direct esthetic restorations based on translucency and ... · light transmission. a transmitting...

Direct Esthetic Restorations Based on Translucencyand Opacity of Composite Resins

MILKO VILLARROEL, DDS, MS, PhD*

NEWTON FAHL, JR., DDS, MS†

ANDREA MARIA DE SOUSA, DDS, MS‡

OSMIR BATISTA DE OLIVEIRA, JR., DDS, MS, PhD§

ABSTRACTLight dynamics is a relevant phenomenon with respect to esthetic restorations, as incorrectanalysis of the optical behavior of natural dentition may lead to potential clinical failures. Thenature of incident light plays a major role in determining the amount of light transmission orreflection, and how an object is perceived depends on the nature of the light source. Naturalteeth demonstrate translucency, opalescence, and fluorescence, all of which must be replicatedby restorative materials in order to achieve clinical success. Translucency is the intermediarybetween complete opacity and complete transparency, making its analysis highly subjective. Innature, the translucency of dental enamel varies from tooth to tooth, and from individual toindividual. Therefore, four important factors must be considered when appraising translucency.Presence or absence of color, thickness of the enamel, degree of translucency, and surfacetexture are essential components when determining translucency. State-of-the-art resin compos-ites provide varying shades and opacities that deliver a more faithful reproduction of the chro-maticity and translucency/opacity of enamel and dentin. This enables the attainment ofindividualized and customized composite restorations. The objective of this article is to providea review of the phenomena of translucency and opacity in the natural dentition and compositeresins, under the scope of optics, and to describe how to implement these concepts in theclinical setting.

CLINICAL SIGNIFICANCEChoosing composite resins, based on optical properties alone, in order to mimic the propertiesof natural tooth structures, does not necessarily provide a satisfactory esthetic outcome. Inmany instances, failure ensues from incorrect analysis of the optical behaviors of the naturaldentition as well as the improper use of restorative materials. Therefore, it is necessary toimplement a technique that enables a restorative material to be utilized to its full potential tocorrectly replicate the natural teeth.

(J Esthet Restor Dent 23:73–88, 2011)

*Professor, Department of Operative Dentistry, Valparaiso University, Valparaiso,Chile and Department of Restorative Dentistry, São Paulo State University—UNESP, Araraquara, Brazil

†Private practice, Curitiba, Brazil‡Professor of Integrated Clinical, Positivo University, Curitiba, Brazil

§Professor, Department of Restorative Dentistry, São Paulo State University—UNESP, Araraquara, Brazil

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I N T R O D U C T I O N

The dental marketplace offersgreat diversity in new direct

resin systems, bringing newoptions, along with new doubts,regarding which choice of materialto use. Given the importance of afully integrated tooth restorationthat fulfills both functional andesthetic requirements, a completeknowledge of the behavior ofdental tissues and the relationshipof restorative materials with thephysical and optical phenomena oflight is required.

The esthetic requirements of com-posite resins are intimately relatedto the optical interactions of lightwith matter. Light is the form ofelectromagnetic energy that isvisible to the human eye. It is alsothe major element that allows per-ception of the color of an object.Perception of light occurs not onlybecause of color but also becauseof physical and optical propertiesthat are inherent to the electro-magnetic waves. Those propertiesare directly related to the environ-ment and the presence of light onthe object. Considering that everysubstance capable of transmittinglight is composed of matter,the tissues that compose thedental area are also capable oftransmitting light. Just as ithappens with other mediums,when light is dispersed on thesurface of the tooth, it can be

reflected, absorbed, refracted,and diffused.1

The Nature of LightTo understand how restorativematerials will present their estheticvalues, it is necessary to firstunderstand the physical propertiesand characteristics of light. Par-ticles named photons comprisewhat we see and experience as“light.” These particles are repre-sented by the different lengths ofelectromagnetic waves. Humanperception of light begins at elec-tromagnetic wave lengths between400 and 700 nanometers.2 Visiblelight, however, is a mix of differentwavelengths and is called whitelight. In contrast, monochromaticlight is produced by the luminousenergy of short span of wave-lengths, displaying as a single coloror single wave of light.3 When lightcollides with an object, it createsphenomena such as absorption,transmission, or reflection. Theinteraction of light with mattertypically results in the union oftwo or more phenomena.2 The tra-jectory of the rays that interactwith matter can be regular, diffuse,or a combination of both.

