Oral Cavity and Tooth Development Part 2 Flashcards
teeth are grossly divided into (2)
root & crown
Portion of tooth embedded in bone
tooth root
where is the tooth root located
part of the jaw called the alveolar ridge, in tooth socket called alveolus
portion of the tooth that projects into the oral cavity
crown
Protected by layer of highly
mineralized —, covers crown
enamel
Enamel
hard, translucent
substance, containing < 1% organic
material & 96-98% hydroxyapatite
enamel is — in origin
ectodermal
what is enamel secreted by
tall,
columnar ameloblastsof enamel organ
Apical, secretory end of ameloblast
forms single, large process,
Tome’s
process
Enamel mineralization is non-uniform,
resulting in highly calcified
enamel rods
or prisms
enamel rods
or prisms
roughly hexagonal, ~4-8m
in diameter
Separated by less mineralized
interprismatic material
Enamel rods extend from
ameloblasts
at enamel surface to dentino-enamel
junction
Bulk of tooth composed of less mineralized
dentine
dentine is — in origin
mesodermal
how is dentin secreted
odontoblasts of dental papilla as pre-dentine
dentine compared to bone
Chemically similar to bone, but more mineralized; ~ 70% hydroxyapatite crystals
what does dentine also contain (2)
Type I collagen & GAG’s
Dentine arranged in
dentine tubules
dentine tubules
hollow, parallel tubes radiating from pulp cavity
contain long, rod-like cytoplasmic processes of odontoblasts called
Tome’s fibers
Central pulp cavity contains
support structures such as (2)
sensory Nn & blood vessels
Dentine innervated by
myelinated
Nn
Dental pulp is — in
origin
mesodermal
dental pulp resembles primitive…
mesenchyme
dental pulp contains (4)
stellate fibroblasts
reticular fibers
collagen
ground substance
dental pulp is richly supplied by capillaries from
arterioles running with
periodontal
ligament
Tooth root is covered by a thin layer of
cementum
cementum is — in origin
mesodermal
cementum
amorphous, collagen-based, calcified tissue
makeup of cementum
~45-50% hydroxyapatite, similar to bone
cementum is manufactured by —, which mature into
cementoblasts
cementocytes
cementoblasts/cytes are similar to — both structurally and functionally
osteoblasts/cytes
Cementum layer anchored to bone
of alveolus with fibers of
periodontal ligament or
membrane
periodontal ligament is composed of
dense, collageous fibers, called Sharpey’s
fibers
how do sharpeys fibers run?
at oblique angles
PD/sharpeys fibers support the
tooth in socket
PD allows for
slight movement of tooth
during mastication
May see occasional clusters of
epithelial cells within periodontal
ligament called
vestigial epithelial rests
of Malassez
Region of tooth between root & crown is — of tooth
neck
neck is protected by masticatory oral mucosa called
gingiva
gingiva covers
upper portion of alveolar ridge
Sometimes divided into (2)
attached gingiva (covers upper alveolar bone) & free gingiva (forms cuff ~ neck of tooth)
Space between free gingiva & crown called
gingival sulcus or crevice
Lined by
crevicular epithelium
crevicular epithelium
very thin, only 2-3 cells thick, easily breached by bacteria
easily breached by bacteria
periodontal disease, gingivitis
Tissues that surround & support tooth collectively referred to as
periodontium
periodontium includes (4)
epithelium, cementum, periodontal ligament & alveolar bone
Tooth formed between opposing layers of
epithelial cells
ameloblasts of — origin
enamel
odontoblasts of
dental papilla
Enamel—origin
ectodermal
Dentine, cementum, pulp, & periodontal ligament are —
mesodermal
~6th week of fetal development, a horseshoe-shaped epithelial — arises from oral epithelium
ridge
Forms —- in position of future jaws
dental lamina
In each quadrant, lamina develops several globular, — — (one for each deciduous tooth)
ectodermal swellings
Superficial half forms — —; deep half forms — —
enamel organs
dental papilla
Enamel organ initially — shaped (cap stage)
cup
Cells of enamel organ progressively differentiate, become — —, with extracellular matrix of GAG’s
stellate reticulum
Later forms — shaped structure (bellstage)
bell
Cells lining outer, convex surface of enamel organ become
external enamel epithelium
Cells lining concave surface of enamel organ form
