13-00
Digestive system
5Teeth
13-00 Digestive system 5 Teeth

13 Digestive system 5
Menu
13-00.
13-01.
13-02.
13-03.
13-04.
13-05.
13-06.
13-07.
13-08.
13-09.
13-10.
13-11.
13-12.
13-13.
13-14.

Digestive system 5 Teeth
Incisor， general view. Human， longitudinal ground section， carbol-fuhsin stain， x 1.3.
Crown of incisor. Human， longitudinal ground section， carbol-fuhsin stain. x 4.0.
Neck of incisor. Human， longitudinal ground section， carbol-fuchin stain， x 4.0.
Root of incisor. Human， longitudinal ground section， carbol-fuchsin stain， x 4.0.
Enamel and dentin of incisor. Human， longitudinal ground section， carbol- fuchsin stain，
x 25.
Dentin and cementum of incisor. Human， longitudinal ground section， carbol- fuchsin
stain， x 25.
Molar in alveolus. Monkey， decalcified longitudinal section， H-E stain， x 1.5.
Roots of teeth in alveoli. Monkey， decalcified transverse section， H-E stain， x 4.0.
Root of a tooth in alveolus， 1. Monkey， decalcified transverse section， H-E stain， x 10.
Root of a tooth in alveolus， 2. Monkey， decalcified transverse section， H-E stain， x 25.
Root of a tooth in alveolus， 3. Monkey， decalcified transverse section， H-E stain， x 64.
Sagittal section of upper jaw through naris. Human newborn， H-E stain， x 1.2.
Development of tooth.
Development of tooth，1. Human embryo， decalcified section， H-E stain， x 1.3.

13-15.
13-16.
13-17.
13-18.
13-19.

Development of tooth，2. Human embryo， decalcified section， H-E stain， x 6.0.
Development of tooth，3. Human embryo， decalcified section， H-E stain， x 25.
Development of tooth，4. Human embryo， decalcified section， H-E stain， x 64.
Development of tooth，5. Human embryo， decalcified section， H-E stain， x 160.
Major molar， shortly before eruption. Monkey， longitudinal section， H-E stain， x 1.6.

CrownEnamelum

Dentino-enamel junction

Pulp cavity

CollumDentinRoot canal
Radix
Cementum13-01 Incisor， general view. Human， longitudinal ground section， carbol-fuhsin
stain， x 1.3.

Stripes of Retzius

Dentino-enamel
junction
Enamelum

DentinPulp cavity

13-02 Crown of incisor. Human， longitudinal ground section， carbol-fuhsin stain. x 4.0.

Dentino-enamel
junction

Pulp cavity

Enamelum

CollumDentinRoot canal

Cementum13-03 Neck of incisor. Human， longitudinal ground section， carbol-fuchin stain， x 4.0.

Root canal

DentinCementum13-04 Root of incisor. Human， longitudinal ground section， carbol-fuchsin stain， x 4.0.

13-05 Enamel and dentin of incisor. Human， longitudinal ground section，carbol- fuchsin stain， x 25.

Cementum
Dentin13-06 Dentin and cementum of incisor. Human， longitudinal ground section， carbolfuchsin stain， x 25.

13-07 Molar in alveolus. Monkey， decalcified longitudinal section， H-E
stain， x 1.5.

13-08 Roots of teeth in alveoli. Monkey， decalcified transverse section，
H-E stain， x 4.0.

Dentin

Cementum

Periodontal
membraneAlveolus (Bone)
13-09 Root of a tooth in alveolus， 1. Monkey， decalcified transverse section，
H-E stain， x 10.

Pulp cavity

DentinCementum

Periodontal
membraneAlveolus

13-10 Root of a tooth in alveolus， 2. Monkey， decalcified transverse section，
H-E stain， x 25.

Cementum

Periodontal
membraneAlveolus

13-11 Root of a tooth in alveolus， 3. Monkey， decalcified transverse section，
H-E stain， x 64.

