Antimicrobial antidegradative dental adhesive preserves restoration-tooth bond

Abstract

Objective: Assess the ability of an antimicrobial drug-releasing resin adhesive, containing octenidine dihydrochloride (OCT)-silica co-assembled particles (DSPs), to enhance the biostability and preserve the interfacial fracture toughness (FT) of composite restorations bonded to dentin. Enzyme-catalyzed degradation compromises the dental restoration-tooth interface, increasing cariogenic bacterial infiltration. In addition to bacterial ingress inhibition, antimicrobial-releasing adhesives may exhibit direct interfacial biodegradation inhibition as an additional benefit.

Methods: Mini short-rod restoration bonding specimens with total-etch adhesive with/without 10% wt. DSPs were made. Interfacial fracture toughness (FT) was measured as-manufactured or post-incubation in simulated human salivary esterase (SHSE) for up to 6-months. Effect of OCT on SHSE and whole saliva/bacterial enzyme activity was assessed. Release of OCT outside the restoration interface was assessed.

Results: No deleterious effect of DSPs on initial bonding capacity was observed. Aging specimens in SHSE reduced FT of control but not DSP-adhesive-bonded specimens. OCT inhibited SHSE degradation of adhesive monomer and may inhibit endogenous proteases. OCT inhibited bacterial esterase and collagenase. No endogenous collagen breakdown was detected in the present study. OCT increased human saliva degradative esterase activity below its minimum inhibitory concentration towards S. mutans (MIC), but inhibited degradation above MIC. OCT release outside restoration margins was below detection.

Significance: DSP-adhesive preserves the restoration bond through a secondary enzyme-inhibitory effect of released OCT, which is virtually confined to the restoration interface microgap. Enzyme activity modulation may produce a positive-to-negative feedback switch, by increasing OCT concentration via biodegradation-triggered release to an effective dose, then subsequently slowing degradation and degradation-triggered release.

Keywords: Biodegradation; Dental caries; Enzyme inhibition; Esterase; Interfacial fracture toughness.

Figure 1:

Mini-SR specimens were prepared, aged (0–180 days), and fractured; DSP-SBMP demonstrated improved dentin bonding of resin composite compared to control stock adhesive (SBMP) after incubation in simulated oral biodegradative environment (SHSE) for 180-days. A mini-SR specimen is shown in A with arrows indicating where force is applied, while an exploded view in B shows the chevron area where composite and dentin are bonded using a test of control adhesive system. 0, 30 and 180-day fracture toughness values are displayed in C with group letters for Tukey HSD test results (p<0.05). A Statistically significant decline in fracture toughness over time in SBMP-bonded specimens, but not DSP-SBMP-bonded specimens, was observed (group marked with *, least squares fit effect tests via ANOVA, p<0.05). No effect of drug-free cDSPs on bonding capability was observed. Results are presented as mean ± standard deviation.

Figure 2:

Protein adsorption of CE and salivary proteins on polymerized SBMP with/without OCT and on DSP-SBMP. No significant differences between CE groups (A) were found in whole-experiment comparisons (ANOVA p>0.05, Tukey’s HSD analysis p>0.05, groups denoted by letters). Comparing individual data points to SBMP without OCT, 20 µg mL⁻¹ OCT (p=0.047) and DSP-SBMP (p=0.04) significantly inhibited CE adsorption (A), however no other inhibition was observed (marked with an asterisk, Welch’s t-test). OCT and DSP-SBMP had no effect on the adsorption of salivary proteins to resin adhesive (ANOVA p>0.05, Tukey’s HSD analysis p>0.05, groups denoted by letters, Welch’s t-tests with control p>0.05). Results are presented as mean ± standard deviation.

Figure 3:

OCT may decrease endogenous MMP-like protease activity and decreases bacterial collagenolytic activity towards human dentin. OCT decreases endogenous dentinal MMP-1-, 2-, and 9-like activity when measured via MMP-specific fluorometric substrate, as well as activity towards generic fluorometric MMP substrate (A, B, D, E), however, no detectable endogenous breakdown of collagen was observed from demineralized dentin specimens at any OCT concentration. OCT decreases the ability of bacterial type-1 collagenase to degrade human dentinal collagen as measured by Hyp production (F). Group letters indicate Tukey’s HSD analysis (p<0.05). Data are presented as mean relative activity ± standard deviation.

Figure 4:

OCT modulates esterase activity in several ways, depending on enzyme, substrate, and OCT concentration. OCT effects on enzyme CE-like activity assay were measured via either colorimetric assay using p-NPB as a substrate (A, C, E) or enzyme hydrolytic activity towards the adhesive’s universal monomer bisGMA via bisHPPP production (B, D, F) is shown. In A, OCT appears to increase the hydrolytic activity of CE towards the p-NPB substrate with increasing concentration. In contrast, OCT decreases the hydrolytic activity of CE towards adhesive monomer of interest bisGMA (B). Activity of HSDE (C, D) is decreased at 20 µg mL⁻¹ toward both p-NPB and bisGMA, but is increased toward bisGMA at lower concentrations (D). OCT reduced the activity of SMU_118c toward both p-NPB and bisGMA only at 20 µg mL⁻¹, and the inhibitory effect was higher toward p-NPB degradation (E, F). Group letters indicate Tukey’s HSD analysis (p<0.05). Data are presented as mean relative activity ± standard deviation.