Satoshi Imazato

Antibacterial properties of resin composites and dentin bonding systems

This paper reviews the research conducted on the evaluation of antibacterial properties of commercial composites and adhesive systems, in addition to the discussion on many attempts to achieve antibacterial composites or adhesives. With regard to composites, commercially available products including fluoride-releasing materials have no antibacterial effect after being cured, which may explain why composites accumulate more plaque than other filling materials. The attempts to provide composites with antibacterial properties involve alterations to the resin components and filler components, and the trials can be subsequently classified into two groups based on the release profile of antibacterial components; agent-releasing or non-agent-releasing materials. Each type of antibacterial composite has advantages and disadvantages, and further modifications are needed to achieve clinically useful materials. Among proprietary dentin bonding systems (DBS), the products which contain glutaraldehyde or have an acidic property exhibit some antibacterial effects. However, the antibacterial properties shown by these products are only side-effects which are derived from the constituents included to produce superior bonding characteristics, and appear to be unreliable. Inclusion of antibacterial components into DBS has also been attempted using several methods, and the results of in vitro tests indicate that some of the trials seem promising. It is worthy of continuing the attempts to develop DBS which can inhibit invading bacteria after the placement of restoration as well as residual bacteria in the cavity. Achievement of bio-functional composites or DBS with therapeutic effects would contribute to prevent secondary caries.

Antibacterial activity and bonding characteristics of an adhesive resin containing antibacterial monomer MDPB.

OBJECTIVES The aims of this study were to investigate the antibacterial activity of an adhesive resin incorporating the antibacterial monomer 12-methacryloyloxydodecylpyridinium bromide (MDPB) as well as its bonding characteristics in terms of bond strength into dentin and curing ability. METHODS An experimental adhesive resin was prepared by incorporation of 2.5% MDPB into proprietary adhesive (LB Bond), and the inhibitory effect of cured specimen against the growth of Streptococcus mutans on its surface was determined. Bond strength to human dentin and degree of conversion of the experimental adhesive in combination with 1, 2, or 5% MDPB-containing primers, which were previously reported to possess bactericidal effect, were evaluated by conventional tensile bond strength test and Fourier transformation infrared spectroscopy. RESULTS The cured experimental adhesive exhibited an inhibitory effect on S. mutans growth, reducing the number of bacteria to approximately 3% of control adhesive without MDPB. Tensile bond strength of experimental adhesive was not significantly different from that of the control (p>0.05), and use in combination with MDPB-containing primer did not show any adverse influence on bond strength. The degree of conversion of the bonding system was not different (p>0.05) between control and experimental adhesive irrespective of addition of MDPB into primer. SIGNIFICANCE These results indicate that an adhesive resin with antibacterial activity after curing could be produced by incorporation of MDPB without influencing bond strength or curing performance, suggesting that the comprehensive bonding system including MDPB-containing primer and adhesive should be highly effective in its antibacterial effect before and after curing.

Incorporation of Antibacterial Monomer MDPB into Dentin Primer

The polymerizable monomer methacryloyloxydodecylpyridinium bromide (MDPB) shows antibacterial activity when immobilized in a resin-based material. In this study, the antibacterial effect of a dentin primer incorporating MDPB was investigated. The influence of incorporation of MDPB on bond strength to dentin and on the curing performance of the adhesive system was also evaluated. Experimental primers were prepared by addition of MDPB into a proprietary primer at 1, 2, or 5%. Antibacterial effects of experimental primers were compared with those of control primer and two other proprietary primers by an agar disc-diffusion method and bactericidal activity test. Experimental primers produced greater inhibition zones against Streptococcus mutans, Actinomyces viscosus, and Lactobacillus casei than any of three proprietary primers, and inhibition increased as the concentration of MDPB was increased. Bactericidal activity of MDPB-containing primers against Streptococcus mutans was greater than those of the other three primers, with incorporation of MDPB at 5% showing complete killing of bacteria after 30 s contact. No decrease in tensile bond strength was observed for materials containing MDPB. On the contrary, the primer incorporating 1 and 2% MDPB showed higher bond strength than all the others, including the control (p < 0.05). When the degree of conversion of the complex of primer and adhesive resin was determined with Fourier Transform Infrared Spectroscopy, there were no significant differences between any of the experimental primers and the control (p > 0.05). These results indicate that incorporation of the antibacterial monomer MDPB enhanced the antibacterial effect of a proprietary dentin primer before curing, and had no adverse influence on bond strength to dentin and curing of the adhesive system.