NarisPrimordium of
permanent tooth

Primordium of
milk toothUpper lip

Labial gland

Gingiva ofupper jaw

13-12 Sagittal section of upper jaw through naris. Human newborn，
H-E stain， x 1.2.

a: Frontal section of a 4-month-oldhuman embryo.
b: Primordium of tooth of 4-month-oldhuman embryo.
c: Primordium of tooth of 18-day-old
rat embryo.

13-13 Development of tooth.

13-14 Development of tooth，1. Human embryo， decalcified section，
H-E stain， x 1.3.

Ameloblasts
Enamelum

DentinOdontoblasts
Enamel pulp

External enamel
epitheliumInternal enamel
epithelium
Dentalpapilla

13-15 Development of tooth，2. Human embryo， decalcified section，
H-E stain， x 6.0.

Enamel pulp

Ameloblasts
Enamelum
DentinOdontoblasts

Dentalpapilla
13-16 Development of tooth，3. Human embryo， decalcified section，
H-E stain， x 25.

Ameloblasts
Tome’s process

Enamel pulp

Enamelum

DentinOdontoblasts

Dental papilla（Dental pulp）

13-17 Development of tooth，4. Human embryo， decalcified section，
H-E stain， x 64.

１

２

３

４

５

６

13-18 Development of tooth，5. Human embryo， decalcified section，
H-E stain， x 160.

７

８

Dissolved enamelum

DentinePulp cavity

Periodontal
membrane
Root canal
Alveolua

13-19 Major molar， shortly before eruption. Monkey， longitudinal section，
H-E stain， x 1.6.

13-00 Digestive system 5 Teeth

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The teeth are the organs which are adapted for biting ( the incisors ) and for crushing and grinding ( molars ) the food.
In man there are two sets of teeth， the deciduous teeth of childhood and the permanent teeth. Eruption of the former starts
about the seventh month after birth and reach their full completion at 6 to 8 years of age. These teeth are shed between thesixth and the thirteenth year and are gradually replaced by the permanent teeth.
All teeth consist of a crown projecting above the gingiva and one or tapering roots that occupy conforming sockets， alveoli， inthe bone of the maxilla or mandible. The region of junction between the crown and the root is called the neck or cervix. The
tooth has a central cavity， pulp cavity， which corresponds in its shape to the outer form of the tooth. This cavity continues
downward into each root as a narrow root canal that com- municates with the periodontal membrane at the tip of the root. The
blood vessels， nerves and lymphatics enter and leave the tooth through the apical foramen.
The hard portions of a tooth consist of three different tissues: dentin， enamel， and cementum. The bulk of the tooth is made up
of dentin， which surrounds the pulp chamber. In the crown， dentin is covered by a layer of enamel， which is thinnest in thecervical region. On the root， dentin is covered by a thin layer of cementum which extends from the neck to the apical foramen.
Teeth are studied in histological sections after removal of the hard inorganic constituents with acid， or in thin ground sections
without decalcification.

13-01 Incisor， general view. Human， longitudinal ground section， carbolfuhsin stain， x 1.3.
•

This is to show a general view of a ground section through the axis of a human incisor， stained with carbol-fuchsin. The
fundamental structures of an incisor are clearly shown. The axial portion of the dentin is occupied by the pulp cavity， which
extends as root canal to the tip of the root. On the crown dentin is covered by the thick enamel， and on the root by the thincementum. In the dentin there are innumerable radial striations from the pulp cavity toward the dentino-enamel junction， andalso toward the dentino-cement junction. They are called dentinal tubules.

13-02 Crown of incisor. Human， longitudinal ground section， carbol-fuhsin
stain. x 4.0.
•

The enamel consists of innumerable enamel rods or prisms of 4 to 5μｍ in diameter. They run parallel one another andperpendicular to the dentino-enamel junction. In the enamel there are another striations， starting from the dentino-enamel
junction， crossing obliquely with the enamel rods， making large loops over the tip of the crown， and arriving at the dentinoenamel junction on the opposite side. They are called stripes of Retzius.

