assumed the forms of the crowns of the teeth they represent.
There is also a narrowing or constriction taking place at the
bases of the papillae, forming a kind of neck at the free border
of the enamel organ (Fig. 3).
22 OPERATIVE DENTAL SURGERY
Sixteenth Week.
The next important change in the process of development of
the embryonic tooth is seen at about the sixteenth week, when
a tiny but well-defined cap of calcified dentine is seen at the tips
of the incisors and canines, and about a week later in the molars.
Throughout all the stages we have gone through it must be
understood that the enamel organs and dentinal papillae are in
a soft cellular condition, all parts being in a full active condition
of proliferation or multiplying cells. At this period we notice
calcification of a small portion of dentine in the deciduous teeth
mentioned above. Calcification is the term applied to the depo-
sition of calcic or lime salts which form the hard tooth tissue.
It will also be noticed that the dentine is the first part to harden
or calcify. Calcification has not yet begun in the ameloblasts of
the enamel organ, although they are now fully developed and
well defined. The epithelial cord is still attached to the enamel
organ, but the sac is not yet closed (Fig. 4).
There are now two interesting processes at work, one in the
enamel papillae and the other in the dentinal papillae.
The papillae, having been formed within the enamel organ, a
beautiful layer of regular, epithelial cells which produce the hard
enamel rods are now to be seen fully developed and well defined.
Within them appear stellate or star-shaped bodies . The cells of this
beautiful layer are called ameloblasts or enamel-producing cells.
The papillae also having been formed within the dentinal
bulbs, there is now a layer of formative dentine producing cells
fully developed called odontqblasts. They also constitute the
outer layer of the dental pulp, and are columnar in form. They
do not enter the dentinal papilla but remain at its base and send
into it numerous finely branched processes, which run parallel
to each other and which become like so many little channels in
the bony substance.
Although the ameloblasts make their appearance first, calcifi-
cation does not take place in them until after the odontoblasts
have formed a cap of calcified dentine upon which the enamel
rods are to rest. Under the microscope minute glistening bodies
are seen, which indicates the near approach of the process of
calcification .
Another very important development takes place about this
time. The epithelial cords which penetrated the deep tissues
A DESCRIPTION OF THE EMBRYONIC DENTITION 23
and ultimately formed the dental follicles of the deciduous teeth
are now seen to have buds appearing upon them on their lingual
sides and above them in position that is to say, between the
existing follicle and the Malpighian layer. These buds become
FIG. 4. SECTION THROUGH THE LOWER JAW OF A FCETAL PIG.
(Sewill's " Dental Surgery.")
This preparation corresponds with the phase of dental evolution existing
in the human embryo at about the fourth month. (From a prepara-
tion by Mr. Hopewell Smith.)
A, Oral epithelium; B, deeper layer of epithelium; C, deepest layer of
epithelium (rete Malpighii); D, neck of enamel organ (primitive tooth
band) ; E, internal epithelium of enamel organ and stratum inter-
medium; F, external epithelium of enamel organ; G, stellate reticu-
lum; J, permanent tooth germ; K, formed enamel; L, formed den-
tine; M, layer of odontoblasts ; N, basal layer of Weil; O, commencing
formation of dental pulp; P, epithelial sheath of Hertwig; R, artery;
S, vein; T, nerve fasciculus; V, bone of jaw; X, muscular fibres;
Y, periosteum of alveolus.
definite branches and form epithelial cords to furnish the enamel
organs for the ten anterior permanent teeth in each jaw. The buds
rapidly assume a pear-shaped form followed by the appearance of
the dentinal papillse as already described for the deciduous teeth.
2 4
OPERATIVE DENTAL SURGERY
Eighteenth or Nineteenth Week.
At the eighteenth or nineteenth week the sacs of the primitive
dental follicles are closed, and the follicles separate from their
epithelial cords, and from this time development goes on without
connection with the parent epithelial layer. The follicles of the
I
FIG. 5. SECTION OF LOWER JAW OF HUMAN FCETUS AT ABOUT THE FIFTH
MONTH. (Sewill's " Dental Surgery.")
(From a preparation by Mr. Hopewell Smith.)
A, Oral epithelium; B, neck of tooth germ; C, permanent tooth germ;
D, dental pulp; E, odontoblasts ; F, dentine; G, enamel; H, amelo-
blasts and stratum intermedium; I, tooth sac; J, alveolar periosteum;
K. stellate reticulum; L, muscular fibres of jaw; M, artery, vein, and
nerve in transverse section; N, bone of jaw; O, epithelial sheath of
Hertwig.
