Arch. histol. jap., Vol. 38, No. 3 (1975) p. 209-227 Department of Anatomy (Prof. S. ISOKAWA), Nihon University School of Dentistry, Tokyo, Japan

Electron

Microscopic Study of Early Formation of the Tooth Enameloid of a Fish (Hoplognathus fasciatus). I. Odontoblasts and Matrix Fibers Toshihiko INAGE Received June 2, 1975

Summary. An electron microscope study was made on the tooth germs of Hoplognathus fasciatus in early developmental stage. Special attention was given to the odontoblasts, enameloid matrix fibers, calcification of enameloid and the hitherto controversial origin of the enameloid. 1. The ameloblasts and the odontoblasts are demarcated by a single layer of basement membrane which persists until immediately before the calcification of the enameloid matrix. 2. The histogenesis of the enameloid matrix begins with the formation of non-striated fibers

140-180Å

brane

and

640Å

thick.

parallel

periodicity

to later

They the

are

sides

appear

of and

arranged

in

odontoblasts. the

entire

a direction Fibers

enameloid

vertical with matrix

to

regular is formed

the

basement

cross by

mem-

striations these

of

fibers.

3. Along with the formation of the enameloid, the odontoblasts assume a high columnar form, with a marked increase in cell organelles which show marked polarity suggesting active protein synthesis. Numerous odontoblastic processes are noted in the enameloid matrix. Granules, representing precursors of enameloid matrix fibers occur in the odontoblasts. Based on these findings, the enameloid matrix fibers must be of mesodermal origin. 4. Deposition of crystals of small size, needle and tube in shape, occurs in the circumference of the fiber bundles. As calcification progresses, crystals appear in the central portion of the bundles. Later, large crystals of rod and platelet shapes become intermingled. In addition to this, small crystals are fused, forming aggregates.

The hypermineralized is generally called enamel. ent from that in mammals

layer covering the dentin of the crown portion of a tooth Since this portion of a piscine tooth appears to be differmorphologically and embryologically, it has been called by

various names: enamel (ISOKAWA,1954, 1955; YOSHITANI,1959; LERNER,1956; SATOMURA,1972; TSUBOUCHI,1969), mesodermal enamel (KVAM, 1946, 1950, 1953), ganoin (ORVIG,1967), vitrodentin (ROSE, 1898), durodentin (SCHMIDT,1958), etc. POOLE(1967) recently suggested that this hard tissue covering the tooth of these lower animals be called "enameloid." This designation, based on its location and resemblance to the enamel in mammals, has been supported by many investigators. Studies of the enameloid of teleosts were initiated long ago in conjunction with the early studies on fish teeth, though they were concentrated in the period between the latter half of the 19th and the beginning of the 20th century. TOMES (1900), MUMMERY(1916), CARTER (1918) and others studied the developmental process and tissue structure of jaw-tooth enameloid principally in teleosts. Despite these studies, the process of enameloid formation remains unsolved. One of the more important problems in the previous studies of enameloid is the tissue origin of the enameloid. MUMMERY(1916), CARTER(1916) and others proposed the ectodermal

origin

of the enameloid

through 209

the secretion

from ameloblasts

which

210

T. IMAGE

might be produced by certain morphogenetic changes.

KVAM

(1946, 1950, 1953) and

others proposed

based

on the apparent

the mesodermal

origin

of the enameloid

origin

of itsmatrix fibersfrom mesodermal tissue. WAKITA (1974)and others,furthermore, supported the concept of the KVAM and pointed out the morphological changes of the ameloblast. They suggested the participation of ferritin granules in these cells in the maturation of the enameloid. Their view may be called bidermal origin concept. In our department, ISOKAWA conducted histological studies on the enameloid of the porgies in 1954 and on the file-fishes in 1955. ISOKAWA et al., 1967 extended his

studies in Callvodon ovifcons, showing the argyrophile nature of the matrix fibers which suggested the presence of collagen fibers. ISOKAWA et al. (1970) and Misu (1970) conducted histochemical studies of the enameloid of Hoplognathus fasciatus, confirming argyrophily in silver stainings and collagen-like stainability in azan of the enameloid matrix fibers. These and many other studies have indicated the collagenous nature of enameloid matrix fibers. A review of previous studies, including the reports from our department, has however indicated no conclusion as to what kind of cells actually formed the enameloid matrix. The author therefore attempted an electron microscope study on the early stage of tooth germs, especially the odontoblasts, the enameloid matrix fibers, and the calcification in Hoplognathus fasciatus. The nomenclature previously used by ISOKAWA et al.(1970)isemployed in this report. Materials

and Methods

About 500 tooth germs in the early stage of their development were removed from the jaw bones of living Hoplognathus fasciatus with a body length of 15-40cm. After removal from the jaw, these tooth germs were immediately fixed for 2hrs in a glutaraldehyde

solution

at 4℃.

