Dental News - Moving beyond classical shade guides to achieve natural restorations

Lorenzo Vanini

Wed. 8 February 2012

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Color results from the relationship between light and an object and, therefore, restorative composite materials must show optical properties similar to those of the natural dentin and enamel. Enamel is surely the most important structure for this relationship with light, because it covers the dentin structure as a fiber-optic system.

The translucency and refractive index of composites are very important and also should closely approximate those of the natural enamel. The speed of light through a material depends on the material’s density. It is faster through air than water and faster through water than metal.

The refractive index is the ratio of the speed of light in a vacuum compared with a specific medium. The refractive index depends also on wavelength of light. Consequently, it is possible to say that the refractive index indicates the relationship of the propagation speed of light through a body with reference to the light speed in the air.

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The more optically compact a medium is, the slower the speed of light. The refractive index (n) of natural enamel is 1.62, while the average refractive index of composite and ceramic restorative materials is 1.50. The refractive index of glass is 1.52, which means that composite and ceramic restorative materials have optical properties that are more similar to glass than to enamel. This presents some problems in managing the relationship between translucency and value, because increasing material thickness lowers value (i.e., glass effect), while the behavior of natural enamel is exactly the opposite.

Innovation in restorative dentistry

Ena HRi (Micerium S.p.A., Avegno, Italy) composite enamel, thanks to the refractive index of 1.62, has an optical behavior quite similar to that of natural enamel (Fig. 1); and increasing its thickness also increases the value (Fig. 2).

With this enamel it is possible to manage the relationship translucency-value and the esthetic integration better because light passes through two bodies (natural enamel and composite enamel), which have the same refractive index. In this way, there is no light deviation, which is a problem that from a clinical point of view is shown with a gray line on the margin. Moreover, in restorations of the free incisal enamel it integrates perfectly, substituting the natural enamel with a high value without using dentine body. This is impossible with other composites now on the market (Figs. 3, 4).

A higher level of tooth color analysis

Color in dentistry usually is defined using shade guides based on the 1898 theory of American painter Albert Henry Munsell, which Clark applied to dentistry in 1930. According to this theory, color is composed of three dimensions: hue, chroma, and value (Fig. 5).

Hue is the basic shade of the tooth; chroma is the degree of saturation of the hue; and value represents luminosity.

The Classic VITA Shade Guide presents four basic hues (e.g., A, B, C, and D) and four chromas for each hue.

Actually, tooth color is a complex culmination of many factors resulting from the interaction of enamel and dentin with light during the refraction and reflection phenomena of light waves. In the enamel area, shorter waves close to white-blue dominate, while the longer yellow-orange waves are more evident in the dentin.

Tooth color is the complex result of several factors that must be carefully analyzed to understand the unique features that characterize an individual patient’s teeth, and precise matching seems impossible through conventional methods. To determine tooth color, it is necessary to abandon the classical shade guides and, along with them, customary shade-taking habits in favor of performing a higher level of tooth color analysis. I call this approach Doctor Vanini’s Color Theory.

The tooth color that we normally see is a function of the physical properties of dentin and enamel, and their interaction with light.

My personal theory of tooth color includes a detailed analysis of each component responsible for tooth color. Each component can be recorded using a special color chart and subsequently reproduced using specific materials during the stratification phase.

To properly determine tooth color, dentists must be able to look deeply into the tooth structures and identify the five color dimensions and chromatic chords. To facilitate this process, we need a light with a constant color temperature of 5,000° K, which has been shown in several studies to be the ideal for shade evaluation (Fig. 6). Additionally, the use of digital photography is fundamental to the analysis of color dimensions because it quickly enables a deeper examination of the tooth on a computer and a more accurate understanding of the different color dimensions. By underexposing the photograph and increasing the contrast, it is possible to obtain a better visualization of the color dimensions, and it increases the amber and blue hues of the incisal halo.

All tooth-color information must be recorded in a simple manner, and for this purpose, the author developed a specific color-mapping chart for researching and identifying the five color-dimensions and specific materials to be used to achieve the required effects. The color chart represents the scheme for the restoration, and its proper completion is fundamental for correct restorative results.

The front of the chart (Fig. 7) outlines patient details and also includes two blue tooth-shaped spaces. The five color-dimensions are indicated on the left, while the identification initials of the composite system materials (i.e., enamel, dentin) to be used to reproduce the chromatic chords of the color dimensions are indicated on the right.

The back of the chart (Fig. 8) shows the classification of intensives, opalescents and characterizations. Each dimension refers to age biotypes, and each biotype predicts recurring dimensions for shape and chromatic saturation.

The first tooth color dimension to be determined is the basic chromaticity (BC), which is derived from the mean value of the dentin body chromaticities and should be identified on the middle third of the tooth using a shade guide made from the same composite material to be used for the stratification. On the left side of the chart, the basic chromaticity is recorded, while the dentin composites needed should be indicated on the right.

