Parathyroid gland deficiency is thought to contribute to the progression of periapical lesions, and alveolar bone destruction is associated with enhanced osteoclast activity. Parathyroid hormone (PTH) and calcitonin (CT) deficiency induced greater enlargement of alveolar bone destruction in periapical lesion in our study. The purpose of the present study was to investigate the relationship between osteoclast appearance and deficiency of PTH and CT in periapical bone destruction, Sixty 10-week-old female Wistar rats were divided into 22 parathyroidectomized (P-ect) rats, 22 parathyroidectomized and thyroidectomized (T & P-ect) rats and 16 non-ectomized (Control) rats. All experimental and control rats received a treatment of pulp exposure in both mandibular first molars, and all experimental samples were obtained at 1 and 3 weeks after treatment. Serial sections were cut and stained with hematoxylin and eosin for general histological finding. Appearance of osteoclast was identified by TRAP staining, and the number of osteoclasts was measured. It was found that periopical lesions of each experimental group (P-ect group and T & P-ect group) were characterized by the presence of abscess infiltrated by PMNs and macrophages after 1 and 3 weeks, and significant differences from the control groups were not found. The number of osteoclasts lining lesions was quantified at each time point. The osteoclast infiltration in the periapical lesion area was significantly different between the control group (21.1±11.1 cells) and P-ect experimental group (35.0±6.5 cells) after 1 week. The appearance of osteoclasts in the P-ect (42.0±11.7 cells) group and T & P-ect experimental group (37.3±20.0 cells) was compared with the control group (23.0±15.5 cells), and the significant difference increased by 3 weeks. The results showed an increase of osteoclast and periapical bone destruction in the P-ect and T & P-ect rats. The parathyroid and thyroid gland deficiency inducted the development of osteoclast, causing the periapical bone to increase.
