[Condylar position and condylar symmetry in patients with temporomandibular disorders].

PURPOSE: To investigate condylar position and condylar symmetry in patients with temporomandibular disorders (TMD) as well as malocclusion. METHODS: Fifteen patients with TMD and malocclusion were selected for the experiment, 15 asymptomatic patients served as controls. The bilateral temporomandibular joints of all subjects were evaluated by computed tomography (CT) imaging. Both the joint spaces and the condylar symmetry were determined, based on the axial CT images properly chose. All statistical analysis were performed using SPSS17.0 software package. RESULTS: The condyle of the patients in the experimental group were seated more posteriorly, while slight anterior condylar position were found in the control group. In the experimental group, the horizontal angle of the condyle in the symptomatic side was larger than that in the asymptomatic side (P<0.05), while the vertical angle was just opposite (P<0.05). No statistically significant asymmetries were found in the mediolateral diameter,the anteroposterior diameter, the angle of condylar axis, the distance between condylar center to midsagittal plane and anteroposterior difference of condyle center. CONCLUSION: Obvious posterior condylar position and vertical asymmetry exist in patients with temporomandibular disorders.

[3-D finite element analysis on center of resistance of upper anterior teeth].

PURPOSE: To investigate the location of center of resistance(CRe) of six upper anterior teeth. METHODS: A three-dimensional finite element model of premaxillary bone and anterior teeth was established in ANSYS 8.1 software. Anterior teeth were fixed with stainless archwire of 2 mm × 2 mm. A horizontal retraction force of 150 g was applied bilaterally to the segment through hooks of 2 to 14 mm. After loading, solution was done and displacement and maximum principle stress were calculated. RESULTS: Displacement and stress distribution of anterior teeth varied according to the increase of height of horizontal retraction force. Labiolingual displacement of incisors varied from crown lingual tipping to lingual translation and lingual controlling root movement, while canine mainly showed lingual crown tipping. The displacements of teeth increased with the length of hook but their moving tendency remained unchanged. Stress distribution in PDL was in accordance with direction and magnitude of teeth displacement. In all cases, lingual displacement and stress in PDL were most homogeneous when hook was 10 mm long. CONCLUSION: The results of this study suggest that perpendicular location of center of resistance of six upper anterior teeth is about 14 mm gingivally to incisal edge of central incisor.

[Investigation of the possible factors related to root resorption during orthodontic treatment in adolescents].

PURPOSE: The purpose of this study was to investigate the factors relating to root resorption after orthodontic treatment in teenage patients. METHODS: seventy eight teenage patients treated with fixed orthodontic appliances were selected for this study. Root resorption scores of the upper incisors were recorded qualitatively according to their apical root morphology in the panoramic radiographs before and after treatment. All subjects were grouped according to age, gender, tooth location, occlusion stage, extraction or nonextraction approach and treatment duration. Nonparametric tests was used for statistical analysis with SPSS12.0 software package. RESULTS: All patients presented root resorption of different degrees. The results showed that there was significant difference before and after occlusion establishment of the second molar (P<0.01), but no difference between different age groups; Root resorption in extraction group was more severe than in non-extraction group (P<0.01); Root resorption in extraction group was more severe in patients with longer treatment duration (P<0.05). There was no significant difference between different genders and different teeth locations. CONCLUSION: The results suggest that orthodontic treatment before occlusion establishment of the second molar, nonextraction approach and shorter treatment duration lead to less root resorption.

[The study on characteristics of soft tissue profile for different malocclusion].

OBJECTIVE: To study the coordination of facial soft tissue in Angle's Class I, II1, III malocclusion, providing reference for the clinical practice. METHODS: 60 lateral cephalometric radiographs of three classes of Angle's malocclusion were included. 13 measurements were analyzed by SPSS 10.0. RESULTS: Protrusion of the upper and lower lips increased in Angle's II1 comparing with Angle's I and protrusion of the upper lip was larger than the lower lip, no difference was found in the facial convexity. Increase of upper lip inclination and underdevelopment of maxillary in Angle's III comparing with Angle's I. No significant different was found in the form of lower lip, soft tissue facial angle and Z angle. Comparing Angle's II1 with Angle's III, every measurements were significantly different except upper lip inclination, nasolabial angle, representing the formation mechanism of malocclusion. CONCLUSION: Some differences were found in form and position of lip in three classes of Angle's malocclusion. However, the deformity was not obvious in Angle's II1 and Angle's III because of compensation mechanism. Nasolabial angle only reflected change of upper lip, but could not reflect characters of facial profile.