Natural Color of Teeth – The Shade of a Clean Tooth
Teeth have a range of colors naturally – without the effects of any external or internal sources of stain. For the purposes of this course, we define a stain as a source of discoloration that is not of natural origin (Intrinsic stain is of natural origin – blood origin). The sources of natural tooth color include structural features of the teeth including thickness, translucency, dentin color, and in the absence of staining may be dominated by genetic factors.5 Teeth also vary in color between each other, with incisors, canines and molars typically exhibiting different shades.
Historically, the variety of colors seen in natural dentition is generally encompassed by commercial shade guides – including the commonly used Vita Shade. Although visual assessment using shade guides is very useful and used in daily practice, there are some limitations such as incorporating differences in lightness, chroma and hue, as well as accounting for changes seen with the entire tooth versus only certain areas of the tooth. More recently digital shade measurements are taken which removes subjectivity associated with these limitations.
Figure 5. A typical imaging system is comprised of a 3-chip CCD camera, a d50 polarized lighting setup, computer and fixed positioning of the patient.
In digital image analysis (Figure 5) , images of the dentition are captured under controlled and calibrated lighting conditions with cross polarization to eliminate glare. From these images, the color of teeth can be determined for the dentition of interest. Typically, the color values of the teeth are reported in L* a* b* color space where L* measures luminescence (e.g., how bright), a* is the chroma ranging from red to green, b* is the chroma ranging from yellow to blue, as shown in Figure 6. With respect to teeth, they are on the yellow side of b*, the red side of a* and in the upper range on L*. Tooth color changes are quantified by comparing the L*, a* and b* values before and after treatments to establish changes in the color values designated as ∆L*, ∆a* and ∆b*.