Comparison of color change of zirconia materials after different surface finishing processes

The aim of this in vitro study is to investigate the surface properties of zirconia materials with different translucency and different thickness after surface finishing processes, and to compare the surface coloration after thermal cycling and exposure to a surface coloring agent. In this thesis study, monolithic zirconia discs manufactured by Vita (VITA Zahnfabrik, Germany) with 4Y-TZP (super translucent) and 5Y-TZP (extra translucent) compositions were used. The discs were milled using a CAD/CAM system to obtain a total of 128 specimens, with half of them prepared at 0.8 mm and the other half at 2 mm thickness. All specimens were subsequently sintered according to the manufacturer's instructions. Based on the experimental design, no surface finishing or polishing procedures were applied to GrSinter group (n=32). GrFırın group (n=32) specimens were subjected to a repeated firing cycle performed three times following sintering. After surface abrasion with a diamond bur, a glaze layer was applied to GrGlaze group (n=32). GrPolisaj group (n=32) specimens underwent polishing using a polishing kit after surface abrasion. Following surface treatments, all specimens were subjected to thermocycling for 5000 cycles. Initial color measurements (T0) were performed using Vita Easyshade (VITA Zahnfabrik, Bad Sackingen and Germany) spectrophotometer. Specimens were then immersed in a instant coffee solution at 37°C in an incubator, and color measurements were repeated at the 1st week (T1), 2nd week (T2), 1st month (T3), and 2nd month (T4). Surface roughness (Ra) of all specimens was measured using a profilometer device (Perthometer M2, The Universal Standard Instrument, Mahr GmbH and Germany). In this study, color change (ΔE) values between 1 and 3.5 were considered clinically acceptable. In our study, ΔE>3.5 was found in almost all samples. Only the coloration in the samples in the GrGlaze XT 2 mm group was considered clinically acceptable compared to all other groups. It was concluded that the zirconia thickness did not affect the Ra value (p>0.05), but affected the ΔE value (p<0.001). The ΔE value was found to be higher in thin samples compared to thick samples. The highest Ra value was found in the GrSinter and GrFırın groups, while the lowest was found in the GrGlaze group. The difference in the translucency of zirconia did not create a statistically significant difference in the Ra and ΔE values (p<0.05). Since preserving the color stability of translucent monolithic zirconia used in anterior region restorations is important from an aesthetic point of view, it is thought that the results of this in vitro study will provide information on guiding the clinical selection of newly developed translucent monolithic zirconia, which is frequently preferred in the anterior region today, depending on the coloration potential. This study was approved by Baskent University Institutional Review Board (Project no: D-KA24/08) and supported by Baskent University Research Fund. Keywords: Translucent monolithic zirconia, Polishing, Glaze, Staining.