Effect of Radiotherapy on Resin/Dentin Adaptation using One-Step Bonding System

Objectives: Radiotherapy for oral cancer causes irradiation caries. The purpose of this study was to evaluate the effect of γ-rays irradiation on the marginal sealing and cavity wall adaptation of composite restorations using one-step adhesive system. Methods: One group of bovine incisors was irradiated with 60Gy γ-rays using a cobalt 60 therapeutic machine. Cylindrical cavities, 1.5mm deep and 3mm in diameter(C-factor=3) were prepared on flat dentin surfaces. The teeth were restored with two-step bonding system; Clearfil SE Bond (SE:Kuraray Medical), One-step bonding system; Tokuyama Bond Force (BF:Tokuyama dental) or Clearfil Tri-S Bond (TS:Kuraray Medical) adhesive system followed by Clearfil AP-X hybrid composite: shade A3 (Kuraray Medical). The resins were light cured with 600mW/cm² for 40s. After thermocycled for 5000 cycles, dye penetration tests around the cavity margin and cavity wall on cut surface were carried out. Dye penetration length was calculated as a percentage of the total cavity wall length. Dye penetration scores (n=8) were analyzed using the Mann-Whitney U test. Results: Marginal leakage(%) were all groups; 0. Cavity-wall gap formations(%) were Intact Group; SE: 0, BF: 13.3(17.1), TS: 21.4(15.0), Irradiated Group; SE: 4.1(5.7), BF: 13.8(13.2), TS: 26.2(12.9). All adhesive groups showed complete marginal sealing regardless of intact dentin or irradiated dentin. SE showed significantly improved cavity wall adaptation compared with BF and TS for intact group (p<0.05). SE showed significantly better cavity wall adaptation compared with TS for irradiated group (p<0.05). Conclusion: Irradiation with 60Gy γ-rays had no effect on resin composite adaptation to the cavity wall regardless of bonding system. However, one-step bonding system significantly decreased cavity wall adaptation compared with two-step bonding system Clearfil SE Bond. Supported by Grant #17390513 from Japan Ministry of Education, and COE Program, FRMDRTB at TMDU.