Aesthetic Crown Lengthening - Oral Health Group

Introduction
With the continued high demand for esthetic dentistry, gingival health is among the first fundamental esthetic objectives during treatment planning. Diseased gingival tissues will possess a negative impact on a smile. The literature is replete with articles describing cosmetic restorative cases with a brief mention of the preliminary gingival recontouring. It is not always clear what are the diagnostic criteria or treatment rationale for the procedure.¹ The esthetic zone may involve a wide variety of therapeutic approaches. Different treatment modalities may be considered varying from a simple gingivectomy to more complex procedures that involve mucoperiostal flaps, osseous resective surgery and orthognatic procedures.²

The aim of this review is to aid clinicians in reaching a correct diagnosis,understand the key factors involved and to provide the proper treatment for the management of periodontal tissues in the aesthetic area.

Etiology and Diagnosis:
The essentials of a smile involve the relationships between three primary components³:

The gingival scaffold
The teeth
The lips framework

The gingival scaffold may have an irregular appearance that may present as a gingival enlargement/overgrowth, altered passive eruption, short clinical crowns, vertical maxillary excess or a short upper lip.²

Of the predisposing factors associated with disproportionate, disfiguring and functionally compromising overgrowth of gingival tissues, selected anti-convulsant drugs, calcium channel blockers and a potent immunosuppressant (cyclosporin A) have generated the most investigative attention in the scientific community.⁴ Unfortunately, the underlying pathogenic mechanism that mediates gingival overgrowth in affected individuals remains undefined despite intense clinical and laboratory investigation.⁵

The eruption of a tooth involves two phases, active and passive. Active eruption ceases when the teeth come into contact with the opposing dentition. Thereafter, it is the passive eruption, which is the migration of the epithelial attachment apically to expose the anatomic crown of the tooth, that determines the final appearance of the tooth/gingival complex. A delay or failure of this to occur is referred as “altered passive eruption” and will result in the appearance of short clinical crowns and excessive gingival display, a gummy smile.²

The gummy smile is frequently a result of a skeletal dysplasia, such as hyperplastic growth of the maxillary skeletal base. This results in teeth being positioned farther away from the skeletal maxillary base and a display of gingiva below the inferior border of the upper lip. Cases that combine altered passive eruption with maxillary hyperplasia, should first be treated for any altered relationship between gingiva and cemento-enamel junction. This will results in the development of a more aesthetic tooth silhouette form and allows for more accurate diagnosis. Orthognatic procedures may also be suggested as a treatment option for repositioning of the maxilla. These combined cases would require for optimal treatment a multidisciplinary approach involving an orthodontist, a periodontist, an orthognathic surgeon and a restorative dentist.³

Indications:
The need to correct gingival margin asymmetries for esthetic reasons is not the only indication for crown lengthening. A successful restorative treatment of teeth usually requires preparation of well-defined restoration margins.⁶ In addition, in cases of destructive caries, altered passive eruption, or pathologic wear, the supragingival tooth structure may not be sufficient to permit adequate retention of the prosthesis or an appropriate ferrule. Such is defined as sound, non-carious dentin extending circumferencially to 1.5 to 2 mm coronal to the margin. An appropriate ferrule is a significant factor in improving resistance to fracture. Other indications may include teeth that require hemisection or root resection.⁷

One should also consider the crown to root ratio. This is defined as the physical relationship between the portion of the tooth within the alveolar bone compared with the portion not within the alveolar bone, as determined radiographically.⁸ However, the definition of the crown to root ratio has several inherent shortcomings. The ratio is based on linear measurements only. It does not asses mobility, buccal and lingual alveolar bone support, root configuration and angulation and opposing occlusion.⁹ Nevertheless, the ideal crown to root ratio has been suggested to range from 1:2 or 1:1.5 with a suggested minimum ratio of 1:1.¹⁰ Though, it is still unclear how this ratio affects prognosis.¹¹ Disadvantages of surgical crown lengthening treatment are an increase in crown/root ratio caused by the reduced effective root length and the increased effective crown length and the reduced volume of remining root dentin. An alternative approach to treatment is an orthodontic extrusion. From the bio-mechanical point of view when orthodontic extrusion is performed, bone support reduces, but the coronal lever arm does not change.¹²

Based on the accumulated information, it is evident that contraindications will include⁷:

