Surface and optical properties of multilayer zirconia after toothbrushing

The impact of toothbrushing on the surface and optical properties of multilayer zirconia is unknown.

The aim of this in vitro study was to evaluate the effect of finishing procedures on the surface roughness (SR) and relative translucency (RT), as well as the effect of toothbrushing on SR, RT, color difference (ΔE00), and gloss (Δgloss) of multilayer zirconia stabilized with 5 mol% of yttrium oxide (5Y-TZP) following polishing or glazing.

Thirty specimens were fabricated from the cervical layer of pre-sintered blocks of 5Y-TZP. The specimens were divided into 3 groups (n = 10/group): control (C); polishing (P); and glazing (G). The surface roughness was evaluated with a confocal laser microscope, and the RT, ΔE00 and Δgloss were assessed with the use of a spectrophotometer. A total of 50,000 cycles of toothbrushing (2 Hz, 2.5 N) were performed using a dentifrice slurry. The linear mixed-effects model and Bonferroni test (α = 0.05) were employed to analyze SR and RT. The color change and Δgloss were assessed using the one-way analysis of variance (ANOVA) and Tukey's post hoc test (α = 0.05).

The finishing procedures had an influence on SR and RT. The polishing process did not affect SR and increased RT, while the glazing process resulted in an increase in SR and a decrease in RT in the multilayer 5Y-TZP. The impact of toothbrushing on SR was not significant (p = 0.052). However, decreased RT was observed in the P group (p < 0.05), while an increase in RT was noted in the G group (p < 0.001). Additionally, the G group presented the highest mean values for ΔE00, as well as for the difference in lightness (ΔL*), the red/green axis (Δa*) and the yellow/blue axis (Δb*). No statistically significant differences were observed among the groups for Δgloss (p = 0.646).

The polishing process increased RT and resulted in the lowest ΔE00 values after toothbrushing. In contrast, the glazing procedure increased SR and decreased RT, while also promoting the most prominent variation in color parameters after toothbrushing. Toothbrushing with a conventional dentifrice did not influence SR and gloss; however, it led to clinically observable color variations and affected RT of the multilayer 5Y-TZP polycrystals.