13-03 Neck of incisor. Human， longitudinal ground section， carbol-fuchin
stain， x 4.0.
•

At the neck the enamel ends and begins the cementum， which is first very thin and increases in thickness toward the apex. The
cementum consists of bone substance.

13-04 Root of incisor. Human， longitudinal ground section， carbol-fuchsin
stain， x 4.0.
•

The cementum becomes thicker as nearing the tip of the root.

13-05 Enamel and dentin of incisor. Human， longitudinal ground section，carbol- fuchsin stain， x 25.
•••

This is a higher magnification of enamel and dentin of human incisor. In the middle runs the dentino-enamel junction from top
downward and divides the figure into the dentin ( left half ) and enamel ( right half ).
In the dentin there are innumerable parallel striations radiating from the pulp cavity toward the dentino-enamel junction. They are
attributed to the presence of minute canals， dentinal tubules， whose diameter is 3 to 4 µm near the pulp cavity and about 1µm
near the dentino-enamel junction. Near this junction and parallel to it a row of small spots of irregular size and form is recognized. It
is called the interglobular space which reflects the small areas of incomplete calcification. In this figure they appear as red stained
spots.
In the enamel two kinds of striations are observed. The one， fine and faint striations are countless striations， parallel to one
another， start from dentino-enamel junction， run perpendicularly to this junction toward the free surface. They are thin enamelrods or prisms. The other， starting from the dentino-enamel junction， crossing obliquely with the enamel rods， making large loops
over the tip of the crown， and arriving at the dentino-enamel junction on the opposite side. They are called stripes of Retzius andvery conspicuous in this figure.

13-06 Dentin and cementum of incisor. Human， longitudinal ground section，carbol- fuchsin stain， x 25.
••

At about three fifth from the left edge runs the junction of dentin ( left ) and cemen- tum ( right ) from top downward. In thedentin， as figure 13-06， there are innumerable parallel striations of dentinal tubules， perpendicular to this junction. Immediately
under the junction there is a layer of small black dots; This is called the granular layer of Tomes.
The cementum， being identical to the bone， numerous cementocytes providing with many fine processes are scattered. They
appear as small black structures in the deep red stained ground substance.

13-07 Molar in alveolus. Monkey， decalcified longitudinal section， H-E stain，
x 1.5.
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This is a decalcified longitudinal section of a molar with alveolus. The enamel was entirely dissolved and disappeared. Two roots
fit in the axial portion of each alveolus and are firmly connected with alveolus by the periodontal membrane， which serves asperiosteum to the alveolar bone. The periodontal membrane consists， in part， of thick collagen fiber bundles， Sharpey’s fibers，
that run from the alveolar wall into the cemen- tum. The orientation of the fibers varies at different levels in the alveolus. At theneck， fibers are horizontal and especially prominent and firmly attached to the cementum. Lower to this level collagen fiber
bundles connect obliquely between the higher portion of the alveolar wall and the deeper portion of the root. The cementum
appears in this figure as thin layer on the surface of the root， stained deep violet.

13-08 Roots of teeth in alveoli. Monkey， decalcified transverse section， HE stain， x 4.0.
•

In this figure two roots and their alveoli are seen. The lower edge is the epithelium of the gingival mucosa， followed by theconnective tissue of the submucosa. In the periodontal membrane， radial arrangement of the collagen fiber bundles connecting
the root and the alveolar wall is quite conspicuous. The right root and its alveolus are shown at higher magnification in 13-09.

