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KMID : 0370819920070010051
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Yonsei Journal Dental Science
1992 Volume.7 No. 1 p.51 ~ p.69
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THE EFFECT OF FUNCTIONAL CHANGE INDUCED BY EXTRACTION OF OPPOSITE MOLARS UPON THE PERIODONTIUM OF MANDIBULAR 1ST MOLAR OF RAT
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Abstract
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The mandibular molars of the rat undergo continuous physiologic migration. The extraction of the mandibular molar has been used as a method to induce a functional change. The periodontal changes caused by hypofunction have been observed mostly in
the
lingual and distal root of the mandibular first molar. In order to investigate the effect of the functional change upon the direction of migration in each root, the external contour of the mandible, and the periodontal change in the mesial root
of
mandibular 1st molar, the maxillary molars of the rat were extracted. Calcein, tetracycline, alizarin red S were alternatively injected every week intraperitoneally to confirm the new bone formation. The animals were sacrificed 8 weeks after
extraction
and non-decalcified sections including the mandibular first molar were examined under fluoromicroscope. The other animals were sacrificed 1, 2, 4, 8 weeks after extraction and semithin sections of the mesial root were made. The length of the
histological zones in the surface of alveolar bone, and the width and area of the periodontal ligament were measured.
@ES The following results were obtained.
@EN 1. The mandible of non-extracted control group was flat in the lingual surface and convex in the buccal surface. The mesial root of the mandibular first molar was observed migrate mesiobuccally, with the other distally.
2. Under hypofunction, the mandible was to get the contour with the both surface flat and the mesial apex pointed. The direction of migration in the mesial root changed to distolingual.
3. One week after extraction, the necrosis of the cells and degeneration of collagen fibers were observed in the surface of the hypoufunctional alveolar bone.
4. In the hypofunction group, the length of remodeling zone decreased and that of the denuded zone increased. In the remodeling zone, the area of reversal increased with the decrease of bone formation area. The hyperfunction group showed no
difference
to the control group.
5. The width and area of the periodontal ligament in the hypofunction group decreased significantly.
6. The mesial root of hypofunction group had a tendency to migrate toward the remodeling zone within its own alvelar socket, while in the hyperfunction group, toward the modeling zone.
The findings from the above study revealed that the mesial root of mandibular first molar is different from the other roots in the direction of migration, the pattern of alveolar bone remodeling, and the response to functional force. The response
include the change of the direction of migration and the contour of the mandible as well as the remodeling pattern of alveolar bone and the property of the periodontal ligament. Hypofunction modifies the remodeling pattern of the periodontal
ligament,
by which the direction of tooth migration is altered, and as a result, the remodeling of alveolar bone and the external contour of the mandible is affected. The periodontium has and ability to adapt to hyperfunction, in which any other change,
than
the
direction of migration is not provoked.
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KEYWORD
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