# Quantitative and Qualitative Assessment of Enamel Surface Roughness Following High-Concentration Peroxide Bleaching: A Comparative In Vitro Study

## TL;DR

This study compared how two high-concentration peroxide bleaching agents affect enamel surface roughness using two methods, finding both cause significant changes.

## Contribution

The study introduces a comparative in vitro analysis of two bleaching agents using both SEM and profilometry to assess enamel roughness.

## Key findings

- Both 35% hydrogen peroxide and 37% carbamide peroxide significantly increased enamel surface roughness compared to the control.
- SEM detected more microstructural alterations than profilometry, showing a strong method effect.
- SEM and profilometry measurements showed high consistency, especially in the control and hydrogen peroxide groups.

## Abstract

Introduction: Bleaching is a widely practiced aesthetic dental treatment, but high-concentration peroxide-based agents may negatively impact enamel integrity. This in vitro study aimed to compare enamel surface roughness after exposure to 35% hydrogen peroxide and 37% carbamide peroxide using both scanning electron microscopy (SEM) and contact profilometry. This study further explored the correlation between these two methods for evaluating surface topographical changes.

Materials and methods: Fifty enamel specimens were prepared from 30 extracted human premolars and randomly divided into three groups: Group 1 (control, n = 10), Group 2 (35% hydrogen peroxide, n = 20), and Group 3 (37% carbamide peroxide, n = 20). Bleaching was performed for 15 minutes per day for seven days. Surface roughness was assessed at baseline and after bleaching using a contact profilometer (Mitutoyo Surftest SJ-410, Mitutoyo Corporation, Kanagawa, Japan) and SEM (JEOL JSM-6510LV, JEOL Ltd., Tokyo, Japan). For profilometric analysis, the mean surface roughness (Ra) was calculated from three standardized points per specimen. SEM images at 1000× magnification were used to analyse three-dimensional topographic changes. Data were analysed using a mixed model analysis of variance (ANOVA), post-hoc Dunn-Bonferroni test, and Spearman correlation analysis, with significance set at p < 0.05.

Results: Both bleaching agents caused a significant increase in enamel surface roughness compared with the control group (p < 0.001). SEM detected more microstructural alterations than profilometry, as indicated by the strong method effect (effect size = 0.87, p = 0.001). Post-hoc comparisons showed that both bleaching agents significantly differed from the control, whereas no significant difference was found between them. Correlation analysis revealed high consistency between the SEM and profilometer measurements, particularly in the control and hydrogen peroxide groups.

Conclusion: Exposure to both 35% hydrogen peroxide and 37% carbamide peroxide significantly increased enamel surface roughness with comparable etching effects. SEM was found to be more sensitive than profilometry for detecting microstructural changes.