Occlusal Force In Unilateral Condylar Fractures During Perioperative Period: A Comparative Study

Objective: The aim of this study was to analyze the perioperative changes of bite forces in unilateral condylar fractures by electromyography (EMG); The waveform and amplitude on EMG of masticatory muscle, an objective indicator, indirectly reflected bite force, and it provided references for therapeutic schedules and effect assessment. Methods: 1. Examine the reliability of EMG and determine positioning standard of muscle landmarks. 2. EMG was used to analyze sEMG of bilateral masseter muscles in ICP Gritted bits . 3. Repeat measurements and take its average. 4. Measure the bilateral masseter muscle strength of the normal group and preoperative and postoperative patient group. 5. Analysis EMG waveform,EMG amplitude and masseter asymmetric index of the bilateral masseter in the normal group ;Comparative study of the normal group and patient group ; The patient group on the injured side was compared with the patient group on the healthy side; Comparative study of the bilateral masseter EMG waveform,EMG amplitude and masseter asymmetric index of the preoperative and postoperative patient group.Results: The normal group showed a straight line without any electrical activity in resting relaxation state; In intercuspal position, light biting EMG of masseter muscle saw duplex, three-phase and multiphase potential; Maximum biting EMG waveform saw mixed phase, the phase 7.6~9.3ms, multiphase potential 10%. The injured side before operation for the patient group show pure fasciculation wave and complex fasciculation wave in resting relaxation state; the electrical action potentials and amplitude measured on the injured side were obviously worse than those on the healthy side for the patient group in the biggest gritted bits, multiphase potential 30%. The injured side in one week after operation for the patient group showed fibrillation potentials and positive sharp waves in resting relaxation state; the electrical action potentials and amplitude on the injured side in one week after operation were slightly worse than those before operation in the biggest gritted bits. The electrical action potentials and amplitude on the injured side in seven weeks after surgery were obviously improved. From EMG amplitude, the bilateral masseter EMG amplitude measured in normal control group was a no significant difference by paired t-test; Before surgery, masseter EMG amplitude measured on the injured side was remarkably lower than that on the healthy side by paired t-test. After surgery, masseter EMG amplitude of both sides increased as compared with those measured before surgery. It was a significant difference by paired t-test. The asymmetric index of masseter in normal control group, which was lower than that in patient group before surgery, tended to decline after titanium board internal fixation, Significant decline could be seen seven weeks after surgery. Conclusion: Electromyography (EMG) was used to analyze the perioperative changes of bite forces in unilateral condylar fractures; The waveform and amplitude on EMG was an objective indicator to reflect bite force and occlusal function indirectly; The objective indicator provided some references for therapeutic schedules and effect assessment to restore better occlusal function.