E-Book, Englisch, Band 19, 102 Seiten
E-Book, Englisch, Band 19, 102 Seiten
Reihe: QuintEssentials of Dental Practice
ISBN: 978-1-85097-304-1
Verlag: Quintessence Publishing Co. Ltd.
Format: EPUB
Kopierschutz: Adobe DRM (»Systemvoraussetzungen)
Autoren/Hrsg.
Weitere Infos & Material
Chapter 1 Smile Dimensions
Chapter 2 Shade and Colour
Chapter 3 Bleaching and Microabrasion
Chapter4 Laminate Resin Composite Techniques
Chapter 5 Porcelain Laminate Techniques
Chapter 6 Technical and Laboratory Considerations
Chapter 7 Aesthetic Compromises and Dilemmas
Appendix
Index
Chapter 2
Shade and Colour
Aim
Successful shade-taking and colour communication are sources of great difficulty for practitioners. The aim of this chapter is to improve understanding of modern methods of shade-taking and colour communication. The importance of shape and form in successful aesthetics will also be outlined. Outcome
Practitioners will understand the basics of colour theory, be familiar with how to take a shade effectively and understand how shape and form can impact on aesthetic dentistry. Introduction
Colour can be described as having three components – hue, chroma and value – which are defined as follows: Hue – type of colour (for example, red, green, blue). Chroma – depth or saturation of the hue (for example, pink). Value – brightness of the hue (for example, grey or whiteness). The components can be classified on a three-dimensional (3D) scale called a colour sphere. The X, Y and Z axes meet at various points to produce a colour. In clinical practice colour is an important consideration when choosing the shade for tooth-coloured restorations such as direct resin composites and crowns. Equally, in an individual patient the teeth may all have the same hue (colour) but the chroma (depth or saturation of the hue) may differ from one tooth to another. For example, a canine can appear yellower than a small lateral incisor in the same patient’s mouth. The underlying colour may be the same, but in the canine the thickness of enamel and dentine is greater, which gives a darker colour (Fig 2-1). Similarly the shade of a tooth varies within the tooth in that the neck usually appears darker than the tip. Teeth, for the same reasons, become darker the further back they are in the dental arch. For example, lateral incisors appear darker than central incisors because the thickness of the enamel is much reduced, especially in the cervical area. Consequently the underlying dentine, which is largely responsible for the colour of a tooth, comes to the fore. Fig 2-1 Canines are darker than the incisors. Colour changes also occur as a result of tooth wear. As a tooth is affected by abrasion, attrition or erosion, either in isolation or in combination, the thickness of the remaining enamel and dentine gradually reduces. The colour saturation or chroma changes as the effect of the colour of the underlying dentine again becomes more dominant. Often teeth are described as becoming more yellow with age. They are not in fact more yellow, they just appear so as the underlying dentine becomes more opaque (less translucent) through age-related sclerosis and the modifying effects of the overlying enamel. Enamel is more translucent than dentine. This is often very apparent in young people who frequently have translucent incisal edges. To complicate matters further the overlying enamel has variable thickness. As the patient ages this translucency is lost as the tooth wears and the incisal tip reduces. This has various consequences. For example, over the labial face of a tooth different shades are typically present. A tooth is unlikely to be a single shade – for example, towards the incisal tip the colour of A2 is a lighter blue while at the gingival margin a darker red. The incisal translucency frequently represents the relative absence of dentine, while at the gingival margin there will be some reflection of the periodontal tissues. Shade-Matching
To help match crowns to natural teeth most manufacturers of porcelains and resin composites produce shade guides. The most commonly used guide is the Vita Classic shade guide (VITA Zahnfabrik H. Rauter GmbH & Co. KG, D-79713 Bad Säckingen, Germany), which has almost universal acceptance (Fig 2-2). Many manufacturers have produced better-designed guides, but nothing seems to have replaced the original Vita Classic shade guide. The guide is divided into reddish brown (A), reddish yellow (B), grey (C) and reddish grey (D) shades. There are two main hues in the A and B shade guide tabs. The C and D tabs represent lower values of B and A tabs, respectively. In most circumstances the shade guide provides a sufficiently wide spectrum of choice to map most people’s teeth. Fig 2-2 Vita Classic shade guide. The Vita Classic shade guide makes the operator think about hue. For example, the patient’s teeth are matched to an A hue and then, using the Vita Classic shade guide, the shade is selected from A1, A2, A3, A3.5 or A4. In contrast, the new Vita 3D master shade guide, which clusters hues of similar value, makes the operator think about value first and chroma second and is arguably superior in this respect (Fig 2-3). A more accurate method might include the laboratory providing a custom-made shade guide for each tooth made by the technician supporting the practitioner. Fig 2-3 Master shade guide in 3D. Tips for Choosing the Right Shade
