A

Intrinsic dentine permeability is mathematically governed by variables in Fick’s and Poiseuille’s equations—namely dentine thickness (tubule length), the diffusion coefficient of the substance, and pressure-driven fluid convection through the tubules. The smear layer is an extrinsic surface deposit that can modify permeability but is not one of the basic governing variables included in these equations [Reeder et al., 1978, PMID 277512; Pashley, 1994, PMID 7702470].