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t t r f e o Color in Natural Teeth and Direct ssence Resin Composite Restorations: Essential Aspects

Luiz Narciso Baratieri, DDS, MSD, PhD Professor and Chair, Department of Operative Dentistry Federal University of Santa Catarina, Florianópolis, Brazil

Edson Araujo, DDS, MSD, PhD Professor, Dental Clinics Federal University of Santa Catarina, Florianópolis, Brazil

Sylvio Monteiro Jr, DDS, MSD, PhD Professor, Department of Operative Dentistry Federal University of Santa Catarina, Florianópolis, Brazil

Correspondence to: Dr Luiz Narciso Baratieri Rua Presidente Coutinho, 311 10° Andar Bloco A, 88015-230 Centro, Florianópolis, SC, Brazil; e-mail: [email protected].

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t t r f e o Abstract ssence This article presents the essential aspects teeth. The dynamics of color in natural teeth for understanding and reproducing the in relation to age is also discussed, focus- color of natural teeth with the use of direct ing on the age-related changes that occur resin composite. Fluorescence and opal- in enamel, dentin, and pulp. Further, it is escence are discussed, with special em- demonstrated how to reproduce the es- phasis on counter-opalescence, which is thetic features of natural teeth using latest- primarily responsible for the appearance of generation direct resin composites. an orange discoloration at the mamelon dentin tips and incisal edges of anterior (Eur J Esthet Dent 2007;2:172–186.)

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Fig 1 (a) Maxillary central inci- Fig 2 (a) Maxillary central inci- Fig 3 (a) Maxillary central inci- sors of an 8-year-old patient. (b) sors of a 22-year-old patient. (b) sors of a 72-year-old patient. (b) The same teeth 12 years later. Note The same teeth 12 years later. Note The same teeth 12 years later. Note the incisal wear and changes of the changes of surface texture and the increased thickness and satura- surface texture. incisal border. tion of the dentin.

The chromatic expression of natural teeth wear of enamel can also cause areas of is dynamic and depends on the interaction dentin exposure, especially at the incisal of enamel, dentin, and pulp with light dur- edge. In addition, the exposed dentin ab- ing reflection and refraction phenomena. sorbs stains that change the chromatic ex- Enamel, dentin, and pulp suffer noticeable pression of the natural teeth. The changes changes during an individual’s lifetime. that occur in enamel, dentin, and pulp as- Dentin becomes thicker with time as pulp sociated with fluorescence, opalescence, decreases in volume due to the deposition and counter-opalescence create chromat- of secondary dentin. Additionally, dentin ic effects that can be mimicked and repro- becomes less permeable as a result of the duced with the use of specially designed deposition of peritubular dentin. These resin composites. The relation of natural changes increase the chromatic saturation teeth with their antagonists, the soft tissues, of dentin while reducing its opacity.1 Enam- and moisture also interferes in an excep- el becomes more mineralized with time tional manner with color dynamics. The because of the absorption of ions from sali- aim of this article is to help practitioners va and foods. However, it also becomes identify and understand these features in smoother and thinner due to physiologic natural teeth, especially the characteristics wear. This increase of enamel mineral con- of the internal structure of natural dentition, tent and decrease of thickness make it in order to achieve optimal esthetic results.2 more translucent. Physiologic or pathologic

