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For the past 30 years, composite resins have been steadily improving. Manufacturers have focused on advancements in strength, wear resistance, handling, polishing, and esthetics. Several innovations have resulted in the implementation of various layering options using multiple shades of dentin and enamel, including translucent enamel, to achieve optimal esthetic results. The different types of composites can be categorized based on filler size and shape. Earlier composites had larger, irregular-shaped fillers that provided strength but resulted in poor polishability and color stability. Conventional hybrids and microfills then emerged, which offered clinicians the ability to use a stronger base layer composite with a more esthetic top layer composite that could polish exceedingly well. The desire for a more universal composite that could be used in most or all direct restorative applications led to the development of microhybrid, nano, and nanohybrid composites that strive to provide both strength and esthetics and can be used in a more comprehensive manner.1
Given the highly diverse nature of these resins, clinicians often choose to maintain inventory of composites for both posterior (where strength and wear resistance are critical) and anterior (where esthetic properties matter most) usage. The demand from the dental community continues to be for a resin composite that embodies the qualities needed to achieve both strength and esthetics but can be used universally for all areas of the mouth, in both the anterior and posterior, thus reducing office inventory and simplifying procedures for both the staff and doctor.
Traditional Obstacles
Shade Matching
Shade matching presents obstacles to most dentists on a daily basis. Often clinicians may sacrifice a perfect shade match in the posterior to utilize a composite that is engineered for strength and wear resistance. On the other hand, these same properties may be ceded in the anterior to achieve the optical and polishing attributes needed to create a shade match that will enable an ideal blend of the restoration with the tooth. This causes the need for a dental office to maintain a composite inventory that will accommodate various patient tooth shades and restorative situations, which can become quite costly. In the author's experience, a typical syringe of composite ranges in cost from around $85 on the low end to more than $250 on the high end. If a clinician needs a minimum of four to five shades for posterior teeth and at least 10 shades for anterior teeth, and assuming a moderate average cost of around $120 per composite, this would equate to a conservative estimate of $1,800 to $2,000. The common shades get used frequently, however less commonly needed shades, such as A3.5 or darker and D/C shades, often may expire before they are used up.
Moreover, discrepancies have been shown to exist among different composites of the same shade and their matching to corresponding shade tabs.2-4 Some practitioners who are especially esthetically driven may even maintain an inventory of multiple composites for esthetic restorations in the anterior, including options for posterior restorations.5
In recent years, dental manufacturers have developed universal composites that can be used in both the posterior and anterior with acceptable results. However, with the newer generation of universal composites, although they may blend well when the correct color is selected, over time as teeth change color from staining or whitening procedures, the composite can become visible in contrast to the changing natural tooth color.6
Layering Composites for Optimal Esthetics
Recreating and mimicking natural tooth structure can be accomplished with contemporary composite resins through a series of meticulous composite layering. Composite resins have used several types of modifiers to simplify this taxing procedure. These include a variety of shades that have different opacities, translucencies, color modifiers in flowable form, and chromatic versus achromatic shades. While these additions have improved the resin material, each has its own technique sensitivity to achieve the desired esthetic result. Clinicians who are experienced in layered anterior direct composite restorations are likely familiar with these technique sensitivities, some of which are highlighted below.
To achieve ideal esthetics, each layer of tooth structure should be replicated within the layered resin. These layers include lingual shelf enamel, dentin, incisal translucent or opalescent enamel, and facial enamel; other considerations include chromatic and coloring characteristics.7 When restorations are built with these various layers with the correct thickness, the blending of the composite with the natural tooth structure can be achieved very effectively and be imperceptible, even under high magnification photography. Nevertheless, this layering technique has a high degree of difficulty, and achieving perfection with these restorations requires a comprehensive understanding of the characteristics of each composite layer. The layers must maintain proper thickness to mimic natural tooth structure.
