Histomorphometric analysis of microcrack healing after the installation of mini-implants.
OBJECTIVE
The goal of this study was to investigate the histomorphometric characteristics of the healing process of microcracks in the cortical bone after the installation of mini-implants (MIs).


METHODS
Self-drilling MIs were inserted into the tibial diaphysis of twelve adult male New Zealand rabbits. Four MIs per rabbit were placed randomly. The animals were divided into four groups according to the length of the healing period: group A was sacrificed immediately, group B was sacrificed after one week, group C was sacrificed after two weeks, and group D was sacrificed after four weeks. Cortical bone thickness was measured using micro-computed tomography, and histomorphometric analyses of the cumulative length of the microcracks (CLCr) and the total number of microcracks (NCr) were performed using hematoxylin and eosin staining.


RESULTS
The microcracks were radially and concentrically aligned in the peri-MI bone. The CLCr decreased significantly one week after the surgery, mainly due to healing of the concentrically aligned microcracks. The CLCr showed another significant decrease from two weeks after the surgery to four weeks after the surgery, mainly reflecting healing of the radially aligned microcracks. A statistically significant decrease in the NCr occurred as the microcracks healed from zero weeks to two weeks. However, no significant difference in the NCr was found between groups C and D.


CONCLUSIONS
In order to improve the primary stability of MIs, delayed loading and a healing period of a certain length are recommended to ensure the optimal healing of microcracks and bone remodeling.
Department of Orthodontics and Dental Research Institute, Seoul National University School of Dentistry, Seoul, Korea.
Soobin
0000-0001-9308-6672
S
Shin
Department of Orthodontics and Dental Research Institute, Seoul National University School of Dentistry, Seoul, Korea.
Pan-Soo
0000-0001-8869-2715
PS
Park
Department of Orthodontics and Dental Research Institute, Seoul National University School of Dentistry, Seoul, Korea.
Seung-Hak
0000-0002-6586-9503
SH
Baek
Department of Orthodontics and Dental Research Institute, Seoul National University School of Dentistry, Seoul, Korea.
Il-Hyung
0000-0001-6398-4607
IH
Yang
Bone remodeling; Orthodontic anchorage procedures