared with the HeroShaper, Revo-S or ProTaper Universal system. Occlusal forces of 200 N were applied in oblique and vertical directions. Finite element analysis was performed using Abaqus FEA software (Abaqus 6.14, ABAQUS Inc., Providence, RI, USA).
Upon the application of oblique occlusal forces, the palatal external cervical root surface and the bifurcation (palatal side of the buccal root) in tooth models experienced the highest maximum principal (Pmax) stresses. The application of vertical forces resulted in minor Pmax stress values. Models prepared using the ProTaper system exhibited the highest Pmax stress values. The intact models exhibited the lowest Pmax stress values followed by the models prepared with the HeroShaper system.
The differences in Pmax stress values amongst the different groups of models were mathematically minimal under normal occlusal forces. Rotary systems with varying tapers might predispose the root fracture on the palatal side of the buccal root and cervical palatal root surface in two-rooted premolars.
评估三种不同锥度镍钛（Ni-Ti）旋转器械对双根管上颌前磨牙根管内应力分布的影响，并分析其潜在的折裂模式以及易感区域的体积。
使用 HeroShaper（Micro-Mega，Besançon，法国）（30 号，0.04 锥度）、Revo-S（Micro-Mega）（30 号，0.06 锥度）或 ProTaper Universal（Dentsply Maillefer，Ballaigues，瑞士）（30 号，0.09 锥度）镍钛锉预备 3 颗单根管上颌前磨牙的根管，使用微计算机断层扫描（micro-computed tomography，μCT）（Skyscan 1174，Skyscan，Kontich，比利时）对 3 颗根管进行扫描，并根据 μCT 数据进行建模。根据 2 颗根管的上颌前磨牙完整牙模型的 μCT 图像，建立 1 颗牙根长度为 16mm 的完整牙模型。通过将原始的双根管上颌前磨牙模型中的两个原始根管替换为用 HeroShaper、Revo-S 或 ProTaper Universal 系统预备的模型根管，构建新模型。在斜向和垂直方向施加 200N 的牙合力。使用 Abaqus FEA 软件（Abaqus 6.14，ABAQUS Inc.，Providence，RI，USA）进行有限元分析。
在施加斜向牙合力时，牙模型腭侧外颈缘和分叉处（颊侧根的腭侧）的最大主应力（Pmax）最大。施加垂直牙合力时，Pmax 应力值较小。ProTaper 系统预备的模型的 Pmax 应力值最高，完整模型的 Pmax 应力值最低，其次是用 HeroShaper 系统预备的模型。
在正常牙合力作用下，不同模型组之间的 Pmax 应力值差异在数学上最小。不同锥度的旋转器械可能导致双根管上颌前磨牙颊侧根和腭侧颈缘根发生根折。
