Orthodontics in China has experienced two important stages. At its early stage from 1950 s to 1970 s orthodontics was a division of prosthodontic department in China. There were 3 top professors in this field, who got partly training at one time or another in USA and returned to China working in Beijing Medical College, the Fourth Military Medical University and Shanghai Second Medical College. Among them, Professor Mao of Beijing Medical College was regarded as the father of Chinese Orthodontics. Removable appliance was the main tool at that stage and Prof.Mao brought forward Mao’s Classification of Malocclusion which is still used in China. The rapid developing stage began in the 1980 s when China opened its door to the world. More and more orthodontists got further training abroad and brought back advanced techniques since then. Up to now, we have already had more than one thousand of orthodontic specialists and established its own organization——the Chinese Orthodontic Society (COS), which holds domestic orthodontic meetings and organize its members to attend international meetings. Right now, almost all advanced techniques in diagnosis and treatment are adopted in China, including 3D imaging, self-ligating bracket appliance, and implant anchorage. Chinese orthodontists have started to present or publish papers in international meetings and journals and more than tiat, started to develop new app-liances, such as Driving-Force Straight Wire Appliance, which has shown advantages in treating skeletal Class Ⅲ malocclusion.

Objective: To evaluate differences in dental arch forms between the subjects with Angle II division 1(AngleⅡ1 ) and those with normal occlusion. Methods:60 AngleⅡ1 patients and 60 normal occlusion subjects aged 13-17 years old were selected. Fourteen landmarks, corresponding to the cusp tips and incisor edges, were identified on the upper and lower dental casts of all subjects by YM-21115 three dimension measuring machine. Arch form differences between AngleⅡ1 and normal occlusion subjects were assessed by Euclidean distance matrix analysis (EDMA). Results:(1) In both sexes, the upper arch of AngleⅡ1 subjects was larger than that of normal occlusion (1.8% for females and 2.7% for males); and arch shape difference was also significantly different(P

Objective:To establish a system for quantitatively measuring alveolar bone density and to test its precision and validity. Methods: With the aid of computer technique, the system measured the average gray level intensity of regions of interest (ROIs) on standardized exposed direct digital periapical radiograph. To correct the variation resulting from exposure condition, an aluminum stepwedge was exposed simultaneously. By referring the image of aluminum stepwedge on each radiograph the equivalent aluminum thickness(EAT)and corrected gray level intensity(CGL)of the ROIs could be calculated as indicators of alveolar bone density. Nineteen specimens containing different amounts of hydroxy-phosphorite were radiographed. The precision of the system was tested by repeatedly measuring 2 of the specimens. The set of specimens was exposed under two different exposure time in order to test the system's validity to correct the gray level difference caused by different exposure time. Results: After repeated measurement of specimens, we found the Relative Standard Deviation(RSD) of EAT and CGL was between 0.83%-2.15%; At the level of 95%, if the difference of EAT between the two ROIs was larger than 0.05 mm or the difference of CGL was larger than 3, the content of hydroxy-phosphorite in them was different; The two sets of data during different exposure time were processed with Wilcoxon Signed Ranks Test, and the result showed effective correction of the variation caused by different exposure time. Conclusion:The precision and validity of the quantitative alveolar bone density measuring system are acceptable. The system can be used to compare alveolar bone density longitudinally and cross-sectionally.

Objective:To analyze the effect of Bone morphogenesis 4 and its antagonist Noggin on morphogenesis of tongue.Methods: Dissected rats to get embryonic day 13(E13) tongues;fed E13 tongues in standard medium,BMP4(0.03 mg/L,0.3 mg/L,1 mg/L),and the antgonist Noggin(1 mg/L,3 mg/L,10 mg/L) medium;cultured for 3 days;fixed samples,observed tongues with scanning electronic microscope(SEM);measured the whole tongue length,anterior 1/8,1/4 width and middle width of cultured tongues and analyzed data with SPSS 10.0.To further study the effects of BMP4 on epithelial and mesenchymal cell proliferation,Affi-gel blue gel beads were applied.Beads were soaked in PBS and BMP4(667 mg/L),and implanted in the E13 embryonic tongues;then after cultured in standard medium for 3 days,tongues were embedded in O.C.T.and cut into 12 ?m series sections.Ki67 was detected by immunohistochemical method.Results:(1)Whole length of tongues changed greatly(P

Objective: To classify the AngleⅠ malocclusion subgroups using lateral radiographic films according to their ordinary coordinates and standardized coordinates converted by general procrusts analysis (GPA), and to compare the two kinds of classifications and their valne in diagnosis of malocclusion. Methods: 946 pretreatment lateral radiographic films of patients with Angle'I malocclusion were chosen and their ordinary coordinates were acquired via soft ware. The ordinary coordinates were then converted into standardized coordinates by GPA. All of the films were classified by cluster analysis and discrimination analysis applying the upper two kinds of coordinates respectively. Results: (1) Twenty one subgroups were identified according to the ordinary coordinates of the chosen films with the total differentiate rate of 92.7% and leave-one-out differentiate rate of 68.4% (Classification A). Correspondingly, 20 subgroups were identified according to the standardized coordinates with the two differentiate rates of 87.8% and 71.9% (Classification B). (2) If the ordinary coordinates were discriminated by Classification B, the total differentiate rate and leave-one-out differentiate rate were 79.8% and 60.2 % respectively. If the standardized coordinates were discriminated by Classification A, the two differentiate rates were 79.8% and 60.2 % respectively. (3) There were some subgroups having the similar form in Classification A and their difference mainly arose from the difference of the patient age, while there were no such subgroups like that in Classification B. (4)The proportion of the largest subgroup in total subjects is 15.9% and there were 8 subgroups having the number of subjects over 40 in Classification A, whilethe corresponding proportion and number of subgroups were 74.7% and 2 in Classification B.(5)Classification A and Classification B were both suitable to classify a new subject, but Classification B was required to standalize all of the subjects onc again, which was very complex, while Classification A was more simplified. Conclusion: Classification A and Classification B are interelated. GPA could concentrate the subjects in cluster analysis, which reduces some influence of the age to the classification, but the process to classify a new subject is very complex. Thus if quick diagnosis is needed in clinics, Classification A should be recommended, but the influence of the age should be noted.

