reading

Title: Color in dentistry : a clinical guide to predictable esthetics / Stephen J. Chu, Rade D. Paravina, Irena Sailer, Adam J. Mieleszko.

Description: Hanover Park, IL : Quintessence Publishing Co, Inc, [2017] | Includes bibliographical references and index.

Identifiers: LCCN 2017016019 (print) | LCCN 2017018740 (ebook) | ISBN 9780867157611 (ebook) | ISBN 9780867157451 (hardcover)

Classification: LCC RK651 (ebook) | LCC RK651 (print) | NLM WU 507 | DDC 617.6/9--dc23

All rights reserved. This book or any part thereof may not be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, or otherwise, without prior written permission of the publisher.

How can you improve on something that is already the standard in the dental field? Three outstanding clinicians and researchers—Stephen Chu, Rade Paravina, and Irena Sailer—joined forces with master ceramist Adam Mieleszko to do just that. With more information, better explanations, broader topics, clearer images, and input from other experts in this ever-expanding field, this new book Color in Dentistry is an excellent example of what a sequel should accomplish. The original eight chapters from the second edition of Fundamentals of Color (2010) have been enhanced, and there are four new chapters addressing clinical management of hard and soft tissue discolorations; esthetics with pink restorative materials; predictable color reproduction and verification, including seven steps to a successful shade match; and how to create esthetic restorations using the principles detailed in the first 11 chapters. This final chapter serves as an exhaustive how-to guide for successful and functional esthetic restoration. These additional chapters add depth to the book and provide critical information for the clinician, as restorations now relate not only to teeth but also to the surrounding tissues.

Color science and education is still expanding, perhaps at a greater rate than ever before. This is due to the availability of technology, new materials, and techniques in computerized design and machining. The cost of technology is decreasing, making it possible for practitioners to utilize these advances to minimize expensive remakes, patient disappointment, and lost time. Therefore, a primer to help clinicians navigate the dynamics of color, both for the teeth and gingival tissues, is a wonderful complement and guide for any practitioner. This holds true for the student, resident, experienced practitioner, and of course all dental technicians. After all, treatment success depends on collaboration between the dental provider and the dental technician. This book provides the roadmap for getting there.

I encourage everyone to read this book from beginning to end, do the outstanding exercises, and then return to chapter 1. You will have a far better understanding of the power that color holds over your practice upon the second reading.

Stephen F. Bergen, DDS, MSD
Professor of Prosthodontics, New York University College of Dentistry

Since the first edition of Fundamentals of Color was published more than a decade ago and the second edition in 2010, many of the tools and materials used in color and esthetic dentistry have undergone significant improvements with the introduction of new products. As technology continues to evolve, so too does the range of digital shade-matching techniques using technologic systems. Technologic advances in other industries such as photography and lighting and in other subsets of dentistry—eg, intraoral imaging (CAD/CAM), tooth whitening, and restorative materials (both white and pink)—have helped to make the protocols of color dentistry more accurate.

Color dentistry was brought to prominence in the general dental community by the formation of the Society for Color and Appearance in Dentistry (SCAD) and its permanent biannual issue of the Journal of Esthetic and Restorative Dentistry, which is devoted solely to color and appearance. Accordingly, the amount of clinical research and education has also increased, which is extremely important for the expansion of any field. And finally, the development of technology has been complemented by the development of two free programs offered by SCAD intended to increase success in work with color through education and training: the Color Matching Curriculum (CE module) and the Dental Color Matcher (online program).

Color in Dentistry is a new book that strives to consider and reflect these innovative changes with the addition of a new coauthor, Dr Irena Sailer from the University of Geneva, who brings fresh insight and perspective to color in dentistry. The book opens with a critical update to the chapter on color education and training, which is appropriately followed by sound discussions of tooth and gingiva color, color theory, and factors that influence perception of color. The book pragmatically reviews the standard recommended protocols for conventional and technology-based shade matching; these chapters culminate in a straightforward, step-by-step protocol that incorporates both the most current and most respected techniques for successful color reproduction. New chapters addressing discolored tooth substrates, dissimilar material and restoration types, digital photography, gingival (pink) esthetics, and an update on material selection supplement these protocols and are valuable resources in shade matching and color communication. The book concludes with 24 new, in-depth clinical case presentations covering a variety of situations commonly encountered in daily practice.

