Page 143 - My FlipBook

CAEIES OF DENTIN. 69
same membrane, the two salts will pass through the membrane
in opposite directions until they have become equalized in the
two solutions. This process, when used to separate crystallizable
salts from colloid substances with which they may be com-
mingled, is known as dialysis, for it is found that such substances
as gums, resins, albumens, etc., which are not crystallizable, do
not readily pass through membranes in this way. Therefore,
if there is a solution of sugar in the saliva and a solution of
calcium lactate in the depths of a carious cavity, that part of
the matrix of the dentin which is already softened by the solu-
tion of its calcium salts, acts as a dialyzing membrane, passing
the sugar in and calcium lactate out. In this way, the growing
microorganisms receive sugar from the saliva, and lactic acid
(their waste product) which has become calcium lactate by com-
bination with the calcium salts of the tooth, is eliminated. This
process naturally goes on very slowly, so that weeks and months
are required for any considerable cavity to form, and often
several years. Figures 63 and 64 represent a dialyzer used to
obtain salts from the secretions free from the gummy substances
with which they are associated, for microscopic examination
of their crystals. Figure 65 is a photomicrograph of the salts
dialyzed from saliva and crystallized. Figure 66 is a photo-
micrograph, made by polarized light, of sugar dialyzed from a
solution and crystallized.
In penetrating into dentin microorganisms follow the den-
tinal tubules, simply growing into them as a grapevine would
grow through a lattice. The anastomosing loops from tubule to
tubule, which are plentiful near the dento-enamel junction, and
any other openings such as interglobular spaces which they
may encounter, are filled full as they go. There is much dif-
ference found in different teeth in the number and size of the
anastomosing loops from tubule to tubule. In some these are
plentiful, in others very much limited. In all, however, there
is a sufficient number of these near the dento-enamel junction
to afford a moderately free passage of microorganisms from
one tubule to another. In a considerable proportion of teeth
there are many small interglobular spaces along next to the
dento-enamel junction, known as the "granular layer of Tomes,"
through which microorganisms may readily grow. Therefore
among different teeth there are differences in the facility with
which microorganisms will spread along the dento-enamel junc-
tion. The organisms having gained access to the dentin by the
solution of the enamel, they grow into the dentinal tubules