Ergun, Nagas Kruskal-Wallis nonparametric tests. The results dIscuIon of ANOVA and pairwise comparisons indicated The color instability of the lining materials that that there were significant differences among the may affect the patient’s acceptance, have often materials after immersion in DW (except UP and been reported in clinical studies and may lead to DL; MP and TR) (for dw H=25.455; P<.001) and af- a clinical decision to replace the lining.32,33 Even ter aging (except UP and MP) (for aging H=25.974; though the properties of lining materials have P<.001) (Table 5). been much improved, they still have disadvantag- The effects of treatments dependent to each es including water sorption, solubility and obvious material were examined by using Mann-Whitney U color changes.34 The best liner materials available tests (Tables 6 and 7). As seen in Table 6, the most today do not demonstrate an extended service life discoloring treatment was aging (∆E*DL = 16.30, of more than a few years.6,22 P=.004) and the least discoloring treatment was The technology for dental color matching has DW (∆E*UP = 0.41, P=.004). Comparisons between changed over the past several decades. In the pre- these two treatments showed that there were dif- vious studies, colorimeter measurements have ferences in samples of UP, DL, MP, and TR, but been compared with spectrophotometer readings indifferences in samples of UH after immersion in and deemed as reliable and accurate as spectro- DW and aging. photometer for color difference measurements.23,35 Control and aging groups were compared The colorimeter used in this study is new, easy to based on materials by using two-independent- use, portable, offers accurate measurements, the samples Mann-Whitney U tests (Table 7). Compar- spectral range is 380-730 nm and for illumination isons between these two subgroups showed that it uses D65 gas filled tungsten. there were not differences in samples of acrylic CIELAB color space is commonly used in per- and silicone based liner materials after immer- ceptual studies and dental color assessment be- sion in DW, but differences in them after aging. cause of its uniform coverage of the color space. In this system there are three coordinates: L*, Table 2. NBS rating. a*, b*. L* indicates lightness, which ranges from NBS unit CriticalDRifefmeraernkcsesOf Color r0aer(ecbtlciaohcnrkso):mptoaocs1iit0tyi0vce(owaoh*ridctieon)ra.rtTeehsspetohqnaudtasinnttoditiirceeasdtead*ciroaelnoctrdiodbni*-, 0.0 ~ 0.5 Extremely slight change whereas negative a* indicates the green direction; 0.5 ~ 1.5 Slight change positive and negative b* values correspond to yel- 1.5 ~ 3.0 Perceivable change low and blue directions, respectively.20,35,36 In the 3.0 ~ 6.0 Marked change present study, a* values of the tested materials’ 6.0 ~ 12.0 Extremely marked change decreased (to green) either after aging or immer- 12.0 or more Change to other color sion in DW (except MP after immersion in DW). L* Table 3. Color of the liner materials before and after treatments. Material DL Mean SD TR Mean SD UH Mean SD MP Mean SD UP Mean SD Before immersion in DW L* a* b* After immersion in DW L* a* b* 47.35 0.81 39.92 2.48 56.50 1.03 47.08 0.97 42.78 0.17 15.99 0.30 20.06 1.47 9.37 0.33 12.49 0.81 17.15 0.29 8.00 0.26 6.24 0.49 12.25 0.70 11.68 1.41 2.94 0.18 47.39 0.99 40.06 2.47 53.78 2.42 46.74 0.81 42.99 0.27 15.69 0.62 19.11 1.65 9.36 0.62 13.30 0.55 17.00 0.16 7.93 0.27 6.40 0.63 18.47 2.18 13.02 1.11 3.16 0.16 July 2007 - Vol.1 L* 52.31 1.57 39.72 0.71 48.00 0.91 47.11 0.95 44.75 0.90 147 Before aging After aging a* 16.28 0.30 24.22 0.72 12.43 0.83 13.38 0.77 16.21 0.57 b* 7.93 0.27 7.15 0.45 17.66 0.39 11.38 0.60 2.89 0.85 L* 58.69 8.02 42.36 1.92 42.25 0.60 43.81 0.82 43.30 1.09 a* 7.99 3.80 12.09 1.92 12.16 0.42 11.65 0.56 15.83 0.35 b* 16.50 4.69 8.07 3.25 24.05 1.75 13.92 1.42 5.75 1.16 European Journal of Dentistry