The Research On Optical Properties Of Four All-ceramic Materials

Due to their superior aesthetics, suitable thermal expansion coefficient, excellent biocompatibility and no adverse effect on Magnetic resonance imaging, all-ceramic material has become the first choice for aesthetic prosthodontics. In recent years, with the innovation of material technology, resin adhesive technology and computer aided design/computer aided manufacture (CAD/CAM), all-ceramic materials is more and more commonly used and the mechanical properties of them can meet the clinical requirements nowadays. In addition to mechanical properties, all-ceramic material also has many optical properties, such as color parameters and translucency, which is critical during prosthodontic treatment, and can be effected by the complex physical and chemical environment in oral cavity. How about the optical properties of all-ceramic materials? Dose all-ceramic material can correctly reflect the results of colorimetric? Dose those optical properties remain stable? These are all important questions should be considered during aesthetic prosthodontics.Objective:The purpose of this study is:1. To compare the optical properties of four commonly used all-ceramic material and calculate the color difference between them and the standard colorimetric.2. To evaluate the stainability of leucite-reinforced glass ceramic, lithium disilicate glass ceramic, lithium disilicate glass ceramic blocks and feldspathic ceramic blocks upon exposure to different staining agents.Methods:Ten slice specimen 1.00±0.01mm in thickness of each kind of the four ceramic materials(IPS Empress(?) CAD(A2, HT), IPS e.max(?) press(A2, HT), IPS e.max(?) CAD(A2, HT) and VITABLOCS(?) Mark Ⅱ(A2)) were fabricated according to the manufacturer’s instructions and were ground and polished on a grinding machine. Then colour parameters L*、a*、b* and transmittance τ were measured using spectrocolorimeter and transmissivity testing device.Forty flat specimens (1 mm in thickness, n=20;0.5 mm in thickness, n=20) were fabricated for each of a leucite-reinforced glass ceramic (IPS Empress(?) CAD), a lithium disilicate glass ceramic (IPS e.max(?) Press), a lithium disilicate glass ceramic blocks (IPS e.max(?) CAD) and a feldspathic ceramic blocks (VITABLOCS(?) Mark II) ceramic material, according to the manufacturer’s instructions. All of the specimens were wet-ground and polished on a grinding machine.The 4 ceramic material specimens were divided into 4 groups (n=5) and stored for 8 days at 37℃ in four different types of solutions:coffee, red wine, green tea and black tea. Color of all specimens was measured before and after immersion with a colorimeter using CIE L*a*b* system, and color changes (△E) were calculated using the fomula △E=[(△L*)2+(△a*)2+(△b*)2]1/2. The data were analyzed with a standard two-way analysis of variance (ANOVA), and mean values were compared by the Tukey HSD test (a=0.05).Results:There is no statistical difference between the color parameters L*、a*、b* and C*ab of IPS Empress(?) CAD and VITABLOCS(?) Mark Ⅱ. But the color parameters of those two ceramic materials were statistically different from the color parameters of IPS e.max(?) Press and IPS e.max(?) CAD. There is no statistical difference between color parameters b* and C*ab of IPS e.max(?) Press and IPS e.max(?) CAD. However, the color parameters L* and a* of the two materials were statistically different. The transmittance τ data of the four ceramic materials were statistically different too. They were 29.69%(0.31)、25.83%(0.36、28.92%(0.47) and 26.94%(0.33) respectively.For IPS Empress(?) CAD, the lowest △E values were observed in Group Coffee (0.12,0.12) and Group Red Wine(0.13,0.14).The highest color difference was observed in Group Green Tea(0.50,1.08). For IPS e.max(?) Press, the lowest color difference was observed in Group Coffee(0.19,0.22), while the highest color change was observed in Group Black Tea(l.07,0.88). For IPS e.max(?) CAD, the lowest color difference was observed in Group Coffee(0.10,0.12). Group Green Tea(0.50,0.55) and Group Black Tea(0.53,0.56) demonstrated the highest color changes among this material. For VITABLOCS(?) Mark II, the lowest color difference was observed in Group Coffee(0.24,0.27). The highest color change was observed in Group Green Tea(3.39,4.15), which was the highest color change among all the groups in this study. The color difference in Group Black Tea(1.73,2.03) was also higher than the other materials tested.When comparing the four staining agents, the lowests color changes for all ceramic materials were observed in the coffee and red wine groups. While the highest AE values were observed in the green tea and black tea groups.Conclusions:1. The color parameters of these four materials are different. Their transmittance are relatively high but statistically different.2. The ability to reflect the results of colorimetric of IPS e.max(?) CAD is highest during the four materials. It can be used in esthetic prosthodontics.3. The largest color difference was observed in the feldspathic ceramic blocks material and it was found less color stable than the leucite-reinforced glass ceramic, lithium disilicate glass ceramic and lithium disilicate glass ceramic blocks materials tested.4. Green tea and black showed higher discoloring capability compared to coffee and red wine.