Enamel

Question 1

Properties

Answer 1

• Permeable, giving complete or partial passage of certain molecules
• Light yellow to grayish white. sometimes light blue tone. Determined by translucency of enamel where yellow dentin is visible.
• 96% inorganic; hydroxyapatite, crystalline calcium phosphate
• organic proteins; amelogenins and enamelins
• 4%H20

Question 2

• Basic unit of enamel
• 4um-8um diameter
• aka enamel prism, rod sheaths, cementing interprismatic crystals in organized pattern
• resemble fish scales
• 5um width, 9um length so rods can be packed tightly together

Answer 2

enamel rod

Question 3

What are direction of the rods from DEJ?

Answer 3

-from DEJ, run meandering courses outward to the surface of tooth. Running in an oblique direction and have a wavy course.

Question 4

What are enamel rods built up of segments separated by dark lines that give striated appearance?

Answer 4

Striations

Question 5

Direction of rods orientation.

Answer 5

• At right angles to dentin surface
• horizontal at cervical of crown
• oblique direction to vertical as it nears incisal edge

Question 6

• found at cusps of teeth

- twisted appearance results from orientation of enamel rods and the rows in which they lie.

Answer 6

Gnarled Enamel

Question 7

• alternating dark and light strips seen in a longitudinal ground section under oblique reflected light
• also thought to be alternating zones of slightly different permability and a differen content of organic material

Answer 7

Hunter-Schreger bands

Question 8

-Appear as brownish bands in ground section

Answer 8

Incremental lines of retzius

Question 9

what are incremental lines of retzius?

Answer 9

• the successive apposition of layers of enamel during formation of crown. like rings on tree
• in longitudinal sections, they surround tip of dentin
• at cervical they run obliquely
• in transverse, appear concentric

Question 10

-Transverse, wavelike grooves believed to be external manifestations of the striae of Retzius.

What are the characteristics?

Answer 10

• Perikymata

- on surface. continuous around tooth, and lie parallel to each other and to CEJ

Question 11

What are thin, leaf like structures that extend from the enamel surface toward DEJ (from outside to inside?

Answer 11

Enamel Lamellae

Question 12

What are some characteristics of enamel lamellae?

Answer 12

• may extend to and penetrate into dentin
• consisting of organic material, but with little mineral content
• confused w/ cracks
• may develop in planes of tension

Question 13

What is the direction of lamellae?

Answer 13

• extend in longitudinal and radial direction of tooth
• from tip of crown to cervical region
• may be a site of weakness for bacteria of caries

Question 14

-arise at dentinoenamel junction and reach into enamel to about one fifth to one third of its thickness. are narrow, ribbon like structures.

and what do they consists of?

Answer 14

• enamel tufts

- hypocalcified enamel rods and interprismatic substance

Question 15

what appears as a result of abrupt change in the environ and nutrition of newborn infant?

Answer 15

neonatal line or neonatal ring

Question 16

what is a delicate primary enamel cuticle covering the entire crown of the newly erupted tooth but is probably soon removed by mastication?

what are they secreted by?

Answer 16

Enamel cuticle or Nesmyth’s membrane

-ameloblasts when enamel formation is completed, after enamel organ retracts from cervical region

Question 17

What covers erupted enamel and is a precipitate of salvary proteins?

Answer 17

Pellicle

Question 18

When does it form and what happens next?

Answer 18

• reforms within hours after an enamel surface is mechanically cleaned
• within a day or two, it becomes colonized by microorganisms to for a bacterial plaque.

Question 19

What is the surface structure of DEJ?

Answer 19

• is pitted or shallow depressed, to fit rounded projections of enamel
• for firm hold of enamel cap on dentin
• junction has a scallop shape w/ convexities of scallops directed toward the dentin.

Question 20

What originate from processes of odontoblasts that extend into the enamel epithelium before hard substances were formed?

Answer 20

-Enamel spindles that are at right angles to surface of dentin.