Deep Margin Elevation: Next-Level Adhesive Dentistry to Avoid Surgical Crown Lengthening

Teeth with subgingival defects are a common challenge in clinical practice. This is especially true for resin-bonded posterior partial-coverage restorations, such as ceramic inlays and onlays, which require ideal moisture and contamination control. There is no "one-fits-all" solution, and the best possible treatment option should be selected on a case-by-case basis, taking into account all clinical factors as well as patients' expectations and specific needs. Surgical extrusion, orthodontic forced eruption, and reimplantation are "last-resort" treatment approaches for teeth with subgingival fractures, caries, lesions, and cervical resorptions that would otherwise be unrestorable.

Surgical crown lengthening, either by gingivectomy or apically positioned flap with or without osseous resection, is often preferred to relocate the periodontal complex more apically and establish supragingival restoration margins that do not interfere with the supracrestal tissue attachment. However, SCL is associated with lengthy treatment time, high costs, patient discomfort (eg, hypersensitivity), and, in certain cases, compromised dental esthetics.¹ It is quite common that ongoing and even physiological bone remodeling over time causes the created interproximal open spaces, or "food traps," to become even larger, much to the annoyance of the patient trying to keep them clean. In addition, multi-rooted teeth with a short trunk may expose furcations over time.

Deep margin elevation, also known as proximal box elevation, cervical margin relocation, and coronal margin relocation, has been suggested as a viable alternative in select cases.^2,3 The goal is to use a direct adhesive restoration to reposition the cervical margin to a supragingival position. With a direct restoration for DME in place, it is easier to make a conventional and especially a digital impression, bond an indirect restoration, and remove excess luting material. In addition, DME facilitates the preservation of sound tooth structures, and the direct restoration allows for optimization of the preparation design-that is, geometric requirements of indirect restorations can be disregarded in the areas that are restored directly.

A technique elevating a small aspect of the cervical margin for gold crowns with amalgam was previously published in the early 1960s. The first mention of using a direct resin-based composite (RBC) to elevate the cervical margin for an indirect bonded restoration in the dental literature dates back to 1998, when Dietschi and Spreafico published a seminal article on this treatment approach.⁴ Since then, the number of scientific articles on DME has increased significantly, as has the popularity of indirect resin-bonded posterior partial-coverage restorations over the years.

In fact, several systematic literature reviews and a meta-analysis were published very recently.^2,3 Based on mainly laboratory studies, these articles confirm that the fracture resistance of teeth restored with DME is not significantly different from teeth restored without DME. The marginal quality of DME restorations to root dentin is excellent and similar to sites without DME. Different adhesives and restoration materials used for DME were found to differ in their performance in vitro, and RBC of different viscosities seems to perform well for DME. DME restorations are compatible with periodontal health as long as they do not infringe on the supracrestal connective tissue attachment and are well-polished. Meta-analyses found teeth restored with DME and indirect restorations to have a better survival rate than teeth treated with SCL.^2,3 These reviews suggest that further clinical studies are needed.

Follow-up periods in clinical studies on the performance of DME-treated teeth range between 3 months and 21 years, with sample sizes between 10 to 120 patients and a total number of 278 patients and 349 restored teeth included in the available studies combined.² Gingival inflammation levels at sites with DME were found to be similar to untreated sites in patients with very good oral hygiene and a tight follow-up. One study with 120 patients reported an overall survival rate of teeth with DME of 95.6% after 10 years.⁵ All other clinical studies reported similarly high long-term success rates.^2,3

While there is no clear consensus in the literature on which dental material is best suited for DME, a recent systematic review of laboratory studies recommended that proximal cavities that extend beyond the cementoenamel junction (CEJ) be restored with RBC rather than glass-ionomer cement or resin-modified glass-ionomer cement.⁶ Dental practitioners may choose between conventional RBC, flowable RBC, and bulk-fill RBC of different viscosities to restore deep proximal boxes.⁶ Note that self-adhesive resin-based luting materials are not suitable for DME.

With respect to the adhesive strategy, there is also no clear indication of which bonding protocol and adhesive provide the best marginal adaptation of RBC restorations in Class II cavities extending beyond the CEJ.⁶ It should be noted that when an etch-and-rinse or selective enamel etch approach is applied, over-etching or inadvertent etching of dentin should be avoided.² However, following current developments and trends, self-etch adhesives or universal adhesives, applied in self-etch or selective enamel etch mode, are generally preferred for DME.²

As with any adhesive procedure, moisture and contamination control with rubber dam is essential for clinical success. Although DME has been suggested as a technique to facilitate rubber dam placement, typically rubber dam isolation is urged before the bonding process, and the inability to do so is considered a contraindication for DME.^2,3 In such cases, SCL should be the first treatment of choice. And while several alternative suction devices have been postulated for adhesive procedures, rubber dam isolation remains ideal. In fact, a recent clinical in situ study demonstrated that moisture and humidity caused by exhaling significantly decreases adhesive resin bonds to enamel but could be controlled through rubber dam isolation.⁷

Another critical aspect regarding DME is the application of a tight-fitting matrix to ensure excellent marginal adaptation. Circumferential metal matrices are preferred for DME but may be difficult to properly adapt to proximal defects extending beyond the CEJ. Trimming of circumferential matrices to increase their curvature and decrease their height may allow for easier placement. Placing a sectional metal matrix within the circumferential metal matrix and carefully placing a wedge or packing a small piece of Teflon tape at the gingival level between the two has been suggested for challenging cases.² It is advisable to meticulously check DME restorations with a fine explorer and radiographs before proceeding with treatment.

After placement of the DME restoration, the preparation for the indirect restoration, which is typically a ceramic inlay or onlay, is carried out. The bonding procedure for an indirect ceramic restoration follows common protocols. This includes, for silica-based ceramics, hydrofluoric acid-etching and application of a silane coupling agent. On the other hand, proper pretreatment of the occlusal DME surface is critical to enhance the bonding performance of the restoration placed on top. Airborne particle abrasion with aluminum oxide and silane application is the preferred surface treatment for RBC before conditioning the tooth substance and applying adhesive bonding agents. The use of current universal bonding agents that contain silanes may simplify the procedure.

Regular follow-up and maintenance are necessary to monitor and ensure periodontal health after DME. Patients should be instructed to perform proper oral hygiene, especially interproximal cleaning.

Deep margin elevation is viable for restoring teeth with localized subgingival defects. Careful case selection and meticulous clinical techniqe are critical for long-term success. Other key aspects include proper rubber dam isolation, precise matrix placement, avoiding infringement of the connective attachment of the supracrestal tissue complex, and excellent oral hygiene and regular follow-up visits.

Markus B. Blatz, DMD, PhD
Professor of Restorative Dentistry, Chair, Department of Preventive and Restorative Sciences, and Assistant Dean, Digital Innovation and Professional Development, University of Pennsylvania School of Dental Medicine, Philadelphia, Pennsylvania

Florin Eggmann, Dr. med. dent.
Lecturer, Department of Periodontology, Endodontology, and Cariology, University Center for Dental Medicine UZB, University of Basel, Basel, Switzerland; Research Fellow, Department of Preventive and Restorative Sciences, University of Pennsylvania School of Dental Medicine, Philadelphia, Pennsylvania