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Development and Developmental Anomalies of the Teeth
Newborn infants do not have teeth for about first 6 mo after birth (predentate period). At this stage, the upper and lower alveolar ridges in the mouth, also known as gum pads, house the primary (deciduous) and some permanent tooth buds. The primary dentition period starts with eruption of the first primary tooth; all 20 primary teeth erupt by 3 yr of age. The permanent teeth start erupting around age of 6 yr, and the transition to full permanent dentition is completed by 13 yr of age. The transition time between primary and permanent dentition, when a mix of primary and permanent teeth are present, is referred to as mixed dentition.
Development of Teeth
Initiation
The primary teeth form in dental crypts that arise from a band of epithelial cells incorporated into each developing jaw. By 12 wk of fetal life, each of these epithelial bands (dental laminae) has 5 areas of rapid growth on each side of the maxilla and the mandible, seen as rounded, budlike enlargements. Organization of adjacent mesenchyme takes place in each area of epithelial growth, and the 2 elements together are the beginning of a tooth.
After the formation of these crypts for the 20 primary teeth, another generation of tooth buds forms lingually (toward the tongue); these will develop into the succeeding permanent incisors, canines, and premolars that eventually replace the primary teeth. This process takes place from approximately 5 mo of gestation for the central incisors to approximately 10 mo of age for the second premolars. On the other hand, the permanent first, second, and third molars arise from extension of the dental laminae distal to the second primary molars; buds for these teeth develop at approximately 4 mo of gestation, 1 yr of age, and 4-5 yr of age, respectively.
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