What steps should one follow to apply the principles of optical properties and achieve the “perfect shade”? Find below a simplified step by step to help you achieve successful restorations.
• The dental office should be lighted with “corrective” light with a color reproduction index of around 90 and average temperatures of 5500K (there are LED fixtures that hold lamps with those features). It is important to take the shade under another light source for confirmation and to avoid metamerism. Also, pay attention to other light sources to which the patients may be frequently exposed in relation to their activity profile.
• Use neutral and light-colored walls, aprons and bibs, besides recommending that the patient refrain from using heavy make-up for the appointment, not to interfere or modify the perception of color by the observer.
• Consider the effects of translucency and opacity in the distinct areas of a tooth for a balance of the optical effect of the different material thicknesses. For example, a thicker layer of enamel composite (more translucent) may result in a restoration with a lower value (grayish).
• In the case of using shade guides, use a single shade each time, and do not observe for more than a few seconds to avoid confusion and fatigue in the observer’s perception.
• Anatomic shape, texture, flat areas and reflection lines should reproduce the adjacent teeth as faithfully as possible.
Fig 1 – Incisal third showing the greater proportion of light passage and lower amount of reflection. That area, as a rule, preferably should receive translucent enamel material (if necessary) and a thin layer of dentin material.
Fig 2 – Medium third: predominance of light reflection and little passage. That area, as a rule, should receive predominantly dentin material and a thinner enamel layer (0.5mm or less). Opaque material may be used for masking a darkened area.
Fig 3 – Cervical third, where there is the evident domain of light reflection with virtually no passage. In that area, it is possible to observe greater chroma or saturation and one should only use dentin material (opaque material, just to mask, if necessary, an eventual sclerotic dentin). The use of enamel material in that area may lead to a discrete graying of the restoration.
Simplified operatory plan:
- Prophylaxis with pumice stone paste/water for the dental surface to be clean and free of pigmented biofilm.
- Each and every shade taking should be prior to the isolation of the operatory field, since this installation dehydrates the dental element and temporarily increases its opacity.
- Select shade by value and not by hue. When placing a shade guide close to a tooth or applying composite increments on its surface, professionals should take a picture and digitally alter to a black and white filter. That way, the coordinates hue and chroma will be eliminated, there remaining only value or luminosity (fig. 7). In case the composite increment looks darker than the tooth, the professional can choose a lighter tone in the shade guide (from a value 3 shade, whatever the hue, to a value 2 one).
If it is lighter, the professional should do the opposite, and take a new black and white photo, until it looks right. Once the desired value is chosen, the professional may choose hue and a saturation. For example: value 2 was chosen and, if the tooth presents a whiter aspect, the choice will normally be A or B in the Vita guide (A being brownish yellow and B being yellow). If the tooth looks grayish, the professional may choose between C (gray) and D (grayish pink). With that, one avoids the confusion and doubt about different hues and a higher or lower saturation and different degrees of luminosity. The same methodology can be used in other shade guides that can be ordered by value or chroma degrees.
4. Mapping areas of the tooth: teeth are polychromatic and may have distinct shade aspects in different regions. That should be observed clinically (higher or lower saturation) and with the aid of black and white photographs for areas of high or lower value/luminosity. Besides, professionals should note the degree of translucency in the different areas (incisal, medium and cervical). A black or light-blue piece of cardboard as a background may be used to help confirm that mapping. Many times, a second opinion is of great help before the final decision.
5. In more complex cases, a quick direct mock-up (restoration without adhesive techniques) may help the definition of the thicknesses of each composite material.
Practically, all composites undergo a shade change when lightcured, going from a yellowish tone to a lighter tone. Therefore, it is important that those increments are cured before the photograph and clinical observation. Vittra APS (FGM) composite, thanks to its differentiated APS photoinitiators technology, does not show this perceptible shade variation between before and after light-curing. For that reason, it is possible to choose the shade before photopolymerization of the increment in real time.
Enamel (incisal third) and dentin (medium third) composite observed in normal photograph and in a black and white one used to help choosing the value of the composite.
Direct mock-up with the composites shown in figure 8, simulating the final restoration for a more refined evaluation of the selected shades.
Once the principles of optical properties are known and applied in the clinic in a simple and effective way, with the control over the thickness of the different composite layers to be used, it is possible to achieve successful restorations that are esthetically pleasant.
Working towards the best appearance possible for restorations is common place among dental professionals. The article Shade Selection Aspects shows how you can pursue the perfect tooth shade in your office by analyzing the triad: light source, object and observer.