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Shade Matching and Proper Communication With The Dental Laboratory

 

One of the most challenging procedures in restorative dentistry is matching the shade of a single anterior tooth. Lighting, environment, and perception must be considered during the taking of shades to ensure a proper match.1 Restorative team members must use identical standards of measurement and communicate about shade and color. Failure to communicate risks a mismatched restoration and unaesthetic results.2 This article highlights a method of shade and color communication used in aesthetic ceramic restorations.

 

Lighting

Lighting influences shade perception. Color is viewed differently in varying levels of sunlight and the time of day that shade is taken. Orange colors prevail in morning, and blue is dominant at midday.3 "True color" is determined when the sun is in its most northern location. Therefore, it is imperative that operatory and laboratory environments are as uniform as possible.

Color is perceived when light reflected from an object strikes an observer's eye in different wavelengths3; if there is insufficient light, colors with small wavelengths (ie, violet, indigo, blue) cannot be accurately perceived. Sufficient lighting is approximately 5500 K,4. Eight (1.2 m) color-corrected lights per operatory (2.4 m (3.1 m) provide adequate light, allowing for an optimal shade match.5 A color-viewing light selector can be used to determine when a room has been lit at 5500 K.

 

Environment

Natural light, often absent in operatories and laboratories, is an advantage in color matching, since the environment can be controlled artificially.6 Regulate room color to prevent shade misinterpretation. A neutral gray room illuminated by color-corrected fluorescent bulbs is ideal since gray is a combination of all primary and secondary colors of the light spectrum 6.

Patients should be “neturalized” with a gray bib and should not be wearing lipstick. After establishing the environment, the technical process of shade taking can begin.

 

Perception

To evaluate a shade, the clinician determines the hue of the patient's dentition and measures its intensity with a shade tab. However, the clinician must determine an appropriate match independent of such guides as this method is often inaccurate.

Cone cells on the surface of the retina become fatigued when a color is viewed for an extended period, thus decreasing the acuity of the signals relayed to the brain. 3 To prevent fatigue, the patient should wear a blue bib during shade taking since the basic tooth shade is yellow-orange to red-orange. As the clinician views the patient's mouth, the eye muscle becomes fatigued to orange and alters the accurate perception of shade. The blue bib recharges the sensation of orange in the cone cells and corrects the inaccurate shade perception. It also must be considered that teeth - particularly aged teeth - have a glossy surface that absorbs the shade of any color placed in close proximity.

 

Accurate Shade Determination

Shade should be taken prior to preparation for accuracy as the adjacent teeth become dehydrated during this process. Patients should sit with their chins tilted down to minimize light reflection from the tooth surface. Next, place the shade selection system below the patient's closed mouth to ensure that all elements will be equally affected by the surroundings, time of day, or contrasting colors. Finally, manipulate the shade guide to determine the hue and intensity of the color. The closest shade should be selected and modified as necessary.

Alternatively, the shade guide can be placed by value rather than order to improve matching.7 Since value can only be perceived by a squinting viewer,5 this may provide a third means of determining value.

Next, use a second color system to verify the basic shade selection. This system has individual tabs for each aspect of the tooth (eg, dentin, enamel, incisal) permitting the layering of porcelain materials resulting in an accurate shade match (Figure 1). Determine if any color difference exists between the crown and the root (if it is exposed). The gingival region may be warmer or more chromatic than the rest of the tooth. Due to its natural curvature, the body of a tooth generally has a brighter value than its gingival or incisal aspect. Occasionally, a white band can be created across the surface of a tooth to increase its value.

Numerous internal characterizations are present in the incisal aspect of a tooth. In adolescents, the mamelon structure may be intact, adding a challenge in color matching. Older patients may have worn incisal edges, which exposes the dentin layer. As this layer is exposed, the resulting discoloration between the dentin and enamel layer allows multiple colors to be observed in the incisal region. Examine this area with a mirror to determine all the colors in the incisal aspect.

When a difference exists between the color of the gingival and incisal layers, it is common to mask the former while taking the shade of the latter (and vice versa). The shade guide used to measure these colors should be performed with a hemostat to prevent color misperception.

Proper Communication Techniques

After selecting a basic shade, use an overlay or underlay of colored translucent porcelain for a shade match. Additionally, accurate photographs can be used to communicate color. Slightly angle a camera to minimize light reflection that can distort color. Place the shade guide adjacent to the corresponding tooth and similarly angled. This ensures that the correct information is exchanged between the members of the restorative team, who should always utilize identical shade selection systems.

