Enhancing surface energy and characterizing optical properties of ultra-high translucency zirconia via an innovative heat treatment process

Purpose: Ultra-high translucency zirconia (UT-Zr) is known for its high esthetic quality; however, its inert surface results in low hydrophilicity and surface energy (SE). To address this limitation, this study proposes an innovative zirconia heat treatment process (ZHTP) and aims to evaluate the effects of ZHTP on the surface characteristics of UT-Zr, offering a novel and practical approach for surface pretreatment in dental practice. Material and Methods: The plate-shaped UT-Zr samples were fabricated. After sintering, the samples without additional staining or polishing were divided into the following nine groups: NT (no additional pretreatment), AB (airborne-particle abrasion), PL (nonthermal plasma), PO (polishing), HPO (fine-polishing), NTH (treat with ZHTP), POPL (PL followed by PO), POH (ZHTP followed by PO), and HPOH (ZHTP followed by HPO). The surface roughness (Ra), microstructure, transmittance, glossiness, wettability, and SE of the samples (n = 10), and statistical analyses were conducted. Results: AB showed the highest Ra and lowest glossiness (P < 0.05), while HPO and HPOH yielded the smoothest surfaces, with HPOH achieving the highest glossiness (P < 0.05). Although the ZHTP approach slightly improved transmittance, it did not affect the microstructure. PO reduced hydrophilicity and SE (P < 0.05), and HPO slightly increased them. PL significantly enhanced both properties (P < 0.05), and ZHTP also increased them (P < 0.05) to levels similar to PL. Notably, hydrophilicity in nonthermal plasma and ZHTP-treated samples decreased similarly after 24 h. Conclusions: The ZHTP approach enhances UT-Zr wettability and SE, with slight transmittance improvement. HPOH achieves hydrophilicity and SE comparable to PL, validating ZHTP as a promising strategy for UT-Zr surface optimization in dental applications.