The Supragingival Protocol and Indications: Preventing Subgingival Margins
Restorative dentists use two approaches to restoring damaged teeth: Direct and indirect. Direct restorations are reserved for teeth where the damage is moderate, the structure of the tooth is not compromised, and it can be safely restored with material with the ability to set or cure immediately in the tooth, such as amalgam or resin-based composite (Figure 3.1). Indirect restorations, on the other hand, are restorations reserved for badly damaged teeth, which may be structurally weak. The full or partial coverage will help to reinforce the tooth and usually requires materials that are fabricated in a laboratory or more recently by computer-aided design and manufacturing. Adhesive dentistry changed the rules rapidly [1,2] and blurred the lines as to when teeth are truly too weak to be restored with a direct technique and when a cusp or cusps are structurally too weak and need to be covered (Figure 3.2a,b). Bonded composite has been shown to reinforce tooth structure [3,4]. As shown in Chapter 1, traditionally direct and indirect restorations have been performed using techniques requiring mechanical retention that usually lead to subgingival margins with little regard to the periodontal complications. Direct and indirect restorations can be performed using supragingival minimally invasive techniques.
Full crowns are by far the most popular indirect procedure, as evidenced by the level of usage and the literature , and are still considered by most to be the ideal treatment for weak and badly damaged teeth. Adhesively retained partial coverage veneers and onlays have been reserved for limited use only, when several criteria are met [6,7,8,9,10]. The supragingival dentistry approach is a paradigm shift, because it has the unique and intentional goal of using every available technique and clinical trick to intentionally keep restorative margins supragingival and restore the tooth with as little healthy tooth removal as possible . Additionally, unlike traditional dentistry practice, partial coverage supragingival bonded restorations are not limited to easy cases. Research and experience show that even the most damaged teeth can be successfully restored using supragingival minimally invasive partial coverage restorations (Figures 3.3a,b, 3.4a–c).
A supragingival protocol allows the dentist to prevent the unnecessary creation of subgingival margins. When caries or an old restoration are in fact subgingival, then a protocol exists for repairing and isolating the damage, and avoiding further damage to the tooth or the periodontium, employing the great benefits of adhesively retained translucent restoration .
The final gingival margin placement has traditionally been a byproduct of restorative mechanical needs, esthetic needs and old restorative rules. The end result of subgingival margins is thus considered normal and necessary. Breaking through this paradigm requires new rules. It is no longer left to chance, but the location of the final gingival margin is intentional and several rules are followed to preserve supragingival margins when possible and to repair subgingival margins when necessary. The implementation of a supragingival protocol to overcome all the traditional reasons why restorative margins end subgingivally and how to minimize or eliminate the need to prepare traditional full crowns are summarized in the five principles of supragingival dentistry. These five principles will help to prevent or greatly minimize subgingival restorative margins with direct and indirect restorations.
The First Principle: Careful Removal of Caries and Old Restorative Material Removal Close to the Gingival Margin
Because the gingival margin region of the tooth is so crucial to a successful bonding procedure, it becomes mandatory to take great care while removing caries and restorative material in this region. When the preparation is close to gingival, as much care and respect should be placed as when the bur gets close to the pulp (Figure 3.5a–d). Nevertheless, general acceptance that subgingival margins are inevitable and normal, coupled with the lack of an intentional supragingival protocol can be very influential in the decision about the location of the final preparation margin.
A different attitude exists when working close to the pulp. Restorative dentists take great care, employ special techniques and even different tools, such as spoon excavators and large, round, slow-speed burs, and caries-indicating dyes, to carefully remove caries close to the pulp. The literature and experience show that, with care and the proper technique, pulp exposures can be minimized or avoided . The same extreme care should be applied when the preparation reaches the gingival margin. When such care is taken, this will result in a decrease and even prevention of subgingival margins (Figures 3.6a–c, 3.7a–c). Good illumination and magnification are desirable when working in the marginal area.
Even when subgingival caries or restorative material are inevitable, the damage can be limited with careful technique. In this crucial area, 1–2 mm can make all the difference. A slightly subgingival margin of 0.5 mm is manageable, while a subgingival margin of 1.5 mm or more will create many more complications and uncertain results (Figure 3.8a–c).
The following steps are suggested for achieving careful removal of caries and old restorations at or near the gingival margin and to prevent subgingival margins:
- The use of 3.5–4.5 times magnification when working close to the margin area is most desirable (Figure 3.9).
- After efficient removal of gross caries, old restorative material and occlusal reduction, the clinician should:
- slow down when close to gingival margins
- use a longer diamond for better visibility
- take great care in removing the remaining caries or old restorative materials.
- Caries indicator stain is indispensable to prevent the removal of non-infected dentin (the detailed technique for the use of caries indicator is given in Chapter 10).
- Preserve healthy enamel near the gingival margin, including in the absence of dentinal support (enamel margin preservation technique).
The Second Principle: Avoid Boxes, Axial Reduction or Counterproductive Mechanical Retention (Trust In Adhesion)
Interproximal boxes and axial reductions are part of the fabric of restorative dentistry . Lack of trust in adhesion make these a part of normal practice. However, trust in adhesion would render mechanical retention obsolete (Figure 3.10a–d). This lack of trust in adhesion, combined with habit and education, makes it normal for the clinician to make a traditional dimension proximal box every time interproximal caries need to be removed, independently of how large the caries may be (Figure 3.11). When a marginal ridge is weak and occlusal coverage of the marginal ridge is needed, a traditional box is the usual way of proceeding. Proximal boxes have also been used as an indispensable part of a mechanically retentive preparation for direct and indirect restorations (Figure 3.12). Nevertheless, proximal boxes have some serious disadvantages. They require a large amount of usually healthy tooth to be removed, and traditional boxes require proximal clearance, including gingival clearance. The universal approach to gaining gingival clearance has been to continue to drop the gingival floor of the box until clearance is achieved. This technique has two negative consequences. First, as the gingival floor is dropped, the margins become subgingival and bleeding will occur (Figure 3.13). Second, the enamel thickness decreases to the point that sometimes it is lost. Both consequences are counterproductive to adhesive procedures. Dropping the box can be substituted with a different technique, the “cervical margins separation technique”.
Similarly counterproductive is the preparation of axial walls and ferrules, which often forces margins to go subgingival, for the purpose of retention and resistance forms. Adhesive retention is enough to support any restoration, without the need for mechanical retention. Thus, the proper use and trust in adhesion prevents subgingival margins (Box 3.1; Figures 3.14a–d, 3.15).
During an indirect onlay preparation, proximal boxes can be substituted by a simple U-shaped 2+ mm reduction of the marginal ridge and proximal area, followed by an alternative procedure to create clearance (Box 3.2). Instead of dropping the gingival floor for clearance, a “cervical margin separation technique” can be used to gain the necessary clearance and separation needed for a clean impression (Figure 3.16a–c).