The incorporation of crown lengthening surgery in the treatment plan can greatly improve the chances of a predictable success of a prosthodontic and/or esthetic case. Early planning will facilitate treatment and provides for more stable and better esthetic result. This article will outline the rationale for this widely used procedure, indications for it and will offer tips for treatment planning. A few cases will be used to illustrate these concepts.
HISTORICAL BACKGROUND
The crown lengthening procedure has received considerable attention in both the periodontic and the restorative literature since the term ‘biologic width’ was first coined by Walter D. Cohen in 1962. Later, Ingber et al. resurrected the term in 1977 in a descriptive article based on clinical impression alone. Both authors based their proposals on the data compiled by Gargiulo et al. that estimated the length of the dento-gingival junction. In his findings the distance between the connective tissue and epithelial attachment was approximately 2mm — this is referred to as the “biologic width”. The average sulcus depth was 1mm, and thus the dento-gingival complex was estimated to be 3mm in length.
Unfortunately, this study alone cannot be used to justify crown lengthening due to several shortcomings. These were outlined by Dello Russo in 1992: (i) The main focus of the study was the description of the dento-gingival complex through four phases of eruption. As such, measurements were taken from normal subjects without the distinction between periodontal disease and health, and; (ii) The numbers quoted in his paper are averages, whereas the actual data in the study reveals very wide ranges.
In response to Dello Russo’s letter, Mishkin and Gellin noted that a review of the restorative and periodontic literature supports the crown lengthening procedure, but we based it on incorrect literature. Therefore, he concluded, we were doing the right thing for the wrong reasons.
In 1970, Silness showed that crown margins at or below the gingival crest interfered significantly with gingival health. The restorative literature tells us that the average fit of gold and ceramic crowns is between 57-48 um with marginal cement occupying 20-40 um (Holmes et al., 1992). Since the average diameter of a microorganism is 1 um, most crown margins will harbour plaque, especially around their subgingival margins. Waerhaug also showed that loss of attachment was detected only if the plaque front was greater than 2.7mm from the alveolar crest.
Taking in account this evidence the rationale for crown lengthening is to avoid establishing crwon-tissue relationship based on the data outlined by Gargiulo et al, rather to position the plaque harboring margins beyond the 2.7mm inflammatory zone, as measured from he crest of the bone.
In instances where the biologic width is not respected, a periodontal lesion characterized by chronic gingival inflammation, loss of attachment, gingival recession associated with localized bone loss, and alveolar resorption will result (Parma-Benfenati et al., Carnevale et al., Tal et al.).
WHY CROWN LENGTHENING PROCEDURE SHOULD BE AN INTEGRAL PART OF THE PROSTHETIC AND ESTHETIC TREATMENT PLAN?
There are two basic reasons to include crown lengthening in the restorative treatment plan; (i) to increase the stability/retention of the restoration; and (ii) to preserve or create a healthy attachment apparatus. The durability of a crown is improved due to: (i) a longer abutment with greater retention; (ii) superior adaptation of the crown margin facilitated by more precise impressions enhanced by healthy gingival tissues; and (iii) decreased risk of localized periodontitis due to the creation of an adequate distance between the alveolar crest and the apical extent of the restoration.
The preservation of a healthy periodontium is accomplished by creation of an adequate distance between the alveolar crest and the restoration as well as providing the margins accessible for daily cleaning.
PRE-PROSTHETIC CROWN LENGTHENING – WHEN IS IT NEEDED?
The diagnostic acumen of the restorative dentist is often challenged by borderline cases. The clear indications for crown lengthening surgery are: (i) coronal fractures extending below the gingival margin; (ii) root perforations extending subgingivally; or (iii) extension of caries or overextended restorations to the junctional epithelium.
PRESURGICAL CAUTIONS
Once the need has been established and before proceeding with the surgery, the prudent operator asks the following questions: (i) will the surgical procedure compromise adjacent teeth due to (extensive) bone removal; (ii) will the amount of post-surgical periodontal support be adequate to support function without splinting; (iii) is the long-term prognosis sufficiently favourable to justify the treatment; and (iv) will the esthetic outcome be acceptable. Proceeding with the surgery presumes that the answers to these questions are all favourable.