Deep caries or fracture requiring excessive bone removal
Unaesthetic post-surgical outcomes
Tooth with inadequate crown root ratio (ideally 2:1 ratio is preferred)
Non-restorable teeth
Tooth with existing or increased risk of furcation involvement
Unreasonable compromise of esthetics
Unreasonable compromise on adjacent alveolar bone support

Aesthetic gingival margins
What makes an aesthetic smile are the form, balance, symmetry and the combination of these elements. Variations of these components can make a smile attractive or unattractive. Continuity of linear horizontal form between the gingival expanse, the teeth and the upper lip is critical. Any asymmetry in this parallelism disrupts the sense of balance by disturbing the flow and results in an unaesthetic smile.³

Ideal gingival architecture consists of knife edged gingival margins, tightly adapted to the teeth, interdental grooves and cone shaped interdental papilla. Nordland and Tarnow’s classification of a normal interdental papilla is one that fills the embrasure space to the apical extent of the interdental contact area.¹³ Deviation from the normal interdental papilla will result in an undesirable gingival black triangle and gingival asymmetry that can lead to a visual stress and imbalance.¹⁴ As mentioned, the essential of a smile involves the relationship among the teeth, the lip framework and gingival scaffold. To predict the final esthetic result and achieve optimum results in gingival contour rehabilitation (crown lengthening, implant, and orthodontic therapy), it is important to take the gingival contour into account during treatment planning. Some quantifiable clinical parameters may be helpful for the diagnosis and treatment of gingival discrepancy when gingiva is exposed. The lip position during smiling will determine the amount of gingival display.

Understanding the dentogingival interface will allow clinicians to achieve a more satisfactory esthetic outcome during interdisciplinary diagnosis and treatment. One significant feature of gingival morphology is the gingival line, which is defined as a line joining the tangents of the gingival zeniths of the central incisor and canine.

The gingival zenith is the most apical aspect of the free gingival margin.¹⁵

The appropriate placement of the gingival zenith is critical, as it helps to determine the desired axial inclination of the tooth by maneuvering the line angle of the vertical axis of the tooth. Subsequently, knowing the gingival zenith position (GZP) of each maxillary anterior tooth from the vertical bisected midline (VBM) as well as the gingival zenith level (GZL) of the lateral incisors can help facilitate a reference point during esthetic periodontal plastic surgical procedures. A GZP with mean value of 1 mm distal from the VBM axis of each individual maxillary anterior tooth was found to be most esthetic. The lateral incisors showed a mean average of 0.4 mm and the canine demonstrated almost no deviations of the GZP from the VBM. The gingival zenith level (GZL) of the lateral incisors relative to the adjacent central incisor and canine teeth is more coronal by approximately 1 mm. These data could be used as reference points during esthetic anterior oral rehabilitation.¹⁴

Aesthetic tooth size:
The final outcome also depends of the proportion of the size of the teeth between each other and how much of tooth is “showing”. To provide “magic“ numbers for the clinician, mathematic theorems as the golden proportion and golden percentage have been proposed. Taking into account classic elements of art and architecture, Magne suggests the following dimension for tooth width: central – 9.10 to 9.24, Canines – 7.90 to 8.06 mm, Lateral 7.0 mm to 7.38 mm, and Premolars 7.84 mm. The following dimensions were suggested for tooth length: unworn central incisors – 11.69 mm, unworn canines – 10.83 mm worn incisor – 10.67 mm, worn canine 9.90 mm, worn and unworn lateral incisor – 9.34 to 9.55 mm premolars 9.33 mm. Width/length ratio should also be consider for esthetic purposes with 78% for unworn central incisors, up to 87% for worn teeth.

