As I stated in part I of this series, the Nancy case study was used as part of a three-day ceramic enhancement workshop. Each dentist who signed up for the course was given the shade photographs, final impression, the go by model of the temps and the opposing model. The following is a review of some of the additional materials used and clinical impressions at initial try-in.
e.max: There are three ways the technician can work with this this material. The original version of Lithium disilicate, Empress II, was initially designed to be used as a coping with powder and liquid glass ceramics then applied to it.
This approach is still an option with e.max today, and can work very well when an opaque e.max core is fabricated to cover a dark prep or post and core, and then stacked ceramic is applied over the opaque core.
Far more common today, the material is fabricated as a full contour restoration and then either externally colored or the incisal is cut back and layered. The major advantage of the externally colored, or monolithic version is strength. The advantage of the cut back and layered version is esthetics.
This set of e.max was done as a monolith and externally stained, whether this approach is successful esthetically has everything to do with the teeth you are trying to match. If the teeth are uniform in color, without a lot of internal characterization in the body or incisal edge, then external coloring can be successful. It can be challenging however to apply the stain evenly on both units and to create the same color.
On these two units the right central has definitely had additional blue colorant applied to the incisal 1/3. In addition from a surface point of view, externally staining doesn't give you the same control over surface texture and luster you get with layering, followed by texturing and then polishing to achieve the correct surface. In fact the glazed surface of these two crowns is slightly different, the right one having a slight bit of orange peel texture while the right is very smooth.
Finesse: This set of crowns was fabricated by the same technician that created the e.max restorations. What you immediately notice is that the two centrals are two different shades, but the incisal edges are fairly similar. These teeth are on the thin side because the distals have been brought back too much, resulting in the right central being .4mm to .5mm thick on the facial, allowing the slightly discolored prep to show through. In addition, I'm fairly certain there is much more external stain on the right central that amplifies the shade difference between the two even more.
What I hope you're realizing in this article is that the materials really aren't making the difference – it's what the technician chose to do. The technician that followed the Rx the most accurately is featured in the final photograph; they chose to use Feldspathic.
However, it wasn't the fact that they were Feldspathic that made them the best; it was that they incorporated the correct tooth form and alignment that resulted in a uniform 1mm facial thickness. In addition they got the shade, surface texture and surface luster all in the ballpark. The same could have been done with any of the materials described above. So when dentists ask what the best material is for anterior esthetic restorations, my answer is always the same. It is the one your technician knows the best and does the best, because it is all the other factors that make the biggest difference in the final result.
Read Part III, the Final Restoration.