ROLE OF CHELATION IN DECALCIFICATION SYSTEMS 639 



ity that chelation plays an important part in biological processes. 

 Mandl et al. (1952, 1953) and Mandl and Neuberg (1956) have 

 listed the groups of such substances, which include the salts of 

 nucleotides (e.g. adenosine triphosphate), polyphosphates (such as 

 pyrophosphates), phosphorvlated sugars, amino acids, and the hy- 

 droxy, keto, dicarboxylic, and tricarboxylic acids. 



Among the biochemical processes which it has been suggested 

 mav occur bv chelation are the absorption of insoluble salts from 

 the soil bv the root hairs of plants, the transport and deposition of 

 metallic ions (e.g. calcium), and the control of enzvme action by 

 chelation of inhiliitors or activators. In the present paper we are 

 concerned with the possible role of chelation in dissolving the hard 

 tissues in tissue fluids already saturated with calcium phosphate. 



The Phenomena to Be Explained 



Calcified tissues are removed during the physiological processes 

 of bone growth and remodeling, and of resorption of the roots of 

 deciduous teeth, and in meeting a calcium stress such as pregnancy 

 and lactation, especially on a low calcium diet. Pathological proc- 

 es.ses involving decalcification are dental caries, hyperparathyroid- 

 ism, and infection of bones, including periapical abscesses. There 

 are no reasons for believing that all these diverse phenomena can be 

 accounted for bv one single process. 



Although several of the above processes are accompanied by the 

 presence of osteoclasts — and it can no longer be doubted that osteo- 

 clasts do take an active part in resorption — it is far from certain 

 that these are the onlv cells concerned. Apart from the osteolysis 

 described bv Belanger et al. in this symposium (chapter 20), several 

 workers (Woods and Armstrong, 1956; Talmage and Elliott, 1958) 

 have reported that in experimental hyperparathyroidism resorption 

 occurs from bone deposited several months previously which is in- 

 accessible to osteoclasts. Heller-Steinberg ( 1951 ) reported histolog- 

 ical changes, presumably related to bone dissolution, in the matrix 

 surrounding the lacunae containing osteocytes. A photomicrograph 

 by Raisz et al. ( 1961 ) also showed that parathyroid hormone treat- 

 ment produced resorption in the neighborhood of osteocytes and 



