Cracking Crowns

In the dental laboratories around the world, we are now fabricating the hardest crowns and bridges in the history of the dental industry. Zirconia has the hardness of the diamond on the left hand of our loving wives’ fingers. I remember when the thought of the Zirconia crown was being introduced to the dental world, they showed videos of someone hammering a molar into a piece of wood until it had practically disappeared. And behold, when it was retrieved, it was still as good as new. They even told us, “You can cut glass with it!” Although, we found out that it wasn’t such a great feature when the zirconia was opposing a porcelain crown.

So, after all this “hoopla,” they should never break, right? I would guess you already know the answer to that. But there are ways to take some control of the unanticipated event. We have to keep in mind that even though the Vickers’ hardness of Zirconia can be twice that of porcelain, some of the same rules still apply.

One classic problem is overheating the crown. If you are seeing sparks fly while you are adjusting, you might want to slow it down. The aggressive approach can cause micro fissures that aren’t apparent when the patient is still in the chair. You may think all is well until you get that phone call about a broken crown. Micro fissures are like a chip in your windshield. With each bump the problem grows. Patience is key when adjusting. A little water will also have a great cooling effect, reducing the chance of fracture.

A preventive measure can also be taken that proves to be helpful. When preparing the tooth, it is a good idea to avoid a feather edge margin. A chamfer style is more structurally promising. The more depth around the perimeter you can get, the more thickness you can gain to avoid chipping.

The diamond in my wife, Patti’s ring, will probably never chip. That is only because precautions were taken by the jeweler to make sure it was in good condition before it was seated, and the requirements were prepared so it will be sure to stay in its proper place.

Ned LaMarti, CDT