TBU # 013: Treatment Approaches of Subgingival Cavity Margins

deep margin elevation gingivectomy meryem alhalid orthodontic extrusion surgical crown lengthening Mar 21, 2022

Deep margin elevation (DME) is an important procedure that every dentist should master. It is usually applied because its a very beneficial procedure as it helps in the preservation of dental structures, periodontal tissues and alveolar bone. However, this treatment is not always preferred.

In this article, we will discuss the various ways of treating deep subgingival margins and different approaches to each method. Subgingival margins are quite challenging, they carry technical and operative difficulties and as with any operative procedure, are very technique sensitive. When we look at a deep subgingival margin we have many obstacles to deal with and control. Many approaches have been discussed throughout the years. The main approaches include:

Soft Tissue Retraction: Which can be done using a rubber dam, cords, wedges, Teflon tape, and light-cured rubber dam materials, with the help of these materials we can perform a deep margin elevation procedure. Some of the main benefits are the preservation of soft and hard tissues to saving time within our treatments.
Ablation Of The Soft Tissues: This procedure could be done using blades, laser, electrosurgery or soft tissue burs. This procedure is generally called a gingivectomy or gingivoplasty. It is minimally invasive as long as we are not violating the biological width (at least 2–3 mm of the tooth between the bone and the margin of the final restoration).
Surgical Crown Lengthening: This procedure removes soft tissue and bone. It is quite an invasive and time-consuming procedure. The purpose of the treatment is for creating or exposing more tooth structure so a restoration can be placed.
Orthodontic Extrusion: This treatment involves relocating the tooth to a more coronal position. This allows for more workable tooth structure to be used. It's also known as dental tissue elevation. The technique is also considered time-consuming and invasive.

While every procedure comes with its own set of challenges, benefits and contraindications, clinicians should be aware of them all and consider which approach to follow depending on the case and their clinical judgment.

Deep Margin Elevation

This technique has been found beneficial in treating deep cavity margins in the cases where we are doing direct or indirect restorations (bonded or non bonded). The possibility of elevating the margin to a position where it could easily be isolated is the indicator and goal of this procedure. The adhesive composite resin base is used for reinforcing the undermined cusps, providing necessary geometry for only/inlay restorations, sealing the dentin, and filling undercuts along with supragingival elevation of margin. If for any reason, proper isolation and matrix adaptation isn't possible then this procedure is highly contraindicated and other treatment options should be considered.

In the case we are doing an indirect bonded restoration, the main aim is elevating the margin to a supragingival position so we can perform the bonding of the final restoration in a clean and visible safe environment. Here it is important to have the bonding area elevated because we can't bond the final restoration with the use of matrices and wedges, this will have an impact on the seating of the final restoration and also interfere with the removal of the excess luting resin composite.

Indirect non-bonded restorations, however, is quite less challenging because in this case, the types of cement (glass ionomer and zinc phosphate) are humidity tolerant and easy to remove after hardening. The clinician can perform this procedure subgingivally to some extent. Cementing in this approach can often give the clinician some advantages which include, a better emergence profile, reduce soft tissue contact with DME surfaces which can lead to a more healthy junctional epithelium. However, this compromises the potential bond strength of the final restoration.

Direct bonded restorations can also be done after DME. It is very challenging for the dentist to find a matrix that will provide a proper contact area. The clinician should seal the cavity margin and also get the correct contact area at the same time. Some ways have been discussed to make this process easier for the clinician. One way is called the progressive and delayed two-step approach. In the first step, the focus will be on getting a cervical seal with the anatomical emergence profile. The second step concentrates on completing the restoration with a proper contact area. Another way is called the double matrix technique or the MIM (matrix in matrix) technique, where you don't have to remove the matrix and re-insert another one to get the anatomical contact area which might cause bleeding and therefore contaminate the field and time will be wasted to get everything in the proper direction. The double matrix technique consists of two matrices that are both inserted together. Steps include performing the deep margin elevation to get the cervical seal and anatomical emerging profile, then remove the inner band (which is usually the rigid band), then complete the contact area with a separate or different band.

DME can be performed in two ways. Anatomical DME with the help of matrices or Non-anatomical DME without matrices. As the name states, it is self-explanatory. In the anatomical DME, the aim is to have the desired anatomy and emergence profile and it can be achieved with various matrices available on the market. Non-anatomical DME is less technically challenging, it can be performed freehand and then proceed with the removal of overhangs and rough surfaces by burs and strips. Teflon and copper bands can be used to enhance this procedure. This procedure is less common and has to be in the right situation.

