Crown lengthening is an invaluable tool for the restorative dentist in the management of short clinical crown heights.
This procedure, as an adjunct to a holistic restorative treatment plan, can produce predictable results, whilst ensuring good aesthetics and
maintaining periodontal health.
Crown lengthening procedures are invaluable where toothwear or lack of supragingival tooth substance would render full coverage restoration difficult. Gaining access to subgingival caries for strategic abutments can also be achieved in this way. In certain instances, excessive gingival show or inharmonious gingival margin levels can be aesthetically managed with crown lengthening procedures.
Knowledge of crown lengthening techniques, and where these might be prescribed, may be a useful addition to practitioners’ treatment planning options, or to decide when referral may be more appropriate.
Restorative dentistry implies a multidisciplinaryapproach to the provision of dental care and has advanced tremendously in recent times. Modern trends see a shift towards implant-retained restorations and adhesive/resin-bonded techniques to replace missing tooth tissue.
Recent advances in adhesive dentistry make the restoration of worn teeth using these techniques an alternative predictable treatment option.
There are, however, clinical situations where adoption of traditional techniques, namely fullcoverage restorations, is necessary.
For many of these techniques, the importance of retention and resistance form to the success and longevity of restorations,and thus the need to have adequate supragingival tooth tissue, is critical.
The need for healthy periodontal tissues to support these restorations also cannot be overstated.
Crown lengthening surgery is underpinned by our understanding of the relationship of restorative margins to these periodontal tissues.
Biologic width:
The term ‘biologic width’ was originally coined by Gargiulo et al1 in 1961. The original research was based on scientific measurements of the relationship and dimensions of the dentogingival junction in cadaveric specimens.
Functionally, the supracrestal attachment can be divided into two parts: the connective tissue attachment and the epithelial attachment .
In this study, connective tissue attachment measurements were fairly constant, whereas the epithelial attachment (junctional and sulcular) was highly variable.
The mean values of the connective tissue and epithelial attachments were 1.07mm and 1.66mm,respectively (junctional epithelium 0.97mm and sulcular epithelium 0.69 mm). The biologic width is defined as ‘the width of the junctional epithelium and supracrestal connective tissues that lie between the base of the gingival sulcus and the alveolar crest’ and represents the area of attachment of the periodontal
soft tissues to the tooth. The average dimension of biologic width has been shown to be 2.04mm Understanding and application of the concepts of the biologic width is of key importance when planning placement of margins of restorations as impingement into this critical space has been associated with plaque accumulation, gingival inflammation, attachment loss and crestal bone loss. It has therefore been suggested that restoration margins should not be placed more than 0.5–1.0 mm subgingivally, and that there should
be at least a 3 mm distance between the restoration and the alveolar crest to prevent encroachment on to the biologic width.
The biologic width concept is also relevant to dental implants. Some studies have suggested a certain width of periimplant mucosa is necessary to ensure stability of the soft tissue framework and, where this is insufficient, then physiological bone resorption takes place until this dimension is secure.
Indications for crown lengthening:
There are many factors to consider before planning restorative treatment and one of the most fundamental is crown length, especially in cases involving non-carious tooth tissue loss.
Crown length may be defined as the portion of tooth that extends from the soft tissue margin occlusally to the incisal/cusp tip.
Crown lengthening is therefore indicated where insufficient crown length exists to allow predictable restoration of the teeth.
It may also be indicated to gain access to subgingival caries or to improve gingival aesthetics.
Contra-indications for crown lengthening:
There are few absolute contraindications to crown lengthening and these include medical issues that might preclude other oral surgical procedures.
A selection of some of the more important relative contra-indications include:
- Smoking;
- Thin periodontal tissue biotype;
- Narrow-band of attached gingivae;
- Where a furcation on the tooth or an adjacent tooth may be exposed;
- Surgery in the aesthetic zone;
- Concurrent endodontic/periodontal disease
- Presence and extent of caries
Assessment of treatment options:
Crown lengthening is a surgical procedure and a degree of postoperative discomfort and morbidity is to be expected. It is therefore incumbent on a practitioner to consider other potential treatment options as part of the consent process.
Alternative treatment options may include:
- Orthodontic extrusion of teeth +/- crown lengthening
- Overdenture in cases of extreme toothwear
- Extraction and tooth replacement.
Case preparation:
- Tooth preparation
Where possible, the provisional restoration of teeth that are planned for crown lengthening will simplify further management.
Caries should be removed, as far as possible, initially.
This will allow an assessment of the remaining tooth substance and restorability.
Existing crown restorations should be removed and replaced with provisional restorations.
Provisional crowns can provide a clear guide to the surgeon of encroachment on biologic
width, and where bone removal may be a necessary adjunct to crown lengthening .
In addition, wellfitting margins simplify oral hygiene, reduce plaque accumulation and improve post-surgical healing response.
In many cases, crown lengthening is necessary before teeth can be restored, for example in severe tooth surface loss.
In such cases, preparation of a pre-operative diagnostic wax-up is an invaluable planning aid. This will provide informationsuch as how much tooth substance needs to be exposed for crown retention,
likely post-operative crown-root ratio and planned aesthetic result. In addition,a stent constructed on the diagnostic wax-up may also be used as a surgical guide for bone removal
Definitive endodontictreatment should be carried out prior tocrown lengthening, where appropriate.
