Bio-availability of fluoride from black tea and oral acidity studies
Dr Tony Smith

Dr Anthony Smith and his colleagues at the University of Birmingham carried out studies of our topics: the bio-availability of fluoride from black tea; fluoride recovery from the acquired pellicle after mouth rinsing; the effects of black tea upon oral acidity; and the binding of black tea moieties to dental enamel. The subjects in all the studies were healthy volunteers with good standards of oral health. The data make clear that some of the natural fluoride content of tea is retained in the oral cavity after rinsing with a tea solution. The retained fluoride may be associated either with dental hard tissues and integument or muscosal soft-tissues. The second study examined how much of the retained fluoride is sequestered at the tooth surface where it is available for incorporation in the dental enamel or for plaque prevention. The results showed that fluoride from tea is retained at the tooth surface. The third study examined acidity (pH) directly at the tooth surface to assess the influence of tea upon oral acidity. Dr Smith found that a small but detectable fall in pH at the tooth surface took place after rinsing with tea followed by a recovery to resting levels within two minutes. This minimal effect suggests that tea is a suitable beverage to recommend to people at risk from dietary erosion. Dental enamel has a high mineral content capable of interacting with a variety of ions and molecules: Dr Smith carried out binding studies of tea constituents to enamel and, more particularly, the binding of fluoride to enamel. The binding study was carried out by comparing the binding of tea to enamel with a control substance; alizarin red. The results show that tea binds to enamel and blocks the binding of the competing compound and in an additional study it appeared that the blocking due to tea was largely due to the fluoride present in tea.

Black tea inhibits tooth decay in albina rats
Dr L Z G Touyz

Dr Touyz examined the effects of black tea on cariogenesis in 18-day Sprague-Dawley rats. A control (tap water) group was compared with fluoridated water group and a black tea group. The initial control showed that the rats were free of caries. After 14 nights on a cariogenic diet the rats consuming water only had significantly increased caries; both tea and fluoridated water decreased caries although the fluoridated water had the greater effect. Dr Touyz concluded that tea has cariostatic properties.

The effects of black tea upon the acidity of dental plaque, caries formation and the cariogenic properties of plaque bacteria
Dr Christine Wu

Dr Wu, working with Dr P Lingstrom (University of Goteberg) and Dr J S Wefel (University of Iowa), carried out a series of studies. The first of these looked into plaque formation, the acidity of plaque and fluoride concentration in the oral cavity. Healthy human subjects were examined during three seven-day periods during which they rinsed with tea 10 times in the day or 5 times, or rinsed with water. On days 5-7 no oral hygiene took place and fluoride free toothpaste was used throughout. Samples of resting saliva and plaque were taken. Regular exposure to tea had a dose dependent effect upon pH during a 30-minute interval following a 10% sucrose rinse and, on day 7 of the study, tea at 10 rinses/day had a direct effect upon plaque acidity. Similarly there was a dose dependent relation between plaque fluoride concentration following one week of rinsing with tea. Tea reduced the presence of oral streptococci.

A second study examined the effects of black tea extract upon P Gingivalis, the results indicated that black tea extract and other polyphenol components in tea exert an inhibitory effect on protease and hemin binding, both of which are expected to lead to an inhibition of the virulence of P Gingivalis.

A further study of the effects of black tea upon a number of potential dental pathogens [S Mutans, S Sobrinus, S Sanguis P Gingivalis, Prevotella intermedia] showed that tea extracts have a variety of inhibiting effects upon growth, cellular aggregation and viability. The conclusion was that black tea extracts have a differential growth inhibitory effect upon aneoribic pathogens. A final study was carried out on a model system in which caries-like lesion were created in human teeth to examine if tea might have a role in the repair of damage to teeth. It was assumed that fluoride in tea would have a positive effect. In this study the expected beneficial effects of tea were not observed.