October 2008, Volume 4, Issue 9
Published by AEGIS Communications
Question: When is functional crown lengthening appropriate vs extraction?
Betsy Bakeman, DDS; Gary M. Radz, DDS; Lee Silverstein, DDS; Peter C. Shatz, DDS
When extending margin placement onto sound tooth structure would infringe on biologic width or there is a need to gain access to greater tooth structure to establish appropriate ferrule, functional crown lengthening becomes a consideration. The consideration for functional crown lengthening often arises when there is a cervical loss of tooth structure caused by caries or fracture. Crown lengthening can be an appropriate approach to gain access to sound tooth structure when certain parameters can be met.
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. This may be viewed as favorable or unfavorable depending on the pretreatment situation and whether the tooth in question is visible in the esthetic zone. If the facial free gingival margin is coronal to the desired position, then crown lengthening may very well 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 crown lengthening may satisfy the biomechanical requirements of the situation, but at the expense of the esthetic requirements. Pre-surgical orthodontic extrusion can counter the negative esthetic effects of crown lengthening in these situations. Orthodontic extrusion must not create a situation that exceeds a minimum of a 1:1 crown-to-root ratio. The ultimate emergence of the final restoration on a narrower root form and the esthetic implications of this must also be considered.
Crown lengthening interproximally will result in loss of papilla height if a horizontal bone defect is created between adjacent teeth. If the osseous architecture is altered in such a way as to create a vertical defect, with bone removal only occurring adjacent to the tooth that is in need of crown lengthening, the more coronal bone of the adjacent tooth will support the papilla height at or close to the pretreatment situation. However, an increase in the probing depth interproximally on the restored tooth can result. When crown lengthening would result in bifurcation exposure, the ability of the patient to have access to clean these areas must also be considered. Certainly, a patient that is at high risk for periodontal breakdown would not be a good candidate.
In addition to the esthetic factors, the biomechanical risk factors of the patient must be measured. While 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.
With the high long-term success rates for implant-supported restorations, it is important to measure all of the factors that go into a decision to restore or remove a tooth beyond the consideration to crown lengthen the tooth. While 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.
With the improvements in our clinical surgical techniques and the proven effectiveness and predictability of implants, the line between when to crown lengthen and when to extract has become more and more indistinct. I believe there are a couple of major considerations.
First, each tooth is different and requires a specific treatment recommendation. For example, a patient presents with a lower second premolar that has had endo-dontic treatment and has fractured at the level of the soft tissue. The strong recommendation would be to extract and place an implant. Conversely, another patient presents with a lower first molar with a class II amalgam and a fractured mesial buccal cusp that terminates below the level of the soft tissue in an otherwise healthy tooth. The recommendation would be to perform crown-lengthening surgery. These are two examples of the far ends of the spectrum, and clinically we see these and many other situations in the middle of this spectrum.
The second consideration is the dentist’s clinical experience. An example would be an endodontically treated maxillary incisor that has fractured close to the soft-tissue level. A dentist with a lot of clinical experience in anterior implants may be very comfortable with extraction and placing an implant and have excellent esthetic results. Another dentist with less implant experience may choose to perform crown lengthening (or even orthodontic extrusion) and place a post and then a crown. This dentist may be able to get an excellent esthetic result.
Most importantly, the patient should be given the options that are available and the risks/benefits associated with these options. Then, the dentist and the patient can communicate on how to best deal with the situation that has presented. There can be no poor choices if the dentist and the patient are communicating. There is only an understanding of risks and potential outcomes that both agree to pursue together in an effort to provide the patient with the best outcome that modern dentistry can provide.
Dr. Silverstein and Dr. Shatz
Functional crown lengthening is a periodontal surgical procedure that is usually used to increase the size of the available clinical crown, expose the entire anatomic crown, or establish the proper amount of biologic width. Crown-lengthening procedures are very predictable and should be performed using a systematic approach. The goal of the crown-lengthening therapy is to enable the dentist performing the restoration to develop an adequate area for retention of the restoration. Without functional crown lengthening, the restorative margins may extend deep into the periodontal tissues and possibly invade the biologic width. This then would cause a resorptive response by the body, leading to uncontrollable loss of alveolar bone, probably to a greater degree than anticipated. In normal clinical situations, crown lengthening should be performed around teeth with sufficient alveolar bone to give them a good to fair long-term prognosis.
To perform functional crown lengthening, a periodontal flap procedure is used to gain access to and visualize the underlying alveolar supporting bone so that the alveolar crestal bone can be manipulated and reshaped. This procedure is best accomplished with an apically repositioned flap followed by the needed amount of ostectomy (removal of tooth-supporting bone) to establish the required biologic width, the distance between the proposed restorative margin, and the alveolar crest. It is very important for the clinician to remember that bone is like the Holy Grail, and its removal should be done with great caution and no more than what is necessary should be removed. When performing ostectomy during the crown-lengthening procedure, there must be at least 3 mm established between the most apical extension of the proposed new restorative margin and the alveolar crest of bone. Establishment of biologic width will allow sufficient space for the gingival attachment complex to reform. This complex includes the sulcus, the junctional epithelial attachment, and dentogingival fibers.
With the aforementioned background information, the following questions can now be asked: When is it appropriate to crown lengthen a given tooth? When is extraction of the affected tooth the better option? Crown lengthening could be performed predictably if the following criteria are expected to be met after crown lengthening and the establishment of adequate restorative margins: sufficient residual alveolar bone surrounding the tooth following treatment, no more than Miller class I dental mobility, and satisfactory restorative margins. Adjunctive procedures, such as orthodontically forced eruption, also should be considered as part of the treatment-planning process. However, if tremendous loss of periodontal support—for instance, 50% horizontal bone loss coupled with class II or III tooth mobility—is expected, then crown lengthening should not be a recommended option, and extraction would be the treatment of choice.
Furthermore, if crown lengthening could be performed functionally because the teeth are stable, not mobile, surrounded by healthy periodontal tissues, but the proposed final restorative margins are expected to be so deep that the final restoration would be anything but cosmetic, then the authors believe that extraction followed by the replacement with either a dental implant or fixed partial denture would be a better treatment choice.
Lastly, if the recurrent decay was so deep into the tooth and under the existing gum line that after crown lengthening and removal of all the recurrent decay the tooth would become class II or III mobile, or the tooth was so undermined by the decay that there seemed to be a high probability of tooth fracture after restoration, then the authors believe that extraction rather crown lengthening would be the better treatment of choice.
About the Authors
Betsy Bakeman, DDS
Grand Rapids, Michigan
Gary M. Radz, DDS
Associate Clinical Professor
University of Colorado School of Dentistry
Lee Silverstein, DDS
Associate Clinical Professor of Periodontics
Medical College of Georgia School of Dentistry
Peter C. Shatz, DDS
Assistant Clinical Professor of Periodontics
Medical College of Georgia School of Dentistry