Effect of Storage Duration and Vacuum-sealed Storage on the Contact Angle of 3Y-TZP and 4Y-TZP Zirconia after Airborne Particle Abrasion

This study aimed to compare the effects of storage conditions (vacuum-sealed vs. non-vacuum-sealed) and storage duration on zirconia surface wettability following airborne particle abrasion, based on the hypothesis that vacuum-sealed storage can mitigate time-dependent hydrophobic recovery. The influence of zirconia composition (3Y-TZP vs. 4Y-TZP) was also investigated. A total of 180 zirconia specimens were prepared from 3Y-TZP (VITA YZ HT) and 4Y-TZP (VITA YZ ST). After sintering, polishing, and airborne particle abrasion with 50 µm Al2O3, specimens were assigned to non-vacuum-sealed or vacuum-sealed storage. The non-vacuum-sealed groups were stored for 1 hour, 1 week, 2 weeks, 1 month, and 1.5 months (n = 10). Vacuum-sealed groups were stored for 1 week, 2 weeks, 1 month, and 1.5 months (n = 10) and compared with the non-vacuum-sealed 1-hour baseline group. Non-vacuum-sealed specimens were stored in sealed containers, whereas vacuum-sealed specimens were stored in vacuum-sealed pouches at room temperature. Contact angle measurements were performed using an optical contact angle measurement system with SCA20 software and a 10 µL deionized water droplet. Data normality and homogeneity were confirmed before applying two-way ANOVA and Tukey's post hoc test (α = 0.05). In the non-vacuum-sealed condition, both zirconia types showed a marked increase in contact angle over time (3Y-TZP: 58.03 to 89.01 degrees; 4Y-TZP: 62.38 to 90.23 degrees). Material type (p < 0.001) and duration (p < 0.001) showed significant main effects, while their interaction was not significant (p = 0.122). Differences between materials were significant only at early time points. In contrast, vacuum-sealed specimens exhibited minimal changes in contact angle across all time intervals, and duration showed no significant effect (p = 0.110). Storage duration significantly affects zirconia surface wettability following airborne particle abrasion. Progressive hydrophobic recovery was observed in non-vacuum-sealed specimens, whereas vacuum-sealed specimens effectively preserved surface energy for up to 1.5 months. Vacuum-sealed zirconia represents a practical approach to maintaining zirconia surface wettability when immediate bonding cannot be performed.