Biomechanical evaluation of deep margin elevation-assisted overlays for Mesio-Occluso-Distal and sub-CEJ defects in...

This study aimed to evaluate the biomechanical effects of deep margin elevation (DME) and restorative material selection for overlays in maxillary molars with mesio-occluso-distal (MOD) subgingival defects via in vitro deformation analysis, fracture resistance tests, and 3D finite element analysis (FEA).

Three MOD overlay models (Model 1, Model 2, and Model 3) were created for maxillary molars by positioning the mesial and distal margins 1 mm above, at, and 1 mm below the cementoenamel junction (CEJ), respectively. Model 3 underwent DME modification, generating Models 4 (1 mm supragingival) and 5 (CEJ). The five models were restored with two materials (E: IPS e.max CAD; L: Lava Ultimate), yielding 10 test groups (E1-E5/L1-L5). The CEJ deformation, load resistance, and restoration failure modes were evaluated using deformation analysis and fracture resistance tests. 3D FE modeling was used to quantify the von Mises stress (VMS) distributions in the restorations, bonding, and DME layers, which were validated by cross-method correlation with experimental data.

Deformation analysis revealed consistent mesial microstrains greater than distal microstrains, with E-groups having lower values than L-groups. Fracture resistance tests revealed that Model 3 (subgingival margin) was the weakest, with higher catastrophic failure rates than the supragingival designs. Compared with the non-DME group, the L4 (2-mm DME) group presented the best biomechanical performance with a greater load capacity. FE analysis demonstrated that E1 and L1 achieved optimal stress dispersion and that E3/L3 developed critical stress increases. The post-DME groups (E4/E5/L4/L5) exhibited homogeneous VMS distributions compared with the E3/L3 stress increases. DME layers concentrated VMS mesially, and FEA-in vitro correlation showed strong method concordance across all parameters.

As the subgingival defect depth increases, restorations progressively degrade. For sub-CEJ defects, the use of the 2-mm DME method to increase margins to 1 mm supragingival along with Lava Ultimate resulted in optimized stress distributions and improved biomechanical performance, resulting in greater longevity than non-DME methods. Thus, this protocol is recommended.