DIGESTIVE ORGANS 
407 
neglect. When the teeth are not cleaned, a substance called 
tartar forms on them, which prevents the bacteria from being 
rubbed off and sometimes pushes 
the gums away from the teeth. 
The bacteria cause food particles 
to ferment and form acids which 
dissolve the hard outside covering 
(enamel) and then rapidly the 
softer parts of the teeth. This 
results in toothache, a foul breath, 
and the imperfect chewing of 
the food. The teeth should be 
brushed after each meal to re¬ 
move particles of food, particularly 
sugar which ferments easily. At 
least once a year there should be 
a visit to the dentist who will re¬ 
move those portions of teeth that 
are decayed and fill cavities, thus F ' IGURE Vertical Section 
preventing further decay. 
The teeth of children often come in on the outer or inner 
side of the jaw instead of 
on the middle. This re¬ 
sults in an irregular row of 
teeth. Such teeth do not 
meet the opposite teeth as 
they should (Figure 369). 
Dentists know how to 
straighten such teeth and 
produce better results, if 
they can begin their cor¬ 
rective treatment before 
the teeth are fully grown. This is very important not only 
for one's looks but especially for one’s health as without such 
treatment proper mastication is often impossible. 
Figure 368. — Milk Teeth. 
Age 3| to 4 years. Notice the perma¬ 
nent teeth deeper in the jaws. 
