Some General Aspects of the Normal Development of the Dentition
In the preceding chapters the development of the dentition has been presented in separate phases. Some aspects related to the overall development will be treated here. First, the changes taking place in the two dental arches and the alterations in their relation between birth and adulthood will be treated. Second, some facets of eruption will be discussed. Finally, a few general remarks regarding the development of the dentition will be made. The contents of this chapter entail that repetition of some features discussed earlier cannot be avoided.
The regions of the jaws containing the teeth prior to and after emergence do not increase gradually in size. Moreover, the increase in size of the different regions varies distinctly in amount and in timing. The sections of both jaws housing the deciduous dentition from the central incisors through the first deciduous molars grow considerably from birth to 6–8 months of age.23 Thereafter, the increase is limited. The width of the dental arches increases only slightly as it is expressed by the limited enlargement of the transverse dimensions between the left and right deciduous canines. Between the first deciduous molars the increase is even smaller.24, 63, 72, 94 (See also Chapter 17.) A comparable limited increase takes place in the dental arch depth, measured as the distance from the labial surface of the central incisors to the center of the line connecting the distal surfaces of the first deciduous molars. The limited increase in dimensions of the sections of the dental arches discussed here is not restricted to the period of the development of the deciduous dentition. It also applies to the subsequent development to the adult stage.
The changes in transverse width and sagittal depth of the dental arches, occurring after the deciduous dentition has been completed, are primarily associated with processes accompanying the transitions. In both dental arches the increase in distance between the deciduous canines occurs mainly during the process of replacement of the incisors. The second spurt in intercanine distance increase is associated with the transition of the canines. The permanent canines attain a slightly more buccal position in the dental arch than their predecessors. The difference in this respect is more distinct for the maxillary than for the mandibular dental arch. Generally a gradual, continuous, and limited increase in the transverse dimension between corresponding left and right deciduous molars/premolars and permanent molars takes place from the complete deciduous dentition stage until the adult situation is reached. These increases in dental arch width dimensions are larger in the ventral region than in the dorsal region and the increases are smaller in the mandible than in the maxilla. This dissimilarity in increase in dental arch width dimension is associated with the more ventral displacement of the mandibular dental arch than of the maxillary one during normal development while the proper transverse relation between the opposing posterior teeth is maintained.
The discontinuous increases in dental arch width dimensions in the canine region, associated with the transitions, are superimposed on those that are more continuous in nature and correspond with comparable increases in dental arch width dimensions more posteriorly. The changes in the dental arches are illustrated in Figures 8-1 through 8-4. The left and right side drawings in these figures are essentially the same. The only dissimilarity is the thickness and continuity of lines and the presence of the occlusal patterns. In the drawings A and B in each figure, the earlier stage is accentuated; in drawings C and D, the later stage.
Fig. 8-1 Survey of the changes of the sections of the jaws containing the deciduous teeth, from birth to the complete deciduous dentition stage. During this period, the relevant sections of the jaws increase in size considerably. More than sufficient space develops for the deciduous incisors and canines. Substantial extension takes place in the dorsal direction. The increase in size of the anterior regions of the two dental arches takes place for the greater part during the first to eighth months after birth and before the mandibular symphysis begins to calcify. The median maxillary suture persists. In the maxilla, growth at the median plane can continue, in contrast with the situation in the mandible.
Fig. 8-2 Survey of the changes in both dental arches from the complete dentition stage to the intertransitional period.
The permanent incisors have arrived at a more ventral position than that of their predecessors. The intercanine distance has increased. The distance between the corresponding left and right deciduous molars has enlarged also, but more slightly. The first permanent molars have emerged dorsally to the dental arches. The diastemata in the posterior regions have been reduced. In each dental arch, the distal surfaces of the second deciduous molars have attained a more mesial position in relation to the canines.
Fig. 8-3 Survey of the changes in both dental arches from the intertransitional period to the permanent dentition stage (with the exception of the third molars).
The canines have been replaced. The premolars are more buccally positioned than their predecessors were. The first permanent molars, and particularly the mandibular ones, have migrated mesially over some distance. The possibility for this mesial migration was supplied by the difference in mesiodistal crown dimensions between the deciduous molars and the premolars and the presence of diastemata in the dental arches. The second permanent molars have emerged dorsally to the dental arches.
Fig. 8-4 Survey of the changes in both dental arches from the complete deciduous dentition stage to the permanent dentition stage (with the exception of the third molars).
The anterior sections of both dental arches increase only slightly in ventral and transverse dimensions. The transverse changes are more marked in the maxilla than in the mandible as the mandibular dental arch attains a more anterior position in relation to the maxillary one over time. The increase in size of both dental arches is achieved mainly by a dorsal extension. Successively, the first and the second permanent molars have been added to the dental arches. Harmonious emergence of the third molars will take place when it is preceded by sufficient extension of the jaws.
In both jaws the dental arch of the complete deciduous dentition describes a nearly flat occlusal plane. A vertical overbite (the overlap in height of the maxillary and mandibular incisors) is scarcely present. After the transition, the maxillary and mandibular permanent incisors erupt further than their predecessors were positioned. The result is a vertical overbite. An overlap of one-third of the clinical crown height* of the mandibular central incisor, measured perpendicularly to the />
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