ncreased Predictability in Tooth Shade-Matching

ncreased Predictability in Tooth Shade-Matching

Kelvin I. Afrashtehfar, DDS, MSc(C)

FOUNDATION OF ESTHETIC DENTISTRY
Cosmetic and esthetic dental outcomes are essential to meet patients’ high expectations and positively influence their self-esteem.1,2 Shape and color determine the aesthetics of both natural and restored teeth.3-6 Attractive restorative and prosthodontic outcomes begin with a consistent buccal shape and silhouette that reflect light.7 The perceived color of natural teeth depends on the illuminating light source, critical to translucency, opalescence and fluorescence.8,9. 

Selecting the appropriate shade-matching color has many clinical applications: porcelain and composite restorations, removable prosthetic teeth and gingival components. Determining a precise shade is dependent on clinical skill, shade guide system and lighting conditions. This paper reviews some of the significant factors in the process of tooth shade matching and benefits of modern light correcting techniques.

ESSENTIALS OF COLOR CONCEPTS
According to the Glossary of Prosthodontic terms10, color can be defined as ‘the quality of an object or substance with respect to light reected or transmitted by it. Color is usually determined visually by measurement of hue, saturation, and luminous reectance of the reected light.’ The three components of color are: light source (illuminates the object), object (reflects, absorbs or transmits the incident light to the observer) and the observer (perceives the reflected light).11–13

For indirect cases, the clinician must convey the primary tooth shade characteristics of hue, chroma, and value to the technician who, in turn, produces restorations that match to the remaining dental structure.14,15 Huerefers to the varying wavelengths of observed radiant energy (red, yellow, green, blue, purple, etc).10 Approximately 80 percent of natural teeth fall into the A hue range.16,17 Chroma describes the strength or saturation of the hue.10 Value, lightness or brightness, distinguishes a color’s relative darkness,10 Value is often the most important dimension of shade.18-20

Natural teeth exhibit translucency, fluorescence and opalescence, all of which information is necessary for successful shade matching. Translucency is the gradient between transparent and opaque.8 Fluorescence is the absorption of short wavelength light with the spontaneous emission of longer wavelength light.21 Opalescence makes a material appear one color with reflected light and another color with transmitted light.22

TOOLS FOR TRANSMISSION OF TOOTH SHADE COLORThe traditional technique for shade matching is the visual alignment of natural teeth with a shade guide tab. The commonly available shade guides are the standard dental shade-matching instruments.23,24 Computerized spectrophotometer and colorimeter devices use color quantification that generally provides a more accurate color-matching outcome. However, due to their high cost, these instruments are used more in research in practice.15,25,26

OPERATOR LIMITATIONS AFFECTING SHADE MATCHINGShade matching ability varies with experience, age and individual degree of color perception (functional ganglion cell density and rod and cone photoreceptor morphology).27,28

Age. Images are perceived as more yellowish and brownish as eyes age.

Gender. It is commonly believed that women see color more accurately than men. However, there are many studies that show no gender difference.29-35

Experience. The issue of whether the accuracy of shade matching is innate or an acquired (learned) skill is unresolved. Many studies, interestingly, contradict the notion that experience is influential in shade matching.30,31,33,36-39

Eye color. Brown eyes, with more melanin, absorb wavelengths better,40 possibly influencing sight but not color perception.

Astigmatism, hypermetropia and myopia. When these refractive errors are corrected with eyeglasses or contact lenses, their ability to influence shade-matching is insignificant.41

LIGHT SOURCE EVOLUTIONThe most important factor in shade matching is the light source. Since natural light conditions vary, the recommended standard for dental shade matching is a color temperature of 5500°K and a color-rendering index (CRI) greater than 93.42,43 The CRI measures the balance of all the visible wavelengths. Viewing teeth under diffuse illumination minimizes reflected light distortion.21 A lowered light intensity makes fine details hard to see and complicates the perception of hue. The value guide is the first to be used18-20,44 preferably with lower light levels (operator may squint) since this the best environment for determining value.7,19 There is reliable evidence supporting the utilization of a corrected lighting source during tooth shade matching.29-33,35,43,45

