Cr & Br  lec. 8
Dr.Suzan
7/12/2013
Shade Selection 
Guides in this lec could be applicable in composite restoration too.
First we will take about color science :
Understanding the nature of light and how the eyes receive and brain 
interprets light as color is important for a successful aesthetic restoration .
- Without light >> color doesn't exist
 Color is defined as a phenomena of visual perception that enable us to 
differentiate otherwise identical objects; It’s a result of physical 
modification of light by colors as observed by human eyes and interpreted by the brain .
From this definition we can determined the factors that affect colors shade : light, objects, eye and brain (human ) .
Combination of  wavelengths that reflects to the eyes allows us to see the objects in their colors (yellow, blue , red ,etc.)
Objects could refract or absorb or reflect the wavelength , the reflected part of the wavelength allows the determination of the color.
 Light is a visible electromagnetic energy ranges in specific wavelengths (from 400-780 ) and it measures in nano meter  (microwave and UV are also electromagnetic energy) .
Light stimulate the retina which produce response called a vision.
Pure white light consists of relatively equal amounts of all the light spectrum over the visible range . It doesn't really exist in nature . The dr. said we can see   it in the northern hemisphere between 12-3 pm  in sunny days without pollution and clouds , but its very difficult. Pure light when pass in the prisms divided into spectrum of the light.
When light strikes an objects  some light wave are absorbed some are refracted and others are reflected (it is the reflected part that we perceived as the color of the object).
 Every time we get closer to pure white light, our shade selection is becoming better .
Color are determined visually by hue , saturation and luminescence reflected of light
The 3 dimensions of color: 
1)  Hue : the particular variety of the color ( yellow ,red ,blue,etc.)  , the family of the color or the quality of sensation  according to which an observer is  aware of various wavelength. Determined by the wavelength that transmitted or reflected by the object and its place in the visible spectrum . for example , If the object reflect a wavelength around 400 we will see a red or orange color .
Objects are rarely colored by a single (or exact) wavelength but rather a combination of interacting waves and the results of spectrum distribution will give the interpretation of the hue by the brain .(The object doesn't give an exact wavelengths , it transmit a combination of wavelengths and this what our eyes will see as a color ).
2) Chroma: saturation , intensity or the strength of the hue.  Imagine a glass of water with one drop of ink , the color will be lighter but if 2 or 3 drops the saturation will increase . 
chroma and hue always comes together .
3) Value: . It’s the relative brightness or darkness of the color. It’s the amount of energy that reflected (more energy more brighter). Measured in photons , different hues can reflect the same number of photons ( have the same value) .
It's a measure between 0 (black) and 10 ( white) and different degrees of grey in between .
*In black and white photos only the value exists but in the colored photographs the 3 dimensions of colors are exist.
 Hue and chroma depend on the wavelengths but the value depends on the energy that reflected from the objects.
Value is the only dimension that can exist only by itself .
*Natural teeth value is between 5.5-8.5 
Value is the most important thing in shade selection because the eye detects it easily and it's mostly sensitive for it .
Eyes have cons and rods ; rods (every where in the retina ) are responsible for the value ,  but cons (only in the center of the retina ) are responsible for the hue . The sensitivity of the eye for the value more than the hue (if there is a wrong value selection our eyes can detect it easily).
2 systems to measure color : 
1) Munsell color  system:  a wheel of 10 gradations  each one subdivided into 1R 2R depends on the degree (hues), the chroma increases as going towards periphery and the vertical dimension is the value .
most natural teeth are  between yellow and yellow red.
in this system 10 gradations for values ( 0 is black and 10 is white )
· Natural teeth value is between 5.5-8.5 ( so teeth are more brighter )

2)Ceilab system: sphere has 2 axis (x and y) which determine the hue and 
chroma and as the previous system the vertical dimension is the value 
Ex: color (-3,-5) is in the third quarter between  blue and  green.
 Natural teeth between yellow and yellow red so they are have positive x and positive y .

Color perception depends on: 
1- object 
2- nature of Light : the most important factor
3- Observer himself
4- relationship of other objects ( the surrounding  background)
 -These factors can cause a single tooth looks  different for different observers.
If someone else help the dentist in the shade selection , this overcome the observer factor.
If u take the shade selection for the patient in other place (in the lab for example ) , this can overcome the environment factor and the light factor .
