Effect of the double application of universal adhesives on the dentine bond strength after radiotherapy.

This study aimed to evaluate the effect of double application of universal adhesives on bond strength to dentine after ionizing radiation. One hundred and forty caries-free human third molars were used. Half of the teeth were irradiated (IR) (70.2 Gy). The IR and non-IR teeth were assigned into seven groups (n = 10). Universal adhesives Single Bond Universal (3M Oral Care), Gluma Bond Universal (Heraeus Kulzer) and Prime&Bond Elect (Dentsply) were employed (following manufacturer's instructions and double application). Two-step self-etch adhesive Clearfil SE Bond (Kuraray Noritake) was used as control. After composite build-ups were bonded to mid-coronal occlusal dentine surfaces, the specimens were stored in water (37°C/24 h) and sectioned into microspecimens. The specimens were subjected to μTBS testing (1.0 mm/min). Failure analysis was performed using stereomicroscope and scanning electron microscopy. Data were analysed with two-way ANOVA and Tukey's test (P = 0.05). The radiotherapy caused reduction in the bond strength of universal adhesives when the adhesives were used with single application after radiotherapy (P < 0.05). The double application resulted in increased bond strength of the universal adhesives to IR dentine (P < 0.05). The double application was beneficial in improving the dentine bond strength of universal adhesives affected by radiotherapy after ionizing radiation.