December 2017
Volume 13, Issue 12

Peer-Reviewed

From Adequate to Artistry

A polychromatic approach for creating stratified composite restorations

Jason Olitsky, DMD, AAACD

Why would a practitioner want to be great at performing anterior direct composite restorations? One reason is that composite bonding offers many compelling advantages to patients and doctors. The immediate maximization of available tooth structure, minimal preparation of the natural tooth, and improvement of the patient's appearance make it a valuable skill to develop at a high level of expertise. Additionally, the resulting lower laboratory fees can enable dentists to reduce the cost associated with the treatment. The advantages experienced by the doctor include a reduction in the number of visits required to complete treatment, a decrease in overall chair time, and an increase in the profitability of treatment. Furthermore, mastering composite bonding can ultimately lead to a more fulfilling professional life.

The consensus among many dentists today is that a biomimetic incremental layering technique is mandatory to achieve indiscernible, esthetic composite restorations. This technique necessitates employing a number of different shades of enamel-like and dentin-like materials to optimize esthetics.1,2 A large percentage of clinicians still use monochromatic techniques when restoring anterior teeth with composites, relying on only one composite shade to restore the missing tooth structure. When these practitioners decide that they want to achieve superior anterior esthetics, they begin to employ a dual-shade layering technique, which is ideal for beginners who are less familiar with the concept of composite layering.3

Dimensions of Tooth Color

Historically, dentists have chosen shades based on the three dimensions of color (ie, chroma, hue, value) formulated by American artist Albert Henry Munsell in 1898. The dental literature supported this 3-dimensional theory for well over a century. When Lorenzo Vanini, DDS, MD, introduced the concept of anatomic stratification to the dental community, he disrupted the belief that 3D formulations achieve the most natural and esthetic result. Vanini's technique of stratification restores lost enamel and dentin layers to their proper location and thickness using five color dimensions of teeth (ie, chromaticity [chroma and hue], value [luminosity], intensities, opalescence, characterizations) as a guide.4

In terms of chroma and hue, Yamamoto performed a study on natural teeth utilizing a spectrophotometer and concluded that Vita shades A and B were the most prevalent. The A shade is statistically closest to to the average chromaticity of natural teeth.5 Value is classified in terms of its luminosity. High, medium, and low values of enamel are comparable with the enamel values of adolescents, adults, and the elderly, respectively. These categories also express diverse density, translucency, and reflectivity. As teeth age, the enamel loses value and translucency increases.4 Intensities are distributed over various parts of the enamel and appear as opaque, milk white stains. Enamel is responsible for the opalescence of natural teeth and has special optical properties of transparency and iridescence. Opalescence occurs all over the enamel, but is most evident in the incisal third, where light is able to pass through the full thickness of the enamel without interference from the dentin. Blue reflections result from tiny hydroxyapatite crystals that allow the long-wave spectrum of light (ie, red, orange, amber) to pass through.1,6 Characterization refers to the presence of mamelons as well as bands, stains, and cracks. Mamelons help increase value internally in the incisal area. This is achieved by placing a subtle layer of opalescent composite between the dentin body and enamel of the incisal aspect. Mamelons can take many different shapes and forms. Other characterizations occur in the incisal areas, too, as well as throughout the body of the tooth. When performing restorations, practitioners can train their eyes to appreciate all five dimensions of color. Shade matching using the three dimensions of color will ensure a good result; however, shade matching using the five dimensions of color elevates the outcome to excellent.

The Polychromatic Approach

A polychromatic layering technique involves building the composite restoration from the inside out. A thin (0.5 mm) layer of incisal porcelain is placed with the help of a silicon matrix to form the lingual shelf layer of the restoration (Figure 1). The lingual shelf enamel is used as a container to house the dentin and assist in the stratification of the layers. The first layer of dentin, referred to as the “In Layer” by Manauta and Salat in the book, Layers: An Atlas of Composite Resin Stratification, imparts the base chroma to the tooth. Prior to any intervention, a chromatic chart is created based on the patient's tooth color dimensions. Depending on the size of the restoration, one or more chromatic shades are used to restore the opaque dentin. Pay attention to “chromatic desaturation” from the gingival to the incisal third and from the inside to the outside of the tooth.7 Dentin is physically and optically very different than enamel. Generally, dentin is reddish-yellow in color. It has high chromaticity and remarkable opacity. It is also highly fluorescent due to the presence of certain proteins, such as photochrome. One of the most important parameters in shade matching is determining the correct chroma for the natural dentin. Some authors have estimated that about 80% of all teeth have a hue in the Vita shade A range.8 Researchers have measured this hue to be around 580 nm and determined that it most closely corresponds to the A2, A3, and A3.5 Vita shades. For obvious reasons, it is important to have a sufficient quantity of these dentin shades in the restorative kit. Vita shades C and D are rarely observed in the natural dentition.9-13

