Origiinlly published in Kgl. Danske V idenskahernes Selskab. Biologiske Meddelelsei- 



13, 13 (1937) 



20. INVESTIGATIONS ON THE EXCHANGE OF 



PHOSPHORUS IN TEETH USING RADIOACTIVE 



PHOSPHORUS AS INDICATOR 



G. Hevesy, J. J. IIoLST and A. Krouh 



From the Institute of Theoretical Physics, Dc ntistiy School and Zoophysiological 



Laboratory, Copenhagen 



ANATOMICAL INTRODUCTION 



The hard part of a tooth is composed of three distinct substances viz. 

 1he dental substance proper, dentine, the enamel, and the cement. 

 The dentine constitutes by far the largest portion; the enamel is found 

 in a comparatively thin layer partly covering the dentine; and the ce- 

 ment covers the surface of the root in a thin layer. In the case of the 

 canines of cats we found the weight of the enamel ash to be 11.2% of that 

 of the dentine ash, the weight of the enamel before ashing being equi- 

 valent to about 9.7% of that of the dentine. 



The dentine is penetrated throughout by fine tubes (dentinal tubes) 

 starting from that side of the dentine which faces the pulpa cavity; 

 they have an initial diameter of 2 to 8// and do not much diminish 

 in size at first as they approach the surface; the distance between adja- 

 cent tubules is about two or three times their width. From the tubules 

 numerous immeasurably fine branches are given off and penetrate 

 1 he hard intertubular substance. Near the periphery of the dentine, 

 the tubules, which by division and subdivision have become very fine, 

 terminate imperceptibly in free ends. It is reported that tubules have 

 been observed passing into the enamel in the teeth of marsupial animals, 

 and to a less marked degree in human teeth. In this case they pass, not 

 into the enamel prisms, but into the inter-prismatic substance. The ena- 

 mel is made up of microscopic columns, very hard and dense, arranged 

 close side by side, and fixed at one extremity on to the subjacent sur- 

 face of the dentine. The enamel columns have the form of six-sided 

 prisms. Their diameter is about 0.005 mm. They are united by a small 

 amount of substance which appears to be similar to the intercellular 

 substance of an epithelium. The small amount (about 1%)^ of 



' 1. H. Bowos and :\I. M. Muray, (1935) Biochem. J. 29, 12, 2721. 



