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Prosthodontics

Authors: Dr. Surendra Agarwal, Dr. Anjali Bhoyar, Dr. Shilpi K Pandey.

Abstract:

Patient’s satisfaction with shade match is important when constructing or replacing a restoration, and the level of satisfaction of patients might be different from that of the clinician. Esthetic expectations have exponentially increased over the last few years. Color and shade determination have traditionally been one of the greatest challenges in dental field. The measurement of tooth color is possible via a number of methods including visual assessment with shade guides, spectrophotometry, colorimetry and computer analysis of digital images. Each method has its own limitations and set of advantages and disadvantages. Nevertheless, these methods have successfully been used to for shade consideration.

Introduction:
Patient’s satisfaction with shade match is important when constructing or replacing a restoration, and the level of satisfaction of patients might be different from that of the clinician. Esthetic expectations have exponentially increased over the last few years. Color and shade determination have traditionally been one of the greatest challenges in dental field. Esthetics of any restoration depends not only upon the outline form, surface finish and translucency but also the color.1There are about 10 million different shades that can be recognized by means of modern, very precise devices, whereas human brain recognizes approximately one million shades. The human dentition shades vary considerably and there can be about one hundred thousand dental shades distinguished using modern electronic instruments, while human eye can recognise only 1% of the shades.2

The tooth color is mainly determined by dentine with enamel playing only a minor role through scattering at wavelengths in the blue range.3Verbal descriptions of color are not precise enough to describe the appearance of teeth and this forces us to use three variables in order to characterize thoroughly our perception of light reflected from tooth surface: hue, value and chroma. Hue describes the dominant shade of the tooth (more yellowish or reddish), value−the lightness or darkness of the tooth shade measured independently of the hue, chroma – the quality of tooth color that distinguishes the degree of vividness of hue.4
Different techniques are used by clinicians in color selection and they can be divided into two groups:

Visual and Instrumental methods.

Visual Methods:
Visual color determination by comparison of patient’s tooth with a color standard is the most frequently applied method in clinical dentistry. Visual methods are mostly based on clinician’s experience and dependant on conditions existing in dental surgery at the moment of tooth shade assessment. Visual techniques may be supported by the use of tooth color atlases and special shade guides containing samples of different shades. The tooth color atlas is a systematic set of color samples situated regularly according to determined criteria. A dental shade guide is a commonly used method in natural teeth color evaluation in order to obtain aesthetic and naturally looking dental restorations. It contains a certain number of different shades samples made from different materials depending on the kind of restoration that will be performed and is based on a comparison of a patient’s tooth with a color standard.5

Tab-arrangement-of-the-Vita Vitapan-3D-Shade -Chromascop-shade


There are various shade guides for different kinds of composite resin materials, porcelain and acrylic resins (e.g.: Vita 3D−Master, IPS Impulse, Vita Classical Shade guide, Enamel Plus HFO Shade Guide, Classic Shade Guide, Trublend, Filtek Supreme Plus Universal Restorative, Chromascop Shade Guide).6

Vintage-Halo-shade A-composite-shade-analysis- Vita-Easyshade


The Vitapan Classical shade guide (Vident, Brea, Calif) was a gold standard in dentistry for decades and, to a large extent, still is. Vitapan Classical shade tabs are divided into four groups, with primary group division based on hue (Fig 1). Within the groups, tab arrangement is based on increasing chroma-the more chromatic tabs are marked with higher numbers. Group A consists of five tabs (A1, A2, A3, A3.5, A4); groups B and C consist of four tabs each (B1, B2, B3, B4 and C1, C2, C3, C4, respectively); and group D consists of three tabs (D2, D3, D4). The manufacturer also provides an alternative tab arrangement, claimed to be established according to degree of brightness (commonly known as value scale) and with no group division.6