A DESCRIPTION OF THE EMBRYONIC DENTITION 25
permanent teeth remain attached to the cord from which they
had their origin, and sink deeper into the embryonal tissues, and
take their place beneath the follicles of the deciduous teeth,
which at a future period they replace.
I)
FIG. 6. SECTION OF LOWER JAW OF FOZTAL KITTEN WITH TEMPORARY
TOOTH AND PERMANENT SUCCESSOR IN SITU, x 24 DIAMETERS.
(Sewill's " Dental Surgery.")
This preparation corresponds with the phase of evolution in the most
developed teeth in the human infant at about the third month after
birth. (Photo-micrograph by Mr. Charters White.)
A, Gum; B, enamel; C, dentine; D, dental pulp; E, permanent tooth en-
closed in sac; F, jaw partly ossified, and section of inferior dental
artery and nerve.
Seventeenth Week.
The permanent molars do not develop from the epithelial cords
of the deciduous teeth. The follicle of the first permanent molar
develops from the epithelial cord springing from the posterior
end of the Malpighian layer of the mucous membrane, about the
seventeenth week, beyond the origin of the cord of the second
temporary molar (Fig. 5).
26 OPERATIVE DENTAL SURGERY
Second Month after Birth.
The second permanent molar is developed fiom a branch of
the cord of the first permanent molar at about the second or
third month after birth (Fig. 6).
Third Year.
The third permanent molar, or wisdom tooth, is developed from
a branch of the cord of the second permanent molar about the
third year after birth.
The development of the follicles of the permanent teeth are
the same as that described for the deciduous or temporary teeth.
We have endeavoured to describe briefly and clearly the
development of the teeth in the embryonic stages of the foetus.
It consists of the forming of the epithelial cords penetrating into
the deep tissues, then budding at the ends into the enamel-
forming organs and the dentine-forming papillae. Then branches
are formed on the sides of the epithelial cords which, in turn,
penetrate deeper still, and bud into the enamel and dentine-
forming papillae for the twenty permanent teeth, the dental
sacs or follicles ultimately becoming detached from the epithelial
cords and thereafter development proceeds from the dental pulp.
The permanent molars spring from an epithelial cord for the
first one, and branches from that to the twelve-year-old and again
from that to the wisdom tooth.
This description of the cellular development of the teeth will
have prepared us for the consideration of the actual structure of
them, as it is imperative that we should thoroughly understand
the nature of their normal condition before we can be in a position
to undertake the treatment of their morbid condition and their
ultimate restoration to usefulness.
CHAPTER III
THE STRUCTURAL FORMATION OF THE TEETH
THE enamel and dentine layers of the tooth crown having been
formed from their origin in the epithelium of the mucous mem-
brane, we should now observe that there is a definite change
taking place. The crowns have assumed their definite shape,
and the layers now consist of beautiful tubular-shaped cells
ready for the deposition of the hardening material composed of
lime or calcium salts, which will cause the solidifying of the
complex structure, and which when completed is apparently, to
the uninitiated, a solid tooth. The enamel layer now consists of
ameloblasts and the dentinal layer of odontoblasts.
The Existence of Temporary Cellular Organs for the
Deposition of Hardening Materials.
The two layers are formative cells for a specific purpose, and
that is, to form the hard enamel rods, and also the inner dentinal
tubes. They work by depositing the calcium salts, layer upon
layer, and decreasing in size as their depositing work is completed.
The ameloblasts and odontoblasts probably become absorbed.
The formation of the root is now coming into being, but is the
creation of the foster-mother of the tooth viz., the dental pulp.
The follicles or capsules containing the crowns having separated
from their epithelial origin at the eighteenth or nineteenth week
of foetal life, the completion of the tooth is now thrown on to the
dental pulp.
The Formation of the Tooth transferred to a Foster- Parent.
The dental pulp, therefore, is a very interesting part of every
tooth, as its chief work is the formation of the roots and the com-
pletion of the crown. It appears as a streak at the centre of the
tissue of the dentine-forming organ, and develops into a large,
round, bulbous body as large as the base of the crown. It
27
28 OPERATIVE DENTAL SURGERY
becomes smaller in size, and elongated according to the shape of
the completed tooth. Examined under the microscope, there
can be seen the matrix or basic substance of the pulp. Its mass
is composed largely of undeveloped, soft connective tissues,
containing numerous cellular elements of rounded, oval, and
spindle forms, and with hairlike processes.
