Color science and optics, PROSTHODONTICS

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Color Science and Optics

Convened by:

Prof. Dr. R. K. SinghDr. Pramita SuwalDr. Prakash Kumar ParajuliDr. Pragya ShresthaDr. Arati SharmaDr. Indra Kumar Limbu

Presenter:

Rahul GuptaJunior ResidentDepartment of Prosthodontics

2Contents:1. Introduction

2. Description of color3. Munsell color order system 4. CIELAB color system 5. Shade matching 6. Human vision 7. Metamerism 8. Fluorescence 9. Opalescence 10. Shade selection system 11. Guidelines for visual shade matching12. Instrument color analysis 13. Basic shades 14. Cercon ceram kiss15. Conclusion 16. References

3Introduction:

Light is an electromagnetic radiation.

Eye is sensitive to wavelengths from approximately 400 to 700 nm.

4The basics…

5Seeing Around….

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What if the incident light has no red component???

Color perception:

7Description of color

1. Munsell color order system2. CIELAB color system

8Munsell color order system: Devised in 1905 by A. H munsell

3- dimension : Hue , Value , Chroma

Hue : That quality by which we distinguish one color family from another, as red from yellow from blue or purple.

Value : Value relates a color brightness to the specific area on the black-white scale. (Squinting maneuver, rods function)

Chroma : that quality by which we distinguish astrong color from a weak one.

Munsell notation : H V/C Eg . 5R 5/8

9 Sproull determined the volume of natural tooth shades in Munsell color space

Hue: 7.5 YR - 2.7 Y Value: 5.8–8.5 Chroma: 1.5–5.6

Relative clinical importance of hue, value and chroma :

Color matching authorities state that hue differences are easiest to detect and value differences the most difficult.

The authors have approached clinical color matching of teeth with the opinion that value differences are most important, and hue differences the least

Hue differences may well be recognized most easily, but a slight mismatch in hue may not be as objectionable as a slight value mismatch.

10CIELAB color system: Introduced in 1976 and recommended by international

commission on illumination.

Used exclusively in color research in dentistry around the world.

Equal distances across the CIELAB color space represents approximately uniform steps in human color perception.

Defines color space in three coordinates as L*a*bL = proportional to value of munsell system a = red-purple/ blue-green axis b = yellow/ purple-blue axis

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The color difference ∆E between two colors can be calculated from the sum of squares difference among three coordinates.

The system is so arranged that a color difference of 1 is perceptible by 50% of observer with normal color vision

12Shade-matching: Occurs in dentist office.

visual shade matching Quality / Quantity of light source:

o Light source with color temperature close to 5500 Ko Color rendering index > 90o Light intensity in dental operatory : 18-28 luxo Light intensity for dental laboratory : 28 lux

If ambient lighting in dental operatory is not ideal in terms of quality and quantity for visual shade matching, the use of auxiliary lighting is recommended. Its been recommended that the ratio of task (shade matching ) to ambient light should not exceed 3:1

13Shade matching environment: Following may influence the shade selection :

Color of dental operatory Clothing of dentist and dental assistant The patient’s clothing The dental drape

Recommendations : 1. Wall , staff clothing, patient drape and shade matching environment have a

Chroma of 4 munsell units or less, which are pastel or ideal neutral gray tone.2. Ceiling have a munsell value of 9 3. All other major reflectors (E.g. cabinets, wall )should present a munsell value

of 7 and Chroma of no more than 4.4. Countertops not within the working area can have a Chroma of up to 6 and

munsell value retained at 7 or greater.

14Human vision:

Light from any object enters the eye and acts on receptors in the retina (rods and cones )

Impulses then pass to optical center of brain, where an interpretation is made : subjective

Scotopic vision : Under low light conditions only rods are used, Allow only interpretation of brightness. Rods are most sensitive to blue-green objects

Photopic vision: dependent on cones and are dependent on high lighting conditions

15Color adaptation:

Color vision decreases rapidly as a person stares at an object. The original color appears to become less and less saturated until it appears almost gray.

Deceptive color perception:

Colors is influenced by surrounding colors, particularly complementary ones.

When blue and yellow are placed side by side their Chroma may appear to be increased.

16Metamerism:

Two colors that appear to be a match under given lighting condition but have different spectral reflectance are called metamers and the phenomena is known as metamerism.

Yellow objects normally reflect yellow light and hence appear yellow

Some may actually absorb yellow light and reflect orange and green which to an observer appears yellow.

The problem of metamerism can be avoided by selecting a shade and confirming it under different light conditions.

17Fluorescence: Fluorescent material such as tooth enamel, absorb near UV radiations

(300-400 nm ) and then re-emit radiant energy at a lower frequency than it is absorbed

Tooth becomes a source of light and emits in wavelength 400-450 nm (blue- white region )

Fluorescence makes a definite contribution to vital appearance of a tooth

Ceramic crowns and ceramic agent that lack a fluorescent agent appear as missing teeth when viewed in black light.

In theory a mismatch can occur if a mismatch occurs if dental restoration had different fluorescence than the natural tooth.

