Dental Practice Report
August 2006
Lee Ann Brady DMD
The dental laboratory needs many important pieces of information in order to produce exquisite esthetic results. One of the most frustrating moments in a dental practiced is trying in a restoration and realizing it doesn’t match. One part of my laboratory communication is the shade. Three major components contribute to our perception of the shade of a tooth: value, chroma and hue. Value is the most critical of the three parameters when attempting to match an adjacent natural tooth; hue is the least important.
To assess the value of the tooth, we look at whether the tooth appears light or dark. This perception is controlled by the amount of light reflected back to our eye after hitting the surface of the tooth. Value is intimately related to the surface morphology of the tooth. When light hits the surface of a tooth, the more surface texture that is present, the greater the amount of the light reflected away from our eye. Therefore, the tooth appears darker or lower in value. In contrast, a smooth surface allows a larger amount of the light hitting the tooth surface to be reflected back to our eye and gives the tooth a lighter appearance, or higher value.
When communicating the value of a tooth to the laboratory, work with a shade guide that lists value as a separate parameter. Our eyes are better when judging value in a less illuminated environment. Turn off the dental operatory light, close the blinds and even turn off the overhead lights. Allow your eyes a moment to adjust to the reduced light levels before choosing the shade tab that matches in value.(not sure about meaning of the following sentence) The color information that is filtered from our eyes to our brain can act to inhibit our ability to determine value. A digital image of the teeth that has been converted to grey scale will make the different values of teeth much easier to discern than if they were in full color. The Vita classic shade guide links the value and the chroma together. Try taking a digital photograph of your classic shade guide, converting it to grey scale, and reordering the tabs from dark to light by value.
Chroma and Hue are the two components of color that should be provided to the laboratory. Chroma is the intensity or amount of color present, and hue is the name of the color. If I take a bottle of red food coloring and a glass of water, and place one drop of the food coloring in the glass, the intensity or chroma is very low and the hue is red. If I pour the entire bottle of food color into the glass of water, it is much higher in intensity or chroma but the hue is still red. Chroma on a classic shade guide is communicated by a number, with less intensity being a lower number like 1 and greater intensity being a higher number like 4. Hue is indicated by a letter, in the classic system A, B, C or D.
To increase our ability to accurately determine the chroma and hue of a tooth we need to have light that supplies a full spectrum of color wavelengths. Often people discuss choosing a shade in natural daylight. The challenge with this is it works very well at noon on a cloudless day, but most of the time taking a patient into the office parking lot to match shade isn’t very helpful. Set up at least one operatory with color corrected bulbs in the overhead lights. When choosing color corrected bulbs, look for a CRI rating of 100 and a 5500K color temperature.
Our eyes can tire of looking at and perceiving certain colors, or become confused in their ability to ascertain color. It is important not to expose our eyes to vivid red or orange colors prior to choosing the chroma and hue for a restoration. My preference is neutral colors for our patient bibs like light blue or grey as they are restful to our eyes and enhance our ability to perceive the parameters of shade selection. If a patient is wearing very vivid lipstick, we ask them to remove it, and if they are wearing vividly colored clothing we cover it with a patient bib and allow a few moments to pass before completing our shade matching.
Desiccation of the tooth structure causes modified hue, less translucency, increased value and decreased chroma. I obtain all of my shade information prior to commencing any dental procedures whether for indirect or direct esthetic restorations. Accurate photographic information is difficult to obtain if the teeth are dessicated, so I take a set of digital images for the laboratory, including a set with shade tabs prior to preparing the teeth. During the course of treatment I take both stump shade images, as well as prepared teeth, to provide additional valuable information to the lab.
When selecting chroma and hue for a reconstruction where we are not matching any adjacent natural teeth, it is important to discuss with the patient their preferences around tooth appearance. Restorations fabricated with a chroma gradient are more intense in color at the gingival and towards the canines. It is imperative to explore these options with the patient as an increasing number of patients today want the restorations a uniform color throughout.
Many shade guides contain tabs that have been created to mimic the appearance o f natural teeth. They contain a chroma gradient; the true shade of the tab is only contained in the body portion. If you are utilizing this type of shade tab consider a few ideas. First, utilizing the incisal edge on this type of tab can help prevent color blending, which is a phenomenon that occurs when we see similar colors side by side. Our brain will automatically blend the colors together making them look similar. By placing the dissimilar color of the incisal edge of the tab against the incisal edge of the tooth we space the two colors we are actually trying to evaluate. You can also eliminate the color gradient by spending a few minutes with your shade tabs and a lathe and remove the sides and incisal edge of the tab leaving the named chroma and hue behind on the slenderized shade tab. I keep a quantity of the most common shade tabs available. After selecting the matching tab, I photograph the tab and the tooth together for the lab, and send the exact tab used that day with the case to the lab. One final thought about shade tabs: Remember that the tabs are affected over time by sterilization and exposure to chemicals in the operatory, so replace them on a routine basis to maintain color accuracy.
One of the most challenging restorative situations is matching a single central incisor. There are many factors that affect our ability to fool the eye and have a restored central appear to be an identical match to it’s neighbor. One of the factors that is often missed and easy to control is facial embrasure form. Part of the reason we miss this aspect of tooth shape is you can only see it from a different perspective, incisal edge down. When I am shaping provisionals, direct composite or completing a wax-up with intention I shape the facial embrasure form.
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