Spectrophotometers-measure- Portable-handheld-spectroph Digital-camera


The Vitapan 3D Master shade guide (Vident) consists of 26 tabs divided into five groups according to lightness (fig 2). Within this groups, tabs are arranged according to chroma (vertically) and hue (horizontally). The first group consist of two tabs; the second, third, and fourth groups have seven tabs each; and the fifth group consists of three tabs. Three bleaching shades (OM1, OM2, and OM3) were additionally introduced, indicating high lightness (0), three levels of chroma (1, 2, 3), and medium hue (M). The Vitapan 3D Master color guide is designed identically to the corresponding shade guide (i.e., 26 shades), except that its tabs include only the dentine shade, with no cervical or incisal shades. Several important characteristics have been improved with Vitapan 3D Master as compared with the Vitapan Classical shade guide: the lightness range is wider; more chromatic tabs are included; the hue range is extended toward reddish spectra part; the shade tabs are more uniformly spaced; group division is better; and, although certain disharmony still exists, the overall tab arrangement is better.6

The-appropriate-shade-tab


Chromascop shade guide tabs (Ivoclar Vivadent, Amherst, NY) similarly to Vitapan 3D Master, a group 0, consisting of four bleaching shades (010, 020, 030, 040), was additionally introduced (fig 3).6

The Vintage Halo shade guide (Shofu Dental, Menlo Park, Calif) ) is basically keyed to the Vitapan Classical shade guide. It consists of 38 tabs, divided into three sets according to decreasing lightness: Value Plus (14 tabs: VB1, VB2, VB3, VB4, VA1, VA2, VA3, VA3.5, VA4, VR1, VR2, VR3, VR3.5, VR4; (figure 29, A), Standard (16 tabs: B1, B2, B3, B4, root B, A1, A2, A3, A3.5, A4, root A, R1, R2, R3, R3.5, R4; (figure 29, B), and low value (8 tabs: D2, D3, D4, C1, C2, C3, C4, root C; (fig 4)6

Instrumental Methods:
In instrumental techniques many different devices and machine tools are used in order to make the color assessment more simple, rapid, precise and perfect. The instruments used in this techniques, like colorimeters (photoelectric tristimulus colorimetry), spectrophotometers (reflectance spectrophotometry) digital extra and intraoral cameras and color video cameras are an alternative and objective solution in color selection and become more and more popular in everyday dental practice.

Colorimeter is the first instrument designed specifically for color evaluation in dentistry (Chromascan, Sterngold, Stamford, Conn) was introduced in the early 1980s, but it met with minimal success because of the difficult user interface and somewhat limited accuracy. Photometric and colorimetric instruments measure colors and express it in a term of 3 coordinate values (L∗,a∗, b∗), which locate the tooth color within the CIELAB color space. The L∗ coordinate represents the brightness, the a∗ value the red or green chroma, and the b∗ value the yellow and blue chroma. 7 Optilume Trueshade and Demetron Shade Light are the examples of colorimeters, which contain double magnifying lenses, polarising filter and own light source with constant light intensity to ensure more objective color assessment carried out by a clinician.8 Computer aided shade selection can be done by means of portable colorimeter Shade Eye Ex (Shofu Japan) operating with infrared data transfer, which makes measuring unit mobile and convenient (fig 5).7

Spectrophotometer: The Vita Easy shade (Vident) is a handheld spectrophotometer for tooth shade matching (fig 6,7,8). It measure an overall tooth shade, enables to separate the tooth into cervical, middle and incisal areas of shade and verify the color of ready−made restorations.

