Rapid palatal expansion(RPE) is a method of inducing the new bone formation in the palate by separation of the midpalatal suture, which can be done conveniently by placing heavy force across the maxillary dental arch. This experiment was undertaken to examine the histologic changes after RPE and during retention period. Four young adult dogs(a control dog, three experimental dogs) aged 4 to 6 months old were used for this experiment Expansion screw(Hyrax~. Dentarum Inc.) was delevered to the palate and turned 180 degrees every morning and evening for 8 days, giving a total expansion of 72mm. A control dog was sacrified at the starting point of this study without any treatment and three experimental dogs were sacrified after RPE, 14-day retention, and 28-day retention in each. Thereafter, those samples were observed with hematoxylin-eosin(H-E) stain, ground section(Vrillanueva stain), alkaline phosphatase((_ALP) stain, tartrate-resistant acid phosphatase(TRA) stain.
The results were as followings:
1. After RPE.. collagen fiber bundles were stretched along the midpalatal suture and few osteoblasts were flattenedinactive state and also, a little osteoid tissues was observed. Few multinucleated osteoclasts which had TRAPpositive activity in their cytoplasm were seen in horizontal section, whereas a few osteoclasts were seen in frontal section, especially in the nasal floor side of palatal bone.
2. After 14-day retention, collagen fiber bundles were stretched along the midpalatal suture and few osteoblasts which had ALP-positive activity in their cytoplasm were seen. Few multinucleated osteoclasts which had TRAP-positive activity in their cytoplasm were seen in horizontal section, whereas a few osteoclasts were seen in frontal section, especially in the nasal floor side of palatal bone.
3. After 28-day retention, collagen fiber bundles were arranged like those of control dog and osteoblasts which showed a lot of immature bone formation were cuboidal shape and exhibited ALP-positive activity in their cytoplasm. Few multinucleated osteoclasts which had TRAP-positive activity in their cytoplasm were seen in horizontal section, whereas a few osteoclasts were seen in frontal section, especially in the nasal floor side of palatal bone.
According to the above results, the new bone formation after rapid palatal expansion was examined after 14-day retention and significantly increased. after 28-day retention.
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