When these optical phenomenaoccur, light beams interact with anobject and may be detoured, ordeflected, in another direction. Theway in which this occurs dependson the type of surface the light par-ticles collide with, and on the angle

they form with the surface.4 Whenlight collides with the correctsurface and the angle formed withthe surface is correct,reflection occurs.

The reflection of light on a flatsurface is called specular, orregular, reflection. This is becauseof the angle of light breakup and isequal to the angle of reflection. Inrough surfaces, the reaction of thelight is termed diffuse reflection, asthe surface behaves as an infinityof tiny surfaces disposed irregu-larly, reflecting the rays in severaldirections, not as a parallelgroup.1,5 The appearance of diffusereflection is because of the differ-ent angles at which the light travelsafter colliding with a roughsurface. Semi-specular, or mixed,reflection occurs when light breaksup on a flat surface and is reflectedat slightly different angles but stillin the same direction. This gener-ates an intermediate reflection thatis both specular and diffuse.5

Because light can be reflected bycertain surfaces, it also has theability to refract.

The refraction phenomena is pro-duced by the directional changethat the luminous rays incur whenpassing from one medium toanother, at varying speeds, whilechanging its value.2,5 Thus, if abrush of light disperses on thesurface of a translucent body, partof it is reflected and the other part

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is refracted. Specifically, the lightpenetrates the translucent bodywhile changing the direction ofits motion.6

The refractive index, or the rela-tionship between the speed of thelight in a vacuum and in a concretebody, is a distinctive property ofmatter typically used for identify-ing materials.2,5 When the refrac-tive index of light in the vacuumcoincides with the index in themedium, without path modifica-tion, the medium is called transpar-ent. If, however, the refractiveindexes are different, the mediumwill present distinct translucent oropaque characteristics.5,6

Light, aside from being refractedor reflected, can also be absorbedby matter. This absorption iscaused by the decrease of energy ofluminous radiations when collidingwith an opaque body or acrosstransparent surfaces.5 Absorptiontechniques consist of capturing thedifferent wavelengths that composewhite light. In general, bodies donot absorb all of the frequencies ofthe light spectrum with equalintensity. Therefore, a selectiveabsorption is produced.3

Transmission, another property oflight, is considered double refrac-tion.6 When looking at a crystal, itis possible to see light undergoingan initial refraction as it passesfrom the air to the glass. It then

follows its way through the glassand refracts again once it reachesthe air.2,5 After this process, if thelight ray is not diverted from itspath, light transmission is said tobe regular, as in transparent glass.4

If the light is diffused in all direc-tions, diffuse transmission occurs,a typical property of translucentglass. If one direction prevails overthe others, there will be mixedtransmission, as in organic glassand crystals with rugged surfaces.5

Therefore, it is understood that theoptical behavior of each medium isdetermined by not one, but rathermany different factors, includingthe degree of dispersion, refraction,transmission, and absorption oflight rays.5

Optical Phenomena ofColor PerceptionUnder natural conditions, the lightthat illuminates an object is whitelight, which is the result of themixture of all colors in the spec-trum.3 An object presents itself as“colorful” when its surface iscapable of absorbing specific wave-lengths of incident light. When oneor more wavelengths are reflected,an object is recognized as being aspecific color.

For example, an object is whitewhen it is capable of reflecting allwavelengths of which light is com-posed. An object is considered redwhen it absorbs all wavelengths,including violet, blue, green,

orange, and yellow, and reflectsred. When an object completelyabsorbs all wavelengths of light, itis considered to be black.3,4 Thesedefinitions lead to the conclusionthat an object will show colormore proportionally to its opacity,rather than its ability to absorband reflect light. According to thisprinciple, a translucent body pre-sents color in an inversely propor-tionate manner to the level ofits translucency.

Similarly, the capability of a bodyto allow light passage through itsinterior is called the concept oflight transmission. A transmittingmedium can be classified into threecategories that include opaque,transparent, and translucent. Thesecharacteristics are dependent uponhow a specific material or bodyreacts to incident light.2,4,5 Bodiesand materials either have theability to transmit light or nottransmit light. If a specific kind ofmatter allows the passage of light,it is called transparent or translu-cent. When matter is unable toallow passage of light, it isconsidered opaque.

