Effect of different cavity designs and CAD/CAM blocks on fracture resistance of maxillary premolars with MOD cavities

The aim of the study was to evaluate the fracture resistance of maxillary premolars restored by different CAD/CAM blocks with different MOD cavity designs. A total of 56 maxillary premolars were selected and randomly divided into 4 groups. I: intact teeth as a positive control group. Standardized MOD cavities were prepared in the remaining group specimens. II: teeth had MOD cavities but were left unrestored as a negative control group. III: MOD preparations restored with inlays with no cusp reduction. IV: MOD preparations restored with overlays with cusp reduction. Group III and IV were further subdivided into two subgroups according to material used, i.e., either lithium disilicate or composite CAD/CAM blocks. All specimens were subjected to 5000 cycles of thermocycling and then tested for fracture resistance. Failure patterns were also examined. Data were statistically analyzed using Welch one-way ANOVA followed by Games-Howell's post hoc test. The results showed significant differences among the experimental groups (p < 0.001). The highest fracture resistance value was observed in positive control group, followed by overlays restored with lithium disilicate blocks. This was followed by overlays restored with composite blocks, then inlays restored by lithium disilicate blocks, inlays restored with composite blocks, while the lowest fracture resistance value was found in negative control group. Regarding failure modes, there was a significant difference between different groups (p < 0.001). The conclusion was that fracture resistance of maxillary premolars restored by CAD/CAM inlays and overlays are greatly affected by the cavity design and material type.