Aim To investigate the morphological changes in the apical third of the root canal after preparation with three techniques.
Methodology Forty molar teeth were scanned using micro-computed tomography before and after instrumentation with: Group 1 – stainless steel K-files using the balanced force technique; Group 2 – stainless steel K-files (balanced force) and then refining the apical preparation with the equivalent size 0.04 taper FlexMaster instrument; Group 3 – a hybrid ProTaper/FlexMaster (ProFile for sizes 45 and 60) sequence. Eight canals were excluded because of artefacts in the images or unnegotiable blockages leaving 110 canals that could be analysed. Apical root canal preparation was evaluated with respect to the amount of dentine removed, canal roundness, transportation and how the dimensions of the prepared apical root canal correlated with those of the final instrument used.
Results The median apical preparation sizes for the three groups respectively were: 30, 30 and 40. Despite the larger size and less experienced operator, the volumetric change (the amount of dentine removed) in canals prepared with a hybrid rotary nickel–titanium instrumentation technique remained small and, a more rounded preparation (P < 0.001) that closely matched the final instrument dimensions (P < 0.001) was produced. There was a trend for less canal transportation using rotary nickel–titanium instruments.
Conclusions Stainless steel hand preparation was not conservative of apical dentine. When used correctly, even by less experienced operators, rotary nickel–titanium instruments were able to precisely ‘machine’ a canal to larger apical sizes with minimal risk of iatrogenic damage.