13 - Color Science and Shade Selection

dental esthetics

• science → what can be measured and observed

  • shape — anatomical form and position of teeth

  • shade — physics and physiology of color perception

• art → what is pleasing

  • cultural background

  • visual association and experiences

measurement of color

• commission internationale de l’Eclairage (CIE) color system

  • for measuring color of light sources and objects

  • used for colorimeters → automated color measurement system

  • mathematical representation of color

  • L (black to white value) x a (red to green) x b (yellow to blue)

  • additive color mixtures (lights)

    • three primary lights combine to form white; complementary lights form white

• Munsell color system

  • for measuring color of objects only

  • paint chips, color charts

  • value, hue, saturation

  • subtractive color mixtures (pigments)

    • three primary colors combine to form black; complementary colors combine to form black

    • complementary colors enhance each other’s appearance

what is needed to see color

• light source → natural sunlight, incandescent, fluorescent, blacklight (UV), dental examination light

• observer → dentist, dental assistant, patient, patient’s spouse, patient’s dog, etc

• object → tooth and environment (gingiva, oral cavity, lips) and other surfaces nearby

physiology of color perception

• retina → rods (night vision; light/dark) and cones (wavelength of light)

• brain → interprets input from rods and cones

  • distorts information based on experiences and expectations

  • when cones get saturated with one color, the brain looks for the complimentary color

color of a material

most physical materials appear colored due to difference in absorption and scattering properties of material for different wavelengths of light

• yellow → absorbs most strongly in blue and scatters most strongly in red/green

contributions to shade of a tooth

• internal and external color of tooth

  • contributing factors → color/thickness of dentin (age, medications), color/thickness of enamel (wear, staining)

  • appearance → hue (spectral wavelength), value (grayness), chroma (saturation/intensity of hue)

• translucency of enamel and dentin

  • contributing factors → thickness/age of enamel, wet/dry (dry becomes more opaque)

  • appearance → translucent (light transmission), transparent (unaltered transmission), opaque (lack of transmission)

• surface texture and reflectivity of enamel (dry or wet)

  • contribution → polished enamel or restorative material produces specular reflection; rough enamel or restorative materials produce scattered reflection

  • appearance → highlights of reflection for polished surfaces; dull/matte appearance for rough surfaces

• fluorescence of tooth (from UV)

  • contributing factors → natural tooth has blue-white fluorescence under UV

    • some dental porcelains match fluorescence; most composites do not fluoresce

  • appearance → UV component of sunlight can cause fluorescence outdoors but not indoors; composite restorations in UV lit room will appear dark

• incident light (spectrum of illuminating light)

  • contributing factors → apparent color of tooth or restoration depends on spectrum of incident light

    • color of restoration and tooth may match under one type of incident light, but may not match in different lighting conditions

  • appearance → shade to determine color of tooth under various lighting conditions but not direct sunlight

• background (lips, gingiva, interior of mouth, color of clothes, patient napkin)

  • contributing factors → background colors and texture change the apparent color of tooth and restoration; saturation of cones will intensify sensitivity to complimentary colors

  • appearance → use neutral backgrounds when determining shade; facial cosmetics will change apparent value of teeth and restorations

perception of shade of a tooth

combination of:

• brightness (value) of tooth perceived by rods in retina

• color (hue) of tooth perceived by cones in retina

• hue of tooth is very subtle → see differences in value more easily than differences in hue

VITA shade guide sequence, according to value

B1, A1, B2, D2, A2, C1, C2, D4, A3, D3, B3, A3.5, B4, C3, A4, C4

to take a shade

• remove all extrinsic stain from tooth enamel

• tooth should be wet → determine shade before isolating tooth

• use neutral background (grey/white)

• compare tooth color to shade guide using various types of incident light (examination light, room light, sunlight)

• determine value first, then hue and saturation

• glance at shade chip and tooth for brief moment to avoid saturation of retinal cones

• have assistant and/or patient help in shade determination

• perform shade determination on several visits, and record shade each time

• record composite or porcelain shade used for restoration in patient’s chart