thought to respond to stimuli that displace the fluid in the
dentinal tubules resulting in the characteristic short, sharp
pain of dentin hypersensitivity [7]. This type of fluid move-
ment can be quantified by measuring the hydraulic conduc-
tance of dentin [31]. Thus, dentin with a high conductance
has a low resistance, and vice versa. Human studies showed
that the patency of the dentinal tubules is an important
characteristic of sensitive dentin [6], with a significantly
positive correlation between the density of tubules and the
pain responses induced from exposed cervical dentin surfa-
ces [32]. Further studies of extracted teeth provided com-
pelling evidence for this requirement with sensitive teeth
having many more (eight times) and wider (two times)
tubules at the buccal cervical area compared to non-
sensitive teeth [33]. Additionally, dye penetration to the
pulp was only seen in sensitive teeth [34]. Although number
and radius of tubules are relevant to fluid flow and therefore
sensitivity, tubule radius is probably more important as fluid
flow is proportional to the fourth power of the radius [35]
hence if the diameter is doubled, the tubule fluid flow
increases by 16-fold. This explains the concept of why
tubular occlusion, of whatever nature, is thought to reduce
the pain of dentin hypersensitivity. These features of dentin
hypersensitivity lesions clearly have important implications
with respect to the possible aetiological factors involved and
the development of preventive and management strategies
for the condition.