Objective To investigate the biomechanical characteristics of clear aligners combined with Class Ⅱelastics during retraction of upper anterior teeth,and compare the differences between two traction methods.Methods A case with a molar distal relationship and extraction of four first premolars was selected.The finite element method was applied to analyze tooth displacement,force distribution,and periodontal ligament(PDL)stress during 0.2 mm en-masse retraction of the anterior teeth.Three working conditions were defined:en-masse retraction without elastics(Condition 1),120 g Class Ⅱ elastics with aligner-cut hooks on upper canines and lower first molars(Condition 2),120 g Class Ⅱ elastics with aligner windows and bonded buttons on upper canines and lower first molars(Condition 3).Results Class Ⅱ elastics significantly enhanced lingual movement of the upper anterior teeth and mesial movement of the lower posterior teeth,while reducing mesial movement of the upper posterior teeth and lingual movement of the lower anterior teeth.In the transverse direction,the forces exerted on the teeth in all three conditions were minimal.In the sagittal direction,in Condition 2,the mesial force of the upper posterior teeth was effectively reduced by an average of 0.13 N,and the mesial force of the lower posterior teeth was increased by an average of 0.31 N.In Condition 3,the distal force of the upper canine teeth and the mesial force of the lower first molar were significantly increased by 0.40 N and 1.14 N,respectively.In the vertical direction,In condition 2,the average extrusive force of the upper teeth and the extrusive force of the lower molars were increased by 0.22 N and 0.20 N,respectively.In Condition 3,the upper canine extrusive force was increased by 0.91 N,while the lower molar intrusive force and the second molar extrusive force were reduced by 0.27 N and 0.25 N,respectively.The PDL stress distribution in the three conditions was generally similar.In Condition 3,the maximum principal stress distribution area on the lower first molars expanded slightly,but the magnitude did not increase significantly.Conclusions Condition 2 optimized the lower posterior teeth mesialization through balanced force distribution and protected the upper posterior teeth anchorage.Condition 3 significantly increased extrusive and distal forces on the upper canines and mesial forces on the lower first molars but did not substantially elevate periodontal risks for these teeth.

Objective To investigate the biomechanical characteristics of clear aligners combined with Class Ⅱelastics during retraction of upper anterior teeth,and compare the differences between two traction methods.Methods A case with a molar distal relationship and extraction of four first premolars was selected.The finite element method was applied to analyze tooth displacement,force distribution,and periodontal ligament(PDL)stress during 0.2 mm en-masse retraction of the anterior teeth.Three working conditions were defined:en-masse retraction without elastics(Condition 1),120 g Class Ⅱ elastics with aligner-cut hooks on upper canines and lower first molars(Condition 2),120 g Class Ⅱ elastics with aligner windows and bonded buttons on upper canines and lower first molars(Condition 3).Results Class Ⅱ elastics significantly enhanced lingual movement of the upper anterior teeth and mesial movement of the lower posterior teeth,while reducing mesial movement of the upper posterior teeth and lingual movement of the lower anterior teeth.In the transverse direction,the forces exerted on the teeth in all three conditions were minimal.In the sagittal direction,in Condition 2,the mesial force of the upper posterior teeth was effectively reduced by an average of 0.13 N,and the mesial force of the lower posterior teeth was increased by an average of 0.31 N.In Condition 3,the distal force of the upper canine teeth and the mesial force of the lower first molar were significantly increased by 0.40 N and 1.14 N,respectively.In the vertical direction,In condition 2,the average extrusive force of the upper teeth and the extrusive force of the lower molars were increased by 0.22 N and 0.20 N,respectively.In Condition 3,the upper canine extrusive force was increased by 0.91 N,while the lower molar intrusive force and the second molar extrusive force were reduced by 0.27 N and 0.25 N,respectively.The PDL stress distribution in the three conditions was generally similar.In Condition 3,the maximum principal stress distribution area on the lower first molars expanded slightly,but the magnitude did not increase significantly.Conclusions Condition 2 optimized the lower posterior teeth mesialization through balanced force distribution and protected the upper posterior teeth anchorage.Condition 3 significantly increased extrusive and distal forces on the upper canines and mesial forces on the lower first molars but did not substantially elevate periodontal risks for these teeth.

In the field of dental aesthetics,digital aesthetic design plays a crucial role in helping dentists to predict treatment outcomes vis-ually,as well as in enhancing the consistency of knowledge and understanding of aesthetic goals between dentists and patients.It serves as the foundation for achieving ideal aesthetic effects.However,there is no clear standard for this digital process currently in China and abroad.Many dentists lack of systematic understanding of how to carry out digital aesthetic design for treatment.To establish standardized processes for dental aesthetic design and to improve the homogeneity of treatment outcomes,Chinese Society of Digital Dental Industry(CSD-DI)convened domestic experts in related field to compile this consensus.This article elaborates on the key aspects of digital aesthetic data collection,integration steps,and the digital aesthetic design process.It also formulates a decision tree for dental aesthetics at macro level and outlines corresponding workflows for various clinical scenarios,serving as a reference for clinicians.

Objective To investigate the prognostic impact of carcinoembryonic antigen-related cell adhesion molecule 1 (CEACAM1) and CD34 on invasion and metastasis of gastric cancer.Methods CEACAM1 and CD34 expressions were detected by immunhistochemistry in 90 cases of gastric cancer and 30 cases of normal gastric mucosa.Then the relationship among CEACAM1, MVD marked by CD34 antibody and gastric cancer patients` clinical pathological features and prognosis were analyzed.Results The positive rates of CEACAM1 and CD34 protein in gastric cancer were significantly higher than those in normal gastric mucosa (P<0.05).The positive rate of CEACAM1 was closely related to histological differentiation, tumor invasion, nodal metastasis and TNM stage.MVD marked by CD34 was related with tumor size, histological differentiation, tumor invasion, nodal metastasis and TNM stage(P<0.05).Conclusions In gastric cancer, CEACAM1 and CD34 promote its invasion and metastasis, and they are potential indicators of predicting development and prognosis.

Brachytherapy ; Computer-Aided Design ; Humans