Effect of peroxide-free and peroxide-based in-office bleaching on the surface and mechanical properties of CAD/CAM...

The study aimed to investigate the influence of H₂O₂-based and H₂O₂-free in-office bleaching on the surface and mechanical attributes of CAD/CAM composite blocks. CAD/CAM composite blocks from five different composite materials (CC1, CC2, CC3, CC4, and CC5) were randomly divided into two groups according to bleaching application (H₂O₂-based and H₂O₂-free). The surface topography, morphology, nanohardness, elastic modulus, flexural strength, and fracture toughness were measured. A paired and unpaired sample t-tests gauged the effect of pre- and post-bleaching on the substrates. The estimated mean differences (before-after bleaching) suggested an increase in surface roughness for two materials CC2 and CC4, and a significant decrease in nanohardness for material CC4 and in elastic modulus for materials CC2 and CC4 with H₂O₂-based bleaching, whereas H₂O₂-free bleaching resulted in changes compatible with no change in these properties. Flexural strength and fracture toughness showed no evidence of changes, irrespective of the bleaching gel used. Scanning electron microscopic analysis revealed erosive effects and micropore formation due to H₂O₂-based bleaching. H₂O₂-based bleaching deteriorates the surface of CAD/CAM composite materials while H₂O₂-free bleaching gel had an insignificant effect on both surface and bulk properties. The clinician should carefully evaluate the potential effects of H₂O₂-based bleaching on the surface properties of CAD/CAM composites.