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presents less microtexture thant enamel t of r f Features of anterior teeth es o e 2 senc related to age young individuals. Usually, bluish and or- ange shades are clearly visible. The tips of The chromatic appearance of natural teeth dentin mamelons are closer to the incisal varies substantially with age because of edge, and may even be exposed. The pulp changes in enamel, dentin, and pulp. shows a decrease in volume, while dentin Dentin is an opaque (less translucent) and becomes thicker, more saturated, and less complex core—rich in hue, chroma, and opaque (Fig 2). fluorescence. It is covered by enamel, which is translucent and opalescent.3 The Old age variety of features and changes of enamel At 70 to 80 years of age, enamel presents and dentin explain the unique nature of the a considerable decrease in thickness and appearance of a natural tooth.4 surface texture and a significant increase in translucency, changing from a bluish Childhood shade to gray and purple shades. Fre- Young individuals usually present anteri- quently, there are large areas of exposed or teeth with great pulp volume. The dentin at the incisal edges, which usually dentin is opaque and completely covered suffer severe extrinsic staining. The pulp by enamel, and the tips of dentin mamel- virtually disappears, while dentin presents ons are located about 1.5 mm from the in- increased thickness and saturation and cisal edge. decreased opacity (Fig 3). Although the enamel is thicker, it is translucent, brilliant, and often presents a Color milky, chalky white color. In freshly erupted The color of natural teeth usually is deter- teeth, the superficial layers of enamel are mined by the three dimensions of color: more opaque, frequently have a frost-white shade, chroma, and value. Color can be appearance, and are less mineralized.5 identified by conventional methods, such They also have more empty space be- as shade guides, or by automatic shade tween enamel crystals, which causes in- guide systems.9 However, there are other creased opacity.6,7 Further, young enamel is extremely important factors regarding more permeable and dehydrates quickly. chromatic expression that cannot be disre- Deeper layers of enamel have fewer air garded, such as translucency, fluores- spaces, are more mineralized, and more cence, opalescence, counter-opalescence, translucent.8 Generally, anterior teeth of and surface texture. young people present remarkable surface texture, which is generally lost over time. As Translucency enamel becomes thinner with age, dentin Human teeth are characterized by a vari- becomes more visible, and the tooth be- ety of degrees of translucency, which can comes less monochromatic (Fig 1). be defined as the gradient between trans- parency and opacity.10 Generally, an in- Adulthood crease of translucency of a direct resin The enamel of an adult’s natural anterior composite restoration lowers its value be- teeth is thinner, more translucent, and cause less light returns to the eye. With in-

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Fig 4a Buccal and lingual views of an extracted Fig 4b The translucency of enamel is evident when maxillary central incisor. The enamel presents interme- the tooth is immersed in water. Note the bluish aspect diary translucency due to the removal of dentin (the that is acquired. dark background is barely visible through the enamel).

creased translucency, the light is able to resins. The translucency is best evaluated pass through the surface and is scattered with a black background or with the within the bulk of the restoration. The tongue, full of saliva, placed against the translucency of enamel varies with the in- palatal surface of the anterior teeth. A sim- cidence angle and wavelength, surface ple manner to evaluate translucent areas is texture and luster, and degree of dehydra- to look for visible opalescent bluish shades. tion of the tooth. To better understand the A black background prevents red shades influence of moisture on the translucency from the back of the mouth from remixing of natural teeth, observe Figs 4a and 4b, with the blue shades.5 which show the same tooth, without dentin, outside and immersed in water. With more Fluorescence translucent artificial enamel layers, the Fluorescence is the absorption of light by resin composite restoration achieves depth objects such as natural teeth or restorative of color and the illusion of a natural vital materials, and the spontaneous emission of tooth. However, if the resin layer related to light with longer wavelengths.11 In natural superficial enamel is slightly translucent, it teeth, fluorescence occurs primarily in will mask the subtleness created by dentin dentin because of the greater amount of or- layers. Actually, one of the most difficult ganic material.12,13 However, enamel is also tasks in direct resin composite restorations fluorescent, although it presents a smaller is to define the degree of enamel translu- fluorescence index than dentin.14,15 Addition- cency and reproduce it with appropriate ally, in many cases enamel presents high-

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Fig 5a Labial aspect of two extracted central incisors. Fig 5b Labial aspect of the teeth exposed to ultravi- The opaque incisal halo presents an orange aspect. olet light. Note the white opaque appearance achieved Further, the bluish regions at the incisal third and by the teeth, including at the incisal third where dentin mamelon tips present an orange blur. is minimal.

a b

Fig 6a Sections from two maxillary central incisors. Fig 6b Under ultraviolet light, dentin shows an The incisal third was sectioned in the mesiodistal direc- opaque white appearance. Enamel also presents fluo- tion. There is virtually no dentin in this region. Note the rescence, but the restoration does not. incisal opaque halo and the presence of a Class 3 resin composite restoration.

er fluorescence than several of the resin hances the vitality of both the restoration composites available on the market. Ambi- and natural teeth, making them look ent near-ultraviolet light is absorbed and flu- brighter. However, if the restorative materi- oresces back as light, primarily in the blue al does not present fluorescence similar to range of the spectrum, though it occurs in the tooth structure, the contrast will influ- all wavelengths. Ultraviolet light can have a ence the appearance. The more dentin flu- dramatic effect on the level of vitality exhib- oresces, the lower will be the chroma.16 ited by restorations. Fluorescence en- Resin composites with higher fluorescence

