Cranio-maxillofacial soft-tissue surface temperature and brain activity during tapping

Objectives: Cranio-maxillofacial soft tissue and brain activities at the time of jaw movement that are dependent on the amount of construction bite have not been clarified. In the present study, twin block appliances were attached to experimental models in human subjects to achieve mandibular advancement, and cranio-maxillofacial soft-tissue surface temperature and brain activity were determined while performing a tapping activity to obtain a basic understanding of the appropriate amount of construction bite. Methods: The subjects were 10 healthy adults. To set the amount of construction bite of the twin block appliance, the vertical dimension between the anterior teeth of the upper and lower jaws was set at 2 mm, with a screw incorporated into the block of the appliance. The lower jaw was advanced stepwise to 3 protruding positions of 0 mm, 2 mm, and 4 mm, during which tapping at 2 Hz was performed. The experiment was conducted in a temperature–controlled room. The cranio-maxillofacial soft-tissue surface temperature was measured using a Thermo Tracer (NEC San-ei, TH3103) and brain activity was recorded with optical topographic equipment (Hitachi Medico ETG-4000). For statistical analysis, multiple comparison results were examined using a Wilcoxon t-test with Bonferroni correction after Friedman's test.　Results: 1. No significant difference for temperature and activity was observed between before attachment of the appliance and at the 0-mm position. 2. The surface temperature of the soft tissue became elevated at the 2-mm position. 3. Blood flow in the primary sensorimotor field became reduced at the 2-mm and 4-mm positions. Conclusion: The cranio-maxillofacial soft-tissue surface temperature was elevated extensively during performance of a tapping movement with mandibular advancement immediately after attachment of the twin block appliance. Our results suggest that such advancement and tapping exert stress on brain activity in the primary sensorimotor field.