These numbers may serve as guidelines for diagnosis and treatment planning prior to periodontal surgery in the maxillary dentition.¹⁶

Treatment Planning
Establishing the proper biological width is essential mostly in restorative cases. The biologic width is a term that was defined by Cohen in 1962 as the junctional epithelium and supracrestal connective tissue attachment without the depth of the gingival sulcus. This definition was based on a study by Gargiulo that measured the component parts of the dentogingival junction of normal human autopsy specimens. The average dimensions for the biological width were found to be: for the sulcus 0.69 mm (range 0.4-1.09mm), the epithelial attachment 0.97 mm (range 0.44-1.56mm) and the connective tissue attachment 1.07 mm (range 0.69-1.04mm). Width measurements of the epithelial attachment were found to be the most variable and the connective tissue attachment dimensions were the most constant.¹⁷ There is some controversy as to what the term biological width encompasses. Some define it as the total dimension of the epithelial and connective tissue attachment.¹⁸ while others define it as a combined sum of the space occupied by the supracrestal fibers, junctional epithelium, and the gingival sulcus.¹⁹

The definition of ideal tooth dimensions remains a difficult task due to individual variations. It has been shown that the dimensions of the biological width are greater in teeth with restorations and in the posterior segments.²⁰

One important aspect to remember is that the biologic width may vary between different individuals. Also, of importance is that different individual react differently in when the biological width is violated – this reaction is mostly dependent of the so-called biotype. Ochenbein and Ross²¹ and Becker et al.²² proposed that the anatomy of the gingiva is related to the contour of the osseous crest, and that two basic types of gingival architecture may exist, namely the “pronounced scalloped” and the “flat” biotype. The individuals with “pronounced scalloped” (thin) biotype have long and slender teeth with tapered crown form, delicate cervical convexity and minute interdental contact areas that are located close to the incisal edge. The maxillary incisors will present with a thin free gingiva, and buccal margin of which is located at or apical to the cemento-enamel junction. The zone of gingiva is narrow, and the outline of the gingival margin is highly scalloped. The “flat” (thick) gingival biotype subjects have incisors with squared crown form with pronounced cervical convexity. The gingiva of such individuals is wider and more voluminous, the contact areas between the teeth are large and more apically located, and the interdental papillae are short. It was reported that subjects with pronounced scalloped gingiva often exhibited more advanced soft tissue recession in the anterior maxilla than subjects with a flat gingiva.²³ Biotype assessment based on visibility of periodontal probe through the gingival margin has been shown to be a simple, reliable, and reproducible method for gingival thickness assessment in routine practice.²⁴

Although there is no generally accepted value, if subgingival margins are indicated, they should not extend beyond 0.5mm subgingivally.^25,26 The biological width can be violated when a restoration is placed deep within the subgingival tissues. A common consensus is that, when the biologic width is violated, the body will attempt to redefine it by a process of osseous resorption. The precise mechanism for chronic inflammation that develops is not fully agreed upon. One theory is that there is insufficient space for a normal junctional epithelium to reform. The result is a short and weak attachment that does not represent an effective seal on the dentogingival unit that can lead to chronic inflammation. Others believe that placing the restoration too close to the bony crest impairs proper plaque control leading to an environment that is not favorable with periodontal health. Another theory is that violation of the biologic width leads to reestablishment of the dento-gingival unit in a more apical position at the expense of further bone resorption and recession, in a thin biotype or a vertical osseous defect around a tooth in patients with thick biotype. Either way, there is no sound justification, clinical or scientific, to ignore the biological width as an anatomical and functional entity in the practice of restorative dentistry.^27,28

Treatment
Surgical intervention on periodontal and gingival structures may affect the amount of attached gingiva. Several studies have shown that 2 mm band of attached gingiva would be preferable to maintain health around the restored tooth. Because of the resecting nature of this procedure, there is the risk of reducing the width of attached gingiva. Therefore, it is of utmost importance when planning surgical crown lengthening to evaluate and measure the attached gingiva.²⁹

The width of attached gingiva can be identified for each individual patient by probing under anesthesia to the bone level (referred to as bone sounding) and subtracting the sulcus from the resulting measurement. This measurement should be performed on teeth with healthy gingival tissues and should be repeated on more than one tooth to ensure an accurate assessment.¹

Treatment decision should be a function of existing gingival width and the position of the alveolar crest. In cases of a wide zone of attached gingiva, treatment can include gingivectomy and gingivoplasty (Fig. 1). In similar cases with appropriate amount of attached gingiva and when the alveolar crest is at the cemento-enamel junction, treatment options is the gingivectomy with gingivoplasty and osseaous recontoruing leading to ideal gingival position relative to the underlying bone. Osseous recontorring/ resection will establish biological width in relationship to the newly positioned gingival crest. The osseous recontouring results in recapturing the normal form of the alveolar process at a more apical level (Fig. 2).³⁰

Fig. 1

Gingivectomy( Sufficient amount of keratinized tissue/ Adequate crestal bone level).

