Objective: To evaluate the fracture resistance of endodontically treated teeth reinforced with cast titanium posts and prefabricated glass-fiber posts with different diameters. Materials and Methods: 50 recently extracted human maxillary central incisors were endodontically treated and randomly divided into 5 groups of 10 specimens each: Group A: 1.35mm diameter of cast titanium post; Group B: 1.5mm diameter of cast titanium post; Group C: 1.375mm diameter of prefabricated fiber post; Group D: 1.5mm diameter of prefabricated fiber post; Group E: resin restoration. All specimens were subjected to fracture resistance testing in a universal testing machine, statistical analysis was performed and the fracture modes were analyzed. Results: The mean fracture resistance of five groups as follows: 404.22±73.92N for group A, 488.17±78.68N for group B, 280.32±45.23N for group C, 317.53±50.87N for group D, 222.76±38.67N for group E. The fracture resistance of restored teeth between group C and group D had no significant difference (P>0.05). The fracture resistance of the rest pairwise group comparisons had significant difference (P<0.05). Most of cast post samples fractured at the root middle or apical portion, while most of the fiber post samples fractured at the root cervical or post fracture, which could be retreated. Conclusion: Human maxillary central incisors restored with cast posts could bear higher fracture load and fiber post could protect the root from fracture preferably.

A new kind of bainite steel with ultra-low carbon content and Nb, Ti alloys has been developed. By applying thermomechanical control process, water quenching and tempering at different temperature, excellent properties have been obtained when tempered at 450°C, with the yield strength of 813MPa and elongation of 16.2%. The morphology observed by SEM shows that the microstructure consists of fine lath-shaped bainite, polygonal ferrite, quasi-polygonal ferrite and a small fraction of residual austenite or martensite-austenite constituents. In a TEM study plenty of precipitates with the size about 5-10nm were observed interacting with the dislocations, which is very significant for the optimization of strength and ductility.

The co-author networks are important type of social network. In this paper, we establishes the Erdös co-author network and proves that the Erdös co-author network is a complex network which has three main properties, including small world, scale-free and clustering properties. Besides, this article gives the calculation formulas for degree centrality, closeness centrality and betweenness centrality of a network. According to the calculation result we give a ranking order for authors within Erdös co-author network.

Objective: To study the fracture resistance and failure modes of different type of ceramic crowns. Methods: Four groups of crown including zirconia-veneering porcelain crown (Group 1), whole zirconia crown (CAD/CAM, Group 2), cast ceramic crown (Group 3) and glass ceramic crown (CAD/CAM, chairside, Group 4) with the same thickness were manufactured, each group own 12 crowns. The fracture resistance test and failure modes analysis of the specimens were conducted, SPSS22.0 was used to analyze the difference among the groups. Results: The fracture strength of Group 2 is significantly higher than other three group (P<0.05), Statistical significance was found between group 3 and group 1, group 4. No Statistical significance was found between group 1 and group 4. The failure modes of the whole zirconia crown, the cast ceramic crown and the glass ceramic crown are complete crown fracture; 33% of the zirconia-veneering porcelain crown showed veneering layer fracture, the other 67% showed complete crown fracture. Conclusion: The fracture resistance of the whole zirconia crown are higher than the cast ceramic crown, the zirconia-veneering crown and the glass ceramic crown and the glass ceramic crown (CAD/CAM) is a very convenient prostheses. The failure modes are significantly influenced by the type of the crown.

To explore the effect of thickness on the fracture strength and failure modes of zirconia crowns, four crown models with different thickness (1.2 mm, 1.0 mm, 0.8 mm, 0.6 mm) with the same shape were designed by Dental Designer software in CAD/CAM system. They were manufactured to 40 zirconia crowns by CAM carving machine. The fracture strength and the failure modes of each crown was measured, while porcelain fused to metal (PFM) crowns as control. The average fracture strength of different zirconia crowns were recorded as below: 1308.38 ± 111.38 N (Group 0.6 mm), 1841.60 ± 68.21 N (Group 0.8 mm), 2429.88 ± 315.03 N (Group 1.0 mm), 3068.31 ± 233.88 N (Group 1.2 mm). There was no significant difference between Group 1.0 mm and Group 1.2 mm (P > 0.05), and statistical significance was obtained among every other two groups (P < 0.05). The failure modes of different thickness zirconium crowns are similar. There are more broken pieces from thicker crowns compared to thinner ones. It is concluded that the thickness can influence the fracture strength of zirconia crown. With the increase of the thickness, the fracture strength of the zirconium crowns also increases. We recommend zirconia crowns thicker than or at least 1.0 mm in dental practice.