Tooth development and dental anatomy: order of hard tissue formation: practice question

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Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

A. Predentine is laid down first and signals the inner enamel cells to start secreting

Odontoblasts differentiate first under the influence of the inner enamel epithelium and lay down predentine. The predentine and early dentine then induce the inner enamel epithelial cells to become secretory ameloblasts. This reciprocal induction explains why the first enamel appears on a base of dentine.

Option by option

• A. Predentine is laid down first and signals the inner enamel cells to start secreting (correct)

  Correct. Dentine formation begins first and induces ameloblasts to secrete enamel.

• B. Dentine and enamel matrix start together because both layers differentiate at once

  The two do not start simultaneously, since ameloblast secretion depends on the dentine already present.

• C. Enamel matrix is laid down first and signals the papilla to form odontoblasts

  Reversed. Ameloblasts only begin secreting after dentine matrix exists beneath them.

• D. Dentine forms only after enamel formation of the crown is fully complete

  The two tissues overlap in time, so dentine does not wait for enamel to be complete.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

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