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Objective: To study the effect of different wetness degrees in the root canal on the canal sealing. Methods: 160 root canal prepared single rooted teeth were divided into 4 groups (n = 40) by the root canal wetness degree (water content, V): (1) 0. 250 ～0. 299, (2) 0. 300 ～ 0. 599, (3) 0. 600 ～ 0. 899 and (4) 0. 900 ～ 1. 199 respectively. 80 teeth were divided into 4 groups (n = 20) for dye leakage test and another 80 for bacterial microleakage test. Zinc oxide paste (ZOP) and AH-Plus (AH-P) with vertical condensation of warm gutta-percha were respectively used to seal the canals in each group of the samples (n = 10) . The length of in vitro tooth dye penetration was measured by stereomicroscope; the time (days) of turbidity in the bacterial leakage model observed and compared. Results: Of all the canals sealed by ZOP or AH-P with the increase of the wetness the dye infiltration length increased significantly (P ＜0. 05) and the days in which the faecal intestine ball infiltrated into the lower chamber of the model was gradually decreased (P ＜0. 05) . Conclusion: The increase of root canal moisture may reduce the sealing of the root canal.
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Objective To biomechanically study the fixation stability of different numbers and shapes of the titanium miniplates (L-shaped and straight four-hole miniplates) in the treatment of maxillary LeFortⅠ fracture by using three-dimensional finite element method so as to provide reference for clinical treatment of the fractures. Methods Three-dimensional finite element model of maxillary LeFortⅠ fracture was established with four kinds of rigid internal fixation (RIF) methods to calculate the stress of the maxilla and the RIF as well as the displacement of the fracture segment under three kinds of occlusion.Then, the fixation stability of different methods was compared. Results Under the same occlusion condition, the decreasing order of the displacement of the fracture segment was the L-shaped plate fixation at both buttress of the maxillary and nasal maxillary zygomatic, the straight four-hole miniplates fixation at both buttress of the maxillary and nasal maxillary zygomatic, the L-shaped plate fixation at the zygomatic maxillary buttress and the L-shaped plate fixation at naso-maxillary buttress. Under the same fixation method, the decreasing order of the displacement of the fracture segment was molar occlusion, premolar oeclusion and incisor occlusion. Conclusions The fixation stability of the L-shaped plate fixation is better than the straight four-hole miniplate fixation for the treatment of LeFortⅠ fracture. Fixation at the zygomaticmaxillary buttress is better than at the naso-maxillary buttress. Use of only two miniplates to fix the LeFort Ⅰ fracture may not be stable. Molar occlusion is not good for fracture healing.
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Objective To set up the 3D-finite element(FE)model of normal acetabulum-cartilage-femoral head,so that to provide an effective model for biomechanical analysis of femoral head.Methods(1)The hip joint in one healthy adult male volunteer was scanned by MRI at coronal section.The 3D reconstruction model of acetabulum-cartilage-femoral head was constructed with MATLAB and ANSYS software.(2)The 3D orthotropy finite element model of the acetabulum-cartilage-femoral head was constructed by givig the corresponding material parameters to the different structures of the model of acetabulum-cartilage-femoral head and divided into networks through ANSYS software.(3)The standing status was imitated on the model to set boundary condition and loading and then calculated.The effect of the model was evaluated in comparison with that of literature.Results A 3D orthotropy FE model of acetabulum-cartilage-femoral head was established successfully,including 89 961 points of 448 159 units.The maximal displacement was on the femoral head,and the maximal Von Mises stress was on the femur neck.The stress analysis was the same as the results of literature and the actuality.Conclusion A 3D orthotropy FE model of acetabulum-cartilage-femoral head can be setup based on MRI images,which can provide a reasonable and effective model for biomechamical analysis of femoral head.
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Objective:To study the stress distribution dur i ng clenching and rigid internal fixation(RIF)of mandibular symphysis fracture. Methods:ANSYS software was used to establish the models of mandi bular symphysis fracture and the fracture treatment treat with RIF.The stress di stribution of mandibular symphysis fracture under different conditions were then analysed during different period of bone healthing. The value of stress shieldi ng rate was used to represent the level of stress shielding effects.Resu lts:The stress shielding rate decreased with the progression of fracture healing.The stress shielding rate produced by double plates fixation was higher than that by single plate.Stress shielding rate in the mandible fixed with tita nium plate was lower than that with steel plate.Conclusion:Minip late rigid internal fixation system may produce stress shielding effects when it is used to treat mandibular symphysis fractures. Stress shielding effects are a ffected by the attribute, the shape and the position of the plate.