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Reevaluation on the mechanical properties of dentine microstructure

Xiaosong LUO ; Yixia ZHANG ; Yuhong CUI ; Jun PAN

Journal of Medical Biomechanics.2011;26(2):181-188.

Objective:It is demostrated that the porous protein-mineral mechanics model could provide more accurate prediction for biomaterial properties of dentine compared with the other established models.This paper would use the model to reevaluate the mechanical properties and its interacting mechanism of human dentine.Method:By using a porous proteinmineral mechanics model,the effect from the interactions between tubules,pedtubular and intertubular matrix on dentine microstructure was discussed.Results:The dentinal micromechanical properties were dependent on the tubular direction,and the absolute values of the stresses derived from the hydraulic and gas tubular pressures increased parabolically with theincreasing diameter of the tubules.It was also found that the effective elastic constants of the dentine microstructure would vary with the aging and the distribution of mineral and collagen within peritubular and intertubular matrix of detine.Conclusions:The theoretical analyses provided in this paper demonstrated that the microstructural characteristics of tubules,peritubular and intertubular dentinal matdx could have different influences on the micromechanical properties of human dentine,which showed the validity of porous protein-mineral mechanics model,and the limitation of some models that neglected the interacting mechanism.

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Experimental study on biomechanical property of the Skin in pig's back

Xinfeng WU ; Guozheng KANG ; Linmao QIAN

Journal of Medical Biomechanics.2009;24(6):452-457.

Objective To investigate and evaluate the biomechanical property of the skin in pig's back in order to provide the essential theoretical basis for clinical and skin products.Method Taking the skin in pig's back as experimental material,the monotonic tensile and cyclic tension-tension tests with difierent loading rates was researohed respectivaly.Meanwhile,with different loading directions and stress levels the creep and cy-clic tension-tension tests were also been studied experimentally.Result The capacity of resisting tensile,creep and cyclic deformation of pig's skin in the direction along the Langer's line is stronger than that perpen-dicuiar to the Langer's line.The creep curve of pig's skin is load-dependent and consisted of three phases a-bout deceleration phase,stabilization phase and destruction stage.Pig's skin exhibits apparent ratcheting un-der asymmetry stress cycle.Ratcheting deformation displays significant mean stress,stress amplitude and loading speed dependence.Condusion Based on the experiment,the biomechanics property of skin's vis-coelasticity and anisotropic feature have been sysmarie stadied,it's provide necessaw theoretical fundation for clinical and leather products.

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Effects of adhesive thickness on internal stress distribution in fullceramic crowns

Bin LIU ; Chenglin LU ; Xiuyin ZHANG ; Dongsheng ZHANG

Journal of Medical Biomechanics.2010;25(1):56-62.

Objective To investigate the effects of the thickness of the adhesives(3 M ESPE RelyX ARC)on the internal stress distribution of the IPS Empress Ⅱ full-ceramic crowns by using Finite Element Analysis(FEA).Method A dummy Empress Ⅱ ceramic crown restoration of the mandible right first molar was prepared according to standard dental process.Followed by micro-CT scanning,four 3D numerical models with cement thickness 60,90,120 and 150 μm were established respectively.The models were subjected to four loading conditions and stresses in veneer and core layers were presented.Result Numerical results indicate that when adhesive thickness increases from 60 μm to 90 μm,the maximum principal stress either in veneer or core decreases.However,when thickness increases to 150 μm,stress variation trends differ from adhesives.Conclusions The normal stresses in adhesives remain a low level when the thickness varies from 90 μm to 120 μm,while the shear stress is less sensitive to the thickness when it exceeds 90 μm.There is an optimal thickness which can reduce the tensile stress in the core and veneer.Attention should be paid to the shear strength of the adhesives since the shear stress could cause failure in the adhesive layer.

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Three-dimensional finite element numerical analysis of the Ni Ti shape memory alloy clutching internal fixator

Guoping CHEN ; Yubo FAN ; Daiquan ZHANG

Journal of Medical Biomechanics.2010;25(1):36-39.

Objective Clutching internal fixtor(CIF)loose and the fixed part weakly heal up are often found in orthopedic clinic.In the present paper,biomechanics methods were used to try to explain and analyze these issues,providing a helpful suggestion for the application of CIF in clinic.Method Commerical finite element models(FEM)Program ANSYS was applied to set up the finite element models of orthopedic CIF and bone tissue to analyze and evaluate the biomechanical performances of the NiTi shape memory alloy CIF.Results There is an interaction force between embracing force of CIF and resistant force of bone tissue during the orthopedic clinical treatment.The embracing force along two semi-circular arms of CIF is increasing from the open position and reached the maximum value at the open symmetry position where the deformation of the bone occurred.Conclusion It is the key to choose the force loading position during the practical treatment,as the concentration force is the main force when there is an interactive force between the bone and the CIF.

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Diagnosis value of urodynamics in patients with benign prostate hypertrophy

Zhihua ZHOU ; Yawei WANG ; Liang YING ; Ming LUO ; Fang QIU

Journal of Medical Biomechanics.2010;25(1):74-76.

