A Comprehensive Guide To Biologic WidthBy Frank Spear on June 28, 2021 | 3 comments
Biologic width describes the combined heights of the connective tissue and epithelial attachments to a tooth. The dimensions of the attachment were described in 1961 by Garguilo, Wentz and Orban in a classic article on cadavers. Their work showed the connective tissue attachment having an average height of 1 mm, and the epithelial attachment also having an average height of 1 mm, leading to the 2 mm dimension often quoted in the literature for biologic width. In addition, they found the average facial sulcus depth to be 1 mm, leading to a total average gingival height above bone of 3 mm on the facial.
The Term Biologic Width
For historical accuracy, it is interesting to note that Garguilo, Wentz and Orban didn't use the term biologic width in their 1961 article, the actual name, biologic width, came in 1962 from Dr. D Walter Cohen at the University of Pennsylvania.
In 1994, Vacek did further cadaver studies on biologic width that helped give some insight into the clinical findings many of us had seen. He found that biologic width was relatively similar on all the teeth in the same individual from incisors to molars, and also around each tooth. He also found the average biologic width to be 2 mm as the Garguilo group did. What Vacek found that is clinically important was that biologic width varied between individuals, with some having biologic widths as small as .75 mm, and others as tall as 4 mm, but statistically the majority followed the 2 mm average.
The primary significance of biologic width to the clinician is its importance relative to the position of restorative margins, and its impact on post-surgical tissue position. We know that if a restorative margin is placed too deep below tissue, so that it invades the biologic width, two possible outcomes may occur.
One, there may be bone resorption that recreates space for the biologic width to attach normally. This is the typical response seen in implants to allow the formation of a biologic width, the so-called funnel of bone loss to the first thread.
Around teeth, the most common response to a biologic width violation is gingival inflammation, a significant problem on anterior restorations.
The importance of biologic width to surgery relates to its reformation following surgical intervention. Research shows it will reform through coronal migration of the gingiva to recreate not just the biologic width, but also a sulcus of normal depth. This means if the surgery doesn't consider the dimensions of biologic width when placing the gingiva relative to the underlying bone, the gingival position won't be stable, but instead will migrate in a coronal direction. In this example, it also has a strong influence on when and where restorative margins should be placed post-surgically.
Restorative Margin Placement
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.
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.
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 know that individual patient's attachment height.
Possible Gingival Presentations
I'll now describe the two different types of gingival presentations we encounter when approaching subgingival margin placement, as well as the risks of each. Whenever I contemplate placing a subgingival margin, I always start by probing the facial sulcus of the teeth on which I will be placing the restorations.
Biologic Width: Possible Gingival Presentations
It is important to realize that when we probe the sulcus, the probe routinely enters the epithelial attachment .5 mm, meaning the actual sulcus is typically .5 mm less than the probed depth. In patients with inflamed tissue, the probe penetrates even deeper into the attachment.
In patients with normal or shallow facial sulcus depths, typically 1 mm to 1.5 mm, the risk in subgingival margin placement is going too deep and violating the attachment, as the histologic sulcus depth is probably less than 1 mm. The good news is these patients do not typically present a high risk of recession following placement of the restoration, since the gingival dimension above bone is commonly 3 mm on the facial (similar to the Gargiulo diagram in my previous articles). This means there would have to be bone loss for the tissue to recede apically. So going below tissue more than .5 mm to .7 mm is unnecessary, and it is unlikely the margin will violate the attachment or be exposed from future recession. (Figures 1 and 2)
The second presentation is a patient with much deeper facial sulcus depths, 2 mm to 4 mm - or even more. This patient presents a much higher risk of recession following restoration unless the margin is placed farther below tissue. The reason for the risk of recession is due to the fact that there are several millimeters of unattached gingiva above the biologic width. The thickness of the unattached tissue has an influence on the risk of recession; the thinner the tissue and deeper the sulcus, the greater the risk of recession. The good news is it is very difficult to violate the biologic width on these patients, as you would need to prep 2 mm to 4 mm below gingiva to reach the attachment.
In subsequent articles, I'll describe the options and steps to manage these different presentations.
Subgingival Margin Placement in Shallow Sulcus Patients
In patients with sulcus depths less than 1.5 mm, the risk in subgingival margin placement is going too deep and violating the attachment. For these patients, my goal for margin placement (if a subgingival margin is necessary) is to place the margin .5 mm to .7 mm below tissue. This protects the attachment, but still leaves the margin covered by gingiva. And since the risk of recession is low, the .5 mm to .7 mm subgingival placement hides the margin visually.
