Age-related osteogenesis on lateral force application to rat incisor – Part I: Premaxilla suture remodeling

Age-related osteogenesis on lateral force application to rat incisor – Part III: Periodontal and periosteal bone remodeling

Objectives:

This study was aimed to compare the histological pattern of bone modeling on either periodontal or periosteal side induced by lateral orthodontic tooth movement in different age groups.

Material and Methods:

A total of 50 male Sprague-Dawley rats (25 rats in the adult group – 52 weeks and 25 rats in the young group – 10 weeks) were utilized in this study. Each age group was classified into the control, 3 days, 7 days, 14 days, and 21 days groups (five rats in each) by the duration of experimental device application. A double-helical spring was produced using 0.014” stainless steel wire to provide 40 g lateral force to the left and right incisors. Hematoxylin-eosin staining, proliferating cell nuclear antigen (PCNA) immunohistochemical staining, fibroblast growth factor receptor 2 (FGFR2) immunohistochemical staining, and Masson trichrome staining were performed; and the slides were subject to histological examination.

Results:

In 7 days, active bone modeling represented by the scalloped surface was observed on the periosteal side of the crestal and middle alveolus at the pressure side in the young group, while similar changes were observed only on the crestal area in the adult group. In the young group, the number of PCNA-positive cells increased significantly on the crestal area and middle alveolus on the 3, 7, and 14 day groups, with subsequent decrease at 21 days. In the adult group, PCNA-positive cells were localized on the crestal area throughout the period. In the young group, FGFR2-positive cells were observed mainly on the crestal and middle alveolus at 3, 7, and 14 days than the control group. In the adult group, these cells appeared on the crestal and middle alveolus in the 3 days group, but mainly on the crestal area at 14 days. In the young group, FGFR2-positive cells were observed on the crestal and middle alveolus on the 3, 7, and 14 days groups more than on the control group. In the adult group, these cells appeared on the crestal and middle alveolus in the 3 days group, but mainly on the crestal area in the 14 days group. In Masson trichrome stain, an increased number of type I collagen fibers were observed after helical spring activation in both age groups. Large resorption lacunae indicating undermining bone resorption were progressively present in both young and adult groups.

Conclusion:

According to these results, orthodontic tooth movement may stimulate cell proliferation and differentiation primarily on the periosteal side according to progressive undermining bone resorption on the periodontal side. This response may lead to prominent bone modeling during tooth movement in the young group, compared to the relatively delayed response in the adult group.

Age-related osteogenesis on lateral force application to rat incisor – Part II: Bony recession and cortical remodeling

Objective:

The aim of this study is to analyze the age-related changes in the bony recession and cortical bone remodeling induced by lateral orthodontic tooth movement, using a three-dimensional micro-computed tomography (CT) analysis.

Material and Methods:

A total of 40 male Sprague-Dawley rats were divided into two distinct age groups (young, 10 weeks and adult, 52 weeks). Double-helical springs exerting 40 g of force were applied to central incisors to analysis of changes in lateral cortical bone and tooth movement with age and time. The young and adult rats were divided into four subgroups, T0 (0 week), T1 (1 week), T2 (2 weeks), and T3 (3 weeks), depending on the period of wearing the appliance. Micro-CT image was taken on each dissected pre-maxilla specimen. In each subgroup, distance between the center of teeth, suture width, tooth displacement, bony recession, and bone volume was evaluated.

Results:

The changes in the distance between the center of teeth and the suture width were significantly greater in the young group. However, the change in the tooth displacement showed no significant difference between groups. In the young group, bony recession of outer cortical layer was observed at T1 (P < 0.05), but the amount of recession gradually decreased at T2 and T3. In contrast, in the adult group, bony recession increased gradually over observation period (P < 0.05). The bone volume decreased at T1 (P < 0.05), but recovered at T2 and T3 in both groups.

Conclusion:

The compensatory bone formation occurs in the pressure side of cortical bone more significantly in the young group than in the adult according to the lateral displacement of incisor in rats. The reduced bone reaction in the adult is considered a limiting factor of the excessive tooth movement in the compromised treatment of skeletal malocclusion.