Chapter 5

The Dentition in the Intertransitional Period

In the intertransitional period the mandibular and maxillary dental arches consist of sets of deciduous and permanent teeth. Between the four permanent incisors and the left and right first permanent molars, the deciduous canines and first and second deciduous molars are located on each side of the dental arch. The maxillary incisors are labially inclined. A central diastema is present. Frequently no contact exists either between the central and lateral incisors. Likewise, a diastema is often present in the maxillary dental arch mesially to the deciduous canine. In the mandible the incisors are less labially inclined than in the maxilla. A diastema seldom exists between the mandibular central incisors. All incisor crowns are usually in contact with each other and the laterals touch the deciduous canine crowns.

The arrangement of incisors in the intertransitional period deviates from the normal situation in the adult dentition when all incisors are well aligned and in contact with each other. However, the marked, unharmonious-appearing situation characteristic of the preceding first transitional period has disappeared for the greater part. Asymmetry in emergence and associated differences in height levels and lengths of clinical crowns of corresponding left and right teeth have been made up. Under the influence of the tongue, the mandibular lateral incisors have attained the proper sites within the dental arch and their initially lingual location has been eliminated. Small rotations resulting from rotated positions of the tooth buds—quite often encountered in the mandible—are corrected by pressures exerted by the tongue and lips if the spatial conditions in the dental arch permit these improvements to be achieved. The incisal contacts between the maxillary and mandibular incisors also may work in favor of this improvement.

The deciduous teeth still present are normally quite worn down at this developmental stage. The initially present sharp cusp tips of the deciduous canines and molars have disappeared by attrition and the occlusal morphology approaches that of a plane. Through the absence of a distinct intercuspation, the anteroposterior relation between the two jaws is not fixed by the occlusion anymore. The ventral development of the mandible, slightly exceeding that of the maxilla, encounters little or no interferences from the occlusal contacts, so the mandibular teeth attain a slightly more mesial position in relation to the maxillary ones.

Not only the occlusal, but also the approximal surfaces wear off in normal use through rubbing the adjacent surfaces during function. The initially pointed approximal contacts become flat and the mesiodistal crown dimensions reduce in size. These changes caused by attrition are limited in modern Western societies. However, in a life-style that requires greater activity and a more vigorous functioning of the dentition, and one that involves exposure to materials with a rather large abrading effect, as grains of sand, the attrition will be considerably larger. It has been assumed that deciduous molars need the excess in mesiodistal crown dimensions over their successors to be able to maintain the space needed for the premolars even after considerable approximal attrition.43