internal enamel epithelium
Cells lining concave surface of enamel organ form internal enamel epithelium, differentiate into tall, columnar
ameloblasts
enamel formation
Amelogenesis
Deep to developing enamel organs is primitive mesenchyme; develops into — —
dental papilla
Cells lining convex surface of dental papilla develop into
odontoblasts
dentine formation
Dentinogenesis
These two cell layers in apposition—tooth forms — them
between
Together they form future (3) of 1’ dentition
incisors, canine & molars
Development of ameloblasts induces
differentiation of —, but
calcification of dentine induces
deposition of —
odontoblasts
enamel
Tooth formation initiated by deposition
of organic pre-dentineby odontoblasts
on surface of dental papilla—later
calcified into
dentine
Calcificaiton of dentine matrix
secondarily induces
enamel production
by ameloblasts
Odontoblasts have odontoblast
processes, embedded in dentine
matrix—form
dentine tubules
Enamel forms in mineralized columns of enamel rods, separated by less mineralized
interprismatic material
Subsequent to deposit of dentine & enamel, dental lamina (2)
fragments & atrophies
At time of tooth eruption, enamel organ & ameloblasts —
degenerate
Overlying mucosa separates as tooth erupts, exposing —
crown
Dental papilla shrinks, becomes — —, surrounded by dentine
dental pulp
After tooth formation is complete, small amounts of — — continue to be produced, may eventually obliterate pulp cavity
2’ dentine
Overall shape of enamel organ determines
3-D shape of tooth crown
Outer rim of enamel organ known as
epithelial sheath of Hertwig(= Hertwig’s root sheath)
epithelial sheath of Hertwig(= Hertwig’s root sheath) determines
cross-sectional outline of tooth
Surrounding mesenchyme forms
dental follicle
Surrounding mesenchyme forms dental follicle results in
periodontal ligament
Enamel organs of permanent teeth develop as buds from
dental lamina & “deciduous” enamel organ
In case of molars, dental lamina proliferates caudally to form
enamel organs of 2’ dentition
In humans, tooth development begins — of fetal development
~6th week
tooth eruption does not occur until — after birth
6-30 months
P usually – roots
2
M usually – roots
2-4
I & C – roots each
1
Between— of age, deciduous teeth replaced by permanent dentition
6-12 years
—-, administered during development of permanent dentition incorporated into enamel
Tetracycline
Tetracycline, administered during development of permanent dentition incorporated into enamel results in
yellow discoloration of teeth
Distally, get further development of
3 M, sans precursors; erupt at
~6, 12, & 18-21 yrs of age, respectively
=> 32 teeth
Human dental formula
I 2/2, C 1/1,
P 2/2, M 3/3
In — dentition, all teeth similar
homodont
Incisors modified for (2)
cutting & biting
Canines for (2)
puncturing & holding
Premolars & molars generally used for (1)
grinding
TMJ allows lateral & — motion—important for (2)
anterior-posterior
chewing, grinding
Raised points on occlusal surfaces of molars & premolars known as —
cusps
Raised points on occlusal surfaces of molars & premolars known as cusps (include (3))
protocone, metacone, paracone
Flattened posterior surface of lower molars known as
talonid
Premolars and molars can be low crowned, or —, in omnivores, or may be very tall, high crowned, —, as in herbivores
bunodont
hypsodont
Premolars variously
modified (shearing carnassialsin carnivores)
Premolars variously modified (shearing — in carnivores)
carnassials
Dental disorders (2)
Abnormal tooth eruption &/or misalignment
Orthodontia
Orthodontia accomplished by
osteoblast & osteoclast activity in alveolus
Dental caries results when
weak acids in food & drink erode calcified enamel, augmented by bacterial action
— helps harden enamel & kills bacteria
Fluoride
Caries may extend into dentine or pulp cavity, produce abscesses or death of tooth resulting in a
root canal
caused by accumulation of calcified food & bacterial debris (plaque) in gingival sulcus => widening of gingival sulcus, possible inflammation & destruction of periodontal ligament
Periodontal disease
Inflammation of gums
gingivitis
Inflammation of periodontal ligament
periodontitis