This study has shown that the exposure of human dental enamel to acid solutions in vitro produces three basic etching patterns. In the most common, called type 1 etching pattern, prism core material was preferentially removed leaving the prism peripheres relatively intact. In the second, type 2 etching pattern, the reverse pattern was observed. The peripheral regions of prisms were removed preferentially, leaving prism cores remaining relatively unaffected. In the type 3 etching pattern, there was a more random pattern, areas of which corresponded to types 1 and 2 damage together with regions in which the pattern of etching could not be related to prism morphology. These findings differ from previous studies in which the type 1 pattern was ascribed to acid action and type 2 etching pattern to attack by chelators. The results therefore suggest that there is no one specific etching pattern produced in human dental enamel by the action of acid solutions. Such differences produced by acids are difficult to explain on the basis of variation in chemical composition, and crystallite orientation. This further highlights the variation in structure that can occur in enamel not only from tooth to tooth, or surface to surface, but also from site to site on a single tooth surface.

A partial mouth experimental gingivitis model was employed to establish the potential efficacy of a dentifrice containing a zinc salt and the antimicrobial agent Triclosan to prevent or delay the development of gingivitis over a period of 28 days. Initially, gingival health was established in 34 subjects following a 6-week period of professional tooth cleaning and oral hygiene instruction. A toothshield was constructed to fit 4 posterior mandibular teeth. Undiluted test or placebo dentifrice was applied to the experimental teeth via the toothshield, which also prevented plaque removal from these teeth during habitual brushing of the remainder of the dentition. The presence of plaque, bleeding after probing and visual signs of inflammation were independently assessed. Plaque accumulated rapidly and gingivitis developed in both groups. At the 2-wk assessments, lower mean plaque scores were recorded for the group using the test dentifrice. At the 4-wk assessment a significantly lower level of gingivitis was recorded for the test group. It is concluded that (a) the model can be used to establish the potential efficacy of a dentifrice to maintain gingival health, (b) the dentifrice containing zinc citrate and Triclosan was efficacious and (c) the Gingival Index possibly overestimates the proportion of healthy gingival sites.

Few investigations on the development of dental have considered the first changes which can occur on a cleaned tooth surface during the first 4 h of exposure to the Plaque oral environment. The present study has investigated, using the scanning electron microscope, the colonization of enamel surfaces in vivo, and some of the factors influencing plaque formation during the initial 24 h after cleaning. A correlation was established between gingival health and the time of deposition of the organisms, and this fact, together with the presence of bacterial aggregates adjacent to the gingiva, is taken as an indication that the gingival fluid plays an important part in the colonization of the tooth surface. It is concluded that the formation of microbial plaque is an extremely complex and dynamic process encompassing a number of interrelated factors. It is suggested that two major processes are involved, firstly the adherence of bacterial aggregates and secondly growth of organisms within the aggregates and from residual material in enamel defects. The development of the plaque is considerably influenced by the local environment.

Zinc salts have previously been shown to possess antiplaque activity in solution but this activity has as yet not been reported for dentifrices. The purpose of the present investigation was to establish the effect of dentifrices containing zinc citrate (ZCT) on plaque growth and on the concentration of zinc in saliva and plaque. Plaque growth inhibition was studied over periods of time approximating to intervals for normal oral hygiene procedures. Zinc in saliva and plaque was measured by atomic absorption spectroscopy. Elevated zinc levels in saliva were observed for 3-4 h after brushing with the zinc citrate dentifrice. Similarly, raised levels of zinc were encountered in plaque 1 h following contact with a slurry of a dentifrice containing ZCT. Increased concentrations of zinc were observed in plaque fluid and plaque residue. The plaque growth data from 88 participants in 5 studies revealed that plaque regrowth over 16 h or 22 h was reduced by dentifrices containing 0.5% ZCT, compared to placebo dentifrices. Dentifrices which contained 0.5% ZCT or 0.4% stannous fluoride, had similar inhibitory effects on plaque. Further analysis of the data showed that subjects with high rates of plaque growth benefited more from the zinc dentifrices than those with low rates of plaque growth. It is suggested that the effect on plaque was related to zinc concentration in the dentifrice rather than total dose applied, and that the main effect of zinc was to inhibit the extension of existing plaque.