Considerations and Implications in Shade Selection for Dental Restorations: A Review.

Newer trends in shade matching have been driven by the market need for superior grade esthetic restorations. Modernized shade guides, obtainability of shade-taking devices, and research in the field of human color vision have ameliorated the capability of dentists to attain outstanding color-matched restorations. A detailed knowledge of natural teeth' appearance features is needed along with these new devices to increase shade-matching results. Copyright:

INTRODUCTION

In today's world, the success of any dental restoration is centralized around three main linchpins: the use of non-metallic materials involving ceramics and composite resins, adhesion to dental structures, and achievement of a natural cosmetic look.[1] Color combinations improve esthetics and give the restoration a natural look.[2] Color perception can be subjective to individuals and the environment under different conditions.[3] The color of a tooth can be verified by visual methods or instruments.[4] Recent advancements in dental materials have led to a sudden surge in the use of tooth-colored restorations.[5] The achievement of appropriate shade selection for restoration depends on various factors such as dentist's analysis, communication with the technician, interpretation of different shades, the buildup of the restoration, and patient's acceptance and confirmation before cementation.[6]

THE BASIC COLOR SCHEME

In the visible light spectrum, three large bands of colors are noted: red, green, and blue. These three colors are termed primary additive colors, which mix in different degrees to form complementary colors or secondary colors. Combining all three of these colors produces white color with different intensities.[7] The basic tool for combining colors is a color circle or wheel [Figure 1]. The wheel comprises 12 colors, the primary colors being red, yellow, and blue.[2] The arrangement of primary and secondary colors is made in the pattern of a wheel in which the colors make the components of the rim of the wheel. This type of organization of different colors is known as the color wheel or color circle.[7] The color mixing could be explained on two models: additive color mixture and subtractive color mixture model. In the additive color mixture model, two or more primary colors are added to produce new colors such as cyan, magenta, yellow, and white (subtractive primary colors) based on the intensity of the initial colors' mixture used. In a subtractive model, it starts with white, the color with no waves being subtracted, and ends in black, with all color wavelengths being subtracted.[2]

Figure 1

Color wheel

MEASUREMENT OF COLOR

Measurement or determination of color is a challenging requirement in the field of restorative dentistry as well as in other fields such as medicine and industries.[3] Color determination is broadly discussed under two techniques:

Visual technique

Instrumental technique.

The visual technique is a commonly used technique, which uses a popular system known as the Munsell color system.[2] The Munsell color order system is represented in three dimensions, which corresponds to the human color vision's three perceptual components (hue, value, and chroma) [Figure 2]. It is the system of color choice in dentistry and was proposed by Albert Henry Munsell in the early 1900s.[7] The first attribute, hue, differentiates one family of colors from another and is related to wavelength.[27] The second one (chroma) relates to the intensity, saturation, reflectance, or strength of hue, and the third one, value, is related to the relative darkness or lightness of color.[8] In the instrumental technique, the color system dwells with three coordinates: one lightness and two chromaticity coordinates. The instrumental technique has one potential merit over the visual technique because instrumental readings are objective, can be easily measured, and are more instantly achieved.[9]

Figure 2

Munsell color system

COLOR TRIAD

In shade determination, understanding the color triad is crucial, which consists of the light source, the object, and the observer.

Light source

The surface color appearance of an object depends on the quality of color illumination. Natural light is the ideal light source. Different light sources give different colors.

The object: Object has the capability to alter color of the light. When the object absorbs radiating visible light, color appears

The observer: When the visible light enters the eyes, it pass through transparent area of cornea and crystalline lens, and then the image is focused on the retina. The iris, which dilates or constricts depending on the level of illumination, regulates the quantity of light entering the eye.[1]

METAMERISM

Under a certain kind of light, two objects appear to be identical colors, while under another kind of light, they appear totally different, called metamerism.[10] Two types of metamerism are explained:

Object metamerism: This occurs when the two objects appear similar in one lighting condition but appear differently when the light source is changed

Observer metamerism: Here, the light source remains the same, and the observer changes, caused by either human visual stimulus or instrumental stimulus.[211]

COLOR OF HUMAN TEETH

The color of teeth includes only a small portion of the total color space. The 1st data in color ranges in human teeth were measured by Dr. E. B. Clark, a dentist, in 1931 using the Munsell coloring system. Clark suggested that value ranged from 4 to 8, hue ranged from 6 YR (yellow and red) to 9.3 Y (yellow), and the chroma ranged from 0 to 7. The studies suggest that teeth are in the yellow–red to yellow range of the spectrum that is comparatively high in value and low in chroma.[12]

DENTAL SHADE GUIDES

Shade-matching tools are called color standards or shade guides. The order of shade selection is value, chroma, and hue.[1314] Three main shade guide designs include:

The Vitapan Classical design

The VITA three-dimensional (3D)-MASTER shade guide

Other shade guide systems with patented designs include:[15]

Hayashi's shade guide

Clark shade guide (Tooth color indicator)

Spectatone.

Vitapan

It is a popular shade guide that was introduced during 1956.[16] Tabs of hue are categorized into letter groups:

A: Reddish-brownish : A1 - A2 - A3 - A3,5 - A4

B: Reddish-yellowish : B1 - B2 - B3 - B4

C: Greyish : C1 - C2 - C3 - C4

D: Reddish-grey : D2 - D3 - D4

Chroma is designated by 1, 2, 3, and 4.[17]

eVitapan three-dimensional-master shade guide

It is the most recent type of shade guide introduced in 1998.[16] There are three major types:

Tooth guide

Linear guide

Bleached guide.

