Effect of Orthodontic Force on Gingival Blood Flow Measured by Laser Speckle Contrast Imaging: A Randomised Controlled Trial.

Objectives: This study aimed to measure gingival blood flow under different orthodontic forces using laser speckle contrast imaging (LSCI).

Methods: Forty eligible individuals were recruited and randomly assigned into 2 groups: 50 g group and 150 g group. According to the groups, forces of 50 g or 150 g were applied from the maxillary canines to the first molars on the left or right side of each participant. Four regions of interest (ROIs) were selected on the gingiva of the maxillary canine: ROI 1 and ROI 2 were located on the marginal and attached gingiva, respectively, while ROI 3 and ROI 4 were positioned on the mesial and distal interdental papillae. All ROIs was measured using LSCI at different time intervals (baseline, 30 minutes, 1, 3, 7, and 14 days).

Results: In the resting state without force loading, statistically significant differences in blood flow were observed among the marginal gingiva, attached gingiva and interdental papilla. The marginal gingiva exhibited lower blood flow compared to other regions. Evaluation of blood flow between the groups revealed significant differences at ROI 1 at 1 day and 3 days, and at ROI 4 at 1 day and 3 days. Intra-group comparisons showed significant differences in blood flow within each group for each region at each time point (P < .05). After applying orthodontic forces, blood flow reached its nadir within 30 minutes to 1 day. The 150 g group exhibited a more significant decrease compared to the 50 g group. Blood flow peaked at 3 days in the 50 g group and at 7 days in the 150 g group. Both groups finally returned to baseline at day 14.

Conclusions: Laser speckle contrast imaging is a reliable tool for monitoring gingival blood flow in orthodontic treatment. Gingival blood flow decreased after force application, reaching peak values in 3 to 7 days and eventually returning to baseline within 14 days. Although heavier forces induced more severe ischaemia, blood flow returned to baseline within 2 weeks. Given the lack of comparison with other validated methods, emphasis of this study placed on force effects, regional differences and the non-invasive advantages of LSCI.

Clinical significance: In orthodontic treatment, LSCI can ensure the safety of orthodontic diagnosis and therapy by monitoring changes in gingival blood flow. Furthermore, compared to previous technologies, LSCI offers numerous advantages, including rapid assessment and low technical sensitivity. The findings of this study provide important guidance for assessing periodontal tissue health and designing optimal, personalised orthodontic force levels during orthodontic treatment.

Trial registration: The trial was registered in Chinese Clinical Trial Registry (ChiCTR2400082438) on 29 March 2024.