ABSTRACT
BACKGROUND: Segmental defect of mandible is often caused by tumor, trauma and other reasons. Simultaneous mandibular defect by vascularized fibular flap is the most important repair method at present. It is not only useful for the reconstruction with titanium plates, but also useful for small titanium plates for fixation. Clinical retrospective studies have shown that there is no significant difference in postoperative complication rate between patients with the two fixation methods, but relevant biomechanics studies are still lacking at present. OBJECTIVE: The three-dimensional finite element analysis was used to analyze the stress distribution and stability on mandibular segmental defects simulated fibular flaps grafted with reconstruction plates and miniplates fixation. METHODS: A healthy adult male with complete dentition was selected for CT scan and data were input into the computer to reconstruct the mandible and dentition model. Three types of 3D models were built for mandibular defects dependent on Jewer’s classification, including models H (loss of lateral mandible, mandibular angle, ascending branch of mandible, and condyles), L (loss of unilateral mandible) and C (loss of bilateral mandible chin). Mechanical distribution features and stability of fixation with reconstruction plates and miniplates were comparatively studied after fibular repair of mandibular segmental defects. RESULTS AND CONCLUSION: (1) The stress graphs showed that stress was mostly higher in surrounding areas of normal mandibles such as condyle, condylar neck, mandibular angle, molar and titanium screws. In particular, the stress was highest near mandibular angles. (2) For type-H defect, the great stress was generated near the mandibular angles when mandible was reconstructed with reconstruction plate, and the stress value was 185 MPa. The stress values approximately ranged from 117 to 135 MPa on type-H and type-L defects with miniplates. The maximum stress of fibula block was less than 30.4 MPa, and the maximum stress of titanium nail was 56.2 MPa. (3) The relative displacements approximately varied between 15 µm and 18 µm on the fracture sides after repair with type-H and type-L defects with miniplates and reconstruction plates. Almost no relative displacement was generated on the fracture sides after type-C mandibular defects. (4) Both titanium reconstruction plates and titanium miniplates could meet biomechanical requirements for fibular repair of H, C, and L defects.
ABSTRACT
Objective To study corrective method for displacement in the procedure of electronic portal imaging device (EPID)-based intensity-modulated radiotherapy dose valuation by studying the relative mechanical displacement of different vendor EPID (aS1000,Varian; aS500,Varian; iViewGT,Elekta).Methods A 5 cm × 5 cm field was set up to acquire portal images for three kinds of EPID,then a in house software was used to analysis the portal images.The relative displacement was acquired via analyzing a series of comparation between center positions of gantry angle ranging from 0° to 360° and gantry angle at 0°.Results In the lateral direction,the maximum relative displacement of EPID with aS1000,S500 and iViewGT were (-0.23 ±0.17) mm,(2.94±0.17) mm and (0.35 ±0.09) mm,respectively.In the longitude direction,the displacements were (-4.16 ± 0.20) mm,(-4.15 ± 0.25) mm and (-1.66 ±0.11) mm,respectively.As to longitude direction,the displacements could be well fitted with the usage of quadruplicate empiric function.Conclusions There is a significant difference at the aspect of relative displacement between different vendors EPID at different gantry angles.And the displacement in the longitude direction is obviously larger than in the lateral direction.The relative displacement should be corrected when applying EPID to the intensity-modulated radiotherapy dose verification at different gantry angles.
ABSTRACT
Objective To construct and validate the 95th percentile finite element model of Chinese human head, evaluate the relative displacement between the skull and brain according to four types of skull brain relative displacement experiments as references, and investigate the shear strain distributions on the brain. Methods By comparing the relative displacement curve derived from the experiment and simulation and referring to conclusions from animal and physical experiments, the position of higher shear strain was investigated. Results High correlations could be found between the simulated and experimental results for skull brain relative displacement. Peaks and troughs could always appear in curves of skull brain relative displacement due to the fact that the brain tissue tended to return to its initial state. The results that higher strain could occur at temporal lobe of the brain, corpus callosum and brain surface were consistent with conclusions from the animal and physical experiments. ConclusionsT he 95th percentile finite element model of Chinese human head is validated with good biofidelity. Due to the rotational motion of human head, higher shear strain will occur on brain surface and in deep brain, leading to injuries, which provids a scientific theoretical basis for the study on injury mechanism of human head in traffic accidents.
ABSTRACT
STATEMENT OF PROBLEM & PURPOSE: The purpose of this study was to investigate the effect of a mouth guard material properties on the skull and brain when they were under impact loads on mandible. MATERIAL AND METHODS: Two customized mouth protectors having different material propeerst ieach other were made for a female Korean who had no history of brain trauma, no cerebral diseases, nomal occlusion and natural dentition. The 3D finite element model of human skull and brain scanned by means of computed tomography was constructed. The FEM model of head was composed of 407,825 elements and 82,138 nodes, including skull, brain, maxilla, mandible, articular disc, teeth and mouth guard. The stress concentrations on maxillary teeth, maxilla and skull with two mouth guards were evaluated under oblique impact load of 800N onto mandibular 3 loading points for 0.1sec. And the brain relative displacement was compared in two different mouth guard materials under same condition. RESULT AND CONCLUSION: The results were as follows; 1. In comparison of von Mises stress on maxillary teeth, a soft mouth guard material had significantly lower stress values on measuring point than a hard mouth protector materials (P < .05). 2. In comparison of von Mises stress on maxilla and skull, A soft mouth protector material had significantly lower stress values on measuring point than a hard mouth protector materials (P < .05). 3. For impact loads on mandible, there were more stress concentrated area on maxilla and skull with hard mouth guard than soft with mouth protector. 4. For impact loads on mandible, brain relative displacement had little relation with mouth guard material properties. In results of this study, soft mouth guard materials were superior to hard mouth guard materials for mandible impact loads for prevention of sports injuries. Although the results of this study were not enough to figure out the roles of needed mouth guard material properties for a human head, we got some knowledge of the pattern about stress concentration and distribution on maxilla and skull for impact loads with soft or hard mouth protector. More studies are needed to substantiate the relationship between the mouth guard materials and sports injuries.