Mitochondria in Odontoblastic Processes

Abstract

THE odontoblastic processes of human dentin are projections of the odontoblast cytoplasm into spaces in the dense collagenous, highly mineralized dentin matrix¹. These projections can be up to several mm in length resulting in the cytoplasm being a long distance (2,000–3,000µ) from the odontoblast nucleus. The contents of odontoblastic processes in published electron micrographs have shown a varied appearance. In general they display a granular texture but do not contain recognizable cytoplasmic organelles^2–4. Most of these specimens were prepared with standard osmium fixatives which have a very poor penetrating ability. We have investigated the ultrastructure of dentin fixed with glutaraldehyde which is particularly favourable for the preservation of membrane systems and has good penetrating ability. A freshly extracted tooth (severed from its blood supply no longer than 8 min) was broken into small fragments with at least one dimension 0.5–1 mm thick. These were immersed in cold fixative containing 1.25 per cent glutaraldehyde in s-collidine buffered to pH 7.4–7.55 and adjusted to a final osmolality of 360 milliosmols. Samples were post-fixed in 4 per cent osmium tetroxide for 48 h and then decalcified in a nitric acid–formalin mixture⁵ for 12 h. They were then dehydrated in an alcohol series and embedded in ‘Epon’ B (ref. 6). Sections were cut with a diamond knife on an LKB ‘Ultratome’ and examined in an RCA EMU-3-G electron microscope.