In the United Kingdom, a study combining color-correcting devices with a digital recording device improved the success of matching dental shades when compared to the digital device alone under normal light condition.29 It has been demonstrated that a standardizing daylight lamp significantly improves the ability to match colors when compared to natural daylight.45 Shade matching performance under corrected light sources was significant better than natural or clinical light.32 Even a low color-temperature illuminant notably improves color matching in vision deficient individuals.46,47 Another study indicated that, overall, a light-correcting source creates the most beneficial environment for shade taking.43 Ideally, both the clinician and the technician should operate under similar balanced, full-spectrum lighting conditions, creating closely adapted spectral reflectance curves (optical properties) of original and restoration. This offers a successful color match, with minimal metamerism.48,49

RITE LITE 2 Tri-Spectra SHADE MATCHING INSTRUMENT
This portable and wireless light-correcting device (Addent, Danbury CT) has been designed to assist chairside shade matching. The aluminum-clad device consists of a ring with a 3cm window-hole (for viewing the patient’s teeth) attached to an ergonomic handle. The ring contains 12 LEDs that illuminate the dentition equally from all directions to avoid glare, distortion, and direct reflections (Fig. 1). The brightness of the Rite Lite 2 eliminates the color distortion caused by the color of the dental chair, the operatory, and even brightly colored clothing. However, a color neutral grey or blue bib is still recommended. Six of the diodes are set at 5500°K, while the others produce 3200°K. Battery operated (2 AA cells) and lightweight (185g), the Rite Lite 2 can be used by any member of the dental team. If the battery level falls below the critical power required for full illumination, the device notifies the user.

The two sets of diodes offer three separate color temperature settings at the touch of a button:

• 5500°K (CRI of 92.2) is closest to natural daylight, and is considered the standard shade-matching environment. The six 5500°K LEDs are activated by pushing the button once.

• 3200°K simulates incandescent light. It is produced by the other 6 LEDs by pushing the button a second time.

• 3900°K represents a combined incandescent-fluorescent indoor lighting. This light is produced when all 12 LEDs are activated by pushing the activation button a third time.

The 5500°K color temperature is a bright, sunny “outdoors” illumination. The other light settings mimic the indoor ambient illumination to which patients are exposed indoors. By color matching at all three “temperatures”, the dentist can avoid restorative metamerism, whereby the restoration looks good indoors but not outside, or vice versa.

BENEFITS OF TRI-SPECTRA LED TECHNOLOGY
For the clinician: Initial daylight mode shade determination is supplemented by room and ambient light modes to avoid metamerism50 without the patient leaving the dental chair (Fig. 2). The Rite Lite 2 is portable and wireless, and is far less costly than digital spectrophotometers and colorimeters.

For the ceramist: The shade of the fired ceramic can be verified during build-up without leaving the workstation. The shade of the finished restoration can be verified on the model (quality control) prior to returning the case to the clinician.

THE SHADE-TAKING ENVIRONMENT
It is recommended that the shade-matching be conducted with a specified neutral background gray50-53 that has no complimentary color, and is restful to the eyes’ retinal cones.52 A neutral pink may also be used (Fig. 3).

Bright colors adjacent to the teeth to be shade-matched can cause perceptual problems: red lipstick, for example, fatigues the red receptors in the clinician’s eyes while the blue and green receptors remain fresh and fully capable of stimulation. This leads to a color-evaluation that leans more to the blue-green than it should. Brightly colored clothing or jewelry can have a similar distorting effect.54 Thus, lipstick and jewelry should be removed, and clothing covered by a neutral grayish bib, prior to shade taking. While contrast assists visual perception, an excess of it causes glare. A very bright object on a dark background can affect the shade-taker’s perception.9,55

Ideal time of the day for shade matching?“Ideal time-of-day” recommendations are unreliable since daylight varies by location, season, solar position and inclination, windows size and direction, weather conditions, and geography.24,51

Shade matching within the appointmentShade selection is best accomplished before treatment. As the teeth dry out during treatment, their value (whiteness) increases while their chroma and translucency decrease.56 Shade selection is contraindicated after using a curing light.

Eye fatigue awarenessThe high intensity (brightness) and glare of the operatory light cause eye fatigue. Shade selection is best performed prior to turning on the operatory light.57 Eye fatigue may be reduced by utilizing a daylight corrective lamp during shade match selection.32,58 Staring at the teeth for more than five seconds during shade selection causes hue accommodation, and should be avoided.19 First impressions are always better. Eyes can rest by looking at a blue background.51 In a dedicated shade-taking room, the walls should be gray and illuminated by daylight-correcting lamps.58

Surface moistureTeeth should be dry when evaluating value, translucency, surface texture, and luster. Teeth should be wet for evaluating hue and chroma to limit the influence of surface morphology.

