Enhancing severely compromised premolar strength: role of cusp reduction design in CAD/CAM composite restorations

The objective of this study was to assess the effect of different designs and depths of cusp reduction on fracture resistance of maxillary permanent premolars restored with CAD/CAM composite restorations. A total of 42 sound maxillary premolars were used. Standardized MOD cavities were prepared in all specimens. Teeth were randomly divided according to form of cusp reduction into three main groups (n = 14); G1:MOD cavities restored with inlays with no cusp reduction, G2:MOD cavities restored with overlays with buccal and palatal anatomical cusps reduction, G3; MOD cavities restored with overlays with buccal and palatal flat cusps reduction. Groups 2 and 3 were further sub-divided into two sub-groups (n = 7) according to amount of cusp reduction either 1.5 mm or 2.5 mm. All groups were restored by CAD/CAM resin composite indirect restorations and cemented by adhesive resin cement. Thermocycling was done for all specimens. Fracture resistance was tested by universal testing machine and failure modes were examined by stereomicroscope. Statistically analysis was done for all data. Fracture resistance showed significant differences among the experimental groups (p < 0.001) with the highest fracture resistance for overlays with 2.5 mm of anatomical reduction. Regarding the modes of failure, there were no significant differences between experimental groups (p = 0.489). The fracture resistance of the composite CAD/CAM fabricated restorations is highly influenced by the restoration/prep design. The overlay design with anatomical cusps reduction of 2.5 mm can reinforce maxillary premolars teeth with MOD cavities.