Why does my crown keep coming off?

For a crown to withstand the forces of mastication and sticky food, the underlying tooth has to be shaped with precision. It has to be long enough to provide enough surface area to grab the cement and be only slightly tapered. If the prepared tooth resembles a short pyramid, it may not hold the crown. This is why preparing a tooth for receiving a crown is a process, that requires rigorous planning, use of good lighting and magnifying lopes and experience.

Another possible reason for the crown coming off, is poor fit. After tooth preparation, the following delicate step is making a precise copy of it’s shape. If the shape is not accurately copied the crown does not hug the tooth well enough for the crown to stay put. It is like when 2 pieces of furniture don’t have good joinery they are only held by the glue and separate easily. The space between the crown and the tooth should be minimal in order for the “glue” to provide maximum adhesion, since the glue is many times the weak link. Sending the “copy” of the tooth to an excellent dental technician is another important ingredient to a successful outcome.

When a patient presents with a permanent crown that comes off, many dentists will first try to cement it without trying to identify the reason why it came off. In my practice, I first examine to see what was the reason that led to the separation.  Frequently I find that preceding the crown coming off, the poor preparation or fit, allowed bacteria to establish themselves and the tooth has already been broken down by decay too. Before re cementing the crown I remove the bacteria, debris of old cement and the decay to allow for a good fresh bond between the crown, cement and tooth. I cement it using the strongest cement. But many times the initial cause that led to the crown coming off previously, persists and even with the strongest cement, we do not always achieve a long term solution and I am faced with the need of making the crown over. When I do so, I pay special attention to correcting any shortcomings in the preparation and I make sure that I send to the dental technician a perfect copy of the tooth.

There can be other reasons for crowns coming loose. If the way teeth come together  is unfavorable, crowns can be more likely to come loose. This is the reason that before providing a tooth with a crown, there should be sound planning. Some patients have a large overlap between their upper and lower front teeth which is called, a deep bite. The outcome of having a deep bite, are high horizontal forces on the teeth and crows, which can lead to teeth or crowns breaking or come off. Other patients have habits that are just not that friendly to crowns, such as eating pencils or very hard and sticky candies. When chewed often these sweets, tend to loosen even well fitting crowns.

If you are having issues with a crown that keeps on falling off, please call Tooronga Family Dentistry, Phone number 98227006.