How to Troubleshoot an Unclear Margin
Posted on 08/12/2011
While we all strive for perfection, dentistry, like life in general, is often faced with challenging circumstances that limit our ability to perform perfect work. Not all tooth preparations are perfect. The die tech may miss the margin. These are, unfortunately, the reality of doing business even with all the advancements in CAD technologies.
The question really is what to do in circumstances where the margin is just not clear. As a lab, of course, we would love to assume that the doctor can bring the patient in again for another impression. But often that is just not possible. Sometimes it's an upper molar where the patients cannot sit still. Other times, due to excessive bleeding, the doctor cannot capture the margin in the impression. These, and many other, situations occur on a daily basis in our industry.
Through our experience, we have developed the following recommendations to improve communication between dentist and our lab and help trouble shoot difficult cases where the margin is difficult to read. Here are a couple of the recommendations:
1. Make sure your tech is familiar with your general finishing line. As long as the tech knows to look for a bevel, he probably will make the extra effort even if the impression is not 100% clear. However, if he thinks your prepping a chamfer with no bevel, you may end up with short margins.
2. If you decide to change your general finishing line for a specific case (i.e. use a feather edge prep instead of a chamfer), please indicate it on the Rx.
3. If you think the margin may be unclear and it may be impossible to get a better impression, we recommend to slightly overextend the margin in metal (about 0.5mm) on a PFM. With high noble alloys, you can probably burnish the metal to adapt it to the margin.
4. If you are doing an All Ceramic, an unclear margin is really difficult to troubleshoot. There is no way to manipulate the material (whether e.Max, Empress, Zirconia or others) and the risk of fracture is quite high. We recommend to change the restoration to a PFM or Full Cast crown.
The question really is what to do in circumstances where the margin is just not clear. As a lab, of course, we would love to assume that the doctor can bring the patient in again for another impression. But often that is just not possible. Sometimes it's an upper molar where the patients cannot sit still. Other times, due to excessive bleeding, the doctor cannot capture the margin in the impression. These, and many other, situations occur on a daily basis in our industry.
Through our experience, we have developed the following recommendations to improve communication between dentist and our lab and help trouble shoot difficult cases where the margin is difficult to read. Here are a couple of the recommendations:
1. Make sure your tech is familiar with your general finishing line. As long as the tech knows to look for a bevel, he probably will make the extra effort even if the impression is not 100% clear. However, if he thinks your prepping a chamfer with no bevel, you may end up with short margins.
2. If you decide to change your general finishing line for a specific case (i.e. use a feather edge prep instead of a chamfer), please indicate it on the Rx.
3. If you think the margin may be unclear and it may be impossible to get a better impression, we recommend to slightly overextend the margin in metal (about 0.5mm) on a PFM. With high noble alloys, you can probably burnish the metal to adapt it to the margin.
4. If you are doing an All Ceramic, an unclear margin is really difficult to troubleshoot. There is no way to manipulate the material (whether e.Max, Empress, Zirconia or others) and the risk of fracture is quite high. We recommend to change the restoration to a PFM or Full Cast crown.