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THE ANATOMICAL RECORD 252:355–368 (1998)
Three-dimensional Direction and
Interrelationship of Prisms in Cuspal
and Cervical Enamel of Dog Tooth
YOSHINORI HANAIZUMI, YOSHIRO KAWANO, HAYATO OHSHIMA,
MASAAKI HOSHINO, KIICHI TAKEUCHI, AND TAKEYASU MAEDA*
Department of Oral Anatomy II, Niigata University School of Dentistry, Niigata, Japan
ABSTRACT
The three-dimensional architecture of enamel prisms was examined in
cuspal enamel and compared with that in cervical enamel by light and
electron microscopy as well as computer-assisted reconstruction using the
developing enamel of several dog teeth.
Dog tooth enamel consists of two groups of alternately arranged enamel
prisms oriented in opposite sideward directions basically forming thick
horizontal rings, partly branching off from the stem. Along a 8–10 enamel
prism-wide group, the enamel prisms emerge in parallel tilting uniformly to
the same sideward direction. In cervices, groups of enamel prisms are
arranged nearly in parallel displaying a regular arrangement of prisms.
Approaching the cusp of tooth, the groups of enamel prisms fuse to a
concentric cusp-centered arrangement and the prisms exhibit no periodic
arrangement as shown in the cervical enamel.
It is suggested that the three-dimensional structure of enamel becomes
complicated close to the cusp, contributing to the chewing stress of tooth.
Anat. Rec. 252:355–368, 1998. r 1998 Wiley-Liss, Inc.
Key words: Hunter-Schreger band; enamel prism; dog tooth; three-dimensional reconstruction
It is generally accepted that enamel consists of numerous enamel prisms stretching right or left in their passage
from the enamel-dentin junction to the surface. The HunterSchreger bands that correspond to the zones of longitudinally and transversely cut prisms are observed on longitudinal cut surfaces of tooth enamel in the great majority of
mammals. The three-dimensional course and arrangement of enamel prisms in relation to the formation of the
Hunter-Schreger bands have been examined in various
species using a variety of methods (Erausquin, 1949;
Kawai, 1951, 1955; Applebaum, 1960; Boyde, 1964, 1969;
Osborn, 1965, 1968a,b; Hirota, 1982; Koenigswald et al.,
1987). However, no data sufficiently explain the exact
three-dimensional orientation of enamel prisms. Accordingly, the spatio-temporal relationship between the arrangement of enamel prisms and the Hunter-Schreger
bands remains unclear.
Previous study of cervical enamel of the dog tooth in
three dimensions has shown that groups of enamel prisms
having similar courses form regular arrangements of
laminated structures in the next layer, but in the opposite
direction, appearing as the parazone or diazone of the
Hunter-Schreger bands on the longitudinal plane (Hanair 1998 WILEY-LISS, INC.
zumi et al., 1996). This study, however, failed to demonstrate the characteristic features of cuspal enamel where
the Hunter-Schreger bands showed complex arrangements.
As one ameloblast forms the body of one enamel prism
throughout amelogenesis, study of the three-dimensional
course of enamel prisms has provided accurate information about the directions in which ameloblasts have moved
(Osborn, 1970, 1973; Nishikawa et al., 1988, 1990; Nishikawa, 1992; Hanaizumi et al., 1994). On the basis of the
observation of enamel prisms, some investigators have
speculated that ameloblasts are controlled by secretory
(Osborn, 1970, 1973) or contractile forces of terminal web
filaments (Nishikawa et al., 1988, 1990; Nishikawa, 1992),
but conclusive evidence has not been reported.
Grant sponsor: Japanese Ministry of Education, Science, Sports,
and Culture; Grant number: 09771496.
*Correspondence to: Dr. Takeyasu Maeda, Department of Oral
Anatomy II, Niigata University School of Dentistry, Gakkochodori, Niigata, 951-8514, Japan.
Received 1 December 1997; Accepted 11 May 1998
356
HANAIZUMI ET AL.
Figs. 1,2. Light micrograph of longitudinal ground section of a dog
canine tooth stained with hematoxylin in cuspal (Fig. 1) and cervical
(Fig. 2) enamel. Dark and light zones correspond to the parazone (p) and
diazone (d) of the Hunter-Schreger bands, consisting of longitudinally and
transversely cut prisms. Fig. 1 ⫻80, Fig. 2 ⫻150. Scale bar ⫽ 100 µm. D,
dentin; E, enamel.
