Dental Histology Hardest Exam: Quiz!

Narrow (up to 8 μm in diameter, and extend up to 25 μm
into the enamel
* Common beneath cusps
* Result of some odontoblast processes

* Sheet-like, structural faults
* Hypomineralised, narrower, longer and less common than enamel tufts
* May arise developmentally due to incomplete maturation of groups of prisms

EARLY BELL STAGE (CERVICAL LOOP)

A high-power view of the early bell. A = external enamel epithelium; B = cervical loop; C = stellate reticulum; D = enamel cord; E = stratum intermedium; F = internal enamel epithelium; G = dental papilla.

Oral epithelium thickens
and invaginates into the
mesenchyme to form a
primary epithelial band.
• The first sign of tooth
development is the
condensation of
mesenchymal tissue which
are ectomesenchymal
(neural crest) in origin,
having migrated into the
jaws from the margins of
the neural tube.

Early cap stage of tooth development (arrows). A = Meckel's cartilage; B = developing tongue

11th week
morphogenesis- the
deeper surface of the
enamel organ
invaginating to form a
cap-shaped structure.
• Poorly
histodifferentiated.
• External and internal
dental epithelium
forming.

Buccolingual section through a resorbing deciduous tooth (A) and its erupting
successor (B). Arrows indicate multinucleated odontoclasts

Resorption of the hard tissues of the deciduous tooth
takes place by the activity of multinucleated osteoclastlike cells termed odontoclasts. The vascular, resorbing
tissue has been termed the resorbing organ of Tomes.
• Odontoclasts lie within resorption lacunae (Howship's
lacunae). Odontoclasts, like osteoclasts, differentiate
from circulating monocyte-like cells. They are
vacuolated and have long cytoplasmic processes, an
abundance of ribosomes and a large number of
mitochondria. Howship's lacunae in resorbing teeth
tend to be larger and more spherical than lacunae in
bone.

In some areas such as the gingiva the nuclei may be retained, although small and shrunken. These cells are described as parakeratinized (in contrast to the more usual orthokeratinized cells without nuclei)

• Lining of the oral cavity
• Epithelium with an
underlying connective
tissue (the lamina
propria).
• Third layer (the
submucosa) is found
between the lamina
propria and the
underlying bone (palate)
or muscle (cheeks and
lips).

2 LAMINA PROPRIA LAYERS =
Superficial, papillary layer between the
epithelial ridges, in which the collagen fibres are thin
and loosely arranged.
-Deep, reticular layer dominated by thick,
parallel bundles of collagen fibres.

Section showing regions of oral mucosa. A = stratified squamous epithelium; B =
lamina propria; C = submucosa; D = bone

Section of the attached gingiva. The epithelium is a keratinized stratified squamous
epithelium. The lamina propria is dense and relatively avascular and the interface with the
epithelium is highly folded. The lamina propria is directly attached to the underlying alveolar
bone (A), forming a mucoperiosteum. Arrows indicate surface stippling.

Dentine mineraliztion -starts
as globules or calcospherites
which fuse to form a
uniformly calcified tissue.
– Sometimes the fusion may be
incomplete and viewed in
transmitted light, the
uncalcified, interglobular
areas appear dark.
– Dentinal tubules pass through
interglobular areas and since
these areas remain
uncalcified, peritubular
dentine is also absent from
the tubules as they pass
through interglobular
dentine

Change in direction of tubules bw
primary and secondary dentine.
• The same odontoblasts continue to
lay down dentine and the tubules of
primary and secondary dentine are
continuous.
• Secondary dentine formation begins
at the completion of root formation
as the tooth comes into occlusion.
• Secondary dentine formation
continues throughout life leading to
smaller pulp chambers and narrower
root canals in older patients.

Characterized by desmosomes between cells that look 'prickly"

Fig 11.21: Attachment of the periodontal ligament fibres to cementum. The fibres of the periodontal
ligament (B) are seen to run into the organic matrix of precementum (A)

In the teeth, Sharpey's fibres are
the terminal ends of principal fibres
(of the periodontal ligament) that
insert into the cementum and into
the periosteum of the alveolar
bone

Section of the attached gingiva (A) and alveolar mucosa stripped off from underlying
bone. The arrow points to the sharp demarcation site of the mucogingival junction. Note the
keratinized epithelium covering the attached gingiva, the non-keratinized epithelium covering
the alveolar mucosa and the numerous blood vessels in the alveolar mucosa.

