Enamel-2

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