Direct colour printing on zirconia using 222 nm UV-C photons

Area of Science:

• Materials Science
• Biomaterials Engineering
• Photochemistry

Background:

• Zirconia ceramics, specifically 3 mol% yttria-stabilized tetragonal zirconia polycrystal (3Y-TZP), are widely used in dentistry.
• Achieving aesthetic tooth-like coloration on 3Y-TZP often requires complex multi-step processes.
• Exploring novel, direct methods for ceramic coloration is crucial for improving clinical efficiency and aesthetics.

Purpose of the Study:

• To evaluate the feasibility of direct color printing on 3Y-TZP using 222 nm UV-C irradiation.
• To investigate the degree and durability of induced color changes.
• To assess the impact of UV-C treatment on surface, mechanical, and biological properties of 3Y-TZP.

Main Methods:

• 3Y-TZP samples were irradiated with 222 nm UV-C light at an irradiance of 1.870 mW/cm² for durations ranging from 15 minutes to 24 hours.
• Color changes (ΔE*), translucency parameter (TP), crystalline structure, surface morphology, surface roughness (Sa), and biological activities were analyzed.
• Statistical analysis was performed using SPSS 28.0 with a significance level of α = 0.05.

Main Results:

• 222 nm UV-C irradiation successfully imparted tooth-like colors to white 3Y-TZP.
• A logarithmic inverse relationship was observed between irradiation time, color change (ΔE*), and translucency (TP), indicating predictable color modulation.
• The treated surfaces showed enhanced hydrophilicity with a recovery phenomenon; other properties remained unaltered.

Conclusions:

• This study demonstrates the pioneering feasibility of direct color printing on 3Y-TZP using 222 nm UV-C.
• The induced optical changes are predictable and stabilize over time, linked to electron excitation and oxygen vacancies, without affecting material integrity.
• This approach offers a simple, safe, and promising method for achieving satisfactory coloration on 3Y-TZP in clinical settings.