The present study aims to demonstrate the threedimensional architecture of enamel in cusps as compared
with that in cervices and simultaneously proposes a possible force controlling ameloblast movement. The study
examined an erupted dog tooth and the developing enamel
of several dog tooth germs in three-dimensions by light
microscopy as well as by scanning and transmission
electron microscopy. A computer-assisted reconstruction of
the Hunter-Schreger bands was also attempted.
in 5% EDTA (pH 7.4) for 3 weeks. Tooth germs were
postfixed in 1% osmium tetroxide for 3 hours, dehydrated
in ethanol, and embedded in Spurr’s resin.
The molar tooth germ was sectioned in one direction
until the longitudinal plane near the cusp was obtained.
Following the longitudinal sectioning, the resin block was
remounted on the ultramicrotome at a right angle to the
sectioning plane. One-µm thick horizontal serial sections
perpendicular to the tooth axis were made from the cusp
for a distance of 340 µm (see Fig. 6).
The longitudinal and serial tangential semithin sections
of canine tooth previously made (Hanaizumi et al., 1996)
were used for this study. All the sections were stained with
methylene blue and azure II, and photographed with a
light microscope (Nikon Microphot FXA, Tokyo).
MATERIALS AND METHODS
Light Microscopy
Ground sections of enamel were cut and polished from
an erupted canine of an adult dog that had been stored in
5% neutral formalin solution. The longitudinal 80–90 µm
thick ground sections were then etched for 15 seconds with
0.1 N hydrochloric acid, briefly washed in tap water, and
stained with hematoxylin. A 1-month-old pup was anesthetized with Nembutal (0.5 ml/kg body weight intravenouly)
and perfused with a mixture of 0.1 M phosphate-buffered
solution of 2% paraformaldehyde and 1.25% glutaraldehyde at pH 7.4. The jaws were removed and immersed in
the same fixative overnight. Permanent tooth germs were
dissected out and molar tooth germs were demineralized
Scanning Electron Microscopy
Some of the molar tooth germs, dissected as described
above, were immersed in buffered 2% OsO4 solution for
several hours at 4°C. To remove the enamel organ and
expose the enamel surface without causing mechanical
damage, the remaining molar tooth germs were processed
for cell-maceration (Ohtani et al., 1988; Ushiki et al., 1990)
to remove cellular elements and their basal laminae,
DIRECTION/INTERRELATIONSHIP OF PRISMS
357
Fig. 3. Tangential semithin section 50 µm from the enamel-dentin junction.
The tangential semithin section shows many belt-like zones roughly perpendicular to the meridian. A single belt-like zone consists of a group of enamel prisms
oriented in the same direction. Groups of prisms oriented in the opposite
direction are arranged in alternate bands. The belt-like zones of the prisms
oriented to the righthand side are labeled p1–8 and those of the inversely
oriented prisms, d1–8. ⫻120. Scale bar ⫽ 100 µm.
Fig. 4. Micrograph of longitudinal semithin section parallel to the tooth axis
in a cervical region. Parazones (p) and diazones (d) of the Hunter-Schreger
bands were arranged at equal intervals, partly showing confluence and
divergence (ⴱ). Ab, ameloblast; D, dentin; E, enamel. ⫻140. Scale bar ⫽
100 µm.
leaving the extracellular matrix. The fixed specimens were
immersed in a 5% aqueous solution of NaOH for 2–3 days
at room temperature, rinsed with distilled water for 1–2
days, with these processes repeated several times. The
NaOH-treated specimens were then dehydrated, transferred to isoamyl acetate, and critical-point dried with
liquid CO2.
The dried specimens were then affixed on aluminum
stubs with double-sided tape and coated with platinum in
an ion coater (Hitachi E-1032, Hitachi, Tokyo). The specimens were then observed under the scanning electron
microscope (Hitachi S-4000) at an accelerating voltage of
10kV.
graphic printing paper and the boundaries between the
groups of enamel prisms traced on tracing paper. Using
the outline of each section as a reference, the images of the
enamel prisms and the boundaries were read serially into
a personal computer (NEC PC-9801 VM) using software
for three-dimensional graphic analysis (Cosmozone 2SA,
Nikon, Japan). The reconstructed images were photographed from the computer display.
