Today’s clinician faces a myriad of options when considering the best esthetic solution for restorative dentistry or cosmetic changes in anterior teeth. He or she can use numerous materials, each with highly specific properties and qualities, to solve almost any clinical dilemma. Regardless of the material the clinician chooses, however, he or she has only three possibilities in terms of margin placement: supragingival (above the tissue), equigingival (even with the tissue) and subgingival (below the tissue).¹

In classic restorative dentistry, dentists placed supragingival margins only in areas in which esthetics was not a concern. The stark contrast in color and opacity between the restorations and the natural teeth announced their presence loudly and created an undesirable situation in the esthetic zone. Much has changed in the past 30 years. The advent of adhesive procedures coupled with highly translucent restorative materials made it possible to place supragingival margins, even in areas in which the margins are completely visible (Fig. 1). Equigingival margins traditionally were not preferable because they were thought to retain more plaque than supragingival or subgingival margins and therefore resulted in increased gingival inflammation. Today’s reality is that patients tolerate both supragingival and equigingival margins very well; the greatest biological risk occurs with subgingival margins.²

SUPRAGINGIVAL AND EQUIGINGIVAL MARGINS. The primary requirement for a material placed supragingivally or equigingivally is that it exhibit a high level of cervical translucence. Materials such as feldspathic porcelain and pressable ceramics meet this requirement nicely. Consequently, whenever it is possible, dentists should choose supragingival and equigingival margins for their esthetic advantages and their favorable periodontal impact. However, because it is not always possible or appropriate for esthetic reasons to do so, the clinician must be prepared to place the margin subgingivally, in a predictable fashion, when necessary.

SUBGINGIVAL MARGINS. The clinician may need to extend the margin subgingivally for a variety of reasons. He or she should not leave the margin supragingival or equigingival in cases involving:

• Caries that extends below tissue;
• Old restorations that were extended into the sulcus;
• The need for adequate preparation length for retention and resistance;
• The need to create significant contour alterations with the restorations;
• The need to hide the margin to mask discoloration (Fig. 2);
• The need to hide the margin because the restorative material required has optical properties different from those of the natural tooth.

Regardless of the reason for choosing a subgingival margin, two negative periodontal responses may occur: inflammation and recession. Inflammation of the gingival tissue most likely results from a violation of biological width, which occurs if the clinician intrudes too deeply into the sulcus with the preparation, unless bone loss also occurs, thereby recreating the appropriate biological width for the tooth. Many clinicians falsely assume that a violation of biological width results in recession; however, tissue will not recede unless the bone recedes first, as the body always will maintain a certain height of tissue above bone. The most likely reason for recession after completion of a restorative preparation is placement of a margin in unstable tissue.

CREST CLASSIFICATION. One method of dealing predictably with the problem of margin placement is to use total tissue height above bone as a reference for evaluating the periodontium. This concept came out of work evaluating and classifying three types of periodontal heights: average crest, high crest and low crest.⁵

AVERAGE CREST. In a patient with an average crest, sounding the periodontium on the facial aspect generally reveals 3.0 mm of tissue above the bone. If we assume that this patient’s periodontium has a 2.0 mm biological width and that the clinician will place the margin 2.5 mm from bone, the margin will not violate the attachment and will remain covered by gingiva.

HIGH CREST. With a patient who has a high crest, sounding the peridontium on the facial aspect generally reveals less than 3.0 mm of gingival above bone. In this situation, placing the margin below tissue most likely would violate the attachment and result in an inflammatory response. Therefore, a supragingival margin is indicated unless the bone level is altered.

LOW CREST. In a patient with a low crest, there generally is more than 3.0 mm of tissue above bone on the facial aspect. Extending the margin into the sulcus 0.5 mm creates the potential for the recessive process described above to expose the margin. Three options exist for dealing with this dilemma. The first option is to place the margin supragingivally so as not to traumatize the unstable tissue. The second option is to place the margin 2.5 mm from bone. If the patient has 2.0 mm of attachment, the margin will remain hidden even if the tissue recedes to create a 1.0 mm sulcus. The third option is to perform a gingivectomy, thus converting the low crest into an average crest and then proceeding with treatment accordingly.

A concern in using this classification system routinely relates to patients with low crests and the variations in biological width reported by Vacek and colleagues.⁶ For example, if a patient has 5.0 mm of gingival above bone, he or she would be considered to have a low crest according to this classification system and, thereby, would be prone to developing recession. But if the patient has an attachment apparatus 3.0 or 4.0 mm in height, he or she would have a facial sulcus of only 1.0 to 2.0 mm and would not necessarily be prone to developing any greater recession than would a patient with an average crest. Additionally, if the clinician placed the margin 2.5 mm from bone in a patient with an attachment 3.0 or 4.0 mm high, that margin would be within the attachment. The same violation of the attachment would occur if the clinician surgically placed the gingival margin 3.0 mm above bone via a gingivectomy in an attempt to modify the low crest into an average crest. The gingivectomy would leave no sulcus and could remove some of the attachment. This would be followed by tissue regrowth to re-create the patient’s attachment height and sulcus depth (Fig. 3).

