Development of the Dentition from Birth to the Complete Deciduous Dentition
At birth, the maxilla and mandible are small in comparison with the other structures of the head. Further, the lower jaw is more dorsally positioned in relation to the upper one than will be the case when the deciduous teeth have erupted fully. The regions of both jaws that contain tooth buds grow considerably during the first six to eight months of postnatal life. In addition, a significant ventral development takes place during the first year, leading to an anteroposterior relation between the two dental arches that conforms to the one present in the complete deciduous dentition.23, 24, 93, 94, 101
The extensive early transverse development of both jaws can be realized mainly because of the presence of the suture in the median plane of the maxilla and of a synchondrosis in the mandible. Both structures are capable of rapid growth. As the synchondrosis in the mandible calcifies at about six months of age, the potency for rapid transversal growth in the lower jaw is eliminated. After a bony union has been established between the two halves of the mandible, the potency of interstitial growth—a typical characteristic of cartilage and not of bone—is lost. In contrast with the situation in the mandible, the maxilla maintains its rapid median growth potency. The maxillary median suture remains until the development of the dentition has been completed. After the occlusion in the posterior region has been established, the transverse development of the two dental arches becomes coordinated. Thereafter the transverse development of the maxilla will be determined mainly by the above indicated limitations in the mandible. As a consequence, the growth potency of the maxillary median suture is only partly utilized, as the mandibular synchondrosis has already been calcified.
The increase in size of both jaws usually is sufficient to provide the space needed for a harmonious arrangement of the deciduous teeth in the dental arches upon their emergence. The crowding initially present in the arrangement of the anterior teeth at birth has disappeared at the time they emerge. Crowding is rarely encountered in the deciduous dental arches. On the contrary, usually an excess of space is available and diastemata are present between all teeth. Sometimes a not fully corrected rotation of an incisor is observed, in spite of the fact that enough space is available for proper alignment.
The development from birth to complete deciduous dentition is presented in Figure 2-1. For an overview of emergence times, mesiodistal crown dimensions, and different stages in crown and root formation, refer to Chapter 17.