OR42 - **CANCELLED**Micro-Computed Tomographic Analyses of Propagation of Pre-existing Dentinal Microcracks and Propagation of New Cracks After Root Canal Instrumentation with Rotary, Reciprocating and Adaptive file systems

Objectives: To compare propagation of pre-existing and generation of new dentinal microcracks after root canal instrumentation with ProTaper Universal(PTU), ProTaper Gold (PTG), Twisted file Adaptive(TFA) and Reciproc Blue(RB) using micro-CT.

Methods: The mesial-roots of 180 extracted mature mandibular molars were resected at 10 mm from the apex and randomly divided into four groups(n=45) based upon file system used: PTU, PTG, TFA and RB. Each of these four groups were then subdivided into three groups(n=15) based on working length(WL) i.e., instrumentation 1 mm short, flush, and 1 mm beyond the major apical foramen(MAF). Roots were scanned with micro–CT before and after instrumentation. Cross-sectional slices obtained for all the groups were screened to detect the generation of new microcracks. One subgroup (prepared 1 mm short of MAF) was also analysed for the extension of pre-existing dentinal-microcracks by comparing it with corresponding pre-instrumentation image. Results & Statistics: Wilcoxan Rank test and Kruskal Walis test were used to assess new microcrack formation and to evaluate effect of WL on microcrack generation. PTU system showed significant increase in number of new microcracks generation at all WL and significant propagation of pre-existing microcracks at WL 1mm short of MAF(P≤0.05). No significant increase in the number of new microcrack generation and pre-existing microcrack propagation was observed for PTU, PTG and RB (P>0.05).

Conclusions: Conventional rotary instruments induced higher number of new microcrack formation and pre-existing microcrack propagation in comparison to thermally treated and reciprocating file systems. Instrumentation WL did not significantly influence the new microcrack generation.