Impact of Three Cementation Materials on the Fracture Strength of All-Ceramic CAD/CAM Overlay Restorations

To compare and assess the fracture strength of indirect overlay restorations bonded using various bonding techniques: sonically activated composite materials, preheated composite materials, and adhesive resin cement. The restorations were fabricated utilizing two distinct categories of all-ceramic CAD/CAM materials: reinforced resin composite blocks and lithium disilicate blocks. Depending on the CAD/CAM block type utilized for constructing the indirect overlay restorations, two main groups of 24 teeth each were created from the 48 human maxillary first premolar teeth that were ready for restorations. Group A consisted of indirect overlays made of lithium disilicate (IPS e.max CAD) blocks, whereas Group B used reinforced resin blocks (BRILLIANT Crios) for indirect overlays. subsequently according to the type of cement utilized in cementation. After the prepared teeth were scanned using the CEREC Omnicam digital intraoral scanner, indirect overlay restorations were designed utilizing CEREC Premium programme (version 4.4.4), and additional milling was carried out using the CEREC MC XL milling device. A computer-controlled universal testing machine (LARYEE, China) was then used to apply compressive axial loads to all cemented indirect overlay restorations at a crosshead speed of 0.5 mm/min till occurrence of fracture. A Student's t-test, LSD test, and one-way ANOVA test were utilized to analyze the data at a significance level of 0.05. This in vitro investigation revealed the greatest fracture strength mean value in the indirect overlays cemented with resin cement compared to other types of cement, regardless of the CAD/CAM block type. Depending on the findings of this research, regardless of the cement type, the mean fracture strength values of the indirect overlays made from both CAD/CAM blocks exceed the maximum biting force in the premolar area, indicating that both block types may be utilized clinically as overlay restorations in the premolar area.