The closing round or invagination of the dental follicle is
completed by a surrounding membrane. The cells which
stretch out from the base of the dentinal papillae envelop the
sides of the enamel organ, thus forming a complete sac or follicle.
This sac at first appears to be an extension of the cellular activity
of the dentinal papilla. The cells forming the membrane spread
outwards and upwards, gradually enveloping the whole organ.
When the follicle is fully developed the sac membrane, called
the dental sacculus, consists of two layers, an outer one and an
inner one. The inner one contains the cells which form the
cementum of the root. It is of a soft and embryonic nature, and
rich in cellular elements. The outer membranous layer becomes
the peridental membrane or dental periosteum. This consists
of a fairly dense fibrous connective-tissue structure. When the
tooth is fully formed and finally completed the dental perios-
teum becomes the means of attachment of the roots of the teeth
to their sockets. Additional layers of cementum are added from
time to time from this peridental membrane, as will be seen in
the case of exostosis of the roots of the teeth as the result of long-
continued periostitis. On the other hand, absorption of the
roots of the teeth, when the milk teeth are shed, is due to the
action of the osteoblasts contained in the dental periosteum.
During the time occupied by the development of the teeth
another process has been taking place. The upper and lower
jaws have been developing from their original buds or processes
(see p. 18). We must now bring this process into line with the
completion of the dental follicle, showing how they meet together
and develop one with the other, before proceeding with the periods
of dentition at various ages of the patient.
The second or permanent teeth which succeed and take the
place of the deciduous or temporary ones are called " successional
teeth." The permanent molars are called "superadded teeth."
The buds for the successional teeth are formed on the original
epithelial cords of the temporary teeth, and go through the same
processes that we have already described regarding the dental
THE STRUCTURAL FORMATION OF THE TEETH 29
follicle. The successional follicles remain attached to the cords
from which they had their origin, which were above the deciduous
teeth follicles, and then sink deeper into the embryonal tissues,
taking their places below the deciduous teeth follicles, which they
replace at their due time The cords of the superadded teeth
or molars have been described on p. 22.
Origin and Development of the Jaws.
The foetal head, about the eighteenth day after conception,
has a very large open cavity where the parts of the face ultimately
develop. The sides of the head and the region of the orbits
present a number of tubercles which develop into the orbits,
the nose, and the upper and lower jaws. In the cavity of the
mouth, as the soft cellular bones develop, they become invested
with deep soft tissues in which the dental follicles are developing,
but the follicles have no connection whatever with the developing
bones of the jaws in these early stages.
The upper jaw or superior maxilla is seen in the embryo at
about the eighteenth day after conception by the development
of four tubercles near the central portion of that surface of the
rudimentary head which is destined to form the face. These
four tubercles are really two pairs, one pair on each side of the
head. They are called the superior or frontal processes, or
tubercles, and the lateral oblique or maxillary processes. The
superior processes elongate downward and approach each other
towards the centre of the face, where they finally join about the
twenty-fifth day. The lateral processes develop in a similar
way, at about the twenty- eighth day, and meet the superior
processes, uniting with them to form the lateral halves of the
rudimentary superior maxillary bone, palate bones, the cheeks,
the lateral portions of the upper lip and the soft palate. The
non-completion of the fusion causes the condition known as
cleft palate and hare-lip.
At the same period the lower jaw, or mandible, or inferior
maxilla, develops from one pair of tiny buds or processes situated
in the sides of the head about the position of the lower region of
the tongue. They develop forward and meet at the centre of
the chin or symphysis, about the twenty-eighth day, thus com-
pleting the mandibular arch.
These processes develop a small cartilaginous band which makes
30 OPERATIVE DENTAL SURGERY
its appearance about the end of the fourth month in the centre
of the thickness of the rudimentary jaw. This is called Meckel's
cartilage. The function of Meckel's cartilage is to give stability
and form to the mandible until the jaw is fully developed and
ossified, when it disappears either by absorption or calcification.
This really acts as a strengthener, in a similar way that we put
a strengthening wire into a lower wax bite when making a denture
to prevent it spreading.
The bones of the body are originated in two ways; one is
called intra-membranous and the other intra-cartilaginous.
The upper jaw is developed from membrane, but the lower jaw
is developed partly from cartilage and partly from membrane.
