Influences of environmental temperature on the UV-C colour printing performance

To explore the effects of environmental temperature during 222 nm UV-C colour printing on the change of optical properties of 3Y-TZP.

3Y-TZP discs were irradiated with a 222 nm UV-C light (irradiance: 1.870 mW/cm²) for 15 minutes to 24 hours. Environmental temperatures were controlled by a coldplate or hotplate, forming four groups: Heating group 1 (HG1, 360.15 K), HG2 (340.15 K), reference group (RG, 310.15 K), and cooling group (CG, 280.15 K). CIE^⁎L^⁎a^⁎b values were recorded before and at multiple time points (0, 1, 3, 7, 10, and 14 days) post-irradiation to calculate ΔE^⁎, ΔE^⁎₀₀ and TP. SPSS 28.0 was used for statistical analysis (α=0.05).

Lower environmental temperatures enhanced immediate ΔE^⁎ and reduced TP, with quadratic relationships observed. For 24-hour group, immediate ΔE^⁎ ranked CG (15.30) > RG (9.43) > HG2 (6.94) > HG1 (5.75), and TP ranked HG1 (10.11) > HG2 (10.16) > RG (8.56) > CG (6.71). Except in HG1, ΔE^⁎ and TP showed logarithmic relationships with irradiation time. Lower temperatures accelerated recovery for both ΔE^⁎ (Recovery speeds were 3.520, 3.656, 5.694 and 12.308 for HG1, HG2, RG and CG, respectively) and TP. RG showed the highest stabilised ΔE^⁎ for t ≥ 4h, while TP recovery was incomplete in CG groups with longer irradiation times. ΔE^⁎₀₀ has similar trends with ΔE^⁎.

222 nm UV-C direct colour printing on zirconia was significantly influenced by environmental temperature. Lower environmental temperatures yield higher immediate ΔE^⁎, greater TP reduction, and faster recovery. This technique offers aesthetic colouration of dental zirconia restorations, UV-C detection, and reusable short-term information storage.

222 nm UV-C colour printing enables colour customisation, and the colour printing outcomes can be controlled through irradiation time and environmental temperature.