13-09 Root of a tooth in alveolus， 1. Monkey， decalcified transverse
section， H-E stain， x 10.
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The axial portion of the root is occupied by the pulp cavity ( root canal )， which is filled by very loose connective tissue， bloodvessels， lymphatics and nerves. This cavity is lined by the tall columnar cells， odontoblasts， each of that sends a longprotoplasmic process into the dentinal tubule. In the dentine innumerable dentinal tubules radiate from the pulp cavity toward thesurface， which is covered by the cementum. In this figure the cementum appears as a thin layer stained deep violet. The
cementum and alveolar wall are connected by the periodontal membrane consisting of numerous thick collagen fiber bundles thatshow the radial arrangement. Spaces between these thick bundles are filled by very loose connective tissue and thin bloodvessels. The inner surface of the alveolus is covered by the periodontal membrane which serves as periosteum.

13-10 Root of a tooth in alveolus， 2. Monkey， decalcified transverse
section， H-E stain， x 25.
•

Higher magnification of 13-09. In the pulp cavity very loose connective tissue contain- ing blood vessels and nerves is seen. The
inner surface of the cavity is lined by a layer of tall columnar cells. They are the odontoblasts that send the protoplasmic
processes into the dentinal tubules. The thick collagen fiber bundles of periodontal membrane connect the cementum firmly withthe wall of the alveolus. Spaces between these bundles are filled by very loose connective tissue

13-11 Root of a tooth in alveolus， 3. Monkey， decalcified transverse
section， H-E stain， x 64.

•

Higher magnification of 13-10. This figure is to show the cementum， periodontal membrane and alveolus. In the cementum
numerous lacunae of odontoblasts are seen. The periodontal membrane consists of thick collagen fiber bundles which connect
very firmly the cementun with the alveolus. Among these bundles penetrate blood vessels with loose connective tissue at regularintervals.

13-12 Sagittal section of upper jaw through naris. Human newborn， H-E
stain， x 1.2.
•

At upper left corner is the naris; following downward is the upper lip. Rightward to it is the massive upper gingiva which contains
the primordium of a milk tooth ( left ) and that of a permanent tooth. The primordium of the milk tooth is large and its enamel，already formed， was dissolved. Its root is still not formed. The primordium of the perma- nent tooth is small and shows the early
developmental stage.

13-13 Development of tooth. (1/3)

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a: frontal section of a 4-month-old human embryo.
b: primordium of a tooth of a 4-month-old human embryo.
c: primordium of a tooth of a 18-day-old rat embryo.
The enamel is derived from the ectodermal epithelium lining the oral cavity， whereas other components of tooth are thederivatives of the mesenchyme.
In the embryos at about the end of 6th. week ( about 10mm C-R length )， along the inner edge of the upper and lower lips appear
two parallel concentric thickening lines of the ectodermal epithelium; the outer divides in future the lip from the gingiva and iscalled the labio-gingival lamina. The inner， forming in future the enamel， is called dental lamina. The ectodermal cells multiply
actively， enter into the mesenchyme perpendicularly and form a plate of horseshoe form opening backward. At about the end of
the 8th week at 10 sites of the labial surface of this plate develop the spherical cell lumps with a handle; they are called enamel
buds. Around these buds mesenchymal cells come together with blood vessels.
The enamel buds grow rapidly and cells of the distal portion invaginate apicalward， forming the double walled cap-shaped
structures; they are called the enamel organs. The invaginated inner cells are arranged as simple columnar epithelium and called“inner enamel epithelium” or ameloblasts ( iee in figure c )， which later produce the enamel. The cells of proximal ( outer ) side
become simple cuboidal epithelium and are named “outer enamel epithelium ( oee in figure b ). The cells locating in the space
between the outer and inner enamel epithelia are loosely packed， with long processes joined by desmosomes to form a stellate
reticulum， and are called， as a whole， enamel pulp ( enp in figure c ).