Antibacterial activity of dentine primer containing MDPB after curing

OBJECTIVES A monomer methacryloyloxydodecylpyridinium bromide (MDPB) has antibacterial activity before polymerization. Furthermore, the antibacterial agent is immobilized by the polymerization of MDPB and the resin-based material incorporating MDPB is able to show an antibacterial effect even after being cured. The purpose of this study was to investigate the antibacterial effect of a dentine primer containing MDPB after curing. METHODS The inhibitory effect of a cured MDPB-containing primer on the growth of Streptococcus mutans, Actinomyces viscosus and Lactobacillus casei was determined by the agar-disc method. The bactericidal activity of cured primer during a 1-h contact period was assessed using S. mutans, and the elution of unpolymerized MDPB was measured with high performance liquid chromatography. RESULTS Cured MDPB-containing primer showed an inhibitory effect on the growth of all species which were in contact with the specimen surface, and displayed a little bactericidal effect on S. mutans without releasing any unpolymerized antibacterial components. CONCLUSION Incorporation of antibacterial monomer MDPB into dentine primer is beneficial for providing antibacterial activity after curing.

Degree of conversion of composites measured by DTA and FTIR

OBJECTIVE Differential thermal analysis (DTA) using a split fiber optic light source has been reported to be a convenient method of measuring the degree of conversion (DC) of light-activated composites. The purpose of this study was to compare the results by DTA and Fourier transformation infrared spectroscopy (FTIR), and evaluate the usefulness of the DTA method. METHODS Experimental 2,2-bis[4-(3-methacryloyloxy-2-hydroxypropoxy)phenyl]propane-based composites containing SiO2 filler and various amounts of triethyleneglycol dimethacrylate (TEGDMA) were prepared, and the DC of each composite was determined by DTA or FTIR with 60s irradiation. The DC of three proprietary composites containing hybrid filler or prepolymerized resin filler were also measured by both methods with 20 or 60s irradiation. The results were analyzed by ANOVA and Fishers protected least significant difference test. RESULTS By both DTA and FTIR, the DC of experimental composites increased as the proportion of TEGDMA increased, although DTA showed 3-10% greater values (p<0.05) than FTIR. For proprietary composites that contain hybrid filler, the values by DTA were not significantly different from those by FTIR at 20s exposure. Longer irradiation time resulted in greater DC (p<0.05) for both methods, and DTA showed 5-7% greater values than FTIR. However, the DC of the composite containing prepolymerized resin filler was 30% less by FTIR than by DTA, possibly due to the influence of unpolymerized species in the filler. SIGNIFICANCE The DC values determined by DTA and FTIR showed good agreement for most materials including model composites. In addition, DTA may be more useful than FTIR to measure the DC of composites containing prepolymerized resin filler.

Antibacterial activity of MDPB polymer incorporated in dental resin

OBJECTIVES Previously, we have reported that dental composite incorporating the new monomer methacryloyloxydodecylpyridinium bromide (MDB) showed no release of antibacterial components after being cured but still exhibited antibacterial activity against Streptococcus mutants on its surface. In this study, in order to elucidate the mechanism of the antibacterial effect of immobilized MDPB, the bactericidal activity of MDPB polymer in water-soluble and -insoluble form was investigated, and the effect of MDPB polymer on bacterial attachment was estimated. METHODS Solutions of homo-polymer of MDPB and co-polymer of MDPB with acrylamide were prepared and the viability of seven major oral streptococci was determined after incubation with each polymer solution. For the estimation of bactericidal activity of insolubilized MDPB polymer, bacteria were kept in contact with cured unfilled Bis-GMA-based resin discs with or without MDPB, and the recovery of viable cells was measured. Attachment of streptococci to cured resin discs with or without MDPB was also compared using radiolabelled bacteria. RESULTS Water-soluble homo-polymer of MDPB and co-polymer with acrylamide showed bactericidal activity against oral streptococci. However, cured resin incorporating MDPB, which is in water-insoluble form, had little bactericidal activity. Attachment of streptococci, including species which are early colonizers in dental plaque formation, to the cured resin containing MDPB was significantly less than to the control without MDPB. CONCLUSIONS These results indicate that the bactericidal activity of MDPB polymer is reduced after immobilization, but MDPB on the surface of a resin-based material still shows a bacteriostatic effect and antiadhesion property against oral streptococci.

