|Year : 2015 | Volume
| Issue : 4 | Page : 250-256
Biologic width: Concept and violation
M Aishwarya, G Sivaram
Department of Periodontics, Ragas Dental College, Chennai, Tamil Nadu, India
|Date of Web Publication||23-Nov-2015|
19/20 Deccan Jamuna, Kannapan Nagar, Thiruvanmiyur, Chennai, Tamil Nadu
Source of Support: None, Conflict of Interest: None
The tooth and its supporting structures should be viewed as one biologic unit. An understanding of the periodontal-restorative relationship is necessary for the proper form, function, and esthetics of restoration and comfort to the patient. The dimension of the space that the healthy gingival tissue occupies above the alveolar crest is known as the biologic width. The concept of biologic width gains importance in the case of extensive caries management, subgingival margin placement, crown/root fractures, orthodontic banding, subgingival perforation and post, and core placement in endodontic therapy. Biologic width is important for the preservation of periodontal health which eventually decides the success of restorative procedures. This article discusses the anatomy, categories, evaluation, violation, and methods to correct the violation of biologic width.
Keywords: Biologic width, violation of biologic width, restorative margin placement
|How to cite this article:|
Aishwarya M, Sivaram G. Biologic width: Concept and violation. SRM J Res Dent Sci 2015;6:250-6
| Introduction|| |
The tooth, the pulp tissue within it, and its supporting structures should be viewed as one biologic unit. The periodontium and pulp have embryonic, anatomic, and functional interrelationship.
An understanding of this relationship is essential to ensure adequate form and function of dentition and esthetics/comfort to the patients. In case of restorations with Class III/IV caries, fractured (traumatized), severely decayed, partially erupted (delayed passive eruption), worn or poorly restored teeth impingement on the periodontal attachment apparatus, or violation of biological width can occur. This article discusses the concept of biologic width focusing on the cause, effect, and correction of biologic width violation.
The four aspects of restoration design which have a direct effect on the periodontium are: 
- Margin placement.
- Margin adaptation.
- Restoration contour.
- Occlusal function.
It is important to have a healthy periodontium prior to starting restorative treatment, because:
- Gingiva shrinks after periodontal treatment.
- The position of teeth is frequently altered in periodontal disease. Resolution of inflammation after treatment causes the teeth to move again, often back to their original position. Restorations designed for teeth before the periodontium is treated may produce injurious tensions and pressures on the treated periodontium.
- Inflammation of the periodontium impairs the capacity of abutment teeth.
- Discomfort from tooth mobility interferes with mastication and function.
- It is easy to obtain accurate impressions and make precise preparations on healthy gingiva than inflamed one.
- To minimize the risk of trauma to the gingival tissues during preparation and impression procedures.
| Biologic width|| |
The dimension of the space that the healthy gingival tissue occupies above the alveolar bone is called the biologic width [Figure 1]. 
Biologic width is essential for - the preservation of periodontium and removal of irritation that might damage the periodontium.
The dimension of biologic width is not constant, it depends on the location of the tooth in the alveolar, varies from tooth to tooth, and also from one surface of the tooth to another.
| Violation of biologic width|| |
Violation of the biologic width - leads to ultimate failure of the restoration.
Encroachment of biologic width becomes of particular concern when considering the restoration of a tooth that has fractured or been carious near the alveolar crest. Also, esthetic concerns often require hiding of restorative margins below the gingival margin that is pushing them down into the gingival sulcus leading to the violation of biologic width.
Bone loss and gingival recession occur as the body attempts to recreate room between the alveolar bone and the margin to allow space for tissue reattachment. This is more likely to occur in areas where the alveolar bone surrounding the tooth is very thin. This fragile tissue recedes leading to the gingival recession. 
| Evaluation of biologic width violation|| |
If a patient experiences tissue discomfort when the restoration margin levels are being assessed with a periodontal probe, it is a good indication that the margin extends into the attachment and that a biologic width violation has occurred.
The signs of biologic width violation are [Figure 2]: 
|Figure 2: Signs of biologic width violation - inflammation and bone loss|
Click here to view
- Chronic progressive gingival inflammation around the restoration.
- Bleeding on probing.
- Localized gingival hyperplasia with minimal bone loss.
- Gingival recession.
- Pocket formation.
- Clinical attachment loss.
- Alveolar bone loss.
- Gingival hyperplasia (most frequently found in altered passive eruption and subgingivally placed restoration margins).
Bone sounding/transgingival probing
The biologic width can be identified by probing under local anesthesia to the bone level (referred to as "sounding to bone") and subtracting the sulcus depth from the resulting measurement [Figure 3]. 
