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A clinician is faced with 3 options for for margin placement when considering an anterior esthetic restoration: supragingival, equigingival (ie, even with tissue), and subgingival.1 The supragingival or equigingival margin will have the least impact on the periodontium and, classically, was only used in nonesthetic areas because of the stark contrast in color and opacity of traditional restorative materials. With the advent of adhesive dentistry, resin cements, and more translucent restorative materials, the ability to place supragingival or equigingival margins even in esthetic areas is now a reality (Figure 1 and Figure 2). The primary requirement of a material to enable its use in esthetic areas supra- or equigingivally is a high level of cervical translucence. Materials such as feldspathic porcelain, as well as pressable ceramics, meet this requirement. Consequently, whenever possible, these restorations should be chosen not just for their esthetic advantages, but for their favorable periodontal impact as well. The greatest biologic risk occurs when placing subgingival margins.2
The most common reasons to extend a margin below tissue are: caries below gingiva; old restorations that already exist below gingiva; to achieve adequate tooth preparation length for proper retention and resistance; to make significant contour alterations; to hide the margin when the tooth is discolored (Figure 3 and Figure 4); and to hide the margin when the restorative material of choice demonstrates optical properties different from those of the natural tooth such that the margin would be highly visible. Regardless of why a subgingival margin is chosen, there are 2 negative responses that may occur.
First, the margin may be too deep, violating the biologic width. This will most likely result in inflammation unless some bone loss also occurs. The second negative result that can occur following subgingival margin placement is recession that visually exposes the margin of the restoration. This most likely occurs when the margins are placed in unstable tissue.
To clarify this, consider the eruption patterns of normal teeth.3 First, active eruption occurs when root development moves the crown into the mouth and, on average, moves the cementoenamel junction (CEJ) 2mm coronal to the osseous crest. Second, passive recession occurs, causing the gingiva to recede to its normal position 1mm to 2mm above the CEJ, leaving a facial sulcus depth of 1mm to 2mm in the average human. Consider the tissue stability if the patient has not had normal passive recession and instead has several millimeters of excess tissue still covering the crown of the tooth. This tissue margin is now several millimeters coronal to the top of the epithelial attachment (ie, a deep sulcus is present). When the clinician places a subgingival margin in this area, the tissue is traumatized from the restorative procedures and, within a short time, the margins are exposed because the trauma of the procedure caused the unstable tissue to recede.
There are other variables that have been described in the literature as impacting the likelihood of recession.4 These include whether the gingiva is thick and fibrotic or thin and fragile, and whether the periodontium is highly scalloped or flat in its gingival form. It has been found that highly scalloped, thin gingiva is more prone to recession than a flat periodontium with thick, fibrous tissue.
Margin Placement Based on Periodontal Variables
One method proposed to address margin placement and variations in tissue is the use of bone and the total tissue height above bone as a reference for evaluating the periodontium. This concept developed from evaluating and classifying 3 types of periodontium: the high crest, average crest, and low crest periodontium.5 In the average-crest patient, sounding the periodontium on the facial reveals 3 mm of tissue above the bone. The assumption is that this patient has a 2-mm biologic width, and if the margin is placed 2.5 mm from bone, as determined by sounding to bone during preparation, the margin will not violate the attachment and will be covered by gingiva. In the high-crest patient, sounding the periodontium on the facial reveals less than 3 mm of gingiva above bone. In this situation, the assumption is that placing the margin below tissue would most likely violate the attachment. Therefore, a supragingival margin is recommended. Finally, in the low-crest patient, there is more than 3 mm of tissue above bone on the facial, and the concern is that this tissue is prone to recession. In this situation, 3 options exist.
One option is to place a supragingival margin to avoid traumatizing the unstable tissue. A second option is to place the margin 2.5 mm from bone, recognizing that the margin won’t be in the attachment if the patient has a 2-mm attachment. However, the margin will be far enough below tissue that, if the tissue recedes, the margin won’t be exposed. The last option is to perform a gingivectomy, convert the low-crest patient into an average-crest patient, and then treat the patient as such.
