In Part I of this series, I described the fundamental concept of biologic width; the height of the combined connective tissue and epithelial attachment above bone, averaging 2 mm in most patients.
I also mentioned the two possible outcomes that can occur if a restorative margin is placed too close to bone: one being bone loss, the other being gingival inflammation, with the inflammation being far more common.
Your Options and Biologic Width
The first option to consider when placing a restorative margin is to decide if the margin can be left supra or equigingival, or must be placed subgingival. If the margin can be placed supra or equigingival, the concerns over biologic width don’t exist – assuming the gingiva is healthy and mature.
Today if the tooth color is acceptable and there is no structural reason to extend below tissue, such as caries, cervical erosion, old restorations or a need to extend for ferrule, the use of a translucent material, such as Lithium Disilicate, can get an esthetically acceptable result without the need to go below tissue.
There are times, however, when it is necessary to place margins below tissue, specifically if structural issues exist, the tooth is extremely discolored or you need to use a more opaque restoration such as zirconia or metal ceramics. In these instances, a subgingival margin is necessary and the concern of going too far below tissue and violating the attachment exists. (Figures 1 and 2)
When I believed biologic width was the same for every patient, the 2 mm described by Gargiulo in 1961, I thought the solution to margin placement was simple: place the margin 2.5 mm from bone. This would be far enough away from bone that it didn’t violate the attachment, but also leave the margin subgingival, as the facial gingival margin is normally at least 3 mm above bone.
The truth was the 2.5 mm distance worked well for most patients; I would simply use a perio probe and sound to bone to be sure my margin was, in fact, 2.5 mm away from the bone as I prepped. But in many patients, the gingiva became very inflamed following treatment.
The reason was related to what Vacek found in 1994, that, “biologic width is not the same between patients, some having attachment heights as tall as 4mm.” In these patients my 2.5 mm distance from bone was in their biologic attachment. (Figure 3)
Where we really want a subgingival margin is actually easy to describe. We want it below the gingival margin, but above the epithelial attachment – in the sulcus, if you will. The key, though, is we can’t use bone consistently as a reference unless we actually knew that individual patient's attachment height. In the next part of this series, I’ll describe how I have placed subgingival margins since reading Vacek's article in 1994 to predictably achieve the desired position.
(Click this link for more dentistry articles by Dr. Frank Spear.)