Effect of Ionizing Radiation on Shear Bond Strength and Interface Characterization of Various Adhesives to Enamel and Dentin

Abstract

For shear bond strength testing, three hundred bovine anterior teeth were used. 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; Non-irradiated, irradiated before bonding (Pre-rad) and irradiated after bonding (Post-rad), 2- Adhesive system; Single Bond Universal (SBU, 3M-ESPE, USA), Gaenial 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 (37ºC/24h). SBS test was run at a crosshead speed of 0.5 mm/min. Statistical analysis was performed using Three-Way ANOVA, One-Way ANOVA and t-test, p=0.05. Failure mode analysis was evaluated using digital microscope at 40X magnification. For nanoleakage testing, a total of 60 bonded slabs were prepared. Specimens were assigned into 30 groups (n = 2) and divided as for SBS testing. Specimens were prepared according to the protocol stated by Tay et al., using ammonical AgNO3 tracer solution and micrographed using SEM. For surface topography and EDX analysis, specimens were prepared as for SBS testing. Teeth were randomly divided into 4 groups (n=2) according to: 1- Radiation; Non-irradiated, irradiated, and 2- Tooth 131 substrate; enamel or dentin. Analysis was made using SEM-EDX system. Three-way ANOVA for SBS revealed significant effect of all variables of the study (radiation, adhesive system and substrate, p=0.001, p=0.0001 and p=0.0001 respectively). Regarding enamel, GB showed decreased SBS when irradiated before or after bonding, while Pre-rad/ FM+ showed increased SBS. Regarding dentin, GB showed decreased SBS when irradiated before or after bonding, similarly Pre-rad/ FM+, Pre-rad/FU and Post-rad/ SBU groups. GI and GB showed the highest SBS when bonded to enamel and the least when bonded to dentin, contrary to SBU and FM+. Failure mode analysis showed adhesive failure in 63% of the specimens, mixed failure in 27%, cohesive failure in substrate 10%. Nanoleakage results showed tracer penetration at the adhesive / tooth interface in most all of the tested adhesives (except FM+), which was most extensive for GB specimens. Surface topography showed obliteration of surface characterization and melted appearance for the irradiated specimens. Also, EDX analysis showed significant difference in the elemental composition between non-irradiated and irradiated specimens.