The prevalence of caries in southeastern Mexico in individuals aged 20 to 24 is 83.5%. Caries development is multifactorial, including a cariogenic diet, poor oral hygiene, and limited health education. This preliminary longitudinal, single-blind study, utilizing non-probability sampling, aimed to evaluate oral hygiene, Streptococcus mutans prevalence, and caries frequency in undergraduate dental students. Sixty-seven students in their first semester and fifty-four in their second semester follow-up participated. Self-administered questionnaires gathered data on oral hygiene habits. Additionally, caries diagnosis using DMFT, supragingival plaque culture from tooth 46, and PCR with specific primers for S. mutans and its serotypes were performed. Over 74% of participants reported a high consumption of sugary beverages, and the Bass brushing technique was the most known. The overall caries prevalence was 54%. The DMFT index was 3.34 and 3.30 in the first and second semesters, respectively. Colony growth on Mitis-Salivarius agar was significantly higher in the first semester (Z=-4.8, p<0.0001). Culture-based prevalence of S. mutans was 85% and 44% in the first and second semesters, respectively. In contrast, PCR confirmation showed prevalence rates of 41% and 37% for the same periods, serotype c accounting for 80%. Undergraduate dental students exhibited high sugar consumption. The prevalence of caries and S. mutans was lower than that reported for the general population, and no significant association between S. mutans and caries was observed.
