TBU # 017: Deep Margin Elevation: The newly emerging alternative to crown lengthening
Apr 20, 2022
The trend in dentistry has shifted away from more invasive procedures. One of the recent techniques gaining popularity is “Deep Margin Elevation” (DME). In contrast to crown lengthening, deep marginal elevation is a non-surgical procedure. The concept implies using a direct restoration that is only placed at the depth of the preparation to elevate the margin to a more coronal and conducive location before the indirect restoration is set in place (facilitated by a CAD/CAM machine) ensuring ideal fabrication and cementation. DME has previously been resisted because there are concerns that margin-elevated restorations can fail because of an extended restoration interface between the direct restorative material and ceramic. As you go through this article, you will gain a deeper understanding of what makes DME different from the traditional posterior surgical crown lengthening procedure as well as the material compatibility with DME.
DME vs Crown lengthening
Let's brush through one important aspect that plays a significant role in the outcome before diving deep. It's the biological width. Together, the junctional epithelium (0.97mm) and the connective tissue attachment (1.07) make up the gingival attachment along the root surface and coronal to crestal bone. It's worth noting that the connective tissue attachment is much stronger than the junctional epithelium due to the presence of horizontal collagen fibers inserted into the cementum on one side and the connective tissue on the other, which means that, when probing healthy gums, the probe stops at the most apical area of the pocket where there are more epithelial cells. Deep subgingival restorations can result in a loss of biological width, particularly with crown lengthening procedures. Any placement of a restoration that will encroach into the biological width will result in unpredictable healing and regeneration, and eventually possible failure of the restoration.
The goal of crown lengthening (CL) procedures is to create the space needed to accommodate the material/prosthesis to be used during deep restorations whilst preserving the biological width by creating a margin between the material and the biological width. As such, a surgical procedure efficiently increases the clinical crown height and exposes deep cavities, but also exposes tooth structure. CL often extends to the adjacent teeth and is not limited solely to the targeted tooth to achieve harmonious osseous and gingival contours. Consequently, loss of bone support may cause longer clinical crowns, flattened papillae, and black triangles on adjacent teeth. Likewise, margin relocation after surgical crown lengthening can be challenging, as well as its predictability of healing. Having the posterior areas exposed complicates oral hygiene maintenance, root hypersensitivity, esthetic compromise, and the possibility of furcal involvement in several years. Originally known as cervical marginal relocation (CMR), deep marginal elevation (DME) found its way into dentistry as a relatively simple method to expand the margins of the restoration by placing them more coronally if proper isolation is maintained after caries removal, a compatible material is layered to create a relatively elevated margin.
A study assessing the prognosis of teeth restored with CL vs DME found that free gingival margins (FGM) displayed significant displacement while healing, but demonstrated overall stability at 6 months, showing that the prognosis after CL surgery is dictated by anatomical and technical factors. Over the healing period, the gingival margin position gradually changes, this would result in a longer time required for delivery of the final restoration, making CL as a treatment option more time-consuming. Typically, the final restoration post-CL could be done in the posterior tooth areas after six to twelve weeks and in the anterior tooth areas after three to six months.
As for DME, and in conjunction with indirect restorations, has a better survival ratio compared to CL. Even though the initial survival rate can decline over time, DME did not affect the fracture strength of ceramic restorations. The fracture strength of ceramic restorations measured with and without DME was similar. Onlays and inlays fracture, with or without DME, are caused more by oblique forces than bite forces. In other words, both inlays and Onlays are clinically fracture-resistant regardless of the DME.
We can draw several benefits from DME in comparison to classic CL procedures. It significantly improves the bond and marginal seal of indirect adhesive restorations and results in immediate dentin sealing where the adhesive composite resin base is used to reinforce the undermined cusps, providing necessary geometry for only/inlay restorations, sealing the dentin along with raising the supragingival margin, as well as being tolerated by the periodontium with its ability to create another kind of biological width that is healthy with a longer JE and smaller CT attachment beneath the material used. A potential advantage of DME beneath ceramic inlays is that the act of placing a direct restoration on the gingival floor automatically shortens the occluso-gingival height of the inlay, therefore, proximal ceramic inlays with shorter heights are less likely to fracture and fail than bulk ceramic inlays.
According to the limited available research, crown lengthening (CL) surgery is successful for retaining teeth in the long term. Nevertheless, deep margin elevation (DME) has a higher survival rate based on a biological width analysis. Ongoing studies are needed over a longer period to assess the rebound effect of CL surgery over time and degradation in DME.
