Table VII. Figure of Merit
Wavelength
450 580 700 FOM (580-1) / (450-700)
VP2214 41.80 59.88 60.44 -3.16
VP2213 72.30 71.63 68.05 16.63
VP2184 36.34 50.79 50.24 -3.58
VP2141 45.50 62.31 62.87 -3.53
VP2118 37.08 49.87 48.34 -4.34
VP2117 43.07 51.87 49.15 -8.36
VP2116 54.39 57.72 53.05 42.52
VP2115 52.94 51.24 48.18 10.54
VP2114 61.12 60.89 55.38 10.43
VP2076 46.93 57.57 54.42 -7.55
110 35.51 47.53 47.64 -3.84 120 33.21 46.77 46.80 -3.37 130 31.12 44.59 44.98 -3.14 140 32.17 47.56 48.34 -2.88 210 27.30 43.44 44.10 -2.53 220 27.41 42.11 43.43 -2.57 230 23.76 38.60 40.39 -2.26 240 23.10 40.51 43.06 -1.98 310 23.84 41.59 44.03 -2.01 320 21.20 36.78 39.29 -1.98 330 21.83 40.97 44.52 -1.76 340 19.61 36.21 39.59 -1.76 410 28.36 41.14 43.31 -2.69 420 25.21 37.06 39.07 -2.60 430 25.43 38.03 39.95 -2.55 440 25.05 37.65 40.10 -2.44 510 22.72 35.60 38.39 -2.21 520 20.27 33.52 36.77 -1.97 530 18.83 33.59 36.99 -1.79 540 17.41 31.75 36.36 -1.62
Y-can 22.37 35.02 38.55 -2.10
W-cen 37.71 43.62 42.34 -9.21
LL-cen 17.54 30.34 36.65 -1.54
R-lat 33.02 44.08 45.56 -3.43
Y-cen 21.63 39.83 45.87 -1.60
It can be seen from the FOM values depicted in the table above that the values are incongruent. The FOM for some of the samples were similar though there was a significant difference in the actual shades when perceived visually, giving an indication that the figure of merit based on the Abbe number principle would not relate well with the visual perception of the human eye. Hence, this method of deriving a FOM was disregarded.
Tables 4, 5, and 6 illustrate the ∆E values of the glass-ceramic samples, shade- guide teeth and extracted natural teeth, obtained from the CE 7000A spectrophotometer.
As explained before, ∆E values signify the total color difference from that of the standard used. The ∆E values of samples that visually appear similar correlate well and these values can be used for shade comparison and eventually shade determination. As the values obtained were in reference to a white standard, a huge number is obtained for ∆E.
As the ∆E values increase, the perceptible shade difference also increases. The total color difference ∆E can be divided into:
Lightness difference, ∆L,
Red – green coordinate difference, ∆a, Yellow – blue coordinate difference, ∆b, Saturation difference, ∆C and
Hue difference, ∆H
If the ∆E values of any two objects match, along with their ∆C and ∆H values, the objects must appear similar. A ∆E value lesser than one usually indicates that the shades of the two objects compared are visually similar. ∆E values in the range of 1 – 2 are acceptable for visual comparison of shades; as the ∆E value increases, the visual discrimination of the shade of the objects compared becomes easier. Figure IV.57 illustrates the graphical method of acquiring a, b, ∆C, and ∆H parameters which contribute to the final shade difference.
Figure IV.57. Figure showing the color difference calculation using a, b, C and H coordinates.
These values can be calculated using any set of spectroscopic data. Hence, by manipulating the processing procedures, such as heat treatment, incorporation of coloring ions, etc., during the manufacture of glass-ceramics the required ∆C, ∆H, and consequently ∆E values could be attained and the shade required obtained.
Hence ∆E values can be considered as FOM and could be used in the development of custom shades of glass-ceramics.
b
a
∆C
∆H Sample
Standard Standard
Sample b
a
∆a
∆b
V CONCLUSIONS
In this study, glass-ceramic samples obtained from Ivoclar were spectroscopically analyzed and consequently figure of merit (FOM) derived to express a shade into a value.
Though the exact sample composition was proprietary, the samples were Lithium Silicate glass-ceramics of different shades. Diffuse reflectance, diffuse transmittance and specular reflectance values for the glass-ceramics were obtained and compared to similar experiments done on extracted natural teeth and teeth from a commercially available dental shade-guide, Chromascop (Ivoclar).
