Induced Hypoxia inRatPulpandPeriapex Demonstrated by3H-Misonidazole Retention

Cellular hypoxia maybeauseful indication of tissue distress inthedental pulpthatcouldbeusedto investigate theearly stages ofpulpal responses. Tritiated misonidazole (3H-MISO) isamarkerwhichpreferentially labels cells withdecreased oxygentension (hypoxia). The experiments reported herewerecarried outtodetermine whether this agentcoulddistinguish between hypoxic and normoxic pulpandperiapical tissues. Ratswereinjected intra-peritoneally witheither 3H-MISO, unlabeled MISO,or saline, thendivided intonormoxic, hypoxic, andcontrol groups. Normoxicanimals weremaintained atambient pressure. We induced hypoxia bymaintaining animals ina hypobaric chamber at0.5atmfor24hrs. 3H-MISO retention was assessedby quantitative analysis of tissue autoradiographs. 3H-MISO retention rates innormoxic animals showedlittle variation except forincreased retention inmatureameloblasts andimmatureodontoblasts inthe continually erupting incisor. Inbothincisor andmolar pulps, hypobaric hypoxia significantly increased 3H-MISO retention whencompared withnormoxic controls. Hypobaric hypoxia alsoresulted inintense 3H-MISO retention incellular cementum,periodontal ligament, osteocytes, and, occasionally, inmolarpulphornodontoblasts. Thisstudy demonstrated that, withstandard autoradiographic techniques, 3H-MISO canlabel induced hypoxic disturbances inthepulpandsurrounding periodontium.