Effect of Bleaching with Strawberry Extract and Hydrogen Peroxide on Colour Change, Surface Morphology and Micro-Shear Bond Strength of Resin Composite to Enamel Surface

Abstract

Introduction: The search to replace the chemical bleaching agent namely the Hydrogen Peroxide (HP) with a natural substance to whiten the discoloured tooth is a need of the hour, due to the severe roughing and compromised bonding of resin composite to enamel surface by this agent. Aim: To evaluate and compare the colour and surface changes in enamel surface, and the micro-shear bond strength of resin composite to enamel following bleaching with 35% HP and 2% Strawberry Extract (SE). Materials and Methods: In this in-vitro study, 30 bovine maxillary central incisors were decoronated and allocated randomly to two groups: group 1 (negative control) (n=15) and group 2 (experimental) (n=15). To evaluate the bleaching efficacy, group 2 specimens were experimentally stained with tea. Baseline colour coordinates (pre-bleach values) (L*, a*, b*) (∆E) were recorded. The crowns were sectioned to obtain four equal parts to obtain 60 specimens and these were allotted randomly to 4 subgroups a, b, c, d (n=15 each) based on the bleaching protocol. Subgroup a, Hydrogen Peroxide (HP). subgroup b, Strawberry Extract (SE); subgroup c, HP+SE (HPS); subgroup d, HP/P (HP/ Proanthocyanidin). Following bleaching, colour coordinates (post-bleach values) (L*, a*, b*) (∆E) were measured as mentioned before. Qualitative analysis of the surface (n=2) for each group was performed using scanning electron microscopy. Micro-shear bond strength of resin composite to the treated specimens (n=13) was determined using universal testing machine at a crosshead speed of 1 mm/min. Kruskal-Wallis one-way Analysis of Variance (ANOVA) was used to calculate the p-value and Post-Hoc Tukey Honest significant Test (HSD) was used to identify the significant groups, p-value (<0.05). Results: All the post-bleach specimens showed significantly higher mean ∆E (more whiter) values compared to their respective pre-bleach specimens (baseline values) (p-value -<0.05). Among the post-bleach groups, highest ∆E values (more whiter) were observed in subgroup 2c(HPS) (p-value=0.029). Similarly minimal morphological surface irregularities were observed in HPS. Group 1 (negative control) had the highest micro-shear bond strength compared to the experimental groups (group 2). Significantly, higher micro-shear bond strength was observed in subgroups 2b,c,d (SE, HPS, HPP) compared to subgroup 2a(HP) (p-value <0.001). Conclusion: SE alone or in combination with HP is an efficient and effective dental bleaching agent.