This

solution

had

been

diluted

to 2.5%

with

a caco-

dylate buffer at pH 7.4and containing 4.5% sucrose. After washing with another cacodylate buffer, pH 7.4 containing 7% sucrose, the tooth germs were subjected to post-fixation for 1hr in 1% osmic acid. The tooth germs were then dehydrated in ethanol, and embedded in Epon 812. Most of the tooth germs were cut into ultrathin sections with a Porter-Blum MT-1 microtome. These ultrathin sections stained with 3% uranyl acetate and lead tartrate were examined with a Hitachi-12 type electron microscobe.

stained

Some

of the

with toluidine

embedded

tissues

blue and observed

were

under

cut

into

the light

sections

of

1-2μ

thickness,

microscope.

Observation 1.

Ameloblasts In the early

be

separated

by

and odontoblasts stage abasement

in the early

of the tooth germ, membrane

stage

the ameloblasts

of 100-150mμ

thick

and odontoblasts Ameloblasts

appear

to

differentiate

earlier than odontoblasts and they are cuboidal or low columnar as far as their outline is concerned (Fig. 1, 2). The nucleus is pale due to a small amount of heterochromatin and is located at the basal part of the cell. Cell organelles have begun to increase. The Golgi apparatus is located in the perinuclear region and contains small amounts of Golgi vesicles, Golgi vacuoles, and thin Golgi lamellae. Near the Golgi apparatus,

Early Formation

of Fish Enameloid,

I

211

centrioles associated with a single cilium are frequently seen. The rough surfaced endoplasmic reticulum is poorly developed and forms lamellae around the nucleus and in the basal portion of the cell. Free ribosomes are abundant and tend to aggregate in the marginal region of the cytoplasm. Mitochondria, on the other hand, are numerous and have very well developed cristae, they are distributed all over the cytoplasm. In the area adjacent to the basement membrane, cell organelles are sparse. It possesses only a few granules containing materials of high electron density and vesicles coated by bristle-like substances. The cell membrane at the distal end is smooth and microvilli are occasionally seen protruding towards the dental papilla.

Fig.

1.

Schematic drawing of tooth germ in the early developmental stage. Am ameloblast, Od odontoblast, DP dental papilla, DF dental follicle, Cp capillary, E enameloid.

212

T. INAGE:

Adjacent ameloblasts are connected by means of desmosomes, bulb type tight junctions (REITH, 1970) (Fig. 3). The odontoblasts cytoplasmic processes. means of desmosomes.

Fig.

2.

Cervical

interdigitation,

and

at this stage are stellate in shape, with numerous attenuated They are connected to each other with these processes by The nucleus is pale and is located at the approximate center

loop of enamel rix,

Dp

organ dental

and dental papilla,

Od

papilla.

odontoblast.

Cl cervical ×1,500

loop, E enameloid

mat-

Early

Formation

of Fish

Enameloid,

I

213

Fig. 3. Ameloblast and processes of odontoblast in the early developmental stage. N nucleus of ameloblast, M mitochondria, BT bulb type tight junction, G Golgi apparatus, Op processes of odontoblasts.

×9,600

of the cell. Cell organelles are poorly developed, with a small number of rough surfaced endoplasmic reticula and mitochondria in the perinuclear region. Free ribosomes are sparsely distributed in the marginal region of the cytoplasm. Membranebound

granules

of

0.5-1.0μ

diameter

are

observed

in

the

cells.

The

contents

of

the

granules are partly high and partly moderate in electron density. Immediately before formation of the enameloid matrix, the odontoblasts become rather columnar in shape and their height surpasses that of the ameloblasts. There subsequently occur protrusions of numerous cytoplasmic processes towards the basement

membrane.

The

cells

reach

15-17μ

in

hight.

The

nucleus

is located

at

the

basal end of the cell. Cell organelles start to increase and the rough surfaced endoplasmic reticulum and Golgi apparatus begin to occupy the distal portion of the cell (Fig. 4). 2.