Like the previous two editions, this new book is written in a logical, succinct manner that simplifies the study of color and helps readers understand, qualify, and quantify shade so they can more easily and accurately communicate with colleagues and laboratory technicians alike.

We are grateful to VITA Zahnfabrik and VITA North America as leaders in manufacturing shade guides and technology-based systems as well as for their continued support for SCAD. We acknowledge SCAD for advancing multidisciplinary collaboration and discovery among industrial and institutional researchers, clinicians, laboratory technicians, and others and for creating and implementing research, educational, and training programs on color and appearance for dental professionals and students. We would also like to give a special thanks to the staff at Quintessence Publishing, who made this book a reality.

We thank Dr Stephen R. Snow for authoring the chapter on digital photography and Dr Razvan Ghinea for writing sections related to the influence of fatigue, adaptation, emotions, and medications on vision in chapter 3 as well as for scientific editing in chapters 2 and 3. We are also indebted to Dr Didier Dietschi for sharing his work that set the standard in composite resin color science and the corresponding case report.

We thank Mr Vincent Fehmer, MDT, at the University of Geneva for his scientific and dental technical contributions to the field of color in dentistry elaborated in detail in this book. We acknowledge specifically his collaboration with respect to Cases 18 to 23 in chapter 12. We are also grateful to Drs So Ran Kwon, Marcos Vargas, Tommaso Mascetti and Federico Ferraris, Sillas Duarte, Newton Fahl, Dominik Büchi, Nadine Fenner, and Sudarat Kiat-Amnuay and Ms Patricia Montgomery for providing clinical cases for chapter 12.

Thanks also go to Mr Kendall Beachman, Assistant Dean at New York University College of Dentistry; Dr Dennis Tarnow at Columbia University; Dr John M. Powers at Dental Consultants; Dr John A. Valenza, Dean at the University of Texas School of Dentistry at Houston; Professor Christoph Hämmerle at the Clinic for Fixed and Removable Prosthodontics and Dental Material Science of the University of Zurich; and Dr Edward A. McLaren at the University of Alabama School of Dentistry for their motivation, inspiration, and ongoing support in dental education. Finally, our appreciation goes to Mr Jason Kim, CDT, for imparting his knowledge and skill in the fields of color and translucency.

IN THIS CHAPTER:

•Cultivating the skill of shade matching

•Currently available shade-matching publications and programs

Many factors influence our ability to achieve accurate shade-matching results, including subjectivity, shade-matching tools, materials, methods, and conditions. Nonetheless, the importance of color education and training should not be underestimated, as Sproull noted in 1974: “The technology of color is not a simple matter that can be learned without study; neither is it a complicated matter beyond the comprehension of dentists.”¹ Color appearance is frequently of critical importance to the final outcome of dental restorations and their acceptance by patients. This is why education and training should be the first step of a process that should result in the predictable and enhanced esthetic outcome of dental restorations.

Successful musicians, painters, and other artists are both gifted and well educated in their craft, and yet they continue to practice and improve their skills. In contrast, little effort is made to assess whether the average dental professional has an eye for shade matching. Moreover, education on color is frequently not even part of the undergraduate or graduate dental school curriculum.¹^–³ Years of shade-matching experience practiced under inappropriate conditions, using inadequate tools and methods, can hardly be called color training. The literature shows that dentists often overestimate their color-matching and reproduction abilities. When asked to match 16 corresponding pairs from two VITA classical A1-D4 shade guides using the visual method, the pre- and postdoctoral participants correctly matched only 50%.⁴ In another study, which closely resembled clinical dentistry in that there was no exact match, the observer’s choice was the second or third best match.⁵

Several surveys have been conducted on color education. The first one, in 1967, revealed that only three institutions (of the 115 institutions that responded) offered a color science course, and only 2.3 classes, on average, referred to color topics.¹ In another survey, core curriculum and elective courses on color were taught at 26% and 17%, respectively, of the 69 responding schools.² A third survey related to teaching of color in predoctoral and postdoctoral dental education was published in 1992. Responses were received from 138 institutions.³ The mean number of hours devoted to color topics was 6.6, and 50% of the schools reported a lack of a color-balanced environment. In addition, 85% of respondents believed that there was a need to develop a new, systematic shade guide. It was concluded that additional efforts should be made regarding the study, research, and application of color science in the dental profession, particularly in undergraduate education.

