The effect of different biomimetic materials as a remineralization protocol on microhardness and ultramorphology of bleached enamel

Aim: To compare the effect of Nano-HA and Nano-BG as remineralizing protocol on the microhardness and structural morphology of bleached enamel.
Materials and methods: Two different biomimetic materials were used; Nano-bioactive glass powder and Nanohyroxyapatite powder. Five extracted sound human central incisors were selected. The labial of each tooth was divided longitudinal into two equal halves. The mesial half was assigned for BG group and the distal half was assigned for HA group. A total number of 20 Specimens were randomly divided into 4 groups (5specimens each). Group1 represent sound unbleached enamel, group2 represent bleaching enamel surface, and group3 represents remineralization by BG and group4 represents remineralization by HA. The specimens in group2 were bleached using 40% Hydrogen Peroxide following the manufacturers’ instructions. For Nano-BG group: a mixture of bioactive glass 45S5 powder with particle size (25-120 um) with poly-acrylic acid powder was done (PAA –BAG). Then, one milliliter of the artificial saliva was added then was applied on the bleached enamel surface followed by rinsing for one minute.For Nano-HA group: HA mixed with distilled water then was applied to bleached enamel surface followed by rinsing. All specimens were subjected to de and remineralization cycles. Surface Micro-hardness of the specimens (before bleaching after bleaching and after remineralization protocol) was determined and the mean microhardness values of the specimens were calculated, tabulated and statistically analyzed using one way analysis of variance (ANOVA) and Tukey post hoc tests were used to study the significance. The surface morphology of two representative sample of each tested group were examined using scanning electron microscope attached with energy dispersive X-ray analyzer.
Results: Microhardness results revealed that the greatest mean value was recorded in unbleached enamel, followed by remineralized enamel with Nano- BG, then remineralized enamel with Nano- HA, with the least value in bleached enamel. ANOVA test revealed that the difference was extremely statistically significant (p<0.0001). Tukey’s post hoc test revealed no significant difference between unbleached enamel and remineralized enamel with Nano- BG. Moreover, there was no significant remineralized enamel with Nano- HA and remineralized enamel with Nano- BG. This was associated with some morphological changes in the enamel surfaces between different tested groups. Conclusions: The use of bleaching agents greatly affects the structural integrity of enamel surface and resulted in great mineral loss. It is strongly recommended to perform remineralization protocol after any bleaching procedure. The biomimetic materials are very promising due to their ability to perfectly reconstruct partially damaged bleached enamel surface. Bioactive glass material was able to perform almost complete recovery of the structural integrity of bleached enamel. Also, Nanohydroxyapatite successfully restore the damaged bleached enamel surface but to less extend compared to bioactive glass.