25.tooth shade selection - seminar

8/13/2019 25.Tooth Shade Selection - Seminar

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TOOTH SHADE SELECTION

CONTENTS

Introduction: Light and Color

Color has Quantity and Quality.

Color Atlases

Atlases based on Subtractive or Additive Color Mixture

Perceptually Unior!ly Spaced Color Atlases

Color Matching and Colori!etry

Measure!ent and Matching o "u!an #eeth

Color Matching o $ental Prosthetic Materials

Methods o Colori!etry

#he %le!ents o %sthetics&Application o Color Science

#he %le!ents o %sthetics

'ptical %le!ents

"ue

(alue

Chro!a )saturation*

Color 'rdering

Shade +uide Use

Surace #exture

Controlled %nviron!ent

Clinical Procedures

Color Modiications

'ther 'pti!al Properties

,hat lies Ahead-

Su!!ation o #echniue

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INTRODUCTION:

LIGHT AND COLOR

Light is an electro!agnetic radiation in the optical region that is

capable o sti!ulating the eye0 the range o 1avelengths being 234 n! to

564 n!. ,hen light sti!ulates the eye0 a pattern o physiological

perception is aroused. #he perceptions are related to the distribution o

light in the retinal i!age in ter!s o space0 ti!e0 and spectral po1er

distribution. #he light co!ing ro! an ob7ect !ust thereore be treated as

co!ing ro! a unior! ele!ent o area and as constant in respect ti!e.

"o1ever0 1hen tooth 1hich has an a181ard three&di!ensional shape0

1ith texture or !ar8ing and dierences in gloss or si9e0 it is diicult or

any hu!an observers & dentists are no exception & to !atch color. In such

a situation even photoelectric instru!ents !ay not be capable o giving a

valid color speciication.

COLOR HAS QUANTITY AND QUALITY.

#he co!!on units used in photo!etry are the lu!en or lu!inous

lux0 the lux )lu!en per s !* or lu!inance on a surace0 and the candela


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to !a8e a syste!atic color solid has been !uch !ore popular than the

one described irst0 and or!s the basis o !ost types o color atlas.

COLOR ATLASES

A color atlas is a syste!atic arrange!ent o a large range o

colored sa!ples0 usually surace colors0 as described above0 but 1ith an

i!portant additional eature: the colors have been spaced out regularly

according to so!e stated criterion or reuire!ent. ;ecause o the three

di!ensional nature o color space0 all color atlases consist o a collection

o charts0 each to represent a t1o&di!ensional section through the color

space. #he particular color solid represented by the sa!ples in a color

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atlas is a color order syste!. It is i!portant to reali9e that the color

ga!ut that can be covered depends on the glossiness o the sa!ples: the

higher the gloss the !ore saturated or dar8 a sa!ple can be. >urther0 the

value o an atlas depends on the per!anence o its speci!ens.

In the criterion o color spacing bet1een sa!ples and the

unior!ity 1ith 1hich the sa!pling actually ollo1s0 spacing is

i!portant. #here are three basic 1ays o spacing the sa!ples in ter!s o

color dierence in a color atlas: i* by colorant !ixture variation0 ii* by

additive !ixture variations and iii* by sa!pling to obtain perceptual

unior!ity o color spacing.

ATLASES BASED ON SUBTRACTIVE OR ADDITIVE COLOR

MIXTURE

Colorant !ixture spaced atlases have been !ade to de!onstrate the

coloration produced by syste!atic ad!ixture o certain base colorants0

or exa!ple0 using subtractive color !ixture. #hese are o value to dyers

and users o pig!ents in paint0 plastics0 printing etc. #he ?u&"ue custo!

Color Syste! has /0444 !atte painted cards developed ro! a 1hite0 a

blac80 and six chro!atic single&pig!ent paints. #he Colori9er )/@=5* has

/02 !atte painted chips developed ro! a 1hite0 a gray0 a blac80 and


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t1elve chro!atic base paints. #he Plochere Color Syste! )/@=3* is

another exa!ple0 1ith /0=3 !atte painted cards.

#he Pantone Matching Syste! )/@620 revised /@5=* uses a 1hite0 a

blac80 and eight chro!atic base pig!ents to give 35 sa!ples printed in

both a glossy and a !atte series. #he color range is extended by 6

additional saturated colors or!ed by !a8ing use o an extra seven

saturated base pig!ents. #he syste! is 1idely used as an aid to

speciying and or!ulating printed colors.

#he ICI Color Atlas )/@6@* has /025@ opaue sa!ples !ade

1ithout using blac8. #he ICI Color Atlas thus gives the closest gradations

bet1een neighboring colors o any atlas0 and they are close enough or all

co!!ercial dyeing purposes. Additive color !ixture spaced atlases sho1

the seuences o colors that can be produced by additive color !ixture.

#he original conception in /@/5 1as that o 'st1ald )/@24*0 1ho devised

a color syste! 1ith a central gray scale and radial sections containing

colors o nearly the sa!e hue. #he original atlases o 'st1ald had so!e

deects and are not available or practical use0 but in !odern ti!es a

!uch better version called the Color "ar!ony Manual 1as produced.

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#here are t1o notable color atlases that are partly based on

subtractive color !ixture o colorants and partly on additive color

!ixture. #hese are based on screen plate printing color !ixture0 and are

o particular value to the printing industry.

PERCEPTUALLY UNIFORMLY SPACED COLOR ATLASES

#he inal class o color atlas is based on grading the color spacing

o the sa!ples to produce sub7ectively unior! spacing 1ith perceptually

eual dierences bet1een successive sa!ples in a seuence. Such

syste!s are i!portant in psychological0 aesthetic0 and design

applications. #he !ost a!ous color atlas and syste! o this type is the

Munsell. #his 1as originally produced as the Munsell ;oo8 Color using

a central vertical gray scale and =4 radial sections0 each 1ith colors o a

given hue. #he three perceptual attributes o light na!ely lightness0 hue0

and saturation are represented by scales o value0 hue and chro!a0

respectively.

