Dental Update - An update on crown lengthening part 2: increasing clinical crown height to facilitate predictable restorations

Abstract

This is the second paper in this two-part series. Paper one provided an overview of managing gingival tissue excess and paper two will focus on increasing clinical crown height to facilitate restorative treatment. Crown lengthening is a surgical procedure aimed at the removal of gingival tissue with or without adjunctive bone removal. The different types of procedure undertaken will be discussed over the two papers. In order to provide predictable restorations, care must be taken to ensure the integrity of the margins. If this is not taken into account it can lead to an impingement on the biologic width, which may in turn lead to chronic inflammation resulting in recession or the development of periodontal problems which can be hard to manage.

Clinical Relevance: This paper aims to reinforce the need for thorough diagnosis and treatment planning and provides an overview of the various procedures that can be undertaken.

Article

This second of two papers will focus on increasing clinical crown height to facilitate restorative treatment. This type of procedure is often needed in patients who have subgingival caries or restorative margins that impinge upon the biologic width.

Crown lengthening may be defined as a surgical procedure which is aimed at the removal of gingival tissue to increase clinical crown height. It can be undertaken as part of a restorative treatment plan, following full case assessment and having considered all possible alternatives. There are different types of crown lengthening procedures, some of which require osseous recontouring, and some of which do not. In order to understand which type of procedure is required the operator must consider what the intended outcome is, as well as taking into account the aetiology and the biological parameters. This entails taking a detailed history, examination and clinical assessment which includes exploring patient expectations. If these parameters are not fully considered patients can be left in a more compromised position than they were to start with; this is even more important when working in the aesthetic zone.

Crown lengthening surgery is needed to maintain the health of the gingival tissues by preserving the biologic width, the violation of which may lead to chronic inflammation and/or recession.

The biologic width

The ‘biologic width’ concept was first described by Gargiulo et al in 1961, following a histological study in human autopsy specimens, examining the relationship between the various components involved in periodontal attachment.1 Although there were variations, average values were calculated for sulcus depth (0.69 mm), epithelial attachment (0.97 mm) and connective tissue attachment (1.07 mm), which gave a mean length of 2.73 mm for the dentogingival junction, ie between the crestal bone level and gingival margin. If this is encroached upon it can lead to inflammation, clinical attachment loss and bone loss due to the destructive inflammatory response to plaque accumulation around restoration margins. Nevins and Skurow also described the importance of a 3 mm biological dimension separating the osseous crest from the plaque associated with crown margins; it was recommended that the extension of crown margins be limited to 0.5–1 mm subgingivally, as it is impossible for the clinician to detect exactly where the sulcular epithelium ends and the junctional epithelium begins.2 Silness found that subgingival crown margins can significantly compromise gingival health. He evaluated the periodontal condition of 385 bridge abutments and found that supragingival margins were the most favourable. It was found that, in thicker biotypes, impinging on the biologic width leads to pocket formation and, in thin tissue biotypes, it can lead to gingival recession.3 This means that, when placing crown margins, ideally a supragingival margin is the most favourable for cleansability; however, this is not always possible and, in aesthetic areas, the limit should be within the gingival sulcus.

Indications

The main indications for crown lengthening can be divided into two categories:

Restorative needs:

– To increase clinical crown height due to caries, fracture or wear;

– To access subgingival caries;

– To create a 2 mm ferrule for post-crowns;

– To relocate margins impinging on the biologic width; and

Aesthetic needs:

– To increase the length of short teeth in patient with excess gingival show;

– To manage uneven gingival margins;

– Management of delayed passive eruption.

The interventions relating to aesthetic needs which only require management of soft tissue have already been covered in paper one.

Treatment planning

Effective treatment planning forms the cornerstone of successful treatment outcomes. It enables the risks of the procedure to be considered and the patient to be informed in order to make the choice between various treatment options. The patient's medical history must be fully updated to ensure that there is no medical contra-indication. Also, the operator must ensure that all primary disease has been managed as this type of treatment would not be appropriate in a patient with active periodontal disease or caries. Smoking is not an absolute contra-indication. However, studies by Preber and Bergstrom have reported poorer outcomes for surgical and non-surgical periodontal treatment in smokers, therefore the patient should be warned about the increased risk of failure and associated complications.4

The specific factors to consider when planning a surgical procedure include:

Smile line;

Crown-to-root ratio;

Root configuration;

Position of the cemento-enamel junction (CEJ);

Proximity to nerves;

Amount and quality of keratinized tissue.

Smile line

As part of a full case assessment, the amount of gingival show at rest and at full smile should be assessed; this is especially important when planning treatment in the aesthetic zone.