Three-dimensional Reconstruction
The light microscopic images of horizontally or tangentially cut serial semithin sections were enlarged on photo-
RESULTS
Longitudinal Section
In etched and hematoxylin-stained longitudinal ground
sections, parazone and diazone of the Hunter-Schreger
bands, consisting, respectively, of longitudinally and transversely cut prisms were clearly visible (Figs. 1,2). The
distribution of parazones and diazones appeared curved
358
HANAIZUMI ET AL.
Fig. 5. Tangential sections 55 µm (a) and 85 µm (b) from the enameldentin junction. (a) A straight row of enamel prisms perpendicular to the
boundaries of groups of enamel prisms (E1–5) has been selected on the
section and numbered 1 to 27 from the top. (b) The section 30 µm from
section (a). The row of enamel prisms aligned straight in Figure 6a shows
a wavy sine curve. ⫻10. Scale bar ⫽ 50 µm.
with the concavities in the cuspal region (Fig. 1), each zone
alternating in parallel in the cervical enamel (Fig. 2).
A longitudinal semithin section parallel to the tooth axis
revealed parazones and diazones distributing at equal
intervals in the cervical region (Fig. 4), whereas the bands
were arranged irregularly in the cuspal region (see Fig.
7a). Over the tip of cusp, enamel prisms showed a complicated course of enamel prisms. Some prisms extended from
the enamel-dentin junction and changed the angle of tilt
abruptly near the boundaries of the bands (see Fig. 7b).
secretory face of Tomes’ process is situated at right angles to
the longitudinal axis of the prism (Boyde, 1967, 1969; Wakita
et al., 1981; Hanaizumi et al., 1994). With this in mind, the
direction of the enamel prisms here could be estimated from
the inclination of the top of the prism sheaths. A single
belt-like zone consisted of a group of 8–10 enamel prisms
oriented in the same direction. Groups of prisms oriented in
the opposite direction were arranged in alternate bands. The
belt-like zones of the prisms oriented to the right are labeled
p1–8, and those of the inversely oriented prisms, d1- 8 (Fig. 3).
A straight row of enamel prisms aligned perpendicular to the
boundaries between adjacent groups of prisms was selected on
a section 55 µm from the enamel-dentin junction and the
prisms numbered from the top (Fig. 5a, 6). The marked
enamel prisms were traced on the next serial section so they
overlapped each other. On a section 30 µm from the section
where the row of enamel prisms was aligned straight (Fig. 5a),
Tangential Section
The tangential semithin section cut at 50 µm from the
enamel junction showed many belt-like zones roughly perpendicular to the meridian. It has been known that enamel prism
sheath represents the fossilized path traced by the Tomes’
processes during enamel secretion (Boyde, 1967) and that
DIRECTION/INTERRELATIONSHIP OF PRISMS
359
Fig. 6. Diagram showing the spatio-temporal relationship between the longitudinal section (plane L) and
horizontal section (plane H). The middle block of enamel is reconstructed.
the row of enamel prisms appeared to be arranged in a wavy
sine curve (Fig. 5b).
Horizontal Section
Horizontal semithin section 280 µm from the cusp of the
tooth showed a concentric pattern of belt-like zones (Fig.
8b). Each zone was composed of a group of 8–10 enamel
prisms oriented in the same direction similar to the
tangential section shown in Figure 3 (Fig. 8b). The groups
of prisms oriented clockwise were labeled p1–3 and those
inversely oriented, d1–6 (Fig. 8a). A straight row of enamel
prisms perpendicular to the lower edge of the section
crossing the tooth axis has been selected on the section 300
µm from the cusp and are numbered 1–25 from the top
(Fig. 9a). On a section 10 µm from the first, the number 5
prism showed the curved portion changing the angle of tilt
(Fig. 9b). At 35 µm from the first section, the row of enamel
prisms formed a wavy curve but did not display a periodic
pattern as shown in the cervical region (Fig. 9c).
