Abstract
The purpose of this study was to clarify the development of the eruption and root formation of the permanent successors in deciduous dentition. The materials used were serial standardized X-ray films taken every two weeks from thirty-two healthy infant dogs, and were classified into the following three groups for this experiment.
1. Healthy group (Control): Untreated teeth were observed which represented the opposites of all the teeth examined in the previous two groups of thirty-two dogs.
2. Extraction group with infected deciduous teeth: The infected deciduous teeth of twenty-one dogs were extracted after being left for four weeks following pulpectomy.
3. Extraction group with healthy deciduous teeth: Healthy deciduous teeth of eleven dogs were extracted from fourteen weeks old. A total of 1,280 mandibular observed teeth (P2, and P3) were used. The results from this study were made of the rate of crown movement, and the rate of root formation of the permanent successors in three groups. The results were as follows.
1. Rate of crown movement of permanent successors.
1) Healthy group (Control): For the eruption it showed a tendary towards resembling “S” curve and to be related to the period of weeks and rate of crown movement.
2) Extraction group with healthy deciduous teeth: Rate of crown movement of permanent successors was more accelated than the other experimental groups.
3) Extraction group with healthy deciduous teeth: Rate of crown movement of permanent successors appeared little different from that of the control group.
2. Rate of root formation of the permanent successors.
1) Healthy group (Control): For root formation it seemed that the even development tendency related to the period of weeks and rate of root formation.
2) Extraction group with infected deciduous teeth: Rate of root formation of the permanent successors was more accelated than the other experimental groups. But this accelated tendency did not seem stronger than rate of crown movement.
3) Extraction group with healthy deciduous teeth: Rate of root formation of the permanent successors appeared little different from that of the control group.
