Which factor is related to diffusion in dentin?

• A. Tooth color
• B. Dentin thickness
• C. Pulp vitality
• D. Root length

Answer: (B)

Diffusion through dentin is fundamentally about how far a substance must travel. Dentin thickness sets that distance: when the dentin is thin, molecules or ions can reach the pulp (or move outward) more quickly; when the dentin is thick, the diffusion path is longer and the rate decreases. While dentinal tubule openness and sclerosis can modulate permeability, the distance you must diffuse through—the thickness of dentin—is the primary factor among the options. The other choices don’t directly control diffusion through dentin: tooth color reflects dentin and enamel characteristics, pulp vitality relates to the health of the pulp rather than diffusion distance, and root length doesn’t determine diffusion through the dentin.