If this distance is <2 mm at one or more locations, a diagnosis of biologic width violation can be confirmed.
Radiographic interpretation can identify interproximal violations of biologic width.
However, on the mesiofacial and distofacial line angles of teeth, radiographs are not diagnostic because of tooth superimposition.
Parallel profile radiographic technique has been devised which could be used to measure both length and thickness of the dentogingival unit with accuracy. 
| Categories/Profiles of Biologic Width|| |
Kois proposed three categories of biologic width based on the total dimension of attachment and the sulcus depth following bone sounding measurements: ,
- Normal crest.
- Low crest.
- High crest.
Normal crest patient (85%)
The gingival tissue tends to be stable for a long-term. The margin of a crown should be placed no closer than 2.5 mm from alveolar bone [Figure 4].
Therefore, a crown margin which is placed 0.5 mm subgingivally tends to be well-tolerated by the gingiva and is a stable long term in the normal crest patient.
High crest patient (2%)
This is seen more often in a proximal surface adjacent to an edentulous site. In this situation, it is commonly not possible to place an intracrevicular margin because the margin will be too close to the alveolar bone, resulting in a biologic width impingement, and chronic inflammation [Figure 5].
Low crest patient (13%)
The low crest patient has been described as more susceptible to recession secondary to the placement of an intracrevicular crown margin. When retraction cord is placed subsequent to the crown preparation; the attachment apparatus is routinely injured. As the injured attachment heals, it tends to heal back to a normal crest position, resulting in gingival recession [Figure 6].
All low crest patients do not react in the same way to an injury to the attachment. Some low crest patients are susceptible to gingival recession while others have a quite stable attachment apparatus, the difference is based on the depth of the sulcus.
A patient with more substantial attachment apparatus and significantly shallower sulcus is less susceptible to the gingival recession (stable low crest), whereas in a patient with a deeper sulcus and narrower attachment with more of unsupported tissue from the base of the sulcus to the gingival crest, this amount of unsupported gingival tissue does not tend to be stable, and this patient is susceptible to gingival recession (unstable low crest).
| Margin placement|| |
Ingber et al. (1977)
Ingber et al., (1977) suggested that a minimum of 3 mm was required from the restorative margin to the alveolar crest to permit adequate healing and restoration of the tooth. 
Maynard and Wilson (1979)
Divided the periodontium into three-dimensions, all of which affect decision-making during restorative therapy: 
Superficial physiologic: Represents the free and attached gingival surrounding the tooth.
Crevicular physiologic: Represents the gingival dimension from the gingival margin to the junctional epithelium.
Subcrevicular physiologic: Is analogous to the biologic width described (Gargiulo et al. 1961), consisting of the junctional epithelium and connective tissue attachment.
Nevins and Skurow (1984)
Nevins and Skurow (1984) stated that when subgingival margins are indicated, the junctional epithelium, or connective tissue apparatus during preparation and impression taking. Limiting the subgingival margin extension to 0.5-1.0 mm is to be done, because it is impossible for the clinician to detect where the sulcular epithelium ends, and the junctional epithelium begins. A minimum 3.0 mm distance from the alveolar crest to the crown margin is necessary. 
Margin placement - Rules 
- If the sulcus probes 1.5 mm or less, the restorative margin could be placed 0.5 mm below the gingival tissue crest.
- If the sulcus probes >1.5 mm, the restorative margin can be placed in half the depth of the sulcus.
- If the sulcus is >2 mm, gingivectomy could be performed to lengthen the tooth, and create a 1.5 mm sulcus. Then the patient can be treated as per rule 1.
It has the least impact on the periodontium. This margin location has been applied in non-esthetic areas due to the marked contrast in color and opacity of traditional restorative materials against the tooth. With the advent of more translucent restorative materials, adhesive dentistry, and resin cements, the ability to place supragingival margins in esthetic areas is now a reality [Figure 7]. 
- Preparation of the tooth and finishing of the margin is easy.
- Duplication of the margins with impressions that can be removed past the finish line without tearing or deformation is the easiest with supragingival margins.
- The supragingival margins are least irritating to the periodontal tissue.
The use of equigingival margins traditionally was not desirable because, they were thought to favor more plaque accumulation, and hence result in greater gingival inflammation and that any minor gingival recession would create an unsightly margin display. These concerns are not valid today, not only because the restoration margins can be esthetically blended with the tooth but also because restorations can be finished easily to provide a smooth, polished interface at the gingival margin.
