Dentinal tubule diameter at the pulp is ____ um

• A. 0.5 um
• B. 1.0 um
• C. 2.5 um
• D. 3.5 um

Answer: (C)

Dentinal tubules are widest where they approach the pulp, because this region houses the odontoblast processes and the greatest potential for fluid movement between pulp and dentin. The diameter near the pulp is typically around 2.5 micrometers, with a general range about 2 to 3.5 μm. This makes 2.5 μm the best standard estimate for tubule diameter at the pulp. As you go toward the outer dentin, the tubules narrow toward roughly 0.5–1 μm. The larger near-pulp diameter helps explain higher permeability and sensitivity in that region, which is why the 2.5 μm value best fits the question.