Effect of Ionizing Radiation on SBS of Different Adhesive Systems

Objectives: To evaluate effect of ionizing radiation on the shear bond strength (SBS) of different composite adhesive systems to tooth structure applied before or after radiotherapy
Methods: Three hundred bovine anterior teeth were used in this study. Subsequent to teeth grinding and creation of the smear layer, the cervical thirds of the teeth were randomly divided into 30 groups (n=10) according to: 1- Radiation exposure; Non-irradiated, irradiated before bonding (Pre-rad) and irradiated after bonding(Post-rad), 2- Adhesive system; Scotchbond Universal (SBU, 3M-ESPE, USA), G-aenial bond (GB, GC Europe, Belgium), Futurabond U (FU, VOCO, Germany), Futurabond M+ (FM+, VOCO, Germany), GC FUJI BOND LC (GC Europe, Belgium) and 3- Tooth substrate; enamel or dentin. Adhesives were applied according to manufacturer instructions and light cured. One cylinder of Grandio nano-hybrid composite (VOCO, Germany) measuring 4mmx2mm was bonded and light cured. Irradiation was performed using 60 Gray of gamma rays emitted from a cobalt-60 machine (Theraton Phoenix, Canada). Specimens were stored in distilled water (37^○C/24h). SBS test was run at a crosshead speed of 0.5 mm/min. Statistical analysis was performed using Three-Way ANOVA, Tukey HSD test and t-test, p=0.05. Failure mode analysis was evaluated using stereomicroscope at 40X magnification.
Results: Three-way ANOVA revealed significant effect of all variables (irradiation timing, adhesive system and substrate, p=0.0001). The average means of the irradiation time were: Non-irradiated 10.80 ±3.49 MPa > Pre-rad 9.59±3.41 MPa = Post-rad 9.59±3 MPa. Average means of adhesive systems were: SBU (11.06±3.07 MPa) > FU (9.38± 3.03 MPa), FM+ (10.61±3.09 MPa) = GI (9.93±3.91 MPa) = FU, FM+ >GB (8.99±3.20 MPa) and GI=FU=GB. The average means of the substrate were: enamel 10.93±2.92 MPa > dentin 9.06±3.49 MPa. Adhesive failure represents 64%, mixed represents 26% and cohesive represents 10%.
Conclusions: Ionizing radiation before or after bonding decreases the SBS. Change of material formulation affects the SBS.