Enamel dissolution in relation to fluoride concentrations in the fluid of dental plaque-like layers of precultured Streptococcus sobrinus

Investigation to evaluate and validate the Leeds in situ device for the study of enamel remineralisation in vivo

OBJECTIVES

Recently, a novel device to generate dental plaque in situ on a removable human enamel surface was described. The device permitted the recovery of plaque intact and undisturbed on its enamel substrate. The aim of this investigation was to determine the utility and robustness of this model for analysis of the effects of therapeutics on both enamel remineralisation and on the overlying biofilm composition.

METHODS

Enamel slices were taken from extracted sound human teeth, sterilised and a 'flat' area ground on each slice. An artificial lesion was formed within this area using acidified gel and the hardness of the enamel within the area of the lesion was determined at five sites using a 'Vickers' indenter. A nylon ring was then attached over the area of the lesion with cyanoacrylate and the excess enamel removed to form the completed device. Two devices were attached to the upper molars of 22 volunteers. Each volunteer was randomly assigned to receive either a fluoride containing (1500 ppm) or a fluoride free dentifrice. The devices were retained for a 4 week period whilst undertaking normal oral hygiene. All procedures were conducted according to GCP. After a 2 week break, the volunteers were fitted with two further devices, given dentifrice of the alternate type and the procedure repeated. Plaque from each device was harvested for microbiological analyses and the enamel subject to microhardness measurement. Then for each device the change in microhardness of the enamel within the lesion over the 4 week period was calculated.

RESULTS

There were no significant differences in viable counts of total aerobic bacteria, mutans streptococci or lactobacilli, nor in acidic, aciduric or arginolytic populations in plaque from patients using the two different dentifrices. However, devices subjected to the fluoride containing dentifrice demonstrated a significantly greater increase in microhardness of the enamel (P<0.025).

CONCLUSIONS

These results suggest that the novel in situ device is capable of measuring the effect of 1500 ppm fluoride on remineralisation of carious enamel over a 4 week period and is also well suited to determining concomitant effects on plaque ecology.