The McArthur enquirer. (M'arthur, Vinton County, Ohio) 1873-1884, 1873-05-14
behind the sacs of the milk-teeth.

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extensions backward of the bacl
part of the dental groove" Tha
part Of the primitive dental groov'
lying back of the last temporar,
molar follicle, remains open for .
time and in it is developed the frs
molar of second dentition. This il
enveloped or covered by similar sat
or cap as the preceding; it extends
backward forming a like cavity fol
the enclosure and development O
the second molar of replacement
After some time has elapsed the
cavity of reserve undergoes changes
fitting it for the reception and pro
lection Of the third molar or wis
dom tooth, which appears some time
in the interval between the ages O
II and 81 years.
The fourth or eruptive stage is
completed when the teeth are pro
truded from the sacs and make
their appearance through the gums.
The different classes of teeth of
"
the two dentitions make their APP
pearance in the following order, the
temporary dentition being enumera-
ted first.
The four central incisors from
five to eight months after birth:
the four lateral incisors, from seven
to ten months; the four anterior
molars from twelve to sixteen; the
cuspatii, Commonly called eye
teeth J, from fourteen to twenty; the
four posterior molars from eighteen
to thirty.six.
The eruption of the permanent
teeth takes place in time and order
as follows: First molars, from the
fifth to the sixth year; central in
cisors from the sixth to the eighth;
lateral incisors from the seven tn to
the ninth; first bicuspids from the
ninth to the tenth; second bicus-
pids from the tenth to the eleventh;
cuspidati, eleventh to the twelfth;
second molars, from the twelfth to
the fourteenth; third molars from
the eighteenth to the twentieth
Bell Harris.)
When a tooth is split apart a
is found in the crown or
thickest part. This cavity extends
through the root or roots of the
tooth, forming a canal as it is called
which ends in a minute foramen
which can ordinarily be seen with
the unassisted eye. Through this
little oriice small us it is, (some-
scarcely admitting the point
of a fine sewing needle enter an
and nerve, and also q vein
for the return of the blood which
enters for the nourishment of the
tooth-pulp, CASUALLY called the
nerve, but as we have seen but the
smaller portion Of it is really nerv-
Gus substance) which likewise sup
plies the hard portion of the tooth
with nutrient matter.
The sol id part of a tooth consists
structurally of three distinct parts,
ivory or dentine, which forms
the greater portion of the tooth;
the enamel which covers all the ex-
posed part of it, and the crusta pc
trosa or the hard crust, q substance
resembling true bone, which envel-
ops the root, beginning at the neck
Of the tooth where the enamel term
The dentine is a modification of
The osseous tissue, differing from it,
however, in chemical constitute on
and in structure. The glass reveals
numerous lines or delicate tubes
from the pulp to the pc
Of the dentine. These are
dentinal tubuli and are occu-
pied by delicate threads of nervous
called fibrill@. Sometimes
in cutting into the cavity of q
tooth whose pulp remains, pain is
felt; it comes from the cutting of
these fibrils, which may be in a
more or less inlamed condition.
The dental tubili do not extend in
to the enamel.
Chemical analysis reveals den
tine to consist of animal matter in
the proportion Of 20 parts to 70 of
mineral the former may be removed
calcining, and the latter by i'm
mersing in one Of the stronger ac-
ids for a time. The inorganic mat
ter consists chiefly Of phosphate and
carbonate Of lime.
The enamel is the hardest and
densist Of all animal productions,
only the smallest trace Of animal
matter being found in its compost
ton. 1t is deposited thickest on
the masticatinp surface and emitting