Aim: This in vitro study was conducted to measure and compare the incidence of dentinal defects caused by (RECIPROC blue, ProTaper Gold, ProTaper NEXT and RECIPROC) nickel titanium (NiTi) rotary instruments.
Materials and methods: Seventy-five palatal roots of freshly extracted human maxillary first molars were used in this study. The total samples were randomly divided into five groups. Each group contained 15 samples (N = 15): group I: single file RECIPROC system, group II: ProTaper Next system, group III: ProTaper GOLD system, group IV: single file RECIPROC blue system and Group V: control group (No preparation). Root canal instrumentation were carried out according to manufacturer\'s instructions for each instrumentation system to # 40 apical size. Each root sample was sectioned horizontally at 2 mm, 4.5 mm and 7 mm, respectively from the apex. All root sections were observed under a stereomicroscope at 25X magnification.
Results: The roots prepared by Reciproc showed the highest incidence of dentinal defects followed by ProTaper NEXT, ProTaper Gold then RECIPROC blue group which showed the lowest incidence of dentinal defects. The data obtained were analyzed statistically using Fisher\'s exact test at or equal to 5% significance levels. Fisher\'s exact test revealed that RECIPROC groups had a significant difference when compared with RECIPROC blue (p. 0.01) and with ProTaper Gold (p. 0.05) groups. While, other comparisons between each pair of groups revealed a non-significant difference between groups (p > 0.05). Regarding dentinal defects at different levels (apical, middle, coronal), Fisher\'s exact test showed that there was a non-significant difference in the incidence of dentinal defects when comparing among different levels in the same group or when comparing among different groups at the same level (p > 0.05).
Conclusion: all experimental groups showed dentinal defects while no dentinal defects were observed in the negative control group.
Clinical significance: the potential of root fracture is reduced using more flexible Ni Ti rotary instruments.
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