Failed attempts at root canal treatmentafter crown lengthening surgery mayresult in tooth loss and therefore thepatient may have been exposed tounnecessary surgery. Where isolationdue to short crown height is difficult, asplit dam technique may be used
2. Informed consent
Crown lengthening surgery has similar risks to other forms of periodontal surgery. In particular, the risk
of an adverse aesthetic impact should be discussed carefully. Often, this surgery is
in the aesthetic zone.
Loss of interdental papillae and subsequent ‘black triangles’ may be a significant consequence.
Bone removal around teeth adjacent to those to be crown lengthened may compromise their own support. The risk of exposing a furcation has to be carefully evaluated. Orthodontic extrusion of teeth may be valuable in some instances as the alveolar bone and gingivae will tend to move with the tooth.
This may help place the gingival margin in an ideal position and prevent excessively long clinical crowns.
Exposure of root dentine may also predispose to dentinal hypersensitivity.
Another, not uncommon, consequence is relapse of the gingival margin.Bone removal does not come
naturally to restorative dentists and, where this is inadequate, the gingival margin will tend to return to preoperative levels.
The surgeon should therefore make every effort to ensure that, where necessary, bone removal
is carried out to allow at least 3 mm between alveolar crest and restorative margins.
Needless to say, careful clinical records should be made as part of the planning process and, where aesthetic change is intended, clinical photographs are mandatory.
It is important to record a detailed pocket chart around the teeth planned for surgery, to ensure:
- No untreated periodontitis remains undetected at the planning stage;
- A detailed record of probing sulcus depth is available at the time of surgery.
3. Surgical procedures
There are three main approaches to surgical crown lengthening:
- Gingivectomy;
- Apically-positioned flap (APF) surgery
- APF with osseous reduction
As bone removal is often necessary to avoided encroaching on biologic width, the APF with osseous reduction is probably the most frequently used approach.
- Gingivectomy: represents the simplest approach to crown lengthening. It is generally appropriate where there is an element of gingival overgrowth or false pocketing. It is also valuable where there has beenloss of periodontal attachment. In this respect, a detailed pocket chart will be invaluable.Precise changes in gingival margin location are relatively straightforward with a gingivectomy technique.
This is in contrast with the apically repositioned flap, where location of the gingival margin may be less predictable and technically more demanding.
On the other hand, the gingivectomy approach may be less conservative of attached gingival tissue.
Where this is only present in a thin band, an apically-positioned flap may represent a more tissue-conservative option.
demonstrates a case where simple gingivectomy was used to effect an increase in crown height.
2. Apically-positioned flap surgery: Where this flap is considered, the width of attached gingivae should be carefully assessed.
Where this width is minimal, the incision may be intrasulcular to preserve attached gingivae.
Where there is abundant attached gingivae, the incision may be relatively scalloped and submarginal.
Local gingival conditions should be observed and the flap may incorporate both intrasulcular and submarginal elements.
The flap design for an apically repositioned flap should normally involve two vertical relieving incisions.
This increases flap mobility and makes apical repositioning more straightforward.
The flap will normally extend to include adjacent teeth and thus allow interdental bone removal and recontouring, as appropriate.
Often, the decision to remove bone can be made when the flap is raised and precise measurements may be made of the distance between alveolar crest and restoration margins.
The relieving incisions should be made as vertical as possible and parallel with each other.
This means that, when the flap is repositioned apically, there is good apposition of flap margins at these relieving incisions .
When the apically-positioned flap is sutured, it is convenient initially to place sutures in the vertical relieving incisions.
The needle penetration in the flap margin should be relatively more apical in the bound tissue than the reflected flap as this will generate apical rather than coronal tension.
Interdental sutures are placed to provide soft tissue coverage of interdental bone.
This is done with minimal tension to avoid coronal movement of the flap.
It is very difficult to attain perfect closure of an apically repositioned flap and, in some places, healing will be by secondary intention.
It is often prudent to place a periodontal dressing after closure to protect any areas of denuded bone.
3. Osseous reduction: Osseous reduction during crown lengthening is often necessary.
A decision can be made on this when the flap is raised and measurement of alveolar crest to restorative margin can be made with a periodontal probe.
Initial bone removal is accomplished with burs and copious coolant. An osseous contour is created to mirror the parabolic interdental contour and scalloped cervical margins of the original alveolar bone and, ideally, to support the gingival tissues.
It is important to avoid damage to the root surfaces of the teeth to be lengthened. To this end, a thin layer of bone is left on the root surfaces.
This may then be removed with hand instruments, such as a sharp curette or chisel.
4.Post-surgical management: Healing is by secondary intention, in many cases, and periodontal dressings and sutures are left in place for around one week, where possible.
Gingival maturation will continue over time and it is sensible to postpone definitive restoration of teeth until this time.
In particular, definitive restoration of teeth in the aesthetic zone should be carried out at least six months after surgery.
Conclusions
Crown-lengthening surgery represents a useful adjunct to restorative treatment planning and may be very useful, particularly where toothwear necessitates a conventional approach to restoration. As with many
periodontal surgical procedures, case selection and planning is paramount.
Crown-lengthening can be technically demanding and potentially have negative aesthetic consequences.
It is important, therefore, that practitioners anticipate these difficulties and refer for treatment where appropriate.
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