Effect of endodontic access type on the resistance to fracture of maxillary incisors

Objective: To compare the effect of endodontic access cavity location - labial versus palatal - on the resistance to fracture of maxillary incisors. Method and Materials: Sixty intact human maxillary incisors were selected: 20 pairs of central incisors and 10 pairs of lateral incisors. From each pair, 1 tooth was randomly selected to receive a palatal access cavity; the other tooth of the same pair received a labial access cavity. The teeth were divided into 4 test groups: group 1, central incisors with labial access; group 2, central incisors with palatal access; group 3, lateral incisors with labial access; and group 4, lateral incisors with palatal access. A lateral condensation technique was used to fill the canals with gutta-percha cones and AH-26 (Dentsply DeTrey). The access cavities were restored with hybrid resin composite. Specimens were mounted in a jig that allowed loading at the center of the palatal surface of the tooth, over the cingulum, at an angle of 130 degrees to the long axis of the tooth. Continuous compressive force at a crosshead speed of 2 mm/min was applied by an Instron universal testing machine. Load at fracture and mode of failure were recorded. Multiple analysis of variance (MANOVA) with repeated measures was used to statistically compare differences between groups at a significance of 5%. Results: Mean failure loads for the 4 test groups were as follows: 894 N (group 1), 821 N (group 2), 774 N (group 3), and 705 N (group 4). No significant difference in failure load values was found among all tested groups (F = 0.5; P > .05). The mode of failure in all groups was an oblique radicular fracture, either at the level of the cementoenamel junction in 40% to 45% or at the root level in 55% to 60% of the teeth. Conclusion: Different endodontic accesses-labial or palatal-did not affect the failure resistance of maxillary incisors under simulated occlusal load.