To properly understand biologic width, it’s important to define some other terms first. The gingival sulcus is the area of actual or potential space between the tooth and the gingival tissue, which is more commonly known as gum tissue. “Sulcus” is Latin for “groove,” which can help provide a visual: the gingival sulcus is the small groove between the enamel of the teeth and the periphery of the gum tissue. At its base, the gingival sulcus is attached to the root of the teeth with connective tissues, called gingival fibers, that participate in holding the gums securely in place. At its apex, the gingival sulcus is bounded by the crest of the alveolar bone. The natural distance between the base of the gingival sulcus and the apex of the alveolar bone is known as the biologic width. In other terms, the biologic width is defined as the dimension of gingival tissue that is attached from the base of the crown of the tooth to the crest of the alveolar bone; among other functions, the biologic width of gingival tissue protects the roots of the teeth and the alveolar bone from bacteria and other harmful foreign matter which can lead to infection, disease, or trauma.
Biologic width varies from person to person and can range anywhere from .75 to 4.3 millimeters, though the average biologic width in most humans is about 2 mm. Biologic width is important for a variety of reasons. The most basic reason to observe biologic width is for hygiene purposes; a hygienically ideal biological width, in this regard, is 3 mm or less, which allows the gingival sulcus to be adequately and thoroughly cleansed with a basic toothbrush or with other readily available oral hygiene aids.
Biologic width is particularly important when measuring for and placing dental restorations, such as crowns and porcelain veneers. Because it is impossible to measure restorations perfectly, as a portion of the restoration will rest in the unseen area beneath the gum, a general periodontal recommendation is to remove a small amount of bone so that there is a uniform measurement of 3 mm margin between the restoration and the crest of the alveolar bone. If bone removal is not a routine part of a restoration treatment, violation of biologic width may occur, particularly if the restoration is placed too deep in the gums and too close to the bone. This can lead to loss of bone, but more often leads to chronic gingival inflammation, which can be painful and also unattractive. The ideal solution to this source of biologic width violation is to replace the existing restoration, once the cause is confirmed.
Biologic width is also a necessary consideration when treating or managing extensive tooth decay or cracks or fractures in the roots of the teeth, and it comes into play when making decisions about orthodontic treatments and endodontic therapies. Because the tooth and the structures that support it function as a single biologic unit, biologic width is an inextricable element of periodontal health and can determine the success of restorative procedures. Biologic width violation can lead to bleeding or recession of the gingival tissue; chronic inflammation of the gingival tissue, especially immediately around the restoration; the formation of pockets between the gums and teeth; and loss of alveolar bone.