The odontoblasts

and early synthesis

of the enameloid matrix

Matrix fibers of the enameloid are initially formed as extremely fibers

measuring

140-180Å

fibers are arranged attached fibers

in a direction

to the basement

with

a diameter

between

membrane. of 700-800Å

the

basement

vertical These which

membrane

and

to the basement non-striated are

regularly

fine non-striated

odontoblasts.

membrane, fibers are soon

striated

(640Å

These

with

one end

buried

among

intervals)

and

these appear soon afterwards to become the enameloid matrix (Fig. 5, 6). Till the

214

T. INAGE:

Fig. 4.

Ameloblasts

(Am) and odontoblasts (Od) in the early developmental stage. ment

enameloid

matrix

to the basement of

3-5μ

diameter,

reaches

membrane.

a thickness

membrane.

Later,

crossing

each

of

3-4μ,

however,

other

and

B base-

×4,800

the

fibers

the striated branching.

are

simply

arranged

vertical

fibers are arranged The

fiber

bundles

in bundles pass

through

the spaces between the odontoblasts to reach the dental papilla. The intercellular spaces between the odontoblasts become gradually narrower, until the cell walls are joined and crossed by desmosomes. The height of the odontoblasts

increases,

giving

a

columnar

shape

with

a

height

of

20-25μ.

From

the

distal.

end of the cells, numerous fine cytoplasmic processes protrude to the side of the basement membrane along the bundles of enameloid matrix fibers. As the formation of the enameloid matrix continues, the odontoblasts gradually recede towards the dental papilla, leaving their cytoplasmic processes in the enameloid matrix. Over the layers of almost completed enameloid matrix, portions of the cytoplasmic processes of the odontoblasts are seen around the fiber bundles and rarely in the bundles. In the cytoplasmic processes bundles of microtubules are noted to take longitudinal course. Cell organelles are sparse, but mitochondria, intracellular granules and ribosomes are visible. The outline of the processes is irregular, with a frequent infolding of the cell membrane. Frequently there are corted vesicles nearby. In the odontoblasts at this stage, cell organells are markedly increased, and the rough surfaced endoplasmic reticula are arranged around the nucleus forming a thick stack of lamellae (Fig. 7, 8). The inside of the cisterns of the endoplasmic reticulum

Early Formation

Fig.

5.

Enameloid

striations,

B

matrix basement

of Fish Enameloid,

fibers membrane.

with

and

I

without

×9,600,

inset

215

(arrow)

cross

×18,000

is filled with a particulate material. In the supranuclear region, the Golgi apparatus is well developed and contains very thick stacks of lamellae, numerous vesicles and vacuoles. On the mature surface of the Golgi apparatus, formation of granules with moderate electron density is noted (Fig. 9). Near the Golgi apparatus, typical lysosomes and multivesicular bodies are found. Mitochondria also are increased in number and distributed all over cell. Mitochondrial cristae are well developed, and several granules are found within the matrix of mitochondria. Longitudinally in the cell, filaments indicating a cytoskeleton and microtubules are found. In the peripheral portion of the cell, cell organelles are found less frequently than in other parts, giving a light appearance to this portion. All over the cytoplasmic membrane, small processes and coated vesicles are found. Microvilli are well developed in the lateral region of the cytoplasm.

216

T. INAGE:

Fig.

6.

Higher

magnification

of matrix

fibers

show

blasts.

3.

Odontoblasts

and enameloid

The odontoblasts 35-40μ.

The

further

rough

matrix increase

surfaced

640Å

cross

striations.

Op

process

of odonto-

×72,000

about their

endoplasmic

ten micra

height

thick

until

reticulum

the axis of the cell reaches

is increased

in amount,

and

the

Golgi apparatus occupies a large area in the supranuclear region. The cells now contain, in addition to typical lysosomes, numerous intracellular granules of two types. These are surrounded by a limiting membrane consisting of a single laver. Type I granules

are

round

in

shape

with

a diameter

of 0.3-0.5μ

and

contain

an

amorphous

substance with a moderate electron density. They are further divided into those with and those without a perigranular halo (Fig. 10). Type II granules are irregularly oval

in

shape,

Rod-like noted. On

measure

granules The

these

fibrillar

granules,

0.5-0.8μ

with

a long

structures

Ω-like

small

in

long

diameter have

diameter of 1-2μ

regular

projections

and

contain

belonging

striations were

a

to Type with

observed

fibrillar II were

periodicity at several

structure. sometimes

of places

500-550Å. along

the

limiting membrane (Fig. 11). Near the supranuclear portion of the odontoblasts, a single cilium that protruded into the intercellularspace was occasionallynoted (INAGE et al.,1974). 4.

