136 H. Newesely 



steered either to HA or to TCPH by influencing the end-pH. It would even be 

 possible to obtain OCP by this method if an end-pH of at least 9 could be obtained. 

 Such required end-pHs can be obtained by excesses of Ca-^ or PO4 . It is quite 

 logical to use excesses of Ca"^^ and PO4 to obtain the final-pHs required and no 

 other buffers which could bring impurities into the reactives. 



The different pH-curves found during the formation of HA and TCPH and the 

 fact to obtain intermediary amorphous products in the case of HA, and the for- 

 mation of crystalline products from the very beginning in the case of TCPH, brings 

 us to the conclusion that the TCPH is a real and distinct phase. 



Summary 



The continuous measurement of pH during the hydroxyapatite synthesis of 

 Hayek (1960) distinguishes two different kinds of reaction mechanism depending on 

 Ca*^- or PO4 -excesses. By thermic and diffraction methods it was possible to 

 establish the nature of the final products and also one intermediate amorphous product, 

 which appears at the beginning of HA-synthesis (Ca^*-excess or stoicheiometric 

 mixture). With PO4 -excess, the TCPH appears from the beginning of the reaction. 



We wish to thank the Fonds National Suisse, for support of this research. 



References 



Hayek, E., H. Newesely, W. Hassenteufel, und B. Krismer: Zur Bildungsweise und Mor- 

 phologic der schwerloslichen Calciumphosphate. Mh. Chem. 91, 249 (1960). 



Lerch, p., und C. Vuilleumier: Die Herstellung und Identifizierung von Hydroxylapatiten 

 mit ahnlidien Dimensionen wie diejenigen des Knochens. Chimia 18, 20 (1964 a). 



— — Etude thermique de preparations microcristallines d'hydroxylapatites et d'autres phos- 

 phates de I'os prepares in vitro. Chimia 18, 392 (1964 b). 



Vuilleumier, C: Die Herstellung, Identifizierung und das thermische Verhalten von Hydr- 

 oxylapatiten. Diss. Univ. Bern 1965. 



Watson, M. L., and R. A. Robinson: Collagen-crystal relationships in bone. II. Amer. J. 

 Anat. 93, 1583 (1953). 



Umwandlungsvorgange bei Calciumphosphaten 



H. Newesely 



Kristallchemische Abteilung, Institut fiir Kariesforschung und Forschungsgruppe fiir 

 Mikromorphologie im Fritz-Haber-Institut, Berlin-Dahlem, Deutschland 



Bei mikromorphologischen Untersuchungen an der Remineralisationsschicht der 

 Zahnoberflache bzw. in Zahnbelagen wurden Calciumphosphatkristallite mit ver- 

 schiedenen Ausbildungsformen festgestellt (Johannsson, 1965; Muhlemann et al., 

 1964; Lenz und Newesely, 1964; Lenz et al., 1964; Schroeder, 1964; Hohling 

 et al., 1962). Die Zuordnung zu bestimmten Strukturtypen war jedoch nicht immer 

 mit Sicherheit moglich. 



Mit LinterstLitzung der Dcutschen Forschungsgemeinschaft, Bad Godesbcrg. 



Die Untersuchungen werdcn in „Monatshcfte fiir Chcniie" (Wicn: Springer) ausfulirhch verofFcntlicht. 



