In Vitro Effect of Sequential Compressive Loading and Thermocycling on Marginal Microleakage of Digitally Fabricated Overlay Restorations Made from Five Materials

Marginal microleakage compromises the longevity and biological seal of indirect restorations. Despite the growing adoption of computer-aided design and manufacturing (CAD/CAM) and three-dimensional (3D) printing technologies, limited evidence compares the marginal integrity of these materials under combined mechanical and thermal stresses. This study evaluated and compared the marginal microleakage of overlay restorations fabricated from five contemporary restorative materials, IPS e.max® ZirCAD Prime, BioHPP®, G-CAM, VarseoSmile CrownPlus, and IPS e.max® CAD, after sequential compressive loading and thermocycling. A total of 125 extracted human molars were prepared for standardized 1.5 mm-thick CAD/CAM overlay restorations and assigned to three experimental conditions: control, sequential compressive loading (3 × 500 N), and thermocycling (6000 cycles between 5 °C and 55 °C) followed by loading. Microleakage was assessed using 2% methylene blue dye and stereomicroscopy. Data were analyzed using Fisher’s exact test and Fleiss’ Kappa (α = 0.05). G-CAM and IPS e.max® ZirCAD Prime exhibited the lowest microleakage across all testing conditions, while BioHPP® showed the highest values. Both sequential compressive loadings and thermocycling significantly increased microleakage in all materials (p < 0.001). The results indicate that material type significantly influences marginal sealing, with G-CAM and IPS e.max® ZirCAD Prime maintaining superior marginal integrity compared with other materials tested.