Abstract:In recent years, great development has been made in cytomechanics in orthodontic tooth movement（OTM）.The essential role of periodontal ligament in OTM has been widely accepted. The in vitro models have become an important way to reveal the biological mechanism in OTM,largely based on periodontal ligament cells(PDLCs), as well as other cells, including bone marrow mesenchymal stem cells, osteoblast, cementoblast and myoblast.The in vitro models have been renovated from the traditional ways stressing the 2Dcultured cells by deformation of the bottom,gravity, hydrostatic pressure or centrifugation, to the establishment of various novel models loading mechanical stimulation on cells 3Dcultured in bioscaffolds. The molecular expression involved in the osteoblastic differentiation and osteoclastogenesis induction in the bone remodeling cycle has drawn great attention, and will continue to be a focus of study. Furthermore, with the identification of periodontal ligament stem cells(PDLSCs), the cytomechanics involved in OTM and periodontitis, will undoubtedly be a promising new direction.

Abstract:Objective To develop an initial numerical model for bracketless appliance technology, and to analyze the biomechanical effects. To provide the fundamental basis to optimize the clinical application of bracketless appliance technology. Method A 3D numerical model of a dry skull was developed from sequential computed tomography (CT) scan images taken at 0.5mm intervals by using Mimics and ABAQUS software. This model consisted of three parts: a dentomaxillary model of upper anterior section, a matching bracketless appliance model, and their assembly to simulate orthodontic force stressed by bracketless appliance. The nonlinear finite element method (FEM) was used to analyze the instant biomechanical effects. As the control group, the same dentomaxillary model was loaded to simulate fixed appliance working pattern. Results The instant dentoperiodontal stress with bracketless appliance loading was much higher than that with fixed appliance working pattern by 50~500 times. With bracketless appliance loading，the tendency of tooth movement wasn’t exactly performed as planned with orthodontic teeth tending to affect each other. The canine designed to do mesiodistal translation tended to do tipping movement rather than bodily movement. Bracketless appliance itself performed stress concentration mainly in places of great deformation, but the maximal stress was less than its elastic limit of 53.1 MPa. Conclusions In this study, bracketless appliance loading performed unexpected high instant stress on dentoperiodontal tissue, with limit in controlling tooth movements. The bracketless appliance is not suggested to replace the traditional fixed appliance. This study suggested bracketless appliances should be designed more reasonable, and the material of Anglealign appliances used should be further improved, to enhance the control of orthodontic tooth movement. An ideal material for the bracketless appliance was expected to perform smaller elastic modulus, higher elastic limit and better stress relaxation.

Abstract:Objective To identify the differentially expressed proteins and clarify the major proteins involved in the molecular mechanism of osteoblasts under mechanical strain loading. Method Saos2 osteoblastic cells were subjected to 12% elongation for 24 hours by using Flexcell strain loading system. Proteins extracted from Saos2 cells were separated by twodimensional electrophoresis (2DE). Differential expressed protein spots among groups were submitted to matrixassisted laser desorption/ionization time of flight mass spectrometer (MALDITOF MS) assay and peptide mass fingerprinting (PMF) identification. The SwissProt and NCBI databases were used to obtain further information about proteins identified. Results Saos2 stimulated by mechanical strain showed a significant difference in 2DE system compared with the control group. A total of (1031±41) or (928±25) protein spots were resolved by 2DE of controls or experimental groups extractions respectively. 17 significant up  regulated proteins were identified. These associated proteins fell into 6 groups, including stress reaction, energy metabolism, cell proliferation, reconstruction of cytoskeleton, signaling and osteogenesis. Conclusions The Saos2 can express differential proteins stimulated by mechanical strains and these proteins may play an important role in molecular mechanism of osteoblasts under mechanical strain loading.

