The pH and Concentration of Hydrogen Peroxide – Impact upon Dental Enamel Properties and Response to Dietary Staining, Erosion, and Remineralisation

Abstract

Hydrogen peroxide (HP) based whitening products can damage enamel due to their pH and concentration. This in-vitro study investigates the effect of HP pH and concentration on selected enamel properties. In addition, combined effects of whitening/remineralisation and subsequent resistance to simulated dietary erosion and staining were investigated. Polished bovine enamel samples were treated with 6, 20, 40wt.% HP at pH 5, 7 and 9, for 2 hours daily for ten days. Samples were stored in artificial saliva at 37C before and after treatment. Whitening/remineralisation investigations were performed using 6wt.% HP in combination with either casein phosphopeptide–amorphous calcium phosphate (CPP-ACP) or nanohydroxyapatite (nHA). Samples were then subjected to simulated dietary staining using coffee and erosion using 0.3% citric acid (pH3.8). Measurements of enamel roughness (Ra), hardness (HV), and colour change (E) were made before and after treatment using atomic force microscopy, micro-hardness testing, and spectrophotometry. Mineral loss and qualitative surface evaluations were undertaken using energy dispersive x-ray spectroscopy (EDX) and scanning electron microscopy (SEM), respectively, after treatment. As HP concentration increased and pH decreased there was a statistically significant increase in E (P<0.05). Greatest increase in Ra and decrease in HV occurred in enamel treated with pH9 40% HP. Remineralisation did not significantly affect E, Ra, and HV of whitened enamel. CPP-ACP was effective in preventing statistically significant changes in Ra and HV values after erosive cycling. Enamel treated with nHA exhibited the greatest dietary stain uptake. No significant changes in enamel Ca, C, and P occurred after whitening, remineralisation, and erosion. SEM images revealed distinct surface changes mostly in pH9 and nHA treated samples. All whitened specimens exhibited significantly greater colour change than the control group. Neutral HP caused the least damage to whitened enamel while producing a satisfactory whitening effect. Remineralising agents did not reduce whitening side effects, however, CPPACP prevented significant Ra and HV changes after dietary erosion.