Relationship between masseter muscle electromyographic activities and the position of the mandible / 南方医科大学学报

<p><b>OBJECTIVE</b>To investigate the changes in electromyographic activities of the temporal and masseter muscles at different positions of the mandible.</p><p><b>METHODS</b>Twenty orthodontic patients with Angle Class II malocclusion and mandibular retrusion (ANB<6°) aged 10-14 years were enrolled in this study. All the patients were treated with Forsus fixed functional appliance combined with MBT straight-wire appliance. The electromyographic activities of the temporal (T) and masseter (M) muscles before, during and after functional treatment were evaluated by assessing the average integrated electromyogram (EMG) and T/M ratio at clenching status in different mandibular positions.</p><p><b>RESULTS</b>After functional forward positioning of the mandible, the electromyographic activities of the temporal and masseter muscles decreased and T/M ratio increased significance at the clenching status (P<0.05).</p><p><b>CONCLUSION</b>The appliance insertion and activation is associated with a decreased EMG activity of the temporal and masseter muscles, and the T/M ratio is correlated to the position of the mandible.</p>

Application of spiral CT three-dimensional reconstruction in treatment planning of impacted teeth / 南方医科大学学报

<p><b>OBJECTIVE</b>To assess the value of three-dimensional (3D) reconstruction in treatment planning of impacted teeth.</p><p><b>METHODS</b>Thirty-two orthodontic patients with impacted teeth aged from 13 to 17 years were enrolled, including 15 with impacted maxillary canines, 8 with impacted premolars and 6 with second molar impaction and retention. All the impacted teeth were examined by spiral CT scan and 3D reconstruction to determine the 3D position of the tooth in relation to both the crown and root, and the proximity to the roots of other teeth. The data were used for treatment planning and determination of the suitable direction of the orthodontic forces, approaches of surgical exposure, and the position of the attachment to be bonded.</p><p><b>RESULTS</b>Normal occlusion was achieved for 15 patients with transposition maxillary canines and 5 with lower position premolar. Three malformed premolars were extracted after traction. For 9 patients with second molar impaction and retention, normal occlusion was achieved after extraction of the third molar or moving the first molar mesial.</p><p><b>CONCLUSION</b>Spiral CT scan and 3D reconstruction can accurately determine the 3D position of the impacted tooth and provide assistance in the treatment planning to achieve a higher success rate of orthodontic correction.</p>