Abstract:Objective To analyze changes of stress and displacement distribution of the mandibular condyle under different occlusal reconstruction conditions by using the Forsus, and to provide clinical reference for the application of the Forsus. Method The software Abaqus6.5 was employed to build the 3D finite element model of mandibular condyle for simulation. Under different occlusal reconstruction conditions, the distances of mandibular protraction were 3 mm, 4 mm, 5 mm, 6 mm and 7 mm and the mandibular's opening distances were got as 4 mm, 3.5 mm, 3 mm, 2.5 mm and 2 mm correspondingly. The stress, displacement and rotation trends of mandibulatemporomandibular articulation were analyzed and the estimation of occlusal reconstruction contributing to the growth of the condyle was made. Results The 3D model showed that the maximum stress distributed on the mandibular condyloid process, sigmoid incisure of mandible and the posterior neck of condyle area under the five different conditions. With the increase of displacement in mandibular condyle, the stress increased slowly on the sigmoid incisure of mandible and the posterior neck of condyle area, but the stress still kept in the same order of magnitude (30 MPa). The stress distribution of mandibular condyloid process was in a steady state with no obvious stress concentration. The displacement of condyle in horizontal direction increased gradually and forward, and the displacement of condyle in vertical direction also increased gradually but downward. When the mandibular was stretched to the designed reconstructive location, the condyle moved downward. Conclusions The range of physiological occlusal reconstruction will not change the stress distribution trends of the condylar cartilage, even when the mandibular moves forwards in varying degrees. Considering the physiological nature of temporomandibular articulation and the growth of the condyle, when the mandibular retrusion is severe, it would be advisable by subsection protrusion.

Abstract:Objective In this experiment, the model of Platform Switching Implant was simulated by adopting threedimensional (3D) finite element method and the stress distribution of implants planted in different depth was analyzed when the platform switching implant system was applied with different loading in front maxilla. Method By using the Solidworks 2007 and Ansys Workbench11.0 software to simulate the 3D finite element models,the stress distribution of implants in the form of platform switching as experimental group and traditional abutment as control group which were respectively planted into the level of alveolar ridge(bone level),1 mm below bone level(minus 1) and 2 mm below bone level(minus 2) were analyzed. Results For platform switching implants, the stress of cortical bone was effectively reduced and smaller as the imlpant was planted deeper, while the traditional abutment did not change significantly with deeper planting level.Under vertical loading, the stress distribution in each model’s abutment of platform switching was basically similar, having no significant correlation with the planting depth, while the stress distribution in the traditional abutment had a significant change: gradually trending up with deeper planting level; the stress distribution of two groups of implants in each planting level and cancellous bone was basically similar, having no significant correlation with the planting depth; the stress distribution of cortical bone was shifted down with deeper planting level for platform switching group, while in the traditional abutment group, the stress distribution of cortical bone always focused on the joint between alveolar ridge top and abutment, which was more concentrated than that in platform switching group. The stress distribution under horizontal loading was similar to that under vertical loading,and the only difference was in that the maximum stress distribution of abutment and implant was mainly concentrated in their corresponding labial parts.In cortical bone, the buccal stress was obviously more concentrated than that in the vertical loading group. Conclusions Platform switching implant planted below the alveolar ridge top can improve the stress distribution, which has obvious advantages over the traditional abutment form. But the component force in horizontal direction would increase the stress on the labial part of alveolar ridge, and should be avoided.

Abstract:Objective To investigate the effects of different magnitudes of mechanical strain on the expression of MMP-13/TIMP-1 and try to determine the signal transduction pathways in response to mechanical strain in human periodontal ligament cells (HPDLCs) in vitro. MethodHPDLCs were subjected to 0%，6%，12% or 18% elongation for 24 h by using cell stress loading system simultaneously. Then the MMP-13/TIMP-1 mRNA and protein expression in cells were tested by reverse transcription polymerase chain reaction (RT-PCR) and western blotting respectively. Furthermore, specific inhibitors were employed to examine the role of different signal transduction pathway on the expression of straininduced MMP-13 /TIMP-1 in HPDLCs. ResultsThe expression of MMP-13 /TIMP-1 in HPDLCs significantly increased in groups of 6%，12%, 18% elongation in a magnitude-dependent manner compared with the control group (0%) after the mechanical strain treatment for 24 h. PD098059 and cycloheximide could inhibit the increase in MMP-13 and TIMP-1 mRNA expression in response to mechanical strain respectively. Conclusions Different magnitudes of mechanical strain can affect the expression of MMP-13/TIMP-1 in HPDLCs in a magnitudedependent manner, and further affect the periodontium remodeling with the characteristics of degradation and synthesis of extracellular matrix in response to mechanical strain. The ERK-MAPK pathway is involved in straininduced MMP-13 expression while the strain-induced TIMP-1 expression depends on de novo protein synthesis.