Objective: To investigate dentoalveolar compensation for vertical craniofacial pattern after orthodontic treatment. Methods:157 post-treatment cases with normal incisor relationships and various vertical craniofacial patterns were studied. Computerized post-treatment cephalometric analysis was performed to evaluate vertical craniofacial pattern and dentoalveolar parameters. Incisor torques were measured from study models. Correlation analysis was performed between skeletal and dental measurements.Results:①There was negative correlation between post-treatment upper central incisor torque and MP-SN angle(P

Objective:To observed the longitudinal changes of the facial growth in vertical dimension in the Chinese adolescents with normal occlusion from 13 to 15 years old.Methods:The subjects were from Beijing area and consisted of 9 males and 14 females aged 12.5-13.5 years with Class I skeletal and dental pattern and without previous orthodontic treatment. Serial 2-year- annual cephalometric radiographs were taken and digitalized. Descriptive statistics for the absolute and incremental changes of the skeletal cephalometric measurements were conducted.Results:Significant gender differences in the changes of facial growth in vertical dimension from 13 to 15 years old were observed. Most of the skeletal measurements in males showed greater value than those in females. The number of the measurements which showed gender difference increased with age. The annual incremental changes of TAFH, TPFH, LAFH, U6-PP in males and those of TPFH and RH in females from 13 to 14 years old were greater than those from 14 to 15 years, However, the average increment of L6-MP in males and that of UI-PP, LI-MP, U6-PP and OB in females from 13 to 14 years old were smaller than those from 14 to 15 years old. There was no significant gender difference in TAFH/TPFH from 13 to 15 years of age. Gender difference from 14 to 15 years old was found in the growth of dental-alveolar height. The main dento-alveolar height changes happened in lower incisors and lower molars in males and in the region of upper molars and upper incisor in females.Conclusion:The skeletal facial growth in vertical dimension from 13 to 14 year old falls into the accelerating period. After 14 years old, the growth velocity is slowed down. There are significant gender differences in the skeletal changes of facial growth in vertical dimension from 13 to 15 years old. From 14 to 15 years old, the gender differences are mainly found in the growth of the dento-alveolar height.

Objective:To investigate whether the changes of anterior arch dimension have an impact on the precision of Bolton analysis. Methods:A mathematic-geometric model was used to evaluate the data. Results:The ideal anterior tooth size ratio may need adjustments, depending on the dimensions in radii of the upper and lower anterior dental arches. The ideal ratio is lower for dental arches with a high anterior curvature. There is a deficiency in the upper arch, a flatter anterior segment may compensate for some of the discrepancy and vice versa. Conclusion:An ideal Bolton value may not guarantee an ideal occlusion. Anterior tooth size ratio is not precise in predicting the anterior inter relationship post-treatment.

Objective:Cluster and discriminant analysis of the morphological characters of Angle's Class Ⅱ malocclusion was performed using Procrusts standardization.The classification of craniofacial morphology with the help of morphometry and multivariate statistics was also discussed.Methods: A total of 894 class Ⅱ patients were collected from the orthodontic department,Peking University School and Hospital of Stomatology during 1997-2000.Using Procrusts standardization and cluster analysis,the samples were divided into different groups,discrimination equations were then established.Results: The samples were divided into 11 subdivisions by Procrusts superimposition and cluster analysis.Three discrimination equations were established.The accuracy rate of cross-validated grouped cases was 80.17%.Conclusion: Procrusts standardization had certain advantages in morphological classification;cluster analysis could be used in classification of Angle class Ⅱ malocclusion;For different types,the differentiate rate was not the same;the discrimination equations was the foundation for future research.

Objective:To design and assemble an orthodontic friction prototype testing apparatus and evaluate its performance.Methods: Simulating progressive tooth tipping movement,results of the opera-ting friction trials are reported at different archwire-bracket angulation.Results: An orthodontic friction testing apparatus was designed and developed,by which the complexity of tooth movements observed with in vivo sliding mechanics was simulated and a series of in vitro friction experiments were conducted.This friction testing apparatus enables previously unattainable testing of the orthodontic archwire-bracket-ligation interface.In the passive configuration or the active configuration with second-order angulation,the friction in sliding mechanics was measured.Conclusion: The apparatus presented has the ability to allow for a high standard of basic hypothesis testing,product development and performance evaluation with relative ease.Furthermore,it will be the prototype of a computer-controlled multifunctional friction testing device in the near future.