Investigation of dentinal cracks with different file systems and different torque values: An in-vitro study

Aim: Preparation of root canals is one of the most important steps in the success of root canal treatment and determines the effectiveness of all subsequent procedures. One of the procedural errors at this stage is the formation of cracks in the dentin. Dentin cracks may cause vertical root fractures that lead to tooth extraction under long-term occlusion forces. The aim of this study is to comparatively examine the formation of dentin cracks by working with different file systems and different torque values. Materials and Methods: In this study, 140 single-root and single-canal lower premolar teeth were used. The crowns of the teeth were cut with the help of a low-speed saw, and the length of the teeth was equal to 15 mm. 20 teeth were allocated as the control group. The remaining 120 teeth were embedded in acrylic blocks after being covered with melted wax. After the acrylic hardened, the waxes on the tooth surface were removed and a polyether impression material was placed in the resulting gap to imitate the periodontal ligament gap and it was re-embedded in the acrylic block. The teeth were randomly divided into 6 groups. Group1: one curve file system and 1N/cm torque, Group 2: one curve file system and 2N/cm torque, Group 3: one curve file system and 3N/cm torque, Group 4: one curve file system and 1N/cm torque , Preparations were completed as Group 5: one reci file system and 2N/cm torque, Group 6: one reci file system and 3N/cm torque. Group 7 was separated as the control group without any preparation. After the preparation was completed, a horizontal section of 3, 6, 9 mm was taken with the help of a low-speed saw under water cooling. The teeth were stained with caries detection dye and examined under a dental operating microscope. Dentin cracks occurring on the teeth were subjected to chi-square statistical test.Results: No dentinal crack formation was observed in any section in the control group. Crack formation was observed in all other groups. When the sections were examined, significantly fewer cracks were found in the middle section in Group 2 compared to the other groups. No significant difference was found between the other groups. When the dentinal crack incidence between the groups was examined regardless of the section level, significantly fewer dentinal cracks were found in Group 1 compared to the other groups. In Group 4, significantly more dentinal cracks were seen compared to the other groups. No significant difference was found in the other groups. When the crack type was examined regardless of the section level, significantly more completed cracks were found in Group 4. No significant difference was found between the other groups. When the crack incidence at the section levels was compared without considering the groups, although there was no significant difference, the crack rate was found to be high in the apical section. Conclusion: We can say that reciprocation movement can create more dentin cracks than rotation movement. Although it is thought that less stress will be applied to the tooth and fewer cracks will be seen in the tooth at low torque, different results can be obtained as the ideal recommended torque usage of Ni Ti files is moved away. Our recommendation is to use Ni Ti files at the torque values recommended by the manufacturer. Keywords: Dentin crack, Torque, One Curve, One Reci