SHADE SELECTION AND SHADE COMMUNICATION: PART-3

Prosthodontics

Dr. Moez I. Khakiani (Prosthodontist), Dr. Mayur Dawda (Private Practice), Dr. Akshay Sharma (Prosthodontist) MIK Dental, Mumbai, India

This article is a direct extract from the book by Dr. Moez Khakiani, titled Clinical Fixed Prosthodontics- Master Volume. It is a color atlas suited for clinicians who wish to expand their horizons in advanced prosthodontics. It has over 400, pages, and over 2500 color illustrations distributed over 25 chapters. It is a MUST-HAVE guide for clinical prosthodontics, including chapters like master level occlusion, full mouth rehabilitation, porcelain veneers, table top prostheses, implant dentistry, digital dentistry, etc.
Why don’t you give this book a try?
It is available for preview and purchase on www.mikdental.in, or you could connect on +91 9833400664 for the same.

COMMUNICATION OF THE SELECTED SHADE (BETWEEN THE DENTAL CLINIC AND THE LABORATORY)

Like in every aspect of life; communication is the key to shade matching.

Communication with the laboratory can be in one or a combination of the following:

A. WRITTEN COMMUNICATION

Written communication ranges from mentioning the shade tab number alone to sharing a shade distribution chart that delineates in detail every finding on the reference tooth, as shown in Fig. 3.36, 3.37.
Shade mapping is a technique that involves dividing the tooth into multiple segments, with specific shade communication for each segment. It helps in the communication of individual characteristics like hairline fractures, hypocalcifications, proximal translucencies, incisal edge effects, etc.
In addition, the surface texture and luster should be described as heavy, moderate or light, since these have an impact on the optical properties of the prosthesis.

Fig. 3.36, 3.37: Shade distribution chart can tremendously help in communication and reciprocation of minute surface and sub-surface characteristics of the tooth.

B. PHOTOGRAPHIC COMMUNICATION

The evolution in digital photography has significantly added to our ability of communicating shades.
Digital photography involves the use of a sensor instead of the traditional film. This sensor contains millions of light sensitive elements that record all the colors at every pixel location. In addition, flashes used for digital photography happen to have the same color temperature as that of natural day-light (between 5500° and 6000° K) that is recommended for shade selection.
The use of shade guides in conjugation with digital photography, makes it one of the simplest and yet most effective means of shade communication.
When communicating shades using dental photography, it is important to ensure:

  • Correct exposure parameters are used. This aspect is explained in detail in Chapter No. 19 on ‘Photography in Dentistry’.
  • All protocols for shade tab position in relation to the reference tooth are followed.
  • The shade tab along with its shade number should be visible in the image.
  • Images should be made with and without contrastors. This is especially relevant in young teeth with opalescent areas and halo effects at the incisal edge.
  • The metallic handles of shade tabs tend to reflect light, as shown in Fig. 3.38 below. Thus, tab handles should not be excessively visible.
  • It helps to make a picture in black and white, for such a photograph helps depict the value of the shade tab in relation to the reference tooth, as shown in Fig. 3.39 below.

Fig. 3.39

C. DIRECT SHADE SELECTION BY THE TECHNICIAN

This option involves the ceramist in the shade selection process. As it removes the subjective variations and overcomes the voids involved with shade communication, it is one of the most effective options for shade matching.
This should however, be attempted for more difficult cases like matching a single anterior tooth and can be done with the technician visiting the clinic or it may be done at the laboratory. The latter benefits from the fact that, final shade matching and surface staining can be verified intra-orally and approved by the patient (prior to the final glaze cycle).

COMMUNICATION OF TRUE COLOR
No camera is capable of recording true colors consistently. This is owing to variables like light source, its angle of incidence, distance and angle between the subject to the camera, etc.
The only way to record colors accurately or to reduce the errors in recording colors is by using a ‘Grey Card’ during photo documentation. This needs to be followed by color correction (in a software), to remove any faulty color casts.

WHAT IS A GREY CARD AND HOW SHOULD IT BE USED?
A Grey Card is a neutral color card about the size of a credit card for easy placement during shade selection.

Fig. 3.40: WhiBal is an example of a Grey Card that can be used in dentistry

When recording the final shade, an image should be made with the grey card in the frame. It is not important as to where or how much of the card is seen, but it is important that there are no shadows on the grey card (shadow of the lips, mirror, retractor, shade tab or shadow of the tooth in question), nor should there be any reflected light back onto the camera (card should not look shiny). Even if a very small part of the grey card is in the frame, it is still acceptable, as shown in Fig. 3.41 below.

In order to identify the true colors, this image is to be processed in a software like Adobe Camera RAW (Camera raw is a bundled software in Adobe Photoshop and is meant for processing RAW files). It is not recommended to process JPEG files in dental photography. Softwares like Picasa which process JPEG files and not RAW files might give inaccurate results.

POST PROCESSING OF RAW IMAGES IN ADOBE CAMERA RAW

Fig. 3.42: Image to be color corrected, as seen in Adobe Camera RAW. The software reveals a lot of details about the camera settings (aperture, shutters speed, ISO and exposure histogram). However, the two most important readings (yellow arrows) are the White Balance (As Shot) and temperature of light used (5150°Kelvin).

Fig. 3.43: To remove the color cast and to reveal the true colors of this picture, the ‘White Balance tool’ of the software (yellow arrow) needs to be activated and the cursor then needs to be clicked on the grey card within the frame.

Fig. 3.44: Upon doing this, the software recognizes this area as being 18% grey. The software has an in-built value for this reading and automatically computes this standard reading with the reading of grey within the image. If there is a difference in color, it corrects the same for the entire image. In doing so, it removes the color cast, thereby revealing the true colors in the image. Note, the change in White Balance (from As Shot to Custom) and color temperature (from 5150°K to 5450°K).

Fig. 3.45, 3.46: This technique can be applied during laboratory communication to overcome issues pertinent with the variable light sources used in different set-ups. Such an image is equivalent to one taken in natural day-light (the best light source for dental photography).

Can this technique be used for mobile dental photography?

Yes, although mobile phone images might not be a good choice, this technique still works. Since mobile phones have a LED light source (which is upfront), it can create a lot of reflections. Keeping the card at a slight angle to the lens would help avoid this error.

CONCLUSION

The human eye is the weakest link in the shade matching chain, making the entire process extremely subjective. Shade selection is complex and requires an understanding of the science of color and color perception; in an attempt to achieve success in the ever expanding field of aesthetic and restorative dentistry. To ensure predictability, shade selection process should be standardized and approached in a methodical manner. The use of a Value based shade guide, incorporation of digital photography and the use of a Grey Card can help add predictability to your work, thereby ensuring personal and patient satisfaction.

Fig. 3.47: Cross polarization showing the vivacious appearance of a tooth in crosssection. Note, the play of colors and the immense beauty within the enamel layer of a human tooth.