Biologic width is one of the most quoted numbers in restorative dentistry and one of the most misunderstood. This article goes back to the original histological studies, explains why the 2017 World Workshop replaced the term with supracrestal tissue attachment, and shows what the evidence says about margins that invade it. You will also get a practical way to decide how deep a subgingival margin can go on the tooth you are actually preparing, and the three options when a defect already reaches the bone.
Where the biologic width numbers come from
In 1961, Gargiulo, Wentz and Orban measured the dentogingival junction on autopsy specimens. Their mean values became the textbook standard: a sulcus depth of 0.69 mm, an epithelial attachment of 0.97 mm and a connective tissue attachment of 1.07 mm. The epithelial and connective tissue components add up to 2.04 mm, the figure later popularised as the biologic width. Dr Hajtó teaches the rounded version: about 0.7 mm of sulcus, about 1 mm of epithelial attachment that varies considerably, and about 1.1 mm of connective tissue attachment that is comparatively constant.
Three decades later, Vacek and colleagues repeated the measurements histometrically on 171 tooth surfaces from ten cadaver jaws and found different means: sulcus 1.34 mm, epithelial attachment 1.14 mm and connective tissue attachment 0.77 mm. The connective tissue showed the narrowest distribution of all components. The combined attachment also increased from front to back, from an average of 1.75 mm on anterior teeth through 1.96 mm on premolars to 2.08 mm on molars.
| Component | Gargiulo et al. 1961 | Vacek et al. 1994 |
|---|---|---|
| Sulcus depth | 0.69 mm | 1.34 mm |
| Epithelial attachment | 0.97 mm | 1.14 mm |
| Connective tissue attachment | 1.07 mm | 0.77 mm |
No universal biologic width
A systematic review by Schmidt and colleagues pooled 14 publications spanning almost a century. Two meta-analyses gave mean values of 2.15 to 2.30 mm, but individual measurements ranged from 0.2 to 6.73 mm. Tooth type, site, the presence of a restoration and periodontal disease or surgery all influenced the dimension, and the authors concluded that no universal biologic width exists. They also advised establishing periodontal health before assessing it. Dr Hajtó draws the practical consequence: the published figures are averages with wide individual scatter, and a patient's own pattern tends to be consistent throughout the mouth.
From biologic width to supracrestal tissue attachment
The consensus report of workgroup 3 of the 2017 World Workshop on the Classification of Periodontal and Peri-Implant Diseases and Conditions formally replaced the term biologic width with supracrestal tissue attachment. It is defined as the junctional epithelium plus the supracrestal connective tissue, which is exactly what Gargiulo measured. The report also states that restorative margins placed within the supracrestal connective tissue attachment are associated with inflammation and/or loss of periodontal supporting tissue. Whether plaque, trauma, toxicity of the restorative material or a combination drives this damage is not yet clear.
The new name has a practical advantage: it describes a tissue, not a ruler measurement. That matters because, as Dr Hajtó emphasises, the attachment is a histological structure. You cannot measure it directly in the chair. What you can measure, under local anaesthesia, is the distance from the gingival margin to the alveolar crest, which contains the sulcus and the attachment together.
What happens when a margin invades the attachment
Tarnow and colleagues placed provisional crowns below the base of the sulcus on 13 teeth that were scheduled for extraction in two patients, and examined the tissues histologically after one to eight weeks. A new supracrestal attachment had formed within one week. The gingiva had receded, the junctional epithelium had migrated apically, and the facial crestal bone had resorbed. The body restores the dimension, but at the expense of gingiva and bone.
Clinical long-term data point the same way. In a 26-year study of 160 Scandinavian men, Schätzle and colleagues compared mesial surfaces of premolars and molars. Surfaces that received a subgingival restoration margin lost more attachment than surfaces without one, and the difference became clinically detectable one to three years after the restoration was placed. Damage from a margin that is too deep therefore often shows up long after the crown has been seated.
A margin in the sulcus is not the problem in itself. Ercoli and Caton's review for the 2017 World Workshop concludes that restoration margins located within the gingival sulcus do not cause gingivitis if the patient keeps up self-performed plaque control and attends maintenance. Margins placed within the junctional epithelium and supracrestal connective tissue, however, can be associated with inflammation and potentially recession.
Hands-on dental courses
Courses for dentists in Munich, several of them taught in English.
See all coursesPlanning subgingival margins in practice
Sound to bone, not to the textbook
Because the averages scatter so widely, Dr Hajtó plans margin depth from the facial distance between the gingival margin and the bone crest, measured with a periodontal probe under anaesthesia:
| Bone crest position | Gingival margin to bone (facial) |
|---|---|
| High crest | less than 3 mm |
| Normal crest | 3 mm |
| Low crest | more than 3 mm |
With a high crest the distance to bone is smallest, so there is correspondingly little room for sulcus and attachment below a subgingival margin.
Follow the scallop
The bone crest follows the cemento-enamel junction and sits considerably more coronally between the teeth than on the facial surface. A margin cut at the same level all the way round will be correct facially and still invade the attachment proximally. The finish line therefore has to follow the scallop: shallower into the sulcus at the interproximal sites, deeper facially only when the sounding allows it.
Check the gingival phenotype
Müller and colleagues identified three periodontal phenotypes in 40 young adults with healthy periodontal conditions. Seventy-five per cent belonged to two clusters with thin gingiva and slender teeth. Features seen in the maxillary anterior sextant were also found elsewhere in the dentition. Thin tissue is therefore the norm rather than the exception, and if you see it on one tooth you can expect it on the others.
