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.

Objective:To develop an original-mirror alignment associated deep learning algorithm for intelligent registration of three-dimensional maxillofacial point cloud data,by utilizing a dynamic graph-based registration network model(maxillofacial dynamic graph registration network,MDGR-Net),and to provide a valuable reference for digital design and analysis in clinical dental applications.Methods:Four hundred clinical patients without significant deformities were recruited from Peking University School of Stomatology from October 2018 to October 2022.Through data augmentation,a total of 2 000 three-dimensional maxillofacial datasets were generated for training and testing the MDGR-Net algorithm.These were divided into a training set(1 400 cases),a validation set(200 cases),and an internal test set(200 cases).The MDGR-Net model constructed feature vectors for key points in both original and mirror point clouds(X,Y),established correspondences between key points in the X and Y point clouds based on these feature vectors,and calculated rotation and translation matrices using singular value decomposi-tion(SVD).Utilizing the MDGR-Net model,intelligent registration of the original and mirror point clouds were achieved,resulting in a combined point cloud.The principal component analysis(PCA)algorithm was applied to this combined point cloud to obtain the symmetry reference plane associated with the MDGR-Net methodology.Model evaluation for the translation and rotation matrices on the test set was performed using the coefficient of determination(R2).Angle error evaluations for the three-dimensional maxillofacial symmetry reference planes were constructed using the MDGR-Net-associated method and the"ground truth"iterative closest point(ICP)-associated method were conducted on 200 cases in the inter-nal test set and 40 cases in an external test set.Results:Based on testing with the three-dimensional maxillofacial data from the 200-case internal test set,the MDGR-Net model achieved an R2 value of 0.91 for the rotation matrix and 0.98 for the translation matrix.The average angle error on the internal and external test sets were 0.84°±0.55° and 0.58°±0.43°,respectively.The construction of the three-dimensional maxillofacial symmetry reference plane for 40 clinical cases took only 3 seconds,with the model performing optimally in the patients with skeletal Class Ⅲ malocclusion,high angle cases,and Angle Class Ⅲ orthodontic patients.Conclusion:This study proposed the MDGR-Net association method based on intelligent point cloud registration as a novel solution for constructing three-dimensional maxillo-facial symmetry reference planes in clinical dental applications,which can significantly enhance diagnos-tic and therapeutic efficiency and outcomes,while reduce expert dependence.

Objective:To establish an intelligent registration algorithm under the framework of original-mirror alignment algorithm to construct three-dimensional (3D) facial midsagittal plane automatically. Dynamic Graph Registration Network (DGRNet) was established to realize the intelligent registration, in order to provide a reference for clinical digital design and analysis.Methods:Two hundred clinical patients without significant facial deformities were collected from October 2020 to October 2022 at Peking University School and Hospital of Stomatology. The DGRNet consists of constructing the feature vectors of key points in point original and mirror point clouds (X, Y), obtaining the correspondence of key points, and calculating the rotation and translation by singular value decomposition. Original and mirror point clouds were registrated and united. The principal component analysis (PCA) algorithm was used to obtain the DGRNet alignment midsagittal plane. The model was evaluated based on the coefficient of determination (R 2) index for the translation and rotation matrix of test set. The angle error was evaluated on the 3D facial midsagittal plane constructed by the DGRNet alignment midsagittal plane and the iterative closet point (ICP) alignment midsagittal plane for 50 cases of clinical facial data. Results:The average angle error of the DGRNet alignment midsagittal plane and ICP alignment midsagittal plane was 1.05°±0.56°, and the minimum angle error was only 0.13°. The successful detection rate was 78% (39/50) within 1.50° and 90% (45/50) within 2.00°.Conclusions:This study proposes a new solution for the construction of 3D facial midsagittal plane based on the DGRNet alignment method with intelligent registration, which can improve the efficiency and effectiveness of treatment to some extent.

Objective: To evaluate the clinical effect and summarize the experience of radiofrequency catheter ablation (RFCA) for children suffered from premature ventricular contractions (PVCs). Methods: This retrospective study was conducted by descriptive analysis. A total of 108 cases with frequent PVCs from Shanghai Children's Medical Center were treated with RFCA under the guidance of CARTO3 system from January 2011 to December 2016. The immediate success rate of the procedure, the recurrence rate and the perioperative complications were summarized. The constituent ratio of different PVCs origins, the trend of overall procedure time and success rate in recent years were analyzed. Statistical analyses were performed using F test. Results: Immediate success of RFCA was achieved in 104 cases (96.3%, 104/108) and 4 cases (3.7%, 4/108) failed. The PVCs recurred during follow-up of over 6 months in 5 cases (4.8%, 5/104) . There were no severe complications related to the procedure. The sites of PVCs origin, in 52 cases originated from right ventricular outflow track (48.2%, 52/108) , 17 cases originated from left ventricular outflow track (15.7%, 17/108) and 26 cases originated from tricuspid annulus (24.1%, 26/108) . Among the three predilection sites of PVCs, the operation time was (141±46) min for right ventricular outflow track, (155±50) min for left ventricular outflow track, and (166±57) min for tricuspid annulus. However, the difference was not statistically significant (F=1.79, P=0.17) . X-ray exposure time was (14±8) minutes for right ventricular outflow track ablation, (32±14) minutes for left ventricular outflow track ablation and (16±8) minutes for tricuspid annulus ablation respectively. The exposure time for the ablation on left ventricle was significantly longer than the other two sites (F=5.12, P=0.018) . Conclusion RFCA is safe and effective for PVCs in children with high success rate and low recurrence and complication rates.