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Color is a phenomenon
we “see” only in our brain. Our eyes serve as incredibly fine transducers of reflected light in varied wavelengths
that our brains process into “colors”. To effectively communicate color, we need to think along the same lines.
To describe the color of mustard, I may envision Gulden’s while you may picture French’s. Both are yellow mustards
yet appear very different.
The need for a mutual standard of color communication is obvious. This service issue is a collection of many
years of study and experience. It is my sincere hope that what follows will help us to better understand, maintain and develop
a sensible and consistent approach to shade selection.
Both operatory and laboratory must be well-versed in the terminology
and practical application of the principals of shade control to avoid costly re-work and strained doctor/technician relations.
Our common goal of providing the recipient of our collected efforts with as natural a crown or bridgework appliance as can
be fashioned must remain paramount.
We are fortunate to have so many fine materials and techniques at our disposal. When I entered this industry, ceramics
were fairly new and acrylic on gold was commonly prescribed. Aluminous porcelain jacket crowns, fashioned upon platinum foil
matrixes were the state of the art. Often, we had to find our own solutions for shade replications, as opacious dentines
and opalescent incisal powders were not yet available.
Credit must be given to the late great Ed Lemme C.D.T. for his service to our nation
and to this craft. As a mentor in the lab, he always gave freely of his time, helping junior technicians out with a kindly
smile and a lighthearted joke now and again.
His skill as a dental ceramist was well known, and many a fine smile
was crafted from this great man’s hands.
Ed was a highly decorated WWII soldier, and a veteran of many combat operations
- but most folks never knew this until his death. The medals and awards he accrued in that war was extensive, filling three
cases full.
If they ever needed a ceramist in heaven, Ed filled the billet. This man of noble character served
his family, friends, community and nation with great honor and dignity.
We understand the terminology pertaining to color as follows:
HUE: Actual color
CHROMA: Saturation (intensity) of the hue
VALUE: Degree of brightness -white (high value) to grey
(low value)
TRANSLUCENCY: Degree of light penetration / absorption
METAMERISM: Phenomenon where two
objects match in one light source, but mis-match in different light sources.
ACHROMATIC: Tooth appears grey with no particular dominant
hue. The hues exist, but neutralize each another evincing this effect. (Example: Bioform 69)
CERAMIC MATERIALS FOR REPLICATING
DENTITION:
OPAQUE: First strata of ceramic material
placed upon oxidized metal surface. The particulate size of opaque is course and is pigmented heavily to accentuate chroma.
Having a low pyroplastic flow, it is applied in two or more thin coats to completely mask the metal and provide the initial
bond to the alloy. This bond is primarily chemical, derived from an exchange of oxides at the metal-ceramic interface. Opacifiers
containing tin or zirconium oxide constitute about 20% of the mass of the material. As the powder becomes a serous glass in
the furnace, it flows over the surface of the alloy exchanging chemical oxides to form a bond. We also obtain a mechanical
bond of the ceramic to the metal surface, roughened with abrasives. Additionally, a compressive bond is obtained as the heated
metal expands and the porcelain contracts. A solid and complete bond must be obtained. Ceramic material is very strong in
compression, yet weak in tension. You can park a bus on a cubic block of sintered porcelain but a needle will snap with slight
pressure. In the absence of sensible and proper design, treatment and conditioning of the alloy, bond failure can easily occur.
DENTINE: Finer grained ceramic powders that complement the hue
of the opaque and establish the primary shade in conjunction with that layer. Dentine powders may be altered for special effects.
ENAMEL: Vary in the amount of blue/grey and degree of translucency.
This is the material that most significantly impacts overall value. Properly layered, it won’t interfere with the pigmentation
of the underlying strata. Carefully modified we obtain superb vitality.
MODIFIERS: Add pigment to increase the chroma of a hue.
TRANSPARENT: Regulates depth of translucency. Added to dentine it decreases chroma. Added to enamel, translucency
is augmented.
STAINS: Metallic oxides used to accentuate chroma
and lower value.
FACTORS AFFECTING TOOTH SHADE SELECTION:
Light source: Reflected light from an object (tooth) in differing wavelengths is what we actually see. Some colors won't be
distinguished if the light source isn't sufficient. Color corrected lights help us to see the entire spectrum. Natural light
is useful to confirm our selections and offset metamerism. There are differing schools of thought on which light source is
best. People socialize frequently in artificial light. Suppose we take a shade on Mrs. Smith at high noon on a sunny day in
natural light. Will the restoration look the same in the candlelight of a restaurant? How will it look in the fluorescent
or incandescent lighting of the powder room? I avoid light sources such as shade wands and rely mainly on a blend of artificial
and natural light.
ENVIRONMENT: A neutral grey background (walls)
provides a prime setting for shade selection. Neutral grey paper on forceps is better to isolate gingival tissue than a gloved
finger. Request lipstick be removed. A neutral grey drape or blue bib helps counter eye fatigue to orange. Have the patient
sit upright to minimize light reflection.
METHOD:(This is
a system that I use. It is only a sample.) Observe the dentition and look for a primary dominant hue. You're looking for the
color range so don't over work this phase and fatigue your eyes. I then select an overall value from a tab and record the
selection. Concentrate on the value - it can be lowered but not raised, therefore we must select an appropriate value
that allows us to enhance color without painting the units with stains that always lower value. Re-check the value. Do this
in different light sources if possible. Have the patient stand near a window. Too many shade guides or tabs will only confuse
you so keep them to a minimum. Chart characteristics that are germane to the adjacent dentition such as calcifications and
striations, craze lines and mammelon structures embedded in blended or clear enamel. If the shade is very difficult to match
I may suggest a bisque bake verification and perhaps a chairside color addition before final glazing.
SUBSTRACTIVE COLOR METHOD: I've been using this method since I saw it in
an industry publication some years ago. It makes use of the color wheel to adjust hue, chroma and value. This is
achieved by negating spectral elements via the use of contrasting or complimentary colors. The technique is most effective
in giving us a dynamic control and tangible understanding of what happens when we modify a tooth with stains.The color wheel is replete with the primary colors of red blue and yellow. Combinations
of these give us our secondary colors of orange green and violet. Therefore, if a tooth appears too yellow, we add a slight blue or violet applique. (The opposite
or contrasting color on the wheel.) If a tooth appears too blue, we may add a small amount of orange and so on. Via this process we are deliberately adjusting color rather
that just painting stains onto the bisque porcelain in hopes of obtaining a match. Stains are metallic oxides that always
lower value and puddle if heavily applied. This is the main reason why the ceramist must build, layer and sculpt the
porcelain structure properly - to keep staining to an absolute minimum.
Some doctors have acquired glazing furnaces
and stain kits of their own to perform shade modifications on the spot. Should you consider this for your practice I’d
be happy to assist you in selecting and using the appropriate equipment and supplies.
SUMMARY: In our endeavor to take
perfect shades we may get confused due to metamerism. We do well to resist the urge to guess. If you cannot get that single
unit anterior right, it may help to record your best selection(s) and allow me to assist you chairside for confirmation of
that selection. Two heads are better than one. Remember the light source and angle and to always recheck the value. The phenomenon
of color is directly related to reflected light, and the absorption/penetration by objects it strikes. Shade selection
in dentistry is a system that we can effectively control. As with many things,we require a sound approach and, above
all - confidence in our technique and abilities.
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