A protocol that protects the attachment
The sequence Dr Hajtó follows for crowns with subgingival margins:
- Get the periodontium healthy first: oral hygiene instruction, professional cleaning a few days before the preparation appointment, and periodontal therapy if needed. Bleeding tissue cannot be prepared precisely or recorded cleanly.
- Chlorhexidine rinse: the patient rinses for 1 minute on each of the three evenings before the appointment.
- Sound and map: measure the gingival margin to bone distance and plan the finish line, including the proximal scallop.
- Initial preparation: prepare to just below the gingival margin, then place a thin first retraction cord.
- Finish with the cord in place: the cord holds the tissue away; in Dr Hajtó's protocol, finishing with the cord in place is what keeps the finish line out of the attachment.
- Record: add a thicker second cord for the impression or scan and leave the first cord in place. The complete technique, including timing and haemostasis, is described in the article on gingival retraction cord technique.
- Provisionalise: a provisional with a smooth, well-adapted margin keeps the gingiva healthy until the definitive restoration is seated.
The choice of chamfer or rounded shoulder, minimum thickness and taper are covered in the crown prep guide for all-ceramic restorations.
When the defect already reaches the bone
Deep caries, root caries or a fracture can leave sound tooth structure only at or below the crest. A margin placed there would sit in the attachment. Three approaches move the restorative margin back to a position the periodontium can tolerate:
| Approach | Principle | Typical indication | Points to watch |
|---|---|---|---|
| Deep margin elevation | relocate the proximal margin coronally with composite | deep proximal boxes in posterior teeth | tight matrix and rubber dam must be achievable |
| Surgical crown lengthening | move bone and soft tissue apically | posterior teeth, one appointment | soft tissue rebounds coronally during healing |
| Orthodontic extrusion | move the tooth out of its socket | anterior teeth, aesthetic zone | can take several months, retention needed |
Deep margin elevation
For partial-coverage restorations with deep proximal margins, elevating the box floor with composite avoids surgery. In a retrospective study by Muscholl and colleagues, subgingival composite restorations with deep margin elevation showed no more inflammation than control teeth after a mean of 2.7 years, although clinical attachment levels were significantly higher at the test teeth; daily use of interdental brushes was associated with less gingival inflammation. Indications and technique are covered in the article on deep margin elevation.
Surgical crown lengthening
Pontoriero and Carnevale followed 84 teeth for twelve months after crown lengthening. Immediately after surgery, the clinical crown was 3.7 mm longer interproximally and 4.1 mm longer on buccal and lingual sites. Over the following year, the gingival margin moved back coronally by 3.2 mm interproximally and 2.9 mm buccally and lingually, more so in patients with thick tissue. A definitive margin prepared too early after surgery can easily end up subgingival again.
Orthodontic extrusion
In the aesthetic zone, extrusion is often preferred because the tooth does not end up looking longer. A systematic review by Reichardt and colleagues on anterior teeth with subgingival fractures considers forced eruption a feasible pre-treatment option that can bring the surrounding hard and soft tissues along; root resorption did not appear to be a relevant side effect. Extrusion and surgery can also be combined. When several compromised teeth are restored as part of a larger treatment plan, the overall approach is described in our article on full-mouth rehabilitation of the worn dentition.
Summary
The 2 mm biologic width is an average from histological studies, not a value you can rely on for an individual tooth. Since 2017 it has been called the supracrestal tissue attachment, and margins that invade it are associated with inflammation and loss of support. Margins within the sulcus are compatible with periodontal health when plaque control is good. Plan the depth from bone sounding, follow the proximal scallop and finish with a cord in place; when a defect reaches the bone, relocate the margin first. Margin placement, tissue management and scanning are practised hands-on in the prosthodontics courses at Munich Dental Academy.
Frequently asked questions
What is the biologic width in dentistry?
It is the combined height of the junctional epithelium and the supracrestal connective tissue attachment between the base of the sulcus and the alveolar crest. The classic figure from Gargiulo and colleagues in 1961 is 2.04 mm, made up of 0.97 mm of epithelium and 1.07 mm of connective tissue. Individual values vary widely, from 0.2 to 6.73 mm in one systematic review.
What is the new term for biologic width?
Since the 2017 World Workshop on the Classification of Periodontal and Peri-Implant Diseases and Conditions, the correct term is supracrestal tissue attachment. The consensus report defines it as the junctional epithelium plus the supracrestal connective tissue. The concept is unchanged, but the new name makes clear that it describes a tissue rather than a fixed measurement.
What happens if the biologic width is violated?
Histologically, a new attachment re-forms further apically: the gingiva recedes, the junctional epithelium migrates and crestal bone resorbs, in one study within a week. Clinically, margins within the attachment are associated with inflammation, recession and loss of periodontal support. Long-term data show that extra attachment loss can take one to three years to become detectable.
How do you measure biologic width clinically?
You cannot measure it directly, because it is a histological dimension. Under local anaesthesia, you can sound with a periodontal probe from the gingival margin to the bone crest. This value includes the sulcus and the attachment and is the most useful planning figure: around 3 mm facially is a normal crest, less than 3 mm a high crest with little room for a subgingival margin.
How far subgingival can a crown margin be placed?
It can sit within the sulcus but should stay out of the attachment. Dr Hajtó plans the depth from the facial distance between gingival margin and bone: less than 3 mm is a high crest, 3 mm a normal crest and more than 3 mm a low crest. The smaller the distance, the less room there is. Interproximally the bone lies higher, so the margin must be shallower there. If sound tooth structure lies deeper, relocate the margin first.
