| Sign In to gain access to subscriptions and/or personal tools. |
Inhibition of Root Caries Progression by an Antibacterial Adhesive
1 Department of Restorative Dentistry and Endodontology, Osaka University Graduate School of Dentistry, 1-8, Yamadaoka, Suita, Osaka 565-0871, Japan; and Correspondence: * corresponding author, imazato{at}dent.osaka-u.ac.jp
A dentin primer containing the antibacterial monomer 12-methacryloyloxydodecylpyridinium bromide (MDPB) has been shown to penetrate and kill the bacteria in artificially demineralized dentin. We hypothesized that an experimental adhesive system, which incorporates the MDPB-containing primer, would be effective in inhibiting the progression of root caries in vitro. Artificial caries lesions were prepared by either an acid-gel or a Streptococcus mutans culture technique on the roots of extracted human teeth. The progression of these lesions after the application of the experimental or proprietary adhesive system was examined. Further demineralization was completely prevented by the experimental adhesive system, while lesions managed with the proprietary materials showed limited ability to inhibit further demineralization. We conclude that the experimental adhesive system can inhibit the progression of root-surface caries in vitro, through a combination of its antimicrobial activity and sealing of the demineralized dentin.
Key Words: root-surface caries • demineralization • adhesive system • antibacterial effects • artificial caries
There has been increasing interest in the treatment of root caries with minimal removal of the tooth structure. Several methods have been proposed to promote remineralization of the caries lesion without surgical intervention. These include daily use of a fluoride-containing mouthrinse (Wallace et al., 1993), professional application of fluoridated gels (Billings et al., 1985), or an antimicrobial varnish (Schaeken et al., 1991). However, a simple method which can arrest root-surface caries in the long term is not currently available. There is an urgent need for the development of simple treatment options that can inhibit the progression of root caries, especially for elderly patients who need home care. An antibacterial monomer, 12-methacryloyloxydodecylpyridinium bromide (MDPB), is a polymerizable biocide and has strong bactericidal activity against oral bacteria (Imazato et al., 1994). Additionally, the antibacterial agent is immobilized in the polymer network by polymerization of MDPB, and the cured resin containing MDPB exhibits an inhibition of bacterial growth (Imazato et al., 1998a). Therefore, a dentin bonding system incorporating MDPB can show antibacterial effects before and after the curing process (Imazato et al., 1997, 1998b, 2003), so that it has the potential to exert a benefit in caries management if absorbed into demineralized dentin or when present on the tooth surface. Previously, we have reported that the MDPB-containing primer was capable of penetrating artificial demineralized lesions and of killing bacteria in dentin (Imazato et al., 2002). In this study, using an in vitro caries model, we examined the hypothesis that progression of root-surface caries can be inhibited by the application of an MDPB-containing adhesive system.
Adhesive Systems Three proprietary adhesives and an experimental antibacterial system were tested. Prime & Bond 2.1 (PB; Dentsply/DeTrey, Konstanz, Germany) and Single Bond (SB; 3M ESPE, St. Paul, MN, USA) are one-bottle adhesives, which can be used with a wet-bonding technique. Liner Bond 2 (LB2; Kuraray, Tokyo, Japan) contains a self-etching primer (LB primer) and an adhesive resin (LB bond), and the experimental system based on LB2 uses 4% MDPB-containing primer and LB bond.
Effects on Progression of Demineralized Lesion by Acid-Gel Each specimen was again immersed in acid-gel and stored for 2 wks at 37°C. After being embedded in epoxy resin, the roots were sectioned longitudinally through the center of the demineralized area and abraded to give a specimen 100 µm thick. A contact microradiograph was recorded with a soft x-ray source (Softex CMR, Softex Co., Tokyo, Japan) at 15 kV and 3 mA, and viewed under a stereomicroscope. The depth of lesion, defined as the distance from the root surface to the base of the demineralized area, was measured with the use of image-analyzing software (WinROOF, MITANI, Fukui, Japan). Since the lesion surface was concave, due to demineralization and shrinkage during specimen preparation, a line was drawn between the sound tissue surfaces on either side of the lesion on the digital image to act as a baseline for depth measurement. The measurement was performed at 5 points in the area of the demineralization front for each specimen. The specimen to which no adhesive was applied after 2 wks of demineralization, and the specimen demineralized for 4 wks totally without application of adhesive, served as two- and four-week controls, respectively. Five samples were tested for each group. One further specimen treated with each system and demineralized for 4 wks was cut perpendicularly and observed by means of a scanning electron microscope.
Effects on Progression of Caries Lesions by Streptococcus mutans The data were analyzed by ANOVA and Fisher’s PLSD test at a significance level of 0.05.
When tested by the acid-gel method, the lesion depths for LB2 and the experimental system were significantly less than that for the four-week control. No significant differences were observed between these specimens and the two-week control, indicating no progression of demineralization (Table  , Fig. 1).