The concern with using this classification method routinely relates to low-crest patients in that it doesn’t account for the variations in biologic width that Vacek et al reported.6 For example, if a patient had 5 mm of gingiva above bone, they would be considered low crest and prone to recession. But, if the patient with 5 mm of tissue had a 3-mm or 4-mm tall attachment apparatus, they would only have a 1-mm to 2-mm facial sulcus and not necessarily be prone to any greater recession than an average-crest patient. In addition, if the patient with a 3-mm or 4-mm tall attachment had the margin placed 2.5 mm from bone, the margin would be in the attachment. The same would be true if a gingivectomy was performed 3 mm above bone in an attempt to modify the low-crest patient into an average crest. If the patient had a 2-mm attachment, this would be acceptable. But, if the patient had a 3-mm or 4-mm tall attachment, the gingivectomy would leave no sulcus and may remove some of the attachment. This would be followed by tissue rebound to recreate the patient’s attachment height and sulcus depth (Figure 5).
An alternate method to determine where to place margins relative to the attachment when subgingival placement is necessary is using sulcus depth. The base of the sulcus can also be considered the top of the attachment and, therefore, variations in attachment height are accounted for by ensuring that the
margin is placed in the sulcus and not in the attachment.7-10 Variations in probing depth are then used to predict how deep the margin can safely be placed below tissue.
If the sulcus depth on the facial probes very shallow (eg, 1 mm to 1.5mm) preparing more than 0.5 mm to 0.7 mm below tissue will risk violating the attachment. This assumes an average probe penetration into the epithelial attachment in healthy gingiva of 0.5 mm. However, this shallow 1-mm to 1.5-mm probing indicates that recession is unlikely because the free gingival margin is located near the top of the attachment. If the sulcus probes 2.5 mm or more, violating the attachment would require the margin to be placed 2 mm or more below tissue. The tissue in this example is much more prone to recession because the free gingival margin is not supported as closely by the attachment. That is not to say that all 3-mm facial sulci will recede. However, in most circumstances the deeper the sulcus the greater is the risk of recession.
The first step in using sulcus depth for margin placement is to manage gingival health. Once the tissue is healthy, the following 3 rules can be used to place intracrevicular margins.
Rule 1: If the sulcus probes 1.5 mm or less, place the margin 0.5 mm to 0.7 mm below tissue on the facial. This prevents violating biologic width in a patient
who is at a higher risk of biologic width violation.
Rule 2: If the sulcus probes greater than 1.5 mm, place the margin one-half the depth of the sulcus below tissue. This places the margin far enough below
tissue that it most likely will not be visible if any recession occurs in a patient who is at a higher risk of recession.
Rule 3: If a sulcus greater than 2 mm is found on the facial, evaluate the teeth esthetically to see if a gingivectomy could be performed to lengthen the teeth and create a 1.5-mm sulcus. Then, treat using Rule 1 (Figure 6, Figure 7, Figure 8, Figure 9, Figure 10 and Figure 11).
The rationale for Rule 3 is that it is more difficult to place a margin one-half the depth of a deep sulcus as compared to 0.5 mm to 0.7 mm below tissue. In addition, the stability of the free gingival margin is less predictable with a deep sulcus than with a shallow sulcus. Therefore, if it is possible to perform a gingivectomy, lengthening the tooth and leaving a
1-mm to 1.5-mm sulcus, doing so will create a more predictable situation in which to place an intracrevicular margin. This does not, however, ensure that the tissue will remain at the level placed, because gingivectomies are frequently followed by some gingival rebound.
The challenge of using sulcus depth for margin placement is the penetration of the probe into the epithelial attachment during probing. For this reason, the tissue must be healthy to use this technique for defining final margin placement.
Clinical Procedures in Margin Placement
The placement of supragingival or equigingival margins is simple because they require no tissue manipulation. Regarding overall tooth preparation, the amount reduced incisally or occlusally, facially, lingually, and interproximally will be dictated by the choice of restorative materials. Before extending subgingivally, prepare every tooth right to the free gingival margin facially and interproximally. This allows the margin of the tooth preparation to be used asa reference for subgingival extension once the tissue is retracted (Figures 13, Figure 14, Figure 15 and Figure 16).
