Crown lengthening for improved aesthetics

Introduction

The general practitioner is presented with a severe tooth-periodontal mal-relationship necessitating a restoration. In order to correct the aesthetic and functional problem, a multi-disciplinary approach is frequently necessary. In order to recreate a harmonious appearance to the smile, it is essential to undertake an analysis that takes into account the line of the smile, the lips and the free gingival margins of the incisor and canine teeth, as well as the size, shape and position of the teeth in planning the final aesthetic outcome (^{Decup and Renault, 1995}). One should note that amongst all these criteria, freedom of action is often restricted by the teeth (shape, colour, position) and of the gingival-bone relationships (gingival surgery, bone…). It has been demonstrated that it is possible to achieve a highly aesthetic dentition if the ideal aesthetic environment has been re-established (^{Nowzari, 1998} ; ^{Kay, 2002}).

Crown lengthening covers a combination of mostly surgical techniques aimed at rearranging the periodontal tissues around the teeth in order to make the margins of restorations supragingival and to increase crown height for the purposes of improving aesthetics or for crown retention whilst, at the same time, taking into account or creating biological space. The latter, made up of the junctional epithelium and the connective tissue attachment, represents the minimum distance between the base of the sulcus and the crest of alveolar bone. Its mean value in a healthy periodontium has been measured by ^{Gargiulo et al. (1961)} as 2.04 mm with extreme values of 1.77 mm and 2.43 mm (^{fig. 1}). It is imperative to respect the integrity of biological space (^{Ingber et al., 1977}). Any encroachment, whether by the subgingival location of a bridge abutment crown preparation or by a restoration following a carious lesion or tooth fracture, will lead to an inflammatory reaction in the periodontium with an increase in gingival fluid, apical migration of the junctional epithelium and eventually, bone resorption (^{Flores de Jacoby et al., 1989}).

In order to recreate this biological space, whilst at the same time respecting or restoring the aesthetics, the practitioner will be led to a choice of therapeutic options. This article aims to study the clinical that necessitate crown lengthening by surgical means.

Diagnosthis

The various situations with which the practitioner may be confronted may be classified into two distinct groups. The first of these concerns the management of the « gummy » smile (^{Kawamoto, 1982} ; ^{Levine and Mc Guire, 1997}). Very often, the reason for the patient's attendance is to request an improvement of aesthetics. There may be three main causes of this problem :

- incomplete passive eruption (^{Evian et al., 1993}) ;

- gingival hypertrophy and/or hyperplasia (^{Meraw and Sheridan, 1998}) ;

- anterior maxillary overgrowth.

The second group brings together all those factors that touch upon the restoration of the biological space and the subsequent periodontal environment :

- crown-root fracture ;

- subgingival caries ;

- inadequate retention for the restoration ;

- insufficient space for the periodontium.

Pre-operative assessment should clarify the key elements of the decision making process as well as determine the indications, contra-indications and, finally, point to the most appropriate surgical intervention for the clinical situation (^{Lormée et al., 1986} ; ^{Smukler and Chaibi, 1997}).

Indications

To an extent, the indications will depend upon tooth-periodontal factors such as :

- the quality and quantity of the gingiva and the width of attached gingiva ;

- the presence of periodontal pockets ;

- root anatomy (length, shape, location of the furcation) ;

- the thickness of the healthy tooth tissue wall ;

- the distance between the bone crest and the apical limit of healthy tooth tissue.

In addition, there are restorative factors to be determined :

- the location of crown margins ;

- the type of margins ;

- the minimum clinical crown height to provide adequate retention.

Also, it is necessary to take into account aesthetic factors, in particular the appearance of the gingival margins and the smile line.

Contra-indications

The following factors should be assessed in order to determination the contra-indications :

- a crown-root ratio less than 1 ;

- an endodontic problem not amenable to successful treatment ;

- significant bone loss involving the furcation of the tooth concerned and possibly other collateral teeth ;

- a poor aesthetic result in the anterior region ;

- bone surgery that could lead to excessive loss of support.

Key elements of the diagnosthis

There are several elements to the clinical assessment that will lead the clinician to the treatment of choice (^{Taieb et al., 1999}) :

- the probing of pockets ;

- measurement of the height and thickness of the attached gingiva ;

- radiographic assessment ;

- assessment of the smile line and the relationship of the edges of the lips to the gingival margins.

Periodontal probing

Probing of the pockets is undertaken around the whole circumference of the tooth, using a periodontal probe. This permits assessment of :

- the extent of any fracture or crack ;

- the location of the apical margin of any restoration that must be within the sulcus and its relationship to the gingival attachment ;

- the presence of periodontal pockets.