TREATMENT PLANNING
Planning for the procedure requires diligent communication between the restorative dentist and the periodontist. Since the surgery will establish a new dento-gingival complex in accordance with the planned restorative margins, the prosthetic provider must plan and delineate the placement of margins before the surgery. With the advance of a well fabricated provisional restoration, the periodontist can then determine a zone of sound tooth structure and better plan the extent to which alveolar bone will be removed.
Diagnostic wax-ups, marked clinical models and pictures or computer simulations of the planned restoration are the best modalities of communication.
Two Cases
The sequence of events in this first case highlight the importance of communication between the restorative dentist and periodontist. The patient complained of persistent bleeding and sensitivity on tooth 2.1 following delivery of the crown (Fig. 1A).
Examination revealed violation of the biologic width by the overextended margins of the crown. At this point, the periodontist should have asked the restorative dentist to place a provisional restoration that would delineate the position of the margin of the planned crown. During the surgery the gingival margin was positioned arbitrarily and the resultant restoration was not satisfactory (Fig. 1C) resulting in a “gingival halo” around the new crown. Due to miscommunication, the surgery was driving the procedure (Fig. 1B) rather than the prosthetic plan.
The next case addresses both prosthetic and aesthetic issues. This patient was mainly concerned about the esthetics: miss-alignment of the teeth, colour miss-match and asymmetrical gingival contour. Upon examination, recurrent decay was detected beyond the crown margins (Fig. 2A).
Here, the main objective of the crown lengthening surgery was to establish the biologic width taking in consideration the presence of the decay and the position of the planned crown margins which have to land on sound tooth structure, apical to the most apical extent of the caries. In addition the procedure resulted in symmetrical gingival contours of the anterior maxillary teeth.
The apical extent of the caries was a guide in establishing the position of the new crown margins while the biologic width was respected for all teeth in the surgical site. After complete healing, crowns were placed to restore the anterior maxillary sextant and correct the palatal position of tooth 2.1 (Fig. 2B).
CROWN LENGTHENING IN COSMETIC CASES – IS THERE REALLY A DIFFERENCE?
In most cases the maxillary anterior teeth are the subject of cosmetic complaints. Patients will note that their teeth are too short, the gingiva is too prominent (gummy smile), or complain about asymmetrical gingival contours.
ASSESSMENT
Cosmetic cases are more challenging than the once where the objective of the crown lengthening procedure is pure pre-prosthetic preparation of the abutments.
In case of short clinical crowns, the cemento-enamel junction must be detected below the gingival margin to affirm the diagnosis of delayed passive eruption. If however, short teeth display a cemento-enamel junction at its ideal position, the diagnosis of excessive wear of the dentition is more appropriate. This differentiation has an important impact on the restorative plan.
The conventional ‘gummy smile’ must be differentiated from excessive vertical maxillary growth. This refers to the lack of proportional growth of the maxillary base and the size of the teeth resulting in teeth positioned farther from the base of the maxilla. This leads to the display of excessive amount of gingiva below the inferior border of the upper lip.
Asymmetries of the gingival margins must be carefully investigated so that underlying periodontal disease can be diagnosed. For the treatment of active periodontitis has an impact on the post-surgical position of the gingival margin. This has to be factored into planning the case.
TREATMENT PLANNING
Preparation for crown lengthening done primarily with a cosmetic goal may, and should in most cases, involve provisionalization. The restorative dentist must communicate the desired post-surgical size of the teeth and convey them to the periodontist prior the surgery. A well-fabricated provisional restoration can achieve this goal.
Final restorations for the anterior maxillary sextant should be placed after at lest three, but often six months following the surgery to ensure that all tissue shrinkage has occurred (Bragger et al., 1992) and the dento-gingival complex has matured.