For example, if the dentin layer is too thick the final restoration may appear too bright or opaque. Another issue is that if the semi-translucent lingual shelf is too thick or if some of it runs over onto the facio-incisal line angle then the hard incisal edge of the natural tooth will show through in the final restoration.8,9 If any one of the layers is not completed in its proper proportion or extension, then some aspect of the final restoration will be noticeable and/or unesthetic, thus likely causing the patient to be dissatisfied and the dentist feeling frustrated. For these reasons, many dentists instead opt to treat patients with indirect porcelain restorations and, in essence, hand over the difficult work of color matching to the dental ceramist due to the time and effort involved in layering direct composites.10,11
Single Shade for All Restorations
A recent development has been the emergence of a novel composite comprising a unique resin that offers a single shade to match any tooth color on the VITA shade guide from A1 to D4.12 This new generation of esthetic composite, which clinicians may use for restorations in both anterior and posterior teeth, is aimed at further simplifying the shade-matching process and the challenges of polychromatic layering by providing one shade that can match all teeth.13
The science underlying this new "smart" chromatic technology is based on the principle of structural color as opposed to chemical color. Dental composites are a mixture of glass/ceramic filler ground down to very small micro/nanometer-sized particles that bind together with organic resins and catalysts. With chemical coloring, a pigment or dye is added to the material to provide the resulting color. In the case of dental composites, a specific amount of pigments, such as red, yellow, or brown, is added into the composite mixture and the color cannot be altered afterwards. Structural coloring is achieved by controlling the size and shape of the composite filler particles. Rather than creating the filler particles by means of crushing or grinding, a method known as sol-gel can be used to grow a core spherical particle within an organic solvent to a desired size.14 It was discovered that a spherical shape at exactly 260 µm will reflect red-yellow light waves, which happens to be the same wavelengths that human teeth naturally reflect. When this new composite is bonded to a natural tooth, it is able to reflect the same wavelengths of light and provide a perfect color match.15
As previously discussed, the difficulty for practitioners in selecting composite colors to match a patient's tooth and then applying the skill of proper stratification is quite broad and ambiguous. This often leads to frustration for both the dentist and the patient, especially in the esthetic zone. Having a material whereby one shade matches all teeth alters the dynamics of restorative dentistry, as a material such as this can potentially impact many aspects of general and esthetic direct composite bonding. For dentists it may significantly simplify the challenges of layering multiple shades of traditional composite, reduce the time involved in and the discrepancies of shade selection, and lower the overhead costs of maintaining inventory of traditional composite colors. Patients can benefit from receiving a white filling, in the posterior or anterior, that will match their tooth shade, even over time.
The three clinical cases presented in this supplement (pp. 7-9) illustrate examples of the use of this new-generation composite in both anterior and posterior teeth of varying shades, including how it may be used in conjunction with, or without, a supplemental material to help mask dark or stained tooth structure or block hard lines.
Discussion
In each of the aforementioned case examples presented, challenges were overcome using a single-shade composite versus a traditional layering composite. In the first case, the patient originally was treatment-planned for class VI incisal edge repair of old existing incisal tip composites on teeth Nos. 8 and 9 in addition to a class V restoration on tooth No. 21. The appointment was blocked for 1 hour. As the patient sat in the chair, he expressed concern about the continued wear of his front teeth and wished they were longer. His teeth were quite dark, and a traditional composite that was beyond an A4 shade was not available in the office at the time. The clinician informed the patient that his teeth could be built up to ideal size with minimal tooth preparation and a newly developed composite would match his darker tooth color very well. He was pleased with this option and decided to have it done. With no need for anesthesia, a small facio-incisal bevel was created using a medium-grit diamond bur. The purpose of the bevel was to help increase surface area to aid bonding strength and support color blending over a broader area.16,17
The resin-based single-shade universal composite material used in the case solved several dilemmas general dentists often face. First, it allowed the clinician to avoid having to keep a darker shade composite in stock, which is not cost-effective since typically it is infrequently used and, as mentioned earlier, often may expire before even a fraction of it is used. Second, even if a darker shade composite was available to the clinician, a single shade of composite often looks monochromatic and dull when added to an incisal edge simply because it lacks the 3-dimensional layering effects described earlier.18 Third, when using esthetic layering composites and techniques, considerable time is required to sculpt and manipulate each layer. With the novel one-shade composite, used in conjunction with an accompanying supplementary blocker material, the appointment was completed in the same 1-hour time slot that was scheduled, which included fabrication of a silicone putty index during the procedure and still completing the class V restoration on tooth No. 21.
The final two cases also involved relatively uncommon tooth shades, with the diastema in the second case in the D-shade range, and the posterior tooth in the third case in the darker A-shade range. Although a single shade of a traditional universal composite could have been used in these cases, and the procedures would have taken the same amount of time to complete and an equal color match could have been achieved, the one-shade universal composite used offered the clinician the cost-saving advantage of keeping only one single composite in stock. It also eliminated any guesswork involved in shade matching. An additional benefit is that, because the material is able to be used in virtually any direct resin composite restorative case, it is likely to be used before it expires, potentially reducing waste.
Conclusion
Direct composite resins continue to evolve to become more universal in application while maintaining or enhancing physical and esthetic properties. A novel one-shade universal composite resin restorative material has been introduced that uses structural coloring as the primary shade-matching mechanism, enabling it to match all 16 shades on the VITA shade guide, from A1 to D4. The "smart" chromatic technology incorporated into the material has the potential to allow clinicians to gain significant cost savings by reducing traditional composite inventory and decrease chairtime by simplifying the shade selection and layering techniques. Offering exceptional color stability, the material blends well with existing tooth structure and is projected to maintain its blend with the tooth shade over time. The development of a single-shade composite is aimed at relieving time, stress, and overhead costs for general dental practices.
About the Authors
Kevin M. Brown, DDS
Private Practice, Bellevue, Washington; Accredited, American Academy of Cosmetic Dentistry
Greg Gillespie, DDS
Private Practice, Vancouver, Washington
References
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