Direct Colour Printing on Zirconia Using 222nm UV-C Photons

Abstract

ObjectivesTo proof the feasibility of direct colour printing on 3Y-TZP using 222nm UV-C, investigate the degree and durability of the colour changes and testify whether other properties are influenced by the treatment. Methods222nm UV-C light (Irradiance: 1.870mW/cm2) was used to treat 3Y-TZP for durations from 15minutes to 24hours. ΔE*, TP, crystalline structure, surface morphology, Sa, BFS and biological activities were investigated before and after irradiation. SPSS 28.0 was used for statistical analysis (α = 0.05). Results222nm UV-C irradiation was capable of shading white 3Y-TZP into tooth colours. With the increase of ΔE*, TP decreased, such that the longer the irradiation, the higher the ΔE* (logarithmic relationship) and the lower the TP. Despite the induced optical changes being prone to fade, the process can be predicted by inversely proportional relationships between ΔE*, TP and the testing points. The treated surface exhibited enhanced hydrophilicity, while the recovery phenomenon was observed. Other properties were not altered by the treatment. SignificanceThis is the seminal study demonstrating the feasibility of direct colour printing on 3Y-TZP using 222nm UV-C. The new relationship between the colour centre and Eg of 3Y-TZP was established, whereas the induced optical changes were stabilised after a certain period and were highly predictable by controlling irradiation periods. The irradiation was only related to the electron excitation and oxygen vacancies, and would not lead to changes of other properties. A simple, safe and promising approach to achieve satisfactory colours on 3Y-TZP in clinical practice can be developed.