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BACKGROUND: Post and core crowns are used in the clinic under some conditions, including root fractures, broken posts, and post-core detachment caused by large-scale dental caries and defects. Dentists mainly increase the retentive force by selecting a bonding material with stronger adhesion or by making a retentive groove parallel to the long axis on the surface of the core, but the effect is not obvious. OBJECTIVE: To investigate the effect of different types of retentive grooves and two different adhesives on the retentive force after the post-core crown restoration. METHODS: Sixty cobalt-chromium alloy metal crowns and post-core modules simulating the morphology of mandibular premolars were prepared. The axial cohesion angle of the cores was 8°. These crowns and post-core modules were randomly divided into six groups with 10 crowns/pieces per group. In the smooth group, there was no auxiliary retentive groove on the post-core surface. In the horizontal and vertical groups, there were retentive grooves with equal spacing parallel to(horizontal group) or perpendicular to(vertical group) the long axis of the post and core. In the oblique group, the retentive grooves were placed with an oblique angle of 45° with the long axis of the post-core. In the mesh group, the retentive grooves were at an oblique angle of 45° with the long axis of the post and core and crossed. In the point group, the retentive grooves were dot-shaped. In all six groups, glass ionomer cement and self-curing resin adhesive were used to bond post-and-core with crown. The retentive force in each group was tested by the tensile test, and the displacement change of three-dimensional finite element model during the same time was analyzed by the finite element analysis. RESULTS AND CONCLUSION: (1) Regardless of whether it was bonded with glass ionomer cement or self-curing resin adhesive, the retentive force was highest in the mesh group and lowest in the point group. There was no interaction between adhesives and retentive grooves used to increase retentive force(F=0.26, P=0.91). The effect of different adhesives on retentive force was not significant(F=1.04, P=0.31). The effect of different auxiliary retentive grooves on retentive force was significant(F=14.74, P < 0.05). (2) When the same force was applied at the same time, the displacement of three-dimensional finite element model was smallest in the mesh group. (3) These results suggest that preparation of retentive grooves on the post-core surface can enhance the retentive force. Mesh-shaped retentive grooves provide the greatest retentive force. Different types of adhesives do not provide obviously different effect on the retentive force between the crown and the post and core. [ABSTRACT FROM AUTHOR]

To obtain a larger embedding capacity and better imperceptible stego-images, we propose a new image steganography algorithm using wavelet contrast and modulus operation based on the visual characteristic that humans are not sensitive to rapid changing areas and dark areas. Firstly, the carrier image is divided into blocks with a fixed size and the wavelet contrast is calculated. Secondly, the embedding depth of each block is determined according to the wavelet contrast. Finally, secrete data is embedded into the image through modulus operation. Experimental results show that the proposed approach provides both larger embedding capacity and higher image quality. [ABSTRACT FROM AUTHOR]

Objective To investigate the influence of different neck shaft angle,torsion angle,and elastic modulus in the force characteristics of the cancellous bone of the femoral neck. Methods A sensor was implanted in the cancellous bone of the femoral neck. The bone under two loading rate and four kinds of load was tested using Instron testing machine. Results The larger the neck shaft angle was,the smaller the force of the cancellous bone of femoral neck bore. The larger the torsion angle was,the smaller the force it bore. The modulus of femur neck was related to the force that the cancellous bone of femoral neck bore. Rapid impact made the cancellous bone of the femoral neck stood larger force. When the force was beyond the elastic deformation of the cancellous bone,compressive load under slowspeed made cancellous bone stood greater stress. Conclusion Normal neck shaft angle and torsion angle are beneficial to the bearing capacity of the cancellous bone. When neck shaft angle gets larger,the cancellous bone stands less force,which is not beneficial to the stability of the cancellous bone of femoral neck. Especially in osteoporosis,the cancellous bone becomes sparse,which is vulnerable to the load and is prone to fracture. Larger torsion angle and less force standing by the cancellous bone can also cause the thinning of the cancellous bone and higher risk of fracture. [ABSTRACT FROM AUTHOR]

Glubam is a type of natural bamboo-fiber reinforced polymer composites. This paper focuses on the fundamental mechanical properties of glubam, including its modulus, tensile, compressive, flexural and shear strengths. Because glubam is a new structural material, there is no code or guideline to follow. By referring to relevant timber codes, including GB 1927 ~ 1943--1991 ' Wood physical and mechanical properties test method' and ASTM D143-94 (2007) 'Standard test methods for small clear specimens of timber', considerable number of tests were conducted to obtain the values of modulus, tensile, compressive, bending and shear strengths. The relationships between tensile strength, and modulus and the main fiber orientation were studied. The tests also reveal that cold glued joints between glubam surfaces can weaken the compressive strength. Through the discussion on design methods of glubam structure, the recommended allowable stress values were given based on the Chinese allowable stress design method of timber and favorable design results were found compared with other types of glue laminated timber. [ABSTRACT FROM AUTHOR]