Edge chipping of translucent zirconia

Dental ceramics have evolved to balance aesthetics and durability. Translucency is a key aesthetic factor, but it often comes at the cost of mechanical performance. Zirconia, a popular ceramic, has been modified to increase translucency by altering its phase composition. However, the impact of these changes on edge chipping resistance, a clinically relevant mechanical property, remains uncertain. Prior research has shown that the tetragonal phase in zirconia contributes to transformation toughening, which enhances mechanical strength. No prior work had resolved whether increasing the cubic phase to improve translucency compromises this toughness. This gap motivated the current investigation into the mechanical and optical properties of newly developed translucent zirconia materials.

This study aimed to assess the edge chipping toughness and translucency of two translucent zirconia products, one 3mol% yttria-stabilized tetragonal zirconia polycrystal (3Y-TZP), and one lithium disilicate ceramic. The goal was to determine if increased translucency in zirconia correlates with reduced edge toughness. The materials were selected to represent a range of translucency and mechanical performance. The 3Y-TZP served as a mechanical benchmark, while lithium disilicate was used as a translucency reference. The study sought to clarify the relationship between phase composition, translucency, and edge chipping resistance. This uncertainty drove the need for a controlled in vitro evaluation using standardized testing methods.

The study used four dental ceramic materials: Katana and Lava Esthetic as translucent zirconias, Lava Plus as 3Y-TZP, and IPS e.max Press as lithium disilicate. Phase composition was analyzed using X-ray diffraction (XRD) with three samples per material. Translucency was measured using a spectrophotometer with 20 samples per material. Edge chipping toughness was evaluated using a universal testing machine with a custom-machined holder and diamond indenter, also with 20 samples per material. Statistical comparisons for translucency used 1-way ANOVA, while edge toughness used ANCOVA to account for covariates. The materials were selected to represent different phase compositions and translucency levels. The testing methods were designed to reflect clinical conditions while maintaining experimental control.

X-ray diffraction revealed that Lava Plus (3Y-TZP) was predominantly tetragonal, while Katana and Lava Esthetic (translucent zirconias) were mainly cubic. Translucency measurements showed Katana UTML and IPS e.max Press had similar values, which were higher than Lava Esthetic and Lava Plus. Edge chipping toughness values were 304 N/mm for Katana UTML, 354 N/mm for IPS e.max Press, 394 N/mm for Lava Esthetic, and 717 N/mm for Lava Plus. The ranking was Katana UTM < IPS e.max Press = Lava Esthetic < Lava Plus. Translucency increased with higher cubic content, but edge toughness decreased. The 3Y-TZP material showed the highest edge toughness, while lithium disilicate showed moderate values. These results suggest a trade-off between translucency and mechanical performance in zirconia materials.

The study found that translucent zirconias with higher cubic phase content showed greater translucency but lower edge chipping toughness compared to 3Y-TZP. The lithium disilicate material had translucency similar to some zirconias but lower edge toughness than 3Y-TZP. The results suggest that increasing translucency in zirconia by boosting cubic phase content reduces mechanical performance. The authors propose that clinicians should consider this trade-off when selecting materials for dental restorations. The findings align with the hypothesis that transformation toughening is compromised in cubic-rich zirconias. No prior work had resolved the direct relationship between cubic phase content and edge toughness. The study supports the idea that phase composition significantly influences both optical and mechanical properties.