Optical gradient and translucency behavior of three multilayer monolithic zirconia systems: a spectrophotometric study

This in vitro study evaluated the effects of multilayer zirconia material, anatomical region, substrate shade, and laboratory background conditions on the optical behavior of monolithic zirconia crowns. Sixty crowns fabricated from three multilayer zirconia systems were analyzed at cervical, middle, and incisal regions using standardized white, black, and neutral backgrounds. Color coordinates (L*, a*, b*), color difference (ΔE₀₀), translucency parameter (TP₀₀), and contrast ratio (CR) were measured using a dental spectrophotometer. Material type and anatomical region significantly influenced all optical parameters. Perfit STML demonstrated higher translucency (TP₀₀ ≈ 1.50) and color difference (ΔE₀₀ ≈ 3.71), whereas Dental Direkt exhibited lower translucency (TP₀₀ ≈ 0.99) and higher opacity (CR ≈ 0.98). The incisal region showed the highest translucency (TP₀₀ ≈ 2.33) and lowest contrast ratio, while the cervical region exhibited higher lightness and chromaticity. Laboratory background conditions affected color coordinates and ΔE₀₀ values, whereas intrinsic optical properties such as TP₀₀ and CR remained relatively stable across backgrounds. However, interaction analysis revealed that the influence of background conditions varied depending on the anatomical region. These findings indicate that multilayer zirconia materials are not optically interchangeable and that their optical performance is strongly influenced by both material composition and anatomical location. Clinically, highly translucent materials may be preferred for achieving a natural incisal appearance under favorable substrate conditions, whereas more opaque materials or masking strategies may be required when the underlying substrate is discolored.