13-13 Development of tooth. (2/3)

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The mesenchymal cells in the hollow limited by the inner enamel epithelium multiply actively and fill this space densely. These
are called dental papilla ( dp in figures b and c ). The mesenchymal cells underlying the inner enamel epithelium become
transform- ed into tall columnar cells， with their bases toward the interior of the papilla， and are called odontoblasts， which
later produce the dentin.
The enamel organ and dental papilla are together enclosed by the dense mesenchym- mal tissue， called dental sac ( ds infigure c ).
The lower edge of the cap-like enamel organ， where the outer enamel ( dental ) epithelium is continuous with the inner enamel( dental ) epithelium， will later mark the lower limit of the enamel at the neck of the tooth. As the enamel organ enlarges， it
becomes bell-shaped and its under surface gradually takes on the contour of the crown of the tooth.
In fetuses of about 20 weeks gestation， odontoblasts begin to produce procollagen and release it from their apical portion into
the space between the ameloblasts and odonto- blasts. This collagenous substance is named predentin， which is later calcified
and becomes into dentin. Dentin first appears thus as a thin layer between the odontoblasts and ameloblasts. Calcification
follows soon after deposition of new dentin， but there is always a thin uncalcified layer adjacent to the odontoblasts. As theodontoblasts recede， with the deposition of more dentin， their lengthening apical processes remain in the tubules within thedentin. The predentin around the apices of the odontoblasts is a soft fibrillar zone rich in collagen. It is traversed by fibers fromdeeper in the papilla， called Korff’s fibers. These spread out fan wise within the matrix of the dentin.

13-13 Development of tooth. (3/3)

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Soon after the first appearance of calcified dentin around the dental papilla， the ameloblasts begin to deposit layer after layer ofenamel on its surface facing the dentin， extracellularly. As the mass of enamel increases ameloblasts recedes， and thus the
distance between ameloblasts and odontoblasts increases. The ameloblasts are tall columnar in shape and arranged orderly
perpendicular to the enamel. They have elongated nucleus in the basal cytoplasm. Distal to a conspicuous terminal web in theapical cytoplasm there is a broad apical process， Tome’s process， which continues into the calcified enamel matrix.
Development of the root of the tooth begins shortly before the eruption of the crown of the tooth. Continued downward growthof the inner and outer dental epithelium from the lower edge of the enamel organ gives rise to a bilayered fold， called sheath of
Hertwig， around a lengthening papilla cavity. The cells of this sheath induce neighbor- ing papilla cells to differentiate into
odontoblasts. These align themselves with the layer of differentiated odontoblasts in the cervical region of the tooth and begin tosecrete a layer of predentin that is continuous with that already present in the crown. This is soon followed by the secretion ofdentin by these odontoblasts， initiating the formation of the root of the tooth. Continuing downward growth of sheath of Hertwig
and its induction of more odontoblasts results in progressive elongation of the root until it reaches its definitive length. The
sheath of Hertwig then disappears. After its disin- tegration， cells of the surrounding connective tissue sheath differentiate into
cemrnto- blasts and deposit an acellular layer of cement on the root. Further deposition of cement entraps bundles of collagenfibers that are incorporated， at their other end， in trabecu- lae of the alveolar bone. These fibers， and those that replace themin the continual turnover of the tissue， ultimately form the periodontal ligament that anchors the tooth to its bony socket.
In eruption of the tooth， the crown is moved through the overlying cellular remnants of the enamel organ which seem todisintegrate in its path. It then passes through the gingiva to emerge in the oral cavity.

13-14 Development of tooth，1. Human embryo， decalcified section， H-E
stain， x 1.3.
•

This is a sagittal section of the upper jaw of a human embryo containing primordia of milk ( upper left ) and permanent ( lower
right ) teeth. In the primordium of the milk tooth development of enamel as well as dentin already took place at the top of theinner enamel epithelium. The lower edge of the cup-like enamel organ， where the outer enamel epithelium is continuous with theinner enamel epithelium， will later mark the lower limit of the enamel at the neck of the tooth. As the enamel organ enlarges， it
becomes bell-shaped and its under surface gradually takes on the contour of the crown of the tooth. Higher magnification figures
are shown in 13-15 ～13-18.