CASE EXAMPLES
The most common complaint for patients who present for pre-esthetic crown lengthening is a ‘gummy smile’. Figures 3A and 3B show a patient who presents with very large papillae covering the interproximal line angles obstructing the full width and length of the teeth. Reflection of a full thickness muco-periosteal flap exposes bone within 1mm of the cemento-enamel junction (Fig. 3C). Bone removal allows for at least 3mm between the margin of the planned restoration and the alveolar crest (Fig. 3D). This allows for an esthetic result within a healthy periodontium (Figs. 3E & F).
Figure 4A depicts a patient with short teeth with discolouration of the gingival third of the clinical crown. The patient was warned that immediately following crown lengthening the discoloration would become more obvious (Fig. 4B), but would be masked by the final restorations (Fig. 4C).
Similarly, the patient in Figure 5A was not pleased with the appearance of her short teeth and the disproportionate amount of gingiva on the lateral aspects of her smile. In order to address the lateral aspects of her smile, crown lengthening was done from tooth 1.5 to 2.5 and final restorations resulted in an increase in the dimensions of the clinical crowns (Fig. 5B).
CONCLUSION
As this article focuses on crown lengthening achieved through osseous surgery, an alternate method should be mentioned. Orthodontic extrusion has been used to solve the problem of short abutments (Ingber, 1974). Although this method avoids the surgically induced bone loss, it may alter crown to root ratio unfavourably.
The incorporation of crown lengthening surgery in the planning stages of reconstructive work can greatly improve the outcome of the treatment, both functionally and aesthetically. Respecting the biologic width concept will ensure a healthy and stable result.OH
Dr. Livia Silvestri is a clinical instructor at the University of Toronto, Department of Periodontics and maintains a private practice in Toronto limited to periodontics and implant surgery.
Photographs courtesy of Dr. Herbert Veisman.
Oral Health welcomes this original article.
REFERENCES
1.Bragger U, Lauchenauer D, Lang NP. Surgical lengthening of the clinical crown. Journal of Clinical Periodontology. 1992; 19(1):58-63.
2.Carnevale G, Freni Sterrantino S, Di Febo G. Soft and hard tissue wound healing following tooth preparation to the alveolar crest. International Journal of Periodontics and Restorative Dentistry. 1983;3(6):36.53.
3.Dello Russo N. Re: Biologic width and crown lengthening. Journal of Periodontology 1993. 64(3):240-241.
4.Gargiulo AW, Wentz FM, Orban B. Dimensions and relations of the dentogingival junction in humans. Journal of Periodontology 1961;32:261-267.
5.Holmes JR, Sulik WD, Holland GA, Bayne SC. Marginal fit of castable ceramic crowns. Journal of Prosthetic Dentistry. 1992; 67(5):594-599.
6.Ingber JS. Forced eruption: Part I. A method of treating isolated one and two wall infrabony osseous defects – Rationale and case report. Journal of Periodontology. 1974; 45(4):199-206.
7.Ingber JS, Rose L, Coslet J. Biologic width: a concept in periodontal and restorative dentistry. Alpha Omegan 1977; 70(3):62-65.
8.Mishkin DJ, Gellin RG. Re: Biologic width and crown lengthening. Journal of Periodontology 1993. 64(9):920.
9.Parma-Benfenati S, Fugazzotto PA, Ruben MP. The effect of restorative margins on the post0surgical development and nature of the periodontium. Part 1. International Journal of Periodontics and Restorative Dentistry. 1985;5(6):30.51.
10.Rosenberg ES, Garber DA, Evian C. Tooth lengthening procedures. Compendium Continuing Education in Dentistry. 1980; 1(3):161-173.
11.Tal H, Soldinger M, Dreiangel A, Pitaru S. Responses to periodontal injury in the dog: Removal of gingival attachment and supracrestal placement of amalgam restorations. International Journal of Periodontics and Restorative Dentistry. 1988; 8(3):45-55.
12.Waerhaug J. Temporary restorations: advantages and disadvantages. Dental Clinics of North America. 1980; 24(2):305-316.
