Intra-oral variations in total plaque fluoride related to plaque pH. A study in orthodontic patients.

The aim of the present investigation was to study intra-oral variations in total plaque fluoride, and to examine whether such variations were related to plaque pH. Five orthodontic patients abstained from oral hygiene and daily fluoride rinsing for 2 days. Resting and fermenting plaque pH was measured with a touch micro-electrode at 14-21 localized sites on bonded vestibular tooth surfaces in each subject. Plaque samples from the same sites were analysed with a fluoride micro-electrode. A wide range of plaque pH values and fluoride concentrations were observed. In all subjects plaque pH and total fluoride levels were lower at upper than at lower front teeth. A direct log-linear relationship existed between total fluoride and fermenting plaque pH. In 4 of the 5 subjects this relationship was statistically significant (p < 0.05) and quite strong (adjusted R2 0.2-0.5, Beta 0.5-0.7). The study shows significant intra-oral variations in total plaque fluoride related to plaque pH.