Cao et al.

Int Chin J Dent 2007; 7: 49-52.

Color stability against accelerated aging of alumina- andleucite-based ceramic materials
Jing Cao, DDS, Hui-ming He, DDS, and Zhong-yi Wang, DDS
Department of Prosthodontics, College of Stomatology, The Fourth Military Medical University, Xi’an,P. R. China
Purpose: The purpose of the current study was to examine the effect of accelerated aging on color stability ofthe In-Ceram and Cergogold ceramic materials.
Materials and Methods: Ceramic samples with 1.0 mm in diameter and 1.5 mm in thickness were prepared inthree commonly used shades. CIE Lab readings were recorded with a spectrophotometer prior to experiments
and after 100-hour accelerated aging.
Results: The effect of ceramic type on the color change was similar for three shades (A1, A3, and A4).
In-Ceram had less color change than Cergogold on every shade. When the shades of ceramic were compared,
A1 shade had a greater color change than those of A3 and A4 shades (p<0.05).
Conclusion: Both In-Ceram and Cergogold ceramic materials had small color change with accelerated aging,although the changing was almost undetectable by human eyes. (Int Chin J Dent 2007; 7: 49-52.)
Key Words: accelerated aging, ceramics, color stability.

Introduction
All-ceramic crown possesses color-rendering properties and optical properties that simulate natural teeth.1
Furthermore based on the excellent biocompatibility, strength, and surface texture of the material, it remains thematerial of choice for most clinicians. It is generally believed that ceramic crown has good color stability. A
recent research, however, reported that the accelerated aging process may change the color of different kinds ofheat-pressed ceramic materials.2
An objective evaluation for color differences requires an ordered system for the classification of color, andequipment capable of quantifying color differences. The most commonly used color classification system forresearch purpose was developed by the Commission International de I’Eclairage in 1978. Otherwise known as
the CIE color system, it introduces three attributes to the perception of color named as L, a, and b. The letter L
refers to the lightness variable and it is proportional to value in the Munsell Color System. The letters a and b
are chromaticity coordinates, wherein a corresponds to the red-green axis, while b refers to yellow-blue axis.
Although they do not directly correlate to hue and chroma, the respective numerals serve to determine numericcorrelates for these attributes.3
Color stability of dental restorative materials was investigated by using accelerated aging in many articles.4-7
Although the clinical relevance of accelerated aging on the color stability of ceramics was not studied, it seems
that this method could be used to determine the color difference, which would probably occur over a longclinical period.5,8 The purpose of this study was to examine the effect of accelerated aging on color stability of
the In-Ceram and Cergogold ceramic materials.

Materials and Methods
Two brands of ceramic materials, In-Ceram (Vita Zahnfabrik GmbH, Bad Säckingen, Germany) andCergogold (Golden Gate Degussa Inc., Darmstadt, Germany), were used in this study (Table 1).
Thirty disk shaped ceramic specimens (10 mm in diameter by 1.5 mm in thickness; Vita lumen shades A1=10,A3=10, and A4=10) were prepared with two materials according to the manufacturers’ instructions.

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Table 1.

Int Chin J Dent 2007; 7: 49-52.
Ceramic materials assessed.

Trade name

MaterialComposition

Lot number

In-CeramCore

Al2O3, La2O3, SiO2, CaO

In-Ceram
In-Ceram

DentinEnamelNa2O Al2O3 6SiO2
SiO2, La2O3

Powder 62983, Liquid 0899
Glass powder 6186P, 6436P, 6436O
4536, 4902, 4950
4855

Cergogold
Cergogold

DentinEnamelK2O Al2O3 4SiO2
SiO2, MgO, K2O

0021/9, 0031/6, 0021/1
Powder 0322/5, Liquid 0382/12

After firing and glazing procedures, color analysis of all ceramic specimens was undertake with aspectrophotometer (Datacolor, SF300/47-63HZ, Lawrenceville, NJ, USA).

