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Measurement of Strontium Distribution in Carious Enamel
and Dentin around a Fluoride-containing Material
H. Komatsu a) , Y. Matsuda a) , T. Kijimura a) , K. Okuyama a) , H. Yamamoto b) , Y. Iwami b) ,
S. Ebisu b) , M. Nomachi c) , K. Yasuda d) , T. Satoh e) and M. Kohka e)
a) Graduate School of Dental Medicine, Hokkaido University, b) Graduate School of Dentistry,
Osaka University, c) Graduate School of Science, Osaka University, d) The Wakasa wan Energy
Research Center, e) Department of Advanced Radiation Technology, TARRI, JAEA
Introduction
To estimate caries preventive effect of
fluoride-containing materials (FCMs), we continue to
investigate the fluorine (F) uptake in artificial caries lesion
around FCM during pH-cycling as F uptake resulted from
the precipitation of fluorapatite Ca 10(PO 4) 6F 2 (i.e.,
remineralization). Some FCMs contain strontium (Sr) in
the powder component instead of calcium or as an
additional ion to enhance radiopacity. The remineralization
may be facilitated by the presence of strontium, as it has both
chemical and physical properties close to calcium and is able
to replace Ca in apatite. The purpose of this study was to
measure the strontium distribution in carious enamel and
dentin around a strontium-containing FCM using an in-air
micro-PIXE system at TIARA.
Material and Methods
Cavities in enamel and dentin surfaces of extracted
human teeth were drilled and filled with strontium-
containing FCM (SI-R20607). Two 170 µm longitudinal
sections including the filling material were obtained from
each tooth. All tooth surfaces, except the outer surface of
enamel or dentin, were coated with a wax. The pH-cycling
(pH 7.0-pH 4.5) was carried out for 5 weeks for preparing
artificial carious tooth using an automatic pH cycling
system. Two pairs of demineralizing and remineralizing
solutions of pH-cycling were prepared for simulating caries
risk (Table 1). After pH-cycling, Sr distribution of the
outer lesion in each specimen was evaluated using
micro-PIXE system at TIARA. The strontium distributions
in carious enamel or dentin were analyzed at more than
100 µm separation from the cavity wall. The outermost
surface of the carious lesion was at the spot containing 5%
of the calcium concentration in intact tooth. For the
comparison of strontium distribution, the average strontium
concentration in each specimen was calculated at area of
about 20 µm from the defined surface.
Results
Figure 1 demonstrates the Sr distribution of the
specimens after 5-week pH-cycling. There was a
difference in Sr uptake from material between Sol-A and
Sol-B of pH-cycling. Both enamel and dentin for Sol-A,
Sr uptakes from material into the outer lesion were
confirmed, while no uptake into the lesions of both enamel
and dentin for Sol-B was detected. In the observations of
Sr uptake into the intact tooth adjacent to the material, the
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amount of Sr in both enamel and dentin had high value
compared with those in area of deeper than 100 m in Fig. 1.
In addition, the amount of Sr in enamel was higher than that
in dentin.
Discussion
In this study, although the number of measured
specimens was limited in each group, it can be speculated
that there was a difference in Sr uptake between Sol-A and
Sol-B of pH-cycling. Transverse microradiography
analysis in the previous study indicated that the caries
progression for the pH-cycling with Sol-A was more severe
than that with Sol-A. When calcium dissolution rate of
apatite crystals was high in remineralizing process with
Sol-A, the rate of Sr replacement to Ca with Sol-A was
higher than that with Sol-B. Therefore, it appears that Sr
uptake increased with Sol-A. To estimate caries preventive
effect of FCMs, Sr measurement will be useful.
Measurements for reference materials that made with a
mixture of hydroxyapatite and strontium carbonate were
also performed with selecting areas of uniform mixture.
Results of these measurements were used for obtaining
comfortable values of strontium concentration in the tooth.
Solutions
(Risk)
Sol-A
(High)
Sol-B
(Low)
Sr concentration (ppm)
Table 1 The solutions of the pH-cycling.
2500
2000
1500
1000
500
0
Demineralizing
(pH 4.5)
0.2 M Lactic acid,
3.0 mM CaCl2, 1.8 mM KH2PO4. 0.05 M Acetic acid,
1.5 mM CaCl2, 0.9 mM KH2PO4 Remineralaizing
(pH7.0)
0.02 M HEPES,
3.0 mM CaCl2, 1.8 mM KH2PO4 0.02 M HEPES,
1.5 mM CaCl2, 0.9 M KH2PO4, 0.13 M KCl
0 50 100 150 200 250 300 350
Depth from surface (mm)
Enamel-Sol-A
Dentin-Sol-A
Enamel-Sol-B
Dentin-Sol-B
Fig. 1 Mean Sr distribution of the specimens after
5-week pH-cycling.