If the primary
odontoblasts are killed
by an external stimulus,
or retract before
peritubular dentine
occludes the tubules,
empty air-filled tubules
will be left.
– They may be sealed at
their pulpal end by
tertiary dentine.
Fig. 9.62 : Dead tract (A) beneath a region of attrition that is sealed pulpally by tertiary
dentine (C) and secondary dentine (B).

Enamel and dentine formation
commencing at the tips of future cusps
(or incisal edges).
• Under the inductive influence of
developing ameloblasts (preameloblasts), the adjacent mesenchymal
cells of the dental papilla become
columnar and differentiate into
odontoblasts.
• The odontoblasts then become involved
in the formation of predentine and
dentine. The presence of dentine then
induces the ameloblasts to secrete
enamel.
Fig 21.16: Late bell stage (appositional stage) of tooth development. Dentine matrix stained
blue; enamel matrix stained red. A = permanent tooth.

Dentinal tubules fill in
due to age, external
stimuli (caries,
attrition).
• Type of dentine that
lacks structure and
appear transparent.

Very thin layer of non-prismatic enamel present in the first enamel formed at the enamel–dentine
junction

The outer 20–70 μm of teeth is non-prismatic. Here, the enamel
crystallites are all aligned at right angles to the surface and parallel to
each other. This surface layer is more highly mineralized than the rest of
the enamel because of the absence of prism boundaries, where more
organic material is located. Its thickness is variable. A very thin layer of
non-prismatic enamel, just a few microns wide, has also been reported
to be present in the first enamel formed at the enamel–dentine
junction. Non-prismatic enamel occurs as a result of the absence of
Tomes processes from the ameloblasts in the first and final stages of
enamel deposition. At dentinoenamel junction, the crystallites appear
to lie in random orientations. The final part of the enamel formed at the
surface of the crown is also aprismatic, but in this region the crystallites
are arranged uniformly parallel to each other.

The enamel niche (C). A = lateral
enamel strand; B = medial enamel strand

When the secondary
curvatures coincide they
give rise to an optical
effect, resulting in the
contour lines of Owen.
– They are unusual in
primary dentine but are
sometimes seen.
– An exaggerated line is
found at the border of
primary and secondary
dentine and between
dentine formed before and
that formed after birth

surrounds serous cells, contracts cells and pushes saliva into oral cavity

14th week- further morphodifferentiation and
histodifferentiation of the tooth germ lead to the early
bell stage of the internal enamel epithelium broadly
maps out the occlusal pattern of the crown of the
tooth (differential mitosis).
• The future cusps and incisal margins are sites of
precocious cell maturation associated with cessation of
mitosis, while areas corresponding to the fissures and
margins of the tooth remain mitotically active. Thus,
cusp height is related more to continued downward
growth at the margin and fissures than to upward
extension of the cusps.

Dental lamina breaks down and the enamel organ
loses connection with the oral epithelium.
• A high degree of histodifferentiation is achieved
in the early bell stage.
• The enamel organ shows four distinct layers:
external enamel epithelium, stellate reticulum,
stratum intermedium and internal enamel
epithelium.
• The cervical loop at the margins of the enlarging
bell-shaped enamel organ is a site of mitotic
activity.

granular layer is between prickle (A) and keratinized (C)

Hypercementosis refers to a condition characterized by excessive cementum formation around the roots of teeth. This condition can occur as a result of various factors such as trauma, inflammation, or excessive occlusal forces. It is often observed in response to chronic irritation or stimulation, leading to the thickening of the cementum layer. Hypercementosis can be seen on dental radiographs as an increased radiopaque area around the roots of affected teeth.

Fig 9.47: Ground section of dentine with long
period (horizontal) line 20μm apart and between
them 7-8 short term incremental lines.

Short-period markings may be seen
as alternating dark and light bands,
each pair reflecting the diurnal
rhythm of dentine formation, daily
alteration in dentine deposition.
– Referred to as von Ebner's lines.
– In cuspal dentine, where
deposition is most rapid, the
amount of dentine formed each
day and the distance between
adjacent dark bands is
approximately 4 μm.
– In the root peripherally near the
granular layer, where the dentine
has a calcospheritic pattern, the
distance between lines is nearer 2
μm .
– Seen as banding around the
dentinal tubules. Are perpendicular
to the dentinal tubules

Junctional structures, inner 1/3 of enamel, travel in same direction of prisms
* Hypomineralized and recur at 100μm intervals along the junction
* Contain ‘tuftelin’ (non-amelogenin)

