The Comparison Study Of The Mandibular Track And The Electromyography Of Masticatory Muscles Between Different Age Groups With Normal Occlusion

[Objective]]To explore the differentia and regularity of mandibular track and the electromyography masticatory muscles between different age groups with normal occlusion by recording and analyzing the mandibular track and the electromyography of masticatory muscles via SAM Axioquick recorder, providing a reference for clinic prothodontics.[Materials and methods] Groups aged15-17,18-25and26-30with normal occlusion were employed in the study.20cases were selected for each group, composed of10males and10females. Using the SAM axioquick recorder to record the track and range of different mandibular movement, including notch movement, border movement and masticatory movement, evaluate the moving track features of the condylar kinematic center in the frontal, sagittal and horizontal planes, measure the protrusion condylar slope, detect the lateral condylar slope of the non-working side in the sagittal and horizontal planes, and the surficial myoelectricity of bilateral masseter and temporalis was recorded simultaneously. All the data was analyzed with the software SPSS17.0, using one-way ANOVA and t-test method.[Results]1. It shows a good repeatability of the movement path of the mandibular incisor point in mastication of the three groups in the study. The repeatability of different mandibular movements arranged from high to low as follows:notch movement, protrusion movement, lateral movement and the maximum opening movement.2. The maximum opening amplitude represents a notable difference in the frontal, sagittal and horizontal planes (p<0.05)3. The incisal protrusion movement shows a significant difference between the three groups (p<0.05)4. The lateral movement amplitude shows a significant difference in three dimensions between different groups (p<0.05), and there is a bilateral symmetry and no significant differentia compared with the opposite in the same group (p>0.05)5. The masticatory cycles of the three groups are smooth, the opening and closing paths show a good stability, and no significant difference is observed between the three groups in the fronal, sagittal and horizontal planes (p>0.05)6. The track of the lateral movement in the healthy subjects is smooth and bilateral symmetrical. The inclination of the protrusive condylar path, the inclination of the lateral condylar path of the non-working side in the sagittal plane and the Bennett angle, have no significant difference between the three groups (p>0.05)7. The surficial electromyography of the masticatory muscles shows that the myoelectric amplitude of the masseter and temporalis waves smoothly, and the masseteric amplitude is a little higher than the temporalis’. In the symmetric movement such as the maximum opening and the protrusion, the crest value of the myoelectric amplitude between bilateral homonymous masticatory muscles shows no significant difference (p>0.05). In the lateral movement, the myoelectric crest value of the working temporalis is higher than that of the nonworking side, and the myoelectric apex of the working masseter is higher than that of the nonworking side. In the healthy subject, the myoelectricity is activated in both the mandibular border moment and the masticatory movement, and the myoelectric activity of the latter is more obviously than that of the former. In the masticatory movement, the myoelectric apex of the masseter is higher than that of the temporalis.8. It is showed that in the study, the contraction power as well as the myoelectric crest value of the masticatory muscle of the three groups increased with age. Within the same group, in the symmetric movements, including the maximum opening and the protrusion, the myoelectric crest value of the bilateral homonymous masticatory muscles shows no significant difference (p>0.05); in the lateral movement and masticatory movement, the myoelectric crest value of the working homonymous masticatory shows no significant difference (p>0.05)[Conclusion]1. There is a good regularity of normal mandibular incisor point trajectory and chewing movement of the groups tested in the study. The range of left lateral movement shows no significant difference compared with that of the right lateral movement.2. Differtnt groups have different characteristics of mandibular trajectory and masticatory muscle, and there are notable differences between different age groups.3. The ranges of the value determined in the study could provide a reference for the early diagnosis of TMD, stomatognathic system disfunction and so on.