On the Mechanism of the Plaque Inhibition by Chlorhexidine

The marked plaque-inhibiting activity shown by chlorhexidine1 is a unique prop-erty demonstrated only by the bis-bigua-nides.2,3 Initial killing of the bacteria by the chlorhexidine mouthrinse seems not to be the decisive factor in the plaque inhibi-tion, as antibacterial agents with as high or higher activity against salivary bacteria did not show corresponding clinical effects.2 Considerable evidence has been accum-ulated indicating that a retention of bis-biguanides in the mouth is the basis for the plaque inhibition.4-9 About 30 % of the chlorhexidine introduced into the mouth during a mouth rinse is retained.9,10 The teeth are not a major retention site, at least not quantitatively, but plaque-covered teeth have been shown to bind limited quantities of the drug."1 Results of studies that used mouthrinses at different pH levels strongly indicated that acidic groups, presumably on the macromolecules of the mucous secre-tions covering the oral surfaces, are the receptors responsible for the major share of the retained chlorhexidine. Electrostatic binding between the acidic protein groups and the basic bis-biguanide molecules seems to be the mechanism involved (Fig 1).7,8,10 In the current study, the interaction of chlorhexidine with carboxyl, sulfate, and phosphate groups was studied in vitro, in-cluding factors that might interfere with these interactions. The properties of cetyl-pyridine in the same systems also were in-vestigated for comparison, as this is a basic antibacterial agent with virtually no plaque-inhibiting effect.2 It was believed that such data could supply information that might shed light on the mechanism of adsorption and release of chlorhexidine in the mouth and possibly indicate the properties essen-tial for a substance to be retained onto and released from the oral surfaces. Such sub-stances may be of interest not only in dental research, but could possibly also serve as carriers for other drugs when a gradual, slow oral release is needed. The chlor-hexidine-binding properties of protein ex-tracts from the major salivary glands at dif-ferent pH levels were also investigated.