A fourth survey was published in 2010.⁶ There were a total of 130 responses from North America, Europe, South America, Asia, and Africa. It was reported that a course on color in dentistry was included in the dental curriculum of 80% and 82% of pre- and postdoctoral programs, respectively. Significant differences in the number of hours dedicated to teaching of color were recorded at each level (4.0 versus 5.5 hours, respectively). Significant differences were also reported between the levels for the following: teaching on negative afterimages, color rendering index, VITA Bleachedguide, VITA 3D-Master shade guide, digital camera and lens selection, composite resins, and maxillofacial prosthetic materials, with significantly higher percentages recorded for postdoctoral programs. VITA classical A1-D4 and VITA 3D-Master were the most frequently taught shade guides.

It has been demonstrated in multiple studies that shade-matching devices are more reliable than the predominantly used visual method.⁷ It should be noted that shade-matching results obtained using the visual method were most probably below the expectations of many. Two similar studies, performed on different continents and on different shade-matching tasks, reported pretty similar results: 70% to 80% of the participating dental students were not able to select the best matching tab from the shade guide, while barely 50% of students selected one of three best matches. However, the latter percentage increased to over 72% upon color education and training, which is in accordance with other studies that reported that education and training can improve one’s color-matching skills.⁷^,⁸

Several multimedia color education and training programs are now available (Table 1-1). Each program has its own unique features, but they all are designed with the same intention: to educate/train dental professionals in color matching. A brief description of each program is provided below.

Color Matching Curriculum (CMC; Fig 1-1) is a half-day continuing education (CE) module published by the Society for Color and Appearance in Dentistry (SCAD) and available through the SCAD website upon request.⁹ This CE module has been developed for dental students and dental professionals. The main motivation for this CE course was the notion that shade matching in clinical dentistry still leaves a lot to be desired. Color mismatch of restorations in the anterior zone is a ubiquitous situation causing frustrations to the patient and practitioner alike, while the repetitive corrections of mismatches are time-consuming and expensive. Given patients’ demands to receive restorations that emulate the natural dentition, this state-of-the-art combined didactic/hands-on course is designed to enhance clinical outcomes. The course provides an update on new developments on this subject, revisits traditional teaching materials and introduces improvements, and provides a hands-on section on visual and instrumental shade matching. It consists of the following segments:

The didactic portion of the CMC module provides step-by-step instructions and emphasizes color concepts and resources, methods, conditions, and tools for visual and instrumental shade matching and communication on color and appearance, all of which are essential to master a plan for successful color matching in both the office and dental laboratory. Examples and practical suggestions are provided. Some of the learning objectives include understanding color, learning about advanced shade-matching conditions and methods, contrasting dental shade guides and elaborating color-related properties of dental materials, reviewing the state of the art in tooth-whitening monitoring, and learning about resources for color education and training in esthetic dentistry.⁹

Fig 1-1 Color Matching Curriculum, a free half-day continuing education module published by the Society for Color and Appearance in Dentistry (SCAD).

The hands-on portion is divided into two parts. Based on the fact that tooth color-matching results can improve by using a group-learning approach in a clinical setting, groups of four participants are created in Part I (Fig 1-2). One of the participants serves as “patient,” while the remaining three match the shade of one of his or her maxillary central incisors (an intact natural tooth is preferred over a restored one). This cycle is repeated four times so that each group member serves as the patient. The shade-matching technique introduced in the didactic part of the module is implemented during this hands-on part, with an option for using more than one shade guide in the four cycles. The shade-matching results, the quality of the selected match (rated from 1 [huge mismatch] to 5 [excellent match]), and the difficulty of the task (rated from 1 [very difficult] to 5 [easy]) are recorded on a sheet of paper without allowing group members to see each other’s results. Upon completing each cycle, the three group members that matched the same tooth work as a team and record a team shade match. At the end of these exercises, each user reports his or her results, and all participants provide their comments and perspective.

Fig 1-3 Color competency test. (a) Matching pairs of scattered tabs from two VITA classical A1-D4 shade guides, with the shade designations in one set of tabs being masked. (b) Matched pairs.