The 3D-master tabs are marked by employing a number–letter–number system. The 1st number indicates value, from 0 being the lightest to 5 being the darkest. The middle letter indicates hue with the L, M, and R corresponding to yellowish, medium, and reddish hue. The 2nd number designates chroma, from the least chromatic 1 to the most chromatic 3.[7] Two varieties of shade guides are available for shade selection in the Vitapan 3D master shade guide:

Vitapan 3D master tooth guide (blue chips)

Vitapan 3D master color guide (red chips)[16]

RECENT ADVANCES IN SHADE SELECTION

Colorimeters: Filter colorimeters typically use 3/4 silicon photodiodes with spectral correction filters that closely simulate the standard observer functions. These filters act as analog function generators that restrict the spectral characteristic of the light that hits the detector surface[1618]

Shade vision: It is a hand-operated device with its own light source and LCD screen, through which the device can be modified against the tooth. It is an imaging colorimeter[1618]

Shofu's Shade Natural Color Concept (NCC) Chroma Meter: Shofu's Shade NCC Chroma Meter was introduced in the 1990s. It is fabricated by a handheld probe of 3 mm in diameter[1618]

Vita Easyshade Compact: Vita Easyshade Compact is a contact type spectrophotometer (SP), handy, cordless, cost-effective, and battery-driven. This device has a digital SP and attaches the LED fiberoptic light source. This device can measure areas up to 5 mm in diameter, and no digital images are produced[19]

Shade scan: This was the first system in which digital color image was combined with colorimetric analysis. This system was introduced by Cynovad. It is made up of a handheld device with a color LCD screen, data station, seven flashcards (16 MB each), and software. In shade scan, a handheld display and shade map is available[1819]

Clear Match System (Smart Technology, Hood River, Oregon): This system uses high-resolution digital image software to properly balance the digital color data and compares it with a shade tab. The color data is shared with the lab via email, including a black and white standard with every photograph.[19]

SpectroShade: Another SP developed for clinical usage is the SpectroShade, an imaging SP. The device's design is very difficult and very expensive compared to other instrumental systems used for shade selection. This system is the only system, which mixes digital color imaging with SP analysis.[2021] SPs are traditional devices used in dentistry for measuring color in dentistry, whereas spectroradiometers are newly introduced instruments designed to create the most accurate and detailed color measurements.[2223]

DIGITAL CAMERAS

The latest devices used for dental shade matching are based on digital camera technology. The highest-quality cameras use three separate sensors, each one with a separate filter over it.[24]

Limitations of digital shade analysis

Precision of color measurement is affected by the phenomenon of edge loss

Translucency mapping is not adequate with all the systems

Placement of the mouthpieces or probe seems to be disapproving of the repeatability of the measurement

The instruments should be experienced enough to function in a development model

For the digital analysis to be logical, the laboratory must have a system as well

Availability is less, also very expensive.[24]

PRINCIPLES OF SHADE SELECTION IN DENTISTRY

Patients should be viewed at eye level to engage retina

The shade should be checked under different types of lighting after the initial shade is selected in natural daylight. The shade is then confirmed under fluorescent and incandescent lighting

Teeth should be cleaned before matching is done

At the beginning of the patient visit, shade comparison should be initiated

Any cosmetics such as lipstick should be removed, and bright-colored clothing should be draped

The procedure of shade matching should be done quickly[17]

After comparison, rest should be given to the eye by focusing on a gray–blue surface as this helps resensitize and balance the sensors in our eye.[1725]

THREE-STEP SHADE-MATCHING PROCEDURES

The sequence of lightness, chroma, and hue is followed first during the selection of shade. Then, the tab which is closest or an appropriate combination is chosen. If there is no perfect match, a lighter shade is selected, to which extrinsic correction is done.[17]

Dentist position: The dentist's eye should be at the level of the patient's tooth that is the line of vision perpendicular to the surface. The viewing distance should enable a viewing angle of not <2°

Tab placement: The tab to be positioned parallel to the tooth being matched. It should not be behind the teeth as it will appear darker nor in front as it will appear lighter [Figure 3]

Figure 3

Tabs aligned on the same plane with teeth being matched

Time length and pauses: Each shade-matching trial should be restricted to about 5 s with an interval by observing a blue card in between.[17]

SHADE DISTRIBUTION CHART

A rough sketch of a tooth drawn onto paper is divided into incisal, middle, and cervical third. The value of enamel, the hue of dentine, and color-specific areas are determined. White spots, stain areas, fracture lines, and distribution of translucency are drawn onto the chart. The degree of luster, glaze, and surface texture is also noted down.[2627]

PROBLEMS DURING SHADE MATCHING

Color vision problems/color blindness: It is the absence of one or more photosensitive pigments. Other color vision defects include achromatism, dichromatism, and trichromatism

Age: There is a yellowish coloring of the lens and cornea, with age causing bias in vision

Fatigue: Fatigue can lead to compromised visual accuracy, thus causing inappropriate shade selection

Emotions: Our emotions influence pupil dilatation and constriction that helps to discriminate between colors

Medications: The use of caffeine, drugs, and alcohol affects our color perception

Binocular difference: This is the difference in perception between the left and right eye

Environmental influences: The background or surroundings next to the tooth can affect the color perceived from the tooth. This is why it is advised to remove any makeup and use a neutral gray background to reduce the environment's influence.[2829]

CONCLUSION

Proper shade selection is an essential basis step to achieve perfect esthetic. Color of the teeth is influenced by many factors causing subjective differences. The variation in natural teeth and ceramics material is the main reason for shade selection to be time-consuming and skill demanding.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.