601. Cross striations or short increments:
A. Represent the rhythmic apposition of the E. matrix by ameloblasts.
B. Represent alternating constriction and expansion of E. rods at and in-between
the striations.
C. Represent the daily rate of secretory activity of the ameloblast.
D. All of the above.

602. The formation of the enamel matrix between two short increments needs:
A. One day.
B. Two days.
C. Three drays.
D. Four days.

603. Neonatal line is all the following except :
A. Is one of the brown striae of Retzius that gets accentuated.
B. Is present in deciduous teeth and all permanent molars.
C. Separates enamel formed before birth from that formed after birth.
D. It is due to abrupt change in nutrition and environmental condition at birth.

604. The quality of the prenatal Enamel:
A. Is better than that of the postnatal E.
B. Is not as better as that of the postnatal E.
C. Is equal to the quality of postnatal E.
D. Not related to the quality of postnatal E.

605. The dentinoenamel junction (DEJ) :
A. Appears to be scalloped with convexities of the scallops directed to E.
B. Appears to be scalloped with convexities of the scallops directed to D.
C. Appears to be scalloped with convexities of the scallops directed tocementum.
D. None of the above.

606. The firm attachment between E and D is due to:
A. Under cuts created by the scallops of the DEJ.
B. Interdigitation at the DEJ between fibrils of first formed layer of D and that offirst formed layer of E.
C. Interdigitation between the hydroxyapatite crystals that are deposited duringmineralization of E and D.
D. All of the above.

607. E. lamellae are all the following except :
A. Thin leaf or sheet like structures.
B. Extend from the E surface and may extend to D.
C. Demonstrated in the longitudinal ground section only.
D. Hypo or unmineralized structures

608. Enamel spindles:
A. They are odontoblastic cell bodies pass across the DEJ into the E.
B. They are extended between the preameloblasts after enamel is formed.
C. They are most common beneath cusps.
D. They are best demonstrated in longitudinal decalcified section.

609.Rodless Enamel:
A. Occurs in the outermost 70 microns of the E.
B. Their crystals are aligned at right angel to the surface
C. Found most common at the cervical areas of E surface.
D. All of the above.

610.Perikymata are:
A. Vertically oriented wave like grooves.
B. The external manifestation of the brown striae of Retzius.
C. Numerous at the incisal or cusp regions.
D. Parallel to the AEJ

NOTE
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