Impacto do aumento progressivo das conicidades dos instrumentos endodônticos durante o preparo de canais na formação de microtrincas dentinárias em molares

Abstract

The formation of dentin microcracks can occur after root canal instrumentation, acting as a potential trigger for root fractures and influencing the long-term viability of endodontically treated teeth. Therefore, this study aimed to assess the influence of instruments with the same tip but different tapers on the formation of dentin microcracks after root canal preparation in maxillary molars, using microcomputed tomography (micro-CT) analysis. Forty maxillary molars were initially scanned using micro-CT, and then, twenty maxillary molars with similar volume, area, and 3D configuration were selected. The teeth were then divided into two groups (n=10): those without mesiobuccal canal 2 (MB2) and those with MB2. Subsequently, the teeth were accessed, mounted on a mannequin to simulate clinical practice, and the root canals were prepared with instruments of size tip 25 and different tapers (0.03, 0.05, 0.06, and 0.08v) following the manufacturer's recommendations. After each preparation, the teeth underwent new scans, resulting in five micro-CT acquisitions (prior to preparation, after 0.03, 0.05, 0.06, and 0.08v taper). Cross-sectional images before and after each preparation were reconstructed, registered, and evaluated from the furcation level to the root apex to identify the presence of dentin microcracks. To validate the analyses, microcracks were qualitatively twice, at two-week intervals, by two examiners. The data were descriptively analyzed (frequencies and means), and intra- and inter-examiner calibration was measured using the Kappa index, yielding values of 0.85 and 0.88, respectively. Out of a total of 42,925 cross- sectional images, only 1206 (2.8%) showed dentin microcracks. Notably, all microcracks observed after each root canal preparation were already present in the corresponding images before canal instrumentation. The progressive enlargement of root canals with different tapers did not promote the formation of dentin microcracks in maxillary molars, both with and without MB2 canal.