Scanning Electron Microscopy
The exposed surface of developing enamel showed numerous pits, each consisting of a combination of a flat face and
its enclosing face (Fig. 10b). A group of pits inclined
uniformly toward the same sideward direction was arranged in a concentric pattern around the cusp (Fig. 10a).
The neighboring groups of pits inclined toward the opposite direction. Narrow bands consisting of a few small
round pits with flat faces directed perpendicular to the
developing enamel surface were found between the neighboring band-like groups of pits (Fig. 10c).
Three-dimensional Reconstruction of Groups
of Enamel Prisms
Groups of enamel prisms in the cervical enamel, oriented uniformly in the same direction (as shown in Fig. 3)
were reconstructed from serial tangential sections over an
interval of 80 µm, longer than the 60 µm demonstrated by
360
HANAIZUMI ET AL.
Fig. 7. Micrographs of longitudinal semithin section cut parallel to the
tooth axis in cuspal enamel. (a) Parazone (p) and diazone (d) of the
Hunter-Schreger bands are distributed irregularly. ⫻100. Scale bar ⫽ 100
µm. (b) Enlargement of (a). Some enamel prisms change angle of tilt near
the boundaries of the bands (arrowheads). ⫻320. Scale bar ⫽ 50 µm. Ab,
ameloblasts; D, dentin; E, enamel; p, parazone; d, iazone.
DIRECTION/INTERRELATIONSHIP OF PRISMS
Fig. 8. Micrographs of horizontal semithin section 280 µm from the
cusp of a tooth. (a) The semithin sections show many belt-like zones
approximately arranged around the tooth axis. The groups of the prisms
oriented to the clockwise direction are labeled to p1–3 (yellow area) and
those of the inversely oriented prisms, d1–6. The lower edge of the
horizontal section is adjusted to the longitudinal section shown in Figure 7.
361
Ab, ameloblast. ⫻170. Scale bar ⫽ 100 µm. (b) High magnification of (a).
The belt-like zones consist of groups of prisms oriented in the same
direction. Right pointing arrowheads (䉴) show groups of prisms oriented
to the right. Left pointing arrowheads (䉳) show groups of prisms oriented
to the left. There are groups of round, smaller prisms between neighboring
zones (ⴱ). ⫻340. Scale bar ⫽ 25 µm.
362
HANAIZUMI ET AL.
cervices. The different appearance between cuspal and
cervical enamel was that cuspal enamel showed a concentric belt-like arrangement tilting apically (Fig. 12).
Three-dimensional Reconstruction of
Enamel Prisms
A row of enamel prisms and the boundaries of the groups
of enamel prisms selected in the cervical (Fig. 5) or cuspal
(Fig. 9) enamel were reconstructed at 50 µm intervals and
viewed obliquely from the surface (Figs. 13,14). Reconstructions of the boundaries of the groups of enamel prisms and
a row of enamel prisms demonstrated the three-dimensional interrelationship between the boundaries and the
prisms. Each group consisted of enamel prisms tilting to
the same sideward direction, whereas those in the neighboring zones were oriented in the opposite direction. In the
cervical enamel, the cut ends of the enamel prisms formed
a wavy sine curve approaching the enamel surface (Fig. 13a).
In a single group, the horizontal tilt angles of prisms toward
the enamel-dentin junction tend to be greatest at the center
and smallest near the boundaries (Fig. 13b).
In the cuspal enamel, groups of enamel prisms did not
display a periodic tilting pattern like in the cervical region
because of the irregular distribution of the prism groups
(Fig. 14a). Some prisms twisted to run in the opposite
sideward direction after crossing the boundaries between
the neighboring groups of enamel prisms (Fig. 14b).
DISCUSSION
Three-dimensional Structure of Enamel
Fig. 9. Horizontal semithin sections 300 µm (a), 290 µm (b) and 265
µm (c) from the cusp of the tooth. (a) A straight row of enamel prisms
perpendicular to the lower edge of the section crossing the tooth axis and
the groups of enamel prisms (E1–3) has been selected and is numbered
1–25 from the top. (b) A section 10 µm from section (a). Note the number 5
prism changing its angle of tilt. (c) A section 35 µm from section (a). The
row of enamel prisms form a wavy curve but does not display the periodic
pattern shown in the cervical region. ⫻310. Scale bar ⫽ 50 µm.
our previous reports (Hanaizumi et al., 1996). The reconstructed images viewed obliquely from the tooth surface
showed both the tangential and longitudinal planes. In
cervical enamel, groups of unidirectionally oriented enamel
prisms showed a nearly parallel belt-like arrangement,
with occasional confluences and divergences (Fig. 11a).
