621. At the time Enamel matrix is first formed in a tooth:
A. No predentin has yet been formed.
B. Root of the tooth is largely covered with acellular cementum.
C. Nuclei of ameloblasts move to non secreting end of the cell.
D. Cells of stellate reticulum near the cervical portion of the tooth have lost their
nuclei.

622.Hypomineralized structures which extend from the D.E.J to the surface of the Enamel are called:
A. Hunter schreger bands.
B. E. spindle.
C. Incremental lines of Retzius.
D. Enamel lamellae.

623. Maturation of Enamel is characterized by a percentage increase in inorganic content and a percentage:
A. Increase in water.
B. Decrease in water and organic content.
C. Increase in water and decrease in organic content.
D. Decrease in water and increase in organic content.

624. The stimulus that initiates the actual formation of Enamel matrix seems to be the:
A. Presence of predentin.
B. Reduction of stellate reticulum.
C. Influence of increased vascularization of the dental sac.
D. Reversal of functional polarity of ameloblast.

625. In a routine demineralized histological section of an adult tooth, the area representing Enamel is generally optically clear because:
A. The mounting medium has the same refractive index as enamel.
B. E is very brittle and thus breaks off during sectioning.
C. Ordinary stains don’t stain the organic matrix of E.
D. Enamel is highly calcified.

626. A layer of cells that seems to be essential to enamel formation but does not actually secrete the enamel is:
A. Inner dental epithelium.
B. Stratum intermedium.
C. Reduced dental epithelium.
D. Vestibular lamina.

627. Which of the following are poorly calcified Enamel:
A. Gnarled E .and E rods.
B. E. lamellae and incremental lines.
C. Perikymata and gnarled E.
D. E. rods and incremental lines.

628. Enamel matrix is laid down by ameloblasts:
A. Finally contains about 80% by weight inorganic matter.
B. Includes organic matter that is primarily collagen.
C. Persists as a vital tissue through the life of a tooth.
D. Non of the above.

629. Enamel tufts:
A. Begin on the outer edge of E .
B. Are developmental defects and are worn away by masticatory forces.
C. Have a brush like appearance and are hypo calcified areas in E.
D. Represent hypercalcified E. rods.

630. The rod sheath:
A. Has cross striations.
B. Is more calcified than the E. rod.
C. Is less calcified than the E. rod.
D. Has lesser amount of organic matter than the E. rod.

NOTE
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