Color stability, surface topography, and phase transformation of zirconia fabricated by additive and subtractive manufacturing after exposure to different artificial saliva formulations

Abstract

Statement of problem: How variations in salivary chemistry affect the long-term stability of additive manufacturing (AM) and subtractive manufacturing (SM) zirconia is unclear. Purpose: The purpose of this in vitro study was to evaluate the effects of different salivary environments on the color stability, surface roughness, and phase transformation of zirconia fabricated by AM and SM. Material and methods: Disk-shaped specimens (n=160) were fabricated from 4 zirconia materials: 2 AM-AMZ-LI (LithaCon 3Y, produced via lithography-based ceramic manufacturing [LCM]) and AMZ-IN (INNI Cera, produced via digital light processing [DLP])-and 2 SM-SMZ-ST (monolayer Katana ST) and SMZ-ML (multilayer Katana STML). Each material group was divided into 4 subgroups (n=10) based on the aging medium: distilled water (DW), neutral artificial saliva (AS7), acidic artificial saliva (AS4), or enzymatic artificial saliva containing α-amylase (ASE7). Surface roughness (Ra), color change (ΔE₀₀), and phase transformation were assessed. Data were analyzed using a 3-way repeated measures ANOVA with Tukey HSD or Bonferroni post hoc tests (α=.05). Results: Ra was significantly affected by material type, aging condition, and fabrication method (all P≤.001), with AMZ-LI and SMZ-ML maintaining the lowest Ra values (<0.60 µm) after aging. Color stability was similarly influenced (P<.001), with all groups remaining within clinically acceptable limits (ΔE₀₀≤1.8). AMZ-LI (0.60 ±0.08 in DW; max=1.26) and SMZ-ML (0.84 ±0.05 in DW; max=1.20) showed the highest color stability, while SMZ-ST and AMZ-IN had higher ΔE₀₀ in acidic and enzymatic media. Phase transformation was more pronounced in SM groups (P<.05), with SMZ-ML showing the greatest monoclinic increase, and AMZ-LI exhibiting the highest phase stability. Conclusions: Both manufacturing techniques and aging environments significantly affected zirconia's surface, optical, and phase properties. AMZ-LI showed superior resistance to surface and phase degradation, while AMZ-LI and SMZ-ML exhibited the highest optical stability.