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Biologic Width

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As a 4th year dental student I have done a number of crowns and bridges. Most of my margins have been supra gingival, but a handful have been sub gingival. Last week I did a preparation on tooth #5 and was forced to take my margin sub gingival due to a facially inclined #6. The inclination made it so that the contact between #5 and #6 was sub gingival. The patient complained of sensitivity and soreness after the preparation. Hemostasis was difficult to control. 

 

My supervising faculty at the time told me that, because of the tight/ broad contact, the patient had been unable to floss and adequately clean the area. He explained that, his poor hygiene in this area caused the interdental papilla to be chronically inflamed. Because of the heme, I decided a definitive impression would not be possible at that appointment and that he should come back after a week with a temporary bridge. 

 

When the patient presented this week for removal of the temporary and a definitive impression, the patient complained of increased soreness, sensitivity and discomfort. The sensitivity increased when I removed the temporary. I asked out periodontist for a consult and the first thing he asked me was, "is your margin sub gingival?" Immediatley I knew what he was implying…the potential violation of the biologic width. Without him even looking, I took a vertical bitewing image and discovered, sure enough, the margin was less than 1mm from the crestal bone.

 

I have know the definition of the biologic width: the dimension of space that the healthy gingival tissues occupy between the base of the sulcus and the underlying alveolar bone is comprised of the junctional epithelial attachment and the connective tissue attachment

(Newman, Michael, Henry Takei, Perry Klokkevold, Fermin Carranza. Carranza's Clinical Periodontology, 12th Edition. W.B. Saunders Company, 2015. VitalBook file.) This means that, on average, the margin of a restoration should be at least 3mm above the crestal bone to account for 1mm connective tissue, 1mm junctional epithelium and 1 mm sulcus depth.  If this depth is encoarched upon, gingival recession, bone loss and/or gingival inflammation can occur.

 

Even though I have know the definition for a few years, I had not been keeping it in mind while performing crown preparations in clinic. Although the patient will have crown lengthening surgery and the outcome will remain the same, I wished I had warned the patient of the potential need for crown lengthening before treatment began. Additionally, I wish I had not followed the assumption that his bleeding and sensitivity was due to poor hygiene. From now on when I am performing crown preparations, I will keep in mind that if I need to go sub gingival, I should monitor my proximity to bone with radiographic images.