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Abstract Introduction: yttrium-stabilized zirconium dioxide (zirconia) has been used to manufacture fixed partial prosthesis due to its high flexural strength. However, there are no available studies comparing the effect of two sintering techniques on flexural strength. This study aims to compare the flexural strength of zirconia sheets manufactured with two sintering techniques. Method: for this in vitro study, three zirconia disks were used (Upcera: Super Translucent (ST): 1200 MPa, Multi-Layer (ML): 600 MPa and High Translucent (HT): 1200 MPa), using an Isomet® cutter to prepare 60 sheets 2 mm thick, 5 mm wide and 37 mm long. These sheets were randomly distributed into two groups of 30: the first group was sintered for 8 hours at 1,530°C and the second group was subjected to fast sintering for 3 hours at 1,530°C. The flexural strength in Newton was measured on an Instrom® 3366 Universal Testing Machine. The results were converted from N to MPa and compared by ANOVA and t test. Results: no statistically significant difference was found in the flexural strength of the two groups (p>0,05). Conclusion: the two compared sintering procedures do not affect the flexural strength of zirconia sheets.
Resumen Introducción: las restauraciones de dióxido de zirconio estabilizadas con ytrio para prótesis parciales fijas e implantosoportadas se han utilizado por su alta resistencia flexional. En la revisión bibliográfica no se encontraron estudios que comparen la resistencia flexional del dióxido de zirconio con 2 tiempos de sinterización diferentes. El objetivo del presente estudio consistió en comparar la resistencia flexional de láminas elaboradas en 3 tipos de dióxido de zirconio con 2 tiempos de sinterización. Método: en este estudio in vitro, se recolectaron 3 discos de dióxido de zirconio (Upcera: Súper translúcido (ST): 1200 MPa, Multicapa (ML): 600 MPa y Alta translucidez (HT): 1200 MPa), y en un aparato de corte Isomet® se recortaron 60 láminas de 2 mm de espesor, ancho de 5 mm y longitud de 37 mm. Estas láminas se distribuyeron aleatoriamente en dos grupos de 30: el grupo uno se sinterizó por 8 horas a 1.530°C y el otro grupo se sometió a sinterización rápida por 3 horas a 1.530°C. La resistencia flexional se midió en una máquina universal Instrom® 3366. Los resultados fueron convertidos de N a MPa y se compararon mediante análisis de varianza y prueba t. Resultados: no hubo diferencia estadísticamente significativa al comparar la resistencia flexional después de dos tiempos de sinterización diferentes (p>0,05). Conclusiones: no se presentaron diferencias significativas en la resistencia flexional del dióxido de zirconio al comparar los promedios obtenidos con dos técnicas de tiempo de sinterización diferente.
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Flexural StrengthABSTRACT
Objective To design water-equivalent plastic scintillator detector for the measurement of absorbed dose in tumor radiotherapy.Methods The concentration of ZrO2to be doped in polystyrene was estimated according to the empirical formula,and then the Monte Carlo program Geant 4(GEometry And Tracking 4)was used to simulate the energy deposition and transport process of X-rays with different energies in water,solid water RW34(composed of 2.1 wt％TiO2doping polystyrene)and different concentrations of ZrO2particles doped in polystyrene.The dose and attenuation coefficients were compared among different materials at different depths of water.Results The doses at different depths and the attenuation coefficient of polystyrene(doped with about 0.4 wt％ZrO2nanoparticles)were much more consistent with those of water and even exhibit much better water-equivalence than RW34.Conclusions The simulation results provide the basis for the development of water-equivalent scintillator.