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#here is another perceptually unior!ly spaced color atlas and

syste!0 the $I? 6/6= Color Syste! 1hich 1as produced originally as

tinted transparent gelatine ilters in arrays0 1ith surace color versions

beco!ing available later. In the $I? 6/6= Syste! there are three

variables: arbton )hue* #0 sattigung )saturation* S and dun8elstue

)dar8ness* $. As 1ith the Munsell syste!0 the hues o the $I? syste!

are perceptually unior!ly spaced round the co!plete ga!ut o hues. #he

$I? 6/6= colors have been speciied in ter!s o the Munsell and CI%

colori!etric syste!s.

A very recent color atlas0 the ?atural Color Syste!0 described by

"ard )/@54*0 uses perceptual 7udg!ent to subdivide color space in ter!s

o hue0 saturation0 and blac8ness0 1ith sa!ples o a given hue being

arranged in a triangular array 1ith lines o eual saturation and eual

blac8ness sa!ples. A !a7or deect is that the nu!ber o hue steps

bet1een the perceptually BpureB red0 yello10 green0 and blue hues 1as

orced to be eual )i!plying that these particular hues !ust be arranged

at @4to each other in the space*0 1ith the result the si9es o unit steps are

not eual in the our uadrants o the circle o hues.

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In dentistry0 the principle o color !atching and !easure!ent by

reerence to a suitable color atlas has !uch to co!!end it. "o1ever0 the

general&purpose color atlases described above0 are not able to !eet the

needs o dentists or color !atching and !easure!ent0 though they could

be applied to the aesthetic ield. )such has !atching gu! colors in

poly!er. * #he colors o teeth cover a very restricted region o color

space0 and a special&purpose color atlas containing perhaps 44 or 244

sa!ples 1ould enable neighboring sa!ples to be never !ore than three

7ust noticeable dierences apart and usually about t1o.

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COLOR MATCHING AND COLORIMETRY - COLOR MATCHING

PROPERTIES OF REAL OBSERVERS

#he three la1s o +rass!ann and that o Abney or! the basis o

colori!etry. #he !ost i!portant corollary o these la1s is: increasing or

decreasing the a!ounts o t1o lights o the sa!e color by the sa!e

actor0 8eeping the relative spectral co!positions o each unchanged0 1ill

not destroy the color !atch. #he above state!ents provide the basis o

the additive )additivity* concept in colori!etry0 1hich is o unda!ental

i!portance in allo1ing prediction o color !atches and color

speciications0 is per!itting data in ter!s o any triad o !atching sti!uli

to be transor!ed to values in ter!s o any other triad o !atching or

reerence sti!uli. #he la1s o colori!etry and photo!etry stated above

are valid over !ost o the operating range o the eye0 and under all

co!!on conditions. #he la1s apply to light entering the eye0 1hether it

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is directly or! a pri!ary source )an illu!inant* or 1hether it co!es

indirectly ro! such a source via a secondary source )a surace color*.

#he concept o metamerism can be extended to hu!an observers

as 1ell. In this case it is ter!ed observer !eta!eris!0 and it arises

because o the variation in color !atching ound a!ong the nor!al

trichro!atic observers !a8ing up the bul8 o the population. 'bserver

!eta!eris! !eans that 1hat is a color !atch or one observer is not

exactly so or another. #hus i there is !eta!eric color !atch bet1een

t1o suraces o dierent spectral relectance proile0 then or the Standard

observer they 1ill !atch under a stated illu!inant. >or any other

illu!inant or 1ith that illu!inant or those real observers 1ho dier ro!

the Standard 'bserver0 there 1ill probably be so!e degree o !is!atch.

So!e !eta!eric !atched surace colors have spectral dierences such

that they happen to !atch under t1o or even three illu!inants but not

under other illu!inants.

MEASUREMENT AND MATCHING OF HUMAN TEETH

$entistry is an occupation 1here aesthetics is o considerable

i!portance0 especially 1hen patients are stage or public igures.

"o1ever it is interesting to note that color science has not so ar been

applied very successully in dental shade !atching to give uantitative

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ans1ers to the proble!s. #here are very good reasons or this0 1hich are

discussed belo1.

#he needs0 ho1ever0 are clear enough and !ay be stated as the

selection0 coloring0 and processing o the right dental prosthetic !aterials

so as to produce a convincing !atch in appearance to the natural teeth o

the patient. #his is a !uch harder proble! than those !et 1ith by the

color production industries0 such as textiles paints0 and plastics0 or

reasons0 1hich 1ill no1 be explained.

TEETH AS COLORIMETRIC SAMPLES

#he properties o sa!ples presented or !easure!ent 1ith

colori!eters and spectro&photo!eters that give rise to diiculties and

syste!atic errors have been !entioned in previous sections: luorescence0

!eta!eris!0 non&unior!ity across the surace0 inho!ogeneous internal

structure in layers0 translucency0 s!all si9e0 irregular shape0 and

surrounding pro7ections 1hich 1ould prevent their close presentation

against the instru!ent !easuring port. #he reasons 1hy teeth !ust be

7ust about the only ob7ects to have all the properties at once and in

abundant !easure.

#he luorescence is readily seen by illu!inating 1ith near&

ultraviolet light and its e!ission is a pale bluish&1hite in color. As the

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near ultraviolet is present in natural daylight0 it is li8ely that luorescence

inluences the color o teeth 1hen illu!inated by daylight.

Meta!eris! is inevitable 1hen synthetic !aterials such as colored

dental porcelains0 ce!ents0 and poly!ers are !atched against natural

teeth. "o1ever0 it is the geo!etrical properties in the above list o

a181ard sa!ple properties that !a8e instru!ental colori!etry unli8ely

to be ully successul.

