[Effects of human growth hormone on restoration process of midpalatal suture areas after maxillary expansion in rats].

Posterior crossbite due to narrow maxillare is treated with maxillary rapid expansion devices in clinic. It takes long time to be restored by the new bone formation in midpalatal suture after maxillary expansion. It is well-known that Human Growth Hormone (hGH) stimulates the growth of long tubular bones and mandibles. Recently, it has been suggested that hGH promotes wound healing and bone fracture healing, when applied, due to hGH promotion of albumin anabolism. The present study examines histopathologically the process of new bone formation in the midpalatal suture after maxillary expansion in the rats injected with hGH. Two hundred and fifty eight male Sprague-Dawley rats weighing approximately 200 g were divided into 13 groups consisting of 21 rats each except for normal controls; the 13 groups comprised of one normal control group, 6 expansion control groups (expansion group) and 6 expansion groups receiving hGH (GH group). Except for the normal control group, an expansion device was installed between maxillary incisors for two days. The expansion space was retained throughout the experimental period after treatment. Throughout the experimental period one group received two daily subcutaneous hGH injection of 40 mIU/100 g body weight. The animals were sacrificed at 1, 3, 5, 7, 10 and 14 days after expansion. The specimens were examined with Hematoxylin Eosin stain, Azan Mallory stain and Villanueva Goldner stain. The results were as follows: 1. In the GH groups, many fibroblasts, osteoblasts, collagen fiber bundles and blood vessels were actively observed in the sutural space after maxillary expansion, as compared with the expansion groups. 2. In the GH groups, the new bone formation was facilitated in the midpalatal suture and sutural space was filled with the new bone, as compared with other groups throughout experimental period. 3. In the GH groups, osteoid formation was observed more actively and extensively on the bone wall or the bone edge, as compared with the other experimental groups. 4. The collagen fiber bundles were stretched and were few in the midpalatal suture after maxillary expansion, and the arrangement of collagen fiber bundles became regular by the restoration of collagen fiber bundles and the new bone formation in both groups. In the GH groups, the new bone formation was active and the arrangement of collagen fiber bundles was more regular, as compared with the expansion groups.(ABSTRACT TRUNCATED AT 400 WORDS)