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Objective: To study the bracket placement and arch wire bending based on ethnic differences and individual differences of normal occlusion., Methods: The prominence, tip, torque, upper first molar offset of crown and arch form between Chinese and Caucasian normal occlusion were compared., Results: The results showed the ethnic differences of prominence, tip, torque, upper first molar offset of crown and arch form between Chinese and Caucasian normal occlusion. The placement of bracket was influenced by the crown morphology., Conclusion: The adjustments of the bracket placement and arch wire bending with Edgewise and pre-adjusted appliance are necessary to adapt to ethnic difference and individual difference.

Genetic structure and character of Chaidamu goats were studied through simple random sampling. Genetic structure was analysed from five aspects, and phylogeny status was also investigated. The results indicated that: (1) the average phenotypic heterogeneity degree of coat color and morphological character were 0.3419 and 0.5207, respectively; (2) polymorphous blood albumen existed in 6 loci and the average loci heterozygosity was 0.2584; and (3) polymorphism existed in marked genes by DND-RAPD with diversity of 0.4085 approximately 0.5318. Phylogeny status was investigated through clustering by Ward's method on Chaidamu Goats and other domestic goats. All these indicated that Chaidamu Goats was a domestic goat with less intensively selected breed.

Objective: To study the best parameter of impulse Nd:YAG Laser-aided debracket., Methods: To measure the bonding strength of ceramic bracket and pulp cavity temperature after different laser energy. First group was not irradiated by laser, second group was irradiated by laser of power 5 W and irradiating duration 2 s, third group was power 3 W and duration 3 s, and fourth group was power 2 W and duration 5 s., Results: There were significant differences of bonding strength among the four groups. The bonding strength of ceramic bracket was significantly reduced by laser irradiating. There were significant differences of the pulp cavity temperature increasing among different laser power irradiating groups. The lowest temperature increasing (3.65 degrees C) group was the group of laser power 3 W and irradiating duration 3 s., Conclusion: The bonding strength of ceramic brackets was statistically reduced after laser irradiation and the best parameter of impulse Nd:YAG Laser-aided debracket is laser power 3 W and irradiating duration 3 s.

Objective: To study the influence of loops on the torsion stiffness of rectangular wire., Methods: The torsion moments and angles of 0.018 inch x 0.025 inch rectangular orthodontic arch wires in single 0.022 inch bracket of the first maxillary incisor were measured with a torsion measurement apparatus, and the measured values were analyzed by two-way ANOVA. The wires included straight stainless steel rectangular wires, and 3.5 mm, 7 mm, 10.5 mm, 14 mm high vertical loop wires, and 3 mm, 6 mm, 9 mm, 12 mm long horizontal loop wires., Results: 1. The torsion stiffnesses of straight wire and vertical and horizontal loop wires were 4.909, 4.544, 4.137, 3.851, 3.454, 3.448, 3.024, 2.686, 2.378 N.mm/degree respectively. 2. The arch wires will be twisted 19.143 degrees, 19.377 degrees, 19.851 degrees, 20.949 degrees, 21.632 degrees, 21.812 degrees, 22.418 degrees, 23.254 degrees, 24.316 degrees respectively to obtain 20 N.mm force., Conclusion: The design of loop can reduce the torsion stiffness of rectangular wire. Compared with the length of loop, the shape of loop has more important effect on the reduction of torsion stiffness. The horizontal loop design as a factor for the control of the tongue is more effective than the vertical loop design.

Objective: To find the characteristic of the stress distribution in the periodontal tissue during maxillary canine distal translation., Methods: The model was implemented numerically by means of the 3-dimensional finite element method (FEM) and was used to simulate orthodontic tooth translation movements. The finite element model was loaded with defined force systems. And the stresses at 0, 7, 14, and 21 days of loaded distal force and moment in maxillary canine were calculated., Results: During the whole distal translation of canine, 1. the stress in alveolar bone was higher than that in peridontal ligament; 2. the stresses in the cervical region were higher than those in the apical region of the alveolar bone and periodontal tissues; 3. the stresses in the cervical, medium and apical regions of periodontal tissue were on the decline, and the stress in cervical region declined faster than that in apical region. On the 21st day the stresses in the cervical, medium and apical regions were similar., Conclusion: The 3-D FEM analysis revealed that alveolar bone loss could be most likely to happen during the initial stage of the tooth movement, and the data from this study mihgt be helpful to orthodontists in selecting an appropriate device of force systems to control the initial loading during orthodontic treatment.

Objective: To evaluate the properties of orthodontic rectangular arch wires in torsion., Methods: To measure and analyze the torsional moments and angles of 0.46 mm x 0.63 mm rectangular orthodontic arch wires in single 0.022 inch bracket of the maxillary central incisor with a torsion measurement apparatus., Results: (1) The torsional stiffness of stainless steel arch wires, Chinese nitinol arch wires, 7.0 mm vertical loop arch wires, 3.0 mm and 6.0 mm horizontal loop arch wires is 4.909, 1.325, 4.137, 3.448 and 3.024 Nmm per degree, respectively. (2) The arch wires will be twisted 19.143, 36.832, 19.851, 21.812 and 22.418 degrees; respectively to obtain optimal force. (3) Vertical and horizontal loop decreased the torsional stiffness of the rectangular stainless steel arch wire., Conclusion: The straight rectangular stainless steel arch wire is not well suitable for the torque control of the incisor. Loop design in arch wire is capable of decreasing torsional stiffness. The horizontal loop is more effective than vertical loop.

Objective: To evaluate the bracket bond failure and its causes between adult and adolescent patients during fixed orthodontic therapy., Methods: Bracket bond failure data of 30 adults and 30 adolescents, receiving fixed orthodontic therapy, have been collected within the first 12 visits, respectively. The compliance has been analyzed with survival analyse between the two groups., Result: The general bracket bond failure rate in the adult group is lower than that of the adolescent group and the difference is significant (p < 0.05). In the adolescent group, the failure rate for mandibular anterior teeth is highest and different from that of the adult group (p < 0.05). The failure rate resulted from biting hard food is ranked No. 1., Conclusions: The compliance of the adults receiving fixed orthodontic therapy is better than that of the adolescents. The investigation of bracket bond failure causes is beneficial in helping orthodontists improve orthodontic practice and raise clinical efficiency. The survival analysis is effective in evaluating the bond failure.

Unlabelled: To evaluate the effects of preadjusted bracket base shape, the morphology of tooth surface where bracket locates, and the suitability relevant to location of bracket on the preadjusted edgewise appliance technique. 1 vertical curve and 3 horizontal curves of the clinical crown surface of anterior teeth and bicuspid teeth were measured with the precise contour instrument on the 60 plaster models of the subjects who have normal occlusion in Sichuan province. It was found that variation of identical curve exists at the different heights between the teeth and between the individuals; the surface of the central zone of tooth-crown gradually protrudes from incisors to bicuspid teeth in the vertical direction, and the mesial contour of cuspid is more prominent than the distal in the horizontal direction., Conclusion: The 4 mm X 3 mm contour of the vestibular central zone of identical tooth-crown in different individuals is fairly stable; it is suitable for the location of preadjusted brackets. The vertical shifts of brackets could change the preadjusted torque value and the design of cuspid bracket should have the distinction between mesial and distal shape.