Written by David P. Pitman, DMD Thursday, 31 October 2002 19:00
Teeth needing restoration should have all caries removed. When this is accomplished, adequate supragingival tooth structure may not be left to allow placement of an ideal restoration. To remedy that situation, surgical crown lengthening may be required. This article presents a rational approach to crown-lengthening surgery that can be used to enhance the clinical outcome.
The goal of crown lengthening is to increase the clinical crown of a tooth (that portion of the tooth which is above the gingival margin). There are several indications for the procedure, including: (1) caries that extends apical to the gingival margin; (2) tooth fracture, endodontic or post perforation, and cervical resorption that is repairable following crown lengthening; (3) inadequate tooth structure for crown retention. Teeth with minimal clinical crowns, if unmodified, can result in crowns that are subject to repeated loosening; (4) ease of taking the final impression for a crown or crowns can be improved by crown lengthening performed prior to the impression; and (5) aesthetic dilemmas such as an excess amount of gingiva, asymmetrical gingival margins, and hyperplastic tissue. Often endodontic therapy and crown lengthening are linked. Isolation for endodontic therapy can be best achieved if adequate tooth structure is present. Finally, the preservation or establishment of an adequate biologic width (between the margin of the restoration and the osseous crest) can be achieved by crown lengthening. This is essential for gingival health.
There are several contraindications to crown lengthening: (1) an unfavorable postsurgical crown/root ratio. In this instance, crown lengthening produces a clinical crown that is longer then the remaining root structure; (2) crown lengthening that compromises adjacent teeth by excessive removal of osseous support. This can also expose furcations; (3) the anterior region presents difficulties because aesthetic concerns must be balanced against restorative needs; and (4) local anatomic concerns including a large torus, the maxillary sinus, the ascending ramus, or the proximity of a neurovascular bundle that may make crown lengthening impossible. Medical conditions such as uncontrolled hypertension, bleeding disorders, immunological diseases, or uncontrolled diabetes, which would rule out any oral surgery procedure, would also preclude crown-lengthening surgery. When in doubt, a medical consultation with the patient’s physician is needed. Poor oral hygiene, which would impact on healing, must be rectified prior to crown lengthening.
In 1953, Waerhaug1 observed a poor tissue response when artificial crown margins were placed subgingivally in dogs. He found a greater inflammatory response around poor-fitting crowns versus well-fitting crowns and observed that only perfectly fitting crowns should be placed subgingivally. Silness performed a controlled trial and concluded that a supragingival crown margin was most compatible with periodontal health.2 Block observed that routine subgingival placement of crown margins for aesthetic reasons or to prevent caries is not justified.3 Every clinician has seen patients with poor-fitting crowns. Restorative margins are sometimes overly bulky, rough, or extend too far subgingivally. For a variety of reasons, dentists must often try to help patients maintain the tissues around these margins.
A landmark study in terms of our understanding of the requirements of the dentogingival complex was reported by Gargiulo and coauthors.4 This study re-evaluated the measurements obtained by Orban and Kohler5 regarding the epithelial attachment, and examined the dimensions of the dentogingival complex in patients of different ages and on different tooth surfaces. Thirty human autopsy specimens were examined. They determined that the length of the epithelial attachment decreased with age while the length of the connective tissue attachment remained constant. The total average length of the epithelial attachment was 0.97 mm while the connective tissue attachment was 1.07 mm. The connective tissue and epithelial attachment together are termed the biologic width and represent the distance that is required between the base of the sulcus and the osseous crest to allow for the attachment of crestal fibers.
