Adhesive Direct Restoration in the Posterior Area with Subgingival Cervical Margins

Localized subgingival margins can complicate the use of direct adhesive restorations and subsequently hinder their durability and relation with the periodontal tissues. This article presents a technique involving placement of a modified matrix followed by immediate dentin sealing and coronal elevation of the deep margin to a supra- gingival position using a direct bonded composite resin base (DMR).

The deep margin elevation technique may be a useful non-invasive alternative to surgical crown lengthening. 

Sub-gingival interdental margins may be encountered when replacing large class II restorations.

Such cases generate significant technical and operative challenges during isolation of the operatory field using rubber dam, adhesive procedures, impression taking (traditional or optical), and adhesive luting. When not properly executed, these procedures may affect the longevity of the restoration and its relationship with marginal periodontal tissues.

There are various clinical approaches to such challenges. The gingival margins can be surgically exposed by apical displacement of supporting tissues; however, this may lead to attachment loss and anatomical complications such as the proximity of root concavities and furcations. Once exposed to the oral environment, the gingival margins can be difficult to maintain and may generate additional challenges.

Another approach, presented by Dietschi and Spreafico in 1998, is to place a base of composite resin to coronally displace proximal margins: cervical margin relocation (CMR).

In a following paper, a new classification is based on these two clinical parameters:

1. a technical-operative parameter (possibility of correct isolation through the dental dam) 
2. a biological parameter (depending on the biologic width).

Three different clinical situations and three different therapeutic approaches are identified (1^st, 2^nd, and 3^rd, respectively): coronal relocation of the margin, surgical exposure of the margin, and clinical crown lengthening.

Frequently, cavities of large dimensions extend beyond the cemento enamel junction  (CEJ) with margins more or less deeply located in the gingival tissue and with little or no residual enamel. While adhesion to mordant-treated enamel is predictable and safe, adhesion to dentin and cementum is dependent on numerous and complex phenomena. The formation of an efficient hybrid layer is influenced by many clinical steps (etching, drying, primer application, bonding application), including the polymerization of adhesive resin that stabilizes the structure of the hybrid layer itself. The operating procedure described by Dietschi and Spreafico was then defined by means of an in vitro study by Olsburgh³⁰ and establishes the following: rigorous isolation of the field with a dental dam, positioning of a matrix to guarantee a cervical seal, thorough cleansing of the cavity finishing with a bicarbonate spray, adhesive phase with a three-step etch-and-rinse method, and raising of the cervical step with flowable composite of maxi- mum 1 mm thickness. Following this protocol, 98% of margins obtained by the author were excellent. As mentioned above, the technique requires the use of flowables. Different authors higlined that when flowable is applied as the first cervical increment in Class II restorations, gingival micro-leakage is reduced and marginal integrity is improved.  In particular, in an article by Dietschi et al, the authors clearly suggest that the use of a medium-rigid flowable composite (7.6 GPa) is a potentially valid material to displace, in a coronal position, proximal margins. 

In the absence of reliable scientific evidence, but on the basis of published data and clinical experience, the importance and the systematic use of flowable composite, at the cervical level in the absence of enamel, can be supported according to the following rationale:

• interposition of an “elastic layer” of controlled thickness (0.5 to 1 mm) between the dental substratum and restoration material: this allows contraction stress to be absorbed and the adhesive interface to be preserved; 
• fluid adaptation to the cavity floor with absence of blisters and visual control of the cervical seal prior to correct positioning of matrix and wedge straightening of the cervical margin as a result of burring immediate dentin sealing.

The final restoration issues concern the relation with soft tissue and therefore the frequent presence of subgingival margins. 

The supra-crestal tissue attachment (STA),formerly known as biologic width, consists in the junctional epithelium and supra-crestal connective tissue attachment.

STA violation is believed to trigger adverse periodontal effects, although the specific aetiology (which has been proposed to be biofilm, trauma, material toxicity or a combination of these factors) is not clear.  Mean STA apico-coronal dimension is found to be 2.15–2.30 mm; however, considerable variability exists according to tooth type, site, periodontal health and periodontal phenotype.

In light of the above, a clinical case will be, step by step described, according with the Veneziani classification (Grade 2) in which the rubber dam does not allow a correct isolation of the field but the supra-crestal connective is respected. This situation is made possible by the fact that in the posterior areas, particularly in patients with a thick periodontal phenotype, may presents both a greater height of the junctional epithelium and the gingival sulcus.