Objective: To investigate the effects of tooth extracti on on dental arch width and alveolar bone width. Methods: D ental arch width and relevant alveolar bone width between canines, second premo lars and first molars were measured on dental casts of 20 cases with Angle II 1 malocclusion before and after tooth extraction treatment. All data were analy sed by SPSS 10.0 statistic software. Results: After treat ment, in maxilla the arch width and alveolar bone width between canines were in creased(P

Objective:To analyze the perpendicular force on each tooth produced by the reverse-curve arch wires of various angles and depths using the method of 3-D finite element (3-D FEM) analysis. Methods:3-D FEM models of lower teeth, periodontal ligaments and alveolar bone as well as the 0.46 mm?0.64 mm inch stainless steel reverse-curve arch wires with different angles and depths were developed with the ANSYS finite element software, and the displacements of deformation of the reverse-curve arch wires were established on the models. Results:A ideal 3-D FEM was construct,including 2 709 elements and 1 969 nodes. The depth and angle of the reverse-curve arch wires produced obvious effect on the force exerted to teeth, and they could alter both the strength and the direction of the force. The force was mainly loaded on the canines, the second premolars and the molars, while less loaded on the incisors. Affected by the reverse-curve arch wires, the perpendicular force on the incisors were brought intrusively and on the molars were brought intrusively and distal upright; however, the canines and the bicuspids, in the perpendicular direction, moved along with the transformation of the angle and depth of the reverse-curve arch wires. When the angle of reverse-curve arch wires was fixed, the intrusive force on the incisors and molars was increased along with the increase of depth of the reverse-curve arch wires. Perpendicularly, the canines underwent a process from extrusion to intrusion, while the bicuspids were from intrusion to extrusion. When the depth of reverse-curve arch wires was fixed, the intrusive force on the incisors and molars was increased along with the increase of angle of the reverse-curve arch wires. The canines underwent a process from intrusion to extrusion.Conclusion:The variation of the angle and depth of the reverse-curve arch wires may produce evident effect on the force exerted to teeth.

Objective:To study the effects of recombinant human vascular endothelial growth factor on proliferation and differentiation of rat osteoblasts. Methods: Cell culturing, light microscop, MTT assay and PNPP assay were performed to observe the effects of rhVEGF on proliferation and differentiation of the cells. Results: rhVEGF could stimulate osteoblasts proliferation and differentiation. The maximal effect on proliferation was observed at a concentration of 3.125 ng/ml on the third day. ALP activities in osteoblasts were increased most significantly at a concentration of 12.5 ng/ml. Conclusion: rhVEGF may not only induce angiogenesis to facilitate bone formation, but also stimulate this process in a direct way by inducing proliferation and differentiation of osteoblasts.

Objective To explore the correlation of caries susceptibility of patients with the immediate tooth polish,application of fluoride,and the patients' oral hygiene habits after interproximal enamel reduction (IER) in clinical practice.Methods The present study retrospectively collected 45 cases of IER (18 males and 27 females) in 196 tooth sites.Each sample was examined clinically and radiologically to obtain the incidence of caries,and the outcome was correlated with amount of IER,tooth polish,application of fluoride,and the brushing method and frequency for statistical analysis.Results The present study showed that there was no statistical significance among the amount of IER,the site of IER,the patients' brushing method,and the gender with the susceptibility of caries.However,there was statistical significance among the application of fluoride,tooth polish and brushing frequency with the susceptibility of caries.Conclusions The current research suggests that it is desirable to polish tooth and apply fluoride for patients with IER in clinical practices.In the meanwhile,the clinician should pay attention to patients' oral hygiene habits,especially brushing frequency,due to the positive correlation between the brushing frequency and incidence of caries.

OBJECTIVETo investigate the biomechanics of J-hook headgear in En mass intrusion and retraction of maxillary anterior teeth and provide guidance for clinical treatment.

METHODSA three-dimensional finite element model of maxillary teeth, periodontium, straight wire appliance and maxillary bone was established in ANSYS 14.0. En mass retraction of anterior teeth with force of 1.5 N through J-hook headgear was stimulated. Force was applied mesial to lateral incisor in group A and distal to lateral incisor in group B. The force direction was 30° to the sagittal plane and 20° to 60° to the occlusal plane. Force direction to the occlusal plane was changed every 5° and 18 cases were calculated. Displacement of upper anterior teeth and stress distribution in the periodontium were analyzed.

RESULTSAs the degrees of force direction to the occlusal plane increased, the moving pattern of upper anterior teeth changed from clockwise rotation (lingual movement with intrusion) to bodily retraction and intrusion, and counter- clockwise rotation (intrusion with labial movement). With the force direction of 35° to occlusal plane applied mesial to lateral incisor or force direction of 45° to the occlusal plane applied distal to lateral incisor, bodily movement of upper anterior teeth without rotation was achieved.

CONCLUSIONSPlacement of J-hook mesial to lateral incisor enable orthodontists to maintain better en mass intrusion and retraction of upper anterior teeth. The direction of J-hook should be adjusted according to individual condition and treatment objective.

Activator Appliances ; Biomechanical Phenomena ; Finite Element Analysis ; Humans ; Incisor ; Maxilla ; Periodontium ; Tooth Movement Techniques ; instrumentation ; methods