Mechanical Preparation Showed Superior Shaping Ability than Manual Technique in Primary Molars - A Micro-Computed Tomography Study

Abstract The aim of the study was to evaluate canal preparation in primary molars with hand files, ProTaper Next and Self-Adjusting File (SAF) by 2D and 3D micro-computed tomography (micro-CT) analysis. Canals of 24 primary molars were prepared with hand files (HF), ProTaper Next (PTN) and SAF (n=8/group). The teeth were scanned before and after root canal preparation and the pre- and postoperative micro-CT images were reconstructed. Changes in 2D (area, perimeter, roundness, minor and major diameter) and 3D [volume, surface area, structure model index (SMI)] morphological parameters, as well as canal transportation and lateral perforations were evaluated (Kruskal-Wallis and ANOVA; a=0.05). SAF presented smaller changes in minor diameter, volume and surface area compared with HF and PTN (p&lt;0.05). PTN presented more circular canals after preparation. 3D analysis revealed greater transportation in HF. PTN and SAF presented more centered canal preparation, especially in curved areas. SAF and HF presented, respectively, the lowest (0.05±0.02 and 0.07±0.04) and highest (0.14±0.11 and 0.29±0.17) apical transportation. There were fewer lateral perforations in SAF (4.2%) and PTN (7.7%) than in HF (47.8%) (p&lt;0.05). In primary molars, mechanical preparation showed better shaping ability than hand files, promoting more centered preparations and lower occurrence of lateral perforations and canal transportation. Clinical Relevance: Manual instrumentation is still reported as the main choice in the primary teeth preparation; however, studies have shown limitations in its use. The morphological characteristics of primary teeth and the limited knowledge of shaping procedures in these teeth using mechanical preparation become a challenge for clinical practice and might impair the predictability of endodontic treatment.摘要 本研究旨在通过二维及三维显微计算机断层扫描（micro-computed tomography，micro-CT）分析，评估手用锉（hand files）、ProTaper Next以及自调节锉（Self-Adjusting File，SAF）对乳磨牙的根管预备效果。本研究纳入24颗乳磨牙，分为3组（每组n=8），分别采用手用锉（HF）、ProTaper Next（PTN）以及自调节锉（SAF）进行根管预备。分别于根管预备前后对患牙进行扫描，并对术前、术后的micro-CT影像进行三维重建。本研究评估了二维参数（面积、周长、圆度、最小直径及最大直径）与三维参数[体积、表面积、结构模型指数（structure model index，SMI）]的形态学变化，同时评估了根管偏移与侧穿情况，统计方法采用克罗斯卡尔-沃利斯检验及方差分析，检验水准α=0.05。与HF组及PTN组相比，SAF组的最小直径、体积及表面积变化幅度更小（p<0.05）。预备后，PTN组的根管形态更接近圆形。三维分析显示，HF组的根管偏移程度更显著。PTN组与SAF组的根管预备更居中，在弯曲根管区域尤为明显。SAF组与HF组的根尖偏移程度分别为最低（0.05±0.02、0.07±0.04）与最高（0.14±0.11、0.29±0.17）。SAF组（4.2%）与PTN组（7.7%）的侧穿发生率均低于HF组（47.8%），差异具有统计学意义（p<0.05）。针对乳磨牙的根管预备，机用器械的成形能力优于手用锉，可获得更居中的预备效果，并降低侧穿与根管偏移的发生率。 临床意义：目前临床仍将手用器械作为乳磨牙根管预备的主要选择，但相关研究已证实其应用存在局限性。乳磨牙的形态学特征，以及临床对机用器械用于该类牙体的成形操作认知不足，均为临床实践带来挑战，并可能降低牙髓治疗的可预测性。