DME has been shown to be well tolerated by the periodontium as long as the surface is hard, smooth and clean. Just like the surface of the enamel. If that is achieved, then a healthy environment is achieved. Also, the bond and marginal seal of indirect adhesive restorations is improved which also results in dentin sealing.

Gingivectomy (Soft Tissue Ablation)

Gingivectomy or gingivoplasty has limited applications because most teeth do not have a sufficiently wide band of keratinized attached gingiva. If there is an adequate amount of attached gingiva, a gingivoplasty may be useful in providing access as long as the lesion to be treated will be fully exposed and the biologic width will not be violated. This procedure needs to be done with a tooth that has a remaining tooth structure that is above the crystal bone with sufficient attached gingiva and lack of bony defects. It can be performed with electrosurgery, laser or the routine way by surgical blades and burs. The electrosurgery has better coagulation but you might hurt the surrounding tissue if you are not very careful. However, the healing is better and bleeding is reduced. Laser is also found to be better in the healing time and bleeding control. This procedure can be done only for the cases in which the remaining tooth structure lies above the crestal bone with sufficient attached gingiva and no infra-bony defect. If there is an inadequate zone of attached gingiva, osseous defects, or poor anatomic form, surgical crown lengthening is the treatment of choice.

Another method similar to this procedure but is more conservative is called mini flaps which provide sufficient access to subgingival lesions. It’s usually done by small incisions in gingival tissue, beginning at the gingival margin at the mesial and/or distal aspect of the lesion. The incisions should not extend past the mucogingival junction. Sutures are usually not necessary. All you need to do is to compress with gauze for the fibrin clot to form. If the flap extends past the mucogingival junction, sutures may be required after the restorative procedure has been completed.

Surgical crown lengthening (SCL)

Crown lengthening procedures aims at providing the space needed to establish the biologic width in case a deep restoration is needed. It simply means relocating the margins of the periodontium apically. This procedure increases the height of the crown. SCL is indicated when isolation isn't possible for DME and there is a contraindication of performing gingivoplasty. It’s also been found to be useful in increasing the ferrule effect and preventing restorative failure by managing the restorative margins. It is also found to be helpful in a case of a subgingival fracture of the crown. Aesthetics and the medical status of the patient are the main contraindications as well as the potential bone loss risk.

Surgical crown lengthening is an invasive procedure and some periodontists advise performing it as the last treatment option in the treatment of deep cavity margins because it carries a lot of risks. These risks include exposing the furcation area and the root surface, this might be problematic in the patients with high caries risk. Also increasing the crown to root ratio carries a mechanical risk, while this procedure has a good impact on the ferrule effect, it will negatively affect the biomechanics of the tooth because the dentist is drilling in the cervical area of the tooth.

The lowering of the gingiva and the supporting tissues apically might result in anatomical complications and loss of attachments, especially in the cases where we are dealing with concavities and furcation. Many factors will affect the success and recovery of the periodontium after the SCL procedure. These factors are:

flap type and position
amount of bone removed
gingival biotype
experience of the practitioner
gingival width variations
bone remodelling
healing time

If a successful surgical crown lengthening has been performed, the position of the gingival margin will be favorable and aesthetic, harmonious bone and gingival counters will be achieved as well. Bone loss is still an important risk factor to be considered. If surgical crown lengthening is to be done before the restoration, at least 4-8 weeks must elapse to allow the gingival margin to stabilize before restoration placement. It is considered both invasive and time-consuming but it still carries a high success rate.

Orthodontic Extrusion

Orthodontic extrusion means moving the tooth to a more coronal position. This treatment modality can be applied if the crown to root ratio allows it. The minimum crown-root ratio after extrusion is 1:1. The main goal is to place the tooth supragingival or in a more coronal position to provide a healthy supragingival tooth structure that can be restored later while having a healthy biologic width (The tooth must be extruded so that the biologic width is restored: a minimum of 3 mm of sound tooth structure coronal to the crestal bone.) If the biologic width is invaded during any restorative procedure, it may lead to periodontal breakdown.

Conservative approaches are usually preferred over invasive approaches. The dentist should choose the most effective and acceptable procedure for each case and patient. Overhangs in the proximal restorations are one of the main reasons for periodontitis, therefore it is important to consider this before starting the margin elevation procedure. As a dentist, you should be able to place the materials needed to ensure smooth, well-sealed, overhang free margins. Every case is different from the other and every patient is different. The important thing here is the diagnosis and the proper planning of the treatment before starting the procedure. Determine whether the tooth is periodontally sound and restorable before starting the treatment. You should also know the anatomy, respect the periodontium, know the reaction of the periodontium to different restorative materials, be mindful of the requirement and expectations of the treatment you are performing, and be aware of your limitations and skills.