The person's lifetime grows two pairs of teeth, namely deciduous teeth and constant tooth. The tooth with infantile period strange place calls deciduous teeth, the time of teething is early in the 4 ～ after be born 5 months are produced namely, late to 9 ～ 10 months just come out. 6 ～ go out when 1 year old commonly 8 teeth, 18 ～ go out when 2 years old 20 teeth, the gross of teething is lunar age to decrease 4 ～ about 6. Deciduous teeth in all 20.