Each group of enamel prisms corresponded to the parazone and diazone of the Hunter-Schreger bands on the
longitudinal plane (Fig. 11b).
Groups of enamel prisms in the cuspal enamel, oriented
uniformly in a clockwise direction (Fig. 12a) or in a
counterclockwise direction (Fig. 12b) in Figure 8b, were
reconstructed from serial horizontal sections at 60 µm
(Fig. 12 a-c) or 80 µm intervals (Fig. 12d). The reconstructed images viewed obliquely from the tooth surface
showed both horizontal and longitudinal planes. The basic
arrangement pattern of groups of enamel prisms in cuspal
enamel was the same as that of groups of prisms from
This study demonstrated that dog tooth enamel consisted of two groups of enamel prisms alternately oriented
in opposite sideward directions basically forming thick
horizontal rings, partly branching off from the stem ring.
Along a certain ring composed of 8–10 enamel prisms wide,
the enamel prisms emerged in parallel tilting uniformly to
the same sideward direction. Groups of enamel prisms
showed a nearly parallel belt-like arrangement in cervical
enamel, whereas groups of prisms came to be arranged in a
concentric cusp-centered lamellae close to the cusp (Fig.
15).
A reconstruction of enamel prisms and their successive
Tomes’ processes have demonstrated that a group of ameloblasts with the similarly inclined secretory faces of Tomes’
processes formed a single group of enamel prisms directed
in the same sideward direction (Hanaizumi et al., 1994).
This suggests that each ameloblast develops a Tomes’
process projection inclining the secretory face either clockwise or counterclockwise around the tooth axis at equal
intervals in the beginning of amelogenesis and migrates
away from the enamel-dentin junction. Therefore, the
ameloblasts groupings appear to correlate with the parazones and diazones of the Hunter-Schreger bands on the
longitudinal cut surface.
Considering that the distribution of the Hunter-Schreger
bands are different among species (Kawai, 1951, 1955;
Shobusawa, 1952; Boyde, 1964; Kozawa, 1978; Rensberger
and Koenigswald, 1980; Boyde and Fortelius, 1986; Gilkeson and Lester, 1989; Stefen, 1997), the patterns of ameloblast group arrangements may also vary in mammals.
DIRECTION/INTERRELATIONSHIP OF PRISMS
Fig. 10. Scanning electron micrographs of the exposed surface of the
developing enamel cleaned of cellular components by the cell-maceration
method, viewed from the cusp. (a) Enamel surface shows many groups of
pits arranged in concentric circles approximately central to the cusp
(arrowhead). ⫻750. Scale bar: 20 µm. (b) Each pit consists of a flat (S)
and an enclosing face (N). ⫻5,400. Scale bar ⫽ 2 µm. (c) Groups of pits
363
with flat faces inclined in the same direction are arranged in a band-like
zone. The pits in the neighboring groups are inclined in the opposite
direction. The boundary between the neighboring groups forms a narrow
zone of small pits (ⴱ) with flat faces directed toward the developing
enamel surface. ⫻1,500. Scale bar ⫽ 10 µm.
364
HANAIZUMI ET AL.
Fig. 11. Three-dimensional reconstructed displays of the groups of
enamel prisms (p1–8 green area, d1–8 blue area) marked in Figure 3,
representing the data from 30–120 µm from the enamel-dentin junction.
The reconstructed groups of enamel prisms are viewed obliquely down to
the tangential (left) or longitudinal (right) planes. The groups of enamel
prisms marked d1–8 are shown semitransparent.
