June 06, 2014
Around the age of 6 years the permanent first molars erupt and primary mandibular central incisors are exfoliated. The primary incisors are replaced by their succedaneous permanent teeth at 6 to 8 years of age. Variations in the order of eruption in the early mixed dentition frequently occur between the mandibular first molar and the central incisor. In many children the mandibular central incisor is the first permanent tooth to erupt.
After the eruption of the first permanent molars and the incisors there is a 'quiet' period in the mixed dentition from 8 to 10 years of age, when exfoliation of the primary canines and molars starts. After eruption of the permanent second molars at 12 years of age there is again a long pause antil the third molars finally erupt around the age of 20.
In contrast to the primary teeth, there is for the permanent teeth a sex difference in the time of eruption. The permanent teeth erupt on the average 4 months later in boys than in girls.
The permanent incisors and canines are wider than the corresponding primary teeth. Space for these permanent teeth is provided by:
- the small surplus of space found in most primary dentitions
- greater labial inclination of the maxillary permanent than of the primary incisors
- a small increase in dental arch width during eruption of the permanent anterior teeth
The primary molars, on the other hand, are smaller than the succedaneous premolars. Exfoliation of the primary posterior teeth, therefore, provides surplus space of importance for the establishment of normal intercuspation.