Questions and Answers
At which stage of tooth development does amelogenesis begin?
What is the percentage of minerals in the freshly secreted enamel matrix?
What is the main protein found in the enamel matrix?
What is the function of ameloblasts during the secretory stage?
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What is the source of minerals during enamel maturation?
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During which stage of ameloblast life cycle do IEE cells undergo mitosis?
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What happens to the IEE cells during the differentiation stage of the presecretory stage?
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What is the final percentage of minerals in the enamel after maturation?
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What is the function of the reduced enamel epithelium?
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Which of the following is NOT a characteristic of tetracycline's effect on enamel?
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What happens to the ameloblasts after they complete the formation of the enamel rods?
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What is the primary reason why enamel cannot repair itself?
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What is the final act of the ameloblast cell in enamel formation?
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What is the primary cause of mottled enamel?
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What developmental change occurs in ameloblasts during the secretory stage?
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What role do Tomes' processes play in enamel formation?
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Which of the following processes occurs during the maturative stage?
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What is the outcome of the secretion from the proximal sites of Tomes' processes?
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What characterizes the transitional stage in ameloblast activity?
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What happens to ameloblasts as they transition to smooth-ended forms?
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Which enamel characteristic is typically formed during the transitional stage?
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During which stage is the enamel matrix formation still progressing at the cervical parts of the crown?
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Study Notes
Enamel Formation (Amelogenesis)
- Amelogenesis begins shortly after dentinogenesis at the advanced or late bell stage
- Ameloblasts fully differentiate at the growth centers located at the cusp tips or incisal edges and progress along the sides of the crown toward the cervical margin
Enamel Matrix Deposition
- Involves the secretion of enamel matrix by ameloblasts
- Freshly secreted enamel matrix contains 30% minerals as hydroxyapatite crystals and 70% water and enamel proteins
- Enamel proteins include 90% amelogenin protein and 10% nonamelogenins protein
Mineralization of Enamel
- Occurs when the full thickness of enamel matrix has been deposited
- Involves additional minerals with the removal of organic material and water to reach 96% mineral content
- Sources of minerals during maturation include ameloblasts, other cells of the enamel organ, and capillaries approaching the outer enamel epithelium
Life Cycle of Ameloblasts
- Presecretory stage:
- Includes morphogenic and differentiation phases
- Morphogenic phase: IEE cells undergo mitosis at the cervical region during early bell stage
- Differentiation phase: IEE cells elongate, and their nuclei shift toward the stratum intermedium, becoming polarized cells
- Secretory stage:
- Ameloblasts develop blunt processes that penetrate the basal lamina and protrude into the predentin
- Hydroxyapatite crystals are deposited more or less parallel to each other and interdigitate with the crystals of dentin
- Transitional stage:
- Withdrawal of Tomes' processes
- Reduction in the height of ameloblasts and decrease in their volume and organelle content
- Maturative stage:
- Occurs after most of the thickness of the enamel matrix has been formed
- Ameloblasts undergo significant reduction in height and decrease in their volume and organelle content
- Water and organic materials are selectively removed from the enamel, and additional inorganic material is introduced
- Ameloblasts modulate their morphology between ruffle-ended and smooth-ended forms
- Protective stage:
- Ameloblasts form 3-4 layers of stratified epithelium that cover the enamel and are called reduced enamel epithelium
- Reduced enamel epithelium protects the enamel by separating it from the connective tissue until the tooth erupts
- Desmolytic stage:
- Reduced enamel epithelium has the function of secreting desmolytic enzymes, which cause degeneration of the connective tissue that separates the tooth from the oral epithelium
Defects of Amelogenesis
- Tetracycline: can cause bands of brown pigmentation or total pigmentation
- Fluoride ion: chronic ingestion of fluoride concentration in excess of 5 parts per million can result in mottled enamel as patches of hypomineralized and altered enamel
Clinical Consideration
- Enamel is incapable of repairing itself once it is destroyed because the ameloblast cell degenerates following the formation of the enamel rod
- Diseased, fractured, or otherwise damaged enamel can only be repaired through operative procedures
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Description
Learn about the process of enamel formation, also known as amelogenesis, in dentistry. This quiz covers the stages involved in enamel matrix deposition and more.