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Objective:To evaluate the effects of magnetron-sputtered ZrSiN/ZrO2 gradient coating on the bonding strength of commercially pure titanium to porcelain.Methods:50 cast titanium specimens were prepared according to the ISO 9693 standard,and divided into 2 groups(n =25).The ZrSiN/ZrO2 gradient coating was deposited on specimens by magnetron sputtering technique,and subsequently a low-fusing porcelain was applied for the samples in the expermental group,the samples in the control group were treated by surface sandblasting.The roughness and surface energy of the samples were measured(n =10).The bonding strength of titanium-porcelain specimens was analyzed by three-point bending test (n =10).Scanning electron microscopy (SEM) and energy-dispersive X-ray analysis (EDS) were employed to examine the properties of the delaminated and cross-sectioned surfaces.The results were analyzed by paired t-test (α =0.05) with SPSS 1 1.0 software.Results:The roughness of the experimantal group was lower(P ＜ 0.05) and the contact angle was larger(P ＜ 0.05) than those in the control group.The titanium-porcelain bond strength of gradient-coated group was greater than that of control group(P ＜0.05).The SEM and EDS examination results of delaminated and cross-sectioned surfaces also indicated that the gradient-coated group showed more porcelain residues.Conclusion:The bonding strength of porcelain-fused-to-titanium can be improved by magnetron sputtered ZrSiN/ZrO2 gradient coating.
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Objective Nowadays, in the field of bone tissue engineering , searching for a kind of scaffold , which is both strong enough and biocompatible , is still a hot topic .Objective of this study is to evaluate the three-dimensional nano-zirconia porous scaffold′s effect on bone marrow stromal cells early attachment and proliferation . Methods Preparing nano-zirconia porous scaffold and testing its porosity and its mechanical strength .Hemolysis experiment was taken to evaluate its biosafety .Canine bone marrow stromal cells ( BM-SCs) were extracted from an adult beagle and cultured in vitro.The third generation cells were seeded onto the scaffold and induced to os-teoblasts under condition medium .Cells early attachment on scaffold was observed by SEM .MTT and ALP tests were taken to evaluate cells proliferation and osteogenesis within two weeks . Results Nano-zirconia porous scaffold in our study presented a porous structure with a well connected inner .Its porosity and compressive strength were (92.667 ±0.324)%and 4.38 MPa, respectively.Hemolysis rate was 2.19%, which was demonstrated to be safe to human body .Canine BMSCs could colonize the surface of the materials , bridge macro-poros-ity and proliferate on the scaffold .A values taken by the method of MTT showed that cells could proliferate quickly on the scaffold after 3, 6, 9, 12 d (A values were 0.604 ±0.059, 1.215 ±0.019, 1.385 ± 0.254, and 1.506 ±0.050), comparing with that on the first day (A value was 0.261 ±0.034).Statistical difference was found (P <0.01) .The ALP level raised up significantly on day 7 and 14 ( A val-ues were 0.032 ±0.002 and 0.062 ±0.007), comparing with that on the first day (A value was 0.016 ±0.003).Statistical difference was found (P<0.01). Conclusion The three-dimensional nano-ZrO2 porous scaffold in our study presented satisfactory biocompati-bility.It could offer a microenvironment for osteoblasts growth and secreted osteogenesis marker in vitro .
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Hydroxyapatite(HA) has been extensively used as bone graft materials and tooth implant surface coating materials because of its biocompatibility and osteoconductive properties. However, as HA is intrinsically poor in mechanical properties, zirconia(ZrO2) was incorporated with HA as reinforcing phases for improvement of mechanical properties. The purpose of this study was to investigate the biological activities of HA-coated zirconia through the cell proliferation test, measurements of alkaline phosphatase activity, and histologic examination. Four kinds of tested blocks were prepared according to the pore size (300-500micrometer/500-700micrometer) and the porosity (70%/90%). Cell proliferation and alkaline phosphatase activity was measured at 1, 7, 14 days. The number of cells proliferate after 7, 14 days were significantly increased in all groups when compared with that of the first day, but there was no significant difference between the 4 groups at each time period. At the 7 day, alkaline phosphatase activities of cells cultured in 4 groups were higher than that of the first day, but there was no significant difference between the 4 groups at each time period. The human gingival fibroblast and MG 63 cell was used to evaluate the cell cytotoxicity using MTT test. The materials tested in the current study turned out to be non-cytotoxic. In histologic examination(SEM), at 1 day there were many cells attached on the surfaces of all kinds of tested blocks. The number of cells were increased over time. At the 14 day, there were more cells proliferated than 1 day and some of the pores of blocks were partially filled with the proliferated cells. The in vitro response of osteoblast-like cells to the HA-coated zirconia showed comparable effect on transformation comparable to hydroxyapatite.