PHOTOGRAPHYTo assist in shade communication with the laboratory technician, the following photographs should be included in the prescription: full face, natural smile, retracted lips and cheeks, and the selected shade tabs against the adjacent natural teeth. At the very least, the last photo must be sent.59 Photographic shade matching is a great communication tool, but shade tabs must be selected under specific lighting as well (Fig. 4).

DENTAL LABORATORY PRESCRIPTIONThe ideal prescription is a 3-D representation of the shade-map, preferably from several perspective points (vectoring). The facial surface is divided into 9-16 distinct zones (Fig. 5). The surface texture and luster have an impact on the optical properties of the tooth and should be described.60

ADDITIONAL RECOMMENDATIONS
1. Always use a standardized full-spectrum light source under appropriate conditions when taking shades.

2. Use the shade tabs in the shade guide rather than on their own to significantly increase accuracy.37 (Fig. 6)

3. Hold the incisal edge of the shade tab to the incisal edge of the tooth; the reflectance reduces afterimages.49 (Fig. 7)

4. Use the mid-buccal of the tooth to select the hue.61,62

5. Evaluate shade by looking at the tooth from different angles (vectoring) to accommodate for curved translucent surfaces, the anisotropic properties of enamel, and the complex layering of the tooth structure.50,52,57

6. Delay shade matching for at least one month after bleaching to allow the enamel to rehydrate and achieve color stability.63,64

 

CONCLUSIONRegardless of the operator’s gender, training and experience, shade-matching ability in the clinical practice and the dental laboratory improves significantly when conventional lighting is modified by light-correction. Accurate shade selection that allows restorations to match the natural dentition positively influences the patient’s appearance and esthetic self-esteem. OH

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Dr. Afrashtehfar is a post-graduate research trainee in the field of Oral and Craniofacial Sciences. His training is focused on multidisciplinary research including Health Technology Assessment and Evidence-based Dentistry. He is a Fellow of the Academy of Dentistry International and a reviewer for the European Journal of Oral Implantology. His first textbook entitled ‘Computerized Dental Occlusal Analysis for Temporomandibular Disorders’ will be released this year. Since his arrival in Montreal, Canada, Dr. Kelvin Ian has collaborated with the Jewish General Hospital, Children’s General Hospital, Université de Montréal and McGill University. He can be reached atkelvin.afrashtehfar@mail.mcgill.ca

Oral Health welcomes this original article.

REFERENCES1. Freedman G. Buyer’s guide to cosmetic imaging systems. Cosmetic imaging creates projection of restorative treatment. Dent Today 2009;28(7):134-8.

2. Glick K. Cosmetic dentistry is still dentistry. J Can Dent Assoc 2000;66(2):88-9.

3. Jeannin T, Ubassy G. [Anterior prosthetic restoration]. Cah Prothese 1984;12(46):93-100.

4. Ubassy G. [Elaboration and natural stratification of dental ceramics (2)]. Rev Fr Prothes Dent 1990(15):19-26.

5. Ubassy G. [Fabrication and natural stratification of dental ceramics 1]. Rev Fr Prothes Dent 1990(14):61-70.

6. Terry DA, Geller W, Tric O, et al. Anatomical form defines color: function, form, and aesthetics. Pract Proced Aesthet Dent 2002;14(1):59-67; quiz 68.

7. Glick KL. Color management of cosmetic restorations. Curr Opin Cosmet Dent 1995:36-40.

8. Villarroel M, Fahl N, De Sousa AM, De Oliveira OB, Jr. Direct esthetic restorations based on translucency and opacity of composite resins. J Esthet Restor Dent 2011;23(2):73-87.

9. Meyenberg KH. Dental esthetics: a European perspective. J Esthet Dent 1994;6(6):274-81.

10. The glossary of prosthodontic terms. J Prosthet Dent 2005;94(1):10-92.

11. Burkinshaw SM. Colour in relation to dentistry. Fundamentals of colour science. Br Dent J 2004;196(1):33-41; discussion 29.

12. Jaint N, Verma P, Mittal S, Singh AK, Munjal S. Gender based alteration in color perception. Indian J Physiol Pharmacol 2010;54(4):366-70.

13. Fondriest J. Shade matching in restorative dentistry: the science and strategies. Int J Periodontics Restorative Dent 2003;23(5):467-79.

14. Winkler S, Boberick KG, Weitz KS, Datikashvili I, Wood R. Shade matching by dental students. J Oral Implantol 2006;32(5):256-8.

