Site-specific dental plaque pH in 13-year-old Thai schoolchildren

The aim of this paper was to study pH conditions between dental sites, taking account the presence of caries, calculus, and microbial composition and alkali production.

One hundred 13-year-old Thai schoolchildren were recorded for caries experience (DMFT, DT), calculus, plaque, and gingivitis. Ex vivo urease activity was measured on 11, 26, 31, and 46 (distal aspect) with the rapid urease test and pH at baseline and after rinse with 0.25 % urea solution on mesial site in vivo. Interproximal plaque from contralateral teeth was microbiological analysed with the checkerboard technique.

Thirty-four children were caries free. Plaque and calculus were abundant; all children showed a high resting plaque pH and the mandibular incisor showed significantly (p < 0.01) higher pH at baseline, max pH and AOC7.0 after urea challenge, ex vivo urease activity and calculus but lower caries experience than other teeth. A significant inverse correlation (p < 0.02) was found between caries frequency and ex vivo urease activity for tooth 11. Anaerobes predominated over streptococci, but no significant differences between dental sites were found.

The study group had a high baseline plaque pH, in vivo and ex vivo urease activity, and calculus but low caries experience, which was best reflected in the lower incisor region.

Urease activity and pH on site level may be important determinants for individuals at caries risk.