Effects of High-concentration Doxycycline versus Chlorhexidine as Dentin Pretreatment on Composite Resin Micro-tensile Bond Strength

Objective To assess the effect of 10% doxycycline (DOX) compared to 2% chlorhexidine (CHX) on the longevity of dentin-bond strength. Methods Sixty-six extracted molars were collected and prepared and divided into two groups based on the test to be performed. Group I (n=48) for the micro-tensile bond strength (µTBS) test and Group II (n=18) for the confocal laser scanning microscopy (CLSM) test. Group I was divided into 3 subgroups (n=16) according to pretreatment agent following acid etching. Group A (control): without pretreatment, group B: 10% Doxycycline pretreatment, Group C: 2% Chlorhexidine pretreatment. Palfique universal bond (PU) and Composite resin were applied according to the manufacturer's instructions. Group II was divided into 3 subgroups (n=6) based on the same pretreatment protocols used in Group I. However, for resin-dentin bond evaluation using CLSM, 0.1 mg/mL Rhodamine B fluorescent dye was mixed with the adhesive. After that, all subgroups of group I and group II were subdivided into 2 subdivisions:(T1) without thermocycling and (T2) thermocycling for 10000 cycles. µTBS testing was achieved via a digital universal testing machine. The failure mode was tested by a stereomicroscope (30x magnification). Results Intergroup comparison of mean µTBS values (MPa) was performed using one-way ANOVA, then by Tukey post-hoc test with statistical significance at p ≤ 0.016. In contrast, intragroup comparison was achieved using a paired t-test with a statistical significance of p ≤ 0.05. Comparison between categorical data was made using a chi-square test. The 10% DOX pretreatment group showed significantly higher µTBS values than CHX and the control group with and without thermocycling ( p < 0.001). No statistically significant difference in failure modes was recorded among groups without and with thermocycling. There was no correlation between µTBS and failure mode performed using Spearman’s rank correlation. CLSM revealed that the 10% DOX group exhibited greater resin infiltration with a thicker hybrid layer. Both matrix metalloproteinase (MMP) inhibitors created a uniform hybrid layer. Discussion 10% DOX showed the highest MMP inhibition, the higher concentration of DOX may have increased the inactivation effect of DOX on MMPs. Conclusion Pre-treatment with MMP inhibitors might have inhibited the degradation of resin-dentin interfaces. In addition, 10% DOX pretreatment for 60 seconds after etching appears to be more efficient in enhancing the durability of the bond. Additionally, the composition of PU may influence bond strength, warranting further investigation. Moreover, thermocycling may adversely impact the micro-tensile bond strength.