The dental follicles of the teeth have penetrated the soft
tissues in which they have developed, and are in such a position
that the dental borders of the rudimentary jaws approximate to
them and close up and around them to form the tooth crypts
(Fig. 7). These bony crypts completely enclose the follicles,
which are round in shape, until their time is due to move towards
their places in the dental arch of the surfaces of the jaws. As
the movement proceeds the alveoli or sockets are then formed
according to the final shape of the completion of the roots.
The stages of the calcification of the roots of every tooth should
be noted by every dental operator in dealing with children's
teeth, as serious trouble can be caused through not taking these
stages into consideration both in filling teeth and in regulating
them.
The root of the tooth is completed by the elongation of the
pulp, which takes between four and six years to accomplish
after the eruption of the crown at the gum margin. Accom-
panying the very complex changes in the formation of the teeth
within the jaw is an equally complex process taking place within
the bone itself, and the nature of these changes is of vital import-
ance in considering any operative procedure on children's teeth.
A glance at the plate showing a " child's skull " will at once
awaken appreciation of this point. The cubic space occupied by
the temporary or deciduous teeth, coupled with the crowns of
the permanent ones, leave very little actual bony process which
must obviously be weakened at every point, especially in
the legion of the lower canines and six-year-old molars. The
deciduous or temporary teeth are similar in form to the permanent
ones, but have slight differences which are characteristic of
THE STRUCTURAL FORMATION OF THE TEETH
them. They are whitish in colour, and the enamel is more
bulbous, and ends somewhat abruptly at the neck. The roots
also are more conical and end sharply to a round point as in the
canines, or a flattened sharp end as in the centrals and molars.
MALPIGHIAN
ENAMEL OR6AN
BUDS
ENAMEL FORMING
_ ORGANS
EPITHELIAL
_ /-none
SUCCE&S/ONAL,
- ENAMEL BVDS
DENTINE OR&dltt
COMPLETED
FOLLICLES
SEPARATING
CORDS
SUCCESSIONAL
DENTINE ORGANS
BONE CELLS FORMING
CRYPTS AROUND FOLLICLES
I WISDOM
I I TOOTH
snt VEAR
MOLAR !
TWELVE YEAR
MOLAR
FIG. 7. SCHEME SHOWING DEVELOPMENT OF FOLLICLES
The process of eruption of the teeth is attended by changes in
the bone of the jaws surrounding them (Fig. 8). When the
calcification of the tooth tissues is sufficiently advanced to allow
of the pressure to which they will be subsequently subjected, the
32 OPERATIVE DENTAL SURGERY
process of eruption or upward movement commences. The
tooth makes its way through the bone upwards to the gums.
The gum is absorbed by the pressure of the crown of the tooth
FIG. 8. SECTION OF LOWER JAW OF KITTEN, WITH TEMPORARY CANINE
FULLY ERUPTED AND PERMANENT SUCCESSOR IN SITU. x 10.
(Sewill's " Dental Surgery.")
This preparation displays the conditions immediately after complete
eruption of a temporary tooth before absorption of the root has
commenced. (Photo-micrograph by Mr. Charters White.)
A, Deciduous canine ; B, mucous membrane of germ ; C, inferior maxilla
cartilaginous with islands of forming osseous tissue; D. permanent
canine in its sac; E, inferior dental canal, and section of dental artery
and nerve.
against it, which is itself pressed up by the increasing size of the
fang. At the same time the bony septa or walls of the alveolar
sockets between the dental sacs or follicles, which at first are
THE STRUCTURAL FORMATION OF THE TEETH 33
FIG. 9. INFANT'S SKULL AT BIRTH.
A, Front view; B, side view.
34
OPERATIVE DENTAL SURGERY
FIG. 10. CHILD'S SKULL.
Front view. Aged 5^ years.
Photographed by Mr. Geo. Houlson from a skull in his possession.
(From the Mouth Mirror.)
fibrous in structure, become ossified or calcified and constitute
the alveoli. The alveoli in this way become firmly compacted
against the necks of the teeth and afford a solid basis of support.
THE STRUCTURAL FORMATION OF THE TEETH 35
FIG. ii. CHILD'S SKULL.
Side view. Aged 5^ years.
Photographed by Mr. Geo. Houlson from a skull in his possession.
(From the Mouth Mirror.)
Periods of Eruption of Temporary and Permanent Dentition
compared.
The ages of eruption of temporary or deciduous teeth and
those of the permanent ones may be seen at a glance by the
table on p. 36. This gives the approximate period of the tem-
porary ones and the permanent teeth which replace them. These
are termed " successional permanent teeth." The remaining ones
are called "superadded permanent teeth" (see p. 28).
