Microtrincas dentinárias: um fenômeno experimental pós-extração?

The present study had a two-fold purpose. The study 1 has investigated the potential cause-effect relationship between the incidence of preexisting dentinal microcracks and root fracture resistance in endodontically non-treated lower incisors (in vitro experimental model). The study 2 has investigated the prevalence, location and pattern of preexisting microcracks in endodontically untreated teeth of fresh cadavers (ex vivo experimental model) using Micro-computed tomography (microCT). Methodology. In the first study, 60 teeth with a dentinal volume varying between 107.46 and 187.33 mm³, similar dentinal thickness and having circularshaped canals were selected and scanned at a resolution of 14.16 μm. All crosssections produced were screened to determine the frequency of dentinal microcracks (%). Afterwards, the 60 roots were embedded with polyester resin receiving an artificial simulation of the periodontal ligament in polyether. The specimens were then subjected to a 1.0 mm / min load fracture test to establish the force required to fracture; the fractography analysis was performed by the visual inspection of the 3D models considering 2 modes of fracture: (i) cervical fractures or (ii) vertical root fracture. Study 2: 33 cadaveric bone blocks containing 132 right and / or left premolars and molars, with complete apex formation, were collected and coded. Surgical removal of the cadaveric bone blocks were done using a low-speed saw drill (701 JET, Morrisburg, Ontario, Canada). The scanning of the bone blocks containing the teeth was performed with a resolution of 13.18 μm and the cross-section imagens produced were screened for dentinal microcracks. Results. Study 1: The results showed that 79% of the specimens had dentinal microcracks (n = 44); the number of microcracks per sample varied from 0 to 1605 (between 6% and 42%) with a mean of 412 ± 484 (median = 221 and 25% IQR = 15/75% = 658). The forces required to produce the fracture during the test ranged from 227N to 924N, with a mean of 560.3 ± 168.1N (median 561 and 25% IQR = 458/75% = 694). The correlation of the Spearman's coefficient (rho) was equal to 0.065. Study 2: The evaluation of 48,530 cross-sectional images from teeth inserted in the cadaver bone-blocks reveled no preexisting microcracks. Conclusions: (1) there is no cause-and-effect relationship between the number of micro-fractures and fracture resistance in endodontically untreated lower incisors, and therefore the presence and quantity of micro-cracks does not determine which roots are more susceptible to fracture; (2) there are no microcracks in tooth non-endodontically treated teeth in fresh cadaveric bone blocks. The conclusions induce us to reflect on the real role / existence of the dentin microcracks phenomenon in Endodontics.