الفهرس 
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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), 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 (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 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.
Conclusions:
Within the limitations of this study, the following could be concluded:
The effect of exposure of enamel and dentin to ionizing radiation; before or after bonding, is adhesive-dependent.
Glass ionomer adhesive (GI) as well as low pH self-etching adhesive (GB) are preferred upon bonding enamel. On the other hand, high pH MDP (SBU and FM+) and non-MDP (FU) containing adhesives are preferred when bonding to dentin.
The adhesive systems used in this study did not achieve perfect seal at the composite/tooth interface except for FuturaBond M+ (FM+).
Ionizing radiation affects the surface morphology as well as the surface composition of enamel and dentin, enhancing calcium (Ca) availability at the surface while negatively affecting the trace elements (Mg and Al). .