Prospective study of patients with medically related osteonecrosis of the jaw admitted to the Maxillofacial Surgery Clinic, St. Marina University Hospital, Varna University was conducted in 24 patients with bisphosphonate treatment with (13 pts) and without(11 pts) osteonecrosis of the jaw, biomarkers of bone metabolism vitamin D, osteocalcin, C-terminal telopeptide mature Type I collagen (CTX) were studied. There were low vitamin D levels, low normal levels of osteocalcin and C-terminal telopeptide of mature type I collagen (CTX). There were no statistical differences between MRONJ + and MRONJ-, but the odds ratio showed an increased risk of medically related osteonecrosis of the jaw 3.2 higher with osteocalcin levels below 7.8 ng / ml and 1.92 times higher with CTX values below 0.150 ng / ml.