We would never think of a newborn having teeth. However by birth itself the crowns of the 20 milk teeth are almost completely formed but are not visible as they are embedded in the infant’s jawbones. The primary teeth gradually erupt through the gums by the age of 2.5 years.
Sequence of eruption
The four front teeth, the upper and lower central incisors are the first to erupt and they generally erupt by 6 to 8 months of age. The eruption pattern is as follows.
Generally most children have a complete set of primary teeth by the time they are 3 years of age. Their jaws continue to grow to accommodate the permanent teeth which start erupting by 6 years of age. The primary teeth begin to shed anywhere between 6 to 7 years of age and continues until about 12 years of age.
What is mixed dentition?
Mixed dentition stage is the period in which there is eruption of some of the permanent teeth but before all the deciduous teeth are shed. It usually occurs between 6 and 13 years of age. It is also called as transitional dentition. Mixed dentition can be classified as early mixed dentition stage which is 6 to 9 years of age and the late mixed dentition stage which is 10 to 12 years of age. It is in this mixed dentition stage that dental abnormalities become very visible. Dental conditions such as missing permanent teeth or malformed teeth become obvious. In this stage skeletal and dental malformations will come into view. An orthodontist can be consulted in this stage to make the necessary corrections and treatment.
What happens in the mixed dentition stage?
This period starts when the permanent first molar erupts and lasts till the last primary tooth is shed. There are 32 permanent teeth but the maxillary teeth eruption sequence varies from the mandibular eruption sequence. Since there are no premolars in the primary dentition, the primary molars are replaced by the permanent premolars. If any primary teeth is shed or lost before the permanent tooth is ready to take its place then the posterior tooth drift forward and hence there may be loss of space in the mouth. This causes crowding and malalignment once the permanent teeth eventually erupt. This is referred to as malocclusion and is a very common finding in the mixed dentition stage. Orthodontics play a major role in this stage for functional and esthetic corrections of the malocclusion.
How does the permanent tooth replace the primary teeth?
The first sign of tooth formation is the development of dental lamina from the oral epithelium.
20 areas of enlargement appear on the lamina which form the tooth buds for the 20 primary teeth.
After the primary teeth develop from the buds the lamina continues to grow to accommodate the permanent teeth which succeeds the 20 primary teeth.
The lamina continues posteriorly in the elongating jaw and from it come the posterior teeth which forms right behind the primary teeth.
In this manner 20 of the permanent teeth replace the 20 primary teeth. And the 12 permanent molars develop behind the primary dentition.
The last teeth to develop are the third molars which form almost 15 years after birth.
This replacement process goes on from 6 years till about 12 years of age. Generally by the 12th year only the permanent teeth will be remaining in the oral cavity.
What is the ugly duckling stage?
It is an ugly arrangement of anterior teeth, which is merely a temporary phase during the process of missed dentition. It usually occurs between ages 7 and 12 years preceding the eruption of the permanent canines, when the upper central and lateral incisors are tipped laterally because of the un-erupted crowded canines thus creating a midline gap between the central incisors. This arrangement looks ugly and hence the name. But this stage does not need any orthodontic intervention and is self-correcting. It usually corrects itself once the permanent canines erupt and the midline gap closes.
What are the precautions and points to follow during the mixed dentition stage?
The exfoliation pattern varies from individual to individual. Hence there is no need to extract the deciduous teeth.
If the underlying permanent tooth has already erupted and the un-shedded milk tooth is prohibiting it from securing its correct position then it is mandatory to extract that milk tooth.
It is common to find some wobbly deciduous teeth in this stage but oral hygiene needs to be maintained by proper brushing in order to protect the already erupted permanent teeth.
Regular dental checkups need to be followed in this stage to be able to correct malocclusions for functional and esthetic purposes.
This period starts when the permanent first molar erupts and lasts till the last primary tooth is shed. There are 32 permanent teeth but the maxillary teeth eruption sequence varies from the mandibular eruption sequence. Since there are no premolars in the 