Intraoral digital cameras (Nikon Coolpix 990, Kodak, Nikon D−50, Olympus) enable to record tooth shade variations and provide quick and more detailed prescription of the selected colour in a form of digital data or printed photographs sent to the dental laboratory. It provides the transfer of subtleties in shade transition, craze marks, translucency, occlusal groove stains, incisal haloes, texture and gingival body colour to a dental technician, which is impossible while using traditional analogous cameras or photos. The use of photos processed traditionally might be not a perfect manner of direct colour communication, as there is a great variability among cameras and printers that can make the obtained images different from the actual tooth colour. The extraoral digital camera is a comparable to the intraoral camera tool, helpful in tooth shade assessment, but more time consuming and with less precise data transfer. Digital camera (fig 9) imaging systems are more reliable in tooth colour quantification than colourimeters and spectrophotometers, which are designed for flat, bigger surfaces (edge−loss effects), rather than curved, small, semitranslucent surfaces found on the teeth.9

Guidelines for shade taking:
1. The most important circumstance of shade matching is the lighting condition. No matter what technique used, without a light source that approaches 5500K, CRI of 100, with the proper luminosity, a superior shade rendering is not possible.6
2. All shade guide selection should be done BEFORE we turn on the dental unit light.9
3. First impressions are the best due to eye fatigue. The teeth should not be starred for more than 5 seconds to prevent hue accommodation.6
4. Teeth are viewed with lips relaxed (indirect light) and reflected (with direct light at 900). Assessment in muted or non-direct light will determine how much brightness is from the dentin.10
5. The dentist’s eyes should be on the level of the patient’s tooth (fig 10). Regarding shade matching distance, visual acuity for near vision (close inspection) is tested in ophthalmology at the standard reading distance of 25 or 33 cm.11 The suggested minimum standard of visual acuity for dental practitioners is 6/7.5 at 33 cm.12
6. The shade tab placement should be placed parallel with the tooth whose shade is being matched, and with the same relative edge position (fig 11). If possible, it should be in the same plane with the tooth-not in front of it, or it will appear lighter and not behind it, or it will appear darker. The tab carrier, especially if metal, should be put along its normal axis to avoid possible impact on the tab color, especially in the incisal/occlusal region, where teeth are the most translucent.6

Conclusion:
The color and appearance of teeth is a complex phenomena, with many factors such as lighting conditions, translucency, opacity, light scattering, gloss and the human eye and brain influencing the overall perception of tooth colour. The measurement of tooth color is possible via a number of methods including visual assessment with shade guides, spectrophotometry, colorimetry and computer analysis of digital images. Each method has its own limitations and set of advantages and disadvantages. Nevertheless, these methods have successfully been used to for shade consideration. Although we tend to focus on color matching, it is an appearance match that we are after and so the basic principles of esthetics, including tooth size and proportion, symmetry, outline form, and overall harmony are just as important, if not more so, to a successful restorative match. Academic training plays a significant role in the development of color selection skills.

Shade matching is much more complicated task than it may look like. In the selection of shade, patience may is the essential factor for good shade matching rather than the experience. Although, it might be preferable to consider the patient’s choice in shade selection on ethical grounds, yet the final decision could be made by the dental intern, Prosthodontist or the dentist, rather than just relying on the patient or dental technician, especially when teeth are more homogenous.

Variability of the factors which influence shade matching procedure should be minimalised. There is a need for new, better, logically and scientifically arranged shade guides which would cover complete color range of natural teeth. Thus, the possibility of matching the proper shade increases.

References

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  3. Brodbelt RHW, O 'brien WJ, FA .Translucency of Human Dental Enamel.Dent Res 1981; 60: 1749-53.
  4. Munsell AH: Color notation, 5th ed, Baltimore. Munsell Color Company. 1946.
  5. Napadłek P, Panek H, Dąbrowa T.Comparison Methods Used in Tooth Colour Selection Dent. Med. Probl 2008; 45: 1:65–9.
  6. Rade D. Paravina, John M. Powers. Esthetic Color training in dentistry. China: Elsevier, 2004.
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  8. Schanda J. CIE Colorimetry and Colour Displays University Veszprém, Hungary and CIE Central Bureau, Vienna.
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  11. Ostwald W. The Color primer: a basic treatise on the color system of Wilhelm Ostwald. New York. 1969.
  12. Richter M. The official German standard color chart. J Opt Soc Am 1986.