Measurement of the total height of the gingiva and the height of the attached gingiva

The height of the gingiva is the distance between the free gingival margin and the muco-gingival line. It is measured by placing a periodontal probe against the gingiva. The height of the attached gingiva is calculated by subtracting the depth of the sulcus from the total height of the gingiva. A pocket depth of 3 mm is acceptable when associated with a gingival height of 5 mm (^{Maynard and Wilson, 1979}). Such heights do not seem to be essential in the case of supragingival restorations. The height of the gingival attachment alone does not indicate the potential of resistance of the marginal gingiva to the effects of the restoration. An estimate of the thickness of the attached gingiva is an important qualitative factor to be considered (^{Wennström, 1987}). Clinically, this can be indicated by the greater or lesser transparency of the gingiva : if one can see a periodontal probe placed in the pocket through the marginal gingiva, it is unlikely that such a tissue will remain stable in the presence of a restoration. These gingival measurements are the key elements in making the decisions for treatment and will be a function of the replies to the following questions :

- is the gingival height sufficient ? Is it likely to reduce whilst maintaining good periodontal health ?

- if the height of the gingiva is insufficient, or even absent, is it possible to increase it or to create it ?

Radiographic assessment

The intra-oral radiograph will, after the affected tissues have been eliminated, allow the distance between healthy tooth tissue and the bone crest to be determined. This space corresponds to the pre-prosthetic surgical space (^{fig. 2}) which is composed of the biological space added to the depth of the sulcus. If this is above or equal to 3 mm, the bone level will not be altered. On the other hand, if it is less than 3 mm, it will be necessary to undertake bone surgery by ostectomy and osteoplasty.

In the course of this radiographic evaluation, it is necessary to pay particular attention to :

- the thickness of the teeth ;

- root length and morphology ;

- the position of the furcation areas ;

- places where roots are in close proximity ;

- the quality of endodontic treatments.

Assessment of the smile

This is to determine the line of the smile. It is defined by an imaginary line that follows the lower border of the upper lip as it is stretched back by the smile. ^{Tjan and Miller (1984)} have defined three categories of smile lines :

- a high line (the smile reveals the whole of the teeth as well as a band if gingiva) ;

- a middle line (exposure of the papillae) ;

- a low line (2/3 of the teeth are exposed.

It is interesting to note that 80 % of patients have a smile line in the middle category (^{Tjan and Miller, 1984}).

This preoperative clinical examination enables us to evaluate the various elements of the decision making process in relationship to the ideal clinical situation that will be :

- a sulcus depth of 1-2 mm ;

- a gingival height in excess of 5 mm, with 3 mm of attached gingiva ;

- a pre-prosthetic surgical space of 3 mm ;

- an absence of factors detrimental to aesthetics after surgery.

Surgical techniques

The choice of surgical technique for crown lengthening will depend on the combination of the key factors that have just been described (^{table 1}), especially :

- the height of the attached gingiva, which determines the line of incision ;

- the pre-prosthetic surgical space, which determines the amount of bone to be removed.

As in all types of periodontal surgery, the intervention is part of the treatment plan. The following sequence must be adhered to :

- clinical and radiographic assessment ;

- reduction of inflammation by scaling and possibly by root planing ;

- temporary restorations ;

- reassessment ;

- periodontal surgery.

Following this appraisal, the intervention will be justified if it does not compromise the adjacent teeth, if the aesthetics in the area are satisfactory after the surgery and if the long term prognosis for the restoration is favourable (^{Wagenberg, 1998}).

Internal (reverse) bevel gingivectomy

The aim of gingivectomy is to remove excess gingival tissue in order to obtain an aesthetically harmonious gingival contour that is compatible with effective personal and professional hygiene procedures. It should only be contemplated where there is at least 5 mm of gingiva, of which 3 mm is attached gingiva, associated with a surgical space of 3 mm (^{Ramfjord, 1952} ; ^{Rateitschak et al., 1986}).

In the following clinical case : a 50-year-old patient requires complete restoration in the maxilla. The clinical situation shows fairly short teeth which would provide insufficient retention, a gummy smile, an adequate height of gingiva and a pre-prosthetic surgical space greater than 3 mm (^{fig. 3}). An internal bevel gingivectomy is the required surgical technique (^{fig. 4}). The result shows the change in the length and shape of the teeth, the attention paid to the interdental spaces as well as to all the periodontal tissues (^{fig. 5}).

