Quantitative analysis of Streptococcus mutans, Bifidobacterium, and Scardovia Wiggsiae in occlusal biofilm and their association with Visible Occlusal Plaque Index (VOPI) and International Caries Detection and Assessment System (ICDAS)

To quantitatively detect S. mutans, Bifidobacterium, and S. wiggsiae in occlusal biofilm from permanent first molars based on the Visible Occlusal Plaque Index (VOPI), and to analyse the association between their levels and the occlusal enamel caries occurrence following the diagnosis of the International Caries Detection and Assessment System (ICDAS).

One hundred twenty plaque samples were collected from children aged 6–8 years and divided into four groups (n = 30 each group) according to VOPI scores (0 = no visible plaque, 1 = thin plaque, 2 = thick plaque, and 3 = heavy plaque). Scores 0 and 1 were identified by running dental probe on the groove. Scores 2 and 3 were visually identified. ICDAS scores were recorded by scoring 0–3 (0 = sound tooth surface, 1 = opacity or discoloration of enamel after air drying, 2 = visual change in enamel when wet, and 3 = localised enamel breakdown).

DNA was extracted from plaque samples and performed quantitative real-time PCR using SYBR green and specific primers for total bacteria including the 16S rRNA gene sequences conserved in all bacteria (BAC16S), S. mutans, Bifidobacterium, and S. wiggsiae.

Ages of the children were different amongst VOPI groups (p < 0.001). Levels of total bacteria (p < 0.001) and S. mutans (p = 0.026) increased when VOPI increased. The ratio of S. mutans to total bacteria (p = 0.015) and the ratio of Bifidobacterium to total bacteria (p < 0.001) decreased from VOPI 0 to VOPI 3. Significant differences in total bacteria (p < 0.001) and S. mutans (p = 0.018) were detected from VOPI 0 to VOPI 2. A difference in Bifidobacterium (p < 0.001) was detected from VOPI 0 to VOPI 1.

Quantities of total bacteria (p < 0.001), S. mutans (p = 0.02) and ICDAS scores (p < 0.001) and VOPI scores were positively correlated. Quantities of ratio of S. mutans to total bacteria (p = 0.003) and ratio of Bifidobacterium to total bacteria (p < 0.001) and VOPI scores and ICDAS scores (p < 0.001) were negatively correlated.