A cross&section through a hu!an tooth is sho1n in plate 30 1hich

sho1s the three principal layers 1ithin it: ena!el0 dentine0 and nutritional

pulp. #hese layers have dierent scattering coeicients0 and hence

dierent opacity and translucency properties. #he spectral absorption

property o the pulp is !ar8edly dierent ro! that o the ena!el and

dentine0 giving it the pin8y red color. #he ena!el and dentine are a

yello1ish 1hite0 but the ena!el 1ith about @5 hydroxyapatite content

is !ore translucent than the dentine0 1hich has about 54 hydroxyapatite

content. So!e teeth that are very translucent see! al!ost bluish&1hite in

parts. #his is probably due to the bluish rays light scattering o s!all sub&

1avelength particles0 seen against the yello1ish 1hite o the !ore

densely scattering parts 1here the short 1ave absorption and natural

yello1ish color predo!inate.

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>ro! the preceding inor!ation it is clear that teeth are translucent

and inho!ogeneous in several dierent 1ays. #his0 co!bined 1ith the

s!all si9e and the geo!etrically co!plicated shape o a tooth and o its

neighboring teeth and gu! tissue0 !eans that a dierent raction o an

incident ray o illu!inating light 1ill be scattered bac8 as relected light

or al!ost every angle o illu!ination0 and 1ith each given angle o

illu!ination or al!ost every portion o a tooth illu!inated. #he only

1ay to try to even out the selective local and angular eects 1ould be to

use he!ispherical0 or nearly he!ispherical0 diuse illu!ination o a tooth

as 1ell as its ad7oining teeth and gu! tissues.

In vie1 o 1hat has been !entioned earlier0 it is clear that the

general&purpose co!!ercial colori!etric instru!ents do not oer the

possibility o !easuring teeth in vivo satisactorily. #he !ain

reuire!ent thereore0 is that the 1hole !outh should be diusely and

unior!ly illu!inated 1ith only a s!all area vie1ed0 o perhaps 2 or =

!! across. #his i!plies a large integrating sphere and hence a lo1

overall optical eiciency0 so that a high po1er la!p or la!ps 1ould be

needed. #here are instru!ents that can be applied locally to a tooth

surace. So!e colori!eters )photoelectric and visual* have a ibre&optic

lexible !easuring head 1ith =D4or 4D= illu!inating and vie1ing

geo!etry.

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A eature o teeth that urther co!plicates the issue is local

staining0 oten conined to crac8s or supericial issures. ,hereas the

hu!an observer can ignore this and concentrate on the !ain tooth body

color0 photoelectric instru!ents cannot do anything but !easure the

average color 1ithin the sa!pled area. A dentist needs to !atch the !ain

body color o the natural teeth and can apply artistically si!ulated stain

!ar8ings ater 1ards to the selected prosthetic cro1n !aterial. A

unior! !aterial o the average color o the natural teeth 1ould not loo8

right0 i the teeth have stain !ar8ings0 a point discussed by McLean

)/@5@* and Preston and ;ergen )/@34*.

Measuree!"s #! Tee"$ a" "$e Na"%#!a& P$'s%(a& La)#ra"#r'

In order to support a progra!!e o 1or8 at ;ritish Cera!ic

Eesearch Association on dental porcelains0 the ?ational Physical

Laboratory !ade an investigation o the color and luorescence o teeth

and o so!e dental porcelain. %xtracted teeth preserved in or!alin

solution 1ere observed to be unnaturally dar8 and bro1nish0 due to their

being 1aterlogged because o the correct os!otic balance no longer being

!aintained. Atte!pts at drying the! led to the !easured color being

progressively lighter and lighter 1ith no stable endpoint. Ater a 1hile

they loo8ed unnaturally light and started to cra9e0 eventually alling to

pieces. ;ecause o this it 1as decided that no credible colori!etry could

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be carried out on extracted teeth0 even 1hen stored under ideali9ed

conditions0 and that !easure!ents in vivo 1ere necessary.

#he i!plication o this 1or8 is that dental prosthetic !aterials

should not only !atch the natural teeth in the visible region o the

spectru!0 but their luorescence should roughly !atch as 1ell. In the

case o sho1&business and other patients 1ho are public igures0 the

luorescence needs to !atch uite 1ell0 to cover public appearances in

discos0 theatres0 or other places 1ith orna!ental ultraviolet illu!ination.

C#r Ma"($%!* #+ De!"a& Pr#s"$e"%( a"er%a&s

#he 1idely used general&purpose colori!etric instru!ents are

unsuitable or dental proble!s0 due to si9e o the !easured area0 and that

the special&purpose instru!ents 1ith s!all !easured areas have

co!pletely unsuitable !eans o illu!inating the 1hole !outh )or at least

part o the !outh to include the tooth and all neighboring structures and

tissues*. In the absence o this special dental spectrophoto!eter0 visual

!ethods 1ill have to be relied on or so!e ti!e to co!e. "o1ever0 the

proble! is that dental prosthetic !aterials are not nor!ally available to

the dentist in the right or!. #hey should be abricated as tooth shaped

sa!ples or!ing a dental color atlas0 that is0 a shade guide constructed to

sho1 the three&di!ensional variation o color ound in natural teeth0 1ith

the variations being syste!atic and unior!ly graded according to so!e

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stated criteria. #he !aterials should be selected to give !ini!al

!eta!eris! 1ith natural teeth0 this is also applying to the luorescence

seen under near&ultraviolet irradiation. #he second step is to deine a

a!ily o spectrophoto!etric curves to avoid proble!s o !eta!eris!

and luorescence. I leave it to the dental proession to suggest the

re!aining steps in such an endeavor.

Me"$#,s #+ C#r%e"r'

#here are three basic !ethods o colori!etry:

Matching the test sa!ple against standardi9ed and inely graded

reerence sa!ples organi9ed as in a color atlas and interpolating to

ind the best esti!ate o the color speciicationF

Measuring the color speciication directly by !eans o a tristi!ulus

colori!eterF and

Measuring the spectrophoto!etric characteristic o the sa!ple and

calculating the tristi!ulus values.

In principle0 all these three !ethods could be i!ple!ented by

visual or by photoelectric !eans. #he use o a color atlas is too slo1 and

inaccurate or nor!al industrial use. Inaccuracies arise !ainly ro!

