561.Striae of Retzius:
A. Result from enamel crack.
B. Separate prenatal from postnatal enamel.
C. Are due to rhythmic apposition of enamel.
D. Are hypermineralized structure.
562. Enamel Rods:
A. Their number varies in different teeth.
B. Have an average width of 1um.
C. Are Present at the enamel surface.
D. Have a straight course at the cusps of teeth.
563. Enamel is formed of:
A. 76% minerals & 24% organic materials and water.
B. 96% minerals & 4% organic materials and water.
C. 86% minerals & 14% organic materials and water.
D. 99% minerals & 1% organic materials and water.
564.which of the following is absent in all premolars:
A. Enamel spindle.
B. Enamel tuft.
C. Neonatal line.
D. Enamel lamella.
565. Cross striations in enamel:
A. Are an optical phenomena.
B. Result from abrupt change in environment before and after birth.
C. Result from mineralization disorder.
D. Appear to be periodic bands at 4 microns interval across the rod.
566. The prism sheath:
A. Is a dense continuous sheath separating rod from inter-rod.
B. Result from abrupt change in crystals orientation.
C. Is more mineralized than rod and inter-rod.
D. Found in prismless enamel.
567. The complex arrangement of rods over the cusps of teeth is termed:
B. Gnarled enamel.
C. Prenatal enamel.
D. Postnatal enamel.
568. The origin of enamel is:
A. neural crest cells
569.Hypocalcified areas in enamel are:
A. Enamel spindles.
D. Enamel tufts.
A. Is less mineralized than prismatic enamel.
B. Is found only in the cervical area of permanent teeth.
C. Is harder than prismatic enamel.
D. Found near the dentino-enamel junction.
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