Changes in midpalatal suture area and adjacent periodontal tissues of individual tooth following rapid palatal expansion in young adult dogs ; Histomorphologic and immunohistochemical study

Lee, Ju Young; Lee, Jin Woo; Cha, Kyung Suk

Abstract

The purpose of this study was to determine the proliferative activity of the osteoblasts and fibroblasts in the midpalatal area and to investigate the adjacent periodontal tissues of individual tooth following rapid expansion of the palate. Ten young adult dogs, aged approximately ten months, were used in the experiment. The experimental design was consisted of 1 week expansion group(Group E1, 3 dogs), 2 week expansion group(Group E2, 3 dogs), 2 week expansion and 2 week retention group(Group E3, dogs), and control group(Group C, 1 dog). For each group, expansion screw was activated one time per day(1/4 turn;90degrees) following Hyrax-screw application. The experimental animals in each group were sacrificed at 1, 2 and 4 weeks following palatal expansion. Maxillary tissue blocks wee obtained and prepared for the histomorphologic and immunohistochemical studies. Light microscope, polarizing microscope, and soft X-ray apparatus were used in this study, and following results were obtained. 1. In polarizing microscopic study, the expansion group(E1 & E2) showed blue color representing bone resorption and new bone formation in midpalatal suture area. E3 groups showed less color compared to the E1 and E2 group. But yellow color increased by calcification in the E3 groups. 2. Immunohistochemical study revealed that positive responses of the osteoblasts to PCNA and undifferentiated fibroblasts to EGF in E1 group were somewhat increased. Positive response to PCNA and EFG were increased in fibroblasts and the osteoblasts forming new bone in E2 group. In E3 group, the positive response cell concentrated the periphery of edge of palatal process in both PCNA and EGF. 3. Throughout the expansion period(E1 & E2), light microscopic study showed the edges of the extensive resorption new palatal processes, indication bone remodeling within the suture. E3 group exhibited less remodeling of midpalatal suture area. E2 group and E3 group showed cementum formation and resorption at the apex of 3rd premolar and 1st molar. E3 group exhibited extensive hyalinized zone on the cervical portion of buccal side of 1st molar. 4. Soft X-ray analysis of E1 group showed hypomineralized defect and microfractures in various parts of the suture areas when compared with control animals. There was no significant difference in the degree of mineralization in the midpalatal suture region between the C and E3 groups. Tooth axis showed tipping of 3rd premolar and 1st molar in the E2 group and E3 group. Based upon these experimental results, it is concluded that the undifferentiated mesenchymal cells always presented in midpalateal suture area following RPE. Differentiated osteoblasts and fibroblasts possess proliferating cellular activity until the 2 week retention period. The posterior teeth area tend to tip buccally as RPE force applied. Retention group exhibited irreversible response with severe hyalinized on the buccal surface of the first molar.