128 JOURNAL OF COSMETIC SCIENCE 658 655---------' 685 684 683 FI s Binding Energy( e V) Figure 7. XPS two-dimensional chemical-state plot of fluorine for HAP created in NaF (0) and H2O2/NaF (e) solutions. The numbers (1,000-10,000) are concentrations of fluoride in solutions (in ppm). saliva in the oral cavity at the same time. In the tooth-bleaching process by H 2 O 2 /NaF, DCPD in the precarious lesion is assumed to play an important role thus, attention was paid to the behavior of DCPD. Typical X-ray diffraction patterns of DCPD treated in H 2 O 2 and H2O2/NaF are shown in Figure 8. No crystal structure change occurred to DCPD treated with H 2 O2 alone. In contrast, DCPD was transformed totally to a low-crystallized apatite structure in H 2 O)NaF, suggesting that fluoride ions were incorporated to form FHAP, and interestingly, that the growth of FHAP was enhanced by the fluoride even in an H 2 O 2 -coexisting system. (a) 20 30 40 50 28(deg. Cuka) Figure 8. Typical XRD patterns of untreated DCPD (a), treated DCPD in H2O 2 solution (b), and in H2O2/NaF solution (c).

H 2 O 2 /NaF TOOTH-BLEACHING SYSTEM 129 The dissolved Ca2+ and Po/- ions in H2O2 solutions and in H2O2/NaF solutions were analyzed, and the results are shown in Table II. The dissolved Ca2 + and Po/- ions increased in H2O2 solutions and were also enhanced by increasing the concentration. The molar ratios of released Ca2+ and Po/- ions from the DCPD were approximately 1.0, and in good accordance with the stoichiometric ratio for DCPD itself. This result indicates that no transformation from DCPD to any other phase occurred. In the H2O2/ NaF solutions, however, an increase in the dissolved Po/- ions was more pronounced. Judging from the ratio of dissolved Ca2 + and Po/- ions (Ca/P), a Ca-rich layer like FHAP definitely formed, and this was in accordance with the XRD results in Figure 8, which show the formation of an apatite structure. To sum up these results: in H2O2 solutions, DCPD, unlike HAP, dissolved congruently when fluoride was present, FHAP was formed. These mechanisms are shown in equations 5 and 6, respectively: CaHPO4 • 2H2O + H + ➔ Ca2 + + H2PO4 - + 2H2O (5) 10{CaHPO4 • 2H2O} + (4 - n)OH- + nF- ➔ Ca 10 (PO4MOH)2_ n Fn DISCUSSION + 4H 2 PO 4 - + 22H 2 O (6) The use of fluoride has been recommended to lessen the discomfort caused by the H 2 O 2 bleaching of teeth (27). We also have been investigating the bleaching effects of an H 2 O2 /NaF system on the stained teeth. The extrinsic dental stains are often associated with calculus, plaque ( 44), and adsorbed salivary film materials known as the acquired enamel pellicle (45). The stains on tooth surfaces are composed of various materials such as the inherent colors produced by incorporated tea and coffee and aged proteins ( 44-4 7). These kinds of colored materials can be removed comparatively easily by mechanical means. In the present work, the colored materials were actually separated from the stained tooth by scrubbing. The materials were hydrolyzed by heating at l l 0°C for two hours under decompression in a glass cell containing 2% hydrochloric acid, and the amino acid composition was analyzed with the Amino-Acid Analyzer System (Shimadzu Co., Japan). The results in Figure 9 show a different composition from that of saliva. Most of the stained materials were removed by scrubbing nevertheless, the colored stain still remained in the subsurface of the tooth. After bleaching with H 2 0)NaF (H202 = 15% F = 1000 ppm), however, the stain was removed and the tooth surface became clean. An example of XPS analysis of the teeth before and after bleaching is shown in Figure 10. Nitrogen (N), which originated probably from proteins, disappeared after Table II Dissolution of Calcium and Phosphate Ions from DCP Treated in H2O2 and H2O2/NaF Solutions, and the Subsequent Crystal Structure Changes No. H2O2 (%) F (ppm) Ca (x 10- 5 mol) P (x 10- 5 mol) Ca/P ratio XRD pattern of product 1 0 0 1.8 1.9 0.95 DCPD 2 15 0 3.4 3.4 1.00 DCPD 3 30 0 5.5 6.1 0.90 DCPD 4 0 1000 0.5 90.0 0.006 HAP 5 15 1000 3.2 97.0 0.033 HAP 6 30 1000 7.5 130.0 0.058 HAP