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Figure 5a shows extractedt maxillaryt in- r f es o e cisors under direct natural light.s eInn thec in- cisal region, an orange opaque halo, a wide bluish area at the incisal third, and an orange “blur” at the region of the mamel- on tips can be observed, along with other important details. Figure 5b shows the same teeth under ultraviolet light. The inci- dence of ultraviolet light reveals the fluo- rescence and makes the teeth whiter and more brilliant, thus eliminating the intricate polychromatism of the teeth. Further, note Fig 7a Maxillary anterior teeth of a young female pa- tient. There is a bluish aspect at the incisal region, with that the hypoplastic areas at the mesial as- an opaque orange coloration and orange blur at the pect of the right central incisor and incisal mamelon tips. Note the presence of a Class 3 restora- aspect of the left central incisor do not tion at the distal aspect of the left central incisor. present fluorescence. Figure 6a presents two sections (mesiodistal and buccolin- gual) from two maxillary central incisors under a flashlight. The mesiodistal section reveals the presence of a Class 3 resin composite restoration. The mamelon tips are white in both sections. Figure 6b shows both sections under direct ultraviolet light. Even though dentin is considerably more fluorescent than enamel, the latter is still considered fluorescent. Note that the resin composite restoration does not present flu- orescence. Figures 7a and 7b show the Fig 7b Under ultraviolet light, the teeth present a maxillary anterior teeth of the same person white-bluish shade, and the microfilled resin compos- ite restoration at the distal aspect of the left central in- under white and ultraviolet light. The cisor does not match the surrounding tissues due to the restorations are visible under ultraviolet lack of fluorescence. light, but not under white light.

Opalescence Opalescence is a phenomenon in which can be added strategically to restorations to objects such as opalescent stones, the sky, increase the amount of light returning to the and tooth enamel appear to have one col- viewer, block out discolorations, and lower or when refracting light and a different col- the chroma. This is especially beneficial or when reflecting light.17 The natural opal with high-value shades placed within lay- is an aqueous disilicate that breaks down ers of resin composite for dentin, as it can transilluminated light into spectral compo- make the value higher without negatively nents by refraction. Opals act like prisms affecting the translucency.5 and refract different wavelengths to varying

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Fig 8 Labial and palatal views of two extracted maxillary central (a) and lateral (b) incisors, after removal of dentin and under direct light. Note the bluish shade of enamel. Under indirect light, the central (c) and lateral (d) incisors show opalescence with an orange/pink shade.

degrees. Shorter wavelengths bend more shades from their bodies; thus, enamel ap- and require a higher critical angle to es- pears bluish even though it is colorless. cape an optically dense material than red Opalescence of enamel brightens the and yellow ranges of the spectrum. The hy- tooth and renders depth and vitality.18 droxyapatite crystals of enamel also act as Maybe the most important issue related prisms. Different wavelengths of light pro- to opalescent objects used in dentistry, duce different degrees of translucency such as tooth enamel and some porce- through teeth and restorative materials. lains and resin composites, is that they When illuminated, opals and enamel will may undergo changes in hue, chroma, transilluminate red shades and scatter blue and value according to the type of light,

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Fig 9a Maxillary anterior teeth of a 24-year-old female Fig 9b The bluish appearance of the enamel is re- patient. With the mouth slightly open, a bluish aspect duced when the teeth are in maximal intercuspation. can be observed at the incisal third. An orange col- This is because light crosses enamel, hits the tips of the oration is visible around the opaque halo and mamel- dentin mamelons of the maxillary teeth (which have a on tips. white aspect), and then reaches the mandibular teeth and returns as background lighting.

a b

Fig 10 Sections from two maxillary central incisors. The incisal third was sectioned in the mesiodistal direction. There is virtually no dentin in this region. Note the incisal opaque halo and the presence of a Class 3 resin com- posite restoration.

without influencing the translucency. An ex- with the total reflection of light in this area.3 cellent example of this occurs in anterior The idea that there are specific areas of teeth, specifically at the incisal edge, in the opalescence in enamel is a common mis- opaque halo area. In spite of the fact that take made by some clinicians. This misun- enamel is a translucent tissue, it usually ac- derstanding occurs because opalescence quires an orange shade with an opaque of enamel is much more evident in the area aspect in this area. This is also associated of the incisal third, whereas other areas with the design of this area and especially have thinner or no dentin. However, Fig 8