Antibacterial activity of bactericide-immobilized filler for resin-based restoratives

This study examined the antibacterial activity of prepolymerized resin filler, in which the bactericide quaternary ammonium was immobilized. The experimental filler was prepared by grinding prepolymerized resin blocks of methacrylate monomers, silica particles, and the antibacterial monomer methacryloyloxydodecylpyridinium bromide (MDPB). The number of Streptococcus mutans after incubation for 18h in contact with the experimental filler with or without protein adsorption by saliva treatment was determined, and adherence of bacteria to the filler surface was evaluated by scanning electron microscopy. Elution of unpolymerized MDPB from the filler and its influence on bacterial growth were also investigated. The growth of S. mutans was completely inhibited by contact with the experimental filler without saliva treatment. Although the effects were attenuated, the saliva-treated filler still exhibited growth inhibition at >99.9%. Less bacteria attached to the experimental filler than the control filler without MDPB, indicating that the reduction in bacterial number after contact with the experimental filler was not due to bacterial adherence to the particles. Unpolymerized MDPB at 1 microg/ml was eluted from the filler particles but was confirmed to have little effect on bacterial growth. The results indicate that the bactericide-immobilized filler containing MDPB shows significant bacteriostatic effects without releasing antibacterial components, and is useful for incorporation into various resin-based restoratives.

Bactericidal activity and cytotoxicity of antibacterial monomer MDPB

The aim of this study was to investigate bactericidal characteristics and cytotoxicity of the newly developed antibacterial monomer 12-methacryloyloxydodecylpyridinium bromide (MDPB). To evaluate the bactericidal activity of MDPB against oral streptococci, the minimum bactericidal concentration (MBC) for seven species and time-kill kinetics against Streptococcus mutans were determined. The cytotoxic effects of MDPB on human pulpal cells were assessed by [3H]-thymidine uptake after contact with MDPB solutions at various concentrations. MDPB showed strong bactericidal activity against seven streptococci, the MBC value ranging from 31.1 to 62.5 micrograms ml-1. Time-kill determination indicated a rapid killing effect of MDPB at 250 micrograms ml-1 or over, and all cells were killed within 1 min by MDPB at 500 micrograms ml-1 or over. No cytotoxic effect was observed on contact with MDPB at concentrations of 10 micrograms ml-1 or less, and the toxicity of MDPB was considered to be similar to those of other monomers used for dental materials. These results suggest that MDPB can be effectively incorporated in dental resin-based materials to provide bactericidal activity against oral bacteria.

The Inhibitory Effects of Quaternary Ammonium Methacrylates on Soluble and Matrix-bound MMPs

Matrix metalloproteinases (MMPs) bound to dentin contribute to the progressive degradation of collagen fibrils in hybrid layers created by dentin adhesives. This study evaluated the MMP-inhibiting potential of quaternary ammonium methacrylates (QAMs), with soluble rhMMP-9 and a matrix-bound endogenous MMP model. Six different QAMs were initially screened by a rhMMP-9 colorimetric assay. For the matrix-bound endogenous MMPs, we aged demineralized dentin beams for 30 days in calcium- and zinc-containing media (CM; control), chlorhexidine, or QAMs in CM to determine the changes in dry mass loss and solubilization of collagen peptides against baseline levels. The inhibitory effects of QAMs on soluble rhMMP-9 varied between 34 and 100%. Beams incubated in CM showed a 29% decrease in dry mass (p < 0.05), whereas beams incubated with QAMs showed only 0.2%-6% loss of dry mass. Significantly more solubilized collagen was detected from beams incubated in CM (p < 0.05). It is concluded that QAMs exhibited dentin MMP inhibition comparable with that of chlorhexidine, but required higher concentrations.

Inhibitory effects of resin composite containing bactericide-immobilized filler on plaque accumulation

OBJECTIVE Previously, we have reported that incorporation of the antibacterial monomer 12-methacryloyloxydodecylpyridinium bromide (MDPB) was effective in immobilizing bactericide in the resin matrix, and an antibacterial composite without release of the agent could be achieved. In this study, an attempt was made to increase the density of bactericide immobilized in composite, and the inhibitory effects of this modified antibacterial composite on plaque accumulation were determined, focusing on the reliability of the effects and the mechanisms to affect the plaque formation. METHODS An experimental composite containing immobilized bactericide at 2.83% was prepared by the incorporation of MDPB into a prepolymerized resin filler of control composite, and elution of antibacterial components and inhibition of in vitro plaque accumulation by Streptococcus mutans were determined. The inhibitory effects of the experimental composite on the attachment, glucan synthesis and growth of S. mutans on the surface were also examined in addition to the comparison of surface roughness and hydrophobicity with controls. The results were analyzed using the Students t-test. RESULTS The experimental composite had reproducible inhibitory effects against plaque accumulation compared with control (p<0.05), although it showed no elution of unpolymerized MDPB. The plaque-inhibitory effect of the experimental composite was found to depend upon the ability to inhibit the attachment, glucan synthesis, and growth of bacteria on its surface as no significant differences in the surface characteristics were obtained between control and experimental composites (p>0.05). SIGNIFICANCE It was indicated that the experimental composite containing bactericide-immobilized filler has the possibility to be used clinically with an effective anti-plaque property.