Laboratory Assessment of Antimicrobial Agents for the Treatment of Chronic Periodontitis

Gum health product formulations: what is in them and why?

Two dominant factors dictate which ingredients are used in formulating toothpaste and mouthwashes. The major one is the type of active ingredient chosen, especially cationic active ingredients such as chlorhexidine; the other factor is the needs of the consumer. Apart from gum health benefits, the consumer expects to obtain from gum health toothpaste and mouthwashes other benefits of clean teeth (abrasive and detergent), fresh breath (antimicrobial agents and flavor) and protection from caries and possibly tartar. Exhaustive testing involving experimental design and validated laboratory and clinical tests is essential to ensure that all these benefits are delivered. Unless products are developed systematically, then products with relatively poor activity can find their way on to the market.

The effect of chlorhexidine on defined, mixed culture oral biofilms grown in a novel model system

In order to develop an improved method to evaluate antimicrobial agents for use in clinical dentistry, a constant-depth film fermenter (CDFF) has been used to generate biofilms of fixed depth comprising nine species of bacteria commonly found in dental plaque in health and disease. These bacteria were grown together initially in a conventional chemostat which was used to inoculate the CDFF over an 8 h period. Medium was then supplied directly to the CDFF and biofilms allowed to develop. The biofilms were then challenged with eight short pulses of two concentrations of chlorhexidine (0.0125 and 0.125% w/v). The lower concentration had a limited effect on the composition of the biofilms while a differential and substantial inhibition was obtained with a higher concentration. Actinomyces naeslundii was lost from the biofilm, and the viable counts of streptococci, Fusobacterium nucleatum and Porphyromonas gingivalis were inhibited by over three orders of magnitude by 0.125% chlorhexidine, whereas Veillonella dispar was only transiently affected. The findings were consistent with those from clinical studies of dental plaque, suggesting that this model would have a predictive value when evaluating novel antiplaque or antimicrobial inhibitors.

Susceptibility of biofilms of Streptococcus sanguis to chlorhexidine gluconate and cetylpyridinium chloride

Biofilms of Streptococcus sanguis and planktonic cells of the organism were exposed to chlorhexidine gluconate and cetylpyridinium chloride, at concentrations used clinically, and survivors enumerated. S. sanguis exhibited a lower susceptibility to both antiseptics when it comprised a biofilm than when the organism was in the planktonic form. No viable bacteria were detectable after 5 min of exposure of planktonic cells to 0.2% (w/v) chlorhexidine gluconate or 0.05% (w/v) cetylpyridinium chloride, whereas viable bacterial survived in biofilms of S. sanguis even after exposure to these agents for 4 h. Older biofilms (7 days old) had similar susceptibilities to the antiseptics as younger biofilms (4 days old). Chlorhexidine achieved kills corresponding to approximately a 2 log10 reduction in the viable count of biofilms, containing approximately 10(7) colony-forming units after 5 min of incubation, whereas the corresponding kills achieved by cetylpyridinium chloride amounted to approximately a 1 log10 reduction. However, on a molar basis, cetylpyridinium chloride was the more effective of the two antiseptics. Minimum inhibitory concentration determinations showed chlorhexidine gluconate to be more effective against S. sanguis than cetylpyridinium chloride. The results of this study have revealed that the minimum inhibitory concentration is not a reliable predictor of the relative effectiveness of antimicrobial agents against S. sanguis biofilms.

Procedures for establishing efficacy of antimicrobial agents for chemotherapeutic caries prevention

Chemotherapeutics are presently considered for use in caries-preventive programs. The laboratory and in vivo testing of these agents, to some extent, parallels the methodology developed for the evaluation of fluoride products. However, fluoride is primarily effective by interfering with the de- and remineralization balance between enamel and the oral fluids. Antimicrobial and chemotherapeutic agents interfere with the bacterial colonization, growth, and metabolism of dental plaque. The initial selection of promising agents is done, therefore, by determination of the minimum inhibitory concentration (MIC) against a wide range of relevant bacterial species, together with tests of the effects of sub-MIC levels on the expression of virulence factors. In the hierarchy of tests proposed in this paper, studies of bacterial adhesion and enamel caries models form the next phase in the evaluation of agents. Also, mixed-culture studies are recommended to determine how a treatment perturbs a stable microflora. A final stage before clinical testing might involve intra-oral studies on limited numbers of volunteers. These should be tests of intra-oral substantivity and activity of the agents in formulated products, and in situ models of enamel caries lesion formation and remineralization. The latter type of study seems particularly appropriate to ensure that new agents do not decrease the efficacy of the other active components (e.g., fluoride) in caries-preventive products.