Enamel Flashcards
What forms enamel?
Ameloblasts
What are 5 key features of enamel?
- Hardest biological tissue
- Abrasion resistance is high
- Low tensile strength and brittle
- Cannot be repaired or replaced
- Avascular
Where is enamel thickest on the tooth?
Over cusps and incisal edges
Where is the enamel thinnest on the tooth?
Cervical margin
What forms the mineral component of enamel?
Calcium hydroxyapatite crystals
What 2 things form the organic component of enamel?
- Amelogenins
2. Non-amelogenins
What is the basic structural unit of enamel?
Enamel rods
What forms enamel rods or interrod enamel?
Crystallites
Where do enamel rods run?
Enamel-dentin junction to the surface of the tooth
What is the main difference between rod and interrod composition?
Interrod crystals deviate 40° - 60° from crystals found in rods
What pattern are enamel rods found in?
Keyhole pattern
What is the name of the banding pattern found in enamel?
Hunter-Schraeger bands
What are 2 functions of Hunter-Schraeger bands?
- Strengthen enamel
2. Prevent cracks from propagating through tooth
How do Hunter-Schraeger bands arise?
10-13 layers of rods follow the same direction but blocks above and below follow paths in different directions
What 3 things cause incremental lines to appear?
- Changes in enamel secretory rhythm
- Chemical composition of enamel
- Position of the developing enamel front
What are 2 types of incremental lines?
- Cross striations (short period)
2. Enamel striae (long period)
What are cross striations?
Lines which cross enamel rods at right angles to their long axes
What are striae of Retzius?
Prominent lines which run obliquely across the enamel rods to the surface
What forms striae of Retzius?
Successive positions of the enamel-forming front
How do striae of Retzius appear in transverse section?
Concentric rings
What is the neonatal line?
Marked stria formed at birth reflecting the metabolic changes which occur at birth
What are perikymata?
Shallow grooves that run circumferentially around the crown
What controls amelogenesis?
Genetic control
What are the 4 stages of amelogenesis?
- Pre-secretory
- Secretory
- Maturation
- Post-maturation
What are 2 stages of the pre-secretory stage of amelogenesis?
- Cells of internal enamel epithelium differentiate into ameloblasts
- Cells become reversed in terms of polarity - Nucleus moves to top
What are 3 stages of the secretory stage of amelogenesis?
- Ameloblasts form aprismatic enamel
- Secretory pole forms Tomes process, where crystallites are formed
- Nuclei move towards Tomes process
What occurs during the maturation stage of amelogenesis?
Ameloblasts die and are phagocytosed
What occurs during the post-maturation stage of amelogenesis?
Ameloblasts regress in height and serve to protect enamel during eruption
What is attrition?
Tooth loss involving tooth to tooth contact
What is abrasion?
Tooth loss involving friction between tooth and outside material
What is erosion?
Tooth loss involving contact with acidic agents
What are 2 causes of intrinsic enamel loss?
- Acid reflux
2. Bulimia
What are 2 causes of extrinsic enamel loss?
- Sugar
2. Fizzy drinks
What is dental caries?
Demineralisation of enamel
What happens when plaque becomes mineralised?
It forms a calculus
