Calculating Variables for Color Consistency

Color, its properties, and how to manipulate it to attain proper results have been studied and practiced for quite some time, specifically in layered ceramics for dental restorations. These concepts are just as relevant with newer monolithic, full-contour restorations. Every laboratory should possess a color wheel, ideally one that turns. This inexpensive item, which can be purchased from a local art store, helps show the technician the properties a color may exhibit and how one color will behave in conjunction with another.

There are three variables in achieving the appropriate shade of color for a tooth: hue, chroma, and value. Hue is the color; chroma is the intensity or saturation of that color; and value is the scale of white to grey. These variables are demonstrated by the color wheel, which is comprised of primary colors (red, yellow, blue); secondary colors (orange, green, purple) that combine two primary colors; and complementary colors, which are directly across the wheel from each other. If a monolithic crown does not exhibit enough chroma, the simple solution is to add more of the same color to achieve the correct level of saturation. However, if a crown's color is too saturated, a technician can add the complementary color to tone down that saturation. The value of the color or its brightness can be reduced, but increasing value is almost impossible.

Finally, the opacity and translucency of these restorative materials directly correlate to the firing parameters and conditions in sintering ovens, specifically the temperatures, ramp rates, and hold times. If either the firing or hold times are manipulated erroneously, the overall look and vitality of the restoration will be affected. Lower temperatures and shorter hold times tend to produce opaque results, while low value outcomes are often the product of too-high temperatures and/or too-long hold times. Following the manufacturer's specifications and maintaining your sintering oven properly by purging and calibrating will provide the laboratory with consistent, repeatable results.

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