231 Introduction Stress may be considered as a process that affects may bodily, mental and psychological functions 1,2 . The central components of the stress response are the hypothalamic-pituitary-adrenal axis and the sympathetic nervous system 3-11 . Adrenal hypertrophy, gastric ulceration, and thymolym- phatic dystrophy are the classical triad of the stress noted many decades ago by Selye 12,13 . Cortisol reduces the utilization of amino acids for protein formation in muscle cells. Stress resulting in cortisol excess can lead to progressive protein loss, muscle weakness and at- rophy, and bone mass loss through increased calcium excretion and less calcium absorption 14 . Three mechanisms are involved in bone loss induced by corticosteroids: First, physiological changes; second, behavioral distortion of eating, drinking, ex- ercise and sleep habits; third, anxiety, depression, loss of social roles and social isolation, further promoting the stress cycle 15 . Bone resorption can be assessed using the urinary biomarker hydroxyproline 16 . This is a useful tool for assessing fracture risk at hip, humerus and other bones, as well as for monitoring the effectiveness of osteoporosis therapy as it provides important information about the antiremodeling efficacy of various treat- ments, particularly the antiresorptive medications 17 . It has been reported that impaired mineralization of the mandible, as shown by low ratios of calcium and inorganic phosphorus to hydroxyproline, occur in rhesus monkeys sub- mitted to postcranial immobilization 18 . Moreover, it is docu- mented that osseointegration of titanium implants may be affected by corticosteroid treatment. In recent years, an interrelationship between systemic loss and resorption of the alveolar bone has been observed. The degree of alveolar bone loss increases with age, and this may be partly related to systemic conditions that also encourage the development of os- teoporosis. The relationship between the mandible and primary os- teoporosis was further established by clinical studies 19-22 . Although the alveolar bone loss is independently influenced by local and systemic factors, including osteoporosis, a cross-sectional study in post-menopausal women, evaluated the influence of oral infection J Musculoskelet Neuronal Interact 2010; 10(3):231-236 Mandibular bone density and calcium content affected by different kind of stress in mice N. Seferos 1 , A. Kotsiou 2 , S. Petsaros 1 , G. Rallis 3 , C. Tesseromatis 1 1 Medical School, University of Athens, Greece; 2 Aretaieion University Hospital Athens, Greece; 3 General Hospital of Athens “KAT”, Oral and Maxillofacial Surgery Abstract Objectives: Stress is considered to affect many body and mental functions. This leads to activation of the hypothalamic-pitu- itary-adrenal axis and the adrenomedullary sympathetic system resulting to increased glucocorticoid release. Corticosteroids are known to cause systemic bone loss. The aim of the study was to investigate the role of different kinds of stress on the mandible bone mass of Wistar mice. Methods: 75 male Wistar mice were divided into three groups (n=25 each). The animals of group C were submitted to stress by electroshock with 22-45 volts for a duration of 4 seconds each minute for one hour each day. Group B was submitted to isolation stress and group A was the control group. The duration of the experiment was 137 days. Results: The adrenals weight was increased (group C vs group A, p<0.001; group B vs group A p<0.05), while urine hydroxyproline was reduced under stress. The calcium content of the mandible and the ratio between calcium content and mandible volume was de- creased (p<0.05 for both groups). Conclusions: Mandibular bone mass was affected by different kinds of stress and may represent a considerable parameter for the diagnosis, prevention and treatment of bone mass deficiency. Keywords: Mandible, Bone Density, Calcium Stress, Mice Original Article Hylonome The authors have no conflict of interest. Corresponding author: Christine Tesseromatis MD, MDD, Associate Professor of Pharmacology, Department of Pharmacology Medical School, Division of Oral Therapeutics, University of Athens, Mikras Asias 75 Goudi 11527, Athens, Greece E-mail: ctesser@med.uoa.gr Edited by: M. Bliziotes Accepted 1 July 2010