Comparative anatomical studies have paid attention to
potential variability in fossil and extant marsupial enamel
of early mammals and indicated that the Hunter-Schreger
bands first appear in Vombatus ursinus of marsupials
(Lester et al., 1987; Gilkeson and Lester, 1989). From an
evolutionary point of view, the early appearance of the
Hunter-Schreger bands in tooth enamel may coincide with
adaptation to changes on occlusion and in diet diversity as
well as in scale (Koenigswald et al., 1987). An increase in
chewing force would produce the chances of a putative
fracture and crack propagating right through the enamel
surface. The Hunter-Schreger band formations resulting
from the grouping of ameloblasts strengthen the enamel in
respect to the functional load owing to the enamel prisms
decussation in overlying and underlying bands (Osborn,
1965; Sundstrom, 1966; Rensberger and Koenigswald,
1980; Boyde, 1983; Boyde and Fortelius, 1986; Koenigsald, 1987).
In comparing cuspal enamel where groups of enamel
prisms show a concentric pattern arrangement tilting
apically with cervical enamel where groups of prisms are
arranged horizontally in parallel bands, it appears advisable to consider that the structure of the former enamel
restrains horizontal bending stress besides compressive
force more strongly than that of the latter, because more a
complicated three-dimensional course and arrangement of
prisms appear to increase the strength of enamel. We were
not able to explain conclusively why ameloblasts are
grouped to form belt-like arrangements synchronously
inclining the secretory faces of Tomes’ processes toward
the same direction. A further examination of the developmental changes of Tomes’ processes in amelogenesis, including a comparative analysis of various species, will be
necessary for this.
Possible Power Inducing Sideward
Displacement of Ameloblasts
There have been two hypothesis on the origins of the
power inducing the sideward displacement of ameloblasts.
Nishikawa et al.(1988, 1990) observed that contractile
proteins of actin, myosin, tropomyosin, and alpha-actinin,
as well as adherent junction protein of vinculin and
radixin, were located at the terminal webs in the secretory
ameloblasts of the rat incisor. They considered that the
terminal web filaments contribute to the power-generating
machinery of ameloblast transverse movement to produce
enamel prism decussation (Nishikawa et al., 1988, 1990;
Nishikawa, 1992).
Although the contractile power may explain decussation
of single layers of enamel prisms as in the inner enamel of
rodents, it remains unclear how to demonstrate more
complex decussation of enamel prisms in another species.
Further, sideward movement of ameloblasts resulting
from shrinking seems to need an anchor of fixation, but
such an anchor has not been shown.
DIRECTION/INTERRELATIONSHIP OF PRISMS
groups in both the tangential and longitudinal planes. (b) Groups of enamel prisms (d1–6,
blue area) oriented in the opposite direction of those in (a). (c) Image combining (a) and
(b). One group of enamel prisms (d1–6, blue area) made semitransparent. (d) A
reconstructed image of two groups of enamel prisms (green area; p1–8, blue area; d1–6)
over an interval of 70 µm. One group of enamel prisms (d1–6, blue area) made
semitransparent.
365
Fig. 12. Three-dimensional reconstructed displays of the groups of enamel prisms
(p1–3, d1–6) in Figure 8b, representing the data from 290–340 µm (a-c) and 270–340 µm
(d) from the cusp of the tooth. In these images, the reconstructed belt-like zones are
viewed obliquely down to the tooth axis to display both the horizontal and longitudinal
planes. (a) Extracted images of groups of enamel prisms (p1–3, green area) oriented in the
same direction over an interval of 50 µm. Groups of enamel prisms appear almost
concentrically arranged around the tooth axis. Note the confluence and divergence of the
366
HANAIZUMI ET AL.
Fig. 13. Three-dimensional reconstructed display of the numbered
enamel prisms (white area) and the groups of enamel prisms (E1,3,5
green area, E2,4 blue area) in Figure 5 over an interval of 50 µm, viewed
obliquely from the surface. (a) The cut ends of enamel prisms (pink area)
initially perpendicular to the boundaries of the groups of prisms come to
show a periodic tilting pattern approaching the surface. (b) A substruction
of the blue colored groups of prisms (E2,4). In a single group, the
horizontal tilt angles of prisms toward the enamel-dentin junction tend to
be greatest at the center and smallest near the boundaries.