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!eta!eris!0 o 8eeping the reerence sa!ples clean0 unda!aged0 and

1ithin calibration. (isual tristi!ulus colori!etry is slo1er and less

precise than photoelectric !ethods0 but is reliable. #he !ost 1idely used

types o visual colori!eter are !ade by the #into!eter Ltd and it !a8es

use o sets o graded colored glass trans!ission standards as described.

Se("r#$#e"r%( C#r%e"r'

Spectrophoto!eters are instru!ents that !easure0 1avelength by

1avelength0 the spectral variation o trans!ittance or relectance o a

sa!ple.

FOUR GREAT PROBLEMS IN COLORIMETRY

F&u#res(e!" Sa&es

Certain substances exhibit the pheno!enon o photolu!inescence0

1hereby radiant energy is absorbed in one part o the spectru! and re&

e!itted in another part o the spectru!. I the e!ission appears to be

si!ultaneous 1ith the absorption0 the eect is co!!only called

luorescence0 although strictly spea8ing those e!issions occurring ater

intervals longer than 10-8 secshould be called phosphorescence. Most

luorescent substances including all organic ones0 have their e!ission

spectra overlapping 1ith their excitation spectra0 but in all cases the

!axi!u! region o e!ission is at a longer 1avelength than the

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!axi!u! region o excitation. #his is because energy is lost in the

optical transition0 and the energy o a photon. An opaue luorescent

sa!ple seen by relected light has its apparent diuse relectance actor

!ade up o to1 parts0 the true relective co!ponent 1here a raction o

the incident light at each 1avelength is scattered bac8 1ithout change o

1avelength and the luorescent co!ponent 1here a raction o the light

incident at 1avelengths in the excitation region is re&e!itted in a

1aveband centered at a longer 1avelength. ?or!al colori!etric

instru!ents or surace colors are capable o handling correctly the

ordinary relected co!ponent o light0 but not the luorescent co!ponent.

#he luorescent co!ponent o the total radiance actor o a sa!ple is0

ho1ever0 dependent on the relative spectral po1er distribution o the

incident light0 as sho1n.

METAMERISM

,hen t1o suraces !atch or nearly !atch or color under so!e

illu!ination0 but !is!atch under one or !ore other illu!inants0 they are

said to be !eta!eric0 and their spectral relection proiles 1ill be ound

to be dierent or any color. #here are0 in general0 !any possible spectral

distributions0 a act that ollo1s ro! the trivariance o hu!an color

vision. Any color0 regardless o spectral distribution0 can be !atched by a

suitable !ixture o any or !any dierent possible sets o !atching

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sti!uli. Meta!eris! arises to so!e extent 1henever a target color

sa!ple is !atched using dierent colorants0 substrates0 or 8inds o

!aterial. It is never possible to duplicate exactly the target colors o

spectral relection proile 1hen such changes o !aterials are involved.

THE ELEMENTS OF ESTHETICS-APPLICATION OF COLOR

SCIENCE

"istory has recorded !an8indGs interest in his personal appearance

and the eect that sel i!age has on conidence0 peror!ance0 and social

inter course. $ental esthetic has igured pro!inently in this role o sel&

i!age and various ethnic groups have adorned and altered their dentitions

in diverse !anners. Si!ilarly0 any treatise on esthetics is sub7ect to

individual interpretation. #he dentist !ust0 thereore0 atte!pt to use the

technical and conceptual ability to develop or the patient a restoration

that best !eets the patientGs psychological and biological needs and

desires. %sthetic excellence is largely an art 1ith pri!arily sub7ective

interpretation0 though not enough has been done to eectively analy9e

and or!ulate it. Although a consideration o color and shade !atching

1ill receive !a7or e!phasis0 the relative role o this ele!ent !ust be

placed in the right context.

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THE ELEMENTS OF ESTHETICS

%sthetic ele!ents can be approached ro! a nu!ber o dierent

vie1points and any approach to taxono!y or grouping results in so!e

redundancy and inadeuacy. #he ele!ents o esthetics 1ithin the

headings o or!0 texture and color. >or 1ant o a better syste! I shall

herein approach the dissection o co!ponents o esthetics into BspatialB0

BopticalB0 and BbiologicalB considerations.

SPATIAL

Spatial co!ponents are those actors0 1hich apply to

tridi!ensional or! and the relation o the teeth to one another as 1ell as

to the approxi!ating or enclosing ele!ents. #here are also perceptual

ele!ents0 1hich include linear har!ony0 perspective vie10 and

orientation to the sot tissue. #hese ele!ents individually and in concert

deliver the greatest i!pact to the vie1er. Additionally0 the actual and

inite !ay not be as i!portant as the eect perceived. Illusion is a !ost

signiicant entity.

OPTICALAnyone 1ho has tried to !atch teeth 1ith a restorative !aterial

recogni9es that the procedure is co!plex. #he optical appearance is not

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!erely one o BcolorB as great a concern as that pheno!enon is0 but also

involves light and shado10 surace texture0 translucency0 and opacity.

BIOLOGIC

#he biologic ele!ents include those vital actors0 1hich separate

the dyna!ic and physiologic ro! the static and lieless.

ANALYTICAL PROBLEMS

,hen all o these considerations are expanded into their

subordinate co!ponents it is little 1onder that obtaining esthetic

excellence has presented so!e analytical proble!s. #his !ay be si!ply

stated by noting that the dentist !ust )a* understand 1hat the patient

1ants )psychologic*0 )b* 1hat the patient needs )physiologic*0 and )c* o

1hat dental science0 especially as expressed by the dental tea! rendering

the speciic service0 is capable )technical*. Unless the psychologic

physiologic0 and technical ele!ents can be brought into consonance0

therapy should not be initiated.

PLANNING

%ssential to the planning o a restoration or prosthesis is an

adeuate set o diagnostic casts that reproduce the patientGs sot and hard

tissues 1ith idelity. It is advisable to !a8e a duplicate set o casts to

provide a baseline record that 1ill have both therapeutic and legal value.


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Such casts should usually be !ounted0 although si!pler procedures can

be acco!plished on un!ounted casts.