The center of the tooth is more chromatic, and as the dentin gets closer to the surface, it becomes less saturated. For these reasons, practitioners can place a deeper layer of higher chroma dentin, then layer in dentin to the base chroma shade (Figure 2). Approximately 90% to 95% of the final volume of the tooth will be formed with the dentin layer. It is of paramount importance to choose the correct thickness of each layer.

Referred to as the “Out Layer” by Manauta and Salat, enamel is responsible for modifying tooth brightness and is characterized by its translucency. The crystalline structure of enamel prisms allows light to pass through, whereas the organic, interprismatic component exhibits high opacity. Without the interprismatic substance, enamel would appear gray or blue.1,14 The combination imparts enamel with both translucency and high value. Unfortunately, the characteristics of natural enamel still cannot be reproduced artificially in the manufacture of enamel composites. Because natural enamel has a higher refractive index when compared with enamel composites, mimicking it requires practitioners to place a thinner layer of enamel composite. Normally, enamel composite should be placed at a thickness that is between one-third and half of the total thickness of the natural enamel—thicker layers lose value. Materials with a higher refractive index that is closer to that of natural enamel (IPS Empress Direct, Ivoclar Vivadent; Enamel plus HRi, Micerium) can be placed in thicker increments without losing value; however, the use of thicker increments may obscure some of the tooth's internal effects.1

The human eye is much more sensitive to light (ie, brightness/darkness) than color (ie, hue). This means that a slight mistake in the value of enamel or dentin (chromatically speaking) is more serious than selecting the wrong hue. For example, choosing Vita shade A when shade B is a closer match would be less perceptible to the human eye than if the practitioner chose the wrong enamel shade or a less saturated dentin shade. We look for enamel materials that best imitate the translucency and opalescent features of the natural enamel. Because it bears a hue, dentin can only be chromatic, whereas enamel can be either chromatic (vita-based) or achromatic (non-vita-based). Enamel composites offer dentists many options. They can be used to impart translucency as well as modify the color value.15 It should be noted that the nomenclature used by manufacturers of composites can be confusing. Some enamel composites are given a name, such as Pearl Frost or Iridescent Blue (Vit-l-escensce, Ultradent). Most enamel composites are paired with dentin composites, however, in some systems, the materials are sorted by value, such as Incisal Light or Incisal Medium (Renamel, Cosmedent). To prevent unnecessary mistakes during composite treatments, it is important to completely understand the chosen system's unique nomenclature.

When performing an anterior composite restoration, the practitioner is able to finesse the thickness of the dentinal body to reproduce the incisal area of the tooth. For highly translucent incisal edges, a thin dentinal core is required; for more opaque incisal edges, a thicker dentinal core is needed. A variety of mamelon shapes can be utilized to give form to the opalescence (Figure 3). Allow space for the opalescent masses that will be placed between the developing mamelons and in the proximal gaps (Figure 4). The enamel located at the incisal edge lets light pass through freely. This is where the dentin and enamel interact to form the most visually interesting area of a tooth. Initial layering of opalescent composites in this area creates a flat surface for intensities to be placed. White intensities can take various shapes (Figure 5 and Figure 6).

Characterization occurs at both the dentin layer and the enamel layer. After development of the mamelon shapes, practitioners can use highly chromatic amber or white dentin composite to further distinguish the mamelons in the incisal third. White characterization is typical for youthful teeth, and amber characterization is more common in adult teeth. To create a “halo effect” characterization, the incisal edges can be outlined with white composites. Chromatic effects are placed similarly to intensities, but with amber and brown shades instead. Creating mamelons highlighted by masses of opalescent composites, tints, and modifiers results in more lifelike composite restorations. Once the intensities and characterizations have been placed, the final enamel layer is formed.

If the shape needs altering during the layering process, make corrections with a coarse diamond bur or disk, then moisten the entire surface with a brush soaked in modeling liquid (ie, unfilled resin) (Figure 7). Remove the liquid using plenty of air. This process will recover the oxygen inhibition layer that was lost during the correction. No polymerization is needed for this step.

