15.6.2015
Development of Teeth
Dr. Archana Rani
Associate Professor
Department of Anatomy
KGMU UP, Lucknow
Introduction
• Teeth are formed in
relation to the alveolar
process.
• Epithelial thickening:
Dental lamina
• Enamel organs: Series
of 10 local thickenings on
dental lamina in each
alveolar process.
• Each thickening forms
one milk tooth.
Formation of enamel organs
Stages in the formation of enamel organ
Bud stage :
• Characterized by formation of a tooth bud.
• The epithelial cells begin to proliferate into the
ectomesenchyme of the jaw.
Cap stage :
• Formation of dental papilla.
• The enamel organ & dental papilla forms the tooth germ.
• Formation of ameloblasts.
• Formation of odontoblasts.
Bell stage:
•
•
•
The cells on the periphery of the enamel organ separate into three important layers:
Cuboidal cells on the periphery of the dental organ form the outer enamel
epithelium.
The cells of the enamel organ adjacent to the dental papilla form the inner enamel
epithelium.
The cells between the inner enamel epithelium and the stellate reticulum form a
layer known as the stratum intermedium.
The dental lamina begin to disintegrates, leaving the developing teeth completely
separated from the epithelium of the oral cavity.
Crown stage :
1. Mineralization of hard tissues occur.
2. The inner enamel epithelial cells change
in shape from cuboidal to columnar. The
nuclei of these cells move closer to the
stratum intermedium and away from the
dental papilla.
3. The adjacent layer of cells in the dental
papilla suddenly increases in size and
differentiates into odontoblasts, which
form dentin.
4. The inner enamel epithelium and the
formation of odontoblasts continue from
the tips of the cusps.
Crown stage (contd….):
5. The odontoblasts secrete
an organic
matrix into their immediate surrounding
and form the dentin.
6. After dentin formation begins, the cells of
the inner enamel epithelium secrete an
organic matrix against the dentin. This
matrix immediately mineralizes and
becomes the tooth's enamel.
7. Outside the dentin are ameloblasts,
which are cells that continue the
process of enamel formation; therefore,
enamel formation moves outwards,
adding new material to the outer surface
of the developing tooth.
Structural components of teeth
• Enamel: is a hard outer
layer consisting primarily of
calcium and phosphate in
the form of hydroxyapatite.
• Dentin: is the inner layer,
the bulk of the tooth .
• Pulp: is the core, containing
nerves and blood vessels .
• Cementum: is the thin layer
around the root; a bone-like
material which connects the
teeth
to
the
jaw.
Types of teeth according to their attachments
1.
Acrodont: On the alveolar surface
of the jaw. each tooth resides on the
occlusional surface of the jaws in a
very shallow socket. Replacement
teeth arise adjacent to the active
teeth (e.g. in snakes).
2.
Thecodont
:
3.
Pleurodont: Attachment on the
Teeth may be
attached in sockets (replace within
the same socket reptiles). with
sockets
(e.g.
in
mammals,
crocodiles, dinosaurs).
inner side of the jaws (e.g. in
lizards). Teeth is continuously
replaced.
Stages in the formation of a tooth germ
Parts of a developing tooth
An erupting temporary tooth
Origin of germs of permanent teeth
Anomalies of Teeth
•
•
•
•
•
•
•
•
Anodentia
Supernumerary teeth
Gemination
Malocclusion
Precocious eruption of teeth
Delayed eruption of teeth
Improper formation of enamel or dentine
Abnormal location of teeth e.g. in ovary or in
hypophysis cerebri
REFERENCES
1. Langman’s Medical Embryology, 11th
Edition.
3. I.B. Singh. Human Embryology, 10th
Edition.
MCQs
1. The cells of the enamel organ that line the
papilla are called:
a) Ameloblasts
b) Odontoblasts
c) Cementoblasts
d) Dental cuticle
MCQs
2. Mesenchymal cells which cover dentine are
called:
a) Ameloblasts
b) Odontoblasts
c) Cementoblasts
d) Dental cuticle
MCQs
3. Temporary canines erupt at:
a) 6-9 months
b) 8-10 months
c) 16-20 months
d) 24-36 months
MCQs
4. The epithelium overlying the alveolar process
become thickened to form:
a) Dental lamina
b) Dental papilla
c) Dental cuticle
d) Periodontal ligament
MCQs
5. Absence of ameloblasts is a feature of:
a) Crown
b) Enamel
c) Dentine
d) Root