Objective To establish a simplified simulation method of rocking-chair archwire(RCA),explore the biomechanical effect of RCA during anterior teeth retraction with sliding mechanics,and provide guidance for clinical treatment.Methods A standard 0.019 in×0.025 in(0.483 mm×0.635 mm)labial archwire was imported into ANSYS software and preloaded spring was used to simulate RCA at different angles to achieve parameterized modeling.A three-dimensional(3D)finite element model with labial straight wire appliance,teeth,periodontium and maxillary bone was established to analyze the displacement and force of anterior/posterior teeth under 1.5 N intra-arch traction combined with RCA at different angles.Results Preloading forces of 1.5,3,4.5,and 6 N in spring induced angles of approximately 5°,10°,15°,and 20° for RCA,demonstrating the flexibility and convenience of the parameterized modeling method.During intra-arch traction with increased angle of RCA,lingual crown displacement of the middle incisor gradually decreased,while the lateral incisor and canine showed decreased crown tipping and increased lingual root displacement;when the RCA angle was 20°,the lateral incisor and canine achieved almost bodily retraction.Meanwhile,premolars showed an extrusion tendency,while molars demonstrated distal crown tipping and intrusion tendency.As the RCA angle increased from 0° to 20°,intrusive force on the anterior teeth increased,and the moment-force ratio(M/F)at bracket level increased from 0 to near 9 mm.Conclusions RCA can effectively control the moving pattern of the maxillary anterior teeth and prevent their over-erection and extrusion during retraction with sliding mechanics.During intra-arch traction with rigid stainless steel archwire,theoretically RCA of 20° has sufficient torque control on the anterior teeth to achieve their en-masse retraction.

Objective To establish a simplified simulation method of rocking-chair archwire(RCA),explore the biomechanical effect of RCA during anterior teeth retraction with sliding mechanics,and provide guidance for clinical treatment.Methods A standard 0.019 in×0.025 in(0.483 mm×0.635 mm)labial archwire was imported into ANSYS software and preloaded spring was used to simulate RCA at different angles to achieve parameterized modeling.A three-dimensional(3D)finite element model with labial straight wire appliance,teeth,periodontium and maxillary bone was established to analyze the displacement and force of anterior/posterior teeth under 1.5 N intra-arch traction combined with RCA at different angles.Results Preloading forces of 1.5,3,4.5,and 6 N in spring induced angles of approximately 5°,10°,15°,and 20° for RCA,demonstrating the flexibility and convenience of the parameterized modeling method.During intra-arch traction with increased angle of RCA,lingual crown displacement of the middle incisor gradually decreased,while the lateral incisor and canine showed decreased crown tipping and increased lingual root displacement;when the RCA angle was 20°,the lateral incisor and canine achieved almost bodily retraction.Meanwhile,premolars showed an extrusion tendency,while molars demonstrated distal crown tipping and intrusion tendency.As the RCA angle increased from 0° to 20°,intrusive force on the anterior teeth increased,and the moment-force ratio(M/F)at bracket level increased from 0 to near 9 mm.Conclusions RCA can effectively control the moving pattern of the maxillary anterior teeth and prevent their over-erection and extrusion during retraction with sliding mechanics.During intra-arch traction with rigid stainless steel archwire,theoretically RCA of 20° has sufficient torque control on the anterior teeth to achieve their en-masse retraction.

Objective:To explore the clinical value of cluster management in secondary hydrocephalus.Methods:Seventy-seven patients with secondary hydrocephalus admitted to Department of Neurosurgery, Shenzhen Second People's Hospital from January 2016 to June 2021 were chosen; they were divided into traditional management group ( n=30) and cluster management group ( n=47) according to different management methods. Patients in traditional management group accepted craniocerebral CT and 3 consecutive times of cerebrospinal fluid tests, and normal results were achieved and then ventriculoperitoneal shunt (VPS) was performed. In patients from the cluster management group, on the basis of management treatment, cranial plain and enhanced MRI and DNA metagenomic next generation sequencing of cerebrospinal fluid were performed before surgery, and rapid test of cerebrospinal fluid and ventriculoscope observation were performed during surgery; after exclusion of intracranial infection, VPS was performed. The differences of shunt failure rate were compared between the two groups and the positive rates of intracranial infection detected by above 4 methods were compared in the cluster management group. Results:There was significant difference in shunt failure rate between the cluster management group and traditional management group (2.1% vs. 20.0%, P<0.05). The positive rates of intracranial infection by DNA metagenomics (61.7%) and ventriculoscopy (68.1%) were significantly higher than those by preoperative cranial plain and enhanced MRI (14.9%) and rapid test of cerebrospinal fluid (6.4%, P<0.05). Conclusion:Cluster management can effectively decrease the VPS failure rate in secondary hydrocephalus; DNA metagenomics and ventriculoscopy have high efficiency in detecting intracranial infection.

