| Bonding techniques today are widely used in every branch of dentistry. Their improvements accelerate the advancements of conservative dentistry, esthetic dentistry and minimal invasive techniques. The renovation of the adhesive restorative materials has made a substantial basis for the progress of bonding techniques. The development of new materials today not only focuses on the physico-chemical properties of materials, but also on their antibacterial characteristics. Since primary caries and secondary caries account for both teeth defects and restoration failures, their occurrence not only adds difficulties to re-restoration, but also aggravates the prognosis. Therefore, developing antibacterial adhesive materials has much significance on prolonging the longevity of the adhesive restorations and improving the prognosis.Caries-preventive dental restorative materials can be generally arranged under two categories. The first one is fluoride-releasing materials. They aim at increasing the remineralization ability of dental tissues and enhancing their resistance to caries. However, the antibacterial activity of this kind of materials is limited. Such materials still cannot eradicate the harms of cariogenic bacteria on dental tissues. The second category is endowed with antibacterial activity by the antibacterial functionalization of the material matrix. The cariogenic bacteria can be killed or inactivate by contacting with the antibacterial materials. One example is Clearfil Protect Bond (Kuraray Co. Ltd.), which incorporated with an antibacterial adhesive monomer 12-methacryloyloxydodecylpyridinium bromide (MDPB). However, grafting antibacterial functional group onto matrix of materials by chemical methods still has considerable difficulties in techniques. The previous attempts of developing antibacterial materials by the incorporation of organic antibacterial agents were also failed and given up because of the dissatisfied antibacterial effects.With the rapid progress in the antibacterial agents (ABAs), more and more researchers have been making trials on directly incorporation of inorganic ABAs. Comparing with organic ABAs, inorganic ones have received more and more attentions relying on their long-term effectiveness against a wide range of microorganisms, little tendency to induce bacterial resistance, high chemical stability and good biocompatibility, despite their relative slow mode of action. They have become the mainstream in antibacterial product market in recent years and have been taken on trial for the development of dental antibacterial materials. Nevertheless, their applications for the antibacterial functionalization of the adhesive systems have not been reported and there is also no other antibacterial restorative materials newly-invented.For any adhesive system, primer always contacts and reacts with the tooth substrate at the first stage of restoration, followed by the application of bonding agent. Developing primers with antibacterial activity will surely be advantageous to achieve successful restoration and improve prognosis, especially to self-etching primers, for which previous etching and washing tooth substrate is unnecessary. If the antibacterial agents are incorporated into the primer, it can be effective to disinfect the cavity before the curing of the primer. Besides, since the antibacterial component will be immobilized in the adhesive interface between restoration materials and tooth tissues after polymerization of the primer, it can be also beneficial for preventing the invasion of bacteria and the consequent occurrence of secondary caries.An experimental self-etching primer ESP was invented in our group and has been demonstrated to have good etching effect and satisfactory bond strength on enamel and dentin. This thesis was to investigate the preliminary feasibility of antibacterial functionalization of ESP by incorporating different kinds of inorganic antibacterial agents, accordingly develop antibacterial dental materials with caries-preventive properties, and achieve the final goal of realizing high effective preventive-oriented caries treatment.Six different kinds of inorganic antibacterial agents were used in the studies. One is on chlorine basis (Basic magnesium hypochlorite [Mg2ClO(OH)3·H2O]—ABA1), three are loaded with silver, copper, zinc (Longbei inorganic antibiotic powder—ABA2, Antim-AMS2—ABA3, IONPURE-H—ABA4) and two are zinc oxide whisker (ZnOw AT-83—ABA5, ZnOw AT-88—ABA6). Antibacterial activities of ESP containing different antibacterial agents at different incorporating concentrations, different incubation time with bacteria suspension, before or after curing were examined. The influence of incorporating antibacterial agents on the intrinsic physico-chemical characteristics and biocompatibility of ESP were also evaluated.Major results and conclusions from the studies are:Physico-chemical evaluations─ABA2 and ABA4 powders consisted of homogenous particles with relatively smaller size. ABA1, ABA3, ABA5 and ABA6 comprised heterogeneous particles. Specially, ABA5 contained tetrapod-shaped whisker.─ABA1 loaded chlorine in large amount. Silver, copper and zinc were found respectively in the other five ABAs at different concentrations.