In vitro cell proliferation evaluation of porous nano-zirconia scaffolds with different porosity for bone tissue engineering.

The selection of scaffold materials and the optimization of scaffold morphological and mechanical properties are critical for successful bone tissue engineering. We fabricated porous scaffolds of nano-sized zirconia using a replication technique. The study aimed to explore the relationship between porosity, pore size, mechanical strength, cell adhesion, and cell proliferation in the zirconia scaffolds. Macro- and micro-structures and compressive strength were comparatively tested. Beagle bone marrow stromal cells were seeded onto the scaffolds to evaluate cell seeding efficiency and cell proliferation profile over 14 d of incubation. The zirconia scaffolds presented a complex porous structure with good interconnectivity of pores. By increasing the sinter cycles, the porosity and pore size of the scaffolds decreased, with mean values ranging from 92.7-68.0% and 830-577 µm, respectively, accompanied by increased compressive strengths of 0.6-4.4 MPa. Cell seeding efficiency and cell proliferation over the first 7 d of incubation increased when the porosity decreased, with cell viability highest in the scaffold with a porosity of 75.2%. After 7 d of incubation, the cell proliferation increased when the porosity increased, highest in the scaffolds with a porosity of 92.7%. These results showed that the zirconia scaffold with a porosity of 75.2% possesses favorable mechanical and biological properties for future applications in bone tissue engineering.

The effects of repeated heat-pressing on the mechanical properties and microstructure of IPS e.max Press.

OBJECTIVES: We evaluated the effects of repeated heat-pressing on the mechanical properties and microstructure of IPS e.max Press. METHODS: A total of 20 specimens were fabricated including 10 heat-pressed once and another 10 heat-pressed twice. The density, porosity, and surface roughness (Ra) were evaluated. Three-point flexural strength following the ISO 6872 and Vickers hardness were measured, and fracture toughness (KIC) was calculated. Specimens were characterized using X-ray diffraction (XRD) and scanning electron microscopy (SEM). RESULTS: Compared to a single heat-press treatment, the density decreased and porosity increased after two heat-pressing events. A significant difference in density was observed. The flexural strength, Vickers hardness and fracture toughness significantly decreased after two heat-pressing events. The XRD patterns show that the intensity of the crystalline phase better corresponds to lithium disilicate (Li2Si2O5) after two heat-presses than only one. The SEM images detailed the interlocking microstructure of rod-shaped Li2Si2O5 crystals after one heat-press. These became oriented after two heat-presses, and the crystal size became larger. CONCLUSION: This study showed that repeated heat-pressing was detrimental to the density, porosity, strength, hardness, and toughness of IPS e.max Press.

[Study on friction and abrasion behavior of TiN film on dental NiCr alloy by plasma magnetron reactive sputter deposition].

PURPOSE: To investigate the effect of TiN film deposited by plasma magnetron reactive sputter deposition technique on the fiction and abrasion behavior of dental NiCr alloy. METHODS: TiN film was deposited on the surface of dental NiCr alloy by plasma magnetron reactive sputter deposition technique. Surface topography of TiN film was observed by electron microscope. The frictional coefficient and abrasive loss in weight were measured by friction and abrasive apparatus. SPSS11.0 software package was used for Student's t test. RESULTS: The surface topography of TiN film was tiny diffusion and homogeneous distribution common burreed tuber structure. The average frictional coefficient of NiCr of none deposition was 0.651 while 0.525 after TiN deposited (P<0.05). The average abrasive loss in weight of none deposition was 0.0113g while 0.0007g after TiN deposited (P<0.05). CONCLUSIONS: Compared with non deposition NiCr, the fiction and abrasion behavior of NiCr with TiN film deposited by plasma magnetron reactive sputter deposition technique is better.