Fracture resistance and biomechanical behavior of different access cavities of maxillary central incisors restored with different composite resins

Objectives: The aim of this study was to compare the effect of three different access cavities on the tissue removal, deflection, fracture resistance, and stress distribution of extracted maxillary central incisors. Materials and methods: Forty human maxillary central incisors were randomly assigned in four experimental group (n = 10) including conservative access cavity “CAC,” traditional access cavity “TAC,” invasive access cavity “IAC,” and without access cavity (control group). Cone-beam computed tomography “CBCT” scans were used to evaluate the tissue removal during the different access cavities. All specimens were restored with composite resin (Admira Fusion, Voco, Cuxhaven, Germany) and embedded in acrylic resin blocks after simulating the periodontal ligament using red wax, then the specimens were submitted to the deflection test applying a load of 250 N and to the load-to-fracture test after artificial aging in a mechanical cycling machine (150 N, 5 × 10⁶ cycles, 10 Hz). Lastly, stress distribution was assessed by three-dimensional finite element analysis (3D-FEA), simulating the specimens restoration by two types of composite resins of low and high elastic modulus (8 and 18 GPa respectively) after the access cavities. The data were submitted to Shapiro–Wilk and KS normality tests. Then, they were analyzed by one-way ANOVA and Tukey tests with a significance level (α ≤ 0.05). Results: CBCT scans showed a significant difference of worn tissues in CAC and TAC when compared to the IAC (P < 0.0001). In deflection test, CAC showed lower deformation values than the TAC and IAC. Load-to-fracture test presented no significant difference among the three experimental groups (P = 0.6901). 3D-FEA showed that the more conservative the access cavity, the higher the stress magnitude. Conclusions: CAC promote less worn tissue; however, this does not improve the stress distribution or fracture resistance of endodontically treated maxillary incisors. Clinical relevance: Clinicians should reconsider the pros and cons of the conservative access cavity.