Effect of Bleaching on the Surface Roughness of Resin Composites Evaluated by Atomic Force Microscopy (AFM)

<b>Background/Objectives</b>: Composite resins are widely used restorative materials, but their surface properties may be altered by bleaching procedures. This study aimed to compare the effects of two bleaching techniques-light-activated (zoom) and diode laser-activated-on the surface roughness of nanohybrid and microhybrid composites using Atomic Force Microscopy (AFM) for topographic evaluation. <b>Methods</b>: A total of 60 composite resin disks were fabricated, with 30 nanohybrid and 30 microhybrid samples. Each type was divided into three subgroups: control, zoom bleaching, and laser bleaching (n = 10 per group). Zoom bleaching employed 40% hydrogen peroxide gel activated by the Philips Zoom system, while laser bleaching used a 940 nm diode laser (QuickLase, Kent, UK) in combination with QuickLase bleaching gel containing approximately 35-40% hydrogen peroxide. Surface roughness parameters (Sa) were measured using AFM, and statistical analysis was performed. <b>Results</b>: Both bleaching protocols increased surface roughness compared to controls. Microhybrid composites showed higher roughness after zoom (103.12 ± 19.25 nm) and laser bleaching (106.16 ± 25.21 nm), while nanohybrid composites had lower values after zoom (57.77 ± 13.88 nm) and laser bleaching (78.13 ± 23.29 nm). Significant differences were found between composite types post-bleaching (<i>p</i> < 0.001 for zoom; <i>p</i> = 0.019 for laser). However, differences between bleaching methods within the same composite type were not significant (<i>p</i> > 0.05). <b>Conclusions</b>: Both zoom and laser bleaching negatively affect composite surfaces, with laser bleaching showing a greater impact. Nanohybrid composites demonstrated superior resistance to surface alteration, suggesting better clinical durability. These findings are relevant for clinicians when planning restorative treatments in patients likely to undergo bleaching.