Abstract:Objective To investigate the correlation between mechanical tensile stress and the expression of ODF mRNA in osteoblasts differentiated from rBMSCs, and elucidate the mechanism for osteoclastogenesis regulated by osteoblasts in bone modeling and remodeling during the process of orthodontic tooth movement. Method rBMSCs derived osteoblasts were isolated and cultured in vitro, and subjected to static mechanical tensile stress of 1, 3, 5 kPa or dynamic tensile stress of 3, 5 kPa at 0.017 Hz using the cellular tensilestress system for 24 h. The control groups were subjected without any strain. Cells were collected in 0, 3, 6, 9, 12, 24, 48 h respectively after stress loading. The expression patterns of ICAM-1 mRNA were examined by semiquantitative RTPCR assay. Results ODF mRNA level significantly decreased after dynamic tensile strain, compared with the control groups；the effects of inhibition did not positively correlated with the magnitude of strain; the expression of ODF mRNA gradually decreased at 6 h, significantly decreased at 9 h, then slightly rebounded and still stayed at a considerably lower level, reached the minimum transcription at 48 h. Conclusions The mechanical tensile strain can regulate osteoclastogenesis by inhibiting the expression of ODF in osteoblasts derived from rBMSCs. It could lead to a better understanding of the molecular basis for osteoblastosteoclast communication in bone resorption induced by the application of mechanical strain during the orthodontic tooth movement.

Abstract:Objective To establish a 3D finite element model of fixed denture for the preparation of the subsequent study such as biomechanical analysis. Method The computed temography(CT) images were processed by Mimics and Geomagic studio，then the solid model and finite model were established by UG NX. Results A 3D finite element model of fixed denture including alveolar bone, abutment, pericementum and denture were established. Conclusions The use of the initial data of teeth to build finite model can avoid data loss and minimize model distortion to a certain extent, so the 3D finite element model has good similarities in geometry.

Abstract:Objective To analyze the energy of rolling manipulation in different frequency bands and find the features of rolling manipulation dynamics. MethodThe force signals of rolling manipulation of six experts and six beginners were measured and divided into different frequency bands by wavelet transform to calculate the energy. Through statistical analysis, 18 characteristic quantities of horizontal force or vertical force were created and the overall evaluation coefficient R was proposed. ResultsAbout 70% of experts’ rolling manipulation energy was found in 0~0.406 25 Hz and about 20% energy in 1.625~3.25 Hz. The overall evaluation coefficient R of 6 experts was over 0.70, while R of beginners was below 0.70, which showed the difference was significant. ConclusionsThe energy distribution of rolling manipulation reflects the characteristics of softness and periodicity. If the rolling manipulation is in accordance with the manipulative requirement and the overall evaluation coefficients R is over 0.70, it could be said that the operator masters the rolling manipulation well.

Abstract:Objective To study the influence of nasal cavity structure on nasal function of warming and humidifying the inhaled airflow. Method Nine normal persons and two patients with deviation of nasal septum (pre and postoperation) were selected as research subjects. The threedimensional finite element model of nasal cavities of these volunteers was established. Numerical simulations for the airflow distribution, the airflow temperature and the airflow humidity in the nasal cavity were performed. Based on the simulation results, comparisons were made between normal nasal cavities and the patient’s nasal cavities as well as between the pre-and post-operative nasal cavities. ResultsIn the wider side of nasal cavity, the volume flow rate and the velocity of airflow were higher and the effect of warming and humidifying on the airflow was worse. For normal people, the nasal cavity for warming and humidifying the inhaled airflow was in the anterior segment of the nose. While for the patients, the main segment of warming and humidifying the inhaled airflow had to depend on the airway geometry. Conclusions The nasal cavity structure can influence the effect of warming and humidifying on the airflow. The parameters describing the geometry of nasal cavity, such as the surface area of nasal airway and volume of nasal cavity, may be a useful measurement for the nasal function of warming and humidifying the inhaled airflow.