Depending on available resources, it is advised that color-corrected light (ceiling, floor, table, or handheld light), light gray bibs, and gray paper, cloth, or cardboard for resting the eyes are used during Part I of the hands-on portion of CMC. Ideally, an exercise on matching pairs of tabs from two identical VITA classical A1-D4 shade guides, with the shade designations in one set of tabs being masked, should be performed by each participant during the CMC module (Fig 1-3). The results should be recorded and interpreted in accordance with ISO/TR 28642: An observer must correctly match at least 75% (12 pairs) or 85% (14 pairs) of the tab pairs presented in the test to be considered to have average or superior color discrimination competency, respectively.¹⁰ Hands-on II is related to demonstration and/or work with one or more color-measuring devices.

Dental Color Matcher (SCAD and Vita Zahnfabrik; Fig 1-4) is a free online education and training program. It is hosted through the SCAD website (www.scadent.org) and serves as the homework supplement for the CMC module.¹¹ This program has been used by thousands of dental professionals and students from over 100 countries and is a combination of color-matching exercises and a didactic video.

The first of the onscreen exercises, “Closest match I,” asks the user to determine the best match to four target shade tabs using VITA Linearguide 3D-Master tabs (Fig 1-5). Afterward, the 25-minute video provides information on the role of color in contemporary esthetic and cosmetic dentistry, shade-matching skills and success of dental professionals, color dimensions and the color of human teeth, and color-matching methods used in dentistry. The video particularly addresses influences on the visual method, such as years in practice, sex, education and training, color-matching conditions, as well as techniques to achieve predictable success with visual shade matching.¹²

Fig 1-4 Dental Color Matcher, a free educational and training program for esthetic dentistry available online (www.scadent.org) and as a CD-ROM.

Fig 1-6 Dental Color Matcher “Matching pairs” exercise: 14 . darker pairs of shade tabs successfully matched.

After the video, users are prompted to “Matching pairs” exercises to match 29 VITA Linearguide 3D-Master pairs (15 lighter pairs and 14 darker pairs; Fig 1-6). The subsequent “Exact match exercise” is identical to the initial “Closest match” exercise except that there is an exact match to each tab. The next step is a quiz in which users answer 12 multiple-choice questions related to the information provided in the video. After completing the program, users can fill out a survey, rate the program, and list its strengths and weaknesses. Upon request, dental professionals can obtain two continuing education hours, while all users obtain a diploma upon program completion issued by SCAD. Dental educators who want to use this program for undergraduate or postgraduate teaching or continuing education for dental students or professionals are encouraged to request a project code (by sending an email to dcm@scadent.org), which will allow them to independently access the results for each enrolled participant.

Fig 1-7 (a) Toothguide Training Box with the associated computer program. (b) Toothguide Training Box with working area illuminated by color-corrected light.

A Contemporary Guide to Color & Shade Selection for Prosthodontics is a DVD published by the American College of Prosthodontists.¹³ It is a predominantly educational tool with 63 figures and 12 instructional videos that complement the pseudonymous text.

In the first part, general color topics are addressed: color triplet, defective color vision, color mixing, the color wheel, a description of color and the relationship between the dimensions of color, and two color notation systems: Munsell and CIELAB. The second part of the text is related to the color of human teeth, dental shade guides, and digital shade selection.

The DVD also includes detailed guidelines for visual shade selection and suggested procedures and discusses:

•Tooth condition, including light transmission and surface characteristics (texture and gloss)

Shade verification and communication with the dental laboratory technician using diagrams and digital images are also elaborated.

Another multimedia program is the Toothguide Trainer software and Toothguide Training Box (Vita Zahnfabrik; Fig 1-7), which are parts of the color-training program.¹⁴^–¹⁶ The exercises in the training software are essentially the same as those in the training box; both utilize 26 shade tabs from the Toothguide 3D-Master (Vita Zahnfabrik). The software uses the images of tabs, whereas the training box uses physical shade tabs along with color-corrected light and computer support. The program is designed in accordance with the three-step method recommended for three-dimensional shade matching (value-chroma-hue selection). A total of 4, 8, and 15 correct matches, respectively, are needed to pass steps 1 (value selection), 2 (value-chroma selection), and 3 (value-chroma-hue selection). After that, the user proceeds to 15 value-chroma-hue tasks in the final exam.