Calcification Crystal

size

of the

of matrix

deposition crystal

noted

was seen along the external at

first was

15-25Å

in

circumference width

and

280-420Å

of the bundle. in

length;

The their

shape is needle- and tube-like (Fig. 12). The long axis of the crystal coincided with the long axis of the matrix fiber. As calcification progresses, the crystals increase in

Early Formation

of Fish Enameloid,

I

217

number and size and appear at the central portion of the fiber bundle (Fig. 13). The whole fiber bundle becomes occupied by the crystals, and the individual fibers appear more and more indistinct (Fig. 14). Since the crystals are directed approximately

Fig.

7.

Many

odontoblastic

processes

(arrows) blast.

projecting ×7,500

into

the

enameloid

matrix.

Od

odonto-

218

T. INAGE:

Fig.

8.

Fig.

Intracellular

9.

Golgi

organelles

apparatus

of an

odontoblasts.

plasmic

reticulum.

of an

odontoblasts

N

nucleus,

G

Golgi

apparatus,

ER

×9,600

with

some

granules

(GR).

×20,000

endo-

Early Formation

Fig.

10.

parallel

to the

matrix

ameloid

surface

at

Coracerning all

over

the

the fiber

a

Type

fibers

I granules

site

in

2-3μ

cross

section

bundles,

its

(arrows)

their

from

long the

of size

of Fish Enameloid,

in

axis,

the

crystal be

219

odontoblasts.

they

enameloid

may

I

are

×12,000

arranged

vertical

to the

en-

surface. when

its

120-140Å

in

deposition width

is spread and

almost

1,700-2,000Å

in

thickness. In these small crystals, moreover, as seen in Figure 12, crystals with a tubular structure are seen at their central portions. At this stage there are noted, mixed with the crystals described above, large crystals of rod and platelet shapes. In cross section the rod-shaped crystals show irregular hexagonal pattern; their length is variable (Fig. 15). These large crystals are believed to grow gradually from smaller crystals as there is seen every graduation between both. At this stage, in addition, 20-50 small crystals are fused (Fig. 16) into an aggregate. The aggregates measure

400-1,000Å Concerning

most reached

of the

in the

crystals

shorter

longitudinal

measured

dimension

and

section

about

at

2,000Å

3,500-3,600Å a

in

stage

length.

of

in

longer

advanced

In

some

axis. crystal

portions

deposition,

the

length

3,600Å.

Discussion 1.

Ameloblasts and odontoblasts in the early stage The tooth germ of Hoplognathus fasciatus, like that of many other animals, consists of an ectodermal enamel organ and a mesodermal dental papilla, and these two are distinctly demarcated by a basement membrane. This is similar to that found in

220

T. INAGE:

man (TAKUMA, 1970; SISCA and PROVENZA, 1973) and rat (REITH, 1967). The ameloblast at this early stage appears cuboidal or low columnar and each ameloblast is connected by means of desmosomes, interdigitation and bulb type tight junctions, resembling that are found in mammals. In the ameloblasts, cell organelles

Fig. 11. Type II granule (TII) in the odontoblasts. Arrow shows the granule with like projection and intragranular fibrillous structure with regular striations. G Golgi apparatus . TI Type I granule.

×15,000

Early Formation

Fig.

12.

Crystals

appearing

along

of Fish Enameloid,

the

circumference

I

221

of the

bundle.

×24,000

such as rough surfaced endoplasmic ciently differentiated, while numerous are scattered all over the cytoplasm.

reticulum and Golgi apparatus have not suffilarge mitochondria with well developed cristae Free ribosomes are occasionally seen as aggre-

gates,

of protein

probably

indicating

synthesis

consumed

in the intra-cellular

bolism (REITH, 1967) and substances required for specialization MILES, 1973).

meta-

of cells (MEREDITHand

The interpretation of the above findings, especially of the occurrence of numerous mitochondria, in the ameloblasts may be multiple; it may be of interest to postulate a metabolic relationship between the ameloblasts and the odontoblasts which undergo an intense differentiation in this very stage. The odontoblasts are originally stellate in shape, and at the beginning of differentiation

they

assume

a columnar

appearance

with

a hight

of 10-15μ

immediately

before the formation of the enameloid matrix. The odontoblasts and their cytoplasmic processes adhere to each other connected by desmosomes. The odontoblasts at this stage are polarized, and the Golgi apparatus and rough surfaced endoplasmic reticulum begin to occupy the distal portion of the cell. The rough surfaced endoplasmic thesis. 2.

reticulum

The odontoblast

is rapidly

and early

increased

synthesis

indicating

the augmentation

of the enameloid

of protein

syn-

matrix

According to the light microscopic studiesby KVAM (1946,1950, 1953),YOSHITANI (1959)ISOKAWA et al. (1970), and others, the enameloid matrix mshowed argyrophilia in

222

T. INAGE:

Fig.

