Influence of access cavity preparation on the dentine thickness of mesial canals of mandibular molars prepared with reciprocating instruments

Abstract

To evaluate the influence of traditional and conservative access cavity preparations on the remaining dentine thickness in the coronal third of mesial canals of extracted mandibular molars prepared with reciprocating instruments using micro-computed tomography as the analytical tool. Seventy extracted mandibular molars were scanned at a pixel size of 19μm. From this initial sample, 20 teeth were selected, pair-matched and distributed into two groups (n=10) according to the access cavity preparation: traditional (TradAC) or conservative (ConsAC). The root canals were sequentially enlarged with Reciproc Blue R25 (size 25, 0.08v taper) and R40 (size 40, 0.06v taper) instruments. A new scan was performed and the postoperative stacks were coregistered with their respective preoperative datasets. A colour-coded cross sections of the roots were created and used to identify and measure the smallest dentine thickness related to both MB and ML canals at 1.0-mm intervals from the furcation level of up to 5mm in the apical direction, in both mesial and distal aspects of the roots, before and after preparation. The statistical analyses were performed with paired-samples t-test, independent-samples Student T-test and Chi-Square test with a significance level of 5%. At all levels of both groups, dentine thickness before preparation was greater than after preparation (p<.05). No difference in the percentage of dentine reduction was observed between TradAC and ConsAC groups (p>.05), but a significantly greater reduction was observed to the distal aspect of the roots (p<.05). After root canal preparation, dentine thinner than 0.5mm was observed mostly along the distal aspect of the root (10% to 15%) of the MB and ML canals, with no influence of the access cavity type on its incidence to either mesial (X2 =1.66; p=.2) or distal (X2 =0.40; p=.5) directions. In the TradAC group, dentine thickness in most slices was greater than 1.0mm after preparation (n=124) whilst, in the ConsAC, it ranged from 0.5 to 1.0mm (n=136). Traditional or conservative access cavity preparation in extracted mandibular molars did not influence the remaining dentine thickness in the coronal third of mesial canals enlarged with thermomechanically treated nickel-titanium reciprocating instruments.