Resorption of deciduous teeth is not a continuous
process. During rest periods, reparative tissue
may be formed, leading to a reattachment of the
periodontal ligament. The tissue of repair is
cementum-like and the cells responsible for its
formation are similar in appearance to
cementoblasts . If the repair process prevails over
the resorption, the tooth may become ankylosed
to the surrounding bone, with loss of the
periodontal ligament . Ankylosis may also be
caused by trauma or infection of a tooth

Saliva is produced in and secreted from salivary glands. The basic secretory units of salivary glands are clusters of cells called an acini. These cells secrete a fluid that contains water, electrolytes, mucus and enzymes, all of which flow out of the acinus into collecting ducts

Section of oral epithelium showing cells undergoing cell replication (red stain).

Demineralized section showing junctional epithelium (A) having proliferated
rootwards to lie on cemental surface of root (B). C = enamel space; D = dentine.

An erupting deciduous molar before its emergence into the oral cavity. A = enamel
space; B = developing roots; C = developing alveolar crypt; D = oral mucosa and overlying
connective tissue; E = reduced enamel epithelium .

SEMs of fractured surface of root illustrating acellular extrinsic fibre
cementum (AEFC). PLFB = inserting periodontal ligament fibre bundles; CIFC =
underlying cellular intrinsic fibre cementum.

This type of cementum is composed only of intrinsic
fibres running parallel to the root surface. The absence
of Sharpey fibres means that intrinsic fibre cementum
has no role in tooth attachment.
• It generally corresponds to secondary cellular
cementum and is found in the apical third of the root
and in the interradicular areas.
• Although intrinsic fibre cementum is generally cellular
because of the rapid speed of formation, sometimes
intrinsic fibre cementum is formed more slowly and
cells are not incorporated (acellular intrinsic fibre
cementum).

Initial stage of enamel formation. A = odontoblasts; B = ameloblasts; C = stratum
intermedium D = stellate reticulum; E = external enamel epithelium; F = developing enamel; G =
developing dentine

Late cap stage of tooth development. A = stellate reticulum; B = external enamel epithelium; C = internal enamel epithelium; D = dental papilla; E = dental follicle

12th week (late cap stage)- the central cells of the enlarging
enamel organ have become separated (although
maintaining contact by desmosomes), the intercellular
spaces containing significant quantities of
glycosaminoglycans. This is called stellate reticulum.
• The cells of the external enamel epithelium remain
cuboidal.
• Internal enamel epithelium cells become more columnar,
increase in RNA content and hydrolytic and oxidative
enzyme activity.
• The part of the mesenchyme lying beneath the internal
enamel epithelium is termed the dental papilla, while that
surrounding the tooth germ forms the dental follicle.

Appearance of cellular intrinsic fibre cementum (CIFC). Note the absence of
Sharpey fibres and the parallel distribution of the bundles of mineralized intrinsic fibres.
Inset shows that Sharpey fibres (SF) can occasionally be seen inserting into CIFC.

This photo is of the buccal mucosa, which is the lining of the inner cheeks. Additionally, "D" refers to the salivary gland, which is a gland that produces saliva and is located in the buccal mucosa.

Section showing layers of keratinized oral epithelium.
A = basal layer (single cell layer, cuboidal cells, stem cells originate here that generate "transit-amplifying cells that give rise to replacement keratinocytes")
B = prickle cell layer (above basal cell layer, round or ovoid, desmosomes increase in # and become more obvious than basal)
C = granular layer (increased in maturation, cells are larger and flatter contain keratohyaline granules w/ filaggrin that binds keratin filaments together into a stable network)
D = keratinized layer (final stage of maturation, loss of all organelles, autolysis due to proteases. Filled entirely with tonofilaments surrounded by matrix protein filaggrin)

Section of skin of lip. A = keratinized epidermis; B = shaft of hair; C = sebaceous
gland; D = dermis.

•Dentine has regular, incremental, short
period and long period markings.
•They can be attributed to circadian
fluctuations in acid–base balance that
affect both the mineral content and the
refractive index of forming hard tissues
and associated with changes in collagen
fibril orientation.
•The coarser, long-period lines (Andresen
lines) are approximately 16–20 μm apart.
•Between each long-period line there are
six to 10 pairs of short-period lines.
•The cause for the 6–10-day periodicity is
unknown. The same periodicity exists
between the long-period striae of Retzius
in enamel and the long-period Andresen
lines in dentine, making it likely that a
common mechanism exists.

