Abstract

Purpose: Biomechanical preparation is a crucial stage in endodontic treatment, involves the cleaning and shaping of the root canal system. Generally, single file system is widely used which has a simple concept and continuous movement in a clockwise direction. The speed and torque of the endomotor are essential indicators to assess the cleanliness of the root canal. The extent of smear layer distribution and the possibility of microcracks in root canal are indicators of root canal cleanliness and safety considerations in root canal treatment. The present study aimed to evaluate the effects of different torque and speed parameters on smear layer and microcrack formation in apical dentin of root canals with single file instrumentation.
Materials and Methods: This laboratory experimental study used a Confocal Laser Scanning Microscope (CLSM) to observe the formation of a smear layer and possibility of microcrack in the apical third. Forty-eight samples of mandibular first premolars were prepared in different rotation speeds (250rpm, 400rpm) and torque (0.8N.cm, 2.5N.cm). Twenty-four samples observed the formation of smear layer based on Hulsmann score and 24 samples to observe the possibility of microcrack based on Shemesh score. Data were analyzed statistically by Chi-Square and Kruskal-Walls test.
Result: The smear layer evaluation results in the current study only showed scores of 2, 3, and 4. Meanwhile, microcrack analysis shows all scores 1,2, and 3. However, statistical analysis revealed no difference that was significant.
Conclusion: According to the findings of this study, it is recommended to utilize rotary instruments with low torque and speed to remove smear layers dan for safety consideration.

Keywords:Endodontic treatment; Smear layer; Microcrack; Root canal