Induced hypoxia in rat pulp and periapex demonstrated by 3H-misonidazole retention

Cellular hypoxia may be a useful indication of tissue distress in the dental pulp that could be used to investigate the early stages of pulpal responses. Tritiated misonidazole (3H-MISO) is a marker which preferentially labels cells with decreased oxygen tension (hypoxia). The experiments reported here were carried out to determine whether this agent could distinguish between hypoxic and normoxic pulp and periapical tissues. Rats were injected intra-peritoneally with either 3H-MISO, unlabeled MISO, or saline, then divided into normoxic, hypoxic, and control groups. Normoxic animals were maintained at ambient pressure. We induced hypoxia by maintaining animals in a hypobaric chamber at 0.5 atm for 24 hrs. 3H-MISO retention was assessed by quantitative analysis of tissue autoradiographs. 3H-MISO retention rates in normoxic animals showed little variation except for increased retention in mature ameloblasts and immature odontoblasts in the continually erupting incisor. In both incisor and molar pulps, hypobaric hypoxia significantly increased 3H-MISO retention when compared with normoxic controls. Hypobaric hypoxia also resulted in intense 3H-MISO retention in cellular cementum, periodontal ligament, osteocytes, and, occasionally, in molar pulp horn odontoblasts. This study demonstrated that, with standard autoradiographic techniques, 3H-MISO can label induced hypoxic disturbances in the pulp and surrounding periodontium.