In the context of dentin as a barrier to diffusion, which statement is true?

• A. Increased enamel thickness
• B. Larger pulp chamber volume
• C. Increased dentin thickness
• D. Higher fluoride content

Answer: (C)

Dentin acts as the diffusion barrier primarily because the distance a molecule must travel through dentin directly affects how much diffuses through to the pulp or outward. Increasing dentin thickness lengthens that diffusion path, so the rate at which substances move through dentin decreases. This aligns with diffusion principles: the flux of a substance is inversely related to the thickness of the barrier, so more dentin means a stronger barrier to diffusion.

Dentin contains tubules that can allow some diffusion, but when the dentin is thicker, the overall diffusion rate drops because the longer path and greater mineral content hinder movement. That’s why the statement about increased dentin thickness being the true barrier is the best answer.

Other options don’t fit as well. Enamel thickness affects diffusion through the outer tooth structure, not the dentin’s own barrier properties. A larger pulp chamber volume would increase the potential surface area for diffusion rather than strengthen a barrier. Higher fluoride content would influence diffusion gradients and availability, not enhance the barrier function of dentin.