366 Original Article The effect of osteopenia on tooth movement in ovariectomized rats. An experimental study Apostolos I. Tsolakis 1 , Lubna Khaldi 2,3 , Ilias Bitsanis 1 , Constantine Alexandridis 4 , Αggeliki Triantafyllou 3 , Meropi N. Spyropoulos 1 , Ismene A. Dontas 3 1 Department of Orthodontics, School of Dentistry, National & Kapodistrian University of Athens, Greece; 2 Department of Pathology, “Saint Savvas” Anticancer Hospital, Athens, Greece; 3 Laboratory for Research of the Musculoskeletal System, School of Medicine, National & Kapodistrian University of Athens, KAT Hospital, Greece; 4 Department of Oral and Maxillofacial Surgery, School of Dentistry, National & Kapodistrian University of Athens, Greece Introduction Postmenopausal osteoporosis represents the most common metabolic bone disease in women today. It is related to estrogen withdrawal and represents a severe public health problem 1 . It is also generally accepted that among the skeletal sites affected by bone loss, the maxilla and the mandible are also included, both in peri- and post-menopausal women 2,3 as well as in rodent models 4,5 . Changes in bone metabolism are known to influence orthodontic tooth movement in experimental studies 6,7 . Following orthodontic tooth movement, tissue reactions take place in the paradental tissues resulting in differentiated bone turnover. It is well accepted that after the loading of a tooth, alveolar bone formation occurs on the tension side of the movement, whereas resorption is observed on the pressure side 8-10 . The extent and quality of tooth movement are dependent upon the nature of the applied force, the biologic status of the involved tissues and the general health condition of the treated individual 9 . Mechanical and metabolic control of alveolar bone homeostasis may influence the extent, as well as the rate and the quality of orthodontic treatment. Various regulatory mechanisms have been described and several genes are involved in local alveolar bone modeling processes 10 . The purpose of this experimental research study was to investigate in depth the effects of osteopenia related to the Abstract Objective: The purpose of this experimental study was to investigate in depth the effects of osteopenia related to the rate, as well as to the quality of orthodontic tooth movement, by combining experimental ovariectomy and molar movement in rats. Methods: Twenty-four six-month-old female Wistar rats were used in this study. The animals were divided into two groups consisting of twelve animals each: Group A (control group) was subjected to orthodontic movement of the upper right first molars. Group B was subjected to orthodontic movement of the upper right first molar following bilateral ovariectomy. Ovariectomy was performed on the first experimental day and the upper right first molars were subjected to orthodontic forces 60 days post-ovariectomy, lasting for 14 days. Results and Conclusion: Direct inspections of the upper jaws, measurements of orthodontic movement of the upper right first molars of Group A and B, as well as histologic examinations of the alveolar bone in the upper right and left first molar regions, showed that osteopenia affects the rate of orthodontic tooth movement, as well as the quality of alveolar bone remodeling, in ovariectomized rats. Specifically, in the ovariectomized animals the alveolar bone of the non-loaded side showed extensive internal resorption, with large marrow cavities, whereas the alveolar bone of the loaded side was dense with almost no marrow cavity and frontal resorption on the surface. It appears that alveolar remodeling after the exertion of orthodontic forces follows the general paradigm of osteoporotic bone remodeling after loading. Keywords: Bone, Osteopenia, Osteoporosis, Rat, Tooth Movement The authors have no conflict of interest. Corresponding author: Apostolos I. Tsolakis, DDS, MSD, PhD, Leoforos Pentelis 66, Vrilissia, Athens, Greece E-mail: apostso@otenet.gr Edited by: G.P. Lyritis Accepted 4 June 2018 Journal of Musculoskeletal and Neuronal Interactions J Musculoskelet Neuronal Interact 2018; 18(3):366-374