-Light is reflected towards cones and rods then through optic nerve to the 
brain so shade is very subjective depends on the dentist .
 2 types of vision: 
1- Scotopic : Happens under low lightening conditions. Here rods are only 
stimulated and the eyes see the value of the color not the hue.
Blue and green are the most sensitive color for the scotopic vision.
2- Phototopic : happens under high lightening conditions so the eyes see 
the color (hue) , here the cones and rods are working. 
**To know the value in the clinic we can close our eyes slightly to reduce the light and look to the tooth quickly to determine the value; if its bright or dark.
As we know there are 3 types of cones: ( blue, red & green ) that are concentrated in the center of the retina and the rods are more so we are more sensitive to value .
Factors that affect on the observer : 
Color adaptation: 
it’s advised to select the shade in 30 seconds not more than that because you will have color adaptation ( like any other neuroreceptor in our body) and u will see the color less saturated . So the dentist can look to the walls for couple of seconds then continue the selection .
Chroma of the complementary color appears greater when observe after staring at  the same color : if i see red color then suddenly i see the green color (which is the complemantry of the red )  i will see the green color more saturated .
When i start looking for the teeth i will have an adaptation and less saturation for the receptors , so to do re sensitization for your eyes u have to look to pale blue (the complementary color  for the teeth ). so  it’s advised to paint the clinic walls with pale blue color because this color is complementary to the teeth color and the ceiling white to reflects the light.
so the trick in the clinic not to have a lot of color and complementary colors for the tooth in order not to see the teeth more saturated , lipsticks should be removed and we used the apron to reduce the complementary colors.
Color blindness : 
More in male (8% in males ) less in female.
Lots of people have a color blindness but they don't know it why ? because they have been learned to called the color as others called it even though he is seeing it something else.
They can use electric devices to select the color or take the opinion of 
someone else .
We have 3 light sources in the clinic: 
1- Unit light(incandescent) light which is rich in yellow cause its comfortable for the eyes during work  ( but we have to turn it off   before we start shade selection ).
2- clinic (Room) light which is corrected florescent and this is what we need in shade selection.
3- natural day  light depends on weather conditions (humidity , pollution) so the same sun give us different lights according to the weather  .
 Usually during the morning & evening time short wavelengths (blue, green) are scattered, only the longer one (red) they penetrate the atmosphere.
When the dentist wants to buy lights for his clinic there are 2 light references: 
1- CRI (color rendering index) :
-it’s a method for describing the effect of light source on the color appearance of the object. Northern day light is closest to full spectrum white light and it has CRI closed to 100 . So CRI is a measurement of how close the color to the pure white light which is 100. So our light should be more than 90 and this is exist only in the corrected fluorescence (less than 90 is not useful in our clinic) .
-It's a scale from 1 tom 100 to measure how will the particular light source render color as compared to the standard. 
-incandescent light have 50 or 60 CRI so its not good for shade selection .
2- Color temperature: 
a black object when heated on 2000 Kelvin will turns into red and between 3000 to 5000 turns into yellow and  white and above 5000 will turns into blue. So the ideal light we need is between 5500-6500K. below it the light will be red or yellow , above it  will be blue.
Factors that affect the light : 
Light Metamerism: It’s when 2 different objects appear the same under certain light and differs under the other or when the same object differs under 2 lights; That happens because as we said before objects reflect many wavelengths so green color (combination of blue and yellow waves) will appear green under white light but under another light that doesn't contain blue or yellow waves doesn't necessary appears green. To avoid this we do selection under different conditions. 
The cause of  that;  for example the yellow object reflect the yellow light but some may actually absorb yellow and reflect green and red to an observer, the combination gives yellow how ever when  the light changes the two colors may no prolonged matched .
Factors that affect the objects : 
Any object  should have : Florescence, opalescence translucency or  transparency . 
Teeth have florescence (slightly , because its an object ), opalescence(white –blue edges of incisors) and translucent (not transparent).
Porcelain should have florescence, opalescence & translucency to be like the natural teeth.  
Definitions : 
Florescence : its an enamel character (not dentin) of remission of the radiate energy at  lower frequency than the absorbed, UV  light is re emits as visible light . this is exist in certain environments that have florescence lights .
In theory a miss match can occur if the restoration has a different florescence than the natural tooth;  how ever fluorescence does not play  significant role. 