The steps I take to achieve the correct subgingival margin placement are as follows:
Step 1: Prep the tooth completely, right to the existing gingival margin level, leaving only the subgingival margin placement to be completed. (Figure 1)
Step 2: Probe the sulcus and identify that the probing is 1.5 mm or less. (Figure 2)
Step 3: I am a fan of retraction cords for controlled subgingival margin placement on anterior teeth, even though I know many clinicians prefer not to use it. I would now place an Ultradent, Ultrapak cord, #00 (thin tissue) or #1 (most tissue). The key is that the cord is placed .5 mm to .7 mm apical to the prep margin, which was left at the height of the gingival margin. The cord is damp, not soaked, with aluminum chloride solution. (Figure 3)
Step 4: The first cord retracts the tissue, and also represents the correct position for the final prep margin, .5 mm to .7 mm subgingival. Prep to the top of the cord using the bur that provides adequate depth and shape for your finish line. (Figure 4)
Step 5: Place a second layer of cord, pushing it apically so it sits at the level of the prepped margin. If you can't see the second layer of cord it has been placed too deep; you want to visualize the second cord all around the tooth. (Figure 5)
Step 6: Wet the top cord with water, remove it, air dry and impress, traditionally or optically. (Figures 6 and 7)
Step 7: Completed restorations. (Figure 8)
Margin Placement for Deep Sulcus Patients
I want to present what options exist when we are faced with placing restorations on patients who have deeper facial probing depths (greater than 2 mm). The challenge in these patients is the risk of future recession due to the amount of unattached tissue present above the biologic width. The risk is affected by both the depth of the facial sulcus and the thickness of the tissue. A patient with a 3.5 mm facial sulcus and thin tissue is at greater risk of recession than a patient with a 2 mm facial sulcus and thick tissue.
When I am going to restore anterior teeth, and the facial probing depths are greater than 2 mm, the first thing I do is attempt to identify why - which generally comes down to one of two options.
Option one is altered passive eruption. Essentially, the gingiva has not receded to a normal position relative to the bone and CEJ. The hallmark of this is the appearance of the teeth having short clinical crown length. If one measures the width-to-length ratio of central incisors with altered passive eruption, the ratios may be in the 90 percent to 100 percent range, or even higher, as opposed to the more normal 75 percent to 80 percent.
The good news about a diagnosis of altered passive eruption is that the deep sulcus can be eliminated with a gingivectomy. This eliminates the risk of future recession by leaving a normal 1 mm to 1.5 mm sulcus depth, and it also improves the length of the clinical crowns at the same time. To use a gingivectomy, though, it is typically necessary to perform it across all the anterior teeth so that the gingival levels flow correctly from canine, to lateral, to central. (Figures 1-4)
The other key, if considering a gingivectomy, is to never remove so much gingiva that the remaining sulcus is less than 1 mm in depth, as the tissue will simply grow back if you do.
The second option for a deep facial sulcus is bone loss and a lack of recession, effectively created by the attachment migrating apically with the bone loss but the gingiva not following – a pocket formation, if you will. In these patients, the clinical crown lengths are typically normal, so eliminating the deep sulcus with a gingivectomy would actually create excessively long and narrow clinical crowns.
These patients are typically a greater risk to restore than the altered passive eruption patients, as the sulcus depth can't be easily reduced with a gingivectomy to minimize the risk of recession.
Margin Placement For Deep Sulcus Patients
I'll now present a more challenging problem: the patient with deep facial sulcus depths, but a gingiva at an ideal position. This means that the use of a gingivectomy to reduce the sulcus depth will result in the clinical crown appearing too long. This is typically a patient who has had some facial bone loss and apical migration of the attachment, but no subsequent recession of the gingiva.
You generally have two options with these patients to reduce the risk of exposed margins from future recession. The first, and often best option, is to place your margin supragingival, not inducing any trauma to the gingiva. This can be readily accomplished if translucent all-ceramic materials can be used, especially if the existing tooth color is acceptable. Now any future recession really isn't very noticeable, as the margin was already above tissue. If you must go below tissue because of a discolored tooth, or because you need to use a more opaque restorative material (metal ceramics or zirconia for example in the case of an FPD), the risk of future margin exposure is definitely a risk.
