Neuromuscular pre-activation attenuates mandibular impact injuries: Dynamic finite element analysis of stress modulation in craniomaxillofacial structures.

The craniomaxillofacial region is highly susceptible to high-intensity impact injuries during contact sports, however, existing passive protective devices have limited energy absorption capacity. This study aimed to quantitatively assess the protective efficacy of neuromuscular pre-activation against mandibular impact injuries. A high-precision craniomaxillofacial biomechanical model was constructed using CT and MRI data from a healthy male subject (glabello-occipital length: 176 mm; vertex-menton height: 212 mm; bizygomatic breadth: 135 mm). The model included the cranium, maxilla, mandible, masticatory muscles (masseter, temporalis, medial pterygoid, and lateral pterygoid), disc, and capsule. Under varying pre-activation durations (0-50 ms, corresponding to 0-92 % of the maximum activation level), the mandible underwent a 500 N anterior impact (10-ms semi-sinusoidal waveform). Finite element analysis was used to simulate the dynamic biomechanical responses of the craniomaxillofacial system. Prolonged pre-activation significantly reduced stress concentrations in critical structures. Without pre-activation, peak von Mises stresses in the condylar neck and coronoid process reached 141 MPa and 193 MPa, respectively. With 50 ms of pre-activation, these stresses decreased by 73 % (condylar neck) and 90.7 % (coronoid process). Contact stress in the disc decreased by 86.2 %, thereby mitigating the risk of collagen fiber tearing in the intermediate zone. The medial pterygoid muscle exhibited an 83.3 % decrease in maximum principal stress, reducing the likelihood of muscle fiber rupture. Neuromuscular pre-activation modulates mandibular motor stiffness, thereby effectively attenuating impact-induced damage to bone, muscle, and disc. These findings lay a biomechanical foundation for the development of mandibular protective devices (aimed at restricting mandibular opening displacement) to reduce acute and chronic craniofacial injuries in athletes.