Optimizing diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide concentration and post-curing time to balance mechanical properties and color stability in a three-dimensional-printed restorative resin.

Three-dimensional (3D) printing is widely used in dental restorations; however, optimization of photoinitiator concentration and post-curing protocols remains critical to achieve a balance between mechanical and esthetic performance. This study evaluated the combined effect of diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (TPO) concentration and post-curing time on mechanical properties and color stability of a 3D-printed restorative resin. A commercial photoinitiator-free resin (BioPrint Prov, Horus 3D) was supplemented with TPO at 0.5, 1.0, and 1.5 wt% and fabricated using a digital light processing printer. Specimens were post-cured for 30, 45, or 60 min under UV light, while non-post-cured (NoPC) samples served as controls. Flexural strength and elastic modulus were evaluated using a three-point bending test. Color stability and translucency were assessed using spectrophotometry (CIELab/ΔE00) under storage conditions, including dry storage, water immersion, and coffee aging. Data were analyzed using two-way anova and Tukey's test. The 1.0% TPO and 30 min post-curing combination provided best performance, with highest flexural strength and lowest color change after staining. Higher TPO concentration and prolonged post-curing increased color alteration and yellowness. NoPC specimens showed inferior mechanical properties and greater discoloration. Translucency remained more stable in post-curing groups. These findings indicate optimized photoinitiator concentration and controlled post-curing time improve mechanical and esthetic outcomes in 3D-printed restorative resins.