Chlorhexidine preserves dentin bond in vitro

Abstract

Loss of hybrid layer integrity compromises resin-dentin bond stability. Matrix metalloproteinases (MMPs) may be partially responsible for hybrid layer degradation. Since chlorhexidine inhibits MMPs, we hypothesized that chlorhexidine would decelerate the loss of resin-dentin bonds. Class I preparations in extracted third molars were sectioned into two halves. One half was customarily restored (etch-and-rinse adhesive/resin composite), and the other was treated with 2% chlorhexidine after being acid-etched before restoration. Specimens were stored in artificial saliva with/without protease inhibitors. Microtensile bond strengths and failure mode distribution under SEM were analyzed immediately after specimens' preparation and 6 months later. With chlorhexidine, significantly better preservation of bond strength was observed after 6 months; protease inhibitors in the storage medium had no effect. Failure analysis showed significantly less failure in the hybrid layer with chlorhexidine, compared with controls after 6 months. In conclusion, this in vitro study suggests that chlorhexidine might be useful for the preservation of dentin bond strength.

Figure 1

Representative scanning electron micrographs (SEM) of the dentin side of fractured specimens in different groups. (a–c) Immediate testing, control; (a′–c′) immediate testing, chlorhexidine-treated; (d) six-month control, stored in artificial saliva without protease inhibitors; (d′) six-month chlorhexidine-treated, stored in artificial saliva without protease inhibitors. C = resin composite; A = adhesive; H = hybrid layer. (a) Low-power magnification demonstrates a mixed failure (partially cohesive in A and C, partially in H). Magnification: 85x. (b) Higher magnification of the area limited by a rectangle in (a), showing cohesive failure in the adhesive layer (A), and failure localized at the bottom (between black arrows) or top (between white arrowheads) of the hybrid layer. Magnification: 500x. (c) Highest magnification of the area limited by the circle in (a), showing cohesive failure in the resin composite and adhesive (R) and in different depths of the hybrid layer (H) (areas separated with dashed line). Magnification: 1500x. (a′) Low-power magnification evidences a mixed failure, partially cohesive in A and C and partially in H. Magnification: 85x. (b′) Higher magnification of the area limited by a rectangle in (a′), confirming the partial cohesive failures in the adhesive (A) and composite (C). Magnification: 500x. (c′) Highest magnification of the circled area in (a′), showing cohesive failure within the adhesive (A), the rest being located at the top of the hybrid layer (T). Most of the exposed dentinal tubules are filled by resin tags (black arrows), while the intertubular dentin seems to be completely covered by adhesive (asterisk). Magnification: 1500x. (d) Highest magnification of control specimen after 6 months' storage, showing a failure localized in the bottom of the hybrid layer, as evidenced by a high density of the dentinal tubules and an uncovered intertubular dentin, with naked collagen fibrils (asterisk). Magnification: 1500x. (d′) Highest magnification of chlorhexidine-treated specimen after 6 months' storage shows a cohesive failure localized in the middle of the hybrid layer. Dentinal tubules are completely filled by resin tags (black arrow), and intertubular dentin is covered by adhesive (asterisk). Magnification: 1500x.

Figure 2

The bond strengths (mean ± SD) at the immediate testing period (immediate), 6 mos in artificial saliva containing the necessary ions for MMP activation, or in artificial saliva containing additional non-specific protease inhibitors (no inhibitors and with inhibitors, respectively). N = from 19 to 22 in each group. The bars with different letters indicate statistically significant differences (ANOVA with Tukey's test).