Objectives: This in-vitro study aimed to evaluate whether different deep margin elevation (DME) thicknesses (1 mm, 2 mm, 3 mm) influence the fracture resistance and fracture type of molars restored with CAD/CAM lithium disilicate overlays, compared to no elevation. Material & Methods: Seventy-six extracted human molars were randomly divided into four groups (n=19) based on Deep Margin Elevation thickness: 0 mm (control), 1 mm, 2 mm, and 3 mm. Standardized Class II cavities were prepared with cervical margins extending 1 mm below the cemento-enamel junction. DME was performed using a low-viscosity hybrid composite. Using a CAD/CAM workflow, overlays were designed and milled from fully crystallized lithium disilicate blocks. After cementation and aging, all specimens were loaded to failure under vertical compressive force. Fracture resistance was measured in Newton and the fracture analysis was recorded. Results: No significant differences in fracture resistance or fracture type distribution were found among the different deep margin elevation groups (p>0.05). Favorable fractures were more frequent in the control and 1 mm groups, while more severe fractures appeared in the 2 mm and 3 mm groups. Conclusion: Deep Margin Elevation up to 3 mm did not affect the fracture resistance of lithium disilicate overlays. All groups exceeded typical masticatory forces observed in clinical conditions. Therefore, the use of DME in conjunction with CAD/CAM lithium disilicate overlays appears to be mechanically reliable and clinically acceptable, regardless of the thickness of DME.
Daraze et al. (Sun,) studied this question.