INFLUENCE OF CLEAR ALIGNERS ON ORAL HEALTH AND MICROBIAL COMPOSITION DURING ORTHODONTIC TREATMENT: A NARRATIVE REVIEW

Objective: To critically evaluate current evidence regarding the effects of clear aligner therapy on periodontal health, oral microbiome composition, biofilm formation, and caries risk compared with fixed orthodontic appliances. Materials and Methods: A narrative review informed by a structured literature search was conducted in PubMed, Scopus, Web of Science, and CNKI (2015–2025). Eligible studies included randomized controlled trials, cohort studies, observational studies, systematic reviews, and microbiological investigations. A total of 165 studies were identified, and 35 met the criteria for qualitative narrative synthesis. Results: Evidence indicates that clear aligners are generally associated with more favorable short- and medium-term periodontal and hygiene-related indices, including reduced plaque accumulation and mild improvements in gingival bleeding compared with fixed appliances. Microbiome analyses suggest that aligners maintain relatively stable microbial diversity, although mild increases in cariogenic species may occur under poor oral hygiene compliance. Biofilm formation can occur on thermoplastic surfaces due to salivary pellicle deposition and microabrasion. Fixed appliances demonstrate a stronger association with microbial dysbiosis and enamel demineralization. Conclusions: Clear aligner therapy offers more favorable periodontal and hygiene-related indices compared with fixed orthodontic appliances; however, the long-term clinical significance of these differences remains modest. Furthermore, these biological benefits are not automatic and depend greatly on patient compliance, individualized risk assessment, specific appliance designs, and dedicated hygiene protocols.