Permanent teeth consist of 32 teeth, they completely erupt by the age of 18-25. The first in the sequence to erupt being the Lower 1st Molar (6-7 yrs) and the last to erupt is the 3rd Molar(18-21 yrs). The anterior teeth or the incisors mainly the mandibular erupt lingually to that of the deciduous, and the posteriors which are the Premolars and Molars erupt from below the deciduous molars which are the predecessors of the Permanent premolars.
The Permanent teeth dissolve the roots of the Deciduous teeth with the help of cells called osteoclasts. These cells dissolve the dentin and the pulp of the root in the primary teeth, as the Permanent teeth erupt push the Deciduous teeth out of the alveolar bone sockets.
The sequence of eruption of the permanent teeth is different in the mandible and the maxilla, the change seen due to the canine.
Maxilla: I Molar-Central incisor-Lateral Incisor-I,II Premolar-Canine-II Molar-III Molar.
Mandible: I Molar-Central Incisor-Lateral Incisor-Canine-I,II Premolar-Canine-II Molar-III Molar.
Eruption of Permanent Teeth is important both for health and aesthetics as the child is in their growing stage and with good teeth good nutrition can be obtained. There are some variations in the timing of the Eruption of the teeth but there must not be more than 6 months delay in the eruption time mentioned above. In case you observe a delay consult your Dentist to know the cause of the delay.
Over-retention of primary teeth is one of the major causes of delay in eruption. In some cases the Permanent teeth erupt either lingually of buccally in presence of over retained deciduous teeth. The over retentions of primary teeth cane be due to ankylosis of the tooth which is rare or the most common cause being decayed tooth. In some cases the teeth do not erupt because they are missing congenitally, the conditions are called as Anodontia (all teeth are missing) and Hypodontia (some teeth are missing) mostly laterals.