Clinical and laboratory investigations on cervical margin relocation

In the presence of subgingival proximal margins, close to or below the cemento-enamel junction (CEJ), impression taking and adhesive luting procedures for indirect restorations are hampered; surgical crown lengthening or orthodontic eruption are viable options. However, the placement of a small amount of composite, so-called cervical margin relocation (CMR), was proposed as an alternative technique. To date, literature about CMR is scarce and the aim of this PhD thesis was to perform laboratory and clinical investigations to shed light on some crucial missing points. The thesis consists of 5 studies. The first study is a literature review summarizing the existing scientific literature on CMR technique performed prior to the adhesive cementation of indirect restorations. The second study is an in vivo randomized controlled clinical trial assessing the possible influence of CMR on periodontal health, after 12- month of clinical service. The third study is an in vitro study evaluating the marginal sealing of relocated mesio-occluso-distal overlays. The fourth study is an in vitro study analyzing the influence of cervical margin relocation and adhesive system on microleakage of indirect composite restorations. The fifth study is an in vitro study evaluating the possible correlation between two methodological approaches applied to evaluate cervical margin relocation. Different methodological approaches were used to perform the above-reported investigations, such as scanning electron microscopy (SEM) and microleakage analyses. The principal investigator was calibrated and trained before performing the operative procedures and laboratory investigations. All the recorded data were statistically analyzed with dedicated software. CMR is a relatively new restorative procedure and information on its performance is limited. Within the limitations of the performed laboratory and clinical studies, the present PhD thesis allowed to draw the following conclusions: 1. On the basis of the reviewed literature, currently, there is no strong scientific evidence that could either support or discourage the use of CMR technique prior to restoration of deep subgingival defects with indirect adhesive restorations; further randomized controlled clinical trials are necessary to provide reliable evidence on the influence of CMR technique on the clinical performance, especially on the longevity of restorations and periodontal health. 2. A higher incidence of bleeding on probing can be expected around teeth treated with CMR and in coincidence with deep margins placed at or closer than 2 mm from the bone crest; consequently, CMR should be considered as a clinically sensitive-technique, especially when performed on deep subgingival margins. 3. The marginal sealing ability of flowable and microhybrid resin composites is comparable for CMR; furthermore, luting overlays directly onto dentin without CMR appears to be a better method for limiting marginal leakage underneath CAD/CAM overlays. 4. CMR technique and the adhesive system employed for luting indirect restorations might represent a significant factor affecting microleakage at the interface below CEJ. 5. CMR seems to provide less adequate seal of the margin than the one achieved by cementing the restoration directly to dentin without CMR. The sealing ability of the marginal interface depends on the adhesive materials used for performing CMR. Differences in the quality of the marginal adaptation between two different materials used for CMR could not be detected by SEM observations. SEM examination of the marginal adaptation does not allow for the predictions of the functional sealing of the margins. Future in vitro and in vivo studies should evaluate the effectiveness of CMR technique and the marginal seal of different bonding systems and luting cements in combination with CMR. Particularly, randomized controlled clinical trials should investigate the durability of CMR and the response of periodontal tissues