When patients enter the dentist office with a "cracked tooth" it is generally because part of the tooth has actually fractured off leaving the dentin or even nerve exposed. In the vast majority of cases, the tooth cracks because it already had a large dental filling in it, and the remaining real tooth structure was not strong enough to handle the forces of chewing. Without a doubt, this happens because a filled tooth is substantially weaker than an unrestored or "virgin" tooth. When doing a filling, it is the dentists job to remove all of the decayed tooth structure and replace it with restorative material. In the past, this was usually done with amalgam. Currently , dentists prefer composite resins which are tooth colored and actually bond to the tooth. This helps hold everything together, but most of the stress the tooth receives in function must be managed by the tooth structure left over and not the filling. When a tooth has a large dental filling and even more of it fractures away, there is even less healthy tooth structure to handle the forces of mastication. Since there was not enough tooth to handle the forces with the existing dental filling in place, it is very unlikely that a larger filling (replacing the old dental filling and the newly fractured piece) could be placed that would last very long. In these cases the dentist is forced to place a dental crown on the tooth. This is a cast or milled restoration that fits over the entire tooth and holds it all together. They are extremely strong and designed to have the same shape and appearance of the original tooth. They are cemented over the remaining healthy tooth structure and should be extremely precise so that no bacteria can get back under the dental crown.
Often times patients come in and they have been told they have cracked teeth and that they need crowns. Just because you can see craze lines in the enamel of a tooth does not mean you need a crown. In fact, if you use high enough magnification and good lighting you can find micro cracks in most teeth. What our dentist practice uses to determine if a dental crown needs to be done is to find out if the patient is experiencing pain or if the softer dentin of the tooth is exposed. The pain associated with a cracked tooth is either a sharp pain while biting or discomfort when pressureis removed from the tooth. This pain might be intermittent because it only hurts when it hits in just the wrong way. It is important to restore these teeth because if cracks proliferate in the wrong direction they will lead to either a root canal or possible extraction. Teeth that crack vertically up the root and under the bone line can not be successfully restored even with a dental crown.