Biologic Width- An Enigma?

Headnote

Abstract

The term biologic width is familiar to most clinicians, yet there still exists confusion regarding its meaning and relevance to clinical procedures. This article deals with the basic concepts of biological width particularly with regard to interactions at the gingival margin including the success of restorative procedures and reasons for their failure. Evaluation, violation and various procedures regarding reconstruction of biological width are also discussed.

Introduction

Biologic width is defined as the dimension of the soft tissue which is attached to the portion of the tooth coronal to the crest of the alveolar bone. This term was based on the work of Gargiulo et al., who described the dimensions and relationship ofthe dentogingivaljunctioninhumans.1

The dentogingival junction has been described as a functional unit composed ofthe connective tissue attachment of the gingiva and the epithelial attachment.1

Gargiulo et al., reported the mean sulcus depth of 0.69mm, themeanconnectivetissue attachment to be 1.07mm(1.06 to 1.08mm) and the epithelial attachment to be 0.97mm (0.71 to 1.35mm). Thus, the biologic width is commonly stated to be 2.04mm (1.77 to 2.43mm) which represents the sum ofthe epithelial and connective tissue measurements (Figure l).1'2

The dimension of biologic width is not constant, it depends onthelocationofthetoothinthe alveola, varies fromtooth to tooth and also from the aspect ofthe tooth. Its constancy canonlybefoundinhealthy dentition.3

Maynard and Wilson divided the periodontium into 3 dimensions:4

1. Superficial Physiologic Dimension: It represents the free and attached gingiva around the tooth.

2. Crevicular Physiologic Dimension: It represents the gingival crevice extending from free gingival margin to the junctional epithelium.

3. Subcrevicular Physiologic Space: It is analogous to biologic width described by Gargiulo et al., consisting of junctional epithelium and connective tissue attachment.

The authors claimed that margin placement into the subcrevicular physiologic space should be avoided to prevent the placement of calculus beyond the crevice. However, certain clinical situations demand intrasulcular restorative margins. They are:

1. Esthetic and retention requirements

2. Root sensitivity

3. Fracture of tooth at a subgingival level

4. Extent of existing caries or previous restorations

Nevins and Skurow stated that when subgingival margins are indicated, the restorative dentist must not disrupt the junctional epithelium or connective tissue apparatus during thepreparationandimpressiontaking.5

The authors recommended limiting subgingival margin extension to 0.5-lmm because it is impossible for the clinician to detect where the sulcular epithelium ends and the junctional epithelium begins. They also emphasized allowing a minimum 3mm distance from the alveolar crest to the crown margin.

Restorative margin location and biologic width

The location ofthe restorative margins is determined by many factors including esthetics, retentive factors, susceptibility to root caries and degree of gingival recession. While most periodontists prefer restorative margins to remain coronal to the sulcus, in certain conditions restorative margins are needed to be placed subgingival^. These include esthetic concerns, need for increased retention form, refinement of pre-existing margins, root caries, cervical abrasion androot sensitivity.6

Before placing a restoration two basic factors should be considered. First is the shape and the method of preparation, which depends upon the clinician. The second factor is the ultimate success of the restoration which is influenced by a number of factors.7

Preparation

It is desirable to place the margin in a location that will facilitate the following:3

1) Preparation ofthe tooth and finishing ofthe margin.

2) Duplication of the margins during making of the impressions such that the tearing or deformation can be avoided.

3) Fit and finish of the restoration and removal of excess material can be done easily.

4) Verification of the marginal integrity of the restoration.

These can be achieved by placing the margins supraging-ivally.

The ultimate success of the restoration

Many factors are responsible for the success of a prosthetic restoration:

1) Brushing, flossing and maintaining the restoration on a daily basis which can be achieved when the margins are keptsupragingivally

2) The buccal and the lingual crown contours should be flat and less than 0.5mm wider than the CEJ and the furcation areas should be fluted or barreled out to facilitate proper oral hygiene.8

3) The interproximal contacts should be tight to avoid food impaction as it leads to periodontal disease.9

4) Esthetic requirements of the patients often call for intra-crevicular placement of margins. On the contrary in a study published by Watson and Crispin many patients choose the optimum gingival health offered by supra-gingival margin placement over the less healthy subgin-gival margin.10 The study also showed that 83% of dentists do not analyze tooth visibility when deciding on margin placement for esthetic appearance and only 64% of dentists actually assess the patient's desires before deciding where to place the margin.

