Comparative evaluation of effect of different manufacturing process in different torque settings on root dentine crack formation using micro-CT: an in vitro study

Objectives. To compare the effect of different manufacturing processes of NiTi rotary instruments with two different torque levels on the cracks formation in root dentin using Micro-CT. Materials and methods. Forty mandibular single rooted premolars were selected for the study. Samples were randomly divided into four groups (n-10) with two subgroups (n-5) each. Group 1(A) - (PTU-HT), Group 1 (B) - (PTU-LT), Group 2 (A) - (PTN-HT), Group 2(B) - (PTN-LT), Group 3(A) - (HYF-HT), Group 3(B) - (HYF-LT), Group 4 (A) - (TF-HT), Group 4(B) - (TF-LT). Pre-operative Micro-CT scanning was done. Instrumentation was done in high and low torque based on the rotary instruments. The samples were subjected to Post-operative Micro-CT analysis. Preoperative and post-operative Micro-CT images were superimposed by automatic superimposition process with Seg 3D v.2.1.4 software to detect the presence of dentinal cracks. Based on the images, samples were divided into specimens with cracks and without cracks. Statistical analysis was done with Mann-Whitney U test with p-value ˂0.05 regarded to be significant. Outcomes. High torque Group 1 (A) - (PTU-HT) showed more cracks compared to Group 4(A) - (TF-HT), 2(A) - (PTN-HT) and 3(A) - (HYF-HT). In low torque group only one sample in Group 1(B) - (PTU-HT) showed the presence of crack compared to no cracks in other groups. Statistically no difference was found between the groups. Conclusion. Given the limitations of this study, it can be determined that the manufacturing process and the torque settings could play a major role in dentinal crack formation. Nevertheless, no statistical significance was found between the tested groups.