Three spectrophotometers were used for all the experiments: Beckman DU70, CE 7000A, and Perkin-Elmer Lambda-900. The results from the Perkin-Elmer Lambda-900 spectrophotometer were incongruous and hence were disregarded. The diffuse reflectance spectra obtained from the glass-ceramic samples indicated that most of the samples were reflective in the longer wavelength region (yellow) and a few of them in the shorter wavelength (blue) regions. Samples were visually evaluated to confirm the results obtained from the spectroscopic measurements. The diffuse transmittance values obtained indicated the levels of translucency in the glass-ceramic samples and this could be confirmed visually.
Fluorescence studies were conducted on the glass-ceramic samples to examine the level of fluorescence exhibited. From the fluorescent spectroscopy measurements, it was deduced that a rare-earth ion, Terbium was incorporated into the glass-ceramics to mimic the fluorescence exhibited by natural teeth. It was also seen that by varying the levels of rare-earth ions, the desired level of fluorescence could be obtained.
The purpose of this thesis was to develop a FOM from the spectroscopic data obtained from the glass-ceramic samples after comparison with similar data obtained
from natural teeth and shade-guide teeth. A FOM based on the Abbe number principle was evaluated using three random wavelengths, two from the ends and one from the center of the visible spectrum. The figure of merit derived did not correlate well when the samples were evaluated visually. This was repeated at different wavelengths and yet the FOM based on Abbe number principle never corroborated well with the visual findings.
CIE L*a*b* values were obtained from CE 7000A spectrophotometer and the total color difference (∆E) was calculated. The ∆E values corroborated well with the visual findings and these could be used to communicate a shade in the form of a number.
VI SUGGESTIONS FOR FUTURE WORK
Further research would include the spectroscopic analysis of the glass-ceramics using individual dental shade-guide teeth as standard runs rather than the standard calibration tile or a Spectralon standard and comparing the ∆E values obtained during each run. Similar experiments could also be performed on natural teeth of volunteers using a hand-held spectrophotometer. This would give us the actual deviation in the shade of the glass-ceramics from the shade of the shade-guide tooth.
More experiments to study the effect of heat and UV-light on the glass-ceramic samples should be performed and the total color difference observed after these experiments be quantified. The data obtained from these results could also help in confirming the efficacy of the ∆E values in expression of the shade. Once the efficacy of
∆E values in expression of the shade is determined, a hand-held spectrophotometer could be customized for dental use.
References
1. W. Merriam, Merriam-Webster's Collegiate Dictionary, 10th ed. Merriam-Webster, Springfield, MA, 1998.
2. Oxford, "Oxford Online Dictionary" (2002) Accessed on: September 13th 2002.
Available at<http://www.oedonline.com>
3. Microsoft, Microsoft Encarta Encyclopedia [CD-ROM] Microsoft, Seattle, WA, 2002.
4. R. D. Paravina, Instrumental Color Matching Methods in Dentistry; p. 110.
Andrejevic Foundation, Houston, TX, 1999.
5. K. H. Hunt, "Bioaesthetics: The Study of Beauty in Life," Dent. Today, 15 [1] 48, 50-5 (1996).
6. W. Holand and G. Beall, Glass-Ceramic Technology, 1st ed.; p. 372. American Ceramic Society, Westerville, OH, 2002.
7. I. Ahmad, "Three-Dimensional Shade Analysis: Perspectives of Color--Part II,"
Pract. Periodontics Aesthet. Dent, 12 [6] 557-64, 66 (2000).
8. L. L. Miller, "Shade Matching," J. Esthet. Dent., 5 [4] 143-53 (1993).
9. A. V. Pensler, "Shade Selection: Problems and Solutions," Compend. Contin.
Educ. Dent., 19 [4] 387-90, 92-4, 96, 98 (1998).
10. J. D. Preston, "Current Status of Shade Selection and Color Matching,"
Quintessence Int., 16 [1] 47-58 (1985).
11. W. D. Cook and P. Vryonis, "Spectral Distributions of Dental Colour-Matching Lamps," Aust. Dent. J., 30 [1] 15-21 (1985).