5) Earlier subgingival margin placement was done in cases with insufficient or questionable retention so as to provide greater length and surface area. Presently surgical crown lengthening technique is being used to increase the height of the clinical crowns. It provides tooth length for proper restoration of a tooth without compromising the periodontium or retentive qualities of the restoration."

Research in animals and humans showed that margin infection is most commonly connected with subgingivally placed margins and that supragingival placement has a substantial positive effect on gingival health.12-14

Failure of the restoration

The reasons for failure of a restoration in terms of placing the margin subgingivally could be due to:

1) Improper finishing of the margins of crowns, veneers or restoration

2) Placing the margins subgingivally such that the biological width is violated

3) Insufficient zone of attached gingival

4) Improper crown contour in gingival third

In cases where margins have to be placed subgingivally, theissueofconcernisthatitbecomesdifficulttopolishthe margins. Thus coarse margins harbor bacteria hindering periodontal health.15 These places represent ideal bacteria colonizing areas resulting in localized inflammation and gingivitis.

Gunay H et al., showed how margins of restoration in the area of gingival biological width cause pathology of the periodontium.16 It was evaluated in 116 restored and 82 healthy teeth of 41 patients that showed formation of periodontal pockets and increased gingival bleeding in the areas with distance less than 1mm from restoration margin to alveolar bone.

Other studies comparing relationship of restorations and gingival biological width showed similar results. It is necessary to keep minimal distance of 3mm from restoration to alveolar bone to keep the periodontium healthy617 Gingival biological width would be altered if the distance is less than 2mm from restoration margin to alveolar bone, inthatcasegingivalinflammationstarts.18

Human body tries to repair this dimension of 2mm by reso-rbing the bone as much as needed to create the space for gingival attachment between restoration and alveolar bone. Gingival inflammation depending on status of immune system, earlier or later, induces loss of periodontal ligament and bone of this area, till enough width for gingival attachmentis achieved.19

Evaluation of biologic width

* Radiographic interpretation can identify interproximal violations of biologic width. But they are not diagnostic because of tooth superimposition.

* If a patient experiences tissue discomfort when the restoration margin levels are being assessed with periodontal probe, it is a good indication that the margin extends into the attachment and that a biologic width violation has occurred.

* A more positive assessment can be made clinically by measuring the distance between the bone and restoration margin using a periodontal probe. The probe is pushed through the anesthetized attachment tissues from the sulcus to the underlying bone. If this distance is less than 2mm at one or more locations, a diagnosis ofbiologicwidthviolationcanbeconfirmed.

* The biologic, or attachment width can be identified for each individual patient by probing under anesthesia to the bone level ('sounding' to bone) and subtracting the sulcus depth from the resulting measurement. This measurement must be performed on teeth with healthy gingival tissues and should be repeated on more than one tooth to ensure an accurate assessment.

Violation of biological width

In clinical practice, intentional and inadvertent violations of the biological width occur, causing difficult impre-ssioning and hygiene procedures and unacceptable coronal contours of the final restoration.20

The reasons for violation of the biological width include:

1) Attemptto access sound tooth structure

2) Increased need for preparation length

3) Previous restorations

4) Existing caries

5) Resorption defects

6) Traumatic injury

7) Iatrogenic insults

8) Improper identification of sulcus depth

Consequences of violation of biological width are :21

1) Localized gingival hyperplasia

2) Gingival recession

3) Deep periodontal pockets

4) Root caries

5) Furcation defects

6) Tooth mobility because of loss of tooth attachment apparatus

7) Tooth loss

If the biologic width is violated at the facial or lingual aspect and the adjacent alveolar bone is thin, alveolar bone resorption is likely to occur. This may be followed by gingival recession with thin gingival tissue.

Most biological width violations occur on the interproximal surfaces where bone is thick. Often, bone resorption does not occur immediately and the gingival tissue may remain chronically inflamed. However, if bone resorption occurs, intrabony defects develop interproximal^ over time.20

Whenever the biologic width is violated, there is a reaction by the periodontium. Alveolar bone will resorb to provide space for a new connective tissue attachment and the sulcus will be deepened. This re-establishment of the periodontal attachment at a more apical position and deepened sulcus combined with a deep subgingival restoration margin frequently leads to chronic inflammation and localized periodontal breakdown. It has been shown that the inflammatory response is not caused by irritation from the roughness of the restorative material, but rather by the plaque front retained and developed at the restoration-tooth interface.6

