Yuhong Xiao

Effects of a dental adhesive incorporating antibacterial monomer on the growth, adherence and membrane integrity of Streptococcus mutans.

OBJECTIVES This study was attempted to incorporate an antibacterial monomer, methacryloxylethyl cetyl dimethyl ammonium chloride (DMAE-CB), into a commercial dental adhesive and to evaluate the antibacterial activity of the DMAE-CB-incorporated adhesive after being cured against Streptococcus mutans. METHODS DMAE-CB was incorporated at 3% (w/v) into a clinically used dental adhesive, Single Bond 2. Single Bond 2 without DMAE-CB was served as a negative control; Clearfil Protect Bond, containing an intensively researched antibacterial monomer MDPB, was enrolled as a positive control. The effects of the cured adhesives and their eluents on the growth of S. mutans were determined by film contact test and absorbance measurement, respectively. The effects of the cured adhesives on the adherence and membrane integrity of S. mutans were investigated using confocal laser scanning microscopy (CLSM) in conjunction with fluorescent indicators. RESULTS Compared with negative control, the cured DMAE-CB-incorporated dental adhesive and positive control were found to exhibit inhibitory effect on the growth of S. mutans (P<0.05), whereas their eluents did not show detectable antibacterial activity. Moreover, the fluorescence analysis of CLSM images demonstrated that the cured DMAE-CB-incorporated adhesive and positive control could hamper the adherence of S. mutans and exert detrimental effect on bacterial membrane integrity (P<0.05). CONCLUSIONS The incorporation of DMAE-CB can render dental adhesive with contact antibacterial activity after polymerization via influencing the growth, adherence and membrane integrity of S. mutans.

Antibacterial activity and bonding ability of an adhesive incorporating an antibacterial monomer DMAE-CB

This study evaluated the antibacterial effect and microtensile bond strength of a resin-based adhesive containing an antibacterial monomer DMAE-CB (methacryloxylethyl cetyl dimethyl ammonium chloride). Cured specimens of 1, 2, and 3% DMAE-CB-containing Single Bond 2 (crosslinking monomer: Bis-GMA, dimethacrylates; functional monomer: HEMA) were prepared, and their antibacterial effects on Streptococcus mutans ATCC 25175 were investigated. Antibacterial property after 0, 30, 90, and 180 days of aging was also tested. Bonding ability of the experimental adhesive incorporating 3% DMAE-CB was evaluated by microtensile bond strength test. The cured experimental adhesive exhibited an inhibitory effect on S. mutans growth, and the adhesive containing 3% DMAE-CB showed higher antibacterial efficiency compared with those incorporating 1 or 2% anibacterial monomer. Antibacterial activities of the specimens lasted for at least 180 days. Microtensile bond strength test revealed that the bonding ability of the experimental adhesive was not significantly adversely affected by the incorporation of DMAE-CB. Therefore, dental adhesives with strong and long-lasting bacteriostatic property could be achieved by incorporating DMAE-CB without negatively influencing bonding ability.

Antibacterial activity and cytotoxicity of two novel cross-linking antibacterial monomers on oral pathogens

OBJECTIVES The antibacterial activity and cytotoxicity of two novel cross-linking antibacterial monomers, 2-methacryloxylethyl dodecyl methyl ammonium bromide (MAE-DB) and 2-methacryloxylethyl hexadecyl methyl ammonium bromide (MAE-HB) were tested in this study. DESIGN The minimum inhibitory concentration (MIC) and the minimum bactericidal concentration (MBC) of unpolymerized MAE-DB and MAE-HB against eight strains of oral bacteria were tested using a broth dilution test. Time-kill determinations were performed to examine the kinetics of unpolymerized MAE-DB and MAE-HB against Streptococcus mutans UA159 and Streptococcus sanguinis ATCC6715. Bacterial morphology was observed using a field emission scanning electron microscope (Fe-SEM). The cytotoxicity of unpolymerized two new monomers and Bis-GMA on the human gingival fibroblast cell line H2620 was assessed using a methyl thiazolyl tetrazolium assay. RESULTS Unpolymerized MAE-DB and MAE-HB showed strong bactericidal activity against oral bacteria. The MBC value of MAE-DB ranged from 12.2 to 24.4μg/ml and the MBC value of MAE-HB ranged from 6.2 to 48.8μg/ml. Time-kill determinations indicated that unpolymerized MAE-DB and MAE-HB had rapid killing effects against S. mutans UA159 and S. sanguinis ATCC6715 at the concentration of 4× MBC. The Fe-SEM observation showed that MAE-DB and MAE-HB could disturb the integrity of bacteria and cause lysis of bacterial cells. The median lethal concentration values on human gingival fibroblast for both monomers were between 10 and 20μg/ml, and greater than that of Bis-GMA. CONCLUSIONS Unpolymerized MAE-DB and MAE-HB monomers had strong bactericidal activity against eight strains of oral bacteria. Their cytotoxicities were less than that of Bis-GMA.

