Transitional Ameloblastic Activity Zone in Mice Teeth

¹ Howard University College of Dentistry, Washington, D.C.

The ameloblastic transitional region known as zone B or the "zone of compression" is present at birth in the mandibular incisors of mice. This same region is found in anlagen of mandibular cheek or molar teeth of these animals. In each developing molar tooth one of these zones is associated with each cusp, and cross-sections of these teeth show them in similar positions on opposite sides of the crown. While this region persists in continuously growing mandibular incisors, it disappears in the cheek or molar teeth as they reach maturity. Usually only one of these regions is present in the incisors, but at times there may be an auxilliary region that fits all the criteria for this zone. This zone may vary in its size and position in relation to the length of the palisaded ameloblasts of the incisors, but it is always present. Considerable force appears to be exerted against the matrix in this region. This pressure is manifested by a compression of the matrix. This force is presumed to be of a hydraulic nature and related to the mineralization and crystallization processes evidently scheduled to take place at this time in the enamel matrix. It is felt that this region and adjacent regional extracellular spaces represent attempts at solute adjustments that will initiate crystal formation along the fibrils of the newly formed enamel protein matrix.