2. Enamel Defects
• May be of genetic and/or environmental
origins
• Disturbances in initial matrix deposition
result in hypoplasia : manifesting as pits
& grooves on enamel surface
• Defects in enamel maturation result in
hypomineralisation / hypomaturation :
largely intact surface but opaque rather
than translucent appearance and soft
3. What is Hydroxyapatite?
• The main inorganic component found in dental enamel is HAP which
is a mineral composed of calcium and phosphate ions. HAP crystals
are highly organized to form compact enamel rods which extend from
the dentin enamel junction to the outer surface of tooth enamel
which are surrounded by enamel interrod .
• The formula is : Ca5(PO4)3(OH)
• The OH− ion can be replaced by fluoride or chloride,
producing fluorapatite or chlorapatite.
4. Definitions:
The term "hypoplastic" means less quantity of enamel, and the term
"hypomineralised" means less mineralised tissue.
• Enamel Hypoplasia= enamel hypoplasia is a quantitative defect of the
enamel presenting as pits, grooves, missing/thinner enamel or smaller
teeth, which results in small or irregular shaped teeth. It occurs in initial
matrix deposition.
• Enamel Hypomineralisation=Enamel hypomineralisation is a qualitative
defect, with reduced mineralisation resulting in more opaque enamel,
creamy/white or have yellow/brown discolourations, the opacities may be
diffused . This occurs when there is defects during enamel maturation.
-The most common hypomineralisation defect seen in children is Molar incisor
hypomineralisation (MIH), which affects the first permanent molar teeth and
often the permanent incisors.
5. How is surface enamel different from core
enamel?
• Surface enamel differs both physically and chemically from underlying
core enamel as it is harder, less porous and less soluble
7. Amelogenesis Imperfecta
• Inherited defect of dental enamel, affects quality and/or quantity of enamel :
• It is a x-linked disorder.
• DEJ defects result in an enamel layer that shears easily
• Secretory stage defects result in insufficient crystal elongation & leave enamel
layer very thin & disorganised
• Maturation stage defects i.e deficient matrix degradation, produce thick but soft
enamel
• Current estimates suggest that FAM83H, FAM20A, ENam & AMELX mutations
account for 60% of disease burden
• Affected male member of family with X-linked AI presents as brown-mottled
hypo mature enamel
• Affected female member of family with X-linked AI shows alternating areas of
normal and hypomature enamel (have 2 X’s, chromosome masking)
8. Environmental Defects of AI Frequently
Relate To…
• Infectious diseases of childhood such
as measles occurring during tooth
development
• Fluorosis as a result of prolonged
ingestion of fluoride in excess of
5ppm
• Incorporation of ingested
supplements into mineralised matrix
eg tetracycline
• Dietary deficiencies
9. Enamel PH during the
maturation stage
• During enamel maturation pH oscillates between
acidic & neutral
• For every unit cell of HAP deposition 8H+ ions
are released —> acidification of environment
• Carbonic anhydrase II expression by smooth
ended ameloblasts starts at end of secretory
stage and continues through maturation stage -
this enzyme produces HCO3 to neutralise the
acidity generated by the HAP deposition. This
occurs while ruffle ended ameloblasts produce
an extracellular pH of 5-6.
• Ameloblasts pump H+ generated by Ca II into
enamel space using vacuolar H+-ATPase and
the AE2 transporter relocates to the basolateral
membrane
10. Chemical Composition of the Mineral Phase of Enamel
• Bundles of >1000 crystallites form an enamel rod
• Crystallites are long apatite crystals with a thickness of about
25nm extending from DEJ to enamel surface
• Hydroxyapatite is represented by the stoichiometric formula :
Ca10(PO4)6(OH)2 or Ca5(PO4)3OH
• Apatite growth on crystal surfaces progresses in 2 discrete
manners :
• Rapid growth in epitaxial direction (along c-axis) which gives
rise to elongated hexagonal crystals
• Thickening on side prism planes occurs at slow rate by
successively accreting one or several unit-cell-thick layers
11. Substitutions
• F- for OH- : stabilising effect - forms fluoroapatite which is less soluble to acid
• F- is concentrated at enamel surface and falls dramatically toward tissue interior
• caries prevention
• CO32- for OH- or PO43- : has a destabilising effect
• Mg2+ for Ca2+ : has a destabilising effect
-This is very rare/limited, approx. up to 0.3% substitution
• other ions such as Sodium or Lead can also occasionally substitute for Ca2+
• Fluoride ion fits more closely within calcium triangle : high charge density &
symmetry of fluoride ion reduces lattice energy
• Such defects & substitutions do have profound effect on behaviour of apatite,
especially with regard to solubility at low pH
• The youngest secretory enamel is the most soluble & the solubility decreases w/
advancing developmental stages
12. Acid Etching
• Limited acid treatment of enamel generates ‘rough’ surface :
• dependant on nature & conc of acid
• etching pattern depends on orientation of crystals
• Interlocking enhances bonding with material used in restorations -
e.g. 37% phosphoric acid is in ESPE scotchbond.
• Crystal formation is a slow process usually involving different
intermediates i.e the structural arrangement and stoichiometry of
ions in initial solid precipitated is different from one in ultimately
formed crystal
• Several different forms of calcium phosphate mineral can be present
in enamel & ostacalcium phosphate crystals are thought to be
precursor to ultimately formed substituted HAP crystallites
13. Enamel Formation
