Influence of Multiple Firings on the Color Stability and Surface Roughness of Gingival Pink Feldspathic Ceramic

Abstract

The present study was aimed at analyzing the impact of repeated firings on the color stability and surface roughness (Ra) of gingival pink feldspathic porcelain. Twenty specimens (n = 20) were prepared, and repeated firings were carried out. These samples were equally and randomly divided into two groups (n = 10) to assess the color change (ΔE), using a spectrophotometer and Ra using a non-contact profilometer. The ΔE was calculated after the third, fifth, and seventh firings, whereas the Ra was assessed after the first, third, fifth, and seventh firings. The greatest ∆E was observed after the seventh firing (6.86), followed by the fifth firing (3.93). The lowest ∆E was seen after the third firing (2.61). All the inter-group comparisons were statistically significant (p < 0.01). The change in color of gingival pink feldspathic porcelain samples observed after multiple firings could be attributed to pigments in this material becoming unstable, and the possible change in the crystal orientation with increased firings. The highest Ra was observed for the samples after the first firing (1.130 μm), followed by the third firing (0.617 μm) and fifth firing (0.477 μm). The lowest Ra values were seen for the samples after the seventh firing (0.425 μm). All the inter-group comparisons were statistically significant (p < 0.01), except when the Ra values of samples after the fifth and seventh firing were compared (p > 0.01). The decreased Ra could be attributed to the melting of glaze with increased firings, which could have filled the gaps on the porcelain’s surface making it less rough. The present study demonstrated that an increase in repeated firings resulted in an increase in the ∆E values and a decrease in the Ra values of gingival pink feldspathic porcelain samples. The greatest increase in ∆E and the highest reduction in Ra values were noticed after the seventh firing. Future studies, including other parameters (variable thickness of ceramic and firing temperatures), should be conducted to study the impact of repeated firings on the color stability and roughness of gingival pink feldspathic porcelain.