Relationship between the quality of fixation and the presence of stippled material in newly formed enamel of the rat incisor.

Extracellular accumulation of a granular material that is presumed to be an organic "precursor" to mineralized enamel has been reported. This material, generally referred to as ""stippled material," was observed mainly after immersion fixation with osmium tetroxide. In studies with perfusion fixation, the presence of stippled material was inconsistent. Therefore, it appeared that the occurrence of stippled material was dependent on the method of fixation. To test this assumption, tissues were fixed by immersion in either osmium tetroxide or glutaraldehyde and by perfusion with either glutaraldehyde or a mixture of acrolein, glutaraldehyde, and formaldehyde. It was found that as the quality of cellular preservation improved, the occurrence of stippled material decreased. Since no stippled material could be found in material judged to be well fixed, it was concluded that stippled material is not an extracellular precursor to mineralized enamel, but is a breakdown product resulting from poor fixation.