漂白後エナメル質に対するメタリン酸ナトウムの着色抑制効果と吸着性の評価

メタリン酸ナトリウム

Purpose: Sodium metaphosphate has beenadded todentifricesandchewing-gumsforinhibiting the stainingof teeth.As sodium metaphosphate may easilybind to hydroxyapatite,it may block or inhibit stain adsorption tohydroxyapatite. In-office bleaching has beenwidelyused. In the treatment, it is recommended to avoiddark-color foods and drinks for 24 hours after bleaching to prevent discolorationof tooth-surface. If sodium metaphosphate was applied tothe enamel after bleaching, it might be expected to inhibit staining caused by dark-color foods and drinks. In addition, if sodium metaphosphate formsa stable membrane by chemicalreactionwith enamel hydroxyapatite, the effect of the staining inhibition might be expected to continue for a long time. Therefore, the present study evaluatedtheinhibition effect after bleaching and investigatedthe adsorptionof sodium metaphosphate on enamel after in-office bleaching using spectrophotometer, and XRD and FTIR analysis.Methods: Twenty-four extracted human upper incisors were treated with Hi-Lite, and thentooth-surface color was determined by a spectrophotometer. The teeth were then divided into four groups:1) Untreated: Control group (Con), 2) Polished with Merssage(Mer), 3) Applied with Butler Fluodent Foam A(Flu). 4) Immersed in human saliva containing 1 % sodium metaphosphate for 35 min (SMP). Con, Mer, Flu were then immersed in human saliva at 37 ０C for 120 min, and SMP was immersed for 85 min. After that, all groups were stored in 1.4 % coffee at 37 ０C.Color measurement was performed at 24, 48 and 72 h．The color changebetween before and after immersion in coffee was expressed by ΔE*, ΔL*, Δa* and Δb*.Additionally, SEM observation of the enamel surface and XRD and FTIR analyses of hydroxyapatite after immersion in 1 % sodium metaphosphate were performed. Results: Regarding ΔL*at 24 h, ΔL* of SMP was smaller than those of the other groups, which confirmed the staining inhibition effect of SMP. According to SEM, sodium metaphosphate was observed as a thin film on enamel, however, there was no evidence of chemical reactionbetween hydroxyapatiteand sodium metaphosphate by XRD and FTIRanalyses. Conclusion: Sodium metaphosphateprovided a staining inhibition effect for bleached teeth during storage in coffee for 24 h. However, no evidence of chemical reaction between sodium metaphosphate and bleached enamel was found under the conditions of the present study.