The extent of the odontoblast process in the cat.

Earlier work has shown that in the dentine of cats perfused with aldehyde fixatives for short periods the odontoblast process seems to be limited to inner dentine. This could possibly have been an artefact due either to inadequate penetration of the fixative or shrinkage of the cells. Experiments prolonging the duration of the fixation and raising the concentration of the fixatives, examining dentine from regions and species where it is narrow and more accessible to fixatives, and looking at dentine fixed by immersion both in situ and after excision, all showed the process to be limited to inner dentine. Measruing glutaraldehyde penetration through model dentine and also through dentine in the perfused animal showed that this fixative penetrates the dentine well. Variations in fixative osmotic pressure, while having a profound effect on cells and processes in vitro and causing changes in cell shape in the intact animal, do not neasurably alter the extent of the odontoblast process. The conclusion is that the odontoblast process in the cat is limited to the pulpal half of the dentine. As a consequence, no cellular mechanism can be involved in the transmission of stimuli across the outer dentine.