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Mastication-Induced Brain Blood Flow Changes Before and After Surgical-Orthodontic Treatment in Skeletal Class III
Hiroyuki Kanzaki1,2, Chihiro Nakata2,3, Masao Kumazawa2
1Department of Orthodontics, Tohoku University Hospital, Sendai, Japan.
Background:
Mandibular prognathism attenuates chewing-induced brain blood flow (BBF) in the bilateral inferior frontal gyrus, correlating with compromised masticatory function and cognitive performance. Surgical orthodontic treatment restores skeletal and occlusal relationships and reorganises jaw sensorimotor function; however, its effects on masticatory cortical haemodynamics remain unexplored.
Objectives:
This pilot study aimed to characterise longitudinal and cross-sectional BBF changes following surgical orthodontic treatment in skeletal Class III patients, and to explore whether pre-treatment BBF level may be associated with the direction of treatment-related change.
Methods:
BBF in the bilateral inferior frontal gyrus was measured using fNIRS at the initial examination (T1) and treatment completion (T3). Cross-sectional comparison was performed between independent T1 (n = 162) and T3 (n = 55) groups; longitudinal analysis was conducted in 22 paired patients. The longitudinal cohort was stratified at the median T1 BBF into low- and high-BBF subgroups (n = 11 each), with between-group differences assessed using the Mann-Whitney U test and bootstrap resampling (1 000 iterations).
Results:
Neither cross-sectional (p = 0.804) nor longitudinal comparison (p = 0.614) revealed a significant group-level change. Baseline-stratified analysis revealed opposing directional responses: The Low-BBF group showed a tendency toward increase (median change: +3.4%; p = 0.102), while the High-BBF group showed a tendency toward decrease (median change: -16.4%; p = 0.064). The between-group difference in BBF change scores was suggestive (uncorrected p = 0.015; bootstrap 95% CI: +0.7 to +124.6%, excluding zero), consistent with the interpretation that pre-treatment BBF level may be associated with the direction of masticatory cortical haemodynamic change following surgical orthodontic treatment.
Conclusion:
These exploratory, hypothesis-generating findings provide the first effect size estimates for pre-treatment BBF as a potential directional predictor of cortical haemodynamic response to surgical orthodontic treatment, and justify a future pre-registered, adequately powered investigation with formal a priori sample size calculation.
