cosmetic dentistry_ beauty & science

I 09 special topic _ shade analysis I cosmeticdentistry 1_2012 Fig. 12_Image demonstrating chroma levels with the 3D-Master guide. Fig. 13_Image demonstrating chroma levels with the Linearguide. Fig. 14_Choosing the chroma for a patient case. The same image can be used to determine whether the teeth are redder or yellower than the M hue group shown. Fig. 15_Image of hydrated tooth with shade tab. Ibelieveisthefundamentalreasonforthe levelofshademismatcheswiththisguide. Thefirststepinminimisingthisproblem and using this shade guide effectively is to arrange the guide by value as shown. As statedearlier,choosingthecorrectvalueis most important, as is recording the value zones within the tooth being evaluated. After arranging the guide by value, lightly wet the teeth and shade guide with a clear glazeliquid.Thebestwaytochooseashade is not to see first what appears to be a match, but to lookfirstforobviousmismatchesandeliminatethem fromtheshadeguide.Thegoalistoeliminateenough tabs so that you have remaining a range of tabs in which clearly one tab is slightly higher in value and one tab is slightly lower in value. Experience has shown that no fewer than four tabs will accomplish this value range determination (Fig. 6). Several im- ages will be taken and the discussion of how to do it andtheimportanceofcalibratedimageswillcomein the next section. Next, to narrow and simplify the chromaandhuechoices,IuseasecondVITAClassical guide set up conventionally, that is A series, B series, C series and D series. I have found at this point that I can work with just the A and B series. I evaluate the A shades that are in the red-yellow (orange) range and then the B shades next to the teeth. I determine whether the teeth appear to have an orangish or yellowish hue. If they appear yellowish, I use the Bshades;iftheyappearreddishororangish,Iusethe A shades. I then hold up either the A or B shades next totheteethtochoosetheappropriatelevelofchroma and take chroma images (Fig. 7). VITA3D-MasterShadeGuideand theLinearguide The3D-Masterwasdevelopedtobeabletocover the range of measured natural teeth.15 More re- cently, the Linearguide was developed. It is the same shades as the 3D-Master but in a much better tab holder that allows more accurate positioning and evaluation. Because of the similarities be- tweenthetwo,Iwilldescribetheiruseconcurrently. Over ten years of personal experience has shown this to be the superior shade- analysis system. The system is arranged first around choosing the value. There are six value levels that are equally spaced 5 E apart within the colour space.14 E is a mathe- matical measurement of the distance between two points in colour space—the human eye can only differentiate points that are greater than 2 E apart. I have found that the L and R shades can be removed from the shade guide, leaving only the M shades (Fig. 8). This vastly simplifies the value- taking process. The procedure for choosing the value is best done by a process of elimination as described earlier. The two or three closest value groups are chosen so that the range has something that is perceived as slightly higher in value and something slightly lower in value than the natural teeth (Fig. 9). With the Linearguide, it is even easier. Thesixvaluegroupsareintheirownholderandtabs can be evaluated more easily (Fig. 10). Again, work by a process of elimination, choosing two or three of the closest values (Fig. 11). Several value images are then taken. Thenextstepistodeterminethelevelofchroma, of which there are three in most of the M shades. They are labelled 1, 2 and 3 (Fig. 12). Again, it is best accomplishedbyaprocessofelimination,recording the closest match or noting if it is between two chromalevels.Thechromalevelsareallexactlyequi- distant from each other within the colour space. With the Linearguide, all the different chromas of all three hues are in a special holder (Fig. 13). Using thissystemmakesiteasiertodeterminewhetherthe chroma is at an in-between level. I pass the chroma guide of the closest value in the same plane as the natural teeth and then photograph the two closest chromas (Fig. 14). The last step is to choose the specific hue. If the value and chroma are matched, experience has shown that an observer would not notice a shade Fig. 13 Fig. 15 Fig. 12 Fig. 14