Optical, Structural, and Biological Characteristics of Rapid-Sintered Multichromatic Zirconia

Area of Science:

• Dental Materials Science
• Biomaterials Engineering
• Ceramic Engineering

Background:

• Multichromatic zirconia systems aim to improve esthetics in dental restorations by mimicking natural tooth shades.
• Rapid sintering protocols are crucial for chairside fabrication of zirconia restorations, enhancing clinical efficiency.
• This study investigates the impact of rapid sintering on optical properties, phase transformation, and cell interaction of dental zirconia.

Purpose of the Study:

• To evaluate the effect of rapid sintering on the color stability of multichromatic dental zirconia.
• To analyze phase transformation in zirconia after rapid sintering using X-ray diffraction.
• To assess the biocompatibility of rapidly sintered zirconia surfaces through cell assays.

Main Methods:

• Color stability was measured using the CIE L*a*b* color space.
• Phase transformation was analyzed via X-ray diffraction.
• Cellular behavior was assessed by measuring wettability, surface energy, and fibroblast mitochondrial activity.

Main Results:

• Rapid sintering resulted in color changes exceeding the perceptibility threshold in all layers, with the enamel layer surpassing the acceptability threshold (ΔE* = 3.01).
• X-ray diffraction revealed a decrease in cubic phase and an increase in tetragonal phases (T=49%, T1=27%, C=24%) after rapid sintering, with a minor monoclinic phase detected.
• Surface treatments (polishing, glazing) did not significantly affect cell adhesion and proliferation, despite glazing increasing hydrophilicity.

Conclusions:

• Rapid sintering induces clinically perceptible color changes, particularly in the enamel layer of multichromatic zirconia, potentially compromising esthetic outcomes.
• Accelerated heating and cooling rates during rapid sintering hinder equilibrium, leading to altered lattice parameters and the formation of a metastable T1 phase.
• While rapid sintering affects optical and phase properties, the biocompatibility of the resulting surfaces remains comparable to conventionally sintered zirconia.