For the specimens treated with PB and SB after 4 wks of demineralization, a resin layer could hardly be seen on the surface of the lesion (Figs. 2A , 2B). In contrast, a 30-µm-thick layer of adhesive resin could be clearly observed on the lesion treated with LB2 and the experimental system (Figs. 2C, 2D).
In bacterial culture tests, all adhesives demonstrated significantly lower values for the depth of the lesion than the four-week control (Table  , Fig. 3). However, lesion depths for PB, SB, and LB2 were significantly greater than that for the two-week control, and no significant difference was obtained between the experimental system and the two-week control.
When one is attempting to initiate the arrest of active root caries lesions, it is important to inactivate the bacteria within a lesion and, simultaneously, to seal the surface to deprive any viable bacteria from nutrients and ingress of acids (Lynch, 1996). We have undertaken two studies, the first to assess the sealing ability of an MDPB-containing experimental system and the second to determine its effectiveness in a microbial environment.
The application of LB2 or the experimental system resulted in complete inhibition of the progression of demineralization in the acid-gel technique, while no inhibitory effects were observed with PB and SB. The lesion surface was covered with a thick layer of resin when LB2 and the experimental system were applied (Figs. 2C The model that used an S. mutans culture is considered to be a milder acidic challenge, since a gradual decrease in pH occurs after the broth is changed (Bradshaw and Marsh, 1998). Within this model, all of the adhesives were able to inhibit the progression of demineralization. However, the effects of PB and SB were relatively minor, and complete inhibition of demineralization was observed only with the MDPB-containing system. The limited protection offered by PB and SB could be due either to some early protection of the lesion until the resin film was disrupted, or to their limited antimicrobial action as a consequence of their low pH. Application of LB2 demonstrated greater inhibition compared with these two products. The main component of inhibition by LB2 is likely to be its ability to seal the lesion, as shown in the acid-gel model, to prevent the ingress of acid and nutrients for any bacteria in the lesion. Nevertheless, a 50-µm advance in lesion depth was observed after LB2 application. This is likely to be due to acid production by the bacteria, which had already impregnated the lesion before it was sealed by the bonding resin. In addition, it is possible that curing of the bonding resin was hampered by organic material within the body of the demineralized lesion, and that complete seal, as in the acid-gel model, may not have been established. Lesions managed with the MDPB-containing primer did not differ, in depth, from those in the two-week controls. We have demonstrated previously that the MDPB-containing primer was capable of deeply penetrating demineralized dentin and showed a strong bactericidal effect in that situation (Imazato et al., 2002). The results we have reported above are indicative of the ability of this resin to inactivate bacteria in the lesion, preventing further advancement of demineralization. This effect was greater than that of all of the other resins, since this experimental system is both low in pH and contains an effective antimicrobial agent. The low pH of the resin alone would not account for this complete inhibition of further demineralization (Imazato, 2003). An antimicrobial varnish containing chlorhexidine has been reported to be effective in reducing root caries activity (Wicht et al., 2003). However, such varnishes can penetrate demineralized root dentin only up to 40% of the total lesion depth, due to their hydrophobic nature (Arends et al., 1997). The MDPB-containing primer can penetrate more than 140 µm into demineralized root lesion (Imazato et al., 2002), and its penetration ability can be calculated to be more than 70%, based on the results in the present study. Therefore, application of the experimental system, which uses the antibacterial MDPB-containing primer and the adhesive resin for sealing the lesion, is advantageous over other management options. Although the bacterial species associated with the initiation and progression of root caries are not fully understood, it is well-known that actinomyces or lactobacilli, as well as S. mutans, are frequently isolated from root caries lesions (Bowden, 1990; Ozaki et al., 1994; Schüpbach et al., 1996; Brailsford et al., 2001). MDPB-containing primers show antibacterial activity against various bacteria, including these 3 species, and obligate anaerobes (Imazato et al., 1997, 2001), and they are expected to be effective when applied to natural lesions. However, bacteria in the natural caries lesion may be more resistant to biocides than in this in vitro study, since it is possible that they are covered by metabolic products (such as extracellular matrix) that may interfere with the method of action of the antimicrobial agent. Therefore, further research is needed to investigate the effects of the application of MDPB-containing antibacterial adhesive systems in inhibiting the progression of caries lesions in more clinically relevant situations.
This study was supported by Grants-in-aid for Scientific Research (13470402, 15209066, 16390545) from the Japan Society for the Promotion of Science, and the 21st Century COE entitled "Origination of Frontier BioDentistry" at the Osaka University Graduate School of Dentistry, supported by the Ministry of Education, Culture, Sports, Science and Technology. Received for publication July 6, 2003. Revision received September 23, 2004. Accepted for publication October 13, 2004.
Journal of Dental Research, Vol. 84, No. 1,
89-93 (2005)
|
|
||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
 |
|
|
 |
|
Sign In to gain access to subscriptions and/or personal tools.
TOP
ABSTRACT
INTRODUCTION