Opalescence : incisal edges sometimes when they absorbed lights they appear whitish –bluish (in the same manner the cloud droplets scattered light)
Translucence: the physical property of allowing light to pass through a material diffusely.
Transparent : the physical property of allowing light to pass through the material without being scattered
Opacity :  the measure of impenetrability to light. If the patient has a hypoplasia for example  , you need to do a different characterization in the same resotration ,  you need it to be obaque in some areas and incisaly you need it to be opalescence and different from cervically. Sometimes the right side is different than the right side in the same restoration.
Factors affect the environments :
The wall of clinic should be  neutral color (pale blue) and the sealing should be high value (white) to reflect the maximum amount of the light energy.  
There are 3 Shade guides for porcelain; we will talk about 2 of them  which done visually , the 3rd one by machine but it has a lot of disadvantages (ivoclar system) .
the composite shade is different than the porcelain shade.
1- Vita pan classical : divided into 4 groups A, B,C,D as in composite. We 
have :
 A 1, 2, 3, 3.5, 4 (they add A3.5 because mostly we have A teeth between 2 and 3).
B 1, 2, 3, 4 
C 2, 3, 4 (no C1 because rarely we have C1 teeth )
 D1, 2 , 3, 4.
they have a logical order , adequate  distribution and transmit & reflects lights as a natural teeth and they have florescence.
Limitations of this systems :
1) The shade guide are  4 to 5 mm thick but our porcelain is 1.5 mm (because of that sometimes the final restoration  doesn't appear like what we select from shade tap).
2) Its not always made of porcelain .
3) Its difficult to predict the final shade after layering of your porcelain, the crown consist of many layers (layer opaque to cover the metal then layer to dentin then layer to enamel) so its difficult to predict 3 layers in one color.
4) Guide taps lacks metal substructures (no metal behind the guide taps unlike the final crown ).
5) Guide taps made of ceramic material dissimilar to the final restoration.
Guidelines : (we can use it for composite too):
- patient should be viewed  at eye level so the most color sensitive part of the retina will be stimulated and used.
-light should be behind the dentist.
-lipsticks  should be removed and we use a neutral apron (usually pale blue ).
- we start select the shade for 30 sec. 
- at the distance of 25 cm is the position between the patient and the light.
-shade comparison should be done at different light condition.
-teeth should be clean (as in composite we start doing shade selection before we start preparing the tooth).
-shade selection the first thing in the visit  because teeth are not dehydrated .
- bright color clothing should be covered by an apron .
- use guide that match the porcelain.
- you can select the value by squeezing the eye to decrease the amount of light energy (to use scotopic vision).
if an exact match cannot be found, choose a color with lower chroma and higher value because we can modified the brightness (by stains for example) but we cant modified the darkness.
In Vita Lumin Vacuum Classical System : shade taps divided into incisal,  cervical and body .
We first choose the hue ( A , B , C groups are different in the hue, but A1 A2 A3 are different in the chroma ) .
Here we don’t measure value. there is another guide for the value which start  from B1 (white) to C4(most grayish) and this guide dont have a logical distribution .
A : reddish – brownish 
B : reddish – yellowish 
C: grayish 
D : reddish – grayish 
 Mostly the doctor don't use the other guide for the value so they missed it so using a  3D master system is better because it divides the groups according to the value .
2-vita  Master 3D:  (3D=it takes all the axis)
Here we have 5 groups according to the value  (1-5) .
We start from the last one from each group then we choose the chroma , each group have M (medium and teeth are mostly here ) and L(yellow) and R(red)
3M divided into 3m1 3m2 3m3 
3 means the value 
m means the hue
1, 2 , 3 means the chroma 
In groups  2, 3, 4 we have 7 choices, in group  5 we have 3 choices .
 3) ivoclar System .

** Instrumental color analyzer  like:
 -Spectrophotometer : it gives all the spectrum but its difficult in measuring non flat surfaces so we cant use it on the tooth .
- Colorimeter : it works on filters -it has only a green, blue & red filters- and it takes the combination for them .
- Digital image analyzer : its  like the photoshop and its the worst  one for shade selection.
 Read about them (the dr. said)  .
**You can do a surface characterization for your restoration by including anything gives a natural appearance to the teeth like staining .

 Good luck for all
 Farah Alkaraki