COHEX] DEXTAL HVGIEXE 113 



The Social Direction of Human Evolution. William E. Kelli- 

 cott, D. Appleton & Co., publishers, Xew York. 



Eugenics Review, Eugenics Education Society, 6 York 

 Buildings, Adelphi, London. 



Bulletins Xos. i, 2, 3, 4, and 5, Eugenics Record Office. Cold 

 Spring Harbor, Long Island. X. Y. 



Dental Hygiene 



Hyman Cohen, M. D. 



Assistant Chief, Bureau of Medical Inspection, Department of 

 Health, Chicago. 



The teeth, though stationed at the front door of life and 

 readily visible, have been entirely overlooked until recently. At 

 most, they were given some aesthetic recognition by "fastidious" 

 people. The recognition of the fact that they form a vital organ 

 in the human mechanism, upon which depends the proper growth 

 and development of the body, is only of recent date and limited 

 to small circles. That the teeth are the mill stones of life, which, 

 if properly grown and well kept, promote perfect mastication, di- 

 gestion and assimilation, making the greatest contribution to the 

 buoyancy and happiness of life, is not generally understood. 



Each individual is provided with two sets of teeth during his 

 lifetime for his use. The temporary or milk teeth, beginning to 

 appear about the seventh month of life; having fulfilled their 

 duty, they gradually disappear, their roots being absorbed and 

 the crowns falling out, to the great delight of the young person. 

 About the twelfth year all of the temporary teeth have disap- 

 peared. During their sojourn in the mouth they also aid in the 

 symmetrical development of the jaw bones and remain on duty 

 until the permanent teeth appear. The first permanent teeth ap- 

 pear about the sixth year and the set is usually complete about 

 the thirteenth year, excepting the last molars. The milk teeth 

 are there to prepare and hold their places for the permanent teeth 

 until the growth of the jaw bones can accommodate the full set. 

 It is the only instance in the human body where an organ, treat- 

 ing all the teeth as one organ, is entirely discarded to be replaced 

 by a larger, stronger and more durable similar organ. This les- 

 son must be borne in mind. Milk teeth should not be hastened 

 out of the mouth by neglect and decay, or by unnecessary ex- 

 traction. On the other hand, it may frequently become neces- 



