HU Yameng ¹, HU Wei ¹, WANG Tianxiang ¹, YANG Chenchen ¹, LI Lihua ¹,

HUANG Jinliang ¹, KIM Bokhee ², GU Yongjun ¹

(1. School of Materials Science and Engineering, Henan University of Science and Technology, Luoyang 471023, Henan, China; 2. Division of Advanced Materials Engineering, Jeonbuk National University, Jeonju 54896, Republic of Korea)

Extended Abstract:[Background and purpose] With the advancement of society, there is a growing number of people suffering from dental diseases or experiencing tooth loss due to accidents, leading to an increasing demand for oral rehabilitation. With the elevation of material living standards and the enhancement of public aesthetic sensibilities, the demand for dental care has gradually shifted from mere functionality to an emphasis on aesthetic appeal. Consequently, the preparation of gradient dental restorations has begun to gain prominence. In light of this, the present study undertook the task of single-layer coloration of microcline ceramics by incorporating oxide colorants, namely Fe₂O₃ and CeO₂, aiming to lay a theoretical foundation for the subsequent fabrication of gradient restorations.[Methods] In feldspar powder, oxide colorant powders, such as Fe₂O₃ and CeO₂, were added at varying mass fractions. The mixture was uniformly ground with anhydrous ethanol and then dried at 70 ℃ for 1 h. Subsequently, PVA solution was added to the mixture, which was ground again and granulated. The granules were then molded into feldspar ceramic samples measuring Φ10 mm×2 mm. The pressed samples were heated at a rate of 1 ℃·min⁻¹ to 600 ℃, where they were held for 1 h to allow for binder burnout. Following that, the samples were sintered at temperatures of 1180 ℃ and 1200 ℃ for 2 h to fabricate feldspar ceramics. The phase composition and morphology of the samples were analyzed by using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The influence of oxide colorants on coloration effect of the feldspar ceramic samples was assessed using an X-rite precision colorimeter. The impact of the oxide colorants on chemical corrosion resistance of the feldspar ceramic samples was evaluated through chemical solubility experiments, following the methods recommended in the ISO6872 international standard for dental ceramics. Additionally, the sintering behavior of the feldspar ceramic samples was analyzed.[Results] With the addition of oxide colorants, the primary crystalline phase of the ceramics remained microcline, exhibiting short prismatic or platy crystals. The ceramic samples displayed uniform surface coloration with minimal color difference between the front and back surfaces. Ceramics doped with CeO₂ and CeO₂+Fe₂O₃ exhibited a light yellow hue, while those with Fe₂O₃ alone showed a light pink color. Furthermore, the incorporation of CeO₂ and CeO₂+Fe₂O₃ significantly influenced the b* value of ceramics, primarily modulating the yellow-blue hue of the teeth. In contrast, the addition of Fe₂O₃ had a more pronounced effect on the L* value, mainly adjusting the lightness of the teeth. At sintering temperature of 1180 ℃, the coloration of feldspar ceramic samples tinted with CeO₂ or CeO₂+Fe₂O₃ aligns with the chromaticity index range of the Vita 3D Master shade guide. In contrast, the coloration of feldspar ceramic samples tinted with Fe₂O₃ alone falls within the lower region of the Vita 3D Master shade guide's chromaticity index range. When the addition of CeO₂ reached 7 wt.%, the relative density of the colored feldspar ceramic samples could reach 97.7%. The colored feldspar ceramic samples exhibited excellent chemical corrosion resistance, with mass loss after immersion in 4 wt.% acetic acid solution for 16 h, being significantly less than 2000 μg∙cm⁻², while the minimum loss reached a level of as low as 45 μg∙cm⁻². This performance meets the requirements stipulated by the ISO6872 international standard for dental ceramics.[Conclusions] In summary, single-layer feldspar ceramic samples with excellent aesthetic properties and chemical stability were prepared by optimizing the types and amounts of oxide colorants. This work provides a reference for further development and application of gradient dental restorative ceramics.

Key words: microcline feldspar porcelain; oxide colorants; chroma; chemical resistance