Each biotype predicts three basic chromaticities: two pure and one hybrid. The young biotype displays chromaticity from one to two (1-1,5-2); the adult from two to three (2-2,5-3); and the elderly from three to four (3-3,5-4).

The shape of the dentin body and the mamelon contour to be reproduced also must be defined.

The second dimension to be recorded is the value or luminosity of the enamel, which will be high in the young biotype (3), medium in the adult (2) and low in the elderly (1). This evaluation can be performed by taking a black-and-white digital photograph.

To determine intensives, opalescents and characterizations, the photograph is compared with the back of the color chart, and it is helpful to analyze the image underexposed with high contrast. Intensives are present primarily in the young biotype, where type 1 (spot) and 3 (snowflakes) are usually seen. Adult and elderly biotypes more commonly exhibit intensive type 2 (small clouds) and 4 (horizontal bands).

Opalescents in the young biotype appear as gray-blue hues of type 1 (mamelon) and 2 (split mamelon); in the adult they appear as gray-blue hues of type 3 (comb-like) and 4 (window-like); and in the elderly they appear as amber hues of type 5 (stain-like).

The characterizations mostly present in the young biotype are the mamelons (type 1), which can appear white or amber, thus creating a clear-cut boundary with the opalescents and the incisal margin (type 3), which is emphasized by a white or amber line. In the elderly biotype, the characterizations seen are: one or more horizontal bands with a whitish or amber tonality that extend into the interproximal areas; the amber or brown stain-like characterization (type 4) at the incisal third; and crack of the enamel (type 5) produced by brown pigmented fissures or white opaque cracks. In the adult biotype it is possible to find all of the five types of characterization (Fig. 9).

Matching anatomical stratification

My personal anatomic-stratification technique imitates the tooth anatomy, restoring enamel and dentin in their respective locations and thicknesses to achieve a light-composite-color relationship similar to natural tooth structure. The stratification technique for Class IV restorations includes the restoration of the palatal and interproximal enamel, the dentin body and the buccal enamel (Figs. 10a–10b and 11a–11b).

The composite stratification is guided by the color chart, which must be completed with the characteristics of tooth color dimension prior to initiating restorative procedures. This ensures that the anatomic stratification will: demonstrate desaturation of the hue from cervical to incisal, and from palatal to buccal, in a harmonious and modulated way; exhibit contrast in the incisal area between the dentin body, free enamel and darkness of the mouth; and diffuse light inside the tooth. Together these characteristics give a three-dimensional effect to the restoration.

For the reconstruction of the proper anatomic position of the palatal enamel wall, in the Class IV restorations the use of a silicone matrix/stent is advised to support the enamel body application.

The silicone matrix can be provided by a laboratory from the wax-up or created directly in the mouth using a medium viscosity silicone after the temporary restoration of the dry tooth is shaped and adjusted in the incisal guide with burs. Once the silicone has hardened, the stent is removed and adjusted to fit perfectly to the teeth. Then, the buccal wall corresponding to the affected tooth is removed to facilitate the buccal access.

After the removal of the old restoration (Figs. 12-13), the area must be isolated with a rubber dam; the stent fit is controlled; and then the cavity is prepared following the adhesive technique. For Class IV restorations, the ideal margin preparation includes a 90° butt margin on the palatal and interproximal margins and a short chamfer in the buccal margin.

The margin is first prepared using a coarse-grain diamond bur, ball-shaped for the chamfer and cylindrical for the butt margin. The margin is finished using the same burs with fine grain and, afterward, polished using a silicone point because the smooth surface enables flow of the adhesive as well as composite adaptation on the margin (Figs. 14-15).

Class IV stratification begins by applying the palatal/lingual enamel layer, filling the stent with the enamel body before applying it in the mouth. The enamel layer must be applied in a thickness that approximates that of the natural enamel being replaced, avoiding the interproximal areas. The stent is used to verify adaptation, and then removed for light curing.

An acetate matrix and a wedge are used to restore the interproximal walls with the same enamel body composite that was placed for the palatal wall (Fig. 16). Once these two steps have been completed, the complex cavity is transformed into a simple shell, the shape and thickness of which should be verified and eventually corrected prior to continuing with the restoration. The volumes to be filled are now visible and it is easy to check the areas during the stratification of the dentin body.

For the dentin body restoration, the number of dentin shades needed correlates to the size of the preparation: one dentin body for small, two for medium, and three for large. Each tooth exhibits three degrees of chromaticity: high in the cervical third, medium in the middle third, and low at the incisal level. Therefore, one or more composites with increasing saturation should be used to reproduce these chromaticities, based on the size of the cavity. For example, if the basic chromaticity is UD2, the required dentin body composite would be UD2 for a small cavity; UD2 and UD3 for a medium cavity; and UD2, UD3, and UD4 for a large cavity (Ena HRi, Micerium S.p.A., Avegno, Italy).

