Relationship between dental fluorosis, dental caries and salivary levels of Streptococcus mutans

BACKGROUND AND OBJECTIVE: Worldwide, dental caries is an endemic infection and a significant public health problem. Fluoride reduces caries by helping to prevent demineralisation, by remineralising early carious lesions, and by decreasing the activity and growth of Streptococcus mutans (S. mutans). Fluoride intake above the optimal levels leads to a condition known as dental fluorosis, which causes hypo-mineralisation of the tooth. Some studies have revealed that the severity of fluorosis is directly proportional to caries, but some showed opposite results. Hence, with these contradicting results, this study was undertaken to identify the relationship between different grades of dental fluorosis, dental caries and the most common cariogenic bacteria S. mutans in saliva. MATERIALS AND METHODS: A total of 90 subjects within 14- to 16-year age range were selected and categorised depending on the severity of fluorosis into three groups: group I (mild), group II (moderate) and group III (severe) based on modified Dean’s fluorosis index criteria (1942). Unstimulated whole saliva samples were collected using the oral rinse technique and processed for quantification of S. mutans using Mitis Salivarius Bacitracin Agar medium. The number of colony-forming units (CFUs) was determined using a colony counter and expressed as ≥10(2), ≥10(3), ≥10(4) and ≥10(5) CFUs per ml of the sample, in accordance with the scale recommended by the manufacturer (HiMedia Laboratories). The severity of the caries was measured using decayed, missing or filled teeth (DMFT). RESULTS: Observations revealed that the overall DMFT was directly proportional to the level of S. mutans titres. It was observed that 67 to 73% of participants showed fewer colony counts (10(2) and 10(3)) with minimal DMFT scores and 27 to 33% showed higher counts (10(4) and 10(5)) with higher DMFT scores in all the groups. 10(5) CFUs of group III showed the highest mean DMFT scores (2.9) with an increased number of involved subjects than group II (2.3) and group I (1.5). In all, male participants had higher bacterial titres and DMFT scores than females. CONCLUSION: Fluoride in the drinking water served as anticariogenic agent regardless of the severity of fluorosis. Severe fluorosis with a higher incidence of caries and increased CFUs of S. mutans clearly indicates the importance of preventive measures and early treatment to reduce the severity of fluorosis and prevalence of dental caries.