Clinical suggestion for the limitation of application time of NaOCl solution is needed to avoid large reductions in resin-dentin bond strength. The aim of this study was to measure the change of µ-tensile bond strength after the various application time of 5.25% NaOCl solution to pulp chamber dentin in endodontic access cavity, and to evaluate the effect of 10% sodium ascorbate application for 10 min on bond strength after the treatment of 5.25% NaOCl solution. In this experiment, there were no statistical differences(p>0.05) in bond strengths between upper chamber dentin and lower chamber dentin. NaOCl-treated group for 20 min did not show any significant decrease(p>0.05) in bond strength than non-treated control group. In contrast to that, bond strengths of NaOCl-treated groups for 40 & 80 min were significantly lower(p<0.05) than that of non-treated control group.

10% sodium ascorbate retreated group for 10 min after 5.25% NaOCl application for 40 min to chamber dentin showed the recovery of bond strength significantly. However, the bond strength of sodium ascorbate retreated group after 5.25% NaOCl application for 80 min was still significantly lower(p<0.05) compared to the non-treated control group, which means the reductions in resin-dentin bond strength were not fully reversed. On the contrary, sodium ascorbate retreated group after 5.25% NaOCl application for 5 min showed significantly higher(p<0.05) bond strength compared to the control group, which demonstrates its superior recovery effect. In SEM exminations of specimens retreated with 10% sodium ascorbate after NaOCl application for 40 & 80 min showed that resin tags were formed clearly and densely, but weakly in density and homogeneity of individual resin tag compared to the control specimen.

The purpose of this study was to examine the effect of hydrogen peroxide at different application time and concentrations on the microtensile bond strength of resin restorations to the deep and the pulp chamber dentin.

A conventional endodontic access cavity was prepared in each tooth, and then the teeth were randomly divided into 1 control group and 4 experimental groups as follows: Group 1, non treated; Group 2, with 20% Hydrogen peroxide(H₂O₂); Group 3, with 10% H₂O₂; Group 4, with 5% H₂O₂; Group 5, with 2.5% H₂O₂; the teeth of all groups except group 1 were treated for 20, 10, and 5min. The treated teeth were filled using a Superbond C&B (Sun medical Co., Shiga, Japan). Thereafter, the specimens were stored in distilled water at 37℃ for 24-hours and then sectioned into the deep and the chamber dentin. The microtensile bond strength values of each group were analyzed by 3-way ANOVA and Tukey post hoc test(p < 0.05).

In this study, the microtensile bond strength of the deep dentin (D1) was significantly greater than that of the pulp chamber dentin (D2) in the all groups tested. The average of microtensile bond strength was decreased as the concentration and the application time of H₂O₂ were increased. Analysis showed significant correlation effect not only between the depth of the dentin and the concentration of H₂O₂ but also between the concentration of H₂O₂ and the application time(p < 0.05), while no significant difference existed among these three variables(p > 0.05). The higher H₂O₂ concentration, the more opened dentinal tubules under a scanning electron microscope(SEM) examination.

The purpose of this study was to evaluate the influence of sodium ascorbate on microtensile bond strengths of total-etching adhesive system to pulp chamber dentin treated with NaOCl.

Pulp chambers of extracted human non-caries permanent molars were treated as follows: group 1, with 0.9% NaCl; group 2, with 5.25% NaOCl; group 3, with 5.25% NaOCl and 10% sodium ascorbate for 1min; group 4, with 5.25% NaOCl and 10% sodium ascorbate for 1 min and 10ml of water; group 5, with 5.25% NaOCl and 10% sodium ascorbate for 5 min; group 6, with 5.25% NaOCl and 10% sodium ascorbate for 5 min and 10ml of water; group 7, with 5.25% NaOCl and 10% sodium ascorbate for 10 min; group 8, with 5.25% NaOCl and 10% sodium ascorbate for 10 min and 10ml of water. Treated specimens were dried, bonded with a total-etching adhesive system (Single bond), restored with a composite resin(Z250) and kept for 24h at 100% humidity to measure the microtensile bond strength.

NaOCl-treated group (group 2) demonstrated significantly lower strength than the other groups. No significant difference in microtensile bond strengths was found between NaCl-treated group (group 1) and sodium ascorbate-treated groups (group 3-8). The results of this study indicated that dentin treated with NaOCl reduced the microtensile bond strength of Single bond. Application of 10% sodium ascorbate restored the bond strength of Single bond on NaOCl-treated dentin. Application time of sodium ascorbate did not have a significant effect.