Colour is NOT the most important factor when selecting the correct shade for a restoration, and it should not be the first consideration. Look at the patient’s skin tone. Look initially at the adjacent teeth. Consider the surface anatomy, concentrating on shape, form, texture and contour. The eye perceives shape before shade, so it is important to get the shape, texture and contour right at the start. Arguably, a restoration that is correctly shaped and formed but a shade out will pass, while a correctly shaded but poorly contoured restoration will not. Draw a diagram on the laboratory sheet to assist the technician. Include surface characteristics such as cracks, surface-staining, areas of opalescence and other surface topography you wish to include (Fig 2-4). The texture of the surface of the tooth can have a profound effect on the perceived shade, and for this reason a biscuit bake try-in of a metal ceramic crown is not very helpful for assessing its final appearance. Remember to include the age and gender of the patient on the laboratory prescription form, as this information is very helpful for the technician. Colour photographs are useful for communicating the surface characteristics of the tooth to the laboratory and, to a certain degree, with shade assessment. Although many practitioners will have the facilities for colour photography, black-and-white photography can also be very useful, in particular in difficult cases. Black-and-white photographs are particularly helpful in assisting the technician to assess the correct value, provided the photograph is taken under good lighting conditions. To assess the shade of the tooth it is helpful to arrange the shade guide according to value running from the lightest to the darkest – say, from B1 to C4 (Fig 2-5). Alternatively, first choose the hue and then the chroma. For example, the hue may be A and then the choice is A1, A2, A3, A3.5 or A4. In general, the older the patient the darker the tooth. Consequently be wary of choosing very light shades, such as A1, for a 50-year-old; generally the teeth of mature adults have a chroma of 3 or 3.5. There is trend toward lighter shades, with many A1 and A2 being selected. This is almost certainly as a consequence of large numbers of patients having had some form of dental bleaching coupled with patient requests for lighter teeth. Always take the shade with the patient either sitting or standing, never supine. This is because it is sensible to assess shade under similar conditions, in terms of lighting, as the restoration will ultimately be viewed. If a shade is taken with the patient in a supine position, the lighting conditions are completely different. This will affect both shade determination and in turn the aesthetic acceptability of the restoration. Hold the guide at arm’s length, adjacent to the tooth surface. Move the guide from tooth to tooth taking care not to stare too long. Periodically ask the patient to moisten the teeth with saliva. Take short sharp glimpses at the teeth. Glance at the teeth then look away. This is to minimise the effects of fatigue of rods and cones in the operator’s eyes. Be aware of contrast enhancement, given that the background can have an effect on the perceived shade. For example, a shade will look different on white and black backgrounds (Fig 2-6). To assist in shade-taking, always have the tab in the same vertical plane as the tooth you are matching and ask the patient to posture their tongue forward to give a consistent and meaningful (tissue-coloured) background against which to take the shade. Light plays a critical role in assessing colour, remembering that colour is primarily a function of the available light. Try and use natural daylight that is not too bright when selecting a shade. Very bright natural daylight may result in the selection of too light a shade. If the surgery has a window, it is helpful to have the patient stand by the window when taking a shade. If natural light is not possible, use a natural light lamp. Alternatively, make sure the fluorescent lights in the surgery are colour- corrected. Ideally, the lighting source you use should be the same as the one the technician uses in the laboratory to produce the restoration. It is sensible, therefore, to ascertain that your laboratory has the same colour-corrected tubes. Colour-corrected tubes, however, are only part of the answer as they can be somewhat variable. The effects of...
