Dead Tracts in Dentine — MFDS Part 1 MCQ

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HardPhysiologyDead Tracts in DentineMFDS Part 1

An unstained, dry ground section of a tooth is examined using transmitted light. A dark tract extends from an area of attrition along the course of dentinal tubules; adjacent sclerotic dentine appears relatively translucent. What best explains the dark appearance of the tract?

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Correct answer: E — The tubules have lost their vital contents and are air-filled

Explanation lettering: C = shown as A · D = shown as C · E = shown as D · A = shown as E

A is correct. Dead tracts occur when dentinal tubule contents, including odontoblast processes, degenerate after injury such as attrition or caries. In a dry ground section, the patent tubules contain air; the air–dentine refractive-index difference causes scattering and attenuation of transmitted light, giving a dark appearance. In contrast, sclerotic dentine results from intratubular mineral deposition and is relatively translucent because tubular refractive-index differences are reduced. Blood cells are not the characteristic content of dead tracts. Bacteria may enter tubules in carious dentine, but bacterial invasion is not required for a dead tract and does not define its characteristic appearance. Tertiary dentine is laid down at the pulpal aspect as a defensive response, rather than filling the affected original tubules.

Reference: Fish EW. Dead Tracts in Dentine. Proceedings of the Royal Society of Medicine. 1928;22(2):227–236. https://pubmed.ncbi.nlm.nih.gov/19986764/