Effect of Peroxide-based and Peroxide-free Over-the-counter Tooth-whitening Products on Enamel Surface Roughness and Microhardness: An In Vitro Study

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Aim: To compare the effects of peroxide-free phthalimidoperoxycaproic acid-based whitening formulation (PAP+), carbamide peroxide (CP), hydrogen peroxide (HP), artificial saliva, and citric acid positive control protocols on enamel surface roughness and microhardness at baseline, after staining, after bleaching, and after 30-day artificial-saliva storage.Materials and methods: Fifty extracted human premolars were sectioned to expose buccal enamel, polished, and randomized into five groups (n = 10): Negative control (artificial saliva), HiSmile PAP+ with light activation, Opalescence PF 15% CP, Pola Day 7.5% HP, and positive control (0.25% citric acid).Specimens were stained with brewed coffee for 7 days at 37°C, treated according to the allocated protocol over 6 days, and stored in artificial saliva for 30 days.Surface roughness average (Ra, µm) was measured using three-dimensional non-contact optical profilometry, and surface microhardness was measured as Vickers hardness number (VHN).Statistical analysis was performed using IBM SPSS Statistics version 25 with alpha = 0.05.Results: Surface roughness increased most markedly in the positive control group after bleaching and remained elevated after 1 month.Among the bleaching products, PAP+ and HP showed lower numerical Ra values than CP after treatment; however, this difference should be interpreted cautiously because the standard deviations overlapped and the positive control group showed the dominant roughness increase.Microhardness decreased after staining in all groups and partially recovered after bleaching and artificial-saliva storage, except in the positive control group, which remained the most demineralized.Conclusion: Over-the-counter (OTC) whitening products produced measurable but formulation-dependent changes in enamel surface roughness and microhardness under the present in vitro conditions.The tested PAP+ formulation containing hydroxyapatite showed the least sustained alteration among the bleaching products.Clinical significance: Clinicians should counsel patients that OTC whitening products may transiently affect enamel surface integrity and that adjunctive remineralization strategies may support enamel recovery after bleaching.

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