Evaluation of the In Vitro Effects of Cervical Marginal Relocation Using Composite Resins on the Marginal Quality of CAD/CAM Crowns

Purpose: To evaluate the effect of cervical margin relocation (CMR) for crowns designed using CAD/CAM technology, and made of pre-cured resin or lithium disilicate, before and after thermomechanical loading. The test hypothesis was that the marginal quality of the crowns would not be influenced by the CMR with composite resins before or after thermomechanical loading. Materials and Methods: Standard crown preparations were created in 40 human molars. The margins were located in enamel, except for the mesial proximal box, where the cervical margin was 2.0 mm below the cementoenamel junction, with 4.0 mm in the buccolingual and 2.0 mm in the mesiodistal dimension. For the CMR technique, a 2-mm layer of conventional or flowable composite resin was applied to the mesial box. Using the Cerec CAD/CAM system, 40 standard crowns were prepared, and restorations were luted using a dual-curing adhesive cement. SEM analysis was performed using epoxy resin replicas before and after loading to assess the marginal quality of interfaces of the mesial proximal box with CMR/crown and the distal face of the tooth without CMR. Statistical differences between groups were analyzed using the Kruskal-Wallis test and Bonferroni's post-hoc test. Results: The null hypothesis was accepted, since no statistically significant differences were found in marginal quality before and after thermomechanical cycling (p > 0.05). Conclusion: The implementation of CMR before and after thermomechanical cycling had no effect on the quality of cervical margins. To establish whether CMR is a suitable procedure for the adhesive luting of composite resin crowns in deep proximal boxes, additional studies are required. Keywords: marginal adaptation, relocation, resin composite, CAD/CAM crown, resin cements, lithium disilicate