Vertical root fracture resistance and crack formation of root filled teeth treated with or without minimally invasive endodontic shaping

Abstract The aim was to investigate the vertical root fracture (VRF) resistance and crack formation of root filled teeth treated with (+) or without (–) minimally invasive endodontic (MIE) preparation. Human maxillary central incisors of similar size were decoronated, randomized into six groups (n = 18, power = 0.9) and embedded in acrylic blocks with artificial periodontal ligament. In the +MIE group, root canals were prepared with nickel-titanium (NiTi) rotary files up to size #40, taper 0.04 and filled with conventional cement (C) or adhesive (A) sealers in single-cone obturation. Preparations of the –MIE group were enlarged with NiTi rotary and K-files up to ISO size #80 and filled according to C or A. Controls either received no treatment or left unfilled after preparation. After thermocycling and staircase loading in a chewing simulator, the crack formation on the root surface was microscopically examined and classified as no defect, craze line, vertical crack, and horizontal crack. Subsequently, the samples were loaded until root fracture. Data were analyzed by Kruskal-Wallis test and Mann-Whitney U test with Bonferroni correction. Post hoc analysis revealed no significant difference in the incidence of defects between the groups ( P ≥0.0772). VRF resistance was significantly higher in untreated teeth than in +MIE/C ( P = 0.0202), but not significantly different between other groups ( P ≥ 0.0680). Both VRF resistance and crack formation of root filled teeth were statistically indistinguishable with or without MIE preparation. Most dentin defects were vertical root cracks.