Impact of clear aligners on the oral microbiome: a systematic review of current evidence

Objectives: Oral malocclusion affects a large portion of the population, impacting both function and aesthetics. Recent advances in orthodontics offer a variety of treatment options, including traditional fixed appliances (FA) and, more recently, clear aligners (CA). This systematic review aims to synthesize and critically evaluate current evidence on oral microbiological changes during orthodontic treatment, with a focus on CA. Materials and Methods: A comprehensive literature search was conducted using PubMed, Medline, Cochrane Library, Embase, and Scopus. Keywords included: (“Bacteria” OR “Microbio*”) AND (“Orthodontic aligners” OR “Invisalign”). The review was registered in PROSPERO (CRD420240628072), and the final search was completed on October 15, 2024. Two reviewers independently screened studies, extracted data, and assessed risk of bias. Primary outcomes included changes in oropharyngeal microbiota (salivary, lingual, gingival, and pharyngeal) and functional diversity (e.g., alpha and beta diversity, metabolic pathways). Results: Twelve studies met inclusion criteria. Findings revealed that CA use leads to time-dependent shifts in the oral microbiome, with notable changes in beta diversity within 24 h. Over periods from 1 to 12 months, CA users exhibited more favorable oral health outcomes compared to FA users, including lower plaque index (PI), reduced gingival inflammation (GI), and decreased probing pocket depth (PPD). These improvements are likely to be due to the easier hygiene maintenance of CA. Conclusion: Clear aligners appear to promote better oral microbiological balance and periodontal health than FA, likely due to easier hygiene maintenance and reduced plaque accumulation, with consistently lower levels of Streptococcus mutans observed in subjects undergoing CA therapy.