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Fig 11 Extracted maxillary central incisor. (a) The opaque halo effect has an orange aspect, the incisal third is bluish, and the mamellon tips have an orange blur effect. Note the white band between the cervical and middle thirds. (b) With the lingual surface immersed in water, a reduction of the opaque halo effect and orange aspect at the mamelon tips can be observed. (c) When the tooth is totally immersed in water, the opaque halo effect dis- appears and the orange blur is considerably reduced. The bluish appearance of the incisal area is enhanced be- cause the water increases the enamel translucency. (d) After removing the labial enamel, the mamelon tips ap- pear white and opaque.

shows that all areas of the enamel are orange-pink coloration commonly seen opalescent, not just the incisal third. This at the tips of dentin mamelons and the in- explains why the use of opalescent resins cisal edges of anterior teeth (Fig 11). When only in areas without dentin is an error. In enamel is dissolved in acid, the tips of fin- fact, opalescence is essential throughout ger-shaped dentin mamelons no longer the artificial enamel. Figures 9a and 9b appear to have a transparent ivory-white show the anterior teeth of a young female shade; instead, they appear totally white presenting bluish areas at the incisal third. due to increased surface roughness, Observe that the bluish shade is softened which blocks out the color of dentin by the light when the patient’s maxillary (Fig 11d). teeth touch the lower lip, because the light Note that an orange shade is recogniz- is transmitted through enamel in a buccol- able in nearly all incisal edges of natural ingual direction. Figure 10 shows the opal- teeth (Fig 11a). When the lingual aspect of escent effect of the incisal enamel under in- the natural tooth is placed in water, the in- direct light, regardless of the presence of tensity of the orange shade is reduced by dentin. half (Fig 11b). If the entire tooth is im- mersed, the orange shade becomes in- Counter-opalescence creasingly weaker and the tooth becomes According to Yamamoto,3 counter-opales- quite transparent as a result of the chang- cence is the phenomenon in which the ing reflection factor (Fig 11c). The orange light penetrates an opalescent object and shade of the incisal portion of the tooth can is reflected from within. Therefore, this is thus be explained as an optical event. generated by opalescence, and is respon- When ambient light hits the labial surface sible for the appearance of an orange or of the tooth, it is refracted, penetrates

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Fig 12a Natural teeth and restorations under direct light. (left to right) Microfilled resin (Durafill VS, Heraeus Kulzer); hybrid resin (Vit-l-escence, Ultradent); nanofilled resin (Filtek Supreme, 3M ESPE); natural tooth without dentin in the coronal portion; microfilled resin (Charisma, Heraeus Kulzer); hybrid resin (Tetric Ceram, Ivoclar Vi- vadent).

Fig 12b Under ultraviolet light, the microfilled resins and nanofilled resin do not present fluorescence.

enamel, and reaches either the palatal or more light returns as backlight and pro- lingual aspect of the tooth. Parts of the duces an orange shade, due to the count- beam are reflected there and return to the er-opalescence. The incisal edge appears labial side, while other parts shine through bluish because of opalescence. At the the palatal or lingual aspect. The more light same time, transparency is increased by penetrates the natural tooth enamel, the shade and brightness contrast.

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Fig 13a One natural tooth (far left) and six restorations made from different resin composites for enamel (left to right: 4 Seasons, Ivoclar Vivadent; Vit-l-escence, Ultradent; Filtek Supreme, 3M ESPE; Miris, Coltène) under di- rect light. Note the difference of translucency and color.

Fig 13b Under indirect light, all resins and the natural tooth show the same orange shade, regardless of the materials, shade, and degree of translucency of the resin composites used.

When the lingual aspect of the tooth is entire tooth is immersed in water, the trans- placed in water, the relative refraction in- parency increases significantly, and the dex of enamel becomes smaller than that light reflected from the lingual aspect is re- of water, and its translucency increases. duced to an extent that the orange shade The amount of reflected light is also re- is barely recognizable. duced, as is the orange shade. When the

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Fig 14 Disk samples of opalescent resin composites (black background = direct light; white background = in- direct light). The center disk changes its shade based on the background, while the other two samples remain bluish regardless, thus showing their lack of opalescence. Therefore, it is crucial to use opalescent resin compos- ites to reproduce the bluish shade of the incisal third.