The book Esthetic Color Training in Dentistry (Mosby, 2004) and its supplementary color-training exercises on CD-ROM are designed to be used by dental professionals, educators, and students.¹⁷ The training program consists of an introductory set, a training set, and an advanced set. The introductory and training sets each consist of three groups of exercises that progress from easy to difficult. Each of these six different sets consists of 25 small squares and arranging sets that test shade matching based on differences in value, chroma, or hue, and, for further challenge, differences based on all possible pairs of color dimensions (value/chroma, value/hue, and chroma/hue). The advanced set (Fig 1-8) contains 15 rectangles with color differences that originate from all three color dimensions simultaneously. The software records both first and highest scores and includes a “reset score” option that enables repetition of the exercises or addition of other users.

It is obvious that many things have changed since the first color education and training program was administered back in 1975.¹⁸ In addition to changes related to color education and training, the entire profession has changed along the way. With the development of advanced materials, tools, and technologies and the high percentage of tooth-colored restorations, the expectations of both patients and the profession have increased. Color is one of the most significant parameters when it comes to patient satisfaction. As stated by Bergen, “Color is unimportant to the physiologic success of a dental restoration, yet it could be the controlling factor in the overall acceptance by the patient.”¹⁹

Significant advances have been made in color education and training in dentistry. New books and other types of publications—training programs on CD-ROM, online programs, or those that utilize physical shade tabs—are currently available. Based on purpose and scope, all of these publications and programs offer valuable color education and/or training. Online programs provide free access to a wide range of users (clinicians, dental technicians, dental educators, students, and researchers) seeking color education and training. Color Matching Curriculum, a half-day continuing education module, is the most recent and the most comprehensive resource for dental students and dental professionals. Knowledge and skills acquired through these programs complement the skills of dental professionals and provide an appropriate foundation for their work.

•Most color education and training programs are relatively new, and unfortunately few are currently incorporated into undergraduate or graduate dental education. Therefore, the implementation of available programs and the development of new tools should be the next step in color education and training in dentistry.

1.Sproull RC. Color matching in dentistry. 3. Color control. J Prosthet Dent 1974;31:146–154.

2.O’Keefe KL, Strickler ER, Kerrin HK. Color and shade matching: The weak link in esthetic dentistry. Compendium 1990;11:116–120.

3.Goodkind RJ, Loupe MJ. Teaching of color in predoctoral and postdoctoral dental education in 1988. J Prosthet Dent 1992;67:713–717.

4.Okubo SR, Kanawati A, Richards MW, Childress S. Evaluation of visual and instrument shade matching. J Prosthet Dent 1998;80:642–648.

5.Paravina RD. Performance assessment of dental shade guides. J Dent 2009;37(suppl 1):e15–e20.

6.Paravina RD, O’Neill PN, Swift EJ Jr, Nathanson D, Goodacre CJ. Teaching of color in predoctoral and postdoctoral dental education in 2009. J Dent 2010;38(suppl 2):e34–e40.

7.Clary JA, Ontiveros JC, Cron SG, Paravina RD. Influence of light source, polarization, education, and training on shade matching quality. J Prosthet Dent 2016;116:91–97.

8.Ristic I, Stankovic S, Paravina RD. Influence of color education and training on shade matching skills. J Esthet Restor Dent 2016;28:287–294.

9.Society for Color and Appearance in Dentistry. Color Matching Curriculum. http://www.scadent.org/news/free-color-training. Accessed 3 June 2016.

10.International Organization for Standardization. ISO/TR 28642 Dentistry—Guidance on Color Measurement. Geneva: International Organization for Standardization, 2011.

11.Paravina RD. Dental Color Matcher: An Online Educational and Training Program for Esthetic Dentistry. http://ec2-52-53-152-188.us-west-1.compute.amazonaws.com/. Accessed 2 December 2016.

12.Paravina RD. Color and shade matching. In: Hilton TJ, Ferracane JL, Broome I (eds.). Summitt’s Fundamentals of Operative Dentistry: A Contemporary Approach, ed 4. Chicago: Quintessence, 2013:79–93.

13.Goodacre CJ, Paravina RD, Bergen SF, Preston JD. A Contemporary Guide to Color and Shade Selection for Prosthodontists [DVD]. Chicago: American College of Prosthodontists, 2009.

14.Haddad HJ, Jakstat HA, Arnetzl G, et al. Does gender and experience influence shade matching quality? J Dent 2009;37 (suppl 1):e40–e44.

15.Corcodel N, Karatzogiannis E, Rammelsberg P, Hassel AJ. Evaluation of two different approaches to learning shade matching in dentistry. Acta Odontol Scand 2012;70:83–88.

