Cosmetic dentistry - tooth discolouration

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					Professor Laurence J. Walsh
Laurence Walsh is Professor of Dental Science at The University of Queensland. He has been involved in clinical studies of hard and soft tissue cosmetic procedures for more than a decade, and coordinates a research group with a particular interest in tooth whitening technologies. Laurence operates a referral-only practice in the area of special needs dentistry, and teaches in the general practice stream within the undergraduate and postgraduate dental program. Laurence maintains a substantial clinical commitment in the area of special needs dentistry, and is actively involved in the dental profession at a range of levels. Since childhood, Laurence has had a strong affinity for most things of a technical nature, and a love of all the sciences. His hobbies include writing and producing music, bushwalking with his wife Mary, and competing with his three teenage children in table tennis.

Cosmetic procedures are in high demand from dental patients. This CD ROM presents 20 cases, which illustrate the technique and clinical outcomes for a range of relatively simple cosmetic procedures, including matrix and power bleaching, laser-assisted tooth whitening, enamel microabrasion, and odontoplasty. Specific mention is made of the risks which accompany these procedures. A tutorial is presented which outlines a method for digital analysis of shade changes in teeth, due to bleaching and other treatments.

Cases outlined
Internal Bleaching Peroxide compounds placed within the pulp chamber space and apical third of the root canal to achieve bleaching of dentine in root-filled. Case 1: Internal bleaching of a discoloured non-vital central incisor tooth. Home matrix bleaching Carbamide and hydrogen peroxide compounds placed in carrier trays worn by the patient at home Case 2: Dramatic effects achieved with home matrix bleaching

Case 3: A case of home matrix bleaching for digital analysis. Power Bleaching High concentration hydrogen peroxide gels placed on the enamel surface and warmed by the action of curing lamps or other forms of high intensity light. Case 4: The importance of gingival dam in power bleaching. Case 5: Power bleaching in an older adult patient. Case 6: Combining power bleaching with microabrasion. Case 7: Obvious changes in enamel surface topography with power bleaching. OPUS 10 – Diode Laser Bleaching Activation of a high concentration peroxide gel using a specific absorber and a near infrared diode laser. Case 8: Treatment of a single discoloured tooth with diode laser-enhanced whitening. Case 9: Combining laser bleaching with microabrasion. Case 10: Diode laser whitening in an older adult patient. KTP laser bleaching Activation of an alkaline peroxide gel using a specific absorber and visible green KTP laser, with concurrent photochemical reactions from the light alone. Case 11: KTP laser-treated case demonstrating importance of photographic technique. Case 12: Tooth whitening using the KTP laser. Enamel microabrasion A cyclical procedure involving prolonged etching of the surface followed by abrasion, after which the surface is allowed to remineralise. Case 13: Treatment of moderate fluorosis by enamel microabrasion. Case 14: Mild fluorosis treated by microabrasion. Case 15: Moderate fluorosis treated by repeated microabrasion over several years. Case 16: Moderate fluorosis with marked surface pitting and discolouration. Case 17: Treating fluorosis and developmental opacities simultaneously.

Odontoplasty The selective removal of small amounts of enamel to change tooth contours. Case 18: Combining odontoplasty with microabrasion. Case 19: What this patient wants is 'snow capped’ teeth. Case 20: Correcting incisal edges using selective odontoplasty and restorations. A comprehensive and thorough treatment of tooth discolouration – this has proven an extremely popular and useful title with dental practitioners – over 95% of users surveyed described this title as excellent or very good.

Sample of the Tutorial Measurement of tooth shade
Tooth shades in dentistry are described quantitatively in 3 dimensions of colour space by measurement of the value, hue and chroma. Value measures the brightness of the colour in the grey scale. Hue is the colour within the spectrum, while chroma measures the degree of saturation of a particular hue. Value can be measured independent of hue, whereas the chroma is always associated with value and hue. The perception of colour by human eyes is imperfect and is influenced dramatically by the levels of ambient light, and by fatigue of the colour receptors (cones). For example, at low light levels, rod photoreceptors dominate over cone photoreceptors, and colour perception is diminished. When human eyes stare at a particular colour for a prolonged period, the colour receptors become fatigued, resulting in a colour shift in hue toward the complementary colour. For example, if a tooth colour is visualised against green rubber dam, the hue will shift toward the red. While colour vision deficiencies are not uncommon (8% of males and 0.5% of females), common colour vision deficiencies in green and red perception are not critical in dentistry, as tooth shade selection is more dependant on the blue-yellow balance and on value. Shade guides can represent only a limited range of possible tooth colours. For example, the Vita Lumin shade guide has 16 shades, while the Dentsply Esthet•X™ has 23 shades, and the Vitapan 3D master has 26 shades. Image 1 shows the Vita shade guide arranged in order of value (from B1 to C4), while Image 2 is a black and white photograph of the same shade guide showing the increasing value from B1 to C4.

Click to see larger view.

Click to see larger view. For comparison of changes in tooth shade (e.g. before and after bleaching), the method preferred by the author involves digital analysis according to the yellow-blue axis, or more specifically, the mean pixel intensity of the blue channel (MPIb), and comparing this to two internal standards. The concept behind this was introduced into the dental literature in 1999 by Bentley and coworkers, and was developed further by the author and Dr. Jackson Liu, a graduate student at The University of Queensland.

In the 'DOTCAM' method, the internal standards are typically the shade tabs with the lowest and highest value, e.g. B1 and C4. These shade tabes are included as internal controls in each image, and the MPIb is calculated for each, once any areas of highlights (e.g. from the flash) are removed. Being white, these highlights have a high pixel value (255 on a 0-255 scale), and this skews the mean toward the higher end. Once the highlights are converted to black (which has a pixel value of zero), the MPIb for an individual tooth (X) is calculated, and finally normalized according to the following equation: (X-C4) (B1-C4) By having two internal standards, an internal scale is produced such that any variations in lighting, film processing or other variables can be accommodated for without distorting the relative MPIb for the tooth in question. The analysis can be undertaken using common image editing software. In the example below, JASC Paint Shop Pro 7 and Adobe Photoshop 5 have been used. 1. The teeth are photographed with the standards.

Click to see larger view. 2. Highlights (arrows) are selected with the 'magic wand' selection tool and converted to black. In this example, the background has also been removed for clarity, however it is not essential to do this.

Click to see larger view. 3. The tooth or standard in question is highlighted and the blue histogram information displayed. These screenshots are from Paint Shop Pro and Photoshop.

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Click to see larger view. 4. The mean histogram value for blue is recorded.

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Click to see larger view. 5. Steps 3 and 4 are repeated for both standards and for all teeth of interest. 6. The normalized value for each tooth is calculated using the equation above. This value can be compared with the corresponding value before or after treatment. The following images show the effect of changing the mean blue level.

Click to see larger view. • • • • Baseline image Blue pixel value minus 20 compared to baseline Blue pixel value minus 40 compared to baseline Blue pixel value minus 60 compared to baseline