Biological alterations associated with the orthodontic treatment with conventional appliances and aligners: A systematic review of clinical and preclinical evidence

Background&objectives: Mechanical forces applied during an orthodontic tooth movement (OTM) propel several biochemical and molecular responses in the periodontal ligament and alveolar bone. Here, we compile the existing clinical and preclinical evidence on these biological changes, aiming to provide a comprehensive discussion on the influence of the mechanical parameters of the OTM in the biological profile of the periodontium. Material and methods: This systematic integrative review was conducted according to PICOS strategy and PRISMA guidelines. A bibliographic search was performed in three electronic databases (PubMed, Scopus, and Web of Science) to find research articles published until 2023 and written in English. This search resulted in a total of 2279 publications, which were independently assessed by two evaluators using appropriate tools. Results: Forty-six studies were selected for this review. These revealed that compression, and stretching of the periodontal ligament fibers and cells are observed in the initial phase of the OTM. Specifically, on the tension side, high levels of IL-1β, OPG, and TIMPs are identified. On the compression side, an increase of RANKL, RANK, and MMPs levels predominate. Conclusion: This paper describes the release profile of common biomarkers according to the orthodontic protocol, suggesting the most appropriate parameters to keep the teeth and their supporting structures healthy. Overall, this manuscript provides a better understanding of the OTM-associated biological phenomena, also highlighting the importance of early evaluation of oral health, and thus it contributes as a fundamental basis for the development of more effective and safe orthodontic treatments with conventional appliances and aligners.