300 MICROSCOPIC ANATOMY OF THE TEETH 



the deciduous teeth are removed to make room for their 

 permanent successors. In the permanent teeth the process 

 is chiefly a pathological one, although the moulding of the 

 forming roots appears to be by an alternation of absorption 

 and deposition as in the formation of bone. 



In the temporary teeth, absorption commences in the 

 cement, but not necessarily at the nearest point to the 

 erupting permanent tooth, and is not due to pressure from 

 beneath. The cement and dentine show semilunar indenta- 



FIG. 195. Absorption of temporary tooth. Weil process. (x!50. ) 



tions, the lacunae or foveolse of Howship, and if the tooth 

 is not previously shed, absorption will proceed to the 

 excavation of the enamel (figs. 195 and 196). 



These excavations are occupied by large multinucleated 

 cells, the osteoclasts, which are the active agents in absorp- 

 tion both in bone and teeth. By what means they produce 

 this result is not determined. It is considered probable 

 that they secrete an acid which has a solvent effect upon 

 the lime salts, but this has never been definitely proved. It 

 has also been suggested that they cause absorption by the 

 protrusion of amoebiform processes into the hard tissues, 

 but the view more generally held is that they secrete some 