Surface texture Opaque halo effect The surface texture of the natural teeth greatly influences their interaction with light, Although tooth enamel is a hard and which in turn interferes with their chromat- translucent tissue, natural anterior teeth ic expression, especially in relation to present an opaque band at the incisal shine.19 Macro- and micromorphologically edge that varies in thickness, contour, and roughened surfaces diffuse reflected light, proximal extension from tooth to tooth. This whereas flat surfaces with minimal texture band is known as an opaque halo, and significantly increase the surface brilliance provides a clear notion of the actual size of of the tooth or restoration.20 For this reason, the teeth. This effect is present even when when the labial surface of an anterior tooth there is a great area of exposed dentin. will be partially or totally reproduced with di- The halo effect, as suggested by its name, rect or indirect materials, the practitioner is a consequence of an optical phenome- should try to accurately simulate these de- non in which there is a total reflection of the tails. When parallel light rays reach a flat light due to the characteristics of enamel surface of a translucent object, the reflect- and the design of this area. ed rays remain parallel to each other, To produce the halo effect, the practi- whereas in a texture-rich (non-uniform) tioner can use a thin increment of resin surface, they are dispersed in several direc- composite for dentin. Because the incisal tions.1 This is especially important to mask edge usually presents the same coloration the line between the resin composite and as the cervical area of the tooth, the resin tooth structure, especially when no bevel is composite can be of the same shade. The performed at the cavosurface angle, as well problem with using this approach is that as in cases of fractured anterior teeth. this area of the restoration will always ap-

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pear opaque, with identical design, con- translucency, indication, and locationt in thet r f es o e tour, and coloration, regardless of the type restoration (ie, a resin composite fors enam-enc of incident light. Conversely, if more el or for dentin). translucent resin composites especially Nearly all resin composites for enamel designed for enamel are used, the color, present opalescence (Figs 13 and 14) and contour, and design will change according are more translucent than those for dentin. to the type of illumination, just like the nat- These resin composites are classified into ural teeth. four groups according to the level of translucency and specific location in which they will be placed: Direct resin composites for anterior teeth 1. Resin composites for enamel increments (superficial enamel, Traditionally, resin composites for direct generic enamel, translucent shades) use in anterior teeth have been classified 2. Resin composites to emphasize according to the average filler particle size. the incisal opalescence (opalescence Hybrid composites have an average filler enamel, incisal enamel shades) particle size between 0.4 and 1.0 μm; while 3. Resin composites designed for special microfilled composites have an average effects (opaque and effect shades) filler particle size between 0.01 and 0.1 μm. 4. Resin composites to reproduce the Recently, a new type of resin composite for iridescent features of the dentoenamel direct use has been developed: the junction (DE Connector, Ultradent) nanofilled resin composite, which has an average filler particle size between 0.02 Resin composites for dentin are divided and 0.07μm and nanoclusters with an av- into two groups according to their degree erage particle size between 0.6 and 1.4μm. of translucency and sequence of use: Hybrid composites present flexural strength and wear resistance similar to 1. Dentin resin composites nanofilled composites and superior to mi- (opacifying shades) crofilled composites.21,22 Additionally, both 2. Body resin composites microfilled and nanofilled composites offer a long-lasting high-polish surface that is Another difference from a practical point difficult to obtain with hybrid compos- of view is that some resin composites, es- ites.22–25 However, in contrast with hybrid pecially those designed for enamel repro- composites, most microfilled and nano- duction, are grouped together with their filled composites do not present fluores- dentin pairs, while other resin composites cence (Figs 12a and 12b). receive proprietary designations. This ap- Currently, because of improvements in proach may be confusing to inexperi- almost all commercially available resin enced clinicians. composite formulations, it is important to An important subject regarding the use understand that regardless of the average of direct resin composites is the fact that filler particle size, resin composites can al- while the natural dentin presents a de- so be classified according to the degree of crease in opacity over time, spectropho-

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tometry studies have established that the t t r f Conclusion es o e opacity of hybrid composites generally in- senc creases over time.26 This can make the Establishing an appropriate restorative restorations more perceptible earlier. On protocol is essential to understand the the other hand, extending the curing time time-related dynamic behavior of the tooth can minimize changes in opacity of the tissues. Further, it is essential to understand restoration. the changes in the chromatic expression of natural teeth, especially when using di- rect resin composites for anterior teeth.

References

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