Objective: To analyze the impact of the activation mode on the results of space closure in the mandibular arch using a double keyhole loop (DKHL) with a typodont model and reverse engineering technique to provide guidance for clinical treatment. Methods: Nine normal mandibular typodont models after leveling were randomly divided into 3 groups, which then underwent three types of DKHL activation for space closure. Each model was assessed at the initial stage and after the warm water bath, and the images were superimposed to measure the displacement of special crown and root mark points. All statistical analysis of the data was performed using SPSS 19.0 Results: After equal activation times, the root retraction of anterior teeth and the crown forward position of posterior teeth in groups activated at the distal loop (conditions 2 and 3) were much greater than those in the group activated horizontally (condition 1). Activation between mesial and distal loops (condition 3) induced significant anterior tooth intrusion, together with elongation and buccal inclination of posterior teeth. The displacement of mark points among the three conditions showed a statistically significant difference. Conclusion The movement of mandibular anterior and posterior teeth could be flexibly controlled through different DKHL activation modes, which should be chosen carefully according to individual conditions.

Objective To investigate the biomechanics of J-hook headgear in En mass intrusion and retraction of maxillary anterior teeth and provide guidance for clinical treatment.Methods A 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.Results As 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.Conclusions Placement 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.

A three-dimensional finite element model of premaxillary bone and anterior teeth was established with ANSYS 13.0. The anterior teeth were fixed with strong stainless labial archwire and lingual frame. In the horizontal loading experiments, a horizontal retraction force of 1.5 N was applied bilaterally to the segment through hooks at the same height between 7 and 21 mm from the incisal edge of central incisor; in vertical loading experiments, a vertical intrusion force of 1.5 N was applied at the midline of lingual frame with distance between 4 and 16 mm from the incisal edge of central incisor. After loading, solution was done and displacement and maximum principle stress were calculated. After horizontal loading, lingual displacement and stress in periodontal membrane (PDM) was most homogeneous when the traction force was 14 mm from the edge of central incisor; after vertical loading, intrusive displacement and stress in PDM were most homogeneous when the traction force was 12 mm from the incisal edge of central incisor. The results of this study suggested that the location of center of resistance (CRe) of six maxillary anterior teeth is about 14 mm gingivally and 12 mm lingually to incisal edge of central incisor. The location can provide evidence for theoretical and clinical study in orthodontics.
Dental Models ; Dental Stress Analysis ; Finite Element Analysis ; Humans ; Incisor ; Maxilla ; Periodontal Ligament ; Tongue

Objective To study the prognostic factors of gastrointestinal stromal tumors (GIST).Methods A total of 144 GIST patients treated at the First Affiliated Hospital of Guangxi Medical University between January 1996 and December 2011 were analyzed restrospectively.Kaplan-Meier,log-rank test and Cox regression model were used.Results The overall 5-year survival was 59.6％.Log-rank univariate survival analysis showed that the primary location,tumor size,metastasis,operational method,type of tumor cells,invasion of the surrounding organs and tissues,invasion of the smooth muscle,cellularity of the tumor,mitotic counts of the tumor cells,Ki-67 labeling index,P53 expression and targeting therapy were significant prognostic factors (P ＜ 0.05).Cox regression model showed that tumor size,metastasis,operational method,surrounding organs and tissues invasion,cellularity of the tumor,mitotic counts of the tumor cells,P53 and targeting therapy were essential to improve the survival.Conclusions The study suggests that early diagnosis and comprehensive treatment consisting of operation and targeting therapy can significantly improve the survival of GIST.

Objective To investigate the main genotypes and the epidemic characteristics of TEM-type and SHV-type extended-spectrum beta-lactamases (ESBLs) of the gram-negative bacilli in Guangzhou.Methods The phenotype of ESBLs from 3 500 clinical isolates were primary screened and confirmed by the NCCLS confirmatory test according to guidelines of NCCLS(2001). PCR were performed on 3 500 clinical isolates using primers specific for blaTEM and blaSHV, respectively, the PCR product were purified and sequenced by ABI prism 377 DNA sequencer.Results Total of 3 500 un-replicated and consecutive Gram-negative bacilli were isolated from 13 hospitals in Guangzhou in the past two years, and the prevalence of ESBLs-producing clinical Gram-negative isolates was 31.0%(1 084/3 500). The positive rates of PCR results for blaTEM, blaSHV, and both of them in all the clinical Gram-negative isolates were 24.0%(840/3 500),10.8%(378/3 500),and 3.7%(128/3 500), respectively. All PCR products for blaTEM were further identified as TEM-1-type non-ESBLs gene, including TEM-1,TEM-1B,TEM-1D,and TEM-1F,by DNA sequencing analyses. However, almost all of the blaSHV gene were further identified as SHV-type ESBLs gene(the prevalence of SHV-1 is 7.2% only).The prevalence of SHV-12/5a accounted for highest(50.0%,152/304) in Guangzhou. Our test also showed that 53%(340/641) of blaTEM-producers [JP2] were Escherichia coli, and 57.9%(176/304) of blaSHV-producers were Klebsiella pneumoniae.Conclusions [JP]We could conclude from above results that SHV-type ESBLs, especial SHV-12/5a, was the prevalent genotype of ESBLs of clinical gram-negative bacilli in Guangzhou. TEM-type ESBLs did not exist in our city. In addition, SHV-12/5a-producing strains probably were main epidemic strains in Guangzhou. As for detection of ESBLs with regular phenotype methods, there was possibility of false negative and false positive.