Effect of postpolymerization unit characteristics on the color stability and relative translucency parameter of 3D...

This study evaluated the effects of postpolymerization unit characteristics on the color stability and relative translucency parameter of three-dimensional (3D) printed interim crown and bridge resins under simulated aging.

Four commercial resins were postpolymerized using five units. Spectral reflectance was measured before postpolymerization (T0), immediately afterward (T1), and after 6-month dry storage at 37 °C or 5000 thermocycles (T2). CIE L*a*b* (CIELAB) coordinates were calculated under CIE standard illuminant D65 using the CIE 1931 2° Standard Colorimetric Observer. The whiteness index for dentistry (WI_D) and CIEDE2000 color difference (ΔE₀₀) were derived from black-background coordinates, whereas the CIEDE2000 relative translucency parameter (RTP₀₀) was calculated from paired black- and white-background coordinates. Mean ΔL*, Δa*, and Δb* were evaluated using axis-specific visual thresholds, and T1-to-T2 ΔE₀₀, |ΔWI_D|, and |ΔRTP₀₀| using perceptibility and acceptability thresholds.

Postpolymerization generally reduced L* and WI_D, whereas RTP₀₀ responses varied among resin-unit combinations. During dry storage, L* and WI_D generally increased, whereas thermocycling generally decreased RTP₀₀. Several outcomes differed significantly among postpolymerization units within each resin (p < 0.005). For Tera Harz TC-80DP, Tera Harz Cure and ODS Cure Box maintained ΔE₀₀, |ΔWI_D|, and |ΔRTP₀₀| within acceptability thresholds under both aging conditions; with Tera Harz Cure, all three remained below perceptibility thresholds.

Color and RTP₀₀ stability depended on the specific resin-unit combination rather than manufacturer-designated pairing alone. Selected non-designated combinations showed acceptable in vitro outcomes. These findings support resin-specific selection based on verified performance of the complete postpolymerization protocol.