AIM To evaluate the influence of ultraconservative endodontic access cavities (UEC) and the use of instruments with various tapers (.03 or .05) and tip diameters (25 or 40) on the ability to shape canals in mandibular molars and their fracture resistance in comparison with traditional endodontic access cavities (TEC). METHODOLOGY Thirty-two intact extracted mandibular molars were scanned in a micro-computed tomography device, matched based on similar anatomical features and assigned to UEC or TEC groups and to subgroups according to mechanical canal preparation with Bassi Logic™ rotary NiTi instruments with .03 or .05 taper (n = 8 per group). The teeth were mounted onto a mannequin head, and the pulp chambers were accessed and the root canals subjected to instrumentation. In the first stage, size 25 endodontic instruments were used, with .03 or .05 tapers. The teeth were re-scanned. Subsequently, a second canal instrumentation was performed with the size 40 instruments with .03 or .05 tapers and scanned again. The root canals were filled and then the teeth restored before being subjected to fracture resistance tests. The data on untouched canal areas, canal transportation, centring ability, the percentage of removed dentine and maximum load at fracture were analysed. One-way anova and Tukey's tests were performed for inter-group analysis. The paired-samples t-test was performed on the results between size 25 and size 40 apical preparations for each individual specimen (P < 0.05). RESULTS No significant difference was observed for the percentage of untouched canal area when comparing UEC and TEC groups or between the .03 and .05 tapers with the same instrument tip size (P > 0.05). There was a significantly lower percentage of untouched canal area after instrumentation with size 40 instruments when compared to size 25 (P < 0.05). No significant difference in the percentage of dentine removed was observed between the access cavities or the different tapers (P > 0.05). Size 40 apical preparations removed significantly more dentine than size 25 preparations (P < 0.05). No significant differences were observed in canal transportation, centring ability and fracture resistance in any of the tested groups (P > 0.05). CONCLUSIONS Ultraconservative endodontic access cavities did not offer any advantages in comparison with traditional endodontic access cavities on the ability to shape canals, nor the fracture resistance of mandibular molars. No differences were observed in shaping ability and fracture resistance between .03 and .05 taper canal preparations. Apical preparation with larger instruments resulted in significantly less untouched canal area in all groups.

中文翻译：

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对超保守通道和最小根管锥度对下颌磨牙的根管成形能力及其抗断裂性影响的实验室研究。

目的评估超保守牙髓进入腔（UEC）的影响以及使用具有各种锥度（.03或.05）和尖端直径（25或40）的器械对下颌磨牙根管成形的能力及其抗骨折能力的影响与传统牙髓进入腔（TEC）的比较。方法在微计算机断层扫描设备中扫描了32个完整的下颌磨牙，根据相似的解剖学特征进行匹配，并根据使用Bassi Logic™旋转NiTi器械的.03或0.05锥度（每组n = 8）。将牙齿安装在人体模型的头上，进入牙髓腔，并对根管进行检测。在第一阶段，使用尺寸为25的牙髓器械，.03或。05锥度。牙齿被重新扫描。随后，使用尺寸为.03或.05锥度的40号器械进行第二根管器械，并再次进行扫描。进行根管充填，然后恢复牙齿，然后再进行抗断裂测试。分析了未接触的根管面积，根管运输，对中能力，去除的牙本质的百分比以及骨折时的最大负荷的数据。对组间进行单向方差分析和Tukey检验。配对样本t检验是针对每个单独的样本，在25号和40号根尖准备之间的结果上进行的（P <0.05）。结果当比较UEC组和TEC组时，或者在相同的器械尖端尺寸（P> 0）的.03和.05锥度之间，未触及的运河面积百分比没有显着差异。05）。与尺寸25相比，尺寸40的器械在未触及的根管面积百分比显着降低（P <0.05）。进入腔或不同锥度之间的牙本质去除率没有显着差异（P> 0.05）。40号根尖制剂去除的牙本质比25号制剂明显多（P <0.05）。在任何测试组中，在运河运输，定心能力和抗断裂性方面均未观察到显着差异（P> 0.05）。结论与传统的牙髓进入腔相比，超保守牙髓进入腔在塑造根管的能力以及下颌磨牙的抗断裂性方面没有任何优势。在0.03和.05锥形管之间没有观察到成形能力和抗断裂性的差异。用较大的器械进行根尖准备可使所有组的未触及管腔面积明显减少。