Fig. 14. Three-dimensional reconstructed display of the numbered
enamel prisms (white area) and groups of enamel prisms (E1,3 blue area,
E2 green area) shown in Figure 9 over an interval of 50 µm, viewed from
the cusp of tooth. (a) The cut ends of enamel prisms (pink area) tilt
sideward when approaching the cusp, but prisms do not display the
periodic tilting pattern shown in the cervical region. (b) A substruction of
the green colored groups of prisms (E2). Note the number 1–4 prisms
(arrowheads) twisting to run in opposite sideward directions after crossing
the boundaries between the neighboring groups of enamel prisms.
DIRECTION/INTERRELATIONSHIP OF PRISMS
367
hindered by restraints between ameloblasts shifting in
opposite directions, with the restrained sideward displacement being largest at the boundaries of the groups and
smaller near the center of the groups. However, a precise
knowledge of the origin of the power of the sideward
displacement of ameloblasts remains to be more fully
elucidated.
LITERATURE CITED
Fig. 15. Diagrammatic three-dimensional model of dog enamel structure. Groups of enamel prisms are oriented in pairs in opposite sideward
directions and are drawn as light or dark belts. These groups of prisms
appear to be nearly concentrically arranged around the tooth axis and
show confluence and displacement of the prisms in the belt-like zones.
Osborn (1970, 1973) postulated that enamel matrix
secretion from the proximal portion of ameloblasts produces a potentially high hydrostatic pressure, resulting in
a force pushing the ameloblasts radially outward. It has
been necessary to demonstrate the precise three-dimensional structure of the distal end of ameloblasts, the Tomes’
processes, to substantiate Osborn’s interpretation. Scanning (Skobe, 1977; Wakita et al., 1981) and transmission
(Kallenbach, 1977; Wakita et al., 1981) electron microscopic observations demonstrated that Tomes’ processes
were composed of a flat secretory face slanted cervically
and that its enclosing nonsecretory face was directed
cuspally and that the crystallite arrangement within
prisms and the prism arrangement within enamel were
determined by the three-dimensional structure of Tomes’
processes. It is also well known that the long axis of
enamel prisms is oriented at right angles to the secretory
faces of Tomes’ processes (Boyde, 1967, 1969; Wakita et al.,
1981; Hanaizumi et al., 1994). Moreover, the present
results showed that ameloblasts were able to move their
positions within the sheet plane of cells and that one
ameloblast could change from one to another group by
abruptly changing the sideward angle of tilt toward the
enamel-dentin junction.
These findings would allow the hypothesis that ameloblast movement is from the secretion. If there is a
reaction force pushing the ameloblasts sideward due to
secretion, this power may be almost equal because the
secretory faces of Tomes’ processes in a single group of
ameloblasts are nearly equivalent in size. Our previous
studies (Hanaizumi et al., 1994, 1996) and the present
results have demonstrated that a straight row of enamel
prisms initially perpendicular to the boundaries of groups
of prisms came to arrange itself in a half cycle of wavy
curve as it approaches the enamel surface. With respect to
the wavy curve arrangement of enamel prisms, our previous study (Hanaizumi et al., 1994) speculated that the
crossing of ameloblasts as they moved outward might be
Applebaum E. The arrangement of the enamel rods. New York State
Dent. J. 1980;26:185–188.
Boyde A. The structure and development of mammalian enamel,
Ph. D. thesis, University of London, 1964.
Boyde A. The development of enamel structure. Proc. Royal Soc. Med.
1967;60:923–928.
Boyde A. Correction of ameloblast size with enamel prism pattern: Use
of scanning electron microscopy to make surface area measurements. Z. Zellforsch 1969;93:583–593.
Boyde A. Airpolishing effects on enamel, dentine and cement. Br. Dent.
J. 1983;156:287–291.
Boyde A, Fortelius M. Development, structure and function of rhinoceros enamel. Zoo. J. Linn. Soc. 1986;87:181–214.
Erausquin J. The aspect of bands of Schreger in horizontal sections of
the enamel. J. Dent. Res. 1949:28:195–200.
Gilkeson CF, Lester KS. Ultrastructural variation in enamel of
Australian marsupials. Scan. Electron Microsc. 1989;3:177–191.
Hanaizumi Y, Shimokobe H, Wakita M. The three-dimensional structure of Tomes’ processes and their relationship to arrangement of
enamel prism in dog teeth. Arch. Histol. Cytol. 1994;57:129–138.
