The Effect of Radiotherapy on Resin-dentin Bond Strength

Abstract

Radiotherapy for oral cancer causes radiation caries. This study evaluated the effect of γ-ray irradiation on resin/dentin bond strength, dentin microhardness and elastic modulus. One group of bovine incisors was irradiated with 60 Gy γ-rays using a cobalt 60 therapeutic machine. The control group of bovine incisors was not irradiated with γ-rays. Flat dentin surfaces were prepared on the labial side. The teeth were treated with the Clearfil SE Bond adhesive system. Clearfil AP-X hybrid composite was built up to 3×4×3 mm. The resins were light cured with 600mW/cm² for 40s. After storage for 24h, the teeth were sectioned to about 1.0 mm thickness. The slabs were trimmed (ca. 1 mm²) at the adhesive-dentin interface for the micro-tensile bond strength test (μ-TBS). The trimmed specimens were mounted on a testing apparatus, and stressed to failure under tension at 1 mm/min in an EZ test machine. Nano-indentation hardness and elastic modulus on both dentin surfaces were measured using a nano-indentation tester. μ-TBS (n=10), nano hardness (n=20) and elastic modulus data (n=20) were analyzed using Fisher's PLSD test. There was no significant difference in μ-TBS between the intact group and irradiated group (p>0.05). Nano hardness and elastic modulus of the irradiated group were significantly lower than those of the intact group (p<0.05). Irradiation with 60 Gy γ-rays had no effect on resin/dentin bond strength. However, 60 Gy γ-ray irradiation significantly decreased the microhardness and elastic modulus of dentin.