DIAGNOSTIC AXING

Modiication to !eet both esthetic and unctional needs can best be

planned or through the use o a diagnostic 1axing procedure. Although

the diagnostic 1axing procedure is li!ited by the inani!ate properties o

the cast0 it nonetheless can reveal !any o the eatures that !ay indicate

or li!it success. #ogether 1ith clinical 7udg!ent developed ro!

observing the lip lines0 phonetics0 and inor!ation gleaned ro! the

patient intervie10 a precursor o the inal restoration can be developed.

#his incorporation o the patientGs desires enhances acceptance and

greatly reduces the possibility o dissatisaction or disappoint!ent at the

ti!e o place!ent o the co!pleted restoration. It is essential to ascertain

the desired esthetic result or !etal cera!ic units in advance in order to

allo1 1axing0 a ra!e 1or8 that provides proper !etal support0 yet does

not interere 1ith translucency and color nor inringe upon the ad7acent

tissues.

Porcelain is a !aterial that has intrinsic li!itations that !ust be

recogni9ed. #he !arriage o !etal to porcelain in the !etal cera!ic

restoration is an atte!pt to ta8e advantage o the strength o !etal and the

beauty o porcelain. Si!ilarly0 all the cera!ic restoration e!ploying an

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alu!inous core is a procedure that enhances success through dispersion

and strengthening. Porcelain ails in either syste! 1hen there is excess

bul8 or0 to phase it in the negative0 inadeuate support. #hereore0 the

strengthening support syste! )either !etal or alu!ina* !ust be

developed to allo1 as little o the esthetic veneering glass as possible )to

allo1 or strength* yet leave suicient bul8 to cover the substructure and

develop the esthetic optical properties desired. Such an acco!plish!ent

reuires 8no1ledge and planning. #he desired result !ust be pre&

established i both opti!u! strength and esthetic excellence are to be

obtained.

IMPLIED GENDER

Anthropologically0 there is no sexual di!orphis! o hu!an teeth.

,hereas it has been convenient to consider the !ale or! as one that is

!ore cuboidal )robust* and the e!inine as being !ore rounded )gracile*0

atte!pts to veriy this have ailed. As the dentition 1ears as a result o

unction or para&unction0 the !ore 7uvenile incisal edge contours are lost0

and the rounded or! evolves into one that is !ore angular. #hus0 it

appears that 1ear and aging have been translated into B!asculineB0 1hile

the !ore youthul or unaltered or! is as Be!inineB.

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EMBRASURES

All o the our e!brasure spaces )incisal0 cervical0 labial0 and

lingual* are i!portant0 but oten the irst perception o or! is the

silhouette o the teeth against the dar8 bac8ground o the oral cavity.

#his silhouette is generated by the incisal e!brasures and the connecting

incisal edges. #here is0 obviously0 an interace bet1een the incisal and

cervical e!brasures0 1hich or!s the inciso&gingival contact area.

OPTICAL ELEMENTS

#here are !any voids in the 8no1ledge o esthetic or!ulation0 but

so!e o these are slo1ly being illed. #he study o color in dentistry

!ust include translucency0 opacity0 and the eect o light and shado1.

Indeed0 it !ust be recogni9ed that color and light are a single entity 1ith

dierent !aniestations. 'ne cannot study color 1ithout studying light0

As $r. ;ruce Clar8 noted al!ost 4 years ago Bcolor&li8e or! has three

di!ensionsB. #hese three di!ensions or! the cornerstone o the logical

approach to clinical shade !atching. Color is a co!plex pheno!enon

and its recognition involves a physical sti!ulus0 a psycho&physical inter

change bet1een the receptor cells o the eye0 and the sub7ective response

by the brain to the inor!ation trans!itted ro! the receptor organ.

Hust as dental esthetics !ust be dissected into its co!ponent parts

to be co!prehended0 so BcolorB !ust be dissected into its three di!ensions


26/44

i it is to be BseenB and shade co!parisons !ade. ,hen a shade guide and

a tooth do not !atch0 it is not enough to note that a B!atchB is lac8ing0 but

deviations in each o the three di!ensions !ust be noted. #his reuires a

basic and clear understanding o those three di!ensions.

HUE

#he irst di!ension0 hue0 is usually deined as Bthe na!e o the

colorB. #his is an inadeuate deinition because it ails to recogni9e that

hue na!es are very i!precise. #here are !any dierent reds0 oranges0

greens0 etc. "ue is generated by the 1avelength o the sti!ulus. (isible

light is co!posed o 1aves o bet1een 234 ad 564 nano!eters. #he

shortest 1aves are seen as violet0 1hile the longest are red. #he physical

seuence0 dictated by 1avelength0 is violet0 blue0 green0 yello10 orange0

and red. It !ay0 then0 be said0 Bhue is the uality o color designated by a

convenient a!ily na!e0 and deter!ined by the 1avelength o the

sti!ulus.

VALUE

#he second di!ension0 value0 is !erely the uality o blac8ness or

1hiteness. It is the euation o the color to a gray scale. "ue and value

are independent0 or value can exist 1ithout hue )the converse is not true*.

#hese are !erely one&di!ensional renditions. ;ecause the hu!an

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observer is so very sensitive to slight dierences in value0 it is this

di!ension that is !ost i!portant in dentistry.

CHROMA /SATURATION0

Although value exists in the absence o hue0 chro!a is only present

1hen there is hue. Chro!a is !erely the intensity0 concentration0 or

strength o the hue. Any one o the three di!ensions !ay be varied

independent o the others0 but in dentistry this rarely happens.

COLOR ORDERING

Many syste!s have been devised to interrelate the various colors

possible by changing hue0 value0 and chro!a. So!e are best suited to

!easure!ent by colori!eters or spectrophoto!eters. Munsell !erely

related hue0 value0 and chro!a in the sa!e !anner that length0 1idth0 and

depth are related. #he hues 1ere !ade a continuu! by ta8ing advantage

o the act that the shortest 1avelengths )violet* contained visual ele!ents

o the next shorter )blue* and the longest )red*. #hereore0 a visual circle

could be !ade 1ith violet as the connecting lin8. Using the six hues

previously na!ed0 this circle 1ould read Bviolet0 blue0 green0 yello10

orange0 red0 violet0 blue0 etc.B Munsell then established a value scale o 4

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)blac8* to /4 )1hite*. "ues can be related to values !uch the sa!e 1ay a

1heel is related to an axle. "ues o a lo1 value appear dull0 those o high

value0 bright.

