The effect of repeated firings on the color of an alumina ceramic system with two different veneering porcelain shades.

STATEMENT OF PROBLEM

Possible sources of processing variables in porcelain firing include thickness and color of the opaque; thickness, color, and translucency of the body and enamel layers; firing temperature; and number of firings.

PURPOSE

The purpose of this in vitro study was to investigate the color changes of an alumina ceramic system veneered with different veneering porcelain shades and fired different numbers of times.

MATERIAL AND METHODS

Twenty disc-shaped ceramic specimens (10 mm in diameter, with a core thickness of 1 mm), with 2 different veneering porcelain shades (A1, A3), were fabricated from an alumina ceramic system (Turkom-Cera) (n=10). Repeated firings (3, 5, 7, or 9 firings) were performed, and color differences (ΔE) were determined using a spectrophotometer. Repeated-measures ANOVA was used to analyze the data (number of firings, veneering porcelain color). The Duncan test and paired 2-tailed tests were used for multiple comparisons (α=.05).

RESULTS

The Lab* values of the ceramic system were affected by the number of firings (3, 5, 7, or 9) (P<.005) and veneering porcelain shade (P<.001). Significant interactions were present between the number of firings and the veneering porcelain shade for L* (P=.002), a* (P=.001), and b* (P=.001) values. A1 shade specimens maintained their L* value independent of the number of firings, whereas A3 shade specimens became lighter after an increased number of firings. For both A1 and A3 veneering porcelain shades, the a* value decreased after repeated firings, which resulted in less reddish specimens, and the b* value decreased after repeated firings, which resulted in less yellowish specimens.

CONCLUSIONS

Imperceptible (ΔE<1.6) and clinically acceptable color changes (ΔE<3.7) were demonstrated by the alumina ceramic system tested.