─The incorporation of ABAs had no significant influence on bovine enamel bond strength when ESP contained lower concentration of ABA (0.5% w/v); while higher concentration (2.5% w/v) led to significant decreases in bond strength to different extent except for ABA2.─The SEM examination revealed that the incorporation of ABAs had no great influence on the etching effect of ESP on unground bovine enamel and bovine dentin.─The incorporation of 0.5% w/v ABAs, except for ABA1, had no significant differences on gingival or incisal microleakage scores with respect to the ESP empty control. It was also found that all materials showed higher microleakage scores in the gingival side than in the incisal side. ─Color changes of specimens arrived to the most significant and perceptible after 1 year aging, which was primarily due to the increase of lightness. The color changes of each experimental group containing 2.5% w/v ABA were mostly ascribed to those of resin carriers. Even then, the color differences between experimental group and the ESP empty control were still within clinical acceptable limit.─Contact angles of experimental groups containing 0.5% w/v ABAs had no significant differences from those of ESP empty control, regardless of the tooth substrate and reference liquid used. Surface wettability of either enamel or dentin was strongly improved after conditioning by ESP with or without ABA, with enamel the lowest, followed by superficial dentin and deep dentin. Water contact angles were significantly lower than those of resin for each substrate.─The incorporation of 0.5% w/v ABAs into ESP had no significant influence on the curing behavior of the adhesive system. Degrees of conversion increased significantly with the prolongation of the curing time, especially from 20 sec to 40 sec.Microbiological evaluations─The six ABAs notably inhibited the growth of tested common oral bacteria in vitro. Among them, ABA2 was the most effective agent, followed by ABA5, ABA4, ABA1, ABA6 and ABA3. The broth dilution test appears to be more suitable for testing insoluble inorganic ABAs.─ESP itself showed antibacterial effect to some extent either in cured or uncured condition. The addition of ABA2 or ABA5 sensibly decreased the MIC and MBC of ESP.─Although the incorporation of 0.5 w/v ABAs into ESP compromised the antibacterial activities before curing in 30 sec contact, antibacterial ratios of more than 97% still maintained.─Incorporation of 0.5% w/v or 2.5% w/v ABA5, ABA2, ABA3 and ABA4 significantly enhanced the antibacterial effect of ESP after being cured, especially for long incubation period.─Although 1 month aging deteriorated the antibacterial activities of cured specimens comparing to non-aged ones, the incorporation of 0.5% w/v ABAs, except for ABA6, still significantly improved the antibacterial activity of ESP. Among them, ABA5 proved to be the most effective one, followed by ABA2 and ABA3.─Specimens treated by ESP containing 0.5% w/v ABA5, ABA2 or ABA3 had slightly less bacterial adhesion than those without any treatment.─Extracts of cured specimens treated by ESP with or without different 0.5% w/v ABAs had no significant influences on bacterial growth, which suggested that no antibacterial components were extracted after immersing in broth for up to 1 month. Therefore, the antibacterial activities of cured specimens were probably in essence a"contact inactivation effect", and the application of this kind of antibacterial primer would not break the balance of ecosystem in oral cavity.Biological evaluations─Two weeks rat experiments revealed neither toxic manifestations nor significant differences in body weight gain between control animals and exposed groups, in which ESP contained 5.0% w/v ABAs.─No significant differences in cell vitality rates or cell proliferation rates were found between the Thermanox empty control and any one of the other groups, which treated by ESP containing 0.5% w/v different ABAs. The overall calibrated CI (with respect to the Thermanox empty control) of groups tested ranged from 0 to 20 per 100 score points, exhibiting little or only slight cytotoxicity. ABA1, ABA5 and ABA6 were the less toxic agents. Toxic effect was detected only within the area beneath the specimen and/or in the direct vicinity of the specimen edge. There was no influence on the cell density beyond the limit of specimens.Within the limits of this study, it can be concluded that the here tested ABAs can be effectively incorporated in ESP at a proper concentration to provide potential antibacterial activity against cariogenic bacteria, especially S. mutans, without adverse influence to its inherent physico-chemical properties and biocompatibility. ABA5, ZnOw AT-83 was the most promising one. The optimal concentration of incorporation was regarded ranging from 0.5% w/v to 2.5% w/v. The incorporated ABAs were immobilized after curing of ESP; although not so effective in killing the bacteria as before curing, they were deducted to exert a"contact inactivation"effect, thereby safer and would not result in the destabilization of oral flora.By the incorporation of inorganic ABAs, it's hopeful to develop self-etching primers with antibacterial activity and series of other antibacterial dental restorative materials, thereby establishing a substantial basis for the realization of the new"preventive-oriented"pattern for caries treatment.
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