SULCUS DEPTH: AN ALTERNATIVE PERIODONTAL CLASSIFICATION. Using sulcus depth is an alternative method of determining placement of the margin relative to the attachment when subgingival placement is necessary. The base of the sulcus also can be considered to be the top of the attachment. The clinician accounts for variations in attachment height by ensuring that he or she places the margin in the sulcus and not in the attachment.^7-10 Variations in probing depth can predict how deeply below tissue the clinician can place the margin predictably. If the sulcus depth on the facial aspect is shallow — 1.0 to 1.5 mm — placement of the margin more than 0.5 to 0.7 mm below the tissue will risk violating the attachment. This assumes an average probe penetration into the epithelial attachment in healthy gingiva of 0.5 mm. This shallow 1.0 to 1.5 mm probing depth indicates that recession is unlikely, because the free gingival margin is located close to the top of the attachment. If the sulcus is 2.5 mm deep or greater, violating the attachment would require placement of the margin 2.0 mm or more below the tissue. This tissue is much more prone to recession than that with a shallower probing depth because the free gingival margin is not supported as closely by the attachment. That is not to say that all 3.0 mm facial sulci will recede; however, in most circumstances, the deeper the sulcus, the greater the risk of recession.

The first step in using sulcus depth for margin placement is managing the patient’s gingival health. With healthy gingival tissues, the following three rules can be applied when placing subgingival margins.

Rule 1: Shallow Sulcus. If probing shows the sulcus to be 1.5 mm deep or less, the clinician should place the margin 0.5 to 0.7 mm below tissue on the facial aspect. This minimizes the risk of biological-width violation and subsequent inflammation. These patients are at low risk of experiencing recession, but at high risk of experiencing inflammation if the periodontium is invaded.

Rule 2: Average Sulcus. If the sulcus probes, as above, at a depth of more than 1.5 mm but not more than 2.0 mm, the dentist should place the margin one-half the depth of the sulcus below tissue. If recession occurs, the margin most likely will remain far enough below tissue that it will not be exposed. Patients in such situations are at high risk of experiencing recession. As might be expected, they are at low risk of experiencing inflammation because there is no biological-width violation with margins placed in the sulcus.

Rule 3: Deep Sulcus. If the sulcus probes more than 2.0 mm, the clinician should evaluate the teeth esthetically to determine whether he or she should perform a gingivectomy to expose more of the tooth and create a 1.5 mm sulcus. After the gingivectomy, the clinician should continue treatment according to Rule 1.

It is much more difficult to place a margin at one-half the depth of a deep sulcus than to place it 0.5 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. If the clinician can perform the gingivectomy and leave a 1.5 mm sulcus, he or she will be much more capable of placing a subgingival margin predictably. This does not ensure that the tissue will stay at the level at which it is placed, as patients who have undergone gingivectomies frequently experience some regrowth in their gingival tissues.

The difficulty in evaluating sulcus depth in terms of margin placement is the penetration of the periodontal probe into epithelial attachment during probing. For this reason, it is absolutely essential that the clinician use this technique only in healthy tissue.

The placement of supragingival or equigingival margins is simple, as these margins require no tissue manipulation. The amount of tooth reduced incisally or occlusally, as well as facially, lingually and interproximally, will be dictated by the choice of restorative materials. Before extending the preparation subgingivally, the clinician should extend the preparation to the free gingival margin facially and interproximally (Fig. 4). This creates a reference for the gingival margin that the dentist can use for subgingival extension once the tissue is retracted.

TISSUE RETRACTION FOR SHALLOW-SULCUS MARGIN PLACEMENT. After extending the preparation to the height of the gingival margin, the clinician should extend the preparation margin below tissue.^11,12 He or she must achieve three goals through his process:

• Extension of the margin to the correct depth within the sulcus;
• Protection of the tissue so that it does not become abraded, a condition that can cause hemorrhage;
• Creating access to the margin so that the clinician can make the impression in a clean, fluid controlled environment.

The esthetic demands of patients seeking alterations to their anterior teeth have necessitated changes in how dentists evaluate and provide treatment to achieve these alterations. The use of the periodontium to determine appropriate margin placement is an extremely valuable evaluation tool for understanding the biological basis of stability. Using sulcus depth refines that understanding to account for variations in biological width, thereby improving predictability. For dentists who can predict the outcome of a procedure with a high degree of accuracy, treating patients who have extremely high esthetic expectations is a rewarding experience; for those who cannot, it can be a devastating one.

Dr. Frank Spear is founder and director of Spear Education. He is also an affiliate professor in the Graduate Prosthodontics program at the University of Washington and maintains a private practice limited to esthetics and fixed prosthodontics in Seattle. To learn more about Dr. Spear or Spear Education, visit speareducation.com or call 866-781-0072.