UCLA

BackgroundToday, we know that the oral microbiome is the second most abundant microbiome in the human body, after the gastrointestinal tract, and comprises a delicate ecosystem which consists of hundreds of different predominantly commensal but also pathogenic bacteria 2. The average adult can harbor as many as 100 billion bacteria in their mouth, and the accessibility of the oral cavity makes this massive microbiome uniquely convenient for scientific investigation. The most common pathologies associated with oral microorganisms are dental caries and periodontal disease. Numerous studies have shown common microbial shifts associated with oral disease, but it is not clearly exactly which bacteria are involved in these shifts, especially in patients with orthodontic appliances.

ObjectiveIn this study, we analyze the salivary microbiome of patients undergoing orthodontic treatment using either traditional metal braces or removable clear aligners. The salivary microbiome of these patients is compared to the respective microbiomes found in the tooth-associated plaque above the gingival margin, as well as the plaque found on the clear aligner trays themselves, throughout the first 12 months of orthodontic treatment. Clinical data, such as plaque levels and gingival health, are also compared with changes in salivary microbial composition throughout treatment, in order to identify a potential relationship between microbial composition and oral health during orthodontic treatment.

MethodsClinical data, saliva, and plaque samples were collected at the following orthodontic treatment timepoints for both clear aligner and fixed appliance patients: 0 months, 1 month, 3 months, 6 months, and 12 months. Plaque levels were quantified using Turesky et al. Modified Quigley-Hein Plaque Index (PI), and 36; 37 gingival health was measured using the L�e and Silness Gingival Index (GI) 38. Next generation sequencing of the V1 to V3 region of the 16S rRNA gene from DNA extracted from the saliva and plaque samples and microbial community analysis was performed. Standard microbial community data analysis was performed with bioinformatic protocols.

ResultsThe average age of the fixed appliance group (23.0 � 13.6 years) was lower than the average age of the clear aligner group (30.9 � 12.3 years), but the difference was not significant (p = 0.201). Plaque and gingival index scores are significantly (p < 0.05) higher in FA patients than CA patients at both 6 and 12 months. Alpha diversity analysis based on the Shannon Index shows no significant difference between pre-treatment saliva and plaque, but pre-treatment beta diversity analysis shows a distinction between plaque and saliva. During treatment, plaque, saliva, and tray plaque remain distinct in terms of beta diversity analysis, and saliva and plaque became more differentiated as treatment time increased. There was insufficient data to distinguish between microbial data based on plaque or gingival index scores. Each group appears to have a different genus-level bacterial community profile that changes as orthodontic treatment progresses.

ConclusionsPatients who undergo orthodontic treatment with fixed appliances accumulate more plaque and have poorer gingival health as treatment progresses over the first 12 months, but patients who wear clear aligners experience no significant difference in plaque levels or gingival health during the same interval. At baseline, patients without any orthodontic appliances have no significant difference in alpha diversity between plaque and saliva microbial communities but form distinct clusters in beta diversity analysis. Over time, beta diversity analysis shows that plaque and tray plaque microbiomes become more distinct, and salivary microbiomes appear to represent an intermediary between the two.N