Influence of antioxidant agents following intracoronal bleaching with different hydrogen peroxide concentrations on the adhesive interface and fracture resistance

Purpose To evaluate the influence of a 25% alpha-tocopherol antioxidant gel (AT) and a 50% DL-α-lipoic acid antioxidant solution (AL) on coronal fracture resistance and the integrity of the adhesive interface between coronal dentin and a universal adhesive system (Ambar Universal APS), compared with a 10% sodium ascorbate gel (AS), after internal bleaching with 35% or 40% hydrogen peroxide. Materials and methods Two hundred bovine incisors were used: 80 teeth for fracture resistance and fracture pattern analyses, 80 crowns for resin tag evaluation, and 40 crowns for microtensile bond strength and failure mode analyses. Specimens were allocated according to hydrogen peroxide concentration (35% or 40%) and antioxidant protocol: control (CO), sodium ascorbate (AS), alpha-tocopherol (AT), and DL-α-lipoic acid (AL). Data were analyzed using appropriate statistical tests with a significance level of 5%. Results Sodium ascorbate and alpha-tocopherol exhibited the highest fracture resistance and microtensile bond strength values, whereas sodium ascorbate promoted the greatest resin tag formation. The control groups showed the lowest values for the evaluated mechanical and adhesive properties. DL-α-lipoic acid demonstrated intermediate performance. No significant differences were observed between the 35% and 40% hydrogen peroxide protocols. Conclusion The application of antioxidants after intracoronal bleaching resulted in higher fracture resistance and bond strength compared with the bleached control protocols. Under the experimental conditions evaluated, the sodium ascorbate and alpha-tocopherol protocols showed the most favorable overall performance.