Resting dental plaque pH values after repeated measurements at different sites in the oral cavity.

Plaque pH measurements can be used to detect individual's caries susceptibility and the cariogenic potential of ingested foods. However, repeated measurements with a touch electrode at a single site may affect the metabolic state of the dental plaque and result in changes of its inherent pH values. The purposes of this study were to evaluate the influence of repeated measurements of resting plaque pH values and to determine the pH values at different interdental sites. Eleven dental students participated in the study. The dental plaque was built up after thorough oral hygiene care. The subjects were then instructed to maintain a normal diet but to refrain from any oral hygiene care for the next 48 hours. Measurement of plaque pH was performed with an antimony electrode at 6 interproximal sites, including central spaces between the upper and between the lower central incisors, and the area between the second premolar and the first molar in each quadrant. At each tested site, measurements were taken 5 times at 0, 10, 30, 45 and 60 min. The results showed that the plaque pH became slightly alkaline at all the tested locations after repeated measurements. However, only the lower incisor area showed a significant change in pH values. Interdental plaque on the lower arch showed higher pH values than did that on the upper arch. There was no significant difference between the pH values on the right and left corresponding sites as determined using the Wilcoxon signed ranks test.