Electro-mechanical Factors Regulating Bone Architecture 



87 



tendon (Johnson, 1964), and suggests that osteogenic "induction" has a major physi- 

 cal facet. In fact, it has long been recognized that tension above usual limits may lead 

 to ossification of tendon (Murray, 1936). 



MUSCLE TONE -1 



Fig. 5. Diagram ,.1 irl.u lonslup ,.t pci-i..a,.ni,il 

 tooth. Center sketch depicts biting, fibers are taut. At right, tooth is being moved by force which tightens 

 periodontal fibers at trailing surface of root where osteoblastic activity occurs and slac-kens libers at leading 

 surface, where osteoclasts are removing bone 



If osteoclasts occur in regions where the electrical signal is diminished or absent, 

 it should be possible to find a common electrical link between factors known to cause 

 osteolysis. For example, although it has been stated that bone removal depends on 

 vascular changes (Geiser and Trueta, 

 1958), it is not entirely clear yet whether 

 they are attendant upon or responsible 

 for the removal. If, as Johnson (1964) 

 believes, active hyperemia causes bone 

 destruction, it might do so by providing 

 more electron "sinks" through hyperoxia 

 or streaming potentials. Arterial walls 

 are positively charged on the adventitial 

 surface and negatively charged on the 

 endothelial (Sawyer and Pate, 1953). It 

 is conceivable, therefore, that the erosion 

 of bone by an aneurysm may be electri- 

 cally mediated, since the vessel wall 

 could conduct away more electrons than 

 were generated by deformation. 



Finally, since it appears likely that 

 bone mass and orientation may be con- 

 trolled by stress-generated electrical po- 



d, . . c 1-1 fig. ''. four ni.iin sources ,it iiu-cnaiiKii input ti> normal 



s, the origin of mechanical stresses skeleton 



in the skeleton deserve brief attention. 



Actually, bone may function in a manner similar to an exquisitely sensitive, piezo- 

 electric accelerometer, responding to the slightest jar or deformation. There are four 

 main sources of mechanical input for the skeleton (Fig. 6). The cardiovascular system 

 provides a continual deforming force (Gebhardt, 1905) through hydrostatics in the 