Matter is considered to be opaquewhen it only absorbs and/orreflects light but does not have theability to transmit it.2 Opacity istypically observed in materials thatdo not transmit light. Oftentimes,it is used to describe materials thatabsorb or reflect all light by not

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allowing its passage. In this par-ticular case, the property is termedtotal opacity (Figure 1C).4

Differing significantly from opaquematter, a transparent mediumallows light passage through itsinterior, without suffering anymodifications in its path. When amaterial is transparent, an observercan see through it without distor-tion of objects and shapes on theother side (Figure 1A). Transparentmediums may present with achro-matic or chromatic properties.When the medium is achromatic, itwill not influence the perception ofthe object’s color when lookingthrough it. Chromatic mediums,however, will affect the color ofthe observed object when viewingit through the medium.

In comparison with transparentmaterials, translucent bodies andmaterials are distinguished by their

ability to allow the passage of inci-dent light through their interior.Where transparency differs fromtranslucency is through the modifi-cation of direction, which does notallow clear observation of objectsbehind translucent bodies(Figure 1B).2,4 In discussing translu-cent materials, there are fourimportant factors that determinewhether the material is achromaticor chromatic, including presence orabsence of color, thickness of mate-rial, degree of translucency, andsurface texture.

Color, or absence thereof, is aproperty that applies to both ach-romatic and chromatic translucentbodies.2 Typically, a body is calledachromatic-translucent when itallows passage of light by dispers-ing it through its interior and outthe other side. In an achromatictranslucent material, this occurswithout presenting any color

variation. This can be attributed tothe transmission of all wavelengthsof light through the body.

A material, substance, or object iscalled chromatic-translucent whenit allows the passage of light bydispersing it through its interiorbut reflecting only one wave-length.5 This single wavelengthprovides color to the otherwisetranslucent body (Figure 2).2

Therefore, the perception of anobject through an achromatictranslucent body is very differentfrom the perception of the color ofthe same object through a chro-matic translucent body. In thelatter, the perception of the objectis influenced by the color of theinterposed medium.

In the field of dentistry, dentin pre-sents a chromatic translucency,with its saturation increasing overtime (Figure 3). Enamel, however,has the ability to present eitherchromatic or achromatic translu-cency. Although it is often color-less, enamel can gradually becomeachromatically translucent(Figure 4).7–9 According to manyexperts in this field, enamel tendsto have a yellowish-white orgrayish-white aspect. When appliedto composite resins, this conceptabides by the same principles, asenamel resins can be pigmented,presenting chromatic and achro-matic translucencies. The choice ofmaterial and pigment is then very

Figure 1. Properties of transparent bodies (A), translucent(B), and opaque (C).



important, because color percep-tion of the dentin composite resinis influenced by the enamel com-posite resin selected (Figure 5).

When dealing with these types oftranslucent substances, the varia-tion in the refractive index is alsoan important consideration, as itis directly related to the thicknessof the material.1,5 When light isdiffused in the interior, the mate-rial becomes translucent. Thetranslucency of the substance mayalso vary because of the thicknessof the material. For example, ifthere are three bodies of the samematerial with three differentthicknesses (i.e., 0.5, 1, 2 mm),the one with the greatest thicknesswill be the least translucent(Figure 6).10

In natural teeth, the thickness ofthe enamel varies greatly and is

greater at the incisal one-third,decreasing gradually toward thecervical one-third.8,11 Therefore,translucency in the cervicalregion is greater when comparedwith the incisal region, allowingfor a clearer perception of thedentin (Figure 7). The sameprinciple applies to toothage, whereby younger teethpresent more enamel than inolder teeth.11

Young teeth present a high colorvalue, with typically no translu-cency whatsoever. This is becauseof the high quantity of enamelpresent, as the enamel of olderteeth becomes thinner and moretranslucent over time, sometimespresenting as nearly transparent(Figure 8A and B). Older teethalso present a much lower colorvalue than that which is seen inyounger teeth. When this principle

is applied to composite resins,especially to those used to restoremissing natural enamel, the thick-ness chosen is critical. This isimportant because a small thick-ness increase may significantlychange the color value of the res-toration, thereby altering the per-ception of the color beneathit (Figure 9).

