The present invention concerns a group of dental restorative and luting cements which have been combined with antibacterial compounds and thereby have achieved an increased antibacterial activity against oral microorganisms. The cements can be based on glasspolyalkenoats or dental composite resins, to be applied in thicker layers compared to a varnish, thereby containing a larger amount of anitbacterial compounds. The antibacterial compound(s) are leaking from the cement(s) which have been made soluble in oral fluids, having the properties of a matrix that allow sustained release of a drug.

Dental carles and perfodontltis are caused by microbial plaques on the tooth surfaces. Bacteria belonging to the Streptococus mutans group are strongly associated with the developement of caries. These microorganisms are highly sensitive to chlorhexidine In various forms as chlorhexidine-gluconate, chlorhexidine-acetate and chlorhexidine-hydrochloride.

Patients with extensive dental decay often carry mutans streptococci in high numbers, and a causal treatment can be to treat the patient with chlorhexidine gluconate gel, which 1s applied on the teeth in costumeflt trays. By this treatment, the mutans streptococci are eliminated from the mouth for a period of time but very seldom for ever. To maintain a situation with no or occasional mutans streptococci, the treatment has to be repeated after a few months. One reason for reappearence is probably that some microorganisms persists in retentive areas where the concentration of the chlorhexidine is not bactericidal. Another reason is that the concentration of chlorhexidine in this type of treatment is high and other microorganisms will also be more or less eliminated. In an environment where several species have been more or less eliminated and then start at the same time to struggle for survival and recolonization, the mutans streptococci will soon find its ecological nisch again.

Therefore, it is apparent that if chlorhexidine could be administered in such a way that an initially high concentration is present on the teeth to eliminate all mutans streptococci and that the concentration gradually decreases allowing other microorganisms that are less sensitive to the drug to colonize first, the highly sensitive mutans streptococcus would have less chance to survive. This has been demonstrated in part by Sandham and co-workers ( 1 ). Sandhams group used a varnish

However, the varnish was per definition very thin and the procedure had to be repeated at least three times, in different sessions, to be somewhat successful.

The present invention is a thicker layer of resin or cement as carrier, which can contain substantially more chlorhexidine or other antibacterial compunds compared to a convetional varnish.

The idea to mix antibacterial compounds such as chlorhexidine with dental restorative materials is not new. Jedrychowski and co-workers have described a combination of chlorhexidine with composite resin or glass polyalkenoate cements (2). By mixing the antibacterial compund with the restorative materials, they achieved antibacterial effects without comprising the mechanical properties of such materials.

The present invention describes a dental cement that is in contrast to the above, highly soluble in oral fluids and will dissolve after 1-4 weeks on the teeth. This important feature of the material will give a delivery system were a high concentration of an antibacterial compound is combined with a dissolving carrier, it is not an advantage to either have a non-soluble carrier (2) or lower concentration (I ) of antibacterial compounds if one is aiming at eliminating mutans streptococci from the teeth, as in a profylactic approach towards the treatment of dental caries. If a restorative material is permanently placed in a cavity, the damage in terms of a cavity has already been done. If a non-soluble material is placed on sound dental surfaces, eventually, it will lose its antibacterial properties and become a retention site for microorganisms and increase the risk of disease.

The present invention can be described by the following example. Glasspolyalkenoate materials such as a restorative cement (Che fil, De Trey Dentsply Ltd, England) or a luting cement AquaCem (De Trey Dentsply) are mixed with water containing various amounts of chlorhexidine gluconate or acetate rangeing from 0 to 20 per cent. Discs are made and placed on agar medium containing an inoculum of mutans streptococci or lactobacilli. After incubation, an inhibition zone is seen around the discs corresponding to the amount of chlorhexidine present in the disc. The same discs are transferred to freshly inoculated agar plates repeatedlty, until their antibacterial properties are lost. The results show that the cements has a small antibacterial effect even without addition of chlorhexidine, perhaps due to the high fluoride content.

The addition of chlorhexidine gives a clear dose-response inhibition of the bacterial growth. The antibacterial effect is maintained through at least 15 changes of freshly inoculated bacteria with 48 hours of incubation each time. A corresponding antibacterial effect is seen when bacteria are grown in a broth medium and incubated with the chlorhexidine containing discs. The high fluoride content is also important as a caries preventive measure.

When exceding 10 per cent of chlorhexidine in added water to the cements, a substantially higher solubility of the cements is seen. As an example, the addition of 15 per cent chlorhexidine gluconate to the luting cement will render it totally dissolved after 8-10 changes in agar plates as described above. This is an example how the glasspolyalkenoates can become soluble by the addition of high concentrations of chlorhexidine. This addition does not dramatically affect the adhesive properties of the materials and they will attach to dental surfaces even containing high amounts of chlorhexidine. If a lower concentration of chlorhexidine is used the material could be used as a temporary filling material.

The chlorhexidine is relased from the discs as determined by spectrophotometric measurements at 251 nm.

The glasspolyalkenoates has the advantage of containing a substantial amount of fluoride which is also released from the material, making the tooth structures less susceptible to decay.

The above presented formulations of glasspolyalkenoates and chlorhexidine are commonly used in dentistry and they have a low toxicity. Of course, the concept of the invention can be applied not only on glasspolyalkenoates and chlorhexidine, but also dental resin materials and other materials combined with other antibacterial compounds.

Literature cited:

1. Sandham, HJ et al. 1988. A preliminary report on long-term elimination of detectable mutans streptococci in man. Journal of Dental Research 67( 1 ):9-14

2. Jedrychowski JR et al. 1983. Antibacterial and mechanical properties of restorative materials combined with itatio 1 : 373- 81