Effect of sintering regimes and thickness on optical properties of zirconia ceramics for dental applications

Abstract

In dentistry, monolithic zirconia restorations have been preferred over all-ceramic restorations in recent years. Translucency is an aesthetic demand in dental restorations, and it can be identified with translucency parameter (TP). Zirconia thickness, Y 2 O 3 content, and sintering conditions are important parameters that influence the translucency of the restorations. It is crucial to investigate monolithic zirconia ceramics under different sintering regimes and reveal the critical parameters for dental restorations. The aim of this study was to determine the optical and microstructural behaviors of monolithic zirconia ceramics containing different amounts of yttria depending on various sintering regimes and thicknesses. Therefore, a conventional zirconia CopranZri (CZI) and two monolithic zirconia materials, CopraSupreme (CSP), CopraSmile (CSM) were used. Slow, normal, speed, and translucency sintering regimes with thicknesses of 0.7, 1.0, 1.3 mm were selected. TP of the specimens was calculated, and statistical analyses were performed by using one-way ANOVA and Tukey-Kramer post hoc tests. Characterization of the specimens was performed by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive X-ray (EDX) techniques. The results showed that the effect of different sintering programs is more critical for CSP and CSM in terms of translucency variations and translucency program led to the most grain growth.

Effect of sintering procedures on optical properties, chemical composition, and grain size of monolithic zirconia ceramic at different thicknesses after hydrothermal aging: An in vitro study

“…The second null hypothesis was accepted for the TP because the effect of the sintering procedure on the TP of MZ was not statistically significant ( P = 0.445) without considering the thickness [ Table 3 ]. This result is consistent with some previous studies,[ 6 7 8 ] but not others. [ 4 5 9 ] The shorter (speed and high speed) sintering procedures were defined with changes in heating rate, final temperature, dwell time at the final temperature, and cooling rate.…”

“…[ 3 ] The TP is a reliable method used in many studies to assess the transparency of dental materials. [ 4 5 6 7 8 9 ] TP of dental materials is calculated as a color difference against a black and white backgrounds. [ 2 10 11 ] The opalescence parameter (OP) has usually been used to estimate the opalescence of dental materials.…”

“…[ 5 9 ] or did not. [ 6 7 8 ] affect the TP values compared to standard sintering among the studies that examined 3 Mol% Yttria-Stabilized Tetragonal Zirconia Polycrystals (3Y-TZPs). It has also been reported that the OP value of the standard sintering procedure was similar to speed sintering[ 7 8 ] but lower than high-speed sintering[ 14 ] procedure considering the study including 3Y-TZP.…”

“…[ 18 ] Therefore, MZ specimens should be subject to hydrothermal aging to predict the long-term results of the restorations. Only one[ 5 ] of the previous studies[ 4 5 6 7 8 9 14 ] examining the effect of the sintering procedure on the optical properties of MZ (3Y-TZP) includes hydrothermal aging. The present study aimed to assess the impact of sintering procedures and thicknesses, on the optical properties, chemical composition, and GS of MZ after hydrothermal aging.…”

the effect of different sintering cycles on the translucency and biaxial flexural strength of monolithic zirconia

“…Thus monolithic zirconia systems, including a single material without additional veneering were developed to be used by CAD/CAM technologies to overcome these drawbacks. [17] The use of monolithic zirconia used at the present time in the dental field, has higher mechanical and optical properties, allowing clinicians to perform more conservative preparations compared to conventionally veneered ceramic or metal-ceramic restorations [18] However, the prolonged sintering time of the conventional sintering furnaces (up to 12 hours) and the inability to combine high translucency with high mechanical properties restricted the use of monolithic zirconia. [19] but the development of high-speed sintering machines now allows us to mill and sinter monolithic zirconia as a chair-side restoration in just a few minutes.…”