Tissue Retraction for Rule 1,the Shallow Sulcus
Once the preparation is completed supragingivally, it is necessary to extend below tissue.11,12 Three goals exist in this extension process. The first goal is to place the margin at the correct depth within the sulcus. The second goal is to protect the tissue so that it does not get abraded and begin hemorrhaging when carrying the margin below tissue. Finally, access to the margin for impression-making in a clean, fluid-controlled environment is required. To achieve these goals, begin with a layer of appropriately sized retraction cord. Do not use too small a cord because it will not provide adequate retraction. When placing the cord, push it the distance into the sulcus that the margin is to be placed below tissue. For example, in a Rule 1 margin, place the cord 0.5 mm to 0.7 mm below the previously prepared margin, which represents the unretracted free gingival margin. Once the cord is in place, the top of the cord represents the final margin location (Figure 17). Note that on the interproximal, you should routinely push the cord 1 mm to 1.5 mm below tissue because the interproximal sulcus is routinely 2.5 mm to 3 mm. With the first cord in place, extend the preparation to the top of the cord, holding the bur into the tooth so that it does not abrade the tissue. This protects the tissue and creates the correct axial reduction. When completed, the margin is now at the correct level below tissue. It is not possible to take an impression at this time, however, because the margin and the cord are at the same level.
Placing the Impression Cord
To create space and allow access for a final impression, it is now necessary to pack a second cord. The purpose of the impression cord is to create access to the margin for impression material and provide expansion of the sulcus so the impression material does not tear when removed. To accomplish these goals, the impression cord should sit between the margin of the preparation and the gingiva. Many times, dentists pack the cord too deeply, placing it apical to the margin, in which case the tissue at the level of the margin falls back against the tooth, eliminating access to the margin. The impression cord is placed on top of the first cord that is still in place. The impression cord is pushed so it displaces the first cord apically and sits between the margin and the tissue. When properly packed, the cord will be visible around the preparation when viewed from the occlusal. If in any area the cord is not visible or there is gingiva falling in over the cord and margin, it indicates that the cord is packed too deeply. If the cord is packed too deeply, use an explorer and tease the cord up to the correct level.
If the tissue is still falling in over the cord and margin, there are 2 options. One option is to lift the impression cord out of the sulcus where the tissue is falling over and place a small segment of cord over the first cord in the problem area only. Once this is accomplished, replace the impression cord. If it is still not visible, repeat the process, building up multiple small pieces of cord below the impression cord until the impression cord allows access to the margin. The second option is to remove the overhanging tissue using electrosurgery or laser.
I commonly perform electrosurgery using a fine wire tip. Hold the tip parallel to the tooth preparation, against the margin in the sulcus, and move the tip through the overhanging tissue, thereby opening up the margin and the impression cord to visual access. While doing this, let the electrosurgery tip sit on the impression cord. Having the cord in place protects the attachment, and holding the tip parallel to the preparation results in the removal of the least tissue possible. If any hemorrhaging occurs, dabbing with ferric sulfate while rinsing will usually stop it. If not, a small amount of lidocaine with 1:50,000 epinephrine injected into the papilla from the facial is very effective.
The key to an excellent impression is clear access to the margin in a controlled field.13 Be sure the impression cord has been in place at least 4 minutes and that it is moist. For the impression, remove the top cord only, dry the preparation, and verify that the margins are visible. Once this is confirmed, inject the impression material, holding the tip of the syringe on the margin and placing the material around each tooth and into the sulcus. Note that throughout the procedure, the first or bottom cord is left in place. Once you remove the bottom cord, hemorrhage will occur, so it is advisable to leave it in until after temporization.