Such an approach achieves a strong chromatic nucleus that prevents the loss of chromaticity when the buccal enamel is applied and creates a desaturation from cervical to incisal and from palatal to buccal. In a large preparation area, the dentin body stratification begins at the most cervical margin by placing a high saturation dentin composite cervically. In our example, UD4 must be placed and cured, after which UD3 must be applied to completely cover UD4, as well as placed on the buccal chamfer, pushed more incisally, and cured. These two layers then are completely covered with a layer of UD2, which also is placed on the chamfer and extended to the incisal margin, and cured. If mamelons are present, the vertical grooves should be opened first to create the halo shape (Fig. 17). This enables creation of a chromatic composition of the dentin body with different chromas and the balanced desaturation seen in natural teeth.

After building up the dentin body, characterizations, intensives and opalescent are placed before applying the buccal enamel layer. The most important characterizations are the mamelons and the margin (Fig. 18), which are reproduced using white and amber (IW and OA, Ena HRi, Micerium S.p.A., Avegno, Italy).

Following mamelon and margin characterization, create the opalescents using a specific body composite (OBN Ena HRi, Micerium S.p.A., Avegno, Italy) that is placed between the mamelons and the area between the incisal margin and the dentine body (Fig. 19) to produce a natural halo. Finally, reproduce the intensives in the shape determined during the color mapping by using the white opaque body composites (IWS, IM, Ena HRi, Micerium S.p.A., Avegno, Italy).

It is important to remember that when applying the different composites to build up the dentin body, characterization, opalescents and intensives, necessary space must be left to apply the buccal enamel layer, which is thinner in the cervical area and thicker at the incisal edge, with a natural vertical contour that creates the natural tooth shape.

The stratification technique concludes with the buccal enamel layer, which must be applied to reproduce the transition lines and draft both the macro-texture (i.e., the lobes, the grooves and the depressions) as well as the micro-texture, using a brush to create the enamel growth lines (Figs. 20a-20b, 21).

Once the last layer of enamel is cured, and prior to initiating finishing and polishing procedures, it is advisable to cover the surface of the restoration with a layer of glycerin gel and perform an additional cycle of light curing to eliminate the oxygen-inhibited layer and obtain complete composite polymerization.

Protocol for finishing and polishing composite restorations

Finishing and polishing complete the restoration and are important steps because they create the ideal relationship between light and the tooth, which is fundamental to achieving the desired esthetic result. Furthermore, the finished and polished surface reduces plaque deposits and aging of the restoration. Finishing defines shape, dimension and contour of the restoration. The polishing shines the surfaces, maintaining texture details achieved during finishing.

Begin finishing by correcting the shape using medium-grain diamond burs (30 to 40 µ). Finish the vertical contour by following the tooth anatomy, using the bur along three different inclinations, depending on the area of the tooth: cervical, incisal or middle third (Fig. 22).

Finish the horizontal contour by adjusting the shape and length of the incisal edge and corners; finish the interproximal internal margin using abrasive strips; and finish the interproximal external margin using medium-grain diamond burs. This step is important because the correct shape and position of the transition lines (i.e., angles that define the transition from the interproximal margin to the buccal surface) are fundamental to the esthetic integration of the restoration.

After adjusting the shape, finish the surface macro-texture using a medium-grain diamond or multi-bladed bur to create lobes and grooves. The enamel growth lines (micro-texture) are created using the point of a green stone to gently scratch the surface (Fig. 23). Polishing imparts brilliance to the restoration surfaces. The ideal way to polish a restoration is by using diamond pastes and a goat-hair brush, which will not destroy the macro- and micro-texture surface details. Begin polishing with a 3-µ diamond paste, then switch to a 1-µ paste with water spray (Figs. 24-25 Shiny System-Micerium S.p.A., Avegno, Italy).

Polish the interproximal walls using abrasive strips with decreasing grain and diamond pastes. The final glossing can be achieved using an aluminum oxide paste with a felt disc, working at first without water at a very low speed, then increasing the speed but using copious water spray and no pressure on the restoration surface. When the finishing, polishing and final glossing steps are completed, a conservative composite restoration should be achieved (Figs. 26-27).

Learning the Vanini philosophy

At the SaS training center in San Fedele Intelvi, Italy, near Como, we organize several courses related to teeth restoration, both in the anterior and in the posterior region, with the direct technique as well with the indirect one (Fig. 28). During these courses, participants can assist in a live treatment of a patient and participate in a hands-on session on models to test the material used for restorations employing the “five tooth-color dimensions” philosophy (Fig. 29).

Note: A condensed version of this article was published in Dental Tribune U.S. Edition, Vol. 7 No. 2, February 2012.

About the author

Lorenzo Vanini, DDS, MD, is professor of restorative dentistry at the University La Sapienza in Rome, Italy, and visiting professor of restorative dentistry at the University De La Mediterranee in Marseilles, France. He also privately teaches courses, including some sponsored by Micerium. He can be contacted by e-mail at dott.vanini@libero.it.

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