13-15 Development of tooth，2. Human embryo， decalcified section， H-E
stain， x 6.0.
•••

This is a primordium of a milk tooth. At the top， where the development of the enamel and dentin takes place， the amelobasts
and the odontoblasts are tightly opposed with their apical end.
The odontoblasts release the procollagen from their apical portion into the space between the ameloblasts and odontoblasts.
Calcification follows soon after deposition of new dentin， but there is always a thin uncalcified layer adjacent to theodontoblasts. As the odontoblasts recede， with the deposition of more dentin， their lengthening apical processes remain in the
tubules within the dentin. The predentin around the apices of the odontoblasts is a soft fibrillar zone rich in collagen.
Soon after the first appearance of calcified dentin around the papilla， the ameloblasts begin to deposit layer after layer ofenamel on its apical surface， facing the dentin. The ameloblasts are tall columnar in shape and have elongated nucleus in thebasal cyto- plasm. Distal to a conspicuous terminal web in the apical cytoplasm there is a broad apical process， Tome’s
process， which continues into the calcified enamel matrix.

13-16 Development of tooth，3. Human embryo， decalcified section， H-E
stain， x 25.
•

This is a higher magnification of the top region of 13-15， where the deposition of dentin and enamel takes place. At center thereis the dental papilla ( dental pulp )， triangular in shape. On its verge long spindle shaped cells are arranged very densely; they areodontoblasts and surrounded by dentin， stained deep pink. Next to it is a layer of enamel， stained dark reddish-violet， that are
surrounded by the inner enamel epithelium， being the simple tall columnar epithelium. The outermost layer is the enamel pulp
consisting of the ectodermal reticulum.

13-17 Development of tooth，4. Human embryo， decalcified section， H-E
stain， x 64.
•

This is a higher magnification of a portion of 13-16， showing the process of the dentin and enamel formation in detail. Following
structures are lined up from left to right.
①. Enamel pulp consisting of the ectodermal reticulum.
②. Ameloblasts， orderly arranged simple tall columnar epithelium; nuclei of the epithelial cells locate in the basal cytoplasm.
③. On the apical portion of the ameloblasts there is a thin layer of Tome’s process.
④. The enamel， stained dark reddish-violet.
⑤. The dentin， stained deep pink. The dentin is opposite with the enamel directly.
⑥. Between the dentin and odontoblasts there is a thin layer of predentin， stained faint pink.
⑦. Odontoblasts. They are long spindle shaped cells， densely arranged parallel with one another， but they are not epithelium.
Their arrangement is not perpendicular to the basal line of the predentin.
⑧. Dental pulp consisting of mesenchymal reticular tissue.

13-18 Development of tooth，5. Human embryo， decalcified section， H-E
stain， x 160.
•

The structures concerning the formation of the dentin as well as the enamel are seen more precisely. ①. Enamel pulp. ②.
Ameloblasts. ③. Tome’s process. ④. Enamel. ⑤. Dentin. ⑥. Predentin. ⑦. Odontoblasts. ⑧. Dental pulp.

13-19 Major molar， shortly before eruption. Monkey， longitudinal section，
H-E stain， x 1.6.
••

This is a decalcified longitudinal section of a molar， shortly before eruption. The crown consist of enamel and dentin; but
enamel is entirely dissolved， leaving some remnants. Dentin is thick and well formed and its form reflects the surface form ofenamel. Dentin contains a wide dental cavity within it， which continues into the two root cavities. The dental cavity and root
cavities are filled by very loose connective tissue containing numerous blood vessels， i.e. dental pulp. The two roots fit each into
the alveolus， tightly connected by the periodontium
The development of the root begins shortly before the eruption of the tooth， continues after the crown has emerged from themucous membrane， and is not completed until much later. The epithelial sheath disappears when the root is completelydeveloped.