My approach in these instances is to place the margin below tissue, half the depth of the probing. So for a 3 mm facial sulcus depth, I would place the margin 1.5 mm below tissue. The purpose of this is to minimize the risk of margin exposure if some recession occurs, but it can't completely prevent the risk.
Remember, in these deep sulcus patients, violating the attachment is not a risk like it is in shallow sulcus patients. Therefore, going half the depth of the sulcus below tissue is biologically acceptable, but the challenge is how to do it and not overly traumatize the tissue in the process.
The case I am including will show you the step-by-step approach I use to place the margin at the correct depth, and protect the tissue at the same time:
Diagnosing a Biologic Width Violation
I will start to address how to diagnose inflammation around restorations that exists because the margins have been placed too deep, violating the attachment. When we see an anterior restoration, particularly a full crown, that has significant gingival inflammation, a series of possible diagnoses exist:
- It could be plaque control (but if the adjacent teeth have healthy gingiva, that is unlikely).
- It could be marginal fit, which can be examined with an explorer and radiograph.
- It could be poor contour, preventing adequate hygiene (again, possible to examine).
- It could be an allergic response to the restorative material - especially if the restoration was done in the '80s or '90s using a nickel-containing alloy, and the patient is female.
- But it could be because the margin is placed too close to bone, violating the biologic width. (See Figures 1-4 below)
Ideally, if the existing restoration is removed, and a well-fitting temporary placed for at least three months without the return of any gingival inflammation, you would assume the margin location was not the problem, and one of the other etiologies applied. The reason for the three-month wait is that it is not unusual to damage the attachment apparatus when removing an old restoration and placing a temporary.
You may see perfectly healthy-looking tissue until it heals and matures, which is usually between eight to 12 weeks, and then the inflammation returns. Of course, not every patient wants you to take off their restoration to make a diagnosis, so here are some other options to assist in deciding whether or not the margin location is the problem:
- First, simply place a perio probe in the sulcus until it reaches the margin. Do this circumferentially around the tooth. What you are looking for is pain: a margin in the sulcus will result in no response, a margin in the connective tissue attachment will be painful to probe.
- Next anesthetize the tooth you are concerned about. Place the perio probe on the restorative margin, and read the distance from there to the gingival margin. Keeping the probe against the root laterally, slide the probe down to bone, allowing you to compare the previous probe readings vs when the probe is on bone.
- Third, use a periapical radiograph; while it won't let you see the margin location relative to bone on the facial, it will on the interproximal.
If the margin is painful to probe, is within 2 mm of the bone when measuring it, or on a radiograph, you probably have a biologic width violation, and the only thing you will be able to do to eliminate the inflammation is correct the problem.
Surgical Correction of a Biologic Width Violation on the Facial Surface Only
When a restorative margin is placed too close to bone, and gingival inflammation occurs, the only solutions to eliminate the inflammation are to move the margin away from bone, or move the bone away from the margin. In most instances, the classic measurements from Garguilo, Wentz and Orban would be used for the correction; in other words, create 2.5 mm to 3 mm of space between the margin and bone.
There are two ways to move the margin away from bone: one is orthodontic extrusion, and the other is so- called “root reshaping,” where the old margin is smoothed away and a new margin prepped at a more coronal and correct level. This approach can be very useful when the previous tooth preparation was done with minimal tooth reduction, but is much more difficult if a heavy chamfer or shoulder had been previously prepared.
The more common solution for biologic width violations is to move the bone away from the margin with osseous surgery. The challenge with the osseous surgery is the risk of recession occurring. If you were dealing with a single central incisor that had the margin placed too deep on the direct facial, surgery would definitely be my first choice - lay a facial flap, remove the necessary facial bone and replace the flap to its original position.
If the tissue is normal in thickness, it is rare to see much (if any) recession. If the tissue is thin, the risk is higher, but it is always possible to come back with a connective tissue graft to cover the root and margin.
The real challenge is if you were dealing with a single central restoration that has a biologic width violation on the interproximal. Now if you remove bone to correct the violation, there is a much higher incidence of getting some loss of papilla and opening of the gingival embrasure.
