Abstract
Hydroxyapatite (HA) is chemically active in solution and adsorbs protein, lipid, sugar and metal ions. In 1978
the tooth paste containing HA was invented by Hideki Aoki of Japan. Afterwards, the clinical test was carried
out for five years at the Tokyo Medical and Dental University and School of Dentistry, Asahi University. The
clinical results showed that the HA is very effective to prevent generation of caries. Then, it was found that
the HA toothpastes have been commercially sold well in Japan. However, there has been little information
about details of HA toothpastes to dentists and consumer public.
In this paper, seven commercial HA toothpastes were crystallochemically investigated using an X-ray
diffractometry (XRD). The abrasive materials were obtained by filtering the suspension of 500ml water and
3g of each tooth paste. The abrasives were analyzed by XRD to determine the crystal phases and crystallite
size. The XRD patterns of non-heated abrasives revealed that the abrasives in the HA toothpaste included
HA[Ca10(PO4)6(OH)2], monetite (CaHPO4; DCPA), brushite (CaHPO4・2H2O; DCPD), and calcite (CaCO3). The
crystallite size of HA in the toothpaste varied from 30 to 70 nm. The HA content also ranged from 7.1 to
32.8 wt%, and the HA content was lower than detection limits of XRD in some HA toothpaste. These results
indicated that the commercial HA toothpastes have various crystallinities and concentration of HA.
