Effects of Experimental Nanohydroxyapatite Gel on Enamel Surface After Bleaching

The purpose of this study was to investigate the effect of chitosan-added experimental nanohydroxyapatite (n-HA) gel on the physical and morphological changes of the enamel surface after the use of two different vital bleaching agents. Fifty-two intact, caries-free human maxillary incisors were embedded in acrylic resin. Chitosan-added n-HA powder was synthesized using a high-temperature oxidation method and then mixed with phosphate-buffered saline solution (PBS) to form a gel. The teeth were divided into four groups: Group B: Biowhiten in-office 40% n-HP (BioWhiten, Biodent Ltd, Istanbul, Turkey); Group O: Opalescence Boost 40% HP (Ultradent Products Inc., South Jordan, UT, USA); Group BN: Biowhiten in-office 40% n-HP+n-HA gel; Group ON: Opalescence Boost 40% HP+n-HA gel. Color change, surface microhardness, and surface roughness (Ra) measurements were taken before, immediately after, and one week after bleaching. Three specimens from each group were also subjected to scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDS) analysis. The data were statistically analyzed using an analysis of variance (ANOVA) and Bonferroni post hoc test (p<0.05). After bleaching, all groups showed a noticeable change in color (p<0.05), but with no differences among the treatment groups (p>0.05). After bleaching, the highest Ra values were determined in Group O (p<0.05). Group ON showed a statistically lower Ra value than Group O (p<0.05). The lowest microhardness value after bleaching was observed in Group O (p<0.05), which also had the lowest calcium/phosphorus (Ca/P) value. After the experimental chitosan-added n-HA gel application, the Ca/P ratio increased. The use of experimental chitosan-added n-HA gel after bleaching improved the physical and morphological properties of the enamel surface without reducing the effectiveness of bleaching.