Apically repositioned flap

Initially undertaken as a full thickness flap (^{Nabers, 1954}), this surgical technique has been modified to allow partial thickness displacement of the gingival tissues. The dissection of part of the gingiva, followed by apical repositioning, leaves the periosteum exposed in order to protect the alveolar bone and to promote healing (^{Staffileno et al., 1962}). The parameter to be taken into account when making the choice of the surgical technique is the initial width of attached gingiva : if the total height of the gingiva is adequate (5 mm) and yet there is insufficient attached gingiva, it is possible to use a full thickness flap with displacement of the entire gingiva, after raising a muco-periosteal flap as far as the muco-gingival junction. Conversely, if the problem is one of insufficient attached gingiva together with the need for crown lengthening, a partial thickness apically displaced flap will deal with both indications at the same time.

In the following clinical case, a 40-year-old patient presents with moderately severe chronic periodontitis associated with periodontal pockets in the anterior region (^{fig. 6}). There is a secondary diastema (drifting) between teeth 21 and 22 and exposure of the margins of restorations. Analysis of all the factors indicates the need for a full thickness apically displaced flap that will simultaneously eliminate the periodontal pockets (^{fig. 7} and ⁸ ), lengthen the crowns with the aim of improving the aesthetics and also realign all the gingival margins in the incisor-canine sector (^{fig. 9}).

Bone surgery

Bone surgery involves the required relevant diagnostic stages and specific operative procedures (^{Friedman, 1955} ; ^{Ochsenbein, 1986}). Crown lengthening can combined with bone surgery using either a full or partial thickness apically displaced flap if it is necessary to increase the height of attached gingiva at the same time (^{Bragger et al., 1992} ; ^{Caillon and Danan, 2000} ; ^{Jorgensen and Nowzari, 2002)}. The aim of the bone surgery will be to re-establish the pre-prosthetic space as well as the biological space. This will be achieved by ostectomy, which will remove some of the anchoring periodontal ligament fibres, and will be completed by osteoplasty in order to remodel the bone contour (^{Schluger, 1949}).

This is the clinical case of a 35-year-old patient having just lost a second molar and who presents with a broken down first molar that does not even allow temporary restoration because of the subgingival extent of the lesions (^{fig. 10}). The clinical and radiological assessment of the relevant factors indicates the possibility of restoring the first molar following bone surgery (osteoplasty-ostectomy) undertaken with an apically displaced muco-periosteal flap, together with a distal wedge (^{fig. 11}). The restoration can then be effected under optimal conditions (^{fig. 12}).

Orthodontic extrusion

When bone surgery would inevitably lead to a poor aesthetic result or bring about an excessive reduction in bone support, orthodontic extrusion (^{Berglundh et al., 1991} ; ^{Koslovsky et al., 1998}) must be the indication of choice as it can reinstate a favourable crown/root ratio. The orthodontic treatment achieves extrusion of the root through the periodontium by using high forces. This causes rapid tooth movement yet avoids root resorption (^{Fontenelle, 1982} ; ^{Biggerstaff et al., 1986} ; ^{Pontoriero et al., 1987}). Orthodontic extrusion can be complemented by periodontal root lengthening surgery in order to achieve a more favourable result. In all cases, the orthodontic treatment will be combined with circumferential sulcular fribrotomy to reduce the amount of bone remodelling needed (^{Korbendau and Guyomard, 1998}).

In this clinical case, a 50-year-old patient presents with a significant amount of tissue loss around teeth 25 and 27. Analysis of the various factors needed to make a treatment decision showed that 27 had to be extracted and that 25 could not be dealt with by bone surgery (^{fig. 13}). In effect, this would lead to a major loss of attachment and exposure of the interradicular space with 26. The root of 25 could be saved by orthodontic extrusion taking about 6 weeks (^{fig. 14}), together with a partial thickness apically displaced flap to complete the elongation of the crown, to align the anatomical gingival margins and to reinforce the gingiva (^{fig. 15}). The final clinical and radiographic result shows that all the principles of treatment have been upheld and the construction of a functional and aesthetic restoration has been made possible (^{fig. 16} and ¹⁷).

Conclusion

Crown lengthening, by restoring the biological space, improves the periodontal/restoration environment. The success of the procedure depends on a careful assessment of the clinical and radiographic data as well as the precision of the surgical technique. The benefits of crown lengthening will be judged by the longevity of the restoration and the health of the surrounding periodontium. Crown lengthening is rarely confined to one tooth but is part of the overall treatment plan that takes into account all the relevant biological, anatomical and aesthetic factors.

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