Enamel Flashcards
What are the two major enamel impurities and their respective detrimental or beneficial effects on enamel?
carbonate decreases acid resistance of enamel
Fluoride increases acid resistance of enamel
What is the histological feature in human enamel that records the daily activity of ameloblasts?
Cross striation
Which structure in human enamel is a defect but may have “stress shielding” effect?
Enamel tufts
Hypomineralised, ribbon-like structures that run longitudinally to the tooth axis, extending from DEJ to 1//5 or 1/3 into enamel
Wavy look within enamel microstructure
Prevents enamel fractures
What are the percentages by weight of the major inorganic components in enamel?
96-97% inorganic, 1% organic, 2-3% water
How much water is there in enamel by volume?
10-20% by volume
What are the 3 types of water in enamel?
Extra-crystalline water: mobile and comprising bulk of enamel, removable at 100 degrees
Zeolitic (caged) water: caged in the apatite crystals but not tightly bound, removable at 100-800 degrees
Intra-crystalline water: associated with lattice or its hydroxyl columns, removable above 900 degrees
What are the lines of retzius?
Incremental lines across adjacent enamel rods that appear brown in a stained section of enamel due to enamel periodicity with the mean of 7 days
It demonstrates enamel growth and can be used to date events or trace time between events
What is the relationship between enamel prisms and cross striations?
Enamel prisms are the basic structures in human enamel formed by ameloblasts which go through daily cycles
Cross-striations are lines visible under the microscope, formed across adjacent enamel prisms due to daily increments of growth.
What are the major crystallographic defects in human enamel?
Point, line or heteroionic substitution
What is the critical pH of enamel?
pH 5.5
What happens to the enamel when the critical pH is reached.
Enamel structures and crystals start to break down. Demineralisation.
What are the two major diffusion systems in enamel that allow acid to go in and calcium/phosphate ions to go out?
Interprismatic space (highways)
Intraprismatic space (country roads)
What are Hunter-Schreger bands?
Appear as alternating light and dark horizontal bands which run in the same general direction as the enamel rods and are found in the inner part of the enamel
What is gnarled enamel?
As enamel rods do not always follow a straight course throughout its entire length, they are sometimes intertwined, especially near EDJ and in the cuspal/incisal region
How can Hunter-Schreger bands be observed?
Can be seen in longitudinal Ground Section under oblique reflected light
