What is the penetration depth of acids into dentin in micrometers?

• A. Less than 100 μm
• B. 100–200 μm
• C. 0.5 mm
• D. 1 mm

Answer: (A)

Acid diffusion into dentin is limited by its structure and the barriers that protect the pulp. Dentin is full of tubules, but the smear layer, mineralized matrix, and buffering capacity of dentin slow and limit how far acids can demineralize. Under typical clinical acid challenges (like standard etchants or acidic challenges in restorative procedures), the resulting demineralized layer remains shallow—on the order of tens of micrometers—and rarely reaches hundreds of micrometers. That’s why the penetration depth is best described as less than 100 μm. Deeper diffusion, such as 0.5 mm or 1 mm, would imply a much greater risk to the pulp and isn’t characteristic of common exposures. The range of 100–200 μm is possible only in unusual or prolonged/strongly acidic conditions, not in standard situations.