OPERA TI VE DENTAL S URGER Y
TABLE OF DENTITIONAL ERUPTION.
TEMPORARY LOWER.
(Ten in number.)
Lower central incisors
lateral incisors
canines
first molars
second molars
Months.
6 to 9
15 to 21
16 to 20
15 to 21
20 to 24
PERMANENT LOWER.
(Sixteen in number.)
Successional.
Replaced by first bicuspids
Replaced by second bicus-
pids . .
Superadded.
First permanent molars . .
Second permanent molars
Third or wisdom molars . .
Years.
6
7
II to 12
6
12
15 to 30
TEMPORARY UPPER.
(Ten in number.)
Upper central incisors
,, lateral incisors
, , canines
,, first molars
second molars
Months.
8 to 10
8 to 10
16 to 20
15 to 21
20 to 24
PERMANENT UPPER.
(Sixteen in number.)
Successional.
Replaced by first bicuspids
Replaced by second bicus-
pids
Superadded.
First permanent molars . .
Second permanent molars
Third or wisdom molars . .
Years.
7
7
10 to 13
9
10
6
12
15 to 30
TEMPORARY TEETH.
Completion Absorption
of Roots. Begins.
PERMANENT TEETH.
Years.
Years.
Centrals
3
4*
Centrals
Laterals
3
4*
Laterals
Canines
5
6.V
Canines
First molars . .
4
5i
First bicuspids . .
Second molars
5
6*
Second biscuspids
Six-year molar . .
Twelve-year molar
Wisdom teeth
Completion
of Roots.
Years.
10
ii
13 to 14
12
12
9
16
20 tO 30
THE STRUCTURAL FORMATION OF THE TEETH 37
Symptoms of Normal and Abnormal Dentition.
Incidents of dentition are numerous, and pathological changes
take place which lead to serious systemic conditions, and which
sometimes terminate fatally.
In normal dentition there are slight systemic conditions
accompanying these changes, such as restlessness, failure of
appetite, elevation of temperature of the mouth; and the young
child is constantly putting its fingers into its mouth. There is
also a constant dribbling of saliva or a superabundance of it in
the mouth.
In abnormal cases which may be accelerated or even caused
by exposure to cold, and also indigestion, the symptoms of this
may be indicated by a hot skin, gums red and swollen, high fever,
diarrhoea, eruptions on the skin, and sometimes an ulcerous
condition of the tongue, cheeks, and the gums. There is also
irritability of temper and great pain, disturbed sleep and wake-
fulness, great thirst, and oftentimes these conditions lead to
convulsions, and if not checked or relieved by a medical man,
end fatally.
Dentition is more favourable in winter than in summer, as the
child is not so prone to affections which are produced in hot
weather, such as diarrhoea. On the other hand, during winter
there is the danger of the child cutting its teeth with bronchitis,
croup, pneumonia, or a severe cold. These conditions must be
watched and treated by the doctor.
The signs of eruption of the teeth are hot, red, and inflamed
gums, increased saliva, a hard tension of the gums, and later a
peculiar whiteness caused by the pressure on these tissues by
the advancing teeth. Convulsions in a child while teething may
even occur in the dental chair, and if there are undoubted signs
of an erupting tooth, especially indicated by finding a cusp or
cusps sticking through the tightened mucous membrane it may
be instantly relieved by lancing the gums over the particular
tooth so as to ease the pain by relieving the pressure at the gum
surface. The gums are sometimes extraordinarily tough, and
lancing is a definite way of giving relief. For front teeth one
incision along the cutting edge is sufficient, in canines two cross
cuts, and in multicusped teeth a star-shaped incision is suitable.
With the eruption of the permanent successional teeth the roots
of the temporary or deciduous ones are absorbed by the solvent
38 OPERATIVE DENTAL SURGERY
action of a secretion from a fleshy tubercle or layer developed
from the sac of the permanent tooth follicle, and is due to the
working of certain bodies contained therein called "osteoclasts "
or "odontoclasts."
The Vagaries of Dentition.
The normal temporary and permanent dentitions have been
described briefly, "but there are certain forms of teeth which do
not belong to either of these, and are called supernumerary.
These are shapeless-looking organs as a rule, but sometimes are
duplicates of any of the normal teeth already present. Again,
some teeth are joined to their neighbour with a common pulp;
these are termed " geminated teeth." Also some teeth, especially
molars, are separated as far as the parts of each tooth are con-
cerned, but are joined at the cementum of the roots. Some
molars, second ones, have sometimes an elementary-looking peg