Biologic Width Demystified
Richard Erickson, MS, DDS
Much fuss is justifiably made by many clinician speakers over violating the biologic width in crown margin placement. We've all seen seminar slides of chronically inflamed tissue around a crown in violation of this sacred region. But what exactly is this so-called biologic width? Why when despite your best efforts to esthetically hide a crown margin in the sulcus, it comes peeking back at you at the next prophy visit? John Kois answered these questions recently1 much more clearly than I have ever heard in a presentation and here are the highlights.
Some healthy dimensions of the gingival area are needed in order to compare to what is abnormal. As you can see on the diagram at left, a kind of symmetry exists in normal healthy gingiva: 1mm sulcular depth, 1mm attached epithelium and 1mm connective tissue before the crest of the bone is reached. This is the biologic width. 85% of healthy patients will exhibit this 3mm dimension, while 2% will be less than 3mm and 13% will be greater than 3mm. Also, the distance between the CEJ and the crest of bone is 2mm on average. When this CEJ to crestal bone distance is less than 2mm, the gingiva ride up the clinical crown making the tooth appear submerged and short. If the CEJ to crestal bone distance is greater than 2mm, the CEJ may be exposed and the tooth will appear too long.
To summarize then, the biologic width is equal to 3mm: 1mm sulcular depth, 1mm attachment epithelium and 1mm connective tissue above the crestal bone. This is true on the broad facial surface. In the proximal papillae area, the correct biologic width increases to 4mm. This can be measured on any tooth using the "sounding" technique.
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