Vibrational Analysis of the Mechanism of Traumatic Injuries to the Mandible

Objectives: Clinical observation shows that the position of mandible fracture is strongly related to the geometric structure of mandible. However, the dynamic mechanism of mandibular trauma is still unknown. To access the dynamic mechanism of mandibular trauma, modal analysis was carried out to test the resonance frequencies (RF) of human mandible. Methods: A total number of ten human cadavers were tested in this study to analyze the effects of muscles, boundary condition and the dynamic response of mandible. The mandible was triggered to vibrate with an impulse hammer, and the vibrational response was detected by an accelerator. In addition, a geometrically complex finite element mandible model was established to access the effects mentioned above. The modal was first validated against the results obtained from above experiments. Resonance frequencies were then calculated with or without soft tissue and boundary constrain. Results: Both results obtained from model testing experiments and FE modeling show that the first vibration mode of human mandible is a bending vibration with two nodes located at the middle area of mandibular body symmetry at sagital plane. The corresponding frequency of such vibration mode was detected as 598 Hz which was closed to our FE modeling. These results indicated that our FE model was a validated model when used for dynamic simulation. After muscle force was added, the RF value of the model was changed. It decreased when the soft tissue and boundary constrain was removed. Conclusions: The results obtained from this study demonstrated that geometry, muscles and boundary condition play important roles in the mechanism of mandible injuries when the mandible is subjected to a traumatic impact force. These results not only provide an insight into the basic dynamic properties of human mandible but will be also an important reference for future advanced study on the mandibular trauma.