The degree of translucency of amaterial is an inherent property.2

Light does not always pass throughmatter with the same incidence anddirection.1 Many times, a majorfraction is deflected by the actionof particles or anomalies within theobject.5 As previously mentioned,translucency is directly related tothe diffusion of light, and bothconcepts depend on the refractionindex of the material.1 The largerthis index, the larger the degree oflight dispersion and,

Figure 2. Properties of achromatic and chromatictranslucent glass (A), (B), on different coloredbackgrounds.

Figure 3. Different saturations of the dentin; age enhancessaturation.


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consequently, the lower the degreeof translucency.2,5

Surface texture is also an impor-tant characteristic of an object thatcan significantly change the per-ceived translucency of an object.The more a surface reflects light,the less selective absorption isobserved. If surface conditionsenhance light reflection, transmis-sion is proportionally reduced.12

When light reflection is increased,the color of the object tends to bemore luminous and of a highervalue. In objects with a certaindegree of light transmission, reflec-tion of the surface reduces theamount of light that crosses theobject. For example (Figure 10),translucency of a sandblasted glassis greatly reduced as a result ofreflection on its irregular surface.The glass therefore becomes moreluminous, as it is more reflective.

The glass also becomes opaqueon the surface at this time becauseof the reflection limits on translu-cency and light transmission. Thissurface does not only modify colorperception but also the perceptionof the translucency and opacity.

Depth and TranslucencyAn important as well as criticalchallenge in the clinical setting isrestoring the natural shape of atooth. This involves renderingproper anatomy, depth, and trans-lucency in the typical adverse con-ditions encountered in dentalrestorations. Clinicians mustachieve perfect rendering and con-touring in an area that presents alack of space, little material thick-ness, and the need to employopaque materials under thin outerlayers. If done incorrectly, theresult may be inexpressive, lifelessrestorations because translucency

and depth are important character-istics when attempting to replicatewhat was created naturally.

When dealing with depth, or“depth effect,” a challenge oftenfaced is the distance between theextreme positions of a screen, overwhich an optical system can chartimages. This is the result of thedifferent levels of translucency thata structure may present.12 It is nec-essary to note that translucencyand depth are intertwined and areresponsible for the simultaneousperception of various special situa-tions, such as “close and far” and“front or back.”

In applying this concept to naturaldentition, depth is said to be allstructures that are part of thetooth. This is attributed to the dif-ferent levels of translucency anddepth that the enamel and dentin

Figure 4. A side-by-side comparison was made to colorlessyoung enamel and older enamel, which is achromaticallytranslucent.

Figure 5. Interaction of chromatic and achromatic enamelresins, which modify the perception of the dentin resin.



present, which also contribute tothe natural appearance ofthe dentition.

Translucency and Opacity ofDental StructuresThe analysis of the interaction oflight and dental structures isimmensely important, as it is nec-essary to understand the opticalproperties of teeth. Regarding thisinteraction, it can be said thatdentin is the color and enamel isthe color modifier.11,13,14 Althoughthere are variations of composition

and mineralization, it is knownthat enamel allows a 70.1%average light passage, whereas52.6% of light can be transmittedthrough the dentin structure.15,16

There are few reports in the litera-ture that study teeth as a whole,yet for correct understanding ofthe phenomena that occur inenamel and dentin, they should bestudied separately.

EnamelIn dealing with enamel, the rodsthat comprise the basic structure of

the enamel generally rise at a rightangle from the dentin surface. Incervical areas, the rods divert fromhorizontal orientation and leanapically. Near the incisal or cusptip, the rods change directiongradually, becoming oblique andnearly vertical over the edges.17

Rod groups can present wrinkling,referred to as Hunter–Schregerbands, throughout their course ofmovement. Because of this orienta-tion change, less light is transmit-ted, which decreases thetranslucency of the enamel.9

The translucency of the enamel isoften expressed by the transmissioncoefficient, or the relative amountof light that passes through acertain thickness. The transmissioncoefficient of enamel is dependentupon the wavelength of incidentlight, as the total transmission oflight through human enamel

Figure 6. Enhancing the thickness of composite resinsdetermines an increase in translucency: 0.5 mm (A), 1 mm(B), and 2 mm (C).