Managing Interproximal Biologic Width Violations on Single Anterior Teeth
The reason osseous surgery is rarely indicated for correcting an interproximal biologic width violation on a single anterior tooth is that it requires removal of interproximal bone, which is followed by a loss of papilla height, and an open embrasure. Instead, the ideal treatment to expose adequate tooth structure for restoration, and to allow for ideal esthetics with no loss of interproximal papilla height, is orthodontic extrusion (see image above and image below).
It is important to remember the desired outcome for the correction of the biologic width violation (the margin 2.5 mm from bone) and if it is a tooth with endo and a post and core, an additional 1.5 mm of tooth structure exposed for adequate ferrule. So for teeth with endo and post and cores, 4mm of tooth structure must be exposed coronal to the bone (see image below)
There are two ways to accomplish the extrusion:
- Slow extrusion of .5 mm to 1 mm per month, which allows the bone and gingiva to follow the tooth. This is then followed by osseous surgery to reposition the bone and gingiva ideally, which exposes the tooth as well. This approach is highly predictable, and is generally chosen, especially when there are other orthodontic concerns as well.
- The second approach, which is normally chosen only when a single tooth needs treatment (i.e. no other orthodontic needs or other teeth with biologic width violations adjacent to the tooth you desire to treat) is to use rapid extrusion, generally all of the movement within four weeks. The key to this approach is to perform supracrestal fiberotomies weekly, to discourage the bone and gingiva from following. But it is necessary to retain the tooth in position for at least 12 more weeks to prevent re-intrusion, and to evaluate if osseous surgery is necessary due to the bone and gingiva creeping in a coronal direction (see four images below).
Finally, in all cases where forced extrusion is being used to resolve a biologic width violation, the amount of root in bone is being reduced by the amount the tooth is being extruded. While often clinicians worry about keeping a 1:1 crown-to-root ratio at a minimum, my experience has been that leaving 8 mm to 9 mm of root in bone has provided a successful long-term solution.
Managing Facial and Interproximal Biologic Width Violations on Multiple Adjacent Teeth
Patients with multiple adjacent existing anterior crowns, prepped essentially to bone, are some of the most challenging esthetic cases to treat. There is usually significant gingival inflammation, and if the crowns were bonded, there is often significant black staining from the bacterial growth that occurs when attempting to bond in a highly contaminated environment, heaviest in the cervical 1/3, and showing through the translucent crowns. (Figure 1 - see photos below)
The only solution that I have found successful in these cases is to start by addressing the biologic width problem first: the margins being too close to bone. This is done with osseous surgery, by correcting the bone-to-margin distance. The bone removal creates the risk of recession, and this risk is especially high when bone has to be removed on both the facial and interproximal. (Figure 2)
On these patients, my first step is to remove the old crowns so I can visualize the quality of each tooth, and also assess the distance from the margin to bone using a probe 360 degrees around the tooth. Additionally, it lets me see how heavy the prior tooth reduction was, and if the reduction at the margin was minimal. For example, with a slice type finish line, it is often possible to do minor “root reshaping,” by essentially smoothing out the old margin. This needs to be followed by re-prepping a new margin the correct distance from bone, and eliminates the need for any bone removal. When the preps are heavy shoulders or chamfers, bone removal becomes mandatory. (Figure 3)
The amount of bone removal is dictated by how close the existing margins are to the bone, and whether all the teeth were prepped the same or not. As a rule, I would move the bone 2.5 mm to 3 mm away from the existing margins all the way around the teeth to accommodate the biologic width. It would be unusual for a patient to need more space than that. (Figures 4, 5)
At the time of suturing, assuming the pre-treatment crown length was acceptable (i.e. no crown lengthening was desired), the flap should be replaced exactly where it was pre-surgically, not apically positioned. The goal is to hope for a longer attachment apparatus rather then a deeper pocket followed by recession. (Fig 6)
I often get asked about how long to wait following healing before proceeding in these types of patients. Remember, this is not a typical crown lengthening case - the bone has been moved apically, but the tissue has not, so the risk of recession is much higher. Also, we are usually treating a patient who is unhappy about the need for the treatment. I typically wait six months minimum before moving forward. (Figure 7)
Depending upon the patient's gingival thickness, it can be surprising how often no recession occurs on either the facial or interproximal, even when 2 mm of bone has been removed around the teeth. (Figures 8,9)
(If you enjoyed this article, click here for more dentistry articles by Dr. Frank Spear)
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