Abstract
Objective: To evaluate the short-term efficacy of topical fluoride varnish on Streptococcus mutans levels among youth with varying baseline bacterial loads.
Methodology: This clinical pre–post interventional study was conducted at Khanzad Dental Institution, Erbil, Kurdistan Region, Iraq, involving 50 healthy volunteers aged 15–24 years. Participants received a single application of 5% sodium fluoride varnish. Stimulated saliva samples were collected at baseline, Day 1, Day 7, and Day 14. Streptococcus mutans levels were quantified using real-time PCR targeting the gtfB gene. Data were analyzed using the Friedman test with Wilcoxon post-hoc comparisons (α=0.05).
Results: At baseline, 32 participants (64%) exhibited very low bacterial counts, while 18 (36%) fell into low, medium, or high categories. By Day 7, copy numbers of Streptococcus mutans decreased markedly, with several individuals dropping from >50,000 to <5,000 gene copies. The Friedman test demonstrated a statistically significant difference across time points (χ² = 9.96, df = 3, p=0.018). By Day 14, a mild rebound was observed; however, counts remained below baseline levels in most participants. Regarding salivary buffer capacity (n=18), the “very low” category decreased from 4 (22.2%) at baseline to 0 after Day 1, while “normal” buffering increased from 2 (11.1%) to 4 (22.2%) by Day 14.
Conclusion: Topical fluoride varnish provides a short-term antimicrobial effect against S. mutans with modest improvements in salivary buffering. Periodic reapplication may be necessary to maintain microbial suppression in high-risk youth.

Key words: Streptococcus mutans, fluoride varnish, dental caries, youths, oral health.