18Opalescence:

Natural tooth particularly at incisal edges exhibit a light scattering effect that creates the appearance of bluish white color as the teeth are seen at different angles

19Shade selection system Vita lumin vacuum shade guide: A1, A2, A3, A3.5, A4 B1, B2, B3, B4 C1, C2, C3, C4 D2, D3, D4

Hue selection Chroma selection Value selection

20Vitapan 3D master shade guide

manufacturers claim that this system cover the entire tooth color space.

Shade samples are grouped into six lightness level.

Shade guide spacing 4 CIELAB units in lightness dimension 2 CIELAB units in hue and Chroma dimension

Because the guides are evenly spaced intermediate shades can be predictably formulated

Manufacturers recommend selection in value, chroma and hue sequence .

21Custom shade guide:

Certain teeth may be impossible to match to commercial shade samples .

One approach to this problem is to extend the concept of commercial shade guide by making custom shade guide

Time comsuming and generally confined to speciality practice.

22Guidelines for visual shade matching:

Balanced lighting and appropriate shade matching environment

Anything on patient that influences shade matching including brightly colored clothes be draped and lipsticks removed.

Teeth to be matched should be cleaned / prophylaxis done

Shade matching should be done at the beginning of patients visit.

Cheek retractors be used to provide an unhindered intra-oral shade matching area

The patient should be viewed at eye level. A viewing working distance of 25cm be adopted

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If tooth and shade tab have different surface characteristics, wetting the surface helps remove the difference

Shade matching should be made quickly (less than 5 seconds)

Dentist should rest his/her eyes between viewing by focusing on a neutral gray surface.

Select appropriate value by squinting

Shade selection be confirmed at one or two other visits / confirmed with an auxillary staff member / under different light settings

If exact match cannot be selected , a shade tab with lower chroma and higher value should be selected

24Instrumental color analysis

Spectrophotometer / spectroradiometer /colorimeters/ digital color analyzer

Spectrophotometer and spectroradiometer measure light reflectance at wavelengths interval over the visible spectrum to measure the color

25Basic shades Shade A:

Shade in A group are frequently encountered in young individual and account for atleast 65% of the porcelain sales .

Hue is well centered in the natural tooth color space. Being closest yellow hues to orange they allow color diversification into

orange color space.

Shade B: Closer to pure yellow compared to shades in A group. Rarely encountered in natural dentition : because they are located at one extreme of

natural tooth color space

26 Shade C:

Considered a sub group of B family Comparable hue but a lower value to B family Middle-aged and older individuals or in patients with tetracycline stained teeth

Shade D Considered a sub group of A family Comparable hue but lower value to A family

Shades C and D represent only isolated examples of lower value of a given hue of the B and A groups, and as such do not automatically provide the expected value when an A or B tab of lower value is desired.

27Cercon ceram kiss

28Power chroma: The six fluorescent power chromas can reproduce

the bulk of all cervical and mamelon effectsas well as increases in chroma.

Simple 1:1 mixtures between these power chromas result in an additional 15 intermediate shades.

Even the smallest color gradients can be emulatedrapidly and in a systematic manner

29Custom incisals, opal effects and multifunctional Stand-by:

The Stand-by multifunctional material is a strongly transparent opal effect that is one of the keystones of the Kiss system.

It can be used by itself or mixed with any other materials.

The three opal effects, Ocean, Sky and Fog, control value and opalescence in blueish and greyish incisal regions

Sunset and Sunrise are suitable for incisal characterization and for subdued transparent chroma gradations in the body region

30 The individual incisals within the Kiss system allow the emulation of all natural opalescent and

fluorescent effects.

Opal incisals 1 and 2 are intended for lighter (OS 1) and darker (OS 2) shades. For intermediate shades, the two material are simply mixed at a 1 : 1 ratio.

Flu Inside 1 and 2 are highly fluorescent materials designed for the inner layers, covering the liner even where space is at a premium, while at the same time increasing value in the incisal area.

White Surface (WS) is a whitish opalescent effect used to increase surface value (brightness).Here, too, the effect can be attenuated by 50% by adding Stand-by.

To reproduce the effect of teeth that have been bleached, Bleach Liner and Bleach Dentine are available

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32Gingival materials: By mixing Gum 1 to Gum 4 with selected effects

(see chart), natural gingival effects can be emulated very closely and simply.

33Basic build up technique in anterior region:

34Custom build up technique in anterior region:

35Conclusion: A basic understanding of colors objectively, is a prime prerequisite for the

color replication process viz . Shade matching and shade duplication phase. Furthermore it reduces the hovering confusion in communication between a dental clinic and the lab assistant. Knowing colors its various dimension and factors which affect its perception helps us to attain predictable success in cosmetic rehabilitation .

36References:

Contemporary fixed prosthodontics , Rosenstiel, Land , Fujimoto, 4th edition Phillips’ science of dental material Kenneth J.Anusavice, 12th Edition Craig’s restorative dental material, Ronald L. Sakaguchi , John M. Powers, 13th

edition Esthetics of anterior fixed Prosthodontics Fundamentals of fixed prosthodontics , Herbert T. Shillingburg , 3rd edition Cercon ceram kiss, product description and processing manual, Degudent ,

Adentsply company

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