الفهرس 
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Abstract
Objectives : The current study was conducted to synthesize, characterize and evaluate a novel crosslinked collagen/hydroxyapatite (Col/HA) nanocomposite through self-assembly in situ precipitation technique for using it as a dentin pretreatment step for improving the bond strength to caries affected dentin (CAD). Methods: Col/HA nanocomposites in different ratios were prepared through self-assembly in situ precipitation technique, starting from collagen suspension and hydroxyapatite precursors. The chemical composition and microstructure of the prepared Col/HA nanocomposites were characterized by Attenuated Total Reflection Fourier Transform Infra-Red (ATR-FTIR), X-ray diffraction (XRD), Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM). Col/HA nanocomposites were used as a pretreatment step for CAD at two time intervals (10 minutes &1 hour). The bond strength to CAD after crosslinking the prepared Col/HA nanocomposites with dentin matrix was evaluated using microtensile bond strength test. Apatite forming ability of the nanocomposite was evaluated by in-vitro bioactivity test using SBF. Results: The synthesis of Col/HA nanocomposites with different ratios was confirmed by ATR-FTIR, XRD and TEM micrographs. SEM micrographs of CAD specimens treated with the nanocomposite showed the infiltration of the synthesized mineralized collagen into the artificially induced CAD. The highest result in μTBS test in pretreated groups was for Col/HA (30/70 wt%) nanocomposite in both times of application (10 minutes = 25.04 ± 5.47, 1 hour = 25.53 ± 7.64) with no statistically significant difference compared with control (+) group (10 minutes = 26.62 ± 7.99, 1 hour = 26.77 ± 8.74). No statistically significant differences were observed between different application times within each group. A significant decrease in μTBS results after thermocycling, when compared to the immediate evaluation, was observed for control groups, but not significant for all pretreated groups. Col/HA nanocomposite application resulted in a prominent apatite layer formation on dentin surface after immersion in SBF compared with untreated groups. Conclusions: Col/HA (30/70 wt%) nanocomposite prepared through the self-assembly in situ precipitation technique is considered a bioactive material that has the ability to enhance and maintain the bond strength to CAD.