Page 57 - My FlipBook

OP THE STRUCTURE OF A TOOTH, ETC. U
thinner on the sides, as it approaches the neck, where it tcrmi-
of dentine on which they rest, it follows that their direction will be
horizontal ou the sides of the tooth, vertical on the summit of the
crown. Fibres occupying all the intermediate positions between the
vertical and horizontal will be seen in examining the enamel as itpassea
from the grinding or cutting surface downwards to the side of the tooth.
We have said that the fibres, for the most part, extend throughout the
entire breadth of the enamel, and this is undoubtedly true of the greater
number ; but, as the surface of the dentine is more or less conical, and
no separation of the fibres takes place as they proceed outwards, neither
has any increase in their thickness been observed, we cannot doubt the
existence of shorter supplemental fibres, which fill up the intervals
that otherwise would necessarily occur. Such supplemental fibres, how-
ever, are not easily demonstrated, owing to the waved course of the
fibres, and the consequent difficulty in tracing a series of them through-
out their entire length. It is almost impossible to isolate for any
distance the enamel fibres in the adult tooth, although they can be
readily seen in transverse and longitudinal sections : it may, however,
be more readily accomplished in the softer enamel of young or develop-
ing teeth. The breadth of the enamel fibre is, according to Kolbker,
01)0 15'" to 0-0022"'. Isolated prisms obtained from young enamel are seen,
especially after treatment with dilute hydrochloric acid, to have a slightly
varicose outline, and to be marked with transverse lines, or strise, which
occur at tolerably regular intervals, and produce an appearance similar
This striated aspect led Mr
to that of a " colossal muscular fibrilla." (1)
Nasmyth to the opinion that enamel consisted of "nothing more than a
mass of cells arranged in rows, and fitted closely together, but held only
Eetzius and others
slightly in contact by a thin web of membrane." (2)
have also believed the transverse marks to be the indications of pre-
existing walls of coalesced cells. Kolliker, on the other hand, maintains
that they " are the expression of the growth of the fibres through appo-
sition, or are not the expression of their composition of cellules." (3) Mr
Tomes observes that the transverse strise are much more strongly marked
in some specimens than in others, and that they are most evident in
those portions of enamel which, when seen by transmitted light, are of a
brown colour. This condition will sometimes be found in certain un-
healthy subjects to pervade the entire enamel. In such cases he has
found the markedly striated appearance to result from the occurrence,
at regular intervals, of minute granular masses in the central portion of
the enamel fibres. These masses are comparatively opaque, and the
alternation of opaque and transparent parts gives the appearance of
striatum. This appearance is rendered more distinct by the use of
(1) Kolliker, op. cit. , p. 205.
(2) Nasmyth, op. cit., p. 83.
(3) Kolliker, op. et loc. cit.