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The alteration of mast cell staining due to various fixatives and demineralizing agents.

— The effect of several fixatives (Carnoy's, cyanuric chloride, and formalin) and of several demineralizing agents (formic acid, nitric acid, and EDTA) on rat mast cells which were then stained with hemalum-eosin, Giemsa, methylgreen pyronin, toluidine blue, alcian blue, PAS, and acridine orange was studied. Furthermore, ultrastructure of the mast cell was investigated. In the materials which were not exposed to demineralizing agents, mast cells could be equally well demonstrated by all staining methods regardless of fixative, although the PAS reaction was weak. After exposure to demineralizing agents, the best results were obtained with cyanuric chloride fixative and EDTA; the poorest results with formalin fixative and nitric acid; however, even in the latter specimen stained with hemalum-eosin, mast cells could be recognized. Giemsa stain was well preserved regardless of fixation and demineralization, but mast cell fluorescence was totally destroyed by the acid demineralizing agents. In human material demineralized in EDTA, stained with toluidine blue, authentic mast cells were found in gingiva and periodontal ligament but not in pulp tissue in the same block. This study allowed us to evaluate the presence of mast cells in any material treated according to the methods described. It allowed the conclusion that mast cells very infrequently occur in the pulp tissue, although they are abundant in other oral tissues.