Abstract
The role of successional tooth germ and occlusal force in root resorption of mandibular second deciduous molars was studied in 24 beagle dogs by means of radiographic and histologic evaluations.70 days after birth their mandibular right third permanent premolar germs were surgically removed, and in 10 of the dogs the maxillary right and leftsecond deciduous molars were extracted to decrease the occlusal force on the mandibular second deciduous molars.
1) When successional tooth germs were present, whether the occlusal force was normal or decreased, the alveolar bone and deciduous tooth adjacent to the tooth germ were resorbed, accompanied by eruption of the permanent tooth. After the resorption of the deciduous tooth reached half of the root, many odontoclasts were observed in the dental pulp of the deciduous tooth. The root resorption was hastened by internal resorption.
2) When successional tooth germs were removed, whether the occlusal force was normal or decreased, the root resorption was delayed. The resorption from the root surface progressed very slowly, but shortly after this resorption reached the pulp, internal resorption occurred and the deciduous tooth was resorbed in short time.
3) When the occlusal force was decreased, in the deciduous teeth in which successional tooth germs were present, the tooth resorption tended to delay to a later time. However in the deciduous teeth from which the successional tooth germs were removed, the processes of tooth resorption was very different in individuals, the difference between tooth resorption in normal occlusal force and in decreased occlusal force was not clear.
4) In all groups, shallow resorption on the deciduous root surface was observed before the successional tooth started to erupt, and this resorption was apart from the tooth germ. By repeating resorptive periods and resting periods, this resorption progressed according to the increase in age, and in the resting period, resorption was repaired by new deposits of cementum.