Fig. 2

Gingivectomy and osseous surgery ( Sufficient amount of keratinized tissue/ Inadequate crestal bone level)

In cases of insufficient width of attached gingiva and when the alveolar crest is at 1.5-2.0 mm from the cemento-enamel junction, the gingival tissue will be repositioned apically (Fig. 3).³¹ Proper surgical technique of apically repositioning flap may even increase the band of attached gingiva, despite the resective component of the procedure.²⁹ In areas of insufficient zone of attached gingiva and alveolar crest located at the cemento-enamel junction, partial thickness flap and osseous resection should be perform in order to establish biological width (Fig. 4).³¹

Fig. 3

Apically positionned flap and osseous surgery ( Insufficient amount of keratinized tissu/ Inadequate crestal bone level)

Fig. 4

Apically positionned flap ( Insufficient amount of keratinized tissue/ Adequate crestal bone level.

Following osseous recontouring, in order to remove any possible remnant of connective tissue attachment coronal to the alveolar crest, the exposed root surfaces should carefully be planed with sharp curettes or rotating flame-shaped finishing burs. The removal of remaining root cementum with inserting collagen fibers will prevent reattachment of the surgically separated fibers in an undesired coronal position.³²

Regardless of the surgical approach – soft or hard tissue reduction – preservation of interproximal papillae is an integral part of success.

Careful pre-surgical evaluation and planning of the case is necessary to achieve the best result and preserve papilla.²⁹

Healing period/ long terms stability of results.
Understanding the healing process is a crucial step for a desirable result. Histology after a gingivectomy, showed the re-establish of the junctional attachment at 12 days with hemidesmosome³³ and a functional arrangement with collagen maturation after 3-5 weeks.³⁴ However, when a flap is elevated and an osseous surgery is performed, the healing process is longer and collagen fiber bundles will reform only after 2 months and approximately 5-6 months for the collagen fiber bundles to arrange perpendicular to the root surface.³⁵ Bone resorption following surgical crown lengthening provides supracrestal tooth structure for the attachment of connective tissue, leading to reestablishment of the biologic width depending on the amount of scaling and root planning. Failure to perform thorough scaling and root planing will result in regeneration of the tissues that may necessitate retreatment. On the other hand, thorough scaling and root planing during crown-lengthening surgery will enable the practitioner for accurately determine the coronal end-position of the supracrestal connective tissue.³² As mentioned before, various tissue biotypes will influence the amount of coronal displacement. Patients with thick tissue biotype demonstrate significantly more coronal soft tissue regrowth than patients with thin biotype due to the biological differences in respective healing responses.

Many factors seem to contribute to the maintenance of tooth structure gained through surgical crown lengthening procedures. Individual patient healing characteristics, reformation of biologic width, adequacy of positive osseous architecture created during surgery, timing of restorative procedures, and postoperative plaque control may be among these factors.³⁶

The question often asked is how long should one wait before initiating any restorative work after a patient has had a crown lengthening procedure? Clinical studies showed stability of the gingival margin ranging from 6 weeks to 3 months and even up to 6 months.^37,38 In fact, the answer to this question is still controversial. More clinical research is needed to come to conclusion on this issue.³⁶

Conclusion:
In order to have a successful outcome, the practitioner must complete an accurate diagnosis based on clinical and radiographic findings, take into account the various biological parameters, especially in restorative cases. An understanding of various techniques and proper planning are critical. Misdiagnosis followed by poor choice of procedure and lack of skills to perform it can lead to unfavorable results.

Oral Health welcomes this original article.

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About The Author

Dre Nancy Mouradian graduated from the Faculty of Dentistry at the Université de Montréal. Dr. Mouradian completed a two-year multidisciplinary dentistry program in 2006 at the University of Rochester. She received a certificate in periodontics in 2015 and is now a Fellow of the Royal College of Dentists of Canada. In addition, she is a graduate of the American Board of Periodontology.

Tal Rapoport graduated dental school from the Hebrew University and has practiced dentistry since 2006. She is working as an Assistant Professor and clinic director at the EIOH Periodontics department and in private practice. She recently received the 2019 Educator Award for an Outstanding teaching/mentoring in Periodontics from the American Academy of Periodontology.

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