Invisible appliance promotes bone reconstruction via modulating the periodontal immune microenvironment

Objectives: Recently, invisible appliances have become popular due to their aesthetics and comfort, but their impact on periodontal health in periodontitis patients has not been fully elucidated. The purpose of this study was to investigate the effectiveness of fixed and invisible appliance treatment for periodontitis in experimental rats while monitoring the dynamics of Th17/Treg cells and osteoclast-related cytokines during treatment.

Methods: SD rats were randomly divided into six groups: control, periodontitis model, scaling-0 (basic treatment), no appliance, fixed appliance, and invisible appliance. After successful establishment of ligature-induced periodontitis, rats in the treatment groups were first subjected to supra/subgingival scaling and daily brushing for 2 weeks. Next, except rats in the scaling-0 group, the periodontitis rats were treated with uncorrected, fixed, or invisible appliance, respectively. The CEJ-AC was examined using micro-CT. Osteoclast activation was detected with TRAP staining. The proportion of Th17 and Treg cells was measured by flow cytometry. Subsequently, potential mechanisms were explored by detection of RORγt, Foxp3, RANKL, OPG, and pathogenic bacteria (Pg, Aa, and Tf). Finally, the association between Th17/Treg cells and osteoclast-related indicators as well as pathogenic bacteria was evaluated by correlation analysis.

Results: Among the three treatments, invisible appliance treatment provided optimal results in controlling periodontal Infection while promoting periodontal tissue repair. Specifically, in the early phase of treatment (3-7 days), orthodontic force exerted by the appliance stimulates osteoclast and Th17 cell activation by increasing RANKL and RORγt expression, thereby inducing osteoclast generation and accelerating the amount of tooth movement. In the later stages of treatment (7-21 days), Foxp3 and OPG levels gradually increased to induce the dominant role of Treg cells, controlling osteoclast generation and bone resorption. Meanwhile, the invisible appliance can maintain a low number of pathogenic bacteria during treatment. Finally, Th17 cells showed significant positive correlation with RANKL, Pg, osteoclast percentage, and CEJ-AC; Treg cells were positively correlated with RANKL and OPG; Th17/Treg ratio displayed positive correlation with RANKL/OPG or osteoclast percentage.

Conclusions: Invisible appliance has obvious advantages in periodontitis treatment, which can effectively improve periodontal condition and reduce inflammatory response.

Appliance; Osteoclasts; Periodontitis; Th17 cells; Treg cells.