To properly restore a tooth, whether during a routine restorative procedure or the preparation of an aesthetic restoration like a veneer or crown, it is important to understand and respect the Biologic Width. So, what is it and why does it exist?
The biologic width is our name for the special mechanism our body uses to seal and protect the underlying bone from bacteria and food where the erupted tooth breaks the seal of the oral mucosa. It is composed of two parts: connective tissue and epithelium. Based on histological examination it is estimated that, on average, they are each about 1 millimeter in length or height so that the combined “width” is 2 millimeters. Thus, the number most often used for the biologic width is 2 millimeters.
It is important to note that the biologic width does not include any value for the depth of the sulcus above it. It is just the connective tissue attachment and the epithelial adherence or junctional epithelium.
The connective tissue attaches to the cementum on the root surface through what are called Sharpey’s Fibers. The epithelium attaches to the enamel or cementum through a cellular structure referred to as hemidesmosomes. Together they seal the bone against food and the bacteria that colonize our oral cavity.
Our bodies are genetically programmed to do anything to protect the underlying bone. No foreign substance is allowed to get closer than 2 millimeters. This includes not only bacteria and food but our restorative materials as well. So if we place our restorative materials closer to the bone than 2 millimeters then one of two things will happen: either our body will remove healthy bone to recreate this protective zone of 2 millimeters or the area will be in a constant state of inflammation ( the gum will be red and swollen around the margin of our restoration).
Frequently we hear people speak of the biologic width as being 3 millimeters long which is, as discussed above, incorrect. However, 3 millimeters is an important working value because it adds 1 millimeter for a shallow, healthy sulcus. We must allow for this 3 millimeters when we determine how much gingiva and bone must be removed during aesthetic crown lengthening. What technique we use to remove the gingiva and bone will be discussed as we continue.