Tissue Retraction for Rule 2, the Deep Sulcus
The deep-sulcus patient is approached identically to the Rule 1 patient, with one exception. Instead of 1 layer of cord for tissue deflection, use 2 larger-diameter cords to deflect the tissue before extending the margin apically. The 2 cords open the sulcus so that the preparation can be carried easily below tissue. The top of the second cord is placed the correct distance below the previously prepared margin, into the sulcus, to identify the final margin placement. Once the margin is lowered to the top of the second cord, a third cord is placed as the impression cord, as previously described. From that point on, all the steps remain the same, except that there are now 3 layers of cord packed, rather than 2. Also, instead of leaving 1 cord during the impression, now 2 are left in place (Figure 18, Figure 19, Figure 20, Figure 21, Figure 22, Figure 23, Figure 24 and Figure 25). Note that in the deep-sulcus patient where the margin may be 1.5 mm to 2 mm below tissue, electrosurgery is commonly necessary for trimming overhanging tissue. When trimming the tissue, the goal is to only open access to the margin and not to apically position the gingiva. Therefore, it is important to hold the electrosurgery tip parallel to the preparation. Leaning the tip away from the preparation will alter the gingival height.
Managing the Rule 3 Patient
When a deep-sulcus patient with short teeth has been identified, there are 2 ways to manage the gingivectomy. One is to perform the gingivectomy first, allow the tissue to heal, and then proceed as a Rule1 patient. The other is to perform the gingivectomy, leaving a 1-mm to 1.5-mm sulcus, and proceed to tooth preparation the same day. Both techniques can produce acceptable results, and the operator’s comfort level will determine how they choose to proceed.
Margin Placement for Ultra Thin Tissue
The descriptions provided are for normal tissue types. On occasion, there are gingival types that are extremely thin. If the tissue is so thin that it is transparent, there is no reason to extend below tissue to hide the margin. In this situation, use a supragingival or equigingival margin and a translucent restoration whenever possible.
Over the last 2 decades, advances in restorative materials and adhesive technologies have significantly altered our need for subgingival margin placement. However, there still exist several areas in daily practice where it is necessary for margins to be carried below tissue. The purpose of this article has been to describe the options available to predictably place intracrevicular margins esthetically, while maintaining optimal gingival health long term.
1. Tylman SD. Theory and practice of crown and bridge prosthodontics, 5th ed. St. Louis: The C.V. Mosby Co, 1965.
2. Marcum JS. The effect of crown margin depth upon gingival tissue. J Prosthet Dent. 1967;17:479.
3. Coslet JG, Vanarsdall R, Weisgold A. Diagnosis and classification of delayed passive eruption of the dentogingival junction in the adult. Alpha Omegan. 1977;70:24-28.
4. Olsson M, Lindhe S. Periodontal characteristics in individuals with varying forms of the upper central incisors. J Clin Periodontol. 1991;18:78-82.
5. Inber JS, Rose LF, Coslet JG. The “biologic width” a concept in periodontics and restorative dentistry. Alpha Omegan. 1977;10:62-65.
6. Vacek JS, Gher ME, Assad DA, et al. The dimensions of the human dentogingival junction. Int J Periodontics Restorative Dent. 1994;14:154-65.
7. Listgarten MA, Mao R, Robinson PJ. Periodontal probing and the relationship of the probe tip to periodontal tissues. J Periodontal. 1976;47:511.
8. Listgarten MA. Periodontal probing: What does it mean? J Clin Periodontal. 1980;7:165.
9. Armitage GC, Svanberg GK, Löe H. Microscopic evaluation of clinical measurements of connective tissue attachment levels. J Clin Periodontal. 1977;4:173.
10. Robinson PJ, Vitek RM. The relationship between gingival inflammation and the probe resistance. J Periodont Res. 1975;14:239.
11. Hansen PA, Tira DE, Barlow J. Current methods of finish line exposure by practicing prosthodontists. J Prosthodont. 1999;8:163-170.
12. Benson BW, Bomberg TJ, Hatch RA, Hoffman Jr. W. Tissue displacement in fixed prosthodontics.J Prosthet Dent. 1986;55:175-181.
13. Albers HF. Impressions, 1st ed. Santa Monica: Alto Books, 1990.
This article was reprinted with permission from Advanced Esthetics and Interdisciplinary Dentistry, vol. 1, no. 2, 2005.
About the Author
Frank M. Spear, DDS, MSD
Founder and Director
Seattle Institute for Advanced Dental Education
Affiliate Assistant Professor
University of Washington
School of Dentistry