Restorative considerations will frequently dictate the placement of restoration margins beneath the gingival tissue crest because of dental caries or tooth deficiencies, and/or to mask the tooth/restoration interface. When the restoration margin is placed too far below the gingival tissue crest, it will impinge on the gingival attachment apparatus, and a constant inflammation is created and made worse by the patient's inability to clean this area. The body attempts to recreate room between the alveolar bone and the margin to allow space for tissue reattachment, as a result of which gingival recession and bone loss occurs. This is more likely to occur in areas where the alveolar bone surrounding the tooth is very thin in width. Highly scalloped, the thin gingiva is more prone to recession than a flat periodontium with thick fibrous tissue. The more common finding with deep margin placement is that bone level appears to remain unchanged; however, gingival inflammation develops and persists on the tooth restored [Figure 8]. 
If the margin must be placed subgingivally, the factors to be taken into account are:
- Correct crown contour in the gingival third.
- Correct polishing.
- Rounding of the margins.
- Sufficient zone of the attached gingival.
- No biologic width violation.
| Correction of biologic width violation|| |
0Surgical crown lengthening
- Inadequate clinical crown for retention due to extensive caries, subgingival caries or tooth fracture, root perforation or root resorption within the cervical 1/3 rd of the root in teeth with adequate periodontal attachment.
- Short clinical crowns.
- Unequal, excessive, or unesthetic gingival levels for esthetics.
- Teeth with excessive occlusal wear or incisal wear.
- Teeth with inadequate interocclusal space for proper restorative procedures due to supraeruption.
- Restorations which violate the biologic width.
- In conjunction with tooth requiring hemisection or root resection.
- Deep caries or fracture requiring excessive bone removal.
- Tooth with inadequate crown root ratio (ideally 2: 1 ratio is preferred).
- Non-restorable teeth.
- Tooth with increased risk of furcation involvement.
- Unreasonable compromise esthetics/adjacent alveolar bone support.
Gingivectomy can be done in the case of [Figure 9]:
- Hyperplasia or pseudopocketing (>3 mm of biologic width).
- Presence of adequate amount of keratinized tissue.
Apical repositioned flap surgery
• Without osseous resection.
This procedure is done when there is no adequate width of attached gingiva, and there is a biologic width of >3 mm on multiple teeth:
• With osseous reduction [Figure 10].
The alveolar bone is reduced by ostectomy and osteoplasty, to expose the required tooth length in a scalloped fashion, and to follow the desired contour of the overlying gingiva. As a general rule, at least 4 mm of sound tooth structure must be exposed, so that the soft tissue will proliferate coronally to cover 2-3 mm of the root, thereby leaving only 1-2 mm of supragingivally located the sound tooth structure.
Healing after crown lengthening
- In nonesthetic area: Re-evaluated after 6 weeks postsurgery.
- In esthetic areas, a longer healing period is recommended.
Complications after crown lengthening
- Poor esthetics - "black triangles".
- Root hypersensitivity/resorption.
- Transient mobility.
Orthodontic extrusion can be performed in two ways [Figure 11]. 
By applying low orthodontic force, the tooth is erupted slowly, bringing the 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 biologic width violation. The tooth is stabilized in this position and then treated with surgery to correct the bone and gingival tissue levels.
The tooth is erupted the desired amount over several weeks (with supracrestal fibrotomy performed weekly in an effort to prevent the tissue and bone from following the tooth). Then the tooth is stabilized for atleast 12 weeks prior to surgical correction.
Forced tooth eruption
Forced eruption should be considered in the cases where traditional crown lengthening via ostectomy cannot be accomplished as in anterior area, as ostectomy would lead to a negative architecture, and also remove bone from the adjacent teeth, which can compromise the function of these teeth.
- Inadequate crown-to-root ratio.
- Lack of occlusal clearance for the required amount of eruption.
- Possible periodontal complications.
Technique: Orthodontic brackets are bonded to the problem tooth and adjacent teeth and are combined with archwire. Power elastic is tied from the bracket to the archwire which pulls the tooth coronally.
Forced tooth eruption with fibrotomy
If fibrotomy is performed during the forced tooth eruption procedure, the crestal bone, and the gingival margin are retrieved at their pretreatment location and the tooth-gingiva interface at adjacent teeth is unaltered. Fibrotomy is performed with a scalpel at 7-10 day intervals to sever the supracrestal fibers, thereby preventing the crestal bone form following the root in a coronal direction. 
Contraindicated: Angular bone defects and ectopically erupted teeth.
| Conclusion|| |
The health of periodontal tissue is dependent on properly designed restoration. Incorrectly placed restorative margins and poorly adapted restorations violate the biologic width. Repeated maintenance visits, patient cooperation, and motivation are important for the success of restorations and maintenance of periodontal health.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8], [Figure 9], [Figure 10], [Figure 11]