Lines associated with the
primary curvatures of
the dentinal tubules.
– The peaks of the sigmoid
primary curvatures
coincide to form broad
bands in the dentine.
– Known as Schreger
lines.

The relationship between cementum (B), precementum (arrow), a layer of cementoblasts
(A) and the periodontal ligament (C).

Developmentally, cementum is said to be derived from the
investing layer of the dental follicle.
• Like dentine, there is always a thin layer (3–5 μm) of uncalcified
matrix on the surface of the cellular variety of cementum called
precementum.

• These lines represent rest periods in cementum
formation.
• These lines are parallel to the long axis of the tooth.

Dentinoenamel junction showing A=enamel tuft, B= enamel spindle, C- enamel
lamella, D= dentine, E= enamel.

Dentinoenamel junction
• The boundary between enamel and dentine.
• Scalloping pattern (25 μm and 100 μm)
• Present beneath cusps and incisal edges where shearing forces
would be high; the enamel–dentine junction is smoother on the
lateral surfaces of the crown.
• The convexities of the scallops are on the enamel surface with the
concavities on the dentinal surface
• The enamel–dentine junction is less mineralized than either the
enamel or dentine.
• A number of features can be seen at the enamel–dentine junction
(amelodentinal junction), extending from the dentine surface into
the enamel including enamel spindles and tufts.

Longitudinal section of a root showing the granular (A) and hyaline (C) layers beneath
a layer of acellular cementum (B).

In ground sections the periphery of the dentine in the root
is marked by the presence of a dark granular zone, the
granular layer.
– Dentinal tubules in this area branch more profusely and
loop back on themselves, creating air spaces in ground
sections that result in internal reflection of transmitted
light.
– Differences in the rate of formation of coronal and
radicular dentine could explain why this appearance is
seen in the root but not the crown.
– The granular layer is hypomineralized in comparison to
circumpulpal dentine.
– An alternative explanation for the granular appearance is
that it is due to the incomplete fusion of calcospherites
Outside the granular layer is a clear hyaline layer
usually included as a component of the dentine
but whose origin is obscure.
– This narrow band (up to 20 μm wide) appears to
be non-tubular and relatively structureless.
– The hyaline layer may serve to bond cementum to
dentine and may be of considerable clinical
significance when considering periodontal
regeneration.

Bud stage of tooth development. A = enamel organ; B = mesenchymal condensation

The soft tissues overlying the enamel space (A) of an erupting tooth. B = oral
epithelium; C = connective tissue between developing tooth and oral epithelium. Arrow
indicates the reduced enamel epithelium

A= odontoblast, C= predentine, B=mineralized dentine matrix

The salivary glands are composed of two main elements: glandular secretory tissue, also known as parenchyma, and supporting connective tissue, also known as stroma. The glandular secretory tissue is responsible for producing and secreting saliva, while the supporting connective tissue provides structural support and helps maintain the shape and integrity of the glands. These two elements work together to ensure the proper functioning of the salivary glands.

During development changes in the enamel
secretory rhythm, chemical composition
and/or the position of the developing enamel
front are recorded as incremental features.
There are two main types of incremental line:
short period (cross-striations) and long period
(enamel striae)

Extrinsic fibres in ground sections. The arrows indicate that the core of the
extrinsic fibre bundle has been lost during preparation of the ground section and
replaced with air or debris

For this type of cementum all the collagen is derived as
Sharpey fibres from the periodontal ligament (the
ground substance itself may be produced by the
cementoblasts).
• This type of cementum corresponds with primary
acellular cementum and therefore covers the cervical
two-thirds of the root . It is therefore formed slowly
and the root surface is smooth.
• The fibres are generally well mineralized.

A specialized feature associated with the erupting permanent tooth
is the presence of a gubernacular canal. The gubernacular canal
contains the gubernacular cord.
• The cord is composed of a central strand of epithelium (derived
from the dental lamina) surrounded by connective tissue. The
connective tissue is organized into inner and outer layers. Collagen
fibres of the inner layer show greater organization and run mainly
parallel to the long axis of the epithelium. In the outer layer, the
collagen fibres are fewer and less organized. Differences between
the layers can also be discerned with respect to the vasculature, the
vessels in the outer layer being larger. During eruption, the
gubernacular cords decrease in length but increase in thickness and
become less dense.
• Surgical removal of the cord does not prevent eruption of the
permanent tooth.