12. S. Skinner, "Science of Dental Materials," pp. 47-54 in Science of Dental Materials. Edited by R. W. Phillips. Prism Books, Bangalore, India, 1992.
13. W. J. O'Brien, "Double Layer Effect and Other Optical Phenomena Related to Esthetics," Dent. Clin. North Am., 29 [4] 667-72 (1985).
14. J. Neitz and G. H. Jacobs, "Polymorphism in Normal Human Color Vision and Its Mechanism," Vision Res., 30 [4] 621-36 (1990).
15. R. J. Goodkind and M. J. Loupe, "Teaching of Color in Predoctoral and
Postdoctoral Dental Education in 1988," J. Prosthet. Dent., 67 [5] 713-7 (1992).
16. B. E. Clark, "Tooth Color Selection," J. Am. Dent. Assoc., 20 1065-73 (1933).
17. S. R. Hunter, The Measurement of Appearance, 3rd ed.; p. 348. John Wiley &
Sons, New York, 1975.
18. S. Jun, "Communication Is Vital to Produce Natural Looking Metal Ceramic Crowns," J. Dent. Technol., 14 [8] 15-20 (1997).
19. K. O'Keefe, "Improving Shade Matching Techniques. Part II," J. Houston. Dist.
Dent. Soc., 28 (1988).
20. J. A. Sorensen and T. J. Torres, "Improved Color Matching of Metal-Ceramic Restorations. Part I: A Systematic Method for Shade Determination," J. Prosthet.
Dent., 58 [2] 133-9 (1987).
21. R. C. Sproull, "Color Matching in Dentistry. 3. Color Control," J. Prosthet. Dent., 31 [2] 146-54 (1974).
22. C. J. Roberts, "Shade Variation in Dentistry. A Photographic Investigation," Aust.
Dent. J., 29 [6] 384-8 (1984).
23. E. J. Riley and J. M. Filipancic, "Ceramic Shade Determination: Current Technique for a Direct Approach," Int. J. Prosthodont., 2 [2] 131-7 (1989).
24. A. J. McCullock and R. M. McCullock, "Communicating Shades: A Clinical and Technical Perspective," Dent. Update, 26 [6] 247-50, 52 (1999).
25. J. A. Lichter, B. H. Solomowitz, and M. Sher, "Shade Selection. Communicating with the Laboratory Technician," N. Y. State Dent. J., 66 [5] 42-6 (2000).
26. J. C. Kessler, "Dentist and Laboratory: Communication for Success," J. Am. Dent.
Assoc., 1987 [Dec. Spec. No] 97E-102E.
27. R. B. Blackman, "Ceramic Shade Prescriptions for Work Authorizations," J.
Prosthet. Dent., 47 [1] 28-35 (1982).
28. R. A. Weale, "On Matching Colours," Vision Res., 21 [9] 1431-2 (1981).
29. N. R. Hall, "Tooth Colour Selection: The Application of Colour Science to Dental Colour Matching," Aust. Prosthodont. J., 5 41-6 (1991).
30. I. Ahmad, "Three-Dimensional Shade Analysis: Perspectives of Color--Part I,"
Pract. Periodontics Aesthet. Dent., 11 [7] 789-96, 98 (1999).
31. R. C. Sproull, "Color Matching in Dentistry. Part II. Practical Applications of the Organization of Color. 1973," J. Prosthet. Dent., 86 [5] 458-64 (2001).
32. R. C. Sproull, "Color Matching in Dentistry. Part I. The Three-Dimensional Nature of Color. 1973," J. Prosthet. Dent., 86 [5] 453-7 (2001).
33. B. E. Clark, "An Analysis of Tooth Color," J. Am. Dent. Assoc., 18 2093-103 (1931).
34. M. Marui, "Color of the Tooth Crown. I. Color Standards for Tooth Crown and Skin," Kokubyo Gakkai Zasshi, 35 [3] 412-21 (1968).
35. P. A. Lemire and B. Burk, Color in Dentistry; p. 148. JM Ney, Bloomfield, CT, 1975.
36. R. J. Goodkind, K. M. Keenan, and W. B. Schwabacher, "A Comparison of Chromascan and Spectrophotometric Color Measurements of 100 Natural Teeth,"
J. Prosthet. Dent., 53 [1] 105-9 (1985).
37. W. J. O'Brien, H. Hemmendinger, K. M. Boenke, J. B. Linger, and C. L. Groh,
"Color Distribution of Three Regions of Extracted Human Teeth," Dent. Mater., 13 [3] 179-85 (1997).