16.Olms C, Jakstat H. Learning shade differentiation using Toothguide Trainer and Toothguide Training Box: A longitudinal study with dental students. J Dent Educ 2016;80:183–190.

17.Paravina RD, Powers JM. Esthetic Color Training in Dentistry. St Louis: Mosby, 2004.

18.Bergen SF. Color Education for the Dental Profession [thesis]. New York: New York University College of Dentistry, 1975.

IN THIS CHAPTER:

•The physics of color

•Color perception

•Color mixing

•Color in dentistry

Fig 2-1 The wavelengths of light refl ect off the object (a rose), resulting in the perception of color (pink) by the viewer.

Fig 2-2 A red apple. Its specific color description is subjective and debatable, stemming from an emotional or visceral response.

Many have long pondered the question: If a tree falls in the woods and there is no one there to hear it, does it make a sound? In color theory the question becomes: If the petals of a rose are pink and there is no one there to view them, are they actually pink? According to color theorists, the answer is no. The reason for this surprising answer is that in order for a color to exist, there needs to be an interaction between three elements: light, an object, and a viewer (Fig 2-1). If all three elements are not present, color as we know it does not exist.

Color appeals to the visceral and emotional senses. Color is personal; individuals with normal color vision will view the same object similarly, but not exactly the same. Take, for example, the apple shown in Fig 2-2. Most would define its color as red; others might take it a step further and describe it as cranberry red or vibrant ruby red. It is often difficult to come to a consensus based on visual assessment alone. There are numerous factors that influence an individual’s color perception, including lighting conditions, background effects, color blindness, binocular differences, eye fatigue, age, and other physiologic factors (see chapter 3). But even in the absence of these physical considerations, each observer will interpret color differently based on his or her past experiences with color and resulting color references. Each individual also verbally defines an object’s color differently.¹^–⁹

However, there are quantifiable aspects of color that are important for the dental practitioner to understand. Basic knowledge of how color is perceived and reproduced will aid the clinician in evaluating and matching shades in the dental practice.

Although color is generally perceived as an art form, there is a true science behind color theory. Isaac Newton was the first to break down the physics of color. He found that a beam of white light could be separated into component colors, or wavelengths, by passing it through a prism (Fig 2-3). Newton described the resulting continuous series of colors as a spectrum and named these colors in the following order: red, orange, yellow, green, blue, indigo, and violet, as represented by the commonly used mnemonic association Roy G. Biv. These wavelengths are perceived by the three types of color receptors (called L-, M-, and S-cones) in the human eye, mainly as variations of red, green, and blue light, respectively. The human eye can perceive only these wavelengths of light, hence the term visible light spectrum. In physical terms, the wavelengths of visible light range from approximately 380 to 780 nm (Figs 2-4 and 2-5). Each hue is accurately defined by its wavelength or frequency (Table 2-1).

Fig 2-3 Dispersion of light through a prism breaks the light up into its component colored frequencies, which are called wavelengths.

Fig 2-4 The wavelengths of visible light range from 380 nm (violet) to 780 nm (red).

Fig 2-5 The visible light spectrum relative to the whole electromagnetic spectrum.

Newton’s significant breakthrough in the study of color science shifted attention to the light source.¹⁰ His observation was simple: White light contains all colors. If an object appears to be a particular color, this means that the light reaching our eyes when viewing that object has somehow been changed by the object. In other words, it is the interaction of the light with the object that allows perception of color. Therefore, without light, there would be no color.

Psychophysics is a scientific discipline dealing with mathematical relations between physical stimuli and the sensations they cause. Color is a psychophysical sensation provoked in the eye by the visible light and interpreted by the brain. The basic process of color perception can be described as follows. Light is emitted from a light source. This light may reach the eye directly, or it may either strike or pass through an object. If the light interacts with an object, some of the light is absorbed by the object. The wavelengths that are not absorbed (ie, those that are reflected, transmitted, or emitted directly to the eye) are perceived by receptor cells (ie, rods and cones) in the eye and recognized by the brain as a specific color. The individual components of this process are described in more detail below.

