The art of clinical shade matching of resin-based composite materials

Shade guides for matching resin-based composite materials

Traditionally, a shade guide, which is a range of shade tabs, was used by the dentist to determine the required shade of material to be employed by matching the shade of the natural tooth to the closest matching tab. The best known and most widely used shade guide is the Vita Classical system (Vita Zahnfabrik, Bad Säckingen, Germany)(Figure 1).

This shade guide consists of 16 shade tabs arranged with respect to their different hues (A–D) and in varying chroma levels (1–4). The vast majority of human teeth match the ‘A’ shades of the Vita Classical system. Originally, this particular shade guide was introduced in 1956 to match the newly introduced ceramics. The ability to choose the correct shade of these materials using this guide was hampered as the shade tabs are composed of acrylic, and trying to match dissimilar materials accurately is virtually impossible. Furthermore, the colour ranges and distributions within each tab is not natural. Natural teeth have many optical nuances that must be matched to ensure an optimal result, as discussed in the first article of this series (Figure 2).³

Many resin-based composite products on the market recommend the use of the Vita Classical shade guide when selecting the shade of the material to be used. Unfortunately, there can be significant variations in the hue, value, chroma and opacity of different commercially available products, which is demonstrated in Figure 3.

This lack of consistency between different resin-based composite manufacturers for a particular shade, means it is not possible to use the Vita Classical shade guide predictably. Therefore, when shade matching resin-based composite to natural tooth tissue, a shade guide made of said material should be used. These may be divided into two types, one supplied with the product and the other is custom made.

The shade guide supplied with the product may be constructed of simple tabs, similar to the Vita Classical shade guide, composed of the resin-based composite material itself, but consisting of homogeneous shade tabs, for example, A1, A2, A3 etc (Figure 4).

Other layering resin-based composite products offer a more advanced shade guide consisting of ‘shells’ composed of enamel shades, which may be fitted over the ‘cores’ made with dentine shades. This method helps the clinician arrive at a more predictable choice of shade of material.

One such product is Miris 2 (Coltène Whaledent, Altstatten, Switzerland) (Figure 5).

For those products that are not supplied with such a shade guide, other commercially available products are available that allow shells mimicking dental enamel to be made from any resin-based composite. Figure 6 shows one such product in which the ‘enamel’ shell can be used as the enamel shade tab, or may have the dentine shade placed over it to provide a guide as to the final restoration. Equally, the dentine shade tab may be used on its own.

The recommended shade-taking protocol when using such a system can be seen in Figure 5. The shade of the dentine is determined in the cervical region of the tooth where dentine is more plentiful and dental enamel thinnest, and similarly the enamel shade is gauged by comparing the ‘shell’ with the incisal edge of the tooth. With a small amount of glycerine between the core and shell to remove the air barrier, which affects the passage of light through the system and hence its optical properties, the final shade can be readily compared with the tooth. This provides a more predictable method of matching shades when working with layering resin-based composite products.

A custom-made shade guide can be constructed in surgery using the material and micro-brushes as handles⁴ and is shown sequentially in Figure 7.

As with wallpaper and paint, there may be variations between batches of material, so strictly speaking, such a shade guide should be constructed with each new batch of resin-based composite product. However, it is acknowledged that the difference may be so slight as not to warrant the extra expense in terms of time and material.

The use of clinical photography to facilitate shade determination

Some operators advocate the use of a shade map drawn from the pre-operative clinical photograph. This technique, however, may introduce errors and inaccuracies into the drawing. Furthermore, when the contralateral tooth is being drawn to create the shade map, the image must be mentally flipped when determining the placement of the shades and effects. Confusion may therefore occur during the clinical placement of the resin-based composite material. For this reason, the use of clinical photography only is recommended because it can be a useful tool in shade determination, especially in aesthetically demanding clinical situations. The design of restoration shape, surface texture and polychromatic colour may be enhanced by the use of close-up clinical photography, which may then be used as a shade map. Figure 8 illustrates the protocol.

Other practical tips on how clinical photography can be used in the determination of shade include the following.

Clinical determination of the shade of resin-based composite products in the aesthetic zone

The fundamentals and general principles of shade matching were explained in depth in the first article in this series, which the reader may wish to review.³ The remainder of the present article will be devoted to shade matching resin-based composite in the anterior and posterior regions.

General practical tips

Teeth should be cleaned to remove extrinsic stains using a brush and a slurry of flour of pumice and water. Avoid the use of prophylaxis paste as it will have a detrimental effect on the subsequent bonding procedure.

Resin-based composite restorations, being sensitive to moisture, should be placed under rubber dam, the most effective moisture control technique. The shade should be determined prior to rubber dam placement as the teeth will quickly dehydrate and so lighten in shade.

If possible, ideally a shade guide constructed of the selected product should be used, or custom-made as previously described. Which failing, the operator should follow the instructions of the manufacturer as regards the recommended shade guide. Where the tooth to be restored closely matches a specific Vita Classical shade, analogous resin-based composite enamel and dentine shade tabs of varying thickness may be used to determine the optimal translucency and opacity for layered restorations. This is determined in some systems by the use of a ‘recipe wheel’ (Figure 9).

The three or four closest shade tabs should be selected before beginning a process of elimination.

The middle third of the subject or adjacent tooth should be used to determine basic shade, as colour typically ranges from the cervical to the incisal areas (a general decrease in chroma and hue is usually seen).

Translucency is best evaluated using a black background. A photographic contraster may be used for this purpose (Figure 10).

