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OF THE BONY PART OF A TOOTH. 45
much harder than the most compact part of bones in general. (7)
((/) [In the following description of the minute structure of dentine
(termed, in the text, the bony part of a tooth), the account given by
Kolliker has been principally although not solely followed '.
The dentine, ivory, substantia eburnea, ebur, is of a yellowish white
colour, and appears in the fresh specimen to a certain extent transparent
or translucent. In the dried tooth it is white, and has a silky lustre,
from the circumstance that it is permeated in every part of its substance
by a series of microscopic tubes which, in that condition, contain air.
It consists of a matrix and of the tubes just mentioned, dentinal tubules,
dental canals, canaliculi dentium. The dentine alone bounds the pulp
cavity, with the exception of a small portion at the extremity of the root
and in the uninjured tooth it is never exposed, being covered everywhere
by enamel or cement. The matrix is perfectly homogeneous, showing,
according to Kolliker, no trace of organised structure. The dentinal
canals measure in width O'OOOG'" to 0-001'", some of those at the root
0-002'" : they commence by open mouths at the pulp cavity, and proceed
outwards throughout the entire thickness of the tissue. Each canal
appears to have a special wall in the shape of a yellowish ring, which
is generally visible when the tubes are transversely divided. Kolliker
believes, however, that the yellowish ring surrounding the tube is not
to be considered as the real wall. " The apparent walls," he writes, " of
the dentinal tubes, which are usually seen upon the transverse sections,
are not the true walls of the canals, but rings, the appearance of which
arises from this, that a certain length of the canals is always seen with
the microscope in the thickness of the section, never sufficiently fine to
obviate this effect ; and the short tubular segments being curved in
direction, a greater apparent thickness is thus given to the walls than
they really possess. If, upon a transverse section, the openings of the
canals be brought accurately into focus, we perceive, instead of a dark
ring, only a yellowish, very narrow edge; and it is this that I regard as
During life, the canals are generally believed
being the true wall." (1)
to be permeated by a clear, pellucid fluid; in the dried state, they
become filled with air, and appear as dark lines by transmitted, and
shining filaments by reflected light. The dentinal tubes undulate in
their course ; they present two or three larger flexures, and a great
number of smaller ones—according to Retzius as many as 200 in a line.
As they proceed outwards, they divide, branch, and anastomose. The
divisions, which are frequent near the origin of the tubes, are generally
dichotomous ; they may be repeated from two to five times or more—so
that one tube may form four, eight, sixteen, or more tubes. Their calibre
becomes diminished by division ; and they run in a nearly parallel
(1) Kolliker, op. cit., p. 292.
OF THE BONY PART OF A TOOTH. 45
much harder than the most compact part of bones in general. (7)
((/) [In the following description of the minute structure of dentine
(termed, in the text, the bony part of a tooth), the account given by
Kolliker has been principally although not solely followed '.
The dentine, ivory, substantia eburnea, ebur, is of a yellowish white
colour, and appears in the fresh specimen to a certain extent transparent
or translucent. In the dried tooth it is white, and has a silky lustre,
from the circumstance that it is permeated in every part of its substance
by a series of microscopic tubes which, in that condition, contain air.
It consists of a matrix and of the tubes just mentioned, dentinal tubules,
dental canals, canaliculi dentium. The dentine alone bounds the pulp
cavity, with the exception of a small portion at the extremity of the root
and in the uninjured tooth it is never exposed, being covered everywhere
by enamel or cement. The matrix is perfectly homogeneous, showing,
according to Kolliker, no trace of organised structure. The dentinal
canals measure in width O'OOOG'" to 0-001'", some of those at the root
0-002'" : they commence by open mouths at the pulp cavity, and proceed
outwards throughout the entire thickness of the tissue. Each canal
appears to have a special wall in the shape of a yellowish ring, which
is generally visible when the tubes are transversely divided. Kolliker
believes, however, that the yellowish ring surrounding the tube is not
to be considered as the real wall. " The apparent walls," he writes, " of
the dentinal tubes, which are usually seen upon the transverse sections,
are not the true walls of the canals, but rings, the appearance of which
arises from this, that a certain length of the canals is always seen with
the microscope in the thickness of the section, never sufficiently fine to
obviate this effect ; and the short tubular segments being curved in
direction, a greater apparent thickness is thus given to the walls than
they really possess. If, upon a transverse section, the openings of the
canals be brought accurately into focus, we perceive, instead of a dark
ring, only a yellowish, very narrow edge; and it is this that I regard as
During life, the canals are generally believed
being the true wall." (1)
to be permeated by a clear, pellucid fluid; in the dried state, they
become filled with air, and appear as dark lines by transmitted, and
shining filaments by reflected light. The dentinal tubes undulate in
their course ; they present two or three larger flexures, and a great
number of smaller ones—according to Retzius as many as 200 in a line.
As they proceed outwards, they divide, branch, and anastomose. The
divisions, which are frequent near the origin of the tubes, are generally
dichotomous ; they may be repeated from two to five times or more—so
that one tube may form four, eight, sixteen, or more tubes. Their calibre
becomes diminished by division ; and they run in a nearly parallel
(1) Kolliker, op. cit., p. 292.