13.

The

whole

fiber

bundle

is occupied

by

crystals.

×7,600

silver staining and stained violet in azan. The enameloid matrix fibers thus stained similar to collagenous fibers, have been assumed mesodermal in origin. Under the electron microscope, however, it is not always easy to demonstrate that the matrix fibers correspond to collagen fibers. In this study, the matrix fibers are shown to have striations

with

support

to The

the

a regular collagen

formation

periodicity nature

of

the

of

of the

enameloid

about

matrix begins

640Å. fibers with

This of

the

is the

first

fine-structural.

enameloid.

non-striated

fibers

thickness running vertical to the basement membrane, and parallel odontoblasts. They closely resemble the fibers appearing initially

of

140-180Å

to the sides of the in human dentin

formation as shown by TAKUMA(1970), SISCAand PROVENZA(1973). In man and rat, these fibers are buried among subsequently appearing fibers and their visualization becomes soon impossible. In the case of Hoplognathus fasciatus, the striated fibers of 640Å

periodicity

appear,

thus

burying

the

originally

formed

fibers

and

the

forming

enameloid matrix. The process of formation of the fibers, however, resembles that in man and rat teeth. In Hoplognathus fasciatus, the presence of fibers without cross

Early Formation

Fig.

Fig.

15.

Small

14.

crystals

Tube-like

and

large

of Fish Enameloid, I

crystals

crystals

in

of

enameloid.

irregular

222

×54,000

hexogonal

pattern.

×126,000

224

T. INAGE:

Fig.

16.

Aggregates

of small

crystals

are

seen

in

the

calcified

fiber

bundles

(arrows).

×20,000

striation is observed up until the enameloid matrix becomes calcified. This difference in the findings of fibers between the Hoplognathus fasciatus and man or rat may be possibly ascribed to the different time of formation and calcification of the matrix between the fish and mammals. The course of fibers forming the enameloid matrix is vertical to the basement membrane left

and

until right,

the

thickness

forming

of

fiber

the

bundles

matrix of

reaches

about

3-5μ

3-4μ. wide

as

The

fibers

the

enameloid

curve

to

the

increases

in thickness. This arrangement of curving fiber bundles in this study agrees with the enameloid tubes (enamel tubes) observed by previous investigators in the completed enameloid. As the formation of enameloid matrix proceeds, the height of the odontoblasts increases

to

25-30μ.

The

cell

organelles,

especially

the

rough

surfaced

endoplasmic

reticulum, are markedly increased in amount. The Golgi apparatus is quite pronounced, suggesting active protein synthesis in the cells. Since the enameloid matrix fibers first appear along the cytoplasmic processes of the odontoblasts, and the odontoblasts recede leaving the processes in the matrix as it forms, the enameloid matrix fibers are believed to originate in the mesoderm.

In man (TAKUMA,1973) and rat (REITH, 1967), the basement membrane disappears following the formation of predentin. In Hoplognathus fasciatus, however, this does not occur during the formation of the enameloid matrix until immediately before the initiation of calcification. This is in agreement with the finding obtained in the same fish that no calcification of the enameloid takes place until the future outline of the matrix iscompleted (ISOKAWA et al., 1970).

Early Formation

3.

Odontoblasts

At this odontoblasts

and enameloid

matrix

of Fish Enameloid,

about

ten micra

I

225

thick

stage, it is noteworthy that in addition to the typical lysosomes in the two other kinds of intracellular granules are seen. While the Type I

granules are found close to the Golgi apparatus, the Type II granules are seen at the distal end and peripheral portions of the cells. It is most probable that small granules in the Golgi apparatus gradually become mature into the Type I and then into the Type II granules. The Type II granules may contain fibrillar structures that closely resemble the intracellular bodies observed by CARLSON (1973) in the cells of notochordral epithelium of the chick embryo. They are striated with a periodicity of 500550Å,

resembling

the

enameloid

matrix

fibers.

seen in the spaces between odontoblasts, they the enameloid matrix fibers. These findings the enameloid matrix. 4.