Figure 7. Enamel presents itself with differenttranslucencies.

Figure 8. A side-by-side comparison was made to young (A) and old teeth (B).


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increases as the wavelengthincreases. This effect causes theenamel to become more translucentunder larger wavelengths. The cor-relation between wavelength sizeand transmission of light is ofparamount importance duringshade selection because the natureof the light source also influencesthe outcome of translucencyand esthetics.18

Enamel also modifies the chro-matic aspects of the teeth becauseof phenomena such as reflection,transmission, refraction, thickness,and surface texture. It is alsoimportant to note that enamel hasthe ability to attenuate underlyingcolors, which can affect the chro-matic aspects of the teeth.19 There-fore, properties of light reflection,or transmission of enamel, aredependent on its texture, orienta-tion of enamel rods, and its abilityto refract light, in addition to his-tological characteristics.

However, when unreflected, lumi-nous radiation passes throughmatter and reaches prisms ofdiverse orientation, additionalrefraction then occurs. This refrac-tion determines the varying degreesof translucency and opacitypresent. These situations occurwhen light passes through a multi-crystalline structure, such as dentalenamel. Relative translucency ofthe enamel also depends on thelight reflection and/or transmissionproperties of the enamel. Enameltranslucency may also be attributedto variations in calcification levels,because the more porous and lessmineralized the enamel, the largerthe dispersion index.8,20

This variation occurs in youngteeth, as they reflect more light andare brighter because of their highercolor value. Young teeth also tendto exhibit a milkier and less translu-cent appearance. Younger patientstypically display thicker and more

luminous enamel, attenuating thecolor of the dentin. Conversely,more mineralized and less porousenamel becomes more translucentand has a reduced color value. Allachromatic translucent matter over-laying an object produces moregrayish tones because the less lightthat is reflected, the less the objectilluminates. Therefore, translucentenamel imparts a grayish color tothe tooth, whereas opaque enamelpresents itself as whiter, morereflective, and luminous because ofits high value.

Older patients, however, displayenamel that may be slightly thinnerand translucent as a result of per-manent wear. This type of wearpromotes an enhancement of den-tinal chroma toward the cervicalone-third. Both incisal and proxi-mal enamels are also highly trans-lucent. Between the incisal area ofthe enamel and the incisal portionof the dentin, there is an

Figure 9. Value enamel resin can alter theperception of the underlying dentin resin.

Figure 10. An image showing translucent glass at various levelsof sandblasting.



intermediate zone of markedtranslucency. Typically, this is morevisible in young teeth, whereaspractically nonexistent in olderteeth because of incisal wear andlack of sufficient enamel thickness.This intermediate zone relates tothe opalescence phenomenon ofnatural teeth. Incisal bluish-graytranslucency rarely presents itselfin a continuous and uniformmanner, normally showing differ-ent patterns, depending on theshape of dentin mamelons.21

Reflected and refracted light high-lights a high-translucency areabetween the enamel and the dentin,known as the “glass layer” or“high diffusion layer.”21 This layeris visible in the stereomicroscopetrans-illuminated sections as agrayish-white line that can be his-tologically identified as an area ofhigh protein concentration in thematrix. This matrix, likely com-

posed of enamelines or amelo-genines, usually becomes degradedover time, even though a few teethmay still preserve features ofstrong light refraction anddiffusion (Figure 11).13

DentinDentin, however, can be consideredthe dental tissue of higher relevancewhen concerned with color.9,13

From an optical point of view,dentin is a low-translucency struc-ture with various chroma and satu-ration variations. Dentin tubulesare cylindrical structures that arespread throughout the entire depthof the dentin. Their course on thecoronal portion commonly assumesthe smooth curved shape of anitalic “S,” becoming even smoothernear the root. The first convex cur-vature of this double-bent coursebegins at a right angle with the pulpsurface and is oriented toward thetooth apex.

These tubules achieve an endingpoint at the dento-enamel junction.Near the incisal and cusp edges, thetubules are nearly straight.Throughout their length, theypresent relatively regular small sec-ondary bending, with sinusoidalshaping.8,9 This dentin tubulearrangement enables the dentin todemonstrate selective light diffrac-tion, as certain rays are reflectedwhereas others are absorbed. Thisphenomenon produces relativeopacity, which is a special propertyof the dentin.8

As age increases, primary dentinbegins to evolve or change. Origi-nating secondary and tertiarydentins, which have different struc-tures and compositions, affect thetissue’s optical properties.4 Inelderly patients, the reduction inthe diameter of the dentin tubulescauses progressive dentin sclerosisand high saturation.

