| Objectives: To investigate the influence of varying the surrounding gingival porcelains on the color of metal ceramic prosthesises so as to provide experimental reference to the clinical application of correct color matching and recurring.Methods: 1. Models preparation: thirty disks with 15mm in diameter and 0.4mm in thickness were cast by use of a lost wax technique.30 disks were divided into 6 groups,each of which has5 disks.A2 opaque was applied in groups A,B and a . A4 opaque was applied in groups C,D and b.All opaques were fired by use of a twice-fire technique.The opaque thickness was limited to 0.25±0.01mm..Different dentin porcelains and gingival porcelains were used in each group:experimental group:group A:A2 dentin porcelain and pink gingival porcelain;group B:A2 dentin porcelain and dark pink gingival porcelain; group C:A4 dentin porcelain and pink gingival porcelain; group D:A4 dentin porcelain and dark pink gingival porcelain;Control group:group a:A2 dentin porcelain; group d:A4 dentin porcelain.The thickness of all dentin porcelains and gingival porcelains was 1.0±0.01mm.The firing numbers of all specimens were same.After the same final finishing of the porcelain surface,all specimens were ultrasonically cleaned posterior to natural glazing procedure.2,Roughness measuring:each sample was determined by topographer.3,Analysis of samples:A SpectrascanPR-650 spectrophotometer was used to analyze the samples in the dark room,with a D65 light source,45°/0°geometry, at a 45 degree angle. Before evalution session,the instrument was calibrated against a white working standard.After half an hour of warm-up,the center of each sample disk was measured three times.Take the mean value as the result of each sample. Colormetric data were recorded as CIE-LAB values.Results:1 The roughness(Ra) of each group:group A:0.25±0.034, group B:0.23±0.051, group C:0.25±0.06, group D:0.23±0.042, group a:0.24±0.037, group b:0.24±0.09.There were not different statistically among groups.2 The influence of gingival porcelain on the color of dentin porcelain: The colormetric datas of each group were:group A:L~*76.24±0.09,a~*4.26±0.32,b~*23.23±0.22,C~*ab23.62±0.19,H0ab79.35±1.03;group B:L~*76.08±1.21,a~*4.61±0.40,b~*21.95±0.64,C~*ab22.44±0.67,H0ab78.39±1.26;group C:L~*66.04±0.10,a~*6.14±0.13,b~*30.30±0.19,C~*ab30.91±0.16,H0ab78.58±0.46;group D:L~*65.78±0.18,a~*6.22±0.13,b~*30.16±0.27,C~*ab30.80±0.24,H0ab78.27±0.37;group a:L~*77.44±0.24,a~*3.86±0.02,b~*24.02±0.47,C~*ab24.34±0.45,H0ab80.85±0.22;group b:L~*66.56 ±0.20,a~*5.69±0.03,b~*31.11±0.17,C~*ab31.63±0.17,H0ab79.66±0.12。There were differences of gingival porcelain on the color of dentin porcelain:Compared to control group,the color of dentin with surrounding gingival porcelain was changed:There were a decrease of L~*,b~*,C~*ab and H0ab and a increase of a~*. These were different statistically.The color differences(?E) of experimental groups and control groups were: the ?E of group B and group a is 3.41NBS; group A and group a is 1.44NBS; group D and group b is 1.34NBS; group C and group b is 1.06NBS;the influence of dark pink gingival porcelain on the same dentin porcelain is larger than pink gingival porcelain:L~* and b~* are larger,a~* is smaller.And there were differences statistically(P<0.05).Compared to group B,b~*,C~*ab and H0ab of group A were increased. And there were differences statistically(P<0.05).The ?E of group A and group B is 1.34NBS. Compared to group D,L~*of group C was increased. And there was different statistically(P<0.05).The ?E of group C and group D is 0.31NBS.Conclusion: 1 There was influence of surrounding gingival porcelains on dentin porcelains.Different surrounding gingival porcelains lead to the different influence on dentin porcelains.2. The influence of dark pink gingival porcelain on the same dentin porcelain is larger than pink gingival porcelain.3.Lighter dentin porcelain is influnced easier than the darker one ,in the same surrounding of gingival porcelain.
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