Hybrid Zirconia-Silica Interface Developed by Atomic Layer Deposition

Objectives: Yttria-stabilized zirconia (Y-SZ) is a reliable option to restore severely compromised teeth. Y-SZ materials are prone to low-temperature degradation (LTD), which generates a tetragonal-to-monoclinic (t-m) transformed and porous layer. This study aimed to use room- temperature atomic layer deposition (RT-ALD) to infiltrate Y-SZ t-m layer with silica and develop a hybrid interface less prone to LTD.
Methods: Sintered specimens (14 x 4 x 2 mm) were prepared from two different Y-SZ materials (n = 40): low translucency (3Y-LT; Ceramill ZI, Amann Girrbach); and high translucency (5Y-HT - Lava Esthetic, 3M). Specimens were exposed to hydrothermal treatment (HTT) to develop similar depths of crystalline changes. Room temperature atomic layer deposition (RT-ALD) was used to deposit a thin film of silica (SiO₂). Surface roughness and wettability analyses were performed to investigate the effect of treatment (HTT and RT-ALD) and material on Y-SZ surface properties, and data was analyzed by two-way ANOVA, Tukey HSD or Games-Howell (p < 0.05). Silica infiltrated specimens were exposed to further hydrothermal aging (HA) and characterized by time-of-flight secondary ion mass spectrometry (ToF-SIMS).
Results: Two-way ANOVA showed a significant effect of material (p < 0.001), and treatment (p < 0.001) on surface roughness, but no interaction effect (p = 0.132). There was a significant effect of the interaction material and treatment on surface wettability (p < 0.001). HTT did not affect roughness of Y-SZ materials. Regardless of material type, silica deposition resulted in significantly higher surface roughness for RT-ALD (4.89 ± 0.71 µm) and HTT/RT-ALD (4.49 ± 0.66 µm) groups. HTT resulted in the lowest contact angle values for 3Y-LT and 5Y-HT. Tof-SIMS results showed that HTT created a porous 3Y-LT substrate that was effectively infiltrated by silica.
Conclusions: Nanofilms of SiO₂ were successfully deposited on Y-SZ materials and infiltrated 3Y-LT after hydrothermal treatment.