Effect of gamma radiation on bonding to human enamel and dentin.

Purposes: This study evaluated the effect of gamma radiation on the microtensile bond strength of resin-based composite restoration to human enamel and dentin performed either before or after radiotherapy.
Methods: Thirty sound human third molars were sectioned mesio-distally into buccal and lingual halves and then randomly divided into enamel or dentin groups. Enamel and dentin substrates were randomly divided into three sub-groups (n = 10): Control, which received no irradiation; specimens were irradiated before restoration protocol; and specimens were irradiated after restoration protocol. Radiation therapy was defined by application of 60-Gy dose fractionally with daily exposures of 2 Gy, 5 days a week, over 6 weeks. Restorations were carried out using Adper Single Bond adhesive system and Filtek Z250 resin composite. The specimens were sectioned producing 4 sticks per specimen and submitted to microtensile on a testing machine. Data were submitted to two-way ANOVA followed by Tukey test (p < 0.05). Failure modes were examined under optical microscopy and SEM.
Results: Bond strength to enamel was significantly higher than to dentin irrespective radiation therapy. Radiotherapy applied before restoration significantly reduced the bond strength to both substrates. A predominance of adhesive failures was detected for control groups and groups restored before radiotherapy. Cohesive failures in dentin and enamel increased when the specimens were restored after irradiation.
Conclusions: The gamma radiation had a significant detrimental effect on bond strength to human enamel and dentin when the adhesive restorative procedure was carried out after radiotherapy.