EFFECT OF REPEATED FIRINGS ON THE COLOR OF OPAQUE PORCELAIN APPLIED ON DIFFERENT DENTAL ALLOYS

Statement of problem. Although metal ceramic fixed restorations are commonly preferred by clinicians, there remain a limited number of studies on how opaque porcelain color is affected by fabrication procedures, such as the number of firings and types of metal alloys. Purpose. The purpose of this study was to determine the effects of various types of metal alloys on the color of opaque porcelain after repeated firings. Material and methods. Seven different types of metal ceramic alloys (3 base metals: Metalloy CC, chromium cobalt (B-MCC); Heraenium NA, nickel chromium (B-HNA); Argeloy NP, nickel chromium beryllium (B-ANP); 3 noble metals: Ceradelta, palladium silver (N-CD); Cerapall 2, palladium (N-CP2); V-Delta SF, gold palladium (N-VDSF); and I high noble metal: V-Gnathos Plus, gold platinum (HN-GP)) were used to support a 0.1-mm-thick layer of opaque porcelain (IPS d.SIGN Opaquer, shade B1) to determine the metal alloys' effect on the opaque porcelain color after repeated porcelain firings. Opaque porcelain was applied on specimens (16 mm x 1 mm) prepared from each type of alloy. The specimens (n=21) were subjected to 1 opaque firing, 4 consecutive dentin firing cycles, and I glaze firing cycle. Delta E values were calculated for all metal alloy groups from opaque firing (control group) to each subsequent firing stage within each tested alloy group. One-way ANOVA and Fisher's least significant difference tests were performed to determine the differences between alloys. In addition, Delta E values calculated after repeated firings were analyzed by 1-way ANOVA and paired t test, to determine whether repeated dentin firing stages affected the color of opaque porcelain (alpha=.05). Results. After the first and second dentin firings, the color shift in opaque porcelain was significant for all tested alloy groups (P<.001). The color of opaque porcelain changed significantly after the third dentin firing for all groups except for B-HNA and N-VDSF (P<.001). After the fourth dentin firing, the color of opaque porcelain changed significantly for all tested alloy groups (P=.022 for B-ANP, P=.042 for N-VDSF, and P<.001 for remaining alloys). After glaze firing, the color change in opaque porcelain was significant in all but the N-CP2 group (P=.002 for N-VDSF, P=.014 for HN-GP, and P<.001 for remaining alloys). Delta E values showed that B-MCC after the first dentin firing, N-CD after the second dentin firing and glaze firing, and B-ANP after the third and fourth dentin firings showed significantly different Delta E values than all remaining test alloys (P<.001). Conclusions. Subsequent porcelain firings significantly affected the color of a 0.1-mm-thick layer of opaque porcelain for all alloys tested. After the third and fourth firings, 1 base metal alloy (B-ANP) showed significantly greater color change than the remaining dental alloys when the color difference was compared to baseline. In addition, the color change in a noble alloy (N-CD) was significantly less than that of the other alloys after glaze firing. However, color shifts after repeated dentin firings were imperceptible (Delta E<2.6) and clinically acceptable (Delta E<5.5) for each type of alloy. (J Prosthet Dent 2009;101:395-404)