These properties are influenced byhydration levels and orientation aswell as the number and diameterof existing tubules (Figure12). A cross-section of a toothdepicts a great amount of high-amplitude dentin tubules orienteddownrightly to the section frame.If light is directed straight into thecenter of a horizontal cut of theocclusal third, the light insidethe dentin tubules will be travel-ing in the same direction, whichwill determine its translucency.12

Figure 11. View of the area of transition between theenamel and dentin.


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Further from the middle of the cut,the tubules change direction andreach the edge of the cut at nearly aright angle to the incidence oflight, thereby decreasing its translu-cency. On a longitudinal section,their displacement will differ.Therefore, the perception of trans-lucency will be changed. Thus, theorientation of the cross-sectionhighly influences the study of theeffect of light transmission throughthe dentin.

D I S C U S S I O N

Translucency and Opacity ofComposite ResinsTranslucency may be one of theoptical characteristics that ishardest to quantify in natural denti-tion, as it varies from individual toindividual, many times even varyingwithin the same person. Within thescope of composite resins, there arebasically three variations that are

divided by translucency and opacitylevels. This allows the resins toperform a specific role during thelayering process.22 Modern compos-ite resins have different hues andopacities that imitate the chroma-ticity and translucency of enamel,as well as dentin, in the bestpossible manner.23

Among commercial brands, thereis no general agreement on trans-lucency and opacity levels of com-posite resins, or their designations.This is also true regarding the lit-erature on the topic, because thereis no report to date of a terminol-ogy that standardizes these materi-als. Additionally, manufacturersprovide very little or no informa-tion at all on the topic.24

There are, however, terms such as“artificial dentin” and “opaque”that are typically used as synonyms

for high-opacity composite resinsthat present opacity and translu-cency close to that of natural den-tin.25 Other terms like “artificialenamel” or “body” are used todenote composite resins thatpresent translucency and opacity,as well as chromaticity, similar tothat of natural dental enamel.25

There are also composite enamelresins, called translucent or incisal,which display higher than normaltranslucencies to help match high-translucency areas in restorations.Recently, value-changing compositeresins were developed to alter theluminosity of restorations.26

Conversely, some authors catego-rize “body” resins as those thathave intermediate translucencyand opacity between the enameland dentin. This allows cliniciansto substitute both enamel anddentin in only one layer.27 There-fore, the concepts of “artificialenamel” and “artificial dentin”refer to composite resins designedto replace the physical andmechanical, as well as the colorand optical properties, of thetooth.25 The greatest difficultiesappear, however, when designating“artificial enamel” resins, as eachvariation displays specific indi-vidualized properties. Theseresins are usually designed tofulfill only a special areawithin the restoration. Thefollowing describes a classificationof this group:

Figure 12. Evidence of translucency/opacity of differentthicknesses of dentin: 0.5 mm (A), 2 mm (B).



1. Artificial body enamel resins:keyed to the Vita shade guide,provide a chromatic basis to therestoration, responsible for gen-erating color hue

2. Artificial translucent effectenamel: provides translucencyespecially to deep areas through-out incisal and proximal edges

3. Artificial milky-white semi-translucent enamel: used forcreating halos, which arehigh-value areas with whiteeffects

4. Artificial value-modifyingenamel: used as final layers inspecific areas of the labialaspect, in order to enhance, todecrease, or to corroborate thepreexisting natural enamelcolor value.26

Recent reports, based on the afore-mentioned classifications, haveshown that an ideal material forreplacing dentin should presentfeatures such as uniform hue andopacity as well as a wide range ofsaturations.28 These principles arebased on a colorimetric study ofcontrast rates (CR) of humanenamel and dentin, making itunnecessary to choose colors forthe dentin, apart from the Vita A(A1 to A4) and B (B1 to B3)scales. Contrast rate fluctuation,within the same group, does notsupport using different levels oftranslucency and opacity for dentinresins (translucent, regular, andopaque dentins).28,29