Emission of light from a source occurs through a chemical or physical process (Fig 2-6). Every process releases more light at certain wavelengths than at others. To create perfectly white light, a light source would have to emit at each wavelength with the same intensity. In some cases, emissive objects are intended to produce specific colors. These objects, such as computer monitors, produce color by emitting light with distinct wavelength compositions of red, green, and blue light. This process is discussed in greater detail later in this chapter.¹¹

No light source can emit perfectly white light (ie, exactly the same amount of each wavelength). This affects color perception because there are only certain wavelengths (colors) being produced to interact with an object, which explains why the same object will appear to be different colors when viewed using different light sources (see chapter 3).

Transmission occurs when light passes through a transparent or translucent material, such as a slide or film (Fig 2-7). If light encounters molecules or larger particles in the material, some wavelengths of light will be absorbed. The number of light rays and the specific wavelengths (colors) that are absorbed are determined by the density and makeup of the material the light travels through; the wavelengths that are transmitted compose the color that is perceived. If the material is completely transparent, all light is transmitted, and the color white is perceived (if the light source is white). If the material is completely opaque, all light is absorbed, and the color black is perceived (if the object presents no emission.). In most cases, however, some of the wavelengths (colors) are absorbed and others transmitted. If this occurs, the color that is perceived corresponds to the wavelengths that are transmitted. For example, if a material absorbs red wavelengths and transmits green and blue wavelengths, a combination of green and blue (referred to as cyan) is perceived.

Reflection occurs when light rays strike a solid object and then bounce off of it (Fig 2-8). It is a process by which radiation is returned by a surface (surface reflection) or a medium (volume reflection). The volume reflection is predominant in tooth shade matching: Due to the translucency of enamel, light is predominantly reflected from dentin. As far as the angular distribution of the reflected light is concerned, reflection can be specular or diffuse. Specular (mirror-like) reflection is characteristic for smooth surfaces, with the angle of incidence being equal to the angle of reflection but on the opposite side of the normal. Diffuse reflection is reflection in any angle different than the angle of incidence, and it is characteristic for rough surfaces, including microscopically rough surfaces. Total reflection is the sum of specular and diffuse reflection.

Depending on the molecular structure or density of the object or medium, certain wavelengths (colors) may be absorbed rather than reflected. The wavelengths that are reflected compose the color that is perceived (Fig 2-9). Theoretically, an object that reflects all light would be perceived as white (Fig 2-10), and an object that absorbs all light would be perceived as black (Fig 2-11). In most cases, however, the object absorbs some wavelengths (colors) and reflects others (Fig 2-12). If this occurs, the object is perceived to be the color of the wavelengths that are reflected. For example, an object that absorbs green wavelengths but reflects red and blue wavelengths is perceived as a combination of red and blue (referred to as magenta).

Fig 2-9 Diagram showing the percentage of light wavelengths that are reflected by an object. The percentage is measured every 10 nm along the visible light spectrum (380 to 780 nm). The resulting pattern is called a spectral curve and is analogous to the color fingerprint of an object.

The surface properties of the object can affect the reflection, transmission, and absorption of light. Outside conditions such as the lighting and variability of the human eye have no effect.

The wavelengths that reach the eye, whether by emission, transmission, or reflection, are received by the sensory cells on the retina called the rods and cones (Figs 2-13 and 2-14). The color perception of the human visual system mainly depends on the ambient light conditions:

Fig 2-13 The retina of the eye contains three types of cone cells responsible for color perception, as well as rod cells, which are responsible for perception of lightness and darkness.

Fig 2-14 There are fewer cone cells (aqua) in the retina than there are rod cells (green).

•For low luminances (scotopic vision), only rods are used, which have maximum sensitivity at 507 nm. Because only one type of photoreceptor is used (ie, rods) with a narrow spectral sensitivity curve, we cannot distinguish colors at night.

•For medium and high luminances (mesopic and photopic vision), the human eye uses the three types of cones (S-, M-, L-cones), each with different spectral sensitivity curves and peaks at 420 nm, 530 nm, and 560 nm, respectively. For color vision, the signals from the three types of cones are combined in the brain, resulting in a visual stimulus interpreted as color. The three types of cone cells allow us to have trichromatic vision (Fig 2-15).

The key point to understand is that the wavelength pattern that is perceived by the eye is the color’s fingerprint. This fingerprint is formulated from spectral data gathered from the wavelengths of light reflected or transmitted from an object (depending on the measurement setup). It is plotted, in reference to percentage of reflectance and wavelength interval distribution, as a spectral reflectance curve (see Fig 2-9). Therefore, in Fig 2-2, the apple itself is not red; the color that is perceived is only in the form of reflected wavelengths, and the color we sense and remember as red really exists only in our minds (Table 2-2).