Where the closest Vita Classical shade has slight chromatic differences from the natural tooth, customized shade tabs featuring different combinations of enamel and dentine shades in standardized thicknesses may be used for precise shade selection (Figure 6).⁵

Cavity size, shape and position should be studied, and the relative thicknesses of residual dental enamel and dentine should be measured.

A small amount of material of the selected shade should be placed onto the unetched surface of the tooth and light cured. Many products undergo a shade shift on photopolymerization, meaning that the shades between the uncured and cured material may differ. The clinician will be better able to determine the final shade more accurately once the material has been cured. The cured material may then be easily detached from the surface of the tooth (Figure 11).

Deeper resin-based composite layers should be shaped to conform to the anatomy of natural dentine (Figure 15).

As a general rule, The enamel layer should be no thicker than 0.5 mm (Figure 15).

Surface gloss (the ability of the tooth surface to reflect light) has a significant impact on the optical properties of teeth, and many layering resin-based composite materials are designed to allow quick and easy polishing to a high, naturally appearing surface lustre (Figure 15).

During restorative procedures, full dehydration is reported to occur after approximately 30–40 minutes. As it can take up to 2–3 days for teeth to fully rehydrate, it is important to monitor restorations over time to perfect layering techniques (Figure 12).

No deviation should be made from pre-operative shade decisions because teeth lighten during restorative procedures.

Classic polychromatic layering technique⁶ starts with the placement of an enamel ‘shell’, which may be easily formed using a palatal silicone template constructed from a pre-operative wax-up (Figure 13e).

Opaque dentine lobes are then restored and shaped depending on the desired optical effect (Figure 13f).

Based on the pre-operative colour map, specialized tinted ‘effect shade’ flowable consistency composites such as Creative Color (Cosmedent, Chicago, USA) are then applied and light cured on the final dentine layer (Figure 13g).

The labial enamel layer is then placed before carrying out shaping, finishing and polishing procedures (Figure 13h). The labial enamel can be a chromatic enamel shade, an achromatic enamel shade, or layering of both.

Shade matching with resin-based composite placement techniques

There are three placement techniques when providing resin-based composite restorations in the aesthetic zone. These are the use of a single shade, two shades (enamel and dentine) and three shades or more (enamel/dentine/effect shades). These techniques are now considered.

Three-shade + technique

This technique is an enhancement on the two-layer technique and should be employed in cases when aesthetics is of the highest priority and importance. In the same way that a natural tooth is composed of an outer covering of dental enamel with a dentine core, the three-shade technique involves a specific palatal enamel layer to be laid down (a different shade to the labial enamel), cored with a dentine shade with opaquers and tints, and then the final enamel layer(s) placed on the labial surface, so mimicking the structure of a natural tooth. Such a case is illustrated in Figure 16.

Shade matching posterior resin-based composite restorations

Many current commercially available materials can be used posteriorly, although the clinician has a responsibility to ensure that their chosen product is indicated for such a situation. The potential problems that arise from the effects of polymerization shrinkage stress are more relevant in this situation. The type of resin-based composite will determine its clinical placement¹ in that so-called bulk-filled restorative materials may be placed in large increments while the more traditional products need to be placed incrementally so as to ensure full cure of the material while reducing the polymerization shrinkage stress by paying attention to the configuration or C factor.⁷

Traditionally, function was considered more important than aesthetics in the posterior region and so products were developed with enhanced mechanical properties, such as the packables, which were available in only a few shades. This meant there was a decreased importance attached to accurate and exact shade matching. In fact, there is a school of thought that advises that there should be a slight mismatch between the shade of the restorative material and the tooth tissue.⁸ This will facilitate the future removal of the restorative material should this be required. If the shade match is excellent, then this is more challenging with the result that more sound tooth tissue is removed than would be desirable during cavity preparation.

That said, should there be a demand by the patient or indeed the artistic clinician, then excellent aesthetics can be provided with imperceptible margins between the restorative material and the dental hard tissues. Tints, effects and stains are provided with some kits and available to buy as products in their own right as mentioned earlier. An example of what can be achieved when restoring a molar tooth is shown in Figure 17f.

Practical tips for posterior composite restorations using a resin-based composite material

The pre-operative shade is selected using the techniques described previously and prior to isolation (Figure 17a). A rubber dam should be placed prior to cavity preparation (Figure 17b). Restorations composed of metal alloy, if present, should usually be removed entirely to avoid the risk of ‘shine through’, and the carious lesion managed appropriately. In the case of a cavity involving the approximal surface of the tooth, a sectional matrix system should be used (Figure 17c). After etching, adhesive resins are applied and light-cured according to the manufacturer's instructions. Opaque dentine shades may be used to block out darkly stained cavity floors (Figure 17d). The final enamel layer of the material may be quickly and easily shaped to restore occlusal anatomy (Figure 17e). A tinted flowable resin-based composite product, as mentioned earlier, may be applied to define occlusal pits and fissures. Excess ‘fissure stain’ should be blotted with a dry micro-brush before light curing. The advanced aesthetic and handling properties of a layering resin-based composite product enables the quick, efficient and predicable restoration of posterior teeth (Figure 17f).

Conclusion

In order to achieve natural imperceptible restorations constructed in resin-based composite, the treating clinician needs to consider which shade guide they use and how they use it. Careful shade selection, perhaps using clinical photography and the tips described in the present article, will pay dividends in achieving the desired goal. The final article in the series will discuss shade matching in relation to indirect restorative materials.