Inside Dental Technology
Overcoming Bias in Restorative Material Choices
Better ways of doing things sometimes call for change.
Understanding how to build a crown properly can take a lot of time and a careful study of materials and processes. Whether in an academic environment or through an apprenticeship, a “correct” step-by-step method must be learned and mastered. Successes and failures both in the laboratory and in the oral environment help to influence opinion on the efficacy of the learned fabrication processes. Through these experiences, dental laboratory technicians may understandably amass a bias toward restorations that have been successful in their hands, even though better choices may exist.
After finding a predictable comfort zone doing things successfully a certain way with the same materials can be hard to change. Change can be scary. Change can lead to remakes or unwanted long hours in the laboratory. Often technicians find themselves influenced by advertising and manufacturer hype promoting a new material as the latest and greatest, only to find that it is either not what was promised or that it doesn’t meet their clients’ expectations. This may lead them to be wary of newly proposed products or methodologies. It is logical for both clinicians and technicians to want to stick with what is “tried and true,” so when restorative materials are considered, both sides tend to base their decision on what they know works, assuming it is the best choice for the patient and situation. But this may or may not be true; the decision may be a biased one.
One such bias in restorative material choice that is often heard—especially by ceramists, including the author—is that a monolithic stained and glazed crown cannot look lifelike or otherwise as good as a traditionally layered crown. After years of perfecting a build-up style using multiple porcelains that can mimic nature in both shade and shape, it is counterintuitive to think that it could possibly be done any other way.
Dental technicians can be lulled into a state of complacency or even overconfidence by how their restorations look on the model or benchtop. It is only when viewed from the oral environment that their esthetic success can be truly judged. This is a great way to help overcome restorative material bias.
The following two cases demonstrate this point. The first restorations are traditionally layered porcelain-fused-to-metal (PFM), while the second is monolithic lithium disilicate.
The dentist of a 48-year-old man had prescribed PFM crowns for teeth Nos. 2 and 3. The patient came to the laboratory for a custom shade., A combination of four and five shades were selected using VITA’s 3D-Master® shade guide (Vident, www.vident.com) (Figure 1 and Figure 2).
The crowns were built using a variety of modifying porcelains designed to capture both the deep orange and the whitish highlights found in the patient’s dentition (Figure 3).
The crowns, when placed on the model, seemed to have achieved the desired shade and character (Figure 4).
The crowns were conventionally cemented, and both doctor and patient were pleased. The patient then came back to the laboratory for postoperative photographs. Upon initial viewing from the buccal vestibule, the crowns appeared to acceptably blend with the natural dentition (Figure 5). It wasn’t until they were viewed from the occlusal aspect did they appear to be lacking. The orange that seemed to so well define the crowns was barely visible; it was all but washed out, leaving overly defining whitish cusps (Figure 6). It showed that even well executed PFM crowns can be defined by the metal and its lack of light transmission.
While both doctor and patient were initially pleased, was this the best possible choice? The author thought so when fabricating them. Layering porcelain on a metal framework can be the most conservative, esthetically best, long-lasting restorative choice. But was this actually the case, or is it because it is in the author’s comfort zone? If striving for esthetic perfection, could it have been done differently? One possible answer to this question is found in the second case.
A 45-year-old man presented needing full crowns on teeth Nos. 14 and 19. The case was discussed with the dentist, and two monolithic lithium disilicate crowns were prescribed. Doing this type of restoration was out of the comfort zone of both the author and the clinician. They were concerned that the crowns would not have the detail or the vitality found in conventionally layered porcelain crowns. The choice was made because of the strength of pressed monolithic lithium disilicate and the patient’s desire to avoid metal.
The crowns were waxed to full contour, focusing on the proper tooth morphology for the patient (Figure 7 and Figure 8). A custom shade was taken at the laboratory, and a modified 2M1 shade was chosen. The crowns were pressed out of Ivoclar’s IPS e.max® BL4HT ingot (Ivoclar Vivadent, www.ivoclarvivadent.com). This would allow the cusps to be lighter and the body color and characterizations to be achieved with extrinsic stains.
Contrary to initial concerns, the detail of the wax-ups was not lost in pressing (Figure 9 and Figure 10). In fact, the concerns were completely unwarranted, as shown with the help of silver powder (Figure 11).
The crowns were stained to match the adjacent teeth, and a surface glaze was applied. When the crowns were viewed alone out of the mouth, the color seemed too intense (Figure 12). But when the crowns were seated, both doctor and patient were pleased. The patient came to the laboratory for postoperative photos. The crowns, when viewed intraorally, appeared to have achieved the desired goals (Figure 13 through Figure 15). They were lifelike and vital, all while providing a strong conservative “all-ceramic” restoration for the patient. The color saturation that seemed too intense on the benchtop blended nicely in the mouth.
The esthetic success of the restorative material choice is supported even more by the full-arch maxillary photograph showing the PFM crown on the contralateral side and its contrast (Figure 16). This is when the author overcame his own bias for traditionally layered crowns.
Choices are made by both clinician and technician based on experience, and rightfully so. That being said, it is important to acknowledge that even after achieving success or mastery with a certain process, material, or methodology, it can be hard to imagine that there might be a better way of doing things, or at the very least, an additional way of doing things. It takes a long time to master techniques. Very few people like change. It is important when drawing conclusions on the best restorative choices that it not be unduly influenced by bias. Sometimes there are better ways.
About the Author
Kyle Swan, CDT
Functional Esthetics, Inc.