Stained teeth can be restored when shade is recorded and described to the technician. Stain the restoration in an environment with corrected, neutral light so that the crown will match the adjacent teeth (Figure 2). If the basic shade does not precisely match the shade tab, all varying colorations applied to the restoration will be fruitless since it was initially misdetermined.

(Continued from page 1 )

 

Material Considerations

Several porcelains require additional staining to achieve a match. In such procedures, the underlying optical characteristics of the tooth or restoration are masked by metallic-oxide stains, which demonstrate a monochromatic appearance. Perform staining in color-corrected light to prevent mismatched shades postoperatively. The fluorescence of porcelain materials cause an iridescent effect that reacts to and reflects light as a natural tooth (Figure 3).8 A material may prove inadequate if multiple bakes are required to modify the colors and the anatomy of the tooth. The product must maintain morphology and color after repeated firing.

For optimal results, maintain communication between the patient, clinician, and laboratory technician. Computer imaging can be used to provide patients with a picture of the anticipated restoration. However, a diagnostic waxup can be more accurate. (Figures 4-5-6-7). After approval of the restorations, the definitive restorations can be fabricated and cemented into their final position (Figures 8 and 9).

 

Case Presentation

A 33-year-old patient presented restoration of preexisting laminate veneers that had discolored. (Figure 10). A waxup was fabricated and seated intraorally for approval (Figure 11). Softening of the internal characterization and lightening were requested. A matrix was fabricated and duplicated in porcelain. The waxup permitted communication with the patient and allowed the restorations to be fabricated individually (Figure 12).

 

Segmental Buildup

For natural looking restorations, light had to be diffused, and the illusion of depth had to be created. The initial opaque layer was placed unevenly to scatter the light. A white opacious dentin layer was subsequently applied to re-create value lost as the layering progressed. During the layering process, indentations were placed (Figure 13) and filled with clear translucent material to scatter and trap the light (Figure 14). The dentin layer was built up to the exact size and contour of the definitive restorations and cut back as necessary (Figure 15).

Next, the "fingerlike" mamelon structure was created by painting internal stains were painted on the side wall to establish a dynamic characterization. Spaces were filled with alternating variations of colored incisal powders (Figure 16), to compensate for future shrinkage. Additional internal characterizations were then developed.

A bright incisal was utilized to highlight the line angle (Figure 17). The upper two thirds of the tooth were covered with translucent powders of varying colors using the lateral segmentation buildup technique.6,9,10 The enamel crack line was achieved by painting the side wall of the translucent porcelain with a colored stain. Once the buildup had been performed, the translucent layer was completed.

To compensate for shrinkage during the initial firing (Figure 18), an auxiliary layer of colored porcelain material was added (Figure 19) following each firing until completion (Figures 20-21-22). Matching the surface texture and luster were also rendered. Consequently, grinding and polishing were accomplished until the full-coverage restorations had been completed, seated, and cemented (Figures 23-24-25).

Conclusion

Fabrication of natural appearing aesthetic restorations depends on proper communication and understanding the methods used to take and match shades. This article highlights factors that influence proper shade and color determination. In addition, it details communication methods between the members of the restorative team and demonstrates the use of such techniques during the segmental buildup of porcelain restorations.

 

*Laboratory technician, Bay Dental Laboratory, Monterey, CA.  

 

References

  1. Miller A, Long J, Cole J, Staffanou R. Shade selection and laboratory communication. Quint Int 1993;24(5):305-309.
  2. Muia PJ. Esthetic Restorations: Improved Dentist-Laboratory Communication. Carol Stream, IL: Quintessence Publishing, 1993.
  3. Yamamoto M. Metal-Ceramics. Carol Stream, IL: Quintessence Publishing, 1985.
  4. Touati B, Miara P, Nathanson D. Esthetic Dentistry & Ceramic Restorations. London, UK: Martin Dunitz, 1999.
  5. Spear F. Aesthetic communication. Las Vegas, NV: ADA Conference 1985.
  6. Ubassy G. Shape and Color. Carol Stream, IL: Quintessence Publishing, 1993.
  7. 3D-Master, Vident, Brea, CA.
  8. McLaren EA. Luminescent veneers. J Esthet Dent 1997;9(1):3-12.
  9. Aiba N. Fabrication of custom-made ceramic restorations using Willi Geller's Technique. Quint Dent Technol 1992;15:47-56.
  10. McLaren EA. The skeleton buildup technique: A systemic approach to the three-dimensional control of shade and shape. Pract Periodont Aesthet Dent 1998;10(5):587-597.
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