Biomodification to dentin by a natural crosslinker improved the resin–dentin bonds

OBJECTIVES Transient collagen cross-linking treatment by proanthocyanidins (PA), a natural crosslinker, was proved to increase the cross-linking degree and ultimate tensile strength of demineralised dentin. The present study aimed to investigate whether transient pretreatment by PA-based preconditioner can improve the resin-dentin bonds of various etch and rinse adhesives. The influence of solvent type, PA concentration and treatment duration were examined. METHODS PA-based preconditioners were prepared by adding powdered grape seed extract, rich in PA, to various solvents at different concentrations. They were used on demineralised dentin before the application of the bonding agent. Bond strength, failure modes and degree of conversion were evaluated via microtensile testing, field emission scanning electron microscopy and Fourier transform infrared spectroscopy, respectively. RESULTS Collagen cross-linking treatment by PA-based preconditioners presented a concentration- and time-dependent increase in dentin bond strength even in reduced, clinically applicable treatment duration. PA preconditioning improved bond strength of the tested water/ethanol-based adhesive better than the water/acetone-based system. Mixed fracture was the most prevalent failure mode happened on the top of the hybrid layer in PA-pretreated specimens, whilst at the bottom in non-treated controls. The degree of conversion was not significantly affected by PA pretreatment. CONCLUSIONS Transient PA preconditioning improved resin-dentin bonds without compromise on the curing behaviours of the tested adhesives.

Antibacterial effect of a resin incorporating a novel polymerizable quaternary ammonium salt MAE-DB against Streptococcus mutans†

The antibacterial properties of resins incorporating MAE-DB and the underlying mechanisms of action were evaluated. Antibacterial effects against Streptococcus mutans were tested using the film contact method, with accumulation and membrane integrity observed by scanning electron microscopy and confocal laser scanning microscopy, respectively. Quantitative PCR was used to determine expression of the S. mutans glucosyltransferase B (gtfB) gene on the surface of resins containing 10% MAE-DB. Bacterial growth was inhibited on resin containing 10% MAE-DB as compared with the control at 1 day, 7 days, 30 days, or 180 days (p < 0.05). For the 10%-MAE-DB resin, no significant differences in bacterial viability were found regardless of the time of incubation (p > 0.05). The number of bacteria attached to resin containing 10% MAE-DB was considerably lower than the control. The proportion of bacteria with damaged cell membranes was increased in the experimental resin over controls. Expression of gtfB was reduced by 10% MAE-DB compared with the control (p < 0.05). These findings demonstrate that MAE-DB can be incorporated into resin materials at sufficient concentrations for long-term antibacterial effects against S. mutans after polymerization by attenuating gtfB expression and impairing membrane integrity.

The role of grape seed extract in the remineralization of demineralized dentine: Micromorphological and physical analyses

OBJECTIVES Grape seed extract (GSE) is known to have a positive effect on the demineralization and/or remineralization of artificial root caries lesions. The present study aimed to investigate whether biomodification of caries-like acid-etched demineralized dentine, using proanthocyanidins-rich GSE, would promote its remineralization potential. DESIGNS Dentine specimens were acid-etched for 30s, then biomodified using proanthocyanidin-based preconditioners (at different concentrations and pH values) for 2min, followed by a 15-day artificial remineralization regimen. They were subsequently subjected to microhardness measurements, micromorphological evaluation and X-ray diffraction analyses. Stability of the preconditioners was also analyzed, spectrophotometrically. RESULTS A concentration-dependent increase was observed in the microhardness of the specimens that were biomodified using GSE preconditioners, without pH adjustment. Field emission scanning electron microscopy revealed greater mineral deposition on their surfaces, which was further identified mainly as hydroxylapatite. The absorbances of preconditioner dilutions at pH 7.4 and pH 10.0 decreased at the two typical polyphenol bands. CONCLUSIONS Transient GSE biomodification promoted remineralization on the surface of demineralized dentine, and this process was influenced by the concentration and pH value of the preconditioner. GSE preconditioner at a concentration of 15%, without pH adjustment, presented with the best results, and this may be attributed to its high polyphenolic content.

Effects of Type I Collagen Degradation on the Durability of Three Adhesive Systems in the Early Phase of Dentin Bonding

Objective This study was designed to evaluate the effects of type I collagen degradation on the durability of three adhesive systems in the early phase of dentin bonding. Methods Bonded dentin specimens were prepared using three different types of adhesive systems. Micro-tensile bond strength and degradation of collagen were tested before, and after 1 month or 4 months of aging in artificial saliva. The relationship between micro-tensile bond strength and collagen degradation was analyzed by calculating their Pearson’s correlation coefficient. Results Aging induced time-dependent reduction in micro-tensile bond strengths for all the tested adhesive systems, although such reduction for the single-step self-etching adhesive G-Bond (GB) was not statistically significant. The bond strength of the two-step self-etching primer adhesive system Clearfil SE Bond (SEB) was similar to that of the two-step etch-and-rinse self-priming adhesive system Single Bond 2 (SB), and they were both significantly reduced after one or four months of aging. A negative correlation was found between the degree of collagen degradation and magnitude of micro-tensile bond strength (r = - 0.65, p = 0.003). The Pearson’s correlation coefficient was 0.426, indicating that 42.6% of the aging-induced reduction in bond strength can be explained by the degradation of collagen. Conclusions In the early phase of dentin bonding, there was a negative correlation between the degree of collagen degradation and the magnitude of micro-tensile bond strength. The reduction of bond strength was accompanied by the degradation of collagen. These results provide evidence for the causative relationship between the degradation of collagen and the deterioration of dentin-adhesive interface.