The Comparison Of Relative Properties For RF Zirconia Ceramics And Imported Zirconia Ceramics

Zirconia ceramics have many advantages, such as good biocompatibility, excellent aesthetic properties, high mechanical properties, and adopt advanced CAD/CAM techniques, which not only reduce the labor intensity of technicians, but also significantly improve the production efficiency. It is the advantages of processing methods and their performances that promote the development of machinable zirconia ceramics in the area of oral prosthodontics. Now there are more than ten kinds of machinable zirconia ceramic products in the market, but most of them are imported products. Because of high costs and the need of suitable CAD / CAM systems, it has some limitations to clinical use. Compared with those imported products in many aspects of performances, the domestic machinable zirconia ceramics had many defects, and there are few clinical reports on it.Using the technology route of fabricating high performance dental restorations via CAD/CAM system processing -full sintering - veneering with porcelains three steps method, RF zirconia ceramics were developed by Forth Military Medical University and Royal Dental Lab. Early study showed that biocompatibility and radioactivity could meet the national standard with good biological performances and it could be used as clinical material. On the base of early research, this study detected the machinability, shrinkage, physical properties and mechanical properties of RF zirconia ceramics, which could provide experimental basis for its clinical application in the future. At the same time, compared with two widely used zirconia ceramic on abroad, this study evaluated zirconia ceramic in many aspects of performances, in order to replace imported products and reduce costs, finally open the domestic market of the application of zirconia ceramics.Contents and methods:(1) Used the methods of measureing Milling index, cutting time and observing the frameworks, the machinabilities of RF, YZ, ZirCAD zirconia ceramics were evaluated, then the microstructure of each ceramics were analyzed by SEM.(2) Used digital vernier caliper to measure the length of RF, YZ, ZirCAD zirconia ceramic specimens before and after sintering, the linear shrinkage rates of three ceramics were calculated.(3) In order to evaluate the sintering extent, the density of RF, YZ and ZirCAD zirconia ceramics were measured by Archimedes principle. To provide experimental basis for the next step, the CTE of three ceramic were measured.(4) Evaluated the mechanical properties of RF, YZ, ZirCAD zirconia ceramics by measuring hardness, fracture toughness, bending strength, and the study explored the relationship between mechanical properties and microstructure with XRD and SEM methods.Results:(1) The milling indices of RF, YZ and ZirCAD zirconia ceramics were: (2.88±0.02)μm^1/2, (2.90±0.02)μm^1/2, (2.82±0.03)μm^1/2; milling time were: (512±1.82) s, (510±1.92) s, (517±1.92) s. The Milling indices and milling time results showed that there were no statistically significant difference between RF and YZ, but ZirCAD was statistically significant different with the other two(P<0.05). All the frameworks'surface was smooth, without cracks and collapses. All the indications showed that RF, YZ, ZirCAD zirconia ceramic had good machinability. The machinabilities of RF and YZ zirconia ceramics were better than the machinabilities of ZirCAD zirconia ceramics.(2) The linear shrinkage rates of RF, YZ, ZirCAD were: (19.88±0.17) %, (20.00±0.20) %, (20.10±0.21) %, each sample was smooth, and no distortion. The results showed that RF zirconia ceramics's shrinkage could be controled by calculating in order to get good restorations.(3) The density value of RF, YZ, ZirCAD these three sintered ceramic were(6.02±0.02)g/cm³, (6.03±0.03) g/cm³, (6.03±0.02) g/cm³, which showed that these three ceramic could be achieved sintered in accordance with its sintering processing. The RF zirconia ceramics had a same CTE (10.5×10^-6/℃) as YZ, which was lower than ZirCAD zirconia ceramics (10.8×10^-6/℃). It indicated that if the porcelains could be used for YZ and ZirCAD zirconia ceramics, it could be also fit for RF zirconia ceramics.(4) After sintering, the hardness of RF, YZ, ZirCAD these three zirconia ceramic were (12.93±0.38)GP, (13.04±0.39)GP, (13.11±0.16)GP; the fracture toughness were (5.59±0.07) MPμm^1/2, (5.61±0.09) MPμm^1/2, (5.61±0.07) MPμm^1/2; the bending strength were (1083.41±103.81)MPa, (1106.97±224.64)MPa, (1066.82±240.92)MPa. The hardness, fracture toughness and bending strength of the three were not statistically significant different (P>0.05).In conclusions, these studies showed that RF zirconia ceramics could meet the requirements of the CAD/CAM processing and clinical application, and achieved the level of similar foreign products. In addition, the advantage of its low costs will make the application of RF zirconia ceramic a broader outlook.