The Effect Of Different Surrounding Gingival Porcelain On The Color Of Metal Ceramic Prosthesises After Repeated Firings

Objectives: To investigate the influence of varying the surrounding gingival porcelains on the color of metal ceramic prosthesises after repeated firings, so as to provide experimental reference to the clinical application of correct color recurring.Methods: 1. Models preparation: fifty disks with 30mm in diameter and 0.70mm±0.05mm in thickness were cast by use of a lost wax technique. Several models were prepared as follows:Model a with 30mm in inner diameter and 1.1mm in thickness;Model b with 30mm in inner diameter and 2.1 in thickness; Semi-ring-like model c with 10mm in inner diameter,30mm in outer diameter and 1.3mm in thickness. A2 opaque was applied. All opaques were fired by use of a twice-fire technique. The opaque thickness was limited to 0.30±0.05mm. All disks were divided into 10 groups randomly, 5 groups of which as the control group and the others as the experimental group. A2 dentin porcelain and dark pink gingival porcelain were used in experimental group; A2 dentin porcelain was used in control group. All the 5 groups in the control group and experimental group were fired 2,4,6,8,10 times(the opaque not included). The thickness of all dentin porcelains and gingival porcelains was 1.0±0.05mm. 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 evaluation session, the instrument was calibrated against a white working standard. After half an hour of warm-up, the center point (O point) of each sample disk and the G point of the experimental group, which was 10 mm away from O point were 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 was among 0.1-0.3, and there were no statistical differences among groups.2 There was certain relationship between repeated firings and gingival porcelain in L^* value.3 In the control group, L^* (P<0.05) and a^* value(P>0.05) decreased after repeated firings. The color difference△E CIE between the 4th cycle and 8th cycle was the biggest (0.57). In the O group of experimental group, L^*(P<0.05) b^*(P<0.05) C^*ab(P<0.05) decreased.△E_CIE between 4th cycle and 10th cycle was the biggest (1.14). In the G group of experimental group, L^*(P<0.05) increased and a^*,b^*,C^*ab,H°ab(P<0.05) decreased after repeated firings.△E_CIE between 2th cycle and 10th cycle was the biggest (2.60).4 When the O group and the experimental group were compared, L^*,b^*,C^*ab,H°ab value decreased (P<0.05), and a^* increased (P<0.05) in the same cycle.△E CIE in the 10th cycle was the biggest (1.99) and in the 2nd cycle was the smallest (1.36).Conclusion:1 There was influence of repeated firings on the color of the PFM with gingival porcelain.2 In the same cycle the differences were statistically between the color of the PFM with gingival porcelain or not.3 The△E_CIE of the color of the PFM with gingival porcelain increased after repeated firings.4 The influence of repeated firings on the L^* value was the biggest.5 There was certain relationship between repeated firings and gingival porcelain in L^* value.