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Question: How do you decide between functional crown lengthening and extraction?
The ability to predictably and successfully replace lost or severely damaged teeth with dental implants now makes the decision on whether to perform crown lengthening or extracting a tooth more difficult. When making this decision, there are several factors that must be considered.
Close evaluation of the tooth in question is required. How extensively is the tooth compromised? Each clinical situation will be different. One parameter that must be evaluated is what will the crown-to-root ratio be after the crown lengthening is performed. If this ration is less than 1:1, an extraction with implant placement will usually be the more predictable option. If the tooth has had extensive restorative treatment, had a root canal, and/or extensive decay, we know that the tooth is probably structurally compromised. Therefore, the long-term prognosis of the tooth is compromised, and an extraction with an implant replacement may be the better option for the patient.
However, if the tooth has not had a lot of restorative dentistry and/or there appears to be a significant amount of healthy tooth structure remaining, then functional crown lengthening may be an excellent option.
Another consideration is the dentist’s clinical experience. For example, say a maxillary central incisor is fractured to the level of the soft tissue. A dentist with experience with anterior implants may be very comfortable and successful with the extraction and an implant restoration. Conversely, a dentist with little implant experience may be more successful with functional crown lengthening (possibly including orthodontic extrusion) and placement of an all-ceramic crown. The same situation with two different dentists with two different backgrounds can potentially both provide excellent results.
Most important to remember is that the patient should be provided with treatment options. Along with those options, the risks and benefits need to be discussed so that the patient can make an informed decision. If the dentist and the patient have good communication and the patient is properly educated, the patient will be in a position to make a well-informed decision as to how they would best like to proceed. There can be no poor choices if the dentist and patient are openly communicating. With good communication, there is a mutual understanding and agreement of how to proceed with treatment in hopes of obtaining the best possible outcome while clearly understanding the inherent risks associated with the treatment that was mutually decided upon.
One must evaluate the patient’s general and site-specific risk factors to make a determination whether to restore or extract a compromised tooth. The first parameter to be contemplated is the location on the tooth where crown lengthening is required. Crown lengthening on the facial aspect of a tooth will change the position of the free gingival margin. If the facial free gingival margin is coronal to the desired position, then crown lengthening may satisfy both the esthetic and the biomechanical requirements. In instances where the pretreatment free gingival margin is equal with or apical to the desired position, then pre-surgical orthodontic extrusion can counter the negative esthetic effects of crown lengthening; however, orthodontic extrusion must not create a situation that exceeds a minimum of a 1:1 crown-to-root ratio. The esthetic implications of the emergence of the final restoration on a narrower root form must also be considered.
Crown lengthening interproximally often results in a loss of papilla height and the unfortunate consequence of open cervical embrasures, also undesirable in the esthetic zone. Crown lengthening resulting in bifurcation exposure may make daily hygiene more difficult. Certainly, a patient at high risk for periodontal breakdown would not be a good candidate.
In addition to the esthetic and periodontal factors, the biomechanical risk factors must be measured. Although achieving a 2-mm ferrule on the buccal and lingual aspects of the tooth has long been considered sufficient to satisfy the functional demands placed on the restored tooth, the literature suggests the height of the interproximal ferrule plays a role in resistance and retention form, especially when the restoration involves multiple teeth as in a fixed partial denture. The patient’s susceptibility or resistance to future caries must also weigh into the decision. Patients with greater susceptibility to decay have a poorer prognosis for the long-term retention of a structurally compromised tooth.
All manner of functional demands specific to the situation must be considered when making the decision to restore or remove a structurally compromised tooth, such as the location of the tooth in the mouth and whether the patient exhibits signs of acceptable or pathologic function. Signs of parafunction or premature loading of teeth during function decrease the long-term prognosis for a structurally compromised tooth.
Although functional crown lengthening provides a viable adjunct in our ability to restore a compromised tooth, it comes at the price of removing bone—bone that may be beneficial should the tooth eventually be lost and the need for an implant arise. We best serve our patients when we approach the consideration for functional crown lengthening beyond the viewpoint of the individual tooth in question and evaluate all of the patient’s presenting factors.
This is a topic that has guidelines, but a review of the scientific literature produces few hard and fast rules. The goal would always be long-term predictability of the outcome, and it is important to understand the overall risks of the patient. These include periodontal, biomechanical, occlusion, and dento-facial or esthetics. Single-tooth decisions should be made in the context of the overall treatment goals for the patient. Then decisions regarding viability of individual teeth make more sense in the big picture. In this case, if the professional performs the functional crown lengthening, have they reduced the risk of restoration failure, versus the predictability of alternative restorative options following an extraction? Which alternative provides the patient with the best evidenced-based outcome?
There are multiple variables the professional should consider when facing this question. The most obvious is, as my colleagues have mentioned, what is the crown-to-root ratio before and after the crown lengthening? Although an ideal crown-to-root ratio may be 1:2, a ratio of 1:1.5 may be acceptable if there is healthy periodontium and the occlusion is controlled. Ideally, the tooth would have at least 8 mm of root length in bone; less length would increase risk. A ratio of 1:1 may even be acceptable if the opposing occlusion is a tissue-supported prosthesis. Is this a single-tooth restoration or an abutment for a multiple unit prosthesis? A prosthesis will place additional stress on the existing root. In addition to crown-to-root ratio, after the procedure will there be sufficient ferrule height for a successful restoration? Is the tooth vital or non-vital? A non-vital tooth is already more biomechanically compromised.
This brings up two important variables—what is the condition of the periodontium and what does the opposing occlusion look like? Is there mobility? Is the tooth being super-erupted? Will the creation of a new gingival height affect the esthetics? Is the opposing occlusion on a natural tooth or a prosthesis? Additional variables should include the history of the tooth, such as whether this was a dental caries problem or caused by restoration/tooth failure or trauma. What is the caries risk and history for the patient? A high-caries-risk patient places additional future risk on a restoration from a decay standpoint in addition to the biomechanical issues. Does the professional have a known history with the patient, and after communicating the risks and alternative, what does the patient want? If a compromise is being made, is the patient willing to accept the reasonable risk of the compromise?
Although this seems like a rather innocuous question with a simple answer, there are many variables that the professional should consider prior to making a decision. And that decision should include a well-informed patient and be based on our best evidenced-based predictability of the treatment outcomes.
About the Authors
Gary M. Radz, DDS, is associate clinical professor at the University of Colorado School of Dentistry in Denver, Colorado, and a dentist in private practice in Denver, Colorado.
Betsy Bakeman, DDS, is a mentor at the Kois Center in Seattle, Washington, and a dentist in private practice in Grand Rapids, Michigan.
V. Kim Kutsch, DMD, is a mentor at the Kois Center in Seattle, Washington, and a dentist in private practice in Albany, Oregon.