Page 617 - My FlipBook
P. 617
DENTAL RIDGE. 627
be remembered that the cells which occupy the central portion of the
enamel organ are the older cells which have been pushed off' from the
sides by the development of the infant layer, which constitutes the
walls of the organ. The central mass of cells are thus enclosed in
a sac as are the cells of sebaceous glands. The latter, under this con-
dition, pass through a retrograde process and become, through fatty
degeneration, the oily material secreted by the glands. The cells of the
enamel organ become infiltrated by fluid instead of fat ; this fluid is
freely soluble in the fluids whicii are used to harden the tissues. The
cells undergo a sort of retrograde process due to the abnormal confine-
ment between the tunics of the enamel organ, but not the same as that
found in the glands above referred to. The shrinkage due to the giv-
ing up of this water results in the stellate form they assume after death.
In the meshes of the stellate cells prepared by the osmic-acid method are
seen numerous minute granular bodies which have a high refractive
power ; if a few drops of dilute nitric acid be put on the slide near the
edge of the cover-glass and allowed to run under by cai^illary attraction,
these granular bodies will disappear, and at the same time large numbers
of bubbles will accumulate and force themselves out from under the cover-
glass. In this experiment Ave have a positive demonstration of the ])res-
ence of carbonate of lime in the meshes of the stellate cells of the fully-
sufficient quantity to result in completely-calcified tissue, but are held
in a state of suspension ; as the meshes of the stellate reticulum shrink
the graimles of lime are brought nearer together, and by approximation
stiffen the tissue. The presence of a non-shrinkable material in the
meshes of the stellate cells of the enamel organ accounts for the different
results, as regards shrinkage, in the preparation of tissues.
Previous to the beginning of development of the enamel we find little
or no shrinkage of tlie enamel organ during the hardening and decalci-
fying processes, provided the hardening is accomplished first. It is only
after the stellate cells have given up a ])ortion of their lime salts, either
by forming enamel or by being decalcified l>efore hardening, that any
considerable shrinkage occurs. The shrinkage in the first instance is
localized in that portion nearest the forming enamel ; in the latter it is
general. The shrinkage on the part of the enamel organ, in any case,
is more apparent than real, the space formed by the separation of the
enamel from the ameloblasts being largely due to the greater shrinkage
of the dental pulp, which draws the formed dentine and enamel down
from the sides of the cone-sha])ed enamel organ. If the stellate reticu-
lum is, as has been stated, very rich in albumen, and does not contain
calcific material in large quantities, there would be a very great shrink-
age in preparation, due to the rapid taking up of its water by the acids
used in decalcifving, which is not the case previous to the commencement
of the formation of the enamel. But after calcification has begun and
the stellate reticulum has given up a portion of its lime salts, then more
or less shrinkage is noticed ; or if decalcification is first accomplished
by hydrochloric acid, which has no hardening property, and the tissue
is afterward hardened in alcohol, we notice the same phenomenon,