Abstract:Objective To investigate the feasibility of simulating gravity pressure and observe its effect on preosteoblast OCT1 by centrifugation. Method OCT-1 cells were cultured in 1% agarose gel with a final concentration of 2×107 cells per millilitre. The experiment was divided into two groups according to the duration: one day (1 d) and five days (5 d). Each group was further divided into three subgroups: 0 r/min (control), 200 r/min, and 500 r/min. The 200 r/min group and 500 r/min group were centrifuged for three hours once a day for one day or five days respectively. The control group was kept in the same environment without centrifugation. Results The ColⅠpositive staining was slightly strengthened in the 1d 200 r/min group while it was even more strengthened in the 1d 500 r/min group. Conversely, the positive staining was stronger in the 5d 200 r/min group than that in the 5d 500 r/min group. The markers related to osteoblast differentiation such as Alkaline phosphatise (ALP), Type I collagen α2 (Col1α2), Osteocalcin (OC) and runt-related transcription factor-2 (Runx2) mRNA expression were all upregulated after centrifugation. ConclusionsCentrifugation is a practical method for cell pressure and plays a significant role in promoting the differentiation of preosteoblast OCT-1, which can be used as a new method to simulate the gravity.

Abstract:Objective To investigate the setting property and compressive strength of β-TCP (β-tricalcium phosphate)/α-CSH (α-calcium sulphate hemihydrate) combined bone graft. Method βTCP/αCSH combined bone graft and distilled water were mixed with different ratio: 1 g∶0.1 mL、1 g∶0.2 mL、1 g∶0.3 mL、1 g∶0.4 mL、1 g∶0.5 mL, respectively. The initial setting time (Ti), final setting time (TF), compressive strength were recorded, and the X-ray diffraction (XRD) and the scanning electron microscope (SEM) were examined. Results The initial and final setting time of combined bone graft increased along with the increase of solid/liquid ratio. The Ti and TF were (4.6±1.3) min and (13.1±2.9) min respectively when the solid/liquid ratio was 1 g∶0.2 mL. The average compressive strength was 7.86 MPa in one day after setting, which was about two times higher than that of β-TCP alone. The XRD results showed that no other materials were produced except that α-CSH was transformed to CSD in the setting process. The SEM results indicated that thick CSD granules were adhered to the porous surfaces of β-TCP granules after setting. Conclusions The setting time and compressive strength of β-TCP/α-CSH combined bone graft could be adjusted by the different solid/liquid ratio.

Abstract:Objective To build a 2D/3D registration system based on the compute unified device architecture(CUDA) frame with single X-ray image and CT data of knee joints and apply it in the research of knee motion and stability of implanted prosthesis. Method The digital radiography(DR) equipment used in the study was calibrated by the Zhang zhengyou Calibration Method, and then digitally rendered radiographs(DRR) images were generated in the CUDA frame with lighttracing algorithm, and the best 2D/3D registration parameters were calculated with a similarity operator of cross correlation; finally, the results were evaluated by using the method of 3D/3D registration with data obtained from a 3D laser scanner. Results With knee specimen X-ray images and CT data, in 6 degrees of freedom, the average errors of transform were below 1 mm, and those of rotation were below 1°. Conclusions The 2D/3D registration system can meet the precision requirement of motion detection and be used to study the knee motion and prosthesis location.

Abstract:Objective To study the effect of different loading intensity and offaxis angle on changes in spatial distribution and mechanical properties of cancellous bone from femoral head by using threedimensional(3D) finite element method. Method The same size cancellous bone specimens were selected in accordance with the main pressure trabecular direction at 0°, 15°and 45° offaxis angle from 3D model of proximal femoral bone structure based on primary study. The 3D structure parameters of the specimen were calculated, then the finite element analysis was used to simulate the uniaxial compression test, and the stress and strain distribution in different model was observed. The influences of different loading intensity and off-axis angle on biomechanical properties of proximal femoral cancellous bone were investigated. Results Based on the established finite element model of cancellous bone of human femoral head, the uniaxial compression test was simulated. It was found that there were significant differences in the proportion of cancellous bone with ≥5 000μ strain in different mechanical strength or offaxis angle on cancellous bone specimens（P<0.05）. Conclusions Distribution of femoral head cancellous bone is closely related with the mechanical adaptability. The incompatibility between structure and function decreased the biomechanical properties of femoral head cancellous bone and the subsequent bone remodeling caused by repeated negative stimulus may play an important role in femoral head necrosis.

