THE TEETH 229 



when teeth show weakness and seem not to be well 

 nourished, rubbing the gums a few times a day will 

 often improve the circulation and result in general 

 benefit. 



But surely it is not necessary to bother about keep- 

 ing the milk teeth clean, when, at the most, they serve 

 such a short period ! This is a mistaken idea which 

 many people have. The milk teeth should be kept 

 clean from the beginning. They should also be fre- 

 quently examined by a dentist, and any cavities 

 promptly filled. What a waste of time and money 

 such care seems to be ! Not so, when we consider the 

 damage that may follow if they are allowed to decay 

 or are removed too early. The upper central incisors 

 usually come into a baby's mouth about the fifth or 

 sixth month. The other milk teeth keep coming 

 gradually, the second molars, which appear from the 

 twenty-first to the thirty-sixth month, being the last. 

 The first of the permanent set, the sixth-year molars, 

 appear, as a rule, about the sixth year. They usually 

 come before any of the milk teeth are lost, and, for 

 this reason, are often thought to be temporary. How- 

 ever, if the number counted in either jaw is more than 

 ten, one may be sure the new arrival is a permanent 

 tooth. 



The incisors, bicuspids, canines, and second molars 

 of the permanent set come in from the seventh to the 

 thirteenth years. As all the permanent teeth come 

 in ; the roots of the first teeth are gradually absorbed 



