How to Cite: Al-Ali, D. A., & Groosh, D. A. (2022). The influence of fixed orthodontic retainer on oral microbiota. International Journal of Health Sciences, 6(S2), 2214–2223. https://doi.org/10.53730/ijhs.v6nS2.5483 International Journal of Health Sciences ISSN 2550-6978 E-ISSN 2550-696X © 2022. Corresponding author: Al-Ali, D. A.; Email: dhuha11_1aba@yahoo.com Manuscript submitted: 27 Jan 2022, Manuscript revised: 18 Feb 2022, Accepted for publication: 09 March 2022 2214 The influence of fixed orthodontic retainer on oral microbiota Dhuha A. Al-Ali BDS, M.Sc. Ph.D., student, Department of Orthodontics, College of Dentistry/ University of Baghdad, Baghdad, Iraq Email: dhuha11_1aba@yahoo.com D. Al Groosh BDS, M.Sc., Ph.D. Professor of Orthodontics, Department of Orthodontics, College of Dentistry/ University of Baghdad, Baghdad, Iraq Email: d.al-groosh@codental.uobaghdad.edu.iq Abstract---Background: The oral cavity is a wide versatile microbial community in which many microbial species coexist in harmony. However, with certain circumstances, i.e. orthodontic appliances, pathogenic biofilm outgrowth occurs. The aim: The aim of this study was to compare opportunistic pathogens, associated with dental caries and periodontal disease in addition to Candida albicans, between healthy individuals and patient wearing fixed orthodontic retainers. Method: Fourty eight subjects were recruited andwere divided into retainer wearers and control cohort groups. Biofilm samples from the lingual surface of the mandibular anterior teeth of the control group and the fixed retainer surface were evaluated to detect Streptococcus mutans, Lactobacillus acidophilus, Aggrigatibacter actinomycetemcomitans, Fusobacterium nucleatum and C. albicans. Additionally, plaque (PI) and gingival (GI) indices were measured at the mandibular anterior teeth in both groups. The results: The results showed a significant increase in total micobial count in retainer group (p<0.001). The prevalence of microbial cultivity was higher in retainer group with a significant increase in PI and GI. Moreover, there was a high correlation between these genera and the GI. The conclusion: fixed retainer may increase cariogenic and periodontal pathogens and compromise oral health.. Further studies on improving the fixed retainer material and plaque control measures in retainer wearers are needed. Keywords---fixed retainer, opportunistic pathogens, periodontal pathogens, plaque gingival index.