Chroma0 the third di!ension0 1ould be analogous to the spo8es o

a 1heel and represents the intensity o the color at any hue or value. #his

ordered color syste! !a8es possible the expression o all colors in ter!s

o hue0 value0 and chro!a. Color !atching can be done ro! a standard

and interpolation bet1een available color chips can be !ade in hue0

value0 and chro!a. Contrast to this ordered logic 1ith the procedures is

no1 used in dentistry. ?o shading syste! has both logical order and

adeuate distribution. ,or8 done by Clar80 )/@2/*0 Sproull )/@52*0

Le!ire and ;ur8 )/@5*0 and Miller )/@3/* has docu!ented the lac8 o

correlation bet1een the hue0 value0 and chro!a o natural teeth and that

o available shade guides.

+enerally0 shade guides do not include enough lo1 value and

higher chro!a sa!ples. A conservative esti!ate had been !ade that les

than ity percent o the population !ay be satisactorily !atched by

dental shade guides. Should one be ortunate enough to ind a shade tab

that apparently satisies the patientsG needs0 the proble! is not solved.

Meta!eris! is a continually perplexing actor0 since the spectral curves

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o porcelain do not !atch those o natural teeth. As a result0 the B!atchB

that is apparent in the clinical environ!ent !ay not be present in other

areas o illu!ination.

Meta!eris! in shade !atching has evolved ro! !ore areas than

7ust the discrepancy o spectral curves o natural teeth and porcelain )or

resins*. #here are only a very or shade guides that are used or porcelain

!atching although !any co!panies !anuacture porcelain syste!s that

are based on these guides. 'paue and body porcelains0 sho1n by the

1or8 recently done by Miller and "e!!en $inger0 have uite dierent

hue0 value0 and chro!a plots. #his !eans that the opaue is applied to

!as8 the !etal and then the body porcelain !ust be applied in a uantity

great enough to !as8 the opaue.

,hen this co!plex series o inaccuracies is considered0 the

recurring proble! o !is!atched shades is not surprising. Acceptance o

a shade is an individual actor and no absolute para!eters are deinable.

#hus the restoration o a single central incisor continues to be the greatest

challenge or the less co!pensation.

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IMPOSING LOGIC ON AN ILLOGICAL SYSTEM

,hen co!parison bet1een the teeth to be !atched and the shade

guide is !ade then an assess!ent o BdierenceB or Bno dierenceB is then

necessary. I the dierence exceeds the acceptable level0 a description o

that dierence is needed so that !odiication !ay be !ade to correct the

deviation. #hree uestions 1ill !a8e that description possible.

Is the shade guide yello1er than or redder than the tooth being

!atched-B #his uestion deals 1ith the di!ension o hue and

ac8no1ledges that since teeth are only in the yello1&to&yello1 red range0

no other hue error can be present.

BIs the shade guide hue !ore saturated or less saturated than that o

the tooth being !atched-B Again0 this !ay be diicult to separate hue

ro! value0 and either value saturation0 or both deviations !ay be

present.

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#hese three uestions 1ill help deine the dierence bet1een a

shade guide tooth and the tooth to be replicated. I no satisactory !atch

is available0 a guide tooth that is higher in value and lo1er in chro!a

should be selected. A higher value shade can be rather easily lo1ered

1ithout loss o translucency by the use o the co!ple!entary color

externally or gray or co!ple!entary !odiiers internally. ,hen the ten

hues Munsell na!ed 1ere given0 nothing 1as said o Bbro1n0B or bro1n

is not a hue0 it is a color. ;ro1n is a lo1 value o several hues0 but or

our purposes in dentistry0 the bro1ns are lo1 value yello1 reds.

SHADE GUIDE USE

It is helpul or the dentist 1ho oers porcelain restorations to

patients to have 8no1ledge o ho1 such units are abricated. %ven though

there in no intention o actually doing oneGs o1n laboratory 1or80 the

8no1ledge can greatly i!prove.

Suice it to say that porcelain is built up in layers using opaue0

body0 and incisal porcelains. %ach o these contributes to the inal optical

eect and each !ay be !odiied 1ith colorants to create the desired

eects. Shade guides reuently have characteri9ed areas that !ay or !ay

not be appropriate to the teeth being !atched. >or this reason0 at least

three o each o the shade guides used should be available to the dentist.

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#he irst is an un!odiied guide. #his guide !ay )and probably

does* have a cervical or that is dierent ro! the standard body shade.

#he second guide should have this cervical section0 co!posed o Bspecial

eectB porcelain0 re!oved. #he third guide should have the gla9e

re!oved )1ith stones0 discs0 or abrasive spray* or !odiication 1ith

cera!ic colorants. A ourth guide 1ith both cervical and incisal areas

re!oved !ay be desirable.

#he overlay o the ena!el portion on the body !ay be done in

dierent uantities and at dierent angles and !ay not be at all li8e the

standard guide. #he BopticalB ele!ents o translucency and opacity can be

as i!portant as BcolorB in developing an esthetically acceptable

restoration0 but tangible !eans o !easuring or co!!unicating the! are

largely lac8ing. Most porcelain syste!s have a series o dierent incisal

porcelains that !ay be used0 though !ost dentists are una1are o their

i!portance.

#he shade guide tab should be occupied by the restoration being

abricated. #his is easier to do or a pontics than or a cro1n. #he

gingival area o the shade guide should approxi!ate the gingival portion

o the tooth being !atched0 and the incisal edge o the guide should be in

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the sa!e position as that o the natural tooth. #he goal is to have the light

to be incident on the guide the sa!e 1ay the intended restoration 1ill

receive and relect light. >reuently the re!aining teeth 1ill exhibit

dierent shades and the goal !ust be not to !atch any particular one but

to achieve an acceptable blend.

