ABSTRACT
AIM AND OBJECTIVE: To investigate the occurrence of microcracks in the canals containing broken instruments in the middle and apical thirds after instrumentation with various systems. MATERIALS AND METHODS: One-hundred and fifty mature mandibular premolars with single straight canal were collected and stored in distilled water. Samples were checked out from any preexisting deformation or cracks, and then standardized in length. Thirty teeth were never instrumented (NI) as a control group, 60 teeth have received a broken instrument in the middle third, and 60 ones at the apical third. Teeth were placed in resin blocks with simulation of periodontal ligaments. After bypassing the instruments, samples were divided into four groups n = 30; first group was prepared manually MN until 25/0.02, while the other three groups were prepared until 25/0.04 using three different rotary systems; Race RC-2Shape TS-Hyflex CM HCM. Roots were cut transversely at levels of broken instruments and examined under 40× microscopic magnification. RESULTS: All the rotary groups produced microcracks. No significant difference of the partial cracks was observed among all groups at the middle and apical levels p >0.05. TS produced more complete cracks compared to each of NI, MN, RC at middle level and NI, MN at apical level; p <0.05. No significant differences of microcracks incidence were observed between two middle and apical levels among the five groups. CONCLUSION: Dentinal microcracks could be obviously resulted after rotary instrumentation alongside broken instruments, while manual shaping was less likely to cause microcracks. CLINICAL SIGNIFICANCE: Manual files were less likely to induce microcracks alongside broken instruments in comparison with rotary files which could be considered much safer.
