in-vitro comparison of niti tee, race and protaper instruments in dentinal crack formation

Background and aim:root canal preparation with rotary instruments may cause dentinal cracks leading to tooth fracture. the aim of this study was to compare three different rotary systems protaper, race and niti tee on formation of dentinal cracks following root canal preparation. materials and methods: in this experimental study, 50 extracted mandibular first molars were selected. teeth having roots with previous cracks and defects were excluded from the study. the crowns and distal roots of teeth were cut. silicon impression material was used to simulate tooth pdl. the mesial roots were randomly prepared using protaper (up to f3) race and niti tee systems (up to ≠30/0.06) in three groups of 15. five teeth remained unprepared as the control group. the specimens were then sectioned horizontally in 3, 5 and 9 mm distances from the apex. cracks exploration was done by digital stereomicroscope. the occurrence of dentinal cracks with different systems were statistically analyzed by chisquare test. results: dentinal defects were observed in 3 (20%), 4 (26.7%) and 2 (13.3) of root canals following the preparation with protaper, niti tee and race files, respectively. two of the 3 defects in protaper group were as complete crack. the overall incidence of crack among the rotary files was 20%. no significant differences were found in defect formation between the three rotary systems (p>0.05).  conclusion: under the condituion of this study dentinal cracks were observed in all systems. the overall incidence of crack among the rotary files was 20%. although more cracks were observed in ntitee group, the differences were not significant.