Eruption of the Teeth

When the calcification of the different tissues of the tooth is sufficiently advanced to enable it to bear the pressure to which it will be afterward subjected, eruption takes place, the tooth making its way through the gum. The gum is absorbed by the pressure of the crown of the tooth against it, which is itself pressed up by the increasing size of the root. At the same time the septa between the dental sacs ossify, and constitute the alveoli; these firmly embrace the necks of the teeth, and afford them a solid basis of support.	64
The eruption of the deciduous teeth commences about the seventh month after birth, and is completed about the end of the second year, the teeth of the lower jaw preceding those of the upper.	65
The following, according to C. S. Tomes, are the most usual times of eruption:	66
Lower central incisors 6 to 9 months. Upper incisors 8 to 10 months. Lower lateral incisors and first molars 15 to 21 months. Canines 16 to 20 months. Second molars 20 to 24 months.
There are, however, considerable variations in these times; thus, according to Holt:	67
At the age of 1 year a child should have 6 teeth.	68
At the age of 1 1/2 years a child should have 12 teeth.	69
At the age of 2 year a child should have 16 teeth.	70
At the age of 2 1/2 years a child should have 20 teeth.	71
Calcification of the permanent teeth proceeds in the following order in the lower jaw (in the upper jaw it takes place a little later): the first molar, soon after birth; the central and lateral incisors, and the canine, about six months after birth; the premolars, at the second year, or a little later; the second molar, about the end of the second year; the third molar, about the twelfth year.	72
The eruption of the permanent teeth takes place at the following periods, the teeth of the lower jaw preceding those of the upper by short intervals:	73
First molars 6th year. Two central incisors 7th year. Two lateral incisors 8th year. First premolars 9th year. Second premolars 10th year. Canines 11th to 12th year. Second molars 12th to 13th year. Third molars 17th to 25th year.
Toward the sixth year, before the shedding of the deciduous teeth begins, there are twenty-four teeth in each jaw, viz., the ten deciduous teeth and the crowns of all the permanent teeth except the third molars.	74