Nancy Case Study: Material Selection Part I

In my previous articles, I've gone over the treatment planning and lab communication techniques regarding Nancy's case. The case itself 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, go by model of the temps and opposing model.

The dentists then sent this information to their laboratory and the dentist and technician were free to choose any material they believed would produce the best final result. Not surprisingly, the multiple technicians involved ended up using various materials for the crowns. In fact, of the 12 sets of crowns made, seven different materials were used. The goal of this article is to emphasize that it's the technician's capabilities to work with the chosen material that matters, not the material itself. Additionally, it is critical that there is enough reduction for the chosen material, and adequate communication or it is not possible to produce an excellent result with any material.

The first phase of the workshop was to photograph all the crowns from three different views on a lab bench, then project them so all the students could critique tooth form, surface texture and surface luster. Then all 12 sets were tried in clinically and photographed from three perspectives. The entire class reviewed the photos of each set of crowns in the mouth and what could be improved was discussed. The students then went through hands-on exercises using different crowns to learn the skills of adding ceramic, cutting back and layering, external staining, modifying form, texture and luster. Following these learning exercises they modified the actual set of crowns tried in Nancy. The following is a review of some of the materials used and clinical impressions at initial try-in.

Authentic: The set you see in the first photo (above left) is a Leucite-glass reinforced pressed ceramic that is very similar to Empress. Many technicians like to use authentic because it has ingots of the same shade but in multiple different opacities, ranging from 20 to 70 percent, providing excellent control over preps of various colors. Nancy's teeth had a very polished look naturally. What I immediately noticed when these crowns were tried in was the fact that the texture and luster didn't match the rest of Nancy's teeth. You can also notice that the distals are not flared out as much as I had requested and looked too straight overall. Another thing to point out was this particular technician used an ingot too high in opacity, resulting in the crowns appearing too high in value.

Feldspathic: This is a powder liquid porcelain built on refractory dyes. Looking at the photo (above right) the strongest issue that shows up is the translucency of the incisal edges. The deep blue translucency and the glazed surface didn't match her natural surface texture and luster. You can also see that this technician tried to line up the teeth much more than I did in the temporaries.

The problem with this is that the teeth were prepared based upon the form of my temporaries. If the technician tries to straighten out the alignment by bringing the distals in, as we see in this example, the thickness of the restoration will go down to around .5mm and the underlying prep color may show through. In this case the right central is definitely lower in value in the middle because the prep is showing through. This is not a case of inadequate reduction, simply the challenge of creating a contour different than the one the teeth were prepared for. As far as the material goes, Feldspathic ceramic restorations can be beautiful, but it's really about picking the right body and enamel materials, controlling their thickness and how the technician layers them.

In Part II, I'll discuss e.max restorations.

Read Part III, the Final Restoration.