Histology and tetracycline labeling of a single section of alveolar bone of first molars in the rat

We observed the histology and tetracycline (TC) labeling in a single fronta l section of alveolar bone of upper first molars of adolescent rats. A sing le injection of TC was administered intraperitonealy in adolescent rats. Af ter three weeks, the upper jaws were immersed rapidly in liquid nitrogen an d sectioned. Five micrometer unfixed, undecalcified frozen sections were cu t and observed by light and fluorescence microscopy. Frontal sections of th e upper first molar area revealed that the structural relationships among t he roots, the periodontal ligament and the alveolar bone, and also between the cervical enamel and the attachment epithelium were well preserved. The TC labeling lines in the sections were very clear and distinguished new bon e from old bone. The brightness of the lines differed among regions. An ana lysis of the brightness in the same section suggested a difference in the b one forming activity at the time of injection.