Crown-to-root ratio

Good quality periapical radiographs should be taken to assess the crown-to-root ratio, which is the physical relationship between the portion of the tooth within the alveolar bone compared with the portion not within the bone, as determined radiographically.5 Textbooks often quote an ideal crown-to-root ratio of 1:1.5 for bridge abutments, however, this is rarely observed.6 Crown lengthening will increase the crown-to-root ratio and so care must be taken to take this into account, along with the careful assessment of the clinical parameters such as mobility, bone support, root configuration, occlusion, presence of a parafunctional habit and presence of endodontic treatment.7

Root configuration

Radiographs will give an indication of the width of interdental bone that is present. If roots are too close together it may be more challenging to access the bone between adjacent teeth to carry out the required crown lengthening.

An important aspect to consider with multi-rooted teeth is the position of the furcation, as inadvertent exposure of this area would lead to difficulty with maintaining cleaning. Long-term studies have shown that furcation-involved multi-rooted teeth are eight times more likely to be lost, when compared to a single-rooted tooth with similar periodontal attachment levels.8 Dibart and co-workers undertook a radiographic analysis study, comparing teeth restored with cast restorations, with and without surgical crown lengthening. They found that, radiographically, a minimum distance of 4 mm is required from the furcation to the crestal bone pre-operatively, to reduce the risk of furcation exposure.9 Of course the feasibility of this will depend upon the anatomy and position of the furcation; a more coronally placed furcation, with a high risk of exposure following surgery, would not be considered as an ideal tooth for a crown lengthening procedure.

Position of the cemento-enamel junction (CEJ)

This is especially important when managing patients who present with delayed passive eruption. In the young adult with an intact periodontium, the gingival margin normally resides approximately 1 mm coronal to the level of the CEJ, however, some patients may have a height of free gingivae greater than this, which leads to the disproportionate appearance of their clinical crown. In these cases, if patients perceive that their teeth are too small, then this can be addressed by undertaking a gingivectomy procedure. However, if there is bone covering the CEJ, then osseous recontouring and apical repositioning of the flap may be required.10

Proximity to nerves

When carrying out surgery in the mandibular premolar region, care must be taken to avoid damaging the mental nerve as this could lead to permanent numbness of the ipsilateral chin, lower lip and buccal gingivae anterior to the premolars. From a medico-legal point of view, patients must be informed of this risk to ensure valid, informed consent.

Amount and quality of keratinized tissue

The patient's gingival biotype and the amount of keratinized tissue must be assessed as this will determine the type and choices of surgical procedure.

Surgical techniques

Pre-operative surgical planning

The intended clinical crown height is planned before any surgery is undertaken using study casts and a diagnostic wax-up, from which a surgical stent may be constructed to use at the time of surgery. This assists the clinician in ensuring that the bone removal is in line with the restorative needs, and that the desired outcome will be achieved. The same protocol should be followed for all cases, whether working around single or multiple teeth. A case is shown below in Figures 1–3 which demonstrates the use of a surgical stent.

Figure 3. (a–d) Crown lengthening surgery: the surgical stent is placed onto the teeth at the start of surgery (a) and a periodontal probe is used to mark the position of the desired gingival margin within the zone of keratinized tissue (b). This is then used to guide the amount of soft tissue resection that is required, following which the flap can be raised and the stent used again to guide the amount of bone removal required (c). The immediately post-operative photograph is shown in (d).

Case demonstrating crown lengthening of multiple teeth in a patient with toothwear, using a surgical stent as a guide to aid bone removal

A 58-year-old male patient presented to the department complaining of poor anterior aesthetics due to toothwear, which he had been aware of for the past 10 years (Figure 1a, b). He reported awareness of a previous history of parafunctional activity. Medically, he suffered from acromegaly and had a history of a pituitary gland operation. An extra-oral examination revealed a high smile line; intra-orally, toothwear was noted affecting the upper and lower anterior teeth, with the maxillary central incisors being worst affected with up to 60% crown height loss. A treatment plan was formulated which involved localized crown lengthening surgery and composite build-up.

A diagnostic wax-up of the upper maxillary anterior teeth was constructed (Figure 2) and from this a surgical template was made.

This was used during the surgery to plan the ideal gingival margin position and aid bone removal (Figure 3).

Flap design

There are a number of factors that should be considered when designing the type of flap for a particular procedure, including the width of the keratinized tissue, which will have already been assessed during the initial clinical examination stage.

If the band of keratinized tissue is very thin, then it is likely that an intrasulcular incision will be made to preserve this tissue. It may be necessary to mobilize the flap to aid apical repositioning by creating vertical relieving incision(s) and/or relieving the tissue beyond the mucogingival junction.

If there is a thick band of keratinized tissue (>3 mm), then a resective approach may be favoured. This may be especially useful interdentally as this is often where more height for a cast restoration is required.

The design of flap is usually a full thickness mucoperiosteal flap which allows the periosteum to be fully raised and allows access to the underlying bone. Good access is a prerequisite for successful surgery and selecting the correct flap design will directly affect the outcome of the surgery.

Osseous recontouring techniques

Bone removal and recontouring is often required to help to re-establish the biologic width. A number of methods are available to guide the amount of bone removal; ideally there should be a minimum of 3 mm between the proposed crown/restoration margin and the alveolar bone.

