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Enamel-2

 July 18, 2013 |  admin |  Lecture series, Faculty Development Program Series
Questions
Answer
The muscular
skeleton of the lip is formed by the
Orbicularis oris
In the lips, the
skin and oral mucosa are sharply demarcated by the
Vermillion border
In the upper lip the
vermillion border, slightly protrudes along the midline to form the
Tubercle
The tubercle of the
upper lip is
Protruded. In lower
lip the corresponding area is depressed
Labiomarginal sulci
delineate the
Cheeks and lower
lip. A feature that occurs with aging
The groove that
separates the lower lip from the chin is
Labiomental groove
The tooth that lie
close to the labial commisure are the
Maxillary canine and
mandibular first premolar
Modified anterior
oral seal is seen in
Mouth breathers as
normal lip seal is not observed owing to incompetant lips
A tight or over
reactive lip musculature often causes the
Retroclined incisor
What is vestibular
fornix
The  extension of alveolar mucosa in to the lip
and cheek forming a trough. Aka vestibular sulcus mucosa
Mineralized tissues
of teeth
Enamel; dentin;
cementum. Enamel is ectodermal in origin and rest is ectomesenchymal in
origin
Bulk of the teeth is
formed by the
Dentin
Compare surface and
subsurface enamel
Surface enamel is
harder, denser and less porous that subsurface enamel. Hardness and density
also decrease from surface. The same is also for occulsal/incsial to cervical
margin
How is color of
enamel determined
It is a birefringent
crystalline material. The crystals reflect light in varying direction. Young
enamel appears white owing to complete internal reflection of light with no
wavelength internally absorbed. This causes low translucency and white color.
With loss of crystals in old age, preferential reflection of yellow color of
dentin occurs.
What features
renders enamel fracture resistant
Enamel has a low
tensile strength and is brittle but has high modulus of elasticity, wavy
dentinoenamel junction, that provides good mechanical interlocking and
facilitates desipation of forces. Toegther with support of dentin, enamel
minimizes the possibility of fracture
Cross section of
enamel crystallites
Are hexagonal in
shape
Molecular
arrangement of unit cell of enamel crystalline
A hydroxyl group
surrounded by a uniformly spaced calcium ions, which in turn are surrounded
by three similarly spaced phosphate ions.
Replacement of ions
in enamel occurs at
Carbonate ion in
phosphate or hydroxyl ions; magnesium – calicium ion; fluroide – hydroxyl ion
Enamel proteins are
Amelogenins and
non-amelogenins.
Trace of lipid
content in enamel is seen in
Cross striations,
lines of retzius, hunter-schreger bands, prism sheath and prism core