Abstract:Objective To study the deformation and stress distribution of femur after total hip arthroplasty (THA) and its influence on the vibration mode and natural frequency of femur. Method Two finite element models of natural femur and femur after THA were developed on the basis of computed tomography (CT) scans from a normal young man to investigate the biomechanical behavior of the subjectunder gait condition and make the modal analysis. Results (1) After THA, obvious stress concentration was obtained around the prosthesis neck, and the stress shielding was observed; (2) The peak stress of femur model after THA increased to 4.36 times of the original one; (3) The natural frequency for constrained mode was much higher than that of free mode; (4) With the increase of vibration mode, the differences in natural frequency between two models became larger; (5) Bending and twisting were the main vibration mode of femur, and there were no significant changes in vibration mode before and after THA. Conclusions The prosthesis could change the mechanical and structural properties of the original femur. In order to avoid prosthesis loosening derived from sympathetic vibration, the vibration property of femur must be taken into consideration in the design of prosthesis.

Abstract:Objective To test the biomechanical properties of symphysis pubis diastasis fixed by cannulated screw or reconstruction plate and provide the theoretical basis for clinical practice. Method In the experiment, fifteen normal adult specimens’ pelvis along with their intact spines from L5 to the proximal 2/3 of both femora were randomly divided into three groups. The symphysis pubis, unilateral anterior sacroiliac joint and ipsilateral sacropinous and sacrotuberous ligaments were cut; the intact major pelvic ligaments and hip joints were used to simulate Tile B1 pelvic fracture model. The fixation of fivehole reconstruction plate and 6.5 mm cannulated screw were applied successively to cure symphysis pubis diastasis.The pelves were loaded vertically in the testing machine with a standing posture. The loads were applied through the L5 body to a maximum of approximately 400 N, while the displacements of the symphysis pubis were recorded. Results The study showed that two fixations were able to reduce symphysis pubis gapping and restore the biomechanical stability of pelves. Under the same condition，the displacement of symphysis pubis used 3.5 mm fivehole reconstruction plate with 4 cortical screws, and the displacement by using cannulated screw were (0.944±0.983)mm and (-0.03±0.378)mm respectively. There were significant differences (P<0.05) between them. Conclusions The cannulated screw is superior to 3.5 mm fivehole screw in biomechanical stability. The cannulated screw has fine biomechanical properties and is able to provide the firm fixation for symphysis pubis diastasis, which fits the principles of biological osteosynthesis.

Abstract:Tumor metastasis, the main biological characteristic of malignance tumor, is the important cause of death for most cancer patients. The process of tumor metastasis is complex and involves a dynamic combination of vessel, lymphatic system and microenvironment of metastatic organ. Organ specific arrest and adhesion of tumor cells within microvessels of potential target organs is a vital step during the formation of blood borne metastasis. In this article, recent studies on the organ specific arrest and adhesion of circulating tumor cells were comprehensively summarized focusing on the related theory, hypothesis and methodology including the model employed and the research methods involved. The article also discussed the biomechanical factors, endothelial cells and chemokines regulating the arrest and adhesion of circulating tumor cells, and pointed out some recent new phenomena as well as new approaches and directions worthy of investigation.

Abstract:Bisphosphates as a firstline preferred drug for curing osteoporosis has been used for a long time in clinic since it can inhibit the bone remodeling to decrease the risk of bone fracture and increase the bone density. But recent studies show that bisphosphates could cause the accumulation of microdamage to decrease bone quality. The longterm use of bisphosphates may reduce the bone toughness and weaken the mechanical properties of bone. Some clinical reports have indicated that patients with osteoporosis tend to have nontraumatic fractures after their use of bisphosphates. This article will review the effect of bisphosphates on the microdamage and mechanical properties of bone.