| Objective: To analysis the laws of color changes and observe the effects of number of firing on color of nano- ceramic and traditional ceramic in metal-ceramic prosthesis. The relationship between the times of firing and color was discussed. The results were expected to provide effective experimental reference to the clinical application of nano- ceramic.Methods: 1 Models preparation: a metal die of simulating crown core was produced with precision machine. Totally 50 (in 10 groups) metal-ceramic crown models with same thickness were conventionally produced. Groups A-E were traditional ceramic with different times 4, 6, 8, 10,12. Groups A' -E' were nano-ceramic with different number 4, 6, 8, 10,12. 2 Measurement of surface roughness: Model 2205 surface roughness tester was used for measuring the mean surface roughness value (Ra) of every model. According to GB3505- 83 Surface Roughness-Terminology for Surface and Its Parameters and JJF1099-2003 Calibration Standard of Surface Roughness Specimens, the sample length was 0.8mm, the forward velocity was 1mm/second. 3 Measurement of the L*a*b* values of models: Photo Research PR-650 SpectraScan Colorimeter was used for measuring L*a*b* values. The experiment exceeded in darkness under standard lightness of D65, the length between body glasses and the model was 15cm. The light bot of body glasses was 7.0mm. The colorimeter and lighter was heated 30 minutes, then be sured by standard white board before testing. Each model was tested three times and each time tested three times by itself. The mean values were taken as color values of this model. All L*a*b* values were analyzed by SPSS 13.0 to compare the difference between nano-ceramic and traditional ceramic.Results: 1 The surface roughness values measured in various groups were (Ra): 0.376 in group A, 0.366 in group B, 0.390 in group C, 0.380 in group D, 0.364 in group E, 0.270 in group A', 0.274 in group B', 0.282 in group C', 0.262 in group D' and 0.270 in group E'. The pair-wise comparison between multiple sample averages (LSD method) showed that there was no significant difference in surface roughness value between the specimens of group A and groups B-E, group B and groups C-E, group C and groups D-E, group D and group E(P>0.05); There was no significant difference in surface roughness value be- tween the specimens of group A' and groups B' -E', group B' and groups C' -E', group C' and groups D' -E', group D' and group E' (P>0.05); There was significant difference in surface rough- ness value between the specimens of group A and A', B and B', C and C', D and D', E and E' (P<0.05). 2 Three factors of color values measured in various groups were:⑴Value (L*): 71.667 in group A, 71.829 in group B, 70.792 in group C, 70.382 in group D, 68.169 in group E, 71.862 in group A', 71.448 in group B', 72.193 in group C', 71.714 in group D ' and 70.526 in group E'. Analysis of variance (ANOVA) results showed that there was significant difference of Value on models with different times of firing (P<0.01); The pair-wise comparison between multiple sample averages (LSD method) showed that there was significant difference in Value between the models of group A and groups C-E, group B and groups C-E, group C and group E, group D and group E (P<0.05); there was no significant difference in Value between the models of group A and group B, group C and group D (P>0.05); there was significant difference in Value between the models of groups A' - D' and group E', group B' and group C' (P < 0.05); there was no significant difference in Value between the models of group A' and groups B' -D', group B and group D', group C' and group D' (P>0.05).⑵hue (a*): 1.450 in group A, 1.423 in group B, 1.445 in group C, 1.359 in group D, 1.317 in group E, 1.344 in group A', 1.335 in group B', 1.272 in group C', 1.009 in group D' and 0.705 in group E'. Analysis of variance (ANOVA) results showed that there was significant difference of hue on models with different times of firing (P < 0.01); The pair-wise comparison between multiple sample averages (LSD method) showed that there was significant difference in hue between the models of group A and groups D-E, group B and groups D-E, group C and groups D-E (P<0.05); there was no significant difference in hue between the models of group A and groups B-C, group B and group C, group D and group E (P>0.05); there was significant difference in hue between the models of group A' and groups D' -E', group B' and groups D' -E', group C' and groups D' -E', group D' and group E' (P<0.05); there was no significant difference in hue between the models of group A' and groups B' -C', group B' and group C' (P>0.05).⑶chroma (b*): 15.539 in group A, 15.335 in group B, 14.795 in group C, 14.700 in group D, 13.871 in group E, 16.278 in group A', 16.203 in group B', 15.941 in group C', 16.319 in group D' and 15.498 in group E'. Analysis of variance (ANOVA) results showed that there was significant difference of chroma on models with different times of firing (P<0.01); The pair-wise comparison between multiple sample averages (LSD method) showed that there was significant difference in chroma between the models of group A and groups C-E, group B and groups C-E, group C and group E, group D and group E (P<0.05); there was no significant difference in chroma between the models of group A and group B, group C and group D (P>0.05); there was significant difference in chroma between the models of groups A' -D' and group E' (P<0.05); there was no significant difference in chroma between the models of group A' and groups B' -D', group B' and group C' -D', group C' and group D' (P>0.05).⑷T-test results showed that there was significant difference in hue and chroma between the models of group A and group A', group B and group B' (P<0.05), there was no significant difference in Value between the models of group A and group A', group B and group B' (P>0.05); there was significant difference in three factors of color(L*a*b*) between the models of group C and group C', group D and group D', group E and group E' (P<0.05).3 The△E of every groups were: 1) 0.262 in group A and B, 1.148 in group A and C, 1.537 in group A and D, 3.878 in group A and E, 1.169 in group B and C, 1.582 in group B and D, 3.944 in group B and E, 0.430 in group C and D, 2.784 in group C and E, 2.364 in group D and E; 2) 0.421 in group A' and B', 0.477 in group A' and C', 0.369 in group A' and D', 1.674 in group A' and E', 0.792 in group B' and C', 0.437 in group B' and D', 1.320 in group B' and E', 0.664 in group C' and D', 1.816 in group C' and E', 1.476 in group D' and E'; 3) 0.772 in group A and A', 0.952 in group B and B', 1.818 in group C and C', 2.126 in group D and D', 2.929 in group E and E'.Conclusion: 1 With exceeding in the times of firing, L*a*b* of traditional ceramic prosthesis and Nano-ceramic prosthesis were changed. They showed that Value was lightened and then darkened, chroma was degraded and hue was turned into green. So we shoud avoid the times of firing. 2 In the experiment, the standard of 1.5 was the least△E which can be found by naked eyes of human beings. There was significant difference in color of traditional ceramic prosthesis when fired exceeds 10 times, but there was little difference in color of Nano-ceramic prosthesis when fired exceeds 12 times.3 When the firing times was same, the changes in color of Nano-ceramic were less than those of traditional ceramic. |
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