Until 12 ~ 13 years old, all deciduous teeth fell off and permanent teeth were replaced. After that, the single permanent tooth: 12 ~ 14 years old, the second molar grows behind the first molar, and the third molar grows after 18 years old. It is normal for some people not to have a third molar.
Extended data
Problems during tooth replacement
1, retention of deciduous teeth
The phenomenon that deciduous teeth should fall out but not fall out is called deciduous teeth retention.
(1) Main reasons
① Dislocation of permanent tooth embryo;
② Local inflammation;
③ Absence of permanent tooth germ.
(2) The residual teeth that have been treated with permanent teeth but the deciduous teeth have not fallen off should be pulled out as soon as possible, so as not to affect the eruption of permanent teeth in the normal position. Don't pull out the primary teeth after the age of tooth replacement and the permanent teeth before they erupt. If permanent teeth are congenital missing, try to keep deciduous teeth.
2. Early deciduous teeth fall off
The deciduous teeth should not fall off, which is called premature deciduous teeth fall off. It often causes the adjacent teeth on both sides to tilt towards the gap of missing teeth, which makes the gap of missing teeth smaller, and the permanent teeth sprout out of position due to insufficient gap. Wear a gap fixer at the gap between deciduous teeth to prevent the teeth on both sides from tilting until the permanent teeth erupt.
3. Permanent teeth are difficult to erupt.
Permanent teeth do not erupt after the replacement period, which is called delayed eruption of permanent teeth.
Main reasons:
① Early deciduous teeth fall off;
② More teeth;
③ Tooth tumor or cyst obstruction;
④ Abnormal development of permanent teeth;
⑤ Genetic factors;
⑥ Calcium deficiency.
4, tooth dislocation occlusion
Temporary malocclusion sometimes occurs in the process of tooth replacement, and it often adjusts itself to return to normal in the process of tooth development. However, some malocclusion deformities can not be adjusted by themselves, which will affect facial development and should be treated in a hospital.
5, double-layer teeth
Before the deciduous teeth fall off, the permanent teeth come out, resulting in two rows of teeth. This situation is not uncommon, and it is likely that the root of deciduous teeth is not completely absorbed. Children should be taken to the hospital as soon as possible to remove the stranded deciduous teeth and make room for the eruption of permanent teeth.
Baidu encyclopedia-six-year-old tooth