Mothers and nurses ought to know what to look for in their babies' mouths, as the months follow each other in their first two years. Only twenty teeth, be it remembered, come in the first set, or, "milk teeth." Thirty-two follow these, and take their place, in the second set.
About the end of the sixth month (from the fifth to the eighth), it is common for the two lower middle front to appear through the gum; and not long after, even sometimes before these, the two upper middle front ones. These are called cutting or incisor teeth. So are the next to come out - alonside of the first - the lateral incisors (side cutting teeth), below and above; which appear between the eighth and the tenth months. Before the infant is a year old, then, it usually has at least eight front teeth out; four below and four above.
Next, we might expect those nearest these to appear; but they do not. Instead come the first jaw or molar teeth - two below and two above - between the twelfth and the fourteenth months.
Then follow, between the fourteenth and twentieth months, the stomach and eye teeth, as people call them; the four canine teeth, two below and two above; pointed teeth.
After these, and last of the first set, come the second jaw or molar teeth; two below and two above; between the eighteenth and the thirty-sixth months. In each jaw, in all, there are then four incisors, two canines, and four molar teeth; doubling these, we get the twenty of the whole set. The following diagram shows this, with the order of their succession:
I stands for incisor; C for canine; M for molar.
This order is the general mode of succession ; but variations from it are far from rare. Often the upper teeth, front and all, come before the lower ones. The time for each group of teeth is frequently later, and sometimes earlier, than that above mentioned.
As the time comes near (about the sixth or seventh year) for the second dentition the new set, whose germs were in the jaws at birth, grow steadily larger in the gums. The milk teeth are not forced out; but, under the wonderful natural adaptation of parts, their fangs are gradually absorbed, and thus they loosen and drop out, or are easily taken out, and make way for the second set of permanent teeth. These are thirty-two in number. The first to come through the gums are the first molar or jaw teeth. Next, at about seven years of age, the middle incisors ; then the lateral incisors, at or near the end of the eighth year. After these, the first pre-molars (bicuspids) or lesser jaw teeth; and in the ninth year, the second pre-molars. Between eleven and twelve years, the permanent canines, two above and two below. From twelve to thirteen or fourteen years, the second molars ; and from seventeen to twenty-one years, the last molars, or wisdom teeth. These last are often imperfect from the start.
Dentition is a process of growth. A great deal of blood is needed in the tissues of the jaws for this purpose. Moreover, for the teeth to "come out," the gums must give way, by absorption. Should this be slow, a tension of the gum may occur; and, through the nerves, the whole system may be brought into sympathetic excitement. As the nervous apparatus is much more irritable, more easily disturbed, in babyhood than in adult life - we often have, from this cause, worrying; fretfulness; sometimes fits, or convulsions. A child which was "always good" before, now may cry a great deal, losing its reputation for goodness altogether.