In the aesthetic region, especially when a reasonable amount of bone removal is anticipated, a template can be produced from a diagnostic wax-up. This template gives the operator an indication of the desired tooth height, therefore the bone should be removed 3 mm apical to this point. This can be a very useful aid to ensure that adequate removal is undertaken, as often clinicians will tend to err on the side of caution, which may compromise the final result.

Bone removal and recontouring may be achieved using different techniques:

Hand instrumentation: using periodontal hand instruments such as chisels and bone files, however, this can be quite challenging and time consuming to undertake as it is quite technique sensitive.

Use of burs and handpieces: a round bur may be used in a slow handpiece, with adequate irrigation; however, it can be difficult to prevent damage to root surfaces, especially when working interdentally.

Piezosurgery, which will be discussed below.

Piezosurgery

Piezosurgery is a method based upon ultrasonics and was developed by Vercellotti.11 When a voltage is applied across polarized piezoceramic material contained within the handpiece, it causes the material to expand and contract creating micro-movements that, at the correct frequencies (ranging between 60–120 micrometres), is capable of osteoplasty and osteotomy.12 The piezosurgery unit is composed of a handpiece and a foot switch that are connected to the main power unit which also houses the irrigation unit. Saline irrigation is required to remove debris and ensure precise cutting. A number of tips are available in different shapes and sizes which can be used to access difficult areas in a much more predictable manner; also, at the osteotomy/osteoplasty setting, it is not possible to cut tooth, therefore it is very safe to use interproximally. Animal studies have been undertaken which show a more favourable healing response following resective periodontal surgery using the piezosurgery versus a conventional drill.13 An example of a case of crown lengthening of a single tooth is illustrated in Figures 4–7.

Figure 6. (a, b) Periodontal probe used to help mark the incision line using the template as a guide; (c) incision made along this line; (d) flap elevated buccally and palatally; (e) surgical template used to aid bone removal; (f) bone removal undertaken using piezosurgery.

Figure 7. (a) Immediate post-operative view and (b) following composite build-up.

Case demonstrating single tooth crown lengthening using piezosurgery for bone removal

A 21-year-old male patient presented to the department following a course of orthodontic treatment for the replacement of his missing mandibular premolars. He was generally healthy and a non smoker. On clinical examination, he presented with a high smile line (Figure 4), retained poor prognosis mandibular second primary molars and radiographic examination revealed the lower premolars to be missing. His maxillary right lateral incisor was microdont and the gingival margin was coronally positioned (Figure 4). A treatment plan was formulated which involved the placement of dental implants to replace his missing teeth, and localized crown lengthening of his lateral incisor, followed by a composite build-up.

A diagnostic wax-up of the maxillary right lateral incisor was constructed and from this a surgical template was made (Figure 5 a, b). Figure 5b shows the intended gingival margin of the maxillary right lateral incisor being confirmed using a periodontal probe which has been positioned on the gingival margins of the adjacent teeth. This was used during surgery to plan the ideal gingival margin position and to aid bone removal. The crown lengthening surgery was then undertaken (Figure 6 a–f).

As illustrated in the photographs, the surgical template was used at the start of the procedure to aid the gingival resection, and then also to aid bone removal as the aim was to have a distance of 3 mm between the bony crest and the gingival margin in order to maintain the biologic width.

The post-operative photograph is shown below in Figure 7a, demonstrating the new gingival margin position and the final restoration (Figure 7b).

Healing

When planning surgery the gingival biotype of the patient must be taken into account as it can affect the healing post-operatively. Patients with thick gingival biotypes are more likely to suffer from rebound, whereas those with thinner gingival tissue will be more prone to recession.

Studies have shown that the gingival margin does not stabilize until at least 20 weeks post-surgery.14 Bragger and co-workers assessed the changes post crown lengthening surgery over a six-month period; 25 patients with 85 teeth were included and the conclusion was that creating a distance of 3 mm from the alveolar crestal bone level to the restorative margin leads to stable periodontal tissue after 6 months. The mean tissue recession post-surgery was 1.32 mm and 29% of sites showed between 1–4 mm of recession between 6 weeks and 6 months.15 Attachment levels did not change after 6 weeks which supports restoration placement after 6 weeks for teeth not within the aesthetic zone. However, anteriorly it is sensible to wait for 6 months before placement of the definitive restorations.

Conclusions

It was the aim of these two papers to provide readers with insight into the types of crown lengthening surgery techniques that can be used in different clinical situations. The key to success lies within correct diagnosis which can only be achieved by taking a thorough history and undertaking a full clinical examination. If the planning stages are not carefully thought through, it can leave patients in a much more compromised position than when they started.

Amalgam, trams and Northern Ireland

The adult orthodontic–restorative interface. Part 2: treatment strategies for the management of developmental conditions

References

An update on crown lengthening part 2: increasing clinical crown height to facilitate predictable restorations

Authors

Harpoonam Jeet Kalsi

Deborah Iola Bomfim

Ulpee Darbar