Application of pulp tissue genetic profile in orthodontic tooth movement: a needle in a haystack?

A Commentary On: Zhao Z, Attanasio C, Zong C, Pedano M S, Cadenas de Llano-Pérula M. How does orthodontic tooth movement influence the dental pulp? RNA-sequencing on human premolars. Int Endod J 2024; 57: 1783-1801.

Design-cross-sectional Design: Sample selection - The study sample consisted of healthy individuals requiring extraction of maxillary or mandibular premolars for fixed appliance orthodontic treatment. Exclusion criteria included systemic diseases, a history of smoking, antibiotic or analgesic use within the past three months, periodontal probing depths greater than 3 mm, alveolar bone resorption, and premolars with prior endodontic treatment. Participants were randomly divided into 3 groups: control, 7-day, and 28-day groups. Extractions were performed prior to orthodontic treatment, and 7 days and 28 days after application of orthodontic forces (OF) in the control, 7-day and 28-day group respectively. The applied orthodontic forces were in the range of 50-150 g. RNA extraction from pulp tissues was performed using the RNeasy mini kit. After total RNA extraction, a library was prepared, and RNA sequencing was conducted to examine and compare the genetic data among the groups within each jaw.

Data Analysis: Differentially expressed genes (DEGs) were identified in the 7-day and 28-day groups, followed by functional enrichment analysis to understand their biological significance. Furthermore, protein-protein interaction network analysis was conducted to investigate the complex network of protein interactions and locate key genes involved in orthodontic tooth movement.

Results: Immune response, hypoxia, DNA damage, and epigenetic regulation were the pulpal reactions reflected after 7 days of OF. Whereas, at 28 days, processes such as cell adhesion, migration, organization, and tissue repair became prominent. Pulp tissues in the maxilla and mandible responded differently to orthodontic force. The maxilla showed minimal changes, primarily involving immune response at 7 days and tissue repair at 28 days. In contrast, the mandible exhibited significant DNA damage and epigenetic regulation at 7 days, with a return to its baseline condition by 28 days.

Conclusions: Dental pulp demonstrated different reactions at 7 and 28 days, with maxillary and mandibular pulp tissues presenting distinct responses. The study provided knowledge about gene regulatory mechanisms modulating pulp tissue response to OF.