Knowledge of normal
development will aid in the understanding
of the potential reasons and timing of
abnormal occurrences. During the third
and fourth weeks of embryonic development
the face and mouth form. Three important
germ cell layers, ectoderm, mesoderm and
endoderm are all essential in developing
parts of the face and mouth. Along with
the branchial arches the mouth, lips,
parts of the nose and jaws will form
between weeks three and six. At the same
time development of the palate is taking
place that encloses the future tongue
which appears at four weeks.
of the lips, jaw or palate occur during
this early time frame. While
heredity plays a major role, nutritional
deficiencies, infections, disease, and
trauma in utero may contribute. The
tongue may show a red rhomboid shape or
may be bifid due to fusive
irregularities. Thyroid tissue may
be present at the base of the tongue.
Teeth begin (around week 6) to develop from a band of oral
epithelium on the upper and lower jaws.
From this tissue tooth buds form and
eventually a tooth germ develops with ameloblasts (enamel forming cells) and
odontoblasts (forms dentin and pulp).
With the dentin mineralizing and
enclosing the pulp, the ameloblasts will
begin to form enamel.
Alterations in the
enamel content during development can
affect the clinical appearance of the
teeth (shape, color, hardness) and
the susceptibility to caries development.
At birth, the infant
has all the primary
teeth and many of the permanent teeth at
different stages of development.
Dental enamel consists of 96% inorganic
material, 4% organic
enamel matrix and water. Its crystalline
mineral salts make it the hardest
calcified tissue in the body, yet at the same
time it is a semi-permeable membrane.
Its thickness varies over
the tooth (2-2.5mm on cusps of molars, to
knife edge at the necks of teeth).
development of enamel (amelogenesis) can
cause hypoplasia (pitting, furrowing or
total absence of enamel) and
hypocalcification (opaque or chalky areas
on normal enamel surfaces). Nutritional
deficiencies, endocrinopathies, febrile
diseases and certain chemicals (excessive
fluoride <1.5ppm antibiotics) may
causing enamel hypoplasia frequently
occur during the 1st year.
Therefore, the permanent teeth most
frequently affected are incisors,
canines, and first molars. The upper
lateral incisor, since it develops later, is
often not affected.
The dentin, a living
tissue, constitutes the bulk of the tooth.
It closely resembles bone. It is yellow
in color, is highly elastic and is harder than
bone. It contains 30% organic material and
70% inorganic. The primary cells of dentin are odontoblasts. By exposing 1mm of
dentin 30,000 odontoblast cells are
damaged. Dentin is formed throughout the
life of the tooth.
The pulp furnishes
nourishment to dentin, contains nerves,
blood vessels and cells that form
The third molar is
the most common congenitally missing
tooth followed by the lateral incisor and