In the same study, colorimetricand CR values for the enamelvary according to dental age, soowning a wide range of enamelcomposite resins to replace dentaltissue is a must. In the case ofyoung enamel, the choice of resinsshould rely on a low-translucency,milky white color. In the case ofadult enamel, the resins shouldhave a neutral color and mediumtranslucency. For older enamel,resins should have high translu-cency and a yellow hue.28,29

After choosing the correct resins,it is important to consider thethickness of the material to belayered during the application ofthe composites because the per-ception of higher chroma andopacity is related to an increase inthickness.12 The handling of theselayers is crucial for obtaining thedesired chromaticity, translucency,and opacity.23 When using a two-resin system (e.g., bichromatictechnique: “artificial enamel”layer + “artificial dentin” layer),the material with less translucency(more opacity) and higher chromamay be used for the dentin,whereas enamel can be replacedby a more translucent resin. Com-pared with dentin and enamelresins, polychromatic techniquesrequire effect resins that impart amore natural appearance to therestoration. Similarly, tints allowgreater characterization ofthe restoration.

In the incisal third area, therestorative challenge is even morecomplex, as the range of translu-cency and opalescence is greater.30

This area, seen mainly in youngteeth, tends to be highly translu-cent and spreads from themamelon outline to the incisalopaque halo. Using an opalescentmaterial is often insufficient toproperly replicate this phenom-enon in restorations. Rather, adetailed analysis of the opalescentpattern is necessary. Therefore,each case should be undertakenutilizing a special approach,because opalescence presents highvariability.31 It is also advisable touse a translucent compositetermed “incisal” (high translu-cency at the incisal region)between the dentin and enamellayers in order to fill the areasbetween the lobes and theincisal halo.32

This layer’s thickness is closelyrelated to the amount of translu-cency required for the type ofeffect required. The high-translucency resin layer willincrease the perception of depthand will allow the restoration todemonstrate a more natural look.High-translucency resins shouldnot be placed on the surface of thefinal layer of the restoration,however, because they tend toreduce restoration value and maypotentially modify the chroma tosome extent.


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It is important to note that the finaloutcome of a restoration is depen-dent on the thickness as well as thevarying degrees of translucency andopacity of the several layers of com-posite. In comparing two dentincomposite resin discs (e.g., 1 and2-mm thick, respectively), bothcovered with 1 mm of enamel resin,the thicker dentin resin disc willpresent higher opacity, chroma, andvalue. However, in comparing two1-mm thick dentin composite resindiscs (e.g., overlaid with 1 and2 mm of enamel resin), the latterpresents lower value and chroma.Thus, regarding the final enamellayer, it is important to stress that acertain thickness should not beoverlooked, as restorations withexcessively high-translucency resinsmay become gray and demonstratea lower value.

It is also important to rememberthat the thickness of composite

resins determines the limit betweentranslucency and opacity. Whenthicknesses of translucent chro-matic composite resins increase,value decreases and chromaincreases. By increasing the thick-ness of opaque composite resins,both value and chroma increase.12

Chromatic perceptions of translu-cent structures are also closelyrelated to the background used forits observation. The same translu-cent body will present differentlywhen placed against black andwhite surfaces separately becauseof the background’s selectiveabsorption and reflection of par-ticular wavelengths.31

When comparing composite resinsand different colored backgrounds,white backgrounds tend to be thebest choice for visualizing how arestoration will appear, as whiteenhances saturation and value,compensating for any chromatic

shortage.12 Translucent compositeresins are more sensitive to awhite background than opaqueresins, as value and chroma areenhanced (Figure 13). High-opacity resins, or white dyes, havethe ability to act as opacifiers,masking an undesired chromaticsubstrate and enhancing value.33

For the same material in variousthicknesses, a slimmer piece ofmaterial will exhibit far less satu-ration and present a higher trans-lucency than a thicker piece ofmaterial, thereby increasing theperception of the background.

