The effect of fluoride containing toothpastes on sound human enamel in vivo during 3 weeks

The F- uptake in vivo in sound human enamel from fluoridated toothpastes is described. Ten participants brushed for about 1 min twice a day, four enamel specimens in a dental appliance over three week periods. The enamel specimens were prepared so that only the right hand side of the enamel was positioned in the appliance; the left hand side being used as a control. The toothpastes all used hydrate silica as the abrasive and contained either 0.1 ppm F- as nicomethanolhydrofluoride, 1100 ppm F- as NaF or 1350 ppm F- as NaF/MFP. After three weeks brushing with the pastes in vivo the F- contents of three thin layers of enamel were determined in all specimens by means of acid etching. The results showed that 1) there were no statistically significant differences between the mean F- contents of the enamel (p less than 0.05), which were comparable, before and after three weeks brushing in vivo. This observation was independent of the toothpaste employed, 2) in the outer approximately 1.5 micron layer of human enamel there was an equilibrium F- level of about 1200 ppm. The microhardness data on polished enamel specimens showed that there was no statistically significant difference between the mean indentation lengths produced in control specimens and these made in specimens after the use of a placebo toothpaste (0.1 ppm F-) in vivo indentation lengths of all specimens brushed with any of the fluoridated toothpastes for three weeks showed, however, a statistically significant decrease of indentation length and thus an increased hardness.