|Figure 1. A violation of the biologic width led to rapid resorption of the alveolar crest and exposure of the furcation.||Figure 2. An externally beveled gingivectomy was performed by connecting bleeding points with an incision angled at 45º.|
|Figure 3. One week postoperatively healing by secondary intention has occurred.||Figure 4. A surgical-length fissure bur will remove interproximal bone. The length of the fluted portion is approximately 4 mm. Round burs such as the No. 6 shown above are used for removal of bone on the buccal and lingual surfaces.|
|Figure 5. The last step in osseous removal is accomplished with hand instruments such as the Oschenbein Nos. 1 and 2.||Figure 6. The end result demonstrates a smooth transition from tooth to tooth. Reverse architecture should be avoided.|
A failure to appreciate the biologic width can impact the patient’s periodontal health (Figure 1), and demonstrates the deleterious effect that violation of the biologic width can have on periodontal attachment. The furcation was intact 3 months prior to placement of the crown. After placement of the crown the patient developed acute pain and swelling in the area. Exploratory periodontal surgery was done to identify the etiology of the rapid bone loss (the black color on the root is from citric acid conditioning as regenerative therapy was ultimately employed to repair the defect). Note the position of the crown margin relative to the furcation opening. The osseous crest parallels the crown margin. This bone loss was because of the subgingival crown margin that impinged on the biologic zone.
In some instances, crown lengthening can be accomplished with a simple gingivectomy. To employ a gingivectomy to increase the clinical crown, there must be an adequate zone of attached gingiva and more than 3 mm of tooth structure above the osseous crest. Goldman and Cohen6 described a technique for marking the base of the pocket by creating bleeding points with a periodontal probe or specially designed pocket marking pliers. This is shown in Figure 2, where a patient was to have crown lengthening by gingivectomy to facilitate the completion of orthodontic therapy. The practitioner then connects bleeding points made at the base of the sulcus with an inverse bevel incision utilizing either a scalpel blade or a gingivectomy knife held at 45º. The tissue that is removed should be cleanly excised and the area will heal by secondary intention (Figure 3). It may be desirable to cover the area during healing with a periodontal dressing.
It is important to note that crown lengthening can also be accomplished orthodontically. Orthodontic crown lengthening can be used if surgical crown lengthening would harm the affected tooth or a healthy adjacent tooth. Extrusion of roots that is accomplished slowly will advance bone in a coronal direction and may later require surgical revision. Teeth with a favorable crown-to-root ratio can be extruded more rapidly but may require a period of stabilization prior to restorative care.
Incision and flap design are a critical part of all periodontal surgical procedures. Wood et al7 evaluated full versus partial thickness flaps for the effect on the underlying bone. The study found that regardless of the flap procedure used, bone loss following surgery is most dependent on the thickness of the underlying bone. The use of a partial thickness flap in an area where the gingiva was thin resulted in a thin connective tissue layer which exhibited significant osteoclastic activity. The mean bone loss for full thickness flaps was 0.62 mm, while the mean bone loss for partial thickness flaps was 0.98 mm. Therefore, it is generally preferable to employ full thickness flaps where possible. A 15C scalpel blade in a round handle will provide control and precision. The Pritchard elevator and a No. 7 spatula will allow for both flap elevation and retraction.