Objective To evaluate the diagnosis value of urodynamics in patients with benign prostate hypertrophy(BPH).Method With urodynamic device,the full set of urodynamic exam was administrated in 427 patients with BPH,and the externalsphincter urethral myogram was monitored simultaneously in pressure-flow studies(PFS).The umdynamic finding such as Q_(max),P_(det)-Q_(max),DS(descending slope)and post-voiding residual(PVR)were recorded,as well as the situation of bladder detrusor constraction and bladder compliance and urethral sphincter coodination.The bladder outflow obstruction was diagnosed by A-G nomogram,P-Q plot and DS.The IPSS score and prostate volume were also acquired.Results The diagnostic rate of BOO is 81.5%,among them concomitantly detrusor muscle impair in 117 cases (27.4%),decreased bladder compliance in 162 case(37.9%),urethral sphincter dyssynergia in 148 cases(34.7%),and unstable bladder in 164 cases(38.4%).The increase degree of BOO show an increasing tendency with urodynamic finding such as Q_(max),P_(det)-Q_(max),P_(open),DS,IPSS score and prostatic volume respectively,but a decreasing tendency with Q_(max) and bladder compliance.Conclusions The urodynamic exam plays an important role in diagnosis of BOO.There is a positive relation among degree of BOO with urodynamic findings such as P_(det)-Q_(max),P_(open),DS and IPSS score and prostatic volume,however,a negative relation with Qmax and bladder compliance respectively.

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Contribution of co-contraction to arm impedance in the free planar movement

Chunjiang FU ; Rubin WANG

Journal of Medical Biomechanics.2009;24(6):427-433.

Objective Impedance control plays an important role in stability.This paper intends to explore such mechanism through modeling human reaching movement.Method Implemented with revised model,we ap-ply optimal control theory to neuro-muscle-skeleton model to calculate the stiffness ellipses.Result Com-pared with the original model and experimental figures,the model we proposed could overcome the shortage of monotonous changing of the original one and fit the data better.Conclusions So that this paper concludes that co-contraction contributes to impedance control even during free upper limb planar movement.

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Advances of mechanical conditions in engineering cartilage tissue

Chunqiu ZHANG ; Minlin SUN ; Jiang LI ; Jinduo YE ; Haiying LIU

Journal of Medical Biomechanics.2009;24(6):462-467.

There are many physical factors affecting the development of cartilage tissue,the mechanical con-dition is the main important one that particularly act.The mechanical conditions used in engineering cartilage tissue,such as compressive and shear force,fluid flow,hydrostatic pressure and tissue deformation or with some of them combined,were reviewed.From the standpoint of bionics,the mechanical environments ap-plied on tissue engineering should work in three aspects:providing adequately mechanical stimuli to the cells seeded in 3-D scaffold;ensuring the efficient mass-transport of the nutrients and waste products in the cells:promoting the development of functionally extracellular matrix in 3-D scaffold.The mechanical environments currently used only represented the part of mechanical conditions of in vive articular cartilage will be reviewed.In our view that rolling depression load may achieve the fit mechanical environment for cultivation of functional cartilage constructs in vitro.

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Fatigue life analysis of coronary stent by finite element analysis

Jianjun LI ; Qiyi LUO ; Zhiyong XIE ; Yu LI

Journal of Medical Biomechanics.2010;25(1):68-73.

Objective After the implantation,coronary stent is expected at least to keep its integrity and maintain the predicated function for over 10 years or 4e8 cycles under the pulsatile loading conditions,so the fatigue property of the stent should be evaluated.Method The finite method was used to analyze the stress distribution of different phases and evaluate the fatigue life according to Goodman criteria,meanwhile,the accelerated fatigue experiment was also performed.Results It can be concluded that the dangerous points are all but located in the lateral inner surface of stent curvature.Conclusions The results prove that the fatigue property can be simulated through the finite element analysis,which can provide the theoretical guidance for the stent design.

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Three-dimensional limited element analysis of the complication after resection of head of radius for adults

Jianxin ZHANG ; Hongbo TIAN ; Riqi CHEN

Journal of Medical Biomechanics.2009;24(6):444-447.

Objective To adopt a three-dimensional limited element analytic method to research into the cause and mechanism of the complications taking place after resection of head radius.Method To adopt a three-dimensional limited element analytic method to research into the stress transmission action of the head radi-us and the distribution alteration of the stress transmission after resection of head radius impacting on the stability of elbow and wrist.Result In normal cases,the stress value transmitted via head of radius takes 58% of the stress placed,36.85% via humeroulnar joint.The head of radius places a leading role in the stress transmission of the elbow joint.After rasection of the head of radius,the lateral of humeroulnar joint bears about 43% of the stress placed while the medial part bears about 21.6% of the stress.To compare with that before the resection of the head of radius the stress on the lateral is obviously increased more than the medial part.Conclusions The head of radius places a leading role in the stress transm ission of the el-bow joint.The resection of the head radius breaks the normal distribution of the stress on the elbow joint and produces great effect on the stability of the elbow joint and wrist joint.Therefore,in clinics we should pay great attention to the indication of rasection of the head of radius.

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JCS-based method on coordinate transformation of attachment points between muscle and bone

Gang TANG ; Wenting JI ; Yuanchao LI ; Chengtao WANG

Journal of Medical Biomechanics.2010;25(1):40-44.

Objective In order to avoid potential injuries imposed to human body,it could be feasible to use the musculoskeletal models which can be reconstructed from the cadaver color cryosection(CCC)images,computerized tomography(CT)images,magnetic resonance(MR)images or other images to analyze the dynamic properties of muscles in vivo during human movement.Mothod We reconstruct the lower limb musculoskeletal model and define the uniform ioint coordinate system(JCS)on the model and the subject.The coordinate transformation of the muscle attachment points both on the model and the subject is described in detail.Results The length and the moment arm of the biceps femoris(short head)during knee flexion are calculated and analyzed.Conclusion This method plays an important role in improving the kinematics and dynamic simulation and the muscle force estimation.

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