631. Ionic exchanges between erupted Enamel .and Saliva:
A. Don’t occur as the formative cells of the E .are lost once it is formed.
B. Occur only for two to five years following eruption.
C. Cease at puberty.
D. Occur throughout life.
632. The predominant organic portion of mature Enamel. is:
633. Fluorine deposition in Enamel:
A. Increase with age.
B. Decrease with age.
C. Sometimes increases or decreases with age.
D. Not affected by age.
634. Which of the following organic components are present in Enamel:
D. All of the above.
635. The rodless layer of enamel:
A.Is found only in primary teeth.
B.Does not contain rod and rod sheaths.
C.Is found near the amelo-dentinal junction.
D.Contains no hydroxyapatite.
636. Hunter-Schreger bands are:
A.found in the outer surface of enamel.
B.run parallel to the striae of Retzius.
C.best visualized in transverse section of the crown.
D.reflect periodic changes in prism direction of enamel.
637. The direction of enamel rods in general is:
A.parallel to the outer surface of enamel.
B.parallel to dentine.
C.perpindicular to the amelo-dentinal junction.
638. Which of the following contains the highest concentration of hydroxyapatite:
639. Enamel prism of the cusp tip passes:
A. in wavy course.
B. in s-shape course.
C. in straight course.
D. in twisted course.
640.Developmental enamel lamellae is:
A. type A enamel lamellae.
B. type B enamel lamellae.
C. type C enamel lamellae.
D. accidental enamel crack.
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