268
UNIT 3
Organ Systems
Figure 14-9A.
Bud stage
,
weeks 8–9
. H&E,
3
72; inset
3
140
The
bud stage
is a continuation of the
initiation stage
in which the proliferating and thickening oral epithelium forms the
primary
epithelial band
. In the bud stage, the tooth germ forms a budlike structure that is surrounded by proliferating and accumulating
mesenchymal cells. The combination of the dental lamina and condensed mesenchymal tissues is called the
tooth bud
and develops
into a primary tooth. The
maxillary
and
mandibular prominences
lead to the future upper and lower jaws.
T. Yang
Dental
lamina
Oral
epithelium
Oral
epithelium
Mesenchymal
cells
Tooth
bud
Tooth
bud
Tooth
bud
Tooth bud
Tooth bud
Tooth bud
Primary
Primary
epithelial band
epithelial band
Primary
epithelial band
Dental
Dental
lamina
lamina
Dental
lamina
Dental
Dental
lamina
lamina
Dental
lamina
cells
cells
Mesenchymal
Mesenchymal
Mesenchymal
cells
Mandibular
Mandibular
prominence
prominence
(process)
(process)
Mandibular
prominence
(process)
Oral
epithelium
Maxillary
Maxillary
prominence
prominence
(process)
(process)
Maxillary
prominence
(process)
Oral
epithelium
A
During the bud stage, any disturbance can cause the formation of abnormal teeth, such as
microdontia
(abnormally small teeth)
and
macrodontia
(abnormally large teeth).
T. Yang
Dental
papilla
Enamel
organ
Dental
lamina
Oral
epithelium
Dental
sac
Tooth
germ
Dental
Dental
papilla
papilla
Dental
papilla
Dental
Dental
sac (follicle)
sac (follicle)
Dental
sac (follicle)
Dental
Dental
papilla
papilla
Dental
papilla
Enamel
Enamel
organ
organ
Enamel
organ
Dental
lamina
Oral
epithelium
Dental
Dental
sac
sac
Dental
sac
Stellate
reticulum
B
Figure 14-9B.
Cap stage
,
weeks 10–11
. H&E,
3
72; inset
3
204
The
cap stage
is a continuation of the bud stage and results from the enlargement and unequal growth of the tooth bud. At this stage,
the enamel organ is formed and attaches to the remaining dental lamina. The base of the enamel organ becomes concave and appears
as a cap-shaped structure with mesenchymal cells beneath it. These mesenchymal cells are condensed, forming a
dental papilla
that
will form the future dental pulp. Other mesenchymal cell layers surrounding the enamel organ and dental papilla are called the
dental sac (dental follicle)
. At this stage, the morphogenesis and formation of the tooth germ are ongoing. The cell proliferation and
movement determine the shape of the tooth.
A disturbance during the cap stage of tooth development can cause clinical tooth
fusion
(two adjacent tooth germs fuse and
develop into a large macrodontic tooth), or
gemination
(one tooth germ develops into two teeth which share a single pulp but have
two crowns [Fig. 14-13A]) and
dens invaginatus
(or
dens in dente
, meaning, “tooth within a tooth”).
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