3D Finite Element Study of the Physiological Anchorage Control Concept on Anchorage Molars in Lingual Orthodontics.

Objective: To study the effect of the physiological anchorage control concept on anchorage molars in lingual and labial orthodontic techniques. Methods: Three-dimensional finite element models, including the right maxillary first molar, periodontal ligament, alveolar bone, and buccal tube, were established. The models were divided into the McLaughlin-Bennett-Trevisi (MBT™) straight-wire model with 0-degree maxillary first molar axial inclination and the physiologic anchorage Speewire system (PASS) model with -7-degree maxillary first molar axial inclination. Simulated sliding retraction forces (1 N, 1.5 N, and 2 N) were loaded on the buccal side and lingual side, and retraction forces (0.5 N, 0.75 N, and 1 N) were loaded on the buccal and lingual sides simultaneously. The displacements, principal stresses, and von Mises stresses of the periodontal ligament under different conditions were derived. Results: The anchorage molars showed different degrees of rotation, tipping, intrusion, and extrusion. As the force increased, these displacement trends also increased. The mesial displacement of the buccal + lingual force loading was less than that of the other two groups. Under the same force load method, the mesial displacement of the PASS group was less than that of the MBT group. Tilt movement increases the tensile stress of the distal cervical margin and root mesial apical third and the compressive stress of the mesial cervical margin and root distal apical third. The maximum stress of the periodontal ligament was less than that of the other two groups when the lingual force was loaded. Conclusion: The physiological anchorage control concept in lingual orthodontics provides better sagittal anchorage control than in labial orthodontics, but there is no significant difference numerically. Attention should be given to the control of torsion, torque, and arch width. Tilt movement increases the PDL stress of the cervical margin and root apical third. The sliding retraction force should be loaded lingually to maintain the force value of 1∼1.5 N.

[Efficiency of clear aligners in extrusion of posterior teeth evaluated by 3-dimensional model superimposition].

PURPOSE: To explore the efficiency of posterior teeth extrusion with clear aligners by 3-dimensional model superimposition, which provides a reference for the design of clinical programs. METHODS: We selected 24 patients with clear aligners whose posterior teeth were designed to extend more than 0.5 mm, and a total of 126 teeth were included. Digital models were obtained before and after treatment by intraoral scanning with iTero, named as "actual initial" and "achieved" digital models. Initial and final models from the ClinCheck, labeled as "virtual initial" and "predicted" models respectively. Initial, predicted, and achieved digital dental models were exported as stereolithography files and subsequently imported into Geomagic Studio. Extrusive measurements were made from the superimposition of the initial and predicted models (predicted movement) and from the superimposed initial and achieved models (achieved movement). Statistical analysis was performed with SPSS 23.0 and GraphPad Prism 5.0 software package. The extrusion efficiency of the posterior teeth was calculated, at the meanwhile the influencing factors were analyzed. RESULTS: The mean extrusion efficiency of posterior teeth during clear aligners treatment was 30.2%. The actual extrusion was linearly related to the expected(P<0.05), and the linear regression equation was y=0.305x-0.010. The difference between the actual and the predicted extrusion was positively correlated with the number of appliances(P<0.05), and also positively correlated with the predicted extrusion value(P<0.001). This difference was larger in low-angle patients than in patients with average angle (P<0.05). CONCLUSIONS: The extrusion rate of posterior teeth is relatively low during clear aligners treatment, and the average efficiency is 30.2%. Vertical growth pattern affects the extrusion efficiency. So more overcorrections can be designed for average angle patients.

Effects of Two Surfactants and Beta-Cyclodextrin on Beta-Cypermethrin Degradation by Bacillus licheniformis B-1.

The biodegradation efficiency of beta-cypermethrin (ß-CY) is low especially at high concentrations mainly due to poor contact between this hydrophobic pesticide and microbial cells. In this study, the effects of two biodegradable surfactants (Tween-80 and Brij-35) and ß-cyclodextrin (ß-CD) on the growth and cell surface hydrophobicity (CSH) of Bacillus licheniformis B-1 were studied. Furthermore, their effects on the solubility, biosorption, and degradation of ß-CY were investigated. The results showed that Tween-80 could slightly promote the growth of the strain while Brij-35 and ß-CD exhibited little effect on its growth. The CSH of strain B-1 and the solubility of ß-CY were obviously changed by using Tween-80 and Brij-35. The surfactants and ß-CD could enhance ß-CY biosorption and degradation by the strain, and the highest degradation was obtained in the presence of Brij-35. When the surfactant or ß-CD concentration was 2.4 g/L, the degradation rate of ß-CY in Brij-35, Tween-80, and ß-CD treatments was 89.4%, 50.5%, and 48.1%, respectively. The half-life of ß-CY by using Brij-35 was shortened by 69.1 h. Beta-CY content in the soil with both strain B-1 and Brij-35 decreased from 22.29 mg/kg to 4.41 mg/kg after incubation for 22 d. This work can provide a promising approach for the efficient degradation of pyrethroid pesticides by microorganisms.