UCLA

There are approximately 700 bacterial species present in the oral cavity that exist in a complex, delicately balanced ecosystem. Orthodontic treatment with fixed appliances has been shown to disrupt this balance leading to an increased risk of white spot lesions, caries and periodontal disease. With the advent of clear aligners, orthodontic patients are now able to remove their appliances and perform oral hygiene more efficiently. Previous studies have examined the effects of fixed and removable orthodontic appliances on periodontal health with varying results.

We examined patients at the UCLA Orthodontics Clinic with fixed appliances (n=12) and clear aligners (n=12) through the first six months of treatment. Periodontal status was evaluated using the Turesky et al. Modified Quigley-Hein Plaque Index (PI) and the L�e and Silness Gingival Index (GI). Plaque was collected from anterior teeth, posterior teeth and from the inner surface of the clear aligner trays. DNA from the plaque samples was extracted and subjected to next generation sequencing of the 16S rRNA gene.

There was a significant increase in PI and GI in the fixed appliance group over the first six months of treatment. In the clear aligner group, there was no significant increase in PI, but there was a significant, yet transient increase in GI that eventually returned to baseline levels. Distinct, patient-specific shifts in the microbial communities were observed in both groups upon starting treatment. The microbial community inside the clear aligners is unique and less diverse than those found on teeth, but the overall composition of tooth-associated biofilm was similar between both groups.

Patients treated with fixed appliances experienced significantly more plaque accumulation on the surfaces of the teeth compared to patients treated with clear aligners. This increase in plaque accumulation in the fixed appliance group was associated with a significant increase in gingival inflammation, which was localized to the posterior teeth. The inner surfaces of the clear aligner trays harbor a unique microbial community that is less diverse than those found in tooth-associated biofilms.