#he position o teeth in the arch alters light relection and

so!eti!es acco!!odations !ust be !ade. >or exa!ple0 i the tooth that

is !ore pro!inent is !ore li8ely to reuire restoration )because it is !ore

sub7ect to trau!atic da!age*. ,hen the restoration is planned0 a shade

that is slightly lo1er in value !ight be selected in order to blend 1ith the

ad7acent central incisor.

SURFACE TEXTURE

Since color is entirely a result o light0 the !anner in 1hich the

light is relected is i!portant. #he surace topography o both the shade

guide and the tooth !ay alter the uantity and uality o light. #he

replication o surace !orphology is i!portant in order to eectively

produce natural tooth appearances. #his is done by proper carving o the

surace and obtaining the correct degree o gla9e. ?ot only does surace

texture eect the apparent value o a restoration0 but there are indications

that it also aects hue.

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CONTROLLED ENVIRONMENT

It has been repeatedly stated that the light incident to and relected

ro! an ob7ect entirely control color. #he ob7ect has the ability to absorb

or relect certain spectra o light. I it absorbs all light0 it is seen as blac8F

i it relects all light0 it is seen as 1hite0 provided a ull spectral light is

incident upon it. ,hen the ob7ect relects so!e rays and absorbs others0

the nature o the relected rays deter!ines the sti!ulus to the eye to

receive and the brain to perceive BcolorB. I the dental shade !atching

procedure is to be controlled0 then the incident light !ust also be

controlled.

#here are three areas that reuire attention i environ!ental control

is to be eective. >irst0 the light radiated !ust be co!plete spectru!

lighting0 at least co!plete as is reasonably possible. $aylight changes

hour&to&hour0 day&to&day0 and season&to&season. It varies in intensity and

in uality. #o ensure that the tubes selected are acceptable0 three criteria

should be !et. First,the tube should have a correlated color te!perature

si!ilar to that o standard daylight. )Standard daylight is deined in the

U.S as that light available in ,shington0 $.C. during the !onth o Hune

bet1een the hours o /:44 ad /:44 oGcloc80 1ith a slightly overcast s8y*.

#his te!perature is approxi!ately 044 Jelvin. Second, the spectral

curve o the light source should be si!ilar to that o this sa!e Bstandard

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daylightB. >inally0 the illu!inant should have a Color Eendering Index

)C.E.I.* o @4 or greater.

#he uantity o light reuired is !ediated by !any actors0 once

the uantity and uality o light have been achieved. Attention !ust be

given to several actors to preserve both. In order to !aintain the spectral

uality and brightness0 no intense colors or dar8 suraces should be used

in the roo!. Ee!e!ber that 1hen light hits a body0 so!e rays are

absorbed and so!e are relected. #he dar8er that body0 the !ore the hue

1ill be relected. #he dar8er that body0 the e1er are the rays relected.

#he !ore highly colored the body0 the !ore hue 1ill be relected and the

less spectrally pure 1ill be the light in the environ!ent. %very colored

ob7ect alters the light that is incident upon it. #hereore0 the larger the

surace )such as 1alls or cabinet ronts* or the closer it is to the critical

color !atching area&the patientGs !outh )or exa!ple*. A third factor0

ater the light source and relecting suraces0 is the acuity o the vision o

the observer !a8ing the evaluation. #his acuity can be di!inished by

sustained vie1ing0 and the evaluation period should be li!ited to ive

seconds. Ater the shade guide&tooth co!parison0 the vie1er should avoid

hue adaptation by loo8ing at a !ediu! blue or grapy card (this writer

prefers the ble!beore !a8ing another co!parison. #he control o light

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source0 roo! eatures0 and vie1er perception is essential to eective

color !atching.

CLINICAL PROCEDURES

,hen a restoration is received ro! the laboratory0 it !ay be either

in a gla9ed or ungla9ed condition0 although !etal cera!ic porcelains are

al1ays carried to !aturity )gla9ed* and then shaped prior to inal gla9ing.

At the try&in o the restoration0 the !odiications o or! are !ade irst.

#he principles or this procedure have been discussed at length

previously. ?ext0 the proper surace texture is achieved using dia!ond

stones0 dis8s0 or other instru!ents. In the process o reshaping0 the gla9e

!ay be re!oved in so!e areas and not in others. #he gla9e should be

re!oved ro! all suraces 1ith the possible exception o tissue suraces

o pontics or non&visible areas such as the lingual aspect. #he gla9e is

best re!oved 1ith an abrasive spray0 but i this is not possible e!ery

dis8s or ine dia!ond stones !ay be used. Ee!oving the gla9e ro! all

suraces allo1s ho!ogenous regla9ing rather than having suraces 1ith

dierent degrees o gla9e on various areas o the restoration. I colorants

are to be added to the suraces0 they 1ill be ired at the sa!e ti!e the

restoration is regla9ed.

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38/44

23


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COLOR MODIFICATIONS

,hen any shade other than a basic shade guide color is indicated0

the color !odiication !ay be either intrinsic0 i.e.0 added into the

porcelain at the ti!e o abrication0 or extrinsic i.e.0 applied to the surace

ater iring. ;oth procedures have advantages and disadvantages. Intrinsic

additions oer the broadest range o shade alteration. Internal

!odiication0 ho1ever0 reuires s8ill0 and is reversible only by re!oval

o the porcelain itsel0 and cannot be previe1ed prior to iring. "o1ever0

surace colorants are easily applied or re!oved0 loo8 very !uch the sa!e

beore iring as ater0 and do oer a si!ple !anner o !a8ing inal shade

corrections and adding characteri9ations.

>or !ore intense eects0 the !ore concentrated colors called

BstainsB can be added to either the basic porcelain or !odiiers. #hese

stains are !etal oxides in a luxed porcelain base. Metal oxides are

opaue and !ust be dispersed through the glass !atrix to give the desired

optical eect. #he opaue porcelain po1ers !ay be !ore intensely

colored 1ithout any detri!ental eects0 since they are0 by necessity0

already opaue. Conversely0 surace !odiications are li!ited in the

degree o saturation possible0 since the translucency o the restoration

!ay be lost as concentration increases.

