Aim
This study aimed to evaluate the effects of a translucency-enhancing liquid (TEL) and high-speed sintering (HS) on the mechanical behavior, with a focus on the survival rates and fracture forces of anterior zirconia crowns with different yttria contents.
Materials and methods
Anterior crowns (16 groups, n = 8 per group) were fabricated using four different zirconia materials (3Y-TZP, 4Y-TZP, 5Y-TZP, and multilayer (ML)). The 3Y and 4Y groups were treated with a TEL in three variations: no treatment (NL), two-layer penetration (2L), and four-layer penetration (4L). The 5Y-TZP and ML zirconia crowns served as reference groups without TEL treatment. All specimens underwent either conventional (CS) or high-speed (HS) sintering before being subjected to thermocyclic and mechanical loading (TCML), followed by a load-to-fracture test. Statistics: ANOVA, Bonferroni test, Shapiro-Wilk test, Pearson correlation; α = 0.05.
Results
Three specimens in group 5Y-NL-CS and one in group 4Y-NL-HS failed during TCML. Fracture forces varied significantly between different types of zirconia and decreased with increasing yttria content. While mean fracture forces were not affected by HS or TEL treatment, HS of ML and particularly 5Y-TZP crowns was associated with a higher frequency of crown fractures, indicating material- and condition-specific tendencies of potential clinical relevance.
Conclusion
Within the limitations of this in-vitro study - including the use of PMMA abutments, failures during TCML, and material- and failure-specific differences - all specimens withstood forces exceeding the physiological loads expected in the anterior region. Under these conditions, TEL treatment and HS of 3Y-TZP and 4Y-TZP zirconia appear to allow the rapid fabrication of anterior crowns while maintaining their mechanical performance. As optical parameters were not assessed, any potential aesthetic implications of TEL or HS cannot be inferred.