Influence of thermal tempering processes on color characteristics of different monolithic computer-assisted design and computer-assisted manufacturing ceramic materials

Effect of extrinsic pigmentation and multiple firing cycles on the properties of a zirconia-containing lithium silicate ceramic

PURPOSE

To assess the impact of staining and multiple firings on the mechanical, optical, and surface characteristics of zirconia-containing lithium silicate ceramics (ZLS).

MATERIALS AND METHODS

Ninety ZLS discs (Suprinity, VITA Zahnfabrick) were divided according to the "Number of firings" protocol: Ctr-control, no characterization; SC-single firing cycle (for characterization, crystallization and staining simultaneously); and DC-double firing cycle (crystallization firing cycle was performed separately from the staining firing). Extrinsic pigmentation was performed to replicate the characterization of a monolithic restoration. A layer of stain and glaze was applied with a fine brush to the ceramic surface. Specimens were fired two or four cycles, designed to simulate additional staining firings for potential characterization adjustments, but without applying new stain, resulting in six groups (n = 15): CtrII, CtrIV, SCII, SCIV, DCII, and DCIV. X-ray diffraction, color, translucency, and surface roughness analysis were also performed, and the samples were subjected to the biaxial flexural strength test. Data were subjected to one-way ANOVA, Tukey's test (α = 0.05), and Weibull analysis.

RESULTS

No changes in the diffractogram pattern were found, irrespective of the number of firings. The translucency (p = 0.02) and roughness (p < 0.01) of DCIV were significantly reduced compared to DCII. DCIV also showed the highest flexural strength (325.52AMPa), followed by SCII (271.64BMPa).

CONCLUSIONS

Repeated firings increased the flexural strength of ZLS, where the double-step characterization technique demonstrated better statistical results than the other groups. Moreover, despite the ceramic showing good color stability, repeated firings significantly compromised its translucency.

Effect of glass infiltration and modified cooling rates on color characteristics alteration of monochrome and multilayer high yttrium oxide containing zirconia

Background

Sintering technique impacted color of zirconia. This study examined the effect of glass infiltration and altering cooling rate on color alteration of monochrome (Mo) and multilayer (Mu) 5 mol% yttria-partially stabilized zirconia (5Y-PSZ).

Material and Methods

180 specimens (width, length, thickness = 10, 20, 2 mm) were prepared from Mo and Mu (comprising cervical (C) and incisal (I) zone) 5Y-PSZ shade VITA-A2. Unintentionally categorized samples (n=15/group) were sintered with traditional (T) versus glass infiltrated (G) technique and cooled down with slow (S: 5°C/min), normal (N: 35°C/min), and fast (F: 70°C/min). CIE-L*a*b* color characteristics were determined for translucency parameter (TP), contrast ratio (CR), opalescence parameter (OP), and color difference (∆Ediff). Microstructures were investigated with SEM and XRD. ANOVA and Tamhane's comparisons were determined for significant differences (p<0.05).

Results

TP and OP were significantly higher for Mo than MuC and MuI, but no significant difference in CR among them. Comparable ΔEdiff between Mo and MuC were indicated, but both were significantly lesser than MuL. Glass infiltration and raising cooling rate significantly decreased TP and OP, whereas increased CR and ΔEdiff, which amplified color alteration.

Conclusions

Glass infiltration sintering and modified cooling rate significantly altered color parameters of 5Y-PSZ. Monochrome demonstrated higher translucency and opalescence than multilayer, possibly due to colorant additives. Glass infiltration decreased translucency and opalescence due to different refractive indices. Increased cooling rate resulted in decreasing translucency and opalescence due to smaller grain size and t→m transformation. Nevertheless, altered sintering and cooling rates still rendered an acceptable color alteration. Key words:Cooling rate, glass infiltration, optical characteristics, translucency.

Surface treatment, liquid, and aging effects on color and surface properties of monolithic ceramics

PURPOSE

The purpose of this study was to investigate the effects of surface treatments, liquids, and aging on color, translucency, and surface properties of monolithic ceramics.

MATERIALS AND METHODS

Lithium disilicate (LDS) and zirconia-reinforced lithium silicate (ZLS) ceramics (n = 135 each) were cut and divided into three groups [crystallization+glaze (single stage), crystallization-glaze (two stages), and crystallization-polish (two stages)]. One sample from each group was examined using scanning electron microscopy (SEM). Remaining samples were divided into four subgroups (distilled water, coffee, grape juice, and smoothie) (n = 11 each), stored for 12 d in the respective liquids, and thermally aged. One sample from each subgroup was analyzed using SEM. The color, gloss, and roughness values of the samples were analyzed after surface treatment (initial) and storage under different liquids+aging conditions. The initial data and both the aged data and data change values were analyzed using robust two- and three-way analyses of variance.

RESULTS

The glazed groups exhibited smoother surfaces. Ceramic type and ceramic-surface treatment interactions affected the initial translucency parameter (TP) (P < .001) and the initial and aged roughness values (P ≤ .001). Surface treatment type affected the color change (P < .001), and ceramic type affected the aged TP values (P < .001). Type of ceramic, surface treatment, and their interactions affected both the initial and aged gloss (P ≤ .001) and TP change values (P ≤ .015). Surface treatment type and ceramic-surface treatment interactions affected the gloss change values (P ≤ .001).

CONCLUSION

Although both ceramics and all surface treatments are clinically applicable, crystallization-glaze is recommended. When gloss and smoothness are important or when translucency is important, ZLS or LDS may be preferred, respectively.

Effect of sintering programs and surface treatments on monolithic zirconia

PURPOSE

To investigate the effect of sintering programs and surface treatments on surface properties, phase transformation and flexural strength of monolithic zirconia.

MATERIALS AND METHODS

Zirconia specimens were sintered using three distinct sintering programs [classic (C), speed (S), and superspeed (SS)] (n = 56, each). One sample from each group underwent scanning electron microscopy (SEM) and grain size analysis following sintering. Remaining samples were divided into five subgroups (n = 11) based on the surface treatments: control (CL), polish (P), glaze (G), grind + polish (GP), and grind + glaze (GG). One sample from each subgroup underwent SEM analysis. Remaining samples were thermally aged. Monoclinic phase volume, surface roughness, and three-point flexural strength were measured. Monoclinic phase volume and surface roughness were analyzed by Kruskal-Wallis and Dunn tests. Flexural strength was analyzed by two-way ANOVA and Weibull analysis. The relationships among the groups were analyzed using Spearman's correlation analysis.

RESULTS

Sintering program, surface treatment, and sintering × surface treatment (P ≤ .010) affected the monoclinic phase volume, whereas the type of surface treatment and sintering × surface treatment affected the surface roughness (P < .001). Type of sintering program or surface treatment did not affect the flexural strength. Weibull analysis revealed no significant differences between the m and σo values. Monoclinic phase volume was positively correlated with surface roughness in the SGG and SSP groups.

CONCLUSION

After sintering monolithic zirconia in each of the three sintering programs, each of the surface treatments can be used. However, for surface quality and aging resistance, G or GG can be recommended as a surface finishing method.