Objectives To evaluate changes in masticatory performance (MP) during the retention period after extraction and non-extraction treatment and compare it with MP in the subjects with normal occlusion. Materials and Methods Adult patients who had completed orthodontic fixed appliance treatment comprised the extraction and non-extraction treatment groups, and those with normal occlusion comprised the control group. Their mixing ability (MA), maximum bite force (MBF), and occlusal contact area (OCA) were recorded immediately after the fixed appliance was removed and at 1 month, 6 months, and 1 year post-treatment. The MA was measured by the two-color chewing gum MA test using ViewGum software, and the MBF and OCA were measured using Dental Prescale II system. Results MA immediately after orthodontic treatment was lower than that in the normal occlusion group but showed a time-dependent gradual increase during a 1-year retention period (P < 0.01). The MA at 1 month post-treatment was not significantly different between the three groups (P > 0.05). The MA showed a significant correlation with the MBF and OCA (P < 0.01). Conclusions The MP immediately after orthodontic treatment was lower than that in the normal occlusion group but increased gradually, with levels comparable to those of the normal occlusion group at 1 month post-treatment. Further, extraction did not affect the MP after orthodontic treatment. Clinical Relevance: No other study has evaluated the changes in MP during the retention period after orthodontic treatment. The findings show that compared with MBF and OCA, the patients’ MP improved faster to levels found in normal occlusion.
Objective The aim of this retrospective study was to compare changes in hard tissue and soft tissue after the four first premolars were extracted with anterior teeth retraction according to the presence or absence of lip incompetence. Methods Patients who underwent the four first premolars were extracted with anterior teeth retraction were divided into competent (n = 20) and incompetent lip (n = 20) groups. Cephalometric measurements for hard tissue and soft tissue changes were performed pre-treatment and post-treatment. Results In the competent group, the upper and lower lips retreated by 2.88 mm and 4.28 mm, respectively, and in the incompetent group by 4.13 mm and 5.57 mm, respectively; the differences between the two groups were significant ( p < 0.05). A strong positive correlation between retraction of the upper lip and upper incisors was observed in both groups ( p < 0.05), whereas a correlation between retraction of the lower lip and lower incisors was only found in the incompetent group. A simple linear regression analysis showed that the pattern of lip retraction following the retraction of the anterior teeth was more predictable in the incompetent group than in the competent group. Conclusions These findings suggest that the initial evaluation of lip incompetence in patients with skeletal Class II is essential for the accurate prediction of the soft tissue changes following retraction of the anterior teeth in premolar extraction treatment. Therefore, sufficient explanation should be provided during patient consultations.
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