To improve integration with the natural dentition, dental practitioners should focus on the most important details of anterior composites. The first instinct is to put chroma, hue, or value at the top of the list, but shape is actually the most important consideration when restoring a tooth with composites. A restoration with correct shape and surface texture is most likely to achieve successful integration with the natural dentition, even when slight disparities in color are present.1 It is helpful to understand the four properties of tooth morphology: (1) outline, (2) primary anatomy, (3) secondary anatomy, and (4) tertiary anatomy.

The outline is responsible for determining the global tooth shape and is closely related to the primary anatomy. The anatomical crown shape is established by the transitional line angles. Secondary anatomy refers to the macro surface texture as a consequence of tooth development. Growth lobes that become evident on the surface as large, undulating areas covering the enamel are sometimes referred to as vertical texture. Tertiary anatomy is the microsurface texture. It is formed by small lines that cross the buccal surface horizontally.

Achieving an ideal polish is about restoring the surface morphology to natural textures, not making the restoration as smooth and shiny as possible. Making composite restorations shiny provides an adequate result, but creating ideal surface morphology with step-by-step polishing techniques results in a truly excellent and more lifelike restoration.

Creation of the surface morphology begins with the primary anatomy. First, outline the shape; there is no point in starting the polishing process without a finalized outline form (Figure 8). Next, draw the transitional line angles. Define the line angles to create an ideal shape or to mirror another natural tooth that is being matched. Their curvature will depend on the final shape desired. Contour the line angles with a 30 micron flame-shaped or needle-shaped diamond bur (ET® Diamonds Fine, Brasseler USA) or an abrasive disk (FlexiDisc®, Cosmedent; VersaFlex™, Brasseler USA), using delicate movements (Figure 9). Next, contour the incisal edge using a diamond bur and disks. Check the restoration's integration from the incisal or top-down view. The outline of the tooth should be separate from the dental facial line angles. Changing the facial line angles will enable the tooth to take on additional characteristics. After checking the integration, reproduce the secondary anatomy. Begin by recreating the division of the lobes with a fine diamond disk or diamond bur. Next, define the growth of the lobes with a diamond bur, moving gently in a back-and-forth motion. To create an initial gloss on the restoration, this anatomy is further defined and polished with a rubber point or cup (Dialite®, Brasseler; Enhance®, Dentsply; AstroPol, Ivoclar) (Figure 10). Follow up the secondary anatomy with the development of the tertiary anatomy. To replicate these small, horizontal lines, parallel grooves are created with the tip of a diamond bur (Figure 11). Lastly, blend the lines into the restoration using a fine diamond paste (DiaShine, VH Technologies) on a medium bristle brush (ie, at low speed with greater pressure and at high speed with lighter pressure), followed by aluminum oxide paste (Enamelize™, Cosmedent) on a felt wheel or Flexibuffs (Cosmedent).

Conclusion

A polychromatic approach for creating stratified composite restorations is an advanced technique that utilizes a number of different composite shades to build up the affected tooth substrate. With this technique, the clinician is able to control the color and the form of the final restoration. Combinations of chromatic and achromatic enamels can be used to restore the outer layers of the tooth (Figure 12).16 To determine the correct shades for composite restorations, creation of a color map is invaluable. The map should correlate what is seen in the natural dentition with the restorative materials necessary to mimic it. A customized map is preferable to utilizing the Vita shade guide because the latter provides little correlation between the tabs and the actual restorative composites available. To replicate what A2 actually stands for on the guide, dentists must break down the color and its 3 dimensions, then factor in translucency and opacity.17 Custom shade guides can be created by using self-made molds of shade tab teeth or by purchasing an off-the-shelf shade tab making kit.

The performance of superior composite artistry in the anterior requires some knowledge of the properties of dentin and enamel as well as an understanding of the products available to recreate them. Although knowledge is good, practice makes perfect. To improve their skills, many dentists exclusively practice on patients. This limits their opportunities to improve and can create frustration when the initial results are less than ideal. To maximize opportunities for training without relying on patients, dentists can fabricate sets of “practice teeth” utilizing bisacryl composites (Visalys® Temp Shade A2, Kettenbach) and a silicone index of teeth (Virtual®, Ivoclar Vivadent) (Figure 13). Improving your composite proficiency by training with your composite system and instruments in hand will allow you to become a true architect of the smile and use artistry to create it.

References

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