Crown therapy is an option in broken or diseased teeth. Rarely is it medically necessary, although it can improve function and aesthetics of the teeth. Crowns are predominately fabricated to increase the strength and size of a fractured tooth.
Crown therapy is a very common treatment in human dentistry where aesthetics are of prime importance. However, it is not near as common in animal dentistry. Any fractured tooth can be crowned, however it is not always done. There are several reasons for this. The first reason is financial, crowns are typically as or more expensive than the root canal procedure itself. Secondly, due to the curvature of the canine teeth in dogs, shaping the tooth to accept a crown can actually weaken the tooth. This is only true if the tooth is only broken slightly. Finally, an additional anesthetic is required to place the crown after it has been created.
Cast metal alloy, full coverage crowns in a Schutzhund dog placed to prevent wear from bite sleeve training.
One indication for crown therapy is a severely damaged tooth, or one that will likely undergo more damage if left unprotected. A crown can be used to rebuild the loss of the enamel bulge on a fractured tooth. This is an outcropping of the tooth just above the gumline that protects the gums from trauma caused by normal chewing activity. Another indication is in working dogs. Police, Schutzhund and agility dogs may have severe wear or fractures and will likely continue to damage their teeth and in many cases would benefit from a protective crown. Teeth that have significant structural disease with or without fracture should be crowned. The most common syndromes in this class are
enamel hypoplasia and fence chewer or cage biter
Crown therapy in dogs and cats can be an effective tool for maintaining the tooth, as well as increasing the size of the remaining tooth. However, due to the tremendous bite forces animals can develop, there are limits to our ability to increase crown height. The crowned tooth cannot be the same as it was. The incisal edge (tip) of the tooth should be less then the height of the corresponding normal tooth. This is because we want the normal tooth to take more of the trauma. In addition, you cannot build up a tooth completely that is broken off at or near the gum line. The reasons for these rules are physics, the crowns can be made, but they will in all likelihood be broken off due to leverage.
Some of the size limitations can be extended by the use of post and core build-ups. This is accomplished by either gluing a metal post in the root canal and building up an area of restorative material around it, or by creating a mold of the root canal and having the post made as part of the crown. These are very advanced procedures, but can be effective if done properly. However, physics still applies, and we cannot completely rebuild a broken tooth.
The next consideration in crown therapy is the type of material used. The most common is cast metal, titanium, or stainless steel. This crown material is the strongest available, and requires the least crown removal. This is the crown material of choice when strength is more important than aesthetics. “White crowns”, which are porcelain fused over a metal crown, are used in people for the aesthetic properties. However there are several reasons that we do not use these often in animals. First, it is difficult to match the tooth color in animals; this limits usefulness in show dogs, as a judge can usually notice. Second, since there
are two layers, the crown preparation must be thicker than for metal crowns. This further reduces the strength of the crown/tooth structure. Finally, over time the patient will invariably damage the porcelain and therefore expose areas of the base metal underneath. There are some new materials being developed currently to enhance the aesthetics of the crown, while not sacrificing as much strength. “Inceram” is an all ceramic crown that is being developed for use in people and animals. The crown is only slightly thicker than a metal crown, and almost as strong. It is not a perfect tooth match, but from a distance looks good. I would not use this material in a working dog, but for a pet it can be a good choice.