Osseous recontouring should be approached in a stepwise fashion. Figure 4 demonstrates a root with wide interproximal areas. In a clinical setting, access is often limited, and the use of fiber optics and magnification will allow for improved visibility. The primary bone reduction is done interproximally using a fissured surgical length bur (No. 557) with copious irrigation. The fluted portion of this bur is 3 to 4 mm in length and can be used as a guide to the amount of osseous removal required. A No. 6 surgical length round bur is then used to perform the buccal and lingual reduction (Figure 4). Hand instruments such as the Oschenbein Nos. 1 and 2 are used to avoid injuring the roots (Figure 5). Spicules of bone on adjacent teeth should also be removed. A back action chisel can then be used to smooth sharp or jagged edges that could perforate thin mucosa. The completed osteoplasty should exhibit a smooth transition from affected to nonaffected teeth as shown in Figure 6. Ingber et al8 recommended that at least 3 mm of tooth structure should be present coronal to the osseous crest. Herrero et al9 found that adequate bone removal increased with the experience of the operator. Experienced periodontists were likely to remove an adequate amount of bone during crown-lengthening surgery.9
|Figure 7. With the temporary restoration removed, the subgingival nature of the fracture is apparent. An acceptable crown margin is not possible.||Figure 8. A lingual submarginal incision is extended one tooth in both the anterior and posterior direction.|
|Figure 9. An unexpected perforation was found on the mesial aspect of the molar. Crown-lengthening surgery allowed the perforation to be completely covered by the restoration.||Figure 10. Primary closure is accomplished with interrupted silk sutures. Note the height of the clinical crown.|
|Figure 11. One week postoperatively the fracture margin is accessible.|
A fractured tooth is a common reason for crown-lengthening surgery. A 31-year-old male was referred for crown lengthening of tooth No. 30. The tooth had fractured, and the dentist was anxious to retain the tooth as the patient had an intact dentition with no other restorations. The medical history was noncontributory. A full dental examination, including head, neck and intraoral tissues was performed, and the patient was found to have no significant periodontal or other oral diseases. A temporary restoration was in place on the fractured tooth. After reviewing the procedure with the patient, consent was obtained and local anesthetic administered. Figure 7 shows the tooth with the temporary restoration removed; a subgingival fracture on the lingual aspect is seen.
A buccal sulcular incision was made with an attempt to thin the interproximal papillae. A submarginal incision was made on the lingual aspect (Figure 8), as the tissue was to be positioned apically. There was an adequate amount of attached gingiva in this area. The incision was extended one tooth on either side of No. 30 to allow relaxation of the flap for both access and apical positioning of the tissue. While vertical releasing incisions can be useful, they are difficult to suture on the lingual surface. Reflection of the lingual flap was accomplished with the use of a Goldman-Fox No. 7 gingivectomy knife. This instrument has a contra-angle which makes it well suited for this area of the mouth. Instruments should always be sharp, and a sharpening stone should be part of the surgical set. Rotary instruments should be used for gross osseous reduction. A No. 6 round surgical bur in a fiber-optic handpiece was used, with copious irrigation. After gross reduction was completed, hand instruments such as the Oschenbein No. 1 (for mesial surfaces) and the Oschenbein No. 2 (for distal surfaces) can be used adjacent to the root. A back action chisel was used for smoothing rough edges. If these sharp edges are left they can penetrate the thin lingual mucosa. In this case, a perforation was found on the mesial aspect of the tooth (Figure 9). In crown lengthening, as with other operative procedures, one must be prepared for the unexpected. By exposing tooth structure with crown lengthening the mesial perforation can be covered by the permanent crown.
The area was sutured with 4(0) black silk interrupted sutures (Figure 10). An adequate zone of attached gingiva was present. Suturing should not be so tight that the soft tissue is pulled too far coronally, yet the sutures must not be too loose to expose the osseous crest. The temporary crown was replaced, and a periodontal dressing was placed. While dressings are not always necessary, in this instance they helped to protect the area from trauma, position the flaps, and act as a pressure bandage to control hemorrhage. Postoperative instructions given to the patient included: (1) rest the mouth for the first 3 hours; (2) apply ice packs to the face for at least 1 hour; (3) eat a soft diet for the first 24 hours; (4) favor the opposite side of the mouth for 1 week; (5) brush and floss except in the treated area; (6) expect swelling and slight bleeding; (7) take prescription or over-the-counter analgesics as directed; (8) take the prescribed antibiotics or use antiseptic mouth rinse as directed; and (9) call the office with any questions or concerns. Sutures are generally removed at 1 week, and the referring restorative dentist is advised to wait for 6 weeks postoperatively to complete restoration of the tooth. If needed, a post and core buildup can usually begin approximately 3 to 4 weeks after surgery. The 1-week postoperative photograph indicates that the fracture is now supragingival (Figure 11), and the tooth will soon be ready for restoration.