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EXTRINSIC MODIFICATION

#o understand the eect o !odiiers on porcelain color it is

necessary to recogni9e the !any ele!ents that enter into the generation o

color in a restoration.

Since extrinsic colors )stains* are applied to the surace0 they

produce their eect dierently than do intrinsic color !odiiers. Much o

the eect is the result o spectral relectance. #he !ore heavily the

surace stain is applied0 the greater 1ill be the spectral relectance and the

less 1ill the color be generated ro! 1ith in. #he cause o this is

t1oold. First0 less incident light 1ill pass through the surace !odiiers0

since they are opaue0 and 1ill be directly relected ro! the!. Second0

so!e o the light that did pass through the surace layer to the underlying

porcelain 1ill be relected ro! the undersurace o the extrinsic stains

bac8 into the restoration.

In spite o the li!itations o extrinsic !odiication0 the procedure

has !any applications that can enhance the esthetic acceptability o a

restoration and should be in the ar!a!entariu! o every restorative

dentist. An essential prereuisite to eective extrinsic !odiication is the

!ixing o the colorant po1ers 1ith the liuid !ediu! to achieve a

suitable consistency. (arious !edia are used0 but all have a higher

viscosity than 1ater to reduce lo1. Prophylene glycol is oten used.

=4


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I the !odiications are to be !ade at chair&side0 the colorants

should be !ixed and applied to the restoration ater it has been placed in

the !outh. 'nce the proper eect has been achieved the !outh be

cleaned. #his !ay be done !ost eectively 1ith stea!0 but this acility is

rarely available in a dental oice. %ither distilled 1ater in an ultrasonic

cleaner or vigorous brushing 1ith a clean brush under running 1ater 1ill

suice. #he restoration is then dried and the colorants reapplied. #he

need or this apparently repetitious procedure is to obviate conta!ination

ro! saliva0 cervicular luid0 or debris. 'nce the desired colorants have

been !ixed and the eect visuali9ed0 it is a si!ple !atter to reproduce

the eect in the second application.

'ne o the si!plest shade !odiication procedures is increasing

chro!a. I the inal restoration is lo1 in chro!a0 the properly hued

colorant is chosen. $ecreasing value is si!ilarly si!ple. #he perception

is oten expressed as a need or B!ore grayB. +ray stain0 ho1ever0 is not

the colorant o choice. I the value decrease is to give the i!pression o

greater translucency or neutrali9e hue0 violet is the proper colorant. #his

use o a co!ple!entary color to achieve a lo1er value is one o the !ost

co!!on applications o extrinsic colorants.

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#he dental colorants do not !eet the reuire!ents o the

subtractive color syste!. Instead o cyan )pri!ary* and green

)secondary*0 yello1 and red0 !agenta and blue0 cyan is o!itted and

orange is added. >or this reason0 violet 1or8s or nearly all shades 1hen

an increase in apparent translucency is needed or value needs to be

lo1ered !oderately. ;ro1n is !ost eective or !ore signiicant value

decreases 1hen chro!a is being raised conco!itantly. ,hen bro1n is

!ixed 1ith the colorant being used to increase chro!a0 the value

lo1ering eect is !uch greater than 1hen violet is used.

FLUORESCENCE

Another actor that has been the sub7ect o great concern and

reuent consternation to those !anuacturing dental porcelain is that o

luorescence. >luorescence is a or! o lu!inescence 1herein a sti!ulus

belo1 the visible spectru! )ultraviolet* causes a body to e!it light 1ithin

the visible spectru!. ,hen ultra violet )blac8 light* is the pri!ary source0

the dierence bet1een natural teeth and !ost restorations is gross. So!e

recent luorescence or!ulas have been innovatively successul in

achieving excitation e!ission properties si!ilar to natural teeth0 yet so!e

porcelains lac8 any signiicant luorescence.

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OTHER OPTIMAL PROPERTIES

#he replication o ano!alous teeth 1ith porcelain can still be

rustrating. Color is not the only variable that reuires ad7ust!ent0 since

relative translucency and opacity !ust also be considered. So!e teeth

actually !ay be seen to beco!e !ore opaue as they dry0 and each shade

co!parison is dierent. Much o the inal success co!es only 1ith

patience and s8illed artistry0 and so!eti!es success is si!ply not

obtained to the degree desired.

HAT LIES AHEAD1

#he advent o an era in dentistry 1hen porcelain is the ocus o so

!uch attention should not be perceived as an indication that this is the

ulti!ate !aterial. Porcelain has excellent esthetic properties and the

abrication procedures0 1hile not entirely si!ple0 allo1 the production o

a signiicant percentage o the restorative !aterials in use. Porcelain by

itsel lac8s tensile strength and ailures are not unco!!on. ,hen bonded

to !etal to achieve greater strength0 a hostile environ!ent or the

ra!e1or8 is established. #he abrasiveness o porcelain against natural

teeth creates a rather destructive occlusal proble! in so!e situations.

#he iring te!peratures preclude the use o organic pig!ents li!iting the

procedures available or color control. Eesin poly!ers can be bonded to

!etal oxides 7ust as glass poly!ers can. +rating procedures see! to

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!a8e virtually any property possible. It see!s probable that resins

1ithout !etal support can be developed or dental use. >or the present0

ho1ever0 so!e interesting !odiications o current techniues are at

hand.

SUMMATION OF TECHNIQUE

I there is one 1ord that holds the best advice or i!proved

esthetics it 1ould be BobserveB. It is the natural0 pleasing dental

co!position 1e see8 to e!ulate and it is the hu!an dentition and its

associated tissues that beco!e the textboo8 o study.

A second 1ord or success is BplanB. #he result should be

envisioned beore deinitive therapy is initiated. #his anticipated BresultB

!ust be the sa!e in the !ind o the patient as it is in the !ind o the

dentist0 i dissatisaction and esthetic ailure are to be avoided.

==

25.tooth shade selection - seminar

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