10.22376/ijpbs.2019.10.1.p1-12 Volume 11 Issue 3 2020 (July-September) Fixed orthodontic appliances are frequently associated with increased dental plaque accumulation and an increase in caries formation. Several studies have shown that such appliances physically alter the oral microbial environment. Patients who undergo orthodontic therapy have oral ecologic changes such as low pH environment and increased retentive sites for Streptococcus mutans and food particles. The aim of this study is to evaluate the distribution in the load of S. mutans in the buccal vestibule and lingual sulcus of the subjects undergoing orthodontic treatment. A total of 20 subjects undergoing fixed orthodontic treatment aged between 15 to 25 years were randomly selected for the current study and were advised to brush their teeth before 6.00 am and also to have a liquid diet till the sample collection. The patients were instructed to report to the department between 8.00 a.m and 9.30 am. The result analysis was done using Wilcoxon signed ranks test. According to the test, there has been overall increase in the S. mutans load in the subjects after one month of orthodontic treatment, whereas no statistical significance was noted between the load of S. mutans in the buccal vestibule and lingual sulcus. From the above results, it was concluded that there is an increase in the level of S. mutans load after one month of orthodontic treatment but it is not site specific. Dr.Kannan Navaneethan, Dr.S.Rajah Meyyappen, Dr.Kanakam Elizabeth Thomas, Dr.Esther Ann Abraham, Dr.Shrinivaasan Nambi Rammohan and Dr.Lakshmi Ravi Orthodontic treatment, Streptococcus mutans, Lingual sulcus, Buccal vestibule, Fixed appliances, caries risk. Funding 35-38