In micrometers, acids penetrate dentin to less than which depth?

• A. 0.5 mm
• B. 100–200 μm
• C. Less than 100 μm
• D. 2 mm

Answer: (C)

The key idea is how deep acids can demineralize dentin during bonding. In dentin, acid etching creates only a very shallow demineralized layer because diffusion into the mineralized matrix is limited and the smear layer plus tubule fluids hinder deeper penetration. With standard phosphoric acid etching used in dentistry, this demineralization typically stays under about 100 micrometers. That’s why the correct depth is less than 100 μm. Deeper penetration, such as hundreds of micrometers or millimeters, would not occur under normal clinical etching conditions and would risk weakening dentin rather than improving bonding.