Calcification

Since

the

same

fibrous

structures

were presumed to be the precursors also support the mesodermal origin

are

of of

of matrix

The crystals appearing first in the calcification of enameloid show morphological resemblance to the hydroxyapatite seen in the dentin (TAKUMA, 1970; SISCA and PROVENZA, 280-420Å

1973),

bone,

in length

and

at this

calcifying stage,

cartilage.

and

needle-

They and

measure

tube-like

15-20Å in shape

as

in width

and

described

by

IKEDA (1974). As the calcification progresses, there are noted, mixed with these crys-

tals, large crystals of rod and platelet shapes. In human enamel, along with each stage of maturation, the crystals grow uniformly in size, undergoing a shape change from a ribon-like to a rod-like form. In the fish enameloid, however, new crystals are added. Since the crystals so far present simultaneously grow individually, small and large crystals thus coexist within the calcifying enameloid. The aggregates of crystals probably represent the cross section of smalll crystals fusing together after their growth in the lateral direction. Maturation of enameloid is accompanied by its calcification which proceeds and is completed probably by addition of new crystals, crystal growth and fusion. イ シダ イ (Hoplognathus

fasciatus)

の 歯 の エ ナ メ ロイ ドの

初 期 形 成 に 関 す る電 子 鏡 的 研 究 I. と くに象 牙 芽 細 胞, 基 質 線 維 に つ い て 稲







イ シ ダ イ初 期顎 歯 歯胚 を用 い て, と くに象 牙 芽 細 胞, エ ナ メ ロイ ド基 質 線 維, 従 来 議 論 の あ る組 織 発 生 に 注 目 し, 電 子 鏡 的 な観 察 を行 ない, 以 下 の結 論 を得 た. 1.

エ ナ メル芽 細 胞 と象 牙芽 細 胞 は一 層 の基 底 膜 に よ って境 され, 基 底 膜 は 石 灰 化 の 始

ま る直 前 ま で観 察 され た. 2.

エ ナ メ ロ イ ド基 質 の組 織 発生 は, 基 底 膜 に 直 角方 向 で 象 牙 芽細 胞 と平 行 に 横 紋 の

な い太 さ140∼180Åの

線 維 の形 成 で始 ま る. 次 い で約640Åの

規 則 正 しい横 紋 の あ る線

維 が 現 わ れ, これ らの 線維 に よ って エ ナ メ ロイ ド全 体 の基 質 が 完 成 され る.

226

T. INAGE

3.

象 牙 芽 細 胞 は エ ナ メ ロイ ドの 形 成 に伴 い高 円柱 状 の細 胞 とな り, 細 胞 内小 器 官 は著

し く増 加 し, 蛋 白合 成 型 の 極 性 を 示 した. エ ナ メ ロイ ド基 質 内 には 多 数 の 象 牙 芽 細 胞 の 細 胞 質 突 起 が 認 め られ た. 象 牙 芽 細 胞 内 に は基 質 線維 の前 駆 物 質 を含 む と考 え られ る細 胞 内 顆 粒 が 認 め られ た. 以 上 の こ とか ら, 基 質 線 維 は 中胚 葉 に 由来 す る と考 え られ る. 4.

小 型 で, 針 状 や 管 状 の外 形 を 示 す 結 晶 の 沈着 は, は じ め線 維 束 の 周 縁 に沿 っ て見 ら

れ る. 石 灰 化 が 進 む と 結 晶 は線 維 束 全 体 に 出現 す る. 次 い で 大 型 の棒 状 と板 状 の 外 形 を 示 す 結 晶が 混 在 す る よ うに な る. 小 型 の 結 晶 が 癒合 し, 集 合 体 を形 成 す る も の も認 め られ た.

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稲 毛 稔 彦 〒101東 京 都 千 代 田 区 神 田 駿 河台1-8-13 日本 大 学 歯 学 部 解剖学教室

Dr. Toshihiko INAGE Department of Anatomy Nihon University School of Dentistry 1-8-13 Kanda-Surugadai, Chiyoda-ku Tokyo, 101 Japan

Electron microscopic study of early formation of the tooth enameloid of a fish (Hoplognathus fasciatus). I. Odontoblasts and matrix fibers.

An electron microscope study was made on the tooth germs of Hoplognathus fasciatus in early developmental stage. Special attention was given to the od...
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