The Effect of Functional Crown Lengthening Versus Deep Margin Elevation on Periodontal Tissues

In dental practice, restoring cavitated proximal caries lesions is a common routine procedure in dental clinics. However, subgingival margins reaching below the cementoenamel junction are known to have a common clinical concern, especially when restoring severely destructed Class II caries. Ideally, the correct choice of treatment plan is critical to ensure successful outcomes (Padbury et al., 2003).

The use of direct adhesive restoration to restore large interproximal defects is not an ideal treatment option. Due to their size, such defects usually require indirect adhesive restorations. However, this appears to be challenging since cavity preparation, impression taking, the adhesive-bonding procedure, and proper moisture control may be impeded. These challenges are usually overcomed by functional crown lengthening (Mangani et al.,2015; Juloski et al.,2018).

Functional Crown lengthening is a surgical procedure to expose the gingival margins by apical displacement of the supporting periodontal structures, thus can facilitate an access and adequate isolation to achieve the optimum position of deep restorations and avoid violating the biological width (Magne \& Spreafico, 2012; Sarfati \& Tirlet, 2018).

The biological width is defined as the gingival attachment along the root surface, from the most coronal portion of the epithelium attachment to the most apical portion of the connective tissue attachment (Gargiulo et al.,1961). Therefore, a recommended distance of 3 mm or more between the restorative margins and the alveolar crest is considered necessary to avoid detrimental effects on neighbouring soft and hard periodontal tissues (Ingber et al.,1977; Lanning et al., 2003). The violation of the biological width results in severe gingival inflammation and consequently deep pocket formation or gingival recession, in addition to bone level reduction (Nugala et al., 2012).

Recurrence usually occurs particularly in patients with thick biotypes or when surgery comprises only gingivectomy. Moreover, recurrence leads to restoration limits being replaced sub-gingivally, whereas surgery aims to place them sub-gingivally (Ganji et al.,2012)..

A more conservative approach is the deep marginal elevation (DME), which is considered an atraumatic procedure advocated in the presence of deep cervical margins (Dietschi \& Spreafico,1998; Veneziani,2010).

The concept of "deep margin relocation" was introduced in 1998 by Dietschi and Spreaficoas a new approach to deep caries. It was later renamed "deep margin elevation" by Magne and Spreafico in 2012. It is a procedure done to raise the margins of the tooth to either an equi-gingival or supra-gingival position using restorative materials. This technique is referred to by different names, including the "open sandwich technique," "proximal box elevation," and the "margin elevation technique" (Dietschi \& Spreafico,1998; Dietschi et al.,2003).

A dry working field is crucial to the success of restoration, especially in deep cavities reaching the Cemento-enamel junction. The presence of saliva and blood causes contamination and deterioration to the restoration and affects the bonding to the tooth structure (Keys \& Carson,2017).

DME allows appropriate placement of a rubber dam to a perfectly placed margin, adequate light-curing depth to the margin of restoration, accessibility to proper oral hygiene, and an ultraconservative approach to evaluate bone and soft tissue (Frankenberger et al.,2013; Zaruba et al.,2013). Studies have shown promising results using DME and high survival rates of up to 90% over a 12-year clinical evaluation (Bresser et al.,2019).

A randomized clinical trial compared the clinical results of crown lengthening and DME in posterior teeth. At 180 days, clinical attachment loss was higher in the surgical group (Bresser et al., 2019). Many studies have reported that DME procedures do not negatively affect periodontal health status and suggest they are well tolerated by the periodontium when proper isolation is achieved (Frese et al.,2014; Sarfati \& Tirlet, 2018).

However, the gingival phenotype must be analysed as among teeth treated with subgingival restorations, those presenting <2 mm of keratinized tissue showed higher gingival index (Stetler \& Bissada,1987).

Debate continues as to whether a non-invasive elevated margin technique or surgical CL is the better strategy for facilitating the placement of large direct composite resin restorations. Though a conservative approach is often advocated, it fails in situations that demand change in the shape of tissues around the tooth for restoration (Sarfati \& Tirlet, 2018).

To the best of our knowledge, no previous study measured the effect of crown lengthening on inflammatory biomarkers in the gingival crevicular fluid in comparison to deep margin elevation in posterior teeth with deeply located proximal margins.