Correction of biologic width violations

Biological width violations can be corrected by either surgically removing bone away from proximity to the restoration margin or orthodontically extruding the tooth and thus moving the margin away from the bone. Surgery is the more rapid of the two treatment options. In these situations, the bone should be moved away from the margin by the measured distance of the ideal biologic width for that patient, with an additional 0.5mm of bone removed as a safety zone.22

The methods of surgically correcting biological width violations are:

l)Gingivectomy

2) Apically positioned flap

3)Apically positioned flap with osseous surgery

Surgical procedures

1) Gingivectomy

This procedure is useful in cases with fibrotic enlargement of the gingiva in which the crown lengthening procedure will be limited to exposure of subgingival portions of the anatomic crown. In these cases clinical crown is shortened due to excessive gingival display, these can be treated by surgically excising the gingiva.23 25

2) Flap Surgery

It is an internal beveled gingivectomy with internal reduction of excess gingiva combined with elevation of a flap, repositioning and suturing.

1. It is performed by using a scalpel to place an internal beveled incision designed in a scalloped fashion around the teeth to outline the new location of the gingival margin at a pre-determined location.

2. Incision is made in gingival sulcus and a collar of gingiva is removed from around the teeth.

3. Amucoperiosteal flap is raised with a periosteal elevator to allow repositioning of the flap around the teeth. In sites where there is insufficient gingiva for reduction, the initial incision is placed intrasulcularly and a muco- periosteal flap raised and apically positioned to gain the needed crown length.

This procedure is limited, like the gingivectomy to sites not requiring osseous surgery. If it becomes apparent that osseous surgery is required, this approach provides access for such surgery whereas gingivectomy procedure does not.

3) Flap with Osseous Surgery

It is the most common procedure used for clinical crown lengthening.

1. Amucoperiosteal flap is designed and raised as described above.

2. The alveolar bone is reduced by ostectomy and osteoplasty, using a combination of rotary instruments and chisels to expose the required tooth length in a scalloped fashion to follow the desired contour of the overlying gingiva.

3. The process is then completed with curettes directed against the bone. The most difficult area to reduce is the interdental bone because of limited access. This can be done by using one-half round bur and a Wedelstaedt chisel may be helpful in addition to curettes in reducing the narrow interproximal bone.

The final bone should be measured carefully in all locations around the tooth to be certain that the minimal of 3-5mmoftoothheighthasbeen achieved.

4. Suturing is done and dressing is placed to aid in maintaining flap adaptation.

5. Gentle brushing and flossing may begin at 4 to 7 days post surgery.

6. Chlorhexidine mouthrinse should be used for 4-6 weeks to aid in plaque control. Restorative procedures should be delayed until 3 to 6 months post surgery.2629

The longer period reduces the risk for gingival margin shrinkage in areas requiring maintenance of subgingival restoration margins.

If the biologic width violation is on the inter-proximal or if the violation is across the facial surface and the gingival tissue level is correct, then orthodontic extrusion is indicated. The extrusioncanbeperformedin two ways:30'31

1. Slow extrusion

2. Rapid extrusion

1. Slow Extrusion: By applying low orthodontic force, the tooth is erupted slowly by bringing alveolar bone and gingival tissue along with it. The tooth is extruded until the bone level has been carried coronal to the ideal level by the amount that needs to be removed surgically to correct the attachment violation.

It can also be used as a means of reducing pocket depths at sites with angular bony defects.

2. Rapid Extrusion: This procedure may be used for cro wn lengthening when there is sufficient root length so as to notjeopardize the crown-root ratio. The tooth moves faster than the body's ability to remodel the attachment appara tus. Because supracrestal fibers can follow the rapidly extruding root, weekly fiberotomy (cutting the supracres tal fibers) should be considered. The tooth is then stabilized for at least 12 weeks to confirm the position of the tissue and bone and any coronal creep may be corrected surgic ally. It is contraindicated when teeth are associated with angular defects, in such cases, the slow eruption technique shouldbepreferred.

Conclusion

Biologic principles dictate that "subgingival" margin placement be avoided. However, when concerns for esthetics, decay, or other aforementioned variables exist, intrasulcu-lar margins can be accepted, provided they do not extend more than 0.5mm apical to the gingival crest. Furthermore deep margin placement risks invading the soft tissue attachment of gingiva to the tooth, often leading to a more pronounced plaque induced inflammatory response. If restorative margins need to be placed near the alveolar crest, crownlengthening surgery or orthodontic extrusion should be considered to provide adequate tooth structure while simultaneously assuring the integrity of the biological width.

References

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Disclosure : The authors report no conflicts of interest.