Page 170 - My FlipBook

of the tooth, thus producing a broad, flat area of invasion
which would eventually produce a broad, shallow cavity.
The illustrations showed various comparative degrees of
rapidity of invasion by caries in these two directions, which
give differences in the forms of cavities, and yet not differ-
ing essentially in the plan of the invasion.
Photo-micrographs illustrating interglobular spaces in
the dentin were exhibited ; first showing the interglobular
spaces highly magnified, giving good views of the forms
of the individual spaces. These were seen to be spaces
about, or between, globules in which lime salts had not
been deposited. It was explained that dentin seemed to
be first laid down in globules and the spaces between these
were filled with lime salts later. The spaces represented
portions in which this filling-in process failed. The den-
tinal tubules were seen to pass through both the globules
and the spaces as though they did not exist. The spaces
are therefore not actually empty, but contain certain parts
of the normal basis substance not filled with lime salts.
The contents of the interglobular space are different, how-
ever, from the parts of the basis substance that has been
filled with lime salts, for it is found that while micro-organ-
isms will not penetrate the ordinary basis substance except
by the slow process of digesting it, they will grow into the
interglobular spaces as freely as into the dentinal tubules.
This was followed by photo-micrographs made with
lower powers of the microscope, which showed the dispo-
sition of the interglobular spaces in the dentin. This was
seen to be in layers which included portions of the dentin
tha4: was being formed at some given time during the growth
of the tooth. This was explained as being generally coin-
cident with some fault in the formation of the enamel.
Both are caused by some illness which for a time inter-
feres with nutrition, for which reason the deposit of lime
salts is faulty. It was further explained that an invasion
of micro-organisms along the dentinal tubules would, when
coming upon such a layer of interglobular spaces, grow
into them and fill them full, and follow them in preference
to the dentinal tubules, seemingly because they are larger
and give more space for the growth. It is for this reason
that we so often see in the infirmary those first molars

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