Orthodontic appliances promote the accumulation of biofilm in the oral cavity and increase counts of Streptococcus mutans (S. mutans). However, there are few comparative studies of the effects generated by the interaction of saliva and microorganisms in absence and presence of orthodontic appliances. Aim: The aim of this study was to determine the S. mutans colony-forming unit count (CFU/mL) in participants with and without fixed orthodontic appliances. Materials and Method: It was an observational cross-sectional study on 21 participants, all over 18 years of age, non-smokers, without removable oral appliances, who had not been under antibiotic treatment within the previous three months. Sociodemographic variables, oral hygiene habits, S. mutans CFU/mL count, and salivary pH were assessed. Saliva samples were collected, and the data was analyzed using Fisher’s exact and Kruskal Wallis tests. A p-value <0.05 was considered statistically significant. Results: Fourteen (66.7%) of the participants were female; average age was 20.4 ± 2.2 years. The group without fixed orthodontic appliances had the highest salivary S. mutans CFU/mL count (Me: 56.0×103, IQR: 9.2×103 - 75.5×103), but there was no statistically significant difference between groups (p=0.7459). There was a statistically significant difference in salivary pH, with the metal orthodontic appliance group having the lowest pH (p=0.0478). No statistically significant difference in salivary S. mutans CFU/mL count was found between groups. Salivary pH was lower in the group with metal appliances than in the groups with non-metal appliances and without appliances. Keywords: streptococcus mutans - saliva - orthodontics - mouth