The level of polish of a surface alsochanges the chromatic perceptionof composite resins and is inverselyproportional to luminosity.34 Themore polished the surface, thelarger the light transmission and,consequently, the less luminosity.12

Conversely, lack of polishing causesthe surface to become more reflec-tive, making the restoration appearmore luminous.35

Another important aspect thatdeserves attention is photopolymer-ization, as light-curing may createoptical changes. Normally, microfillresins are more translucent andpossess higher chroma before poly-merization. Unpolymerized hybridcomposite resin is more opaque andhas a relatively less intense chroma.Once polymerized, chroma andtranslucency enhance, valuedecreases, and the composite

Figure 13. The translucent resins are more sensitive todifferences in background color (black and white),changing their final perception.



becomes slightly grayer.36 Thesame phenomenon occurs onwet surfaces.

Additionally, dentists should con-sider the color of the underlyingdentin when using chromaticenamel composite resins in order toavoid unwanted chromatic varia-tions. The stratification of translu-cent chromatic enamel resincomposites on the dentin occursfollowing a subjective mixture ofcolors. The resulting phenomena ofthe interaction of light and matterare of great importance for estheticrestorations, as they allow a faithfulreproduction of the properties ofnatural dentition. However, inad-equate analysis of the opticalbehavior of natural dentition maylead to failure of therestorative procedures.

The logical use of the differentcomposite resins available and the

many variations in natural denti-tion make the restorative processmuch more efficient and predict-able. For example, achromaticenamels of different opacities andincreasing thickness, layered over aresin composite dentin substrate ofequal opacity and chroma, willallow the perception of varyingchromas and values (Figure 14). Asthe thickness increases (e.g., from0.3 to 1.5 mm), more light isreflected and scattered throughoutthe achromatic resin substrate,thereby blocking the perception ofthe underlying dentin invarious degrees.

T and P shades of a commerciallyavailable composite resin (Vit-l-escence, Ultradent, South Jordan,UT, USA) will appear to havealmost the same translucency at0.3 mm of thickness while display-ing nearly the same chroma andvalue. As thickness increases, P

shades will block the transmissionof light to a greater extent than Tshades. The resulting effect is acomparatively lower chroma andhigher value for the P shades inrelation to the T shades of thesame thickness. The reported meanrefractive indices for enamel anddentin are 1.631 and 1.540,respectively.37 The refractive indexfor T and P shades is 1.52.38

It should be expected that the useof artificial enamels of the samerefractive index as natural enamelwould account for an ideal repro-duction of the optical characteris-tics found in nature. Unfortunately,having the correct refractive indexis only one of the many compo-nents necessary for rendering a life-like restoration. Choosing artificialdentin and enamel composites ofthe proper opacities, as well asdetermining the correct thicknessof each layer, is of paramountimportance and should be just assignificant as the use of refractiveindices (Figure 15).

F I N A L C O N S I D E R AT I O N S

Of all dental structures, enamelseems to be the optical entity thatis most difficult to imitate. There isa common trend among practitio-ners to layer artificial enamel anddentin composites according to theactual thickness of the missingnatural enamel and dentin. Thisproves futile, however, because noknown composite behaves exactly

Figure 14. Intrinsic opacity and thickness of achromaticenamel shades play a fundamental role in the modulationof the perceived chroma and value.


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as natural enamel or dentin. A res-toration created according to the“anatomic approach” might seemawkward at first, but it is wellworth it. By using composite resinsto imitate dental enamel, and bypursuing anatomic and meaningfulprinciples to mimic the tooth’schromatic variability, the definitiverestoration will beesthetically pleasing.

Currently, composite resin manu-facturers are seeking ways toimprove their optical properties tobetter mimic the natural propertiesof human dentition. For thatreason, many state-of-the-art com-posite resins demonstrate translu-cency similar to that of the natural

teeth. However, with a thoroughunderstanding of light behaviorand the optical properties of thedental structures, as well as utiliz-ing state-of-the-art composite resinrestoratives, clinicians should beable to provide patients withlife-like, seamless restorations.

D I S C L O S U R E

The authors do not have anyfinancial interests in the productsused in this manuscript.

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Reprint requests: Milko Villarroel, DDS,MS, PhD, Rua Pedro Viriato Parigot deSouza, 2664—apto. 74A, Curitba—PR,BRAZIL, CEP 81200-100, Brazil; Tel.:(55-16) 3301-6438; email: [email protected].

This article is accompanied by commentary,“Direct Esthetic Restorations Based onTranslucency and Opacity of CompositeResins,” André V. Ritter, DDS, MS, DOI10.1111/j.1708-8240.2010.00393.x.


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