The spectrophotometer wascalibrated according to the manufacturer’s instructions before the analysis. Values were recorded in the CIE Lab
color system. The L, a, and b values of each specimen were measured. Then, all ceramic specimens weresubjected to an accelerated aging in the Weather-O-meter apparatus (M/s Atlas Electric Devices Co., Chicago,IL, USA). A 4,500-W xenon arc lamp was used to simulate D65 daylight. One hundred hours of weathering
process was applied in 100% relative humidity and 37˚C temperature to all ceramic specimens. After theexperimental procedures, color analysis was repeated for each of the specimens, as previously described. The
pre- and post-experimental CIE Lab color values of each specimen were compared with each other by thefollowing formula:∆E = [(L1-L2)2+(a1-a2)2+(b1-b2)2]1/2
where L1, a1, and b1 represent pre-experimental color values of each specimen, and L2,, a2, and b2 represent
post-experimental color values of each specimen. Thus the degree of color change, ∆E is determined.
Two-way analysis of variance (ANOVA) and Dunnett’s T3 test at the 5% level of significance were used toexamine the effects of ceramic types, shades, and the interaction of these two parameters on color stability. The
statistical analysis was performed using SPSS 10.0 for Windows (SPSS Inc., Chicago, IL, USA).

Results
The pre- and post-experimental L, a, and b as well as ∆E values of each of ceramics in their respective shades
are listed in Table 2. The effect of ceramic type on the color change was similar for the A1, A3, and A4 shades(p>0.05). The In-Ceram material had less color change than the Cergogold material. When the shades ofceramic were compared, A1 shade had a greater color change as compared with A3 and A4 shades (p<0.05).
Table 2.

The pre- and post-experimental L, a, and b values and degree of color change ∆E.

Material

L1

SD

a1

SD

b1

SD

L2

SD

In-Ceram A1
In-Ceram A3
In-Ceram A474.75 2.42
71.99 2.15
65.52 2.36

0.95 0.05
3.10 0.19
4.40 0.15

13.06 1.47
16.25 1.24
20.58 1.23

73.23 2.72
70.82 2.63
64.49 2.54

Cergogold A1 75.20 2.13
Cergogold A3 71.89 2.25
Cergogold A4 65.60 2.47

0.75 0.12
1.55 0.23
0.20 0.14

13.82 1.14
19.75 1.25
20.59 1.34

73.39 2.38
70.39 2.47
64.49 2.45

a2SDb2SD∆E

1.10 0.11
3.20 0.24
4.60 0.24

13.24 1.47
16.85 1.24
20.70 1.23

1.54
1.30
1.06

0.80 0.01
1.65 0.24
0.28 0.35

13.84 1.12
20.02 1.42
20.73 1.25

1.81
1.52
1.12

To relate the amount of color change recorded by the spectrophotometer to a clinical environment, the data50

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Int Chin J Dent 2007; 7: 49-52.

were computed to National Bureau of Standards (NBS) units.9 With the NBS units, ∆E values can be describedthrough the equation NBS unit = 0.92 x ∆E. According to the NBS units, these two ceramic materials except forthe Cergogold with shade of A1 showed slight color change. The results of this conversion are shown in Table 3along with the critical remarks of color differences as expressed by the NBS units.
Table 3.

Color differences converted to the NBS units.

Material∆E

NBS unit

Remark

NBS critical remark

In-Ceram A1
In-Ceram A3
In-Ceram A4

1.54
1.30
1.06

1.42
1.20
0.98

SlightSlightSlightSlightSlightSlight(0.5-1.5)(0.5-1.5)(0.5-1.5)

Cergogold A1
Cergogold A3
Cergogold A4

1.81
1.52
1.12

1.66
1.39
1.08

Noticeable
SlightSlight

Noticeable
SlightSlight(1.5-3.0)(0.5-1.5)(0.5-1.5)

Discussion
With the great emphasis placed on aesthetics by modern society, the color stability of aesthetic restorative
materials gains more critical importance. As a restorative material, ceramics has very good clinical properties atthese topics. Traditional point of view was that ceramics has color stability in the clinical relevance environment.
But there was no related experiment to test this theory. In this study an aging device was used to subject samples
to both visible and UV light and 100% relative humidity at 37˚C.

