Crown lengthening

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Crown lengthening is a surgical procedure performed by a dentist to expose a greater height of tooth structure in order to properly restore the tooth prosthetically. This is done by incising the gingival tissue around a tooth and predictably removing a given height of alveolar bone from the circumference of the tooth or teeth being operated on. While a general dentist may perform this procedure, he or she may refer the procedure to be performed by a periodontist or an oral surgeon.

There is a principal known as biologic width, which is the necessary distance that must exist between a dental restoration and the alveolar bone. This distance is approximately 3 mm, with roughly 1 mm being occupied by the periodontal ligament, another 1 mm being occupied by the soft tissue of the gingiva and the third 1 mm remaining as a morphologically acceptable gingival sulcus. When restorations do not take this distance into account and the biologic width is violated, three things tend to occur:

• chronic pain
• chronic inflammation of the gingiva
• unpredictable loss of alveolar bone

Some uneducated dentists feel that they can ignore these risks of violation of biologic width and instead of having their patients undergo a crown lengthening procedure, they simply proceed with the restoration and assert that the periodontal tissues will adapt, thus removing the necessity to surgically perform what they believe to be the "same" biologic outcome. What these dentists do not realize is that, while bone loss will occur in the area in an attempt to adapt to the violation of the bilogic width, the bone loss in such a situation will be unpredictable. Thus, instead of a 1, 2 or 3 mm that the tooth needed to be exposed to properly restore the tooth, there may be a loss of any amount of bone, from 1 mm to 5 mm or even 10 mm. No one can predict the amount of bone loss when biologic width is violated, because it is inherantly unpredictable. Thus, too much tooth may be exposed, resulting in unesthetic results and possible mobility of the tooth or teeth in question, thereby putting the patient in a much worse situation than had he or she simply undergone a crown lengthening procedure in the first place.

It is important to consider that the alveolar bone surrounding one tooth will naturally surround an adjacent tooth, and that removing bone for a crown lenthening procedure will effectively damage adjacent teeth to some inevitable extent. Additionally, once bone is removed, it is almost impossible to regain it to previous levels, and in case a patient would like to have an implant placed in the future, there might not be enough bone in the region once a crown lengthening procedure has been completed. Thusly, it would be prudent for patients to thoroughly discuss all of their treatment planning options with their dentist before undergoing an irreversible procedure such as crown lengthening.

Similarly, if the tooth, because of its relative lack of solid tooth structure, also requires a post and core, and thus, endodontic treatment, the total combined time, effort and cost of the various procedures, together with the decreased prognosis because of the combined inherent failure rates of each procedure, might make it more reasonable to have the tooth extracted and opt to have an implant placed.

[edit] References

Fermin A. Carranza. CARRANZA'S CLINICAL PERIODONTOLOGY, 9th edition, 2002.