Color is reproduced by means of three-dimensional color models that are based on the same mechanism by which color is perceived by the human eye (referred to as tristimulus data) as well as the emission, reflection, or transmission of light, depending on the medium. Colors may appear to be different depending on how they are reproduced. The amounts of the primaries required to achieve a match are called tristimulus values. A color stimulus can be completely described by the three tristimulus values.

Electronic media such as computer monitors and television sets create color by emitting wavelengths that are mixtures of red, green, and blue (RGB) light to stimulate the cones in the human eye. Such media therefore can produce a color spectrum that includes nearly all of the colors in the visible spectrum. Theoretically, if the RGB wavelengths were to be combined, white light would result (Fig 2-16). For this reason, red, green, and blue are referred to as the additive primary colors: From black, color is created by adding certain amounts of RGB wavelengths of light.

The process by which images are captured to be reproduced on emissive media (eg, the capture of images by a digital camera) is similar to the process that occurs when the human eye perceives color. A digital camera picks up tiny pixels of red, green, and blue light and blends them together in varying intensities to create different colors. With that said, it is important to note that a digital camera carries the same subjective values as the human eye and might not always be an accurate means to assess a patient’s tooth shade (see chapter 5).

Media such as printed materials and photographs are considered reflective, and media such as slides and transparencies are considered transmissive, because, respectively, they are visualized through the reflection of light off of their surfaces and the transmission of light through their surfaces as previously described. Color reproduction in reflective and transmissive media is based on the color-absorbing qualities of materials such as ink or dyes. These materials are formulated to absorb some wavelengths and reflect/transmit others to create specific colors. The primary colors in these color systems are those created by the absorption of one of the RGB wavelengths and the reflection/transmission of the others. They are referred to as cyan, magenta, and yellow (CMY). Cyan is produced when red is absorbed and green and blue are reflected/transmitted; magenta is produced when green is absorbed and red and blue are reflected/transmitted; and yellow is produced when blue is absorbed and red and green are reflected/transmitted. The absence (or subtraction) of these three colors would mean that no wavelengths could be absorbed and therefore all wavelengths would be reflected/transmitted, resulting in the color white. For this reason, cyan, magenta, and yellow are referred to as the subtractive primary colors: Color is created by subtracting (absorbing) certain numbers of RGB wavelengths (Fig 2-17).

Fig 2-16 When red, green, and blue wavelengths are mixed together, white light is created.

Fig 2-17 Subtractive primary colors. Subtractive primaries are formed when one additive primary is absorbed and the remaining two are reflected. For example, cyan is formed when the additive primary color red is absorbed and the remaining two additive primary colors, green and blue, are reflected.

● TABLE 1-1 Shade-matching publications and programs
	Format	Publisher	Features
Color Matching Curriculum	Half-day continuing education module, didactic and hands-on	Society for Color and Appearance in Dentistry (www.scadent.org)	Educational and training tool; good for building foundational knowledge and shade-matching skills.
Dental Color Matcher	Software: Online and CD-ROM	Society for Color and Appearance in Dentistry, Vita Zahnfabrik (www.scadent.org)	Comprehensive training software and video available free online.
A Contemporary Guide to Color & Shade Selection for Prosthodontics	DVD	American College of Prosthodontists	Educational tool; good for building foundational knowledge.
Toothguide Trainer & Toothguide Training Box	Online software and training box	Vita Zahnfabrik (www.toothguide.com)	Easily accessible digital practice can be supplemented by physical shade tabs.
Esthetic Color Training in Dentistry	Book and CD-ROM	Mosby	Interactive CD-ROM enhances understanding of the text.

● TABLE 2-1 Wavelengths of colors
Color	Wavelength (nm)*
Red	620–750
Orange	590–620
Yellow	570–590
Green	495–570
Blue	450–495
Violet	380–450
*1 nm = 0.000001 mm.

● TABLE 2-2 Psychophysiologic realities of color perception
Mode of perception	Psychophysiologic reality
Physical	Wavelength of light
Psychophysical	Reception of light wavelength by the eye
Psychologic	Interpretation of light wavelength by the brain