15. Baltzer A, Kaufmann-Jinoian V. Shading of ceramic crowns using digital tooth shade matching devices. Int J Comput Dent 2005;8(2):129-52.

16. Touati B. Excellence with simplicity in aesthetic dentistry. Pract Periodontics Aesthet Dent 1997;9(7):806-8, 10, 12.

17. Hall NR, Kafalias MC. Composite colour matching: the development and evaluation of a restorative colour matching system. Aust Prosthodont J 1991;5:47-52.

18. Yuan JC, Brewer JD, Monaco EA, Jr., Davis EL. Defining a natural tooth color space based on a 3-dimensional shade system. J Prosthet Dent 2007;98(2):110-9.

19. Miller LL. Shade matching. J Esthet Dent 1993;5(4):143-53.

20. Sorensen JA, Torres TJ. Improved color matching of metal-ceramic restorations. Part I: A systematic method for shade determination. J Prosthet Dent 1987;58(2):133-9.

21. McLaren EA. Luminescent veneers. J Esthet Dent 1997;9(1):3-12.

22. Sundar V, Amber PL. Opals in nature. J Dent Technol 1999;16(8):15-7.

23. Della Bona A, Barrett AA, Rosa V, Pinzetta C. Visual and instrumental agreement in dental shade selection: three distinct observer populations and shade matching protocols. Dent Mater 2009;25(2):276-81.

24. Li Q, Wang YN. Comparison of shade matching by visual observation and an intraoral dental colorimeter. J Oral Rehabil 2007;34(11):848-54.

25. Corcodel N, Zenthofer A, Setz J, Rammelsberg P, Hassel AJ. Estimating costs for shade matching and shade corrections of fixed partial dentures for dental technicians in Germany: a pilot investigation. Acta Odontol Scand 2011;69(5):319-20.

26. Jorgenson MW, Goodkind RJ. Spectrophotometric study of five porcelain shades relative to the dimensions of color, porcelain thickness, and repeated firings. J Prosthet Dent 1979;42(1):96-105.

27. O’Neill-Biba M, Sivaprasad S, Rodriguez-Carmona M, Wolf JE, Barbur JL. Loss of chromatic sensitivity in AMD and diabetes: a comparative study. Ophthalmic Physiol Opt 2010;30(5):705-16.

28. Redmond T, Zlatkova MB, Garway-Heath DF, Anderson RS. The effect of age on the area of complete spatial summation for chromatic and achromatic stimuli. Invest Ophthalmol Vis Sci 2010;51(12):6533-9.

29. McAndrew R, Chan PW, Milward PJ. An assessment of shade taking by dental undergraduates. Eur J Prosthodont Restor Dent 2010;18(1):13-6.

30. Jasinevicius TR, Curd FM, Schilling L, Sadan A. Shade-matching abilities of dental laboratory technicians using a commercial light source. J Prosthodont 2009;18(1):60-3.

31. Curd FM, Jasinevicius TR, Graves A, Cox V, Sadan A. Comparison of the shade matching ability of dental students using two light sources. J Prosthet Dent 2006;96(6):391-6.

32. Nakhaei M, Ghanbarzadeh J, Keyvanloo S, Alavi S, Jafarzadeh H. Shade matching performance of dental students with three various lighting conditions. J Contemp Dent Pract 2013;14(1):100-3.

33. Paravina RD. Evaluation of a newly developed visual shade-matching apparatus. Int J Prosthodont 2002;15(6):528-34.

34. Tung FF, Goldstein GR, Jang S, Hittelman E. The repeatability of an intraoral dental colorimeter. J Prosthet Dent 2002;88(6):585-90.

35. Hassel AJ, Koke U, Schmitter M, Beck J, Rammelsberg P. Clinical effect of different shade guide systems on the tooth shades of ceramic-veneered restorations. Int J Prosthodont 2005;18(5):422-6.

36. Jaju RA, Nagai S, Karimbux N, Da Silva JD. Evaluating tooth color matching ability of dental students. J Dent Educ 2010;74(9):1002-10.

37. Xu MM, Xu TK, Liu F, Ren SX, Feng HL. [Comparison of shade matching accuracy of tabs of shadeguide and tabs out of shadeguide]. Zhonghua Kou Qiang Yi Xue Za Zhi 2009;44(7):430-2.

38. Haddad HJ, Jakstat HA, Arnetzl G, et al. Does gender and experience influence shade matching quality? J Dent 2009;37 Suppl 1:e40-4.