Hanaizumi Y, Maeda T, Takano Y. Three-dimensional arrangement of
enamel prisms and their relation to the formation of HunterSchreger bands in dog tooth. Cell Tissue Res. 1996;286:103–114.
Hirota F. Prism arrangement in human cusp enamel deduced by X-ray
diffraction. Arch. Oral Biol. 1982;27:931–937.
Kallenbach E. Fine structure of secretory ameloblasts in the kitten.
Am. J. Anat. 1977;148:479–512.
Kawai N. The bands of Schreger observed through the enamel surface.
Okajimas Fol. Anat. Jap. 1951;26:25–28.
Kawai N. Comparative anatomy of the bands of Schreger. Okajimas
Fol. Anat. Jap. 1955;27:115–131.
Koenigswald WV, Rensberger JM, Pretzschner HU. Changes in the
tooth enamel of early Paleocene mammals allowing increased diet
diversity. Nature 1987;328:150–152.
Kozawa Y. Comparative Histology of Proboscidean molar Enamel. J.
Stomatol Soc. Jap. 1978;45:585–606.
Lester KS, Boyde A, Gilkeson C, Archer M. Marsupial and monotreme
enamel structure. Scan. Electron Microsc. 1987; 1:401–420.
Nishikawa S, Fujiwara J, Kitamura H. Formation of the tooth enamel
rod pattern and the cytoskeletal organization in secretory ameloblasts of the rat incisor. Eur. J. Cell Biol. 1988;47:222–232.
Nishikawa S, Tsukita S,Tsukita S, Sasa S. Localization of adherent
junction protein along the possible sliding interface between secretory ameloblasts of the rat incisor. Cell Str. Funct. 1990;15:245–249.
Nishikawa S. Correlation of the arrangement pattern of enamel rods
and secretory ameloblasts in pig and monkey teeth: A possible role of
the terminal webs in ameloblasts movement during secretion. Anat.
Rec. 1992;232:466–478.
Ohtani O, Ushiki T, Teshima A. Collagen fibrillar networks as skeletal
frameworks: A demonstration by cell- maceration/scanning electron
microscope method. Arch. Histol. Cytol. 1998;51:249–261.
Osborn JW. The nature of the Hunter-Schreger bands in enamel. Arch.
Oral Biol. 1965;10:929–993.
Osborn JW. Directions and interrelationships of enamel prisms from
the sides of human teeth. J. Dent. Res. 1968a; 47:223–232.
Osborn JW. Directions and interrelationships of prisms in cuspal and
cervical enamel of human teeth. J. Dent. Res. 1968b; 47:395–402.
Osborn JW. The mechanism of ameloblasts movement: A hypothesis.
Calc. Tiss. Res. 1970;5:344–359.
368
HANAIZUMI ET AL.
Osborn JW. Variations in the structure and development of enamel. In:
Melcher AH, Zard GA, eds. Dental Enamel, Vol. 3. Munksgard,
Copenhagen: Oral Science Reviews, 1973.
Rensberger JM, Koenigswald MV. Functional and phylogenetic interpretation of enamel microstructure in rhinoceroses. Paleobiology
1980;6:477–495.
Shobusawa M. Vergleichende Untersuchungen über die Form der
Schmelzprismen der Saugetiere. Okajimas Folia. Anat. Jpn., 1952;
24:371–392.
Skobe Z. Enamel formation in the monkey observed by scanning
electron microscopy. Anat. Res., 1977;187:329–334.
Stefen C. Differentiations in Hunter-Schreger bands of carnivores. In
Koenigswald MV, Sander, PM, eds. Tooth Enamel Microstructure.
pp. 123–136, 1997.
Sundstrom B. Schreger bands and their appearance in microradiographs
of human dental enamel. Acta. Odont. Scand. 1966;24:179–194.
Ushiki T, Ide C. Three-dimensional organization of the collagen fibrils
in the rat sciatic nerve as revealed by transmission- and scanning
electron microscopy. Cell Tissue Res. 1990;260:175–184.
Wakita M, Tsuchiya H, Gunji T, Kobayashi S. Three- dimensional
structure of Tomes’ processes and enamel prism formation in the
kitten. Arch. Histol. Jap. 1981;44:285–297.
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