38. K. McLaren, "The Development of the CIE 1976 (L*a*B*) Uniform Colour- Space and Colour Difference Formula," J. Soc. Dyers Colour., 92 [3] 338-41 (1976).
39. G. Hoffmann, "CIE Color Space" (2002) Accessed on: Oct 16 2002. Available at
<http://www.fho-emden.de/~hoffmann>
40. J. D. Brewer, J. S. Glennon, and D. A. Garlapo, "Spectrophotometric Analysis of a Nongreening, Metal-Fusing Porcelain," J. Prosthet. Dent., 65 [5] 634-41 (1991).
41. P. S. Lund and T. J. Piotrowski, "Color Changes of Porcelain Surface Colorants Resulting from Firing," Int. J. Prosthodont., 5 [1] 22-7 (1992).
42. G. Monsenego, G. Burdairon, and B. Clerjaud, "Fluorescence of Dental Porcelain," J. Prosthet. Dent., 69 [1] 106-13 (1993).
43. G. Monsenego, G. Burdairon, C. Porte, and C. Naud, "Fluorescence of Shade Guides," Cah Prothese, 73 85-91 (1991).
44. A. Obregon, R. J. Goodkind, and W. B. Schwabacher, "Effects of Opaque and Porcelain Surface Texture on the Color of Ceramometal Restorations," J.
Prosthet. Dent., 46 [3] 330-40 (1981).
45. J. D. Brewer, C. K. Akers, D. A. Garlapo, and S. E. Sorensen, "Spectrometric Analysis of the Influence of Metal Substrates on the Color of Metal-Ceramic Restorations," J. Dent. Res., 64 [1] 74-7 (1985).
46. M. W. Jorgenson and R. J. Goodkind, "Spectrophotometric Study of Five Porcelain Shades Relative to the Dimensions of Color, Porcelain Thickness, and Repeated Firings," J. Prosthet. Dent., 42 [1] 96-105 (1979).
47. A. G. Wee, E. Y. Kang, W. M. Johnston, and R. R. Seghi, "Evaluating Porcelain Color Match of Different Porcelain Shade-Matching Systems," J. Esthet. Dent., 12 [5] 271-80 (2000).
48. M. G. Eves, "Shade Selection and Value Control," J. Dent. Technol., 17 [1] 11-7 (2000).
49. J. M. Leon, "Shade Selection - the Art and Science of Color Matching,"
Quintessence Int., 13 [8] 851-9 (1982).
50. G. O'Beirne, "Shade Selection for Porcelain Restorations," J. Ir. Dent. Assoc., 37 [3-4] 78-9 (1991).
51. S. J. Chu, "The Science of Color and Shade Selection in Aesthetic Dentistry,"
Dent. Today, 21 [9] 86-9 (2002).
52. E. Pizzamiglio, "A Color Selection Technique," J. Prosthet. Dent., 66 [5] 592-6 (1991).
53. L. W. Seluk and T. D. LaLonde, "Esthetics and Communication with a Custom Shade Guide," Dent. Clin. North Am., 29 [4] 741-51 (1985).
54. K. O'Keefe, "Improving Shade Matching Techniques," J. Houston Dist. Dent.
Soc., 27 (1988).
55. R. R. Seghi, W. M. Johnston, and W. J. O'Brien, "Spectrophotometric Analysis of Color Differences between Porcelain Systems," J. Prosthet. Dent., 56 [1] 35-40 (1986).
56. R. R. Seghi, E. R. Hewlett, and J. Kim, "Visual and Instrumental Colorimetric Assessments of Small Color Differences on Translucent Dental Porcelain," J.
Dent. Res., 68 [12] 1760-4 (1989).
57. R. R. Seghi, "Effects of Instrument-Measuring Geometry on Colorimetric Assessments of Dental Porcelains," J. Dent. Res., 69 [5] 1180-3 (1990).
58. R. R. Seghi, W. M. Johnston, and W. J. O'Brien, "Performance Assessment of Colorimetric Devices on Dental Porcelains," J. Dent. Res., 68 [12] 1755-9 (1989).