Different areas of the mouth will require modification of the basic crown-lengthening protocol. The maxillary arch requires a split thickness flap on the palatal surface. The greater palatine neurovascular bundle and the incisive neurovascular bundle must be avoided. Split thickness flaps should not be too thin or the blood supply will be compromised resulting in flap necrosis. Vertical releasing incisions are important to allow access to the surgical area and prevent involvement of adjacent teeth that might be compromised aesthetically by inclusion in the surgical field. This might mean exposing a crown margin that would be unacceptable to the patient.
|Figure 12. Subgingival caries on this maxillary canine (excavated) made restoration of this tooth impossible.||Figure 13. The canine root prior to osseous resection is almost flush with the osseous crest.|
|Figure 14. Interrupted silk sutures allow primary closure of the distal wedge.||Figure 15. The final restoration. Note the papilla and zone of attached gingiva.|
Another case is seen in Figure 12. A young woman presented with extensive recurrent caries on the maxillary right cuspid. The loss of the tooth would have required extension of a restoration to the central incisor and a cosmetic match with the contralateral incisors would have been difficult. The patient did not wish to undergo orthodontic extrusion of the tooth, and given that a low lip line was present, surgical crown lengthening was required. In this case a vertical releasing incision on the distal of the lateral incisor was used to minimize the cosmetic impact on this adjacent tooth. The vertical incision also enables apical positioning of the zone of attached gingiva. A distal wedge of tissue was removed from the adjacent edentulous ridge. The cuspid root was found to be almost flush with the osseous crest (Figure 13). Osseous resection was accomplished to expose sufficient tooth for establishment of the biologic width and preparation of the crown margin. Interrupted sutures were placed and every attempt was made to preserve the papilla (Figure 14). Soft tissue healing requires a minimum of 6 weeks to ensure that the gingival fiber groups have reformed. Final impressions should be delayed until this time, although a reline of the temporary crown can sometimes be performed at an earlier stage. The final restoration shows that the zone of attached gingiva was maintained and there is minimal marginal inflammation (Figure 15).
Surgical crown lengthening is a vital part of restorative dentistry. When appropriately utilized, it will save the dentist and patient from many visits of recementing nonretentive crowns and chronic, and sometimes uncomfortable, marginal inflammation. The proper use of this procedure helps the restorative dentist provide ideal treatment.
1. Waerhaug J. Tissue reactions around artificial crowns. J Periodontol. 1953;24:172-185.
2. Silness J. Periodontal conditions in patients treated with dental bridges. J Periodontal Res. 1970;5:225-229.
3. Block PL. Restorative margins and periodontal health: a new look at an old perspective. J Prosthet Dent. 1987;57:683-689.
4. Gargiulo A, Wentz F, Orban B. Dimensions and relations of the dentogingival junction in humans. J Periodontol. 1961;7:261-267.
5. Orban B, Köhler J. Die physiologische zahnfleishtasche, epithelansatz und epitheltiefenwucherung. Z Stomatol. 1924;22:353.
6. Goldman HM, Cohen DW. Periodontal Therapy. 6th ed. St. Louis, Mo: C.V. Mosby Company; 1980:780-794.
7. Wood D, Hoag F, Donnenfeld O, Rosenfeld L. Alveolar crest reduction following full and partial thickness flaps. J Periodontol. 1972;43:141.
8. Ingber JS, Rose LF, Coslet JG. The biologic width-a concept in periodontics and restorative dentistry. Alpha Omegan. 1977:10:62.
9. Herrero F, Scott JB, Maropis PS, Yukna RA. Clinical comparison of desired versus actual amount of surgical crown lengthening. J Periodontol. 1995;7:568-571.
Dr. Pitman is a diplomate of the American Board of Periodontology and an associate clinical professor of dentistry at the Columbia University School of Dental and Oral Surgery. He maintains a private practice in New York City.
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