39. Donahue JL, Goodkind RJ, Schwabacher WB, Aeppli DP. Shade color discrimination by men and women. J Prosthet Dent 1991;65(5):699-703.

40. Sturm RA, Frudakis TN. Eye colour: portals into pigmentation genes and ancestry. Trends Genet 2004;20(8):327-32.

41. Nguyen-Tri D, Overbury O, Faubert J. The role of lenticular senescence in age-related color vision changes. Invest Ophthalmol Vis Sci 2003;44(8):3698-704.

42. Martinez-Verdu F, Perales E, Chorro E, et al. Computation and visualization of the MacAdam limits for any lightness, hue angle, and light source. J Opt Soc Am A Opt Image Sci Vis 2007;24(6):1501-15.

43. Dagg H, O’Connell B, Claffey N, Byrne D, Gorman C. The influence of some different factors on the accuracy of shade selection. J Oral Rehabil 2004;31(9):900-4.

44. McLaren EA, Schoenbaum T. Combine conventional and digital methods to maximize shade matching. Compend Contin Educ Dent 2011;32 Spec No 4:30, 32-3.

45. Corcodel N, Rammelsberg P, Moldovan O, Dreyhaupt J, Hassel AJ. Effect of external light conditions during matching of tooth color: an intraindividual comparison. Int J Prosthodont 2009;22(1):75-7.

46. Gokce HS, Piskin B, Ceyhan D, Gokce SM, Arisan V. Shade matching performance of normal and color vision-deficient dental professionals with standard daylight and tungsten illuminants. J Prosthet Dent 2010;103(3):139-47.

47. Paramei GV, Bimler DL, Cavonius CR. Effect of luminance on color perception of protanopes. Vision Res 1998;38(21):3397-401.

48. Sproull RC. Color matching in dentistry. Part II. Practical applications of the organization of color. 1973. J Prosthet Dent 2001;86(5):458-64.

49. Sproull RC. Color matching in dentistry. 3. Color control. J Prosthet Dent 1974;31(2):146-54.

50. Pensler AV. Shade selection: problems and solutions. Compend Contin Educ Dent 1998;19(4):387-90, 92-4, 96; quiz 98.

51. Capa N, Malkondu O, Kazazoglu E, Calikkocaoglu S. Evaluating factors that affect the shade-matching ability of dentists, dental staff members and laypeople. J Am Dent Assoc 2010;141(1):71-6.

52. Jun S. Communication is vital to produce natural looking metal ceramic crowns. J Dent Technol 1997;14(8):15-20.

53. Pensler AV. Photography in the dental practice (II). Quintessence Int Dent Dig 1983;14(8):855-8.

54. Jun SK. Shade matching and communication in conjunction with segmental porcelain buildup. Pract Periodontics Aesthet Dent 1999;11(4):457-64; quiz 66.

55. Dudea D, Lasserre JF, Alb C, et al. Patients’ perspective on dental aesthetics in a South-Eastern European community. J Dent 2012;40 Suppl 1:e72-81.

56. Monetti L. How to match the real thing. Tips on choosing shades for artificial teeth. Dent Teamwork 1993;6(3):38-9.

57. McCullock AJ, McCullock RM. Communicating shades: a clinical and technical perspective. Dent Update 1999;26(6):247-50, 52.

58. Barna GJ, Taylor JW, King GE, Pelleu GB, Jr. The influence of selected light intensities on color perception within the color range of natural teeth. J Prosthet Dent 1981;46(4):450-3.

59. Christensen GJ. Improving dentist-technician interaction and communication. J Am Dent Assoc 2009;140(4):475-8.

60. Ancowitz S, Torres T, Rostami H. Texturing and polishing. The final attempt at value control. Dent Clin North Am 1998;42(4):607-12, viii.

61. Ray NJ. Some aspects of colour and colour matching in dentistry. J Ir Dent Assoc 1994;40(1):16-9.

62. Hasegawa A, Ikeda I, Kawaguchi S. Color and translucency of in vivo natural central incisors. J Prosthet Dent 2000;83(4):418-23.

63. Schwartz JC. Anterior fixed prosthetic restorations and the bleached dentition: laboratory techniques. Pract Periodontics Aesthet Dent 1998;10(8):1049-55; quiz 56.

64. Kugel G, Ferreira S. The art and science of tooth whitening. J Mass Dent Soc 2005;53(4):34-7..

                                                         

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