Effect of Thermocycling on Color Stability, Fracture Resistance, and Shear Bond Strength of CAD-on Restorations (Lithium Disilicate and Polymer-Infiltrated Ceramic Network) Fabricated on Zirconia Copings

The goal of the current in vitro investigation was to assess how artificial aging via thermocycling affected color stability, fracture resistance, and shear bond strength of CAD-on restorations made on zirconia copings veneered with polymer-infiltrated ceramic network (PICN; VITA Enamic) and lithium disilicate materials. Three groups were created from 18 standardized crown specimens that resembled mandibular molar restorations (n = 6 per group): hand-layered zirconia restorations (control), zirconia copings veneered with PICN (VITA Enamic), and zirconia copings veneered with lithium disilicate using CAD-on technology. To mimic intraoral thermal aging, each specimen was thermocycled for 10,000 cycles between 5 and 55°C. Using a spectrophotometer, color stability was assessed and reported as ΔE00 values. Universal testing equipment was used to evaluate fracture resistance under compressive pressure. A chisel-edge loading method was used to measure the shear bond strength at the veneer–coping interface. One-way ANOVA and Tukey's post hoc test (α = 0.05) were used in the statistical study. Following thermocycling, all ΔE00 values remained within clinically acceptable ranges, and there were no statistically significant differences in color stability between the groups (p > 0.05). The experimental group's fracture resistance values did not significantly alter before or after thermocycling (p > 0.05). However, there were statistically significant differences in shear bond strength between the groups before and after thermocycling (p < 0.05). Shear bond strength values were highest in the hand-layered zirconia group and lowest in the PICN-veneered CAD-on restorations. Within the constraints of current in vitro investigation, CAD-on restorations made on zirconia copings veneered with PICN (VITA Enamic) and lithium disilicate materials showed respectable color stability and fracture resistance following thermocycling. In contrast to the CAD-on designs, the traditional hand-layered zirconia restorations showed better shear bond strength. Zirconia-based CAD-on restorations may provide satisfactory esthetic and mechanical performance following thermal aging. However, the durability of the veneer–coping interface remains influenced by the veneering technique and material selection, which should be considered when planning long-term prosthetic restorations.