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KMID : 0378019640070030085
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New Medical Journal
1964 Volume.7 No. 3 p.85 ~ p.157
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Experimental Studies on the Influence of Mechanical Stimulation to the Growth of Rabbit´s Incisors
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Abstract
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Three experimental works were carried out to observe the growth rate of the teeth in normal rabbits ´ given certain mechanical stimulations e.g. impaction, grinding and setting crown, and to study reparative processes and histopatholgical changes after the removal of the mechanical stimulations.
The following results were obtained.
I. The effects on impaction of the incisors were as follows:
1) A certain impaction to the incisors arrested their growth.
2) The stronger impaction to the incisors brought the severer growth inhibition.
3) A certain impaction given for a long period disclosed a rather gradual decline in inhibition of the growth of the incisors.
4) The inhibited growth of the incisors due to a mild impaction recovered to the, normal in a shorter period than those due to a strong impaction.
5) When a rather sronger impaction was continuously added to the incisors, the pulp tissues and periodontal membranes revealed histologically only congestion and hemorrhage in the first to second week, atrophy of the enamel organs and irregularity of the hard tissues in the third to fourth week, degeneration and necrosis in the sixth to eighth week. and over-all reparative processes in about sixteenth week. On the contrary when a relatively mild impaction was added, congestion and hemorrhage were seen until the sixth week. Then degeneration and necrosis appeared slowly. Reparative processes were taken in place more or less at the seventeenth week, but there appeared to be more necrosis at this week. The congestion and hemorrhage were usually noted predominantly at the apices. The histopathological changes after the cessation of the impaction were slowly restored: reparative processes were started in the third to fourth week and a prominent restoration was seen in the sixth to nineth week. H. The effects of grinding and impaction on the growth rate were as follows:
1) A continuous grinding of the lower incisors produced a gradual increase in the growth rate to show twice beyond the normal rate. When grinding was stopped in this case, the growth rate was gradually diminished to a non-growing state at first, and then the growth, rate was slowly increased and recovered to a normal growth state an a corresponding period of grinding Though there was little difference on their growth between unilateraI and bilateral incisors grinding. the effects were generally same.
When both grinding and impaction of the lower teeth were continuously added, the growth rate of the teeth was increased rapidly and showed. twice beyond the normal rate. However, the growth seemed to be slightly diminished to compare with the cases of grinding only. When both grinding and impaction were stopped at the same time, the growth rate declined gradually to a non-growing state, and these relatively slowly recovered to a normal state.
3) The incisors with continuous grinding demonstrated histologically irregular arrangement of ameloblasts and odontoblasts, increased preenamel material near the apices, enlargement of the `pulp canals, thinning of the dentine, and congestion, hemorrhage in the pulp and periodontal membrane. These changes were similarly observed in both unilateral and bilateral incisors grinding. After the cessation ´ of grinding the histopathological changes returned to the normal at the time of the growth rate of the teeth recovered to the normal state.
4) Histopathological changes in the cases of both grinding and inpaction consisted of changes shown in the cases of grinding only and impaction only. After both grinding and continuous impaction were s stopped, all the changes were gradually, recovered.
III. The effects of setting crown and impaction of the growth rate were as follows:
1) The growth rate with setting crown,-whether on the lower incisors or lower and upper incisors, was ; zr severely impaired to the state of almost complete interruption. With the removal of the crown, the growth rate was gradually recovered and returned to the normal state of the growth at the corresponding period to the setting crown.
2) Setting crown on the incisors with impaction given continuously at the same time showed the severer impairment of the growth than those setting crown alone. As the removal of. both crown and, impaction the growth rate recovered slowly to the normal state. However it took longer period to recover than´the cases with setting crown and its removal only.
3) Histopathological changes in the cases of setting crown revealed marked narrowing of the pulp canals. Atrophy of the enamel organs and an increase in both dentine and enamel. These changes were more marked in the cases of setting crown on both lower and upper incisors. As the removal of the crown, the histological changes gradually dissappeared and recovered to the near normal state.
4) Histopathological changes in the cases of both setting crown and impaction given disclosed irregularity of the dental hard tissues in addition to the above findings. On ceasing impaction at the same time of the removal of the crown, the recovery to the normal state was more prolonged than the cases with the removal of the crown without impaction.
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