The manufacturer of the weathering

instrument estimates 300 hours of aging is equivalent to one year of clinical service. This is applicable forspecimens, which are in direct sunlight and located horizontally.

However the oral environment is morecomplex. Razoog, et al.10 stated that the greatest amount of color change occurred in the first 100 hours ofaccelerated aging. In our study 100 hours of accelerated aging was found satisfactory to demonstrate the earlycolor change at ceramic materials. Although there were differences between the environments and the duration,
this simulated aging treatment is useful for comparing different materials.
In this study, we used two types of ceramic materials. The In-Ceram uses a high strength core material andthe Cergogold was heat-pressed ceramics. In the former system, low-translucency alumina is often used as thecore material. This system has excellent strength but lower translucency. In contrast, leucite crystal used in theheat-pressed ceramics makes the restoration more translucent. Ceramic specimens were prepared in thickness of
1.5 mm which is similar to the thickness of the restoration at one third of middle labial of central incisor.
A spectrophotometer can measure color difference much smaller than that detected by human eyes. Therefore,
the clinical relevance of color changes recorded by the spectrophotometer must be evaluated. According to CIE
Lab specifications, color changes with a ∆E value lower than 1.5 could not be detectable by human eyes. In thisstudy only one group of ceramic material showed a color change with ∆E value slightly higher than 1.5. The
data for color differences was converted to NBS units, which is a practical way of determining the degree ofcolor difference. With the use of NBS units, it was possible to determine what an observer might report
regarding the color differences that in the ceramics. Comparison of the NBS units indicated that 100 hours ofaccelerated aging did lead to slight color change that can be detected clinically.
Causative factors that may contribute to change in color of aesthetic restorative materials include stain
accumulation, water sorption, leakage, and wear of chemical degradation. Color changes of ceramic materials
may also occur from metal oxide content. According to the findings of the present study, it may be concluded51

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Int Chin J Dent 2007; 7: 49-52.

that both In-Ceram and Cergogold ceramic materials have small color change with accelerated aging, although
the changing is almost undetectable by human eyes. However, long-term clinical evaluation of color stability ofceramics is necessary to substantiate these findings.

References
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2.
3.
4.

Mclean JW. The nature of dental porcelains and their clinical use. Sci Art Dent Porcelain 1979; 1: 115-82.
Ertan AA Ahin ES. Color stability of low fusing porcelains: an in vitro study. J Oral Rehabil 2005; 32: 358-61.
Powers JM, Dennison JB, Koran A. Color stability of restorative resins under accelerated aging. J Dent Res 1978; 57: 964-70.
Powers JM, Abraham MM, Ogura H. Color and optical properties of posterior composites under accelerated aging. Dent
Mater 1985; 4: 62-7.
5. Ferracane JL, Moser JB, Greener RH. Ultraviolet light induced yellowing of dental restorative materials under acceleratedaging. J Dent Res 1985; 54: 483-7.
6. Hekimoglu C, Anil N, Etikan I. Effect of accelerated aging on the color stability of cemented laminate veneers. Int J
Prosthodont 2000; 13: 29-33.
7. Wyszecki G, Stiles WS. Concepts and methods, quantitative data and formulae. Color Science 1982; 344-52.
8. Hekimoglu C, Anil N. Effect of accelerated aging on the color stability of cemented laminated veneers. Int J Prosthodont
2000; 13: 29-33.
9. Nimeroff I. Colorimetry: National Bureau of Standards Monograph 1996; 104.
10. Razzoog M, Lang B, Russel M. A comparison of the color stability of conventional and titanium dental porcelain. J Prosthet
Dent 1994; 72: 453-6.

Correspondence to:Dr. Zhong-yi Wang
Department of Prosthodontics, College of Stomatology, The Fourth Military Medical University
145 Changle Xi Road, Xi’an, 710032, P. R. China
Fax: +86-29-8477-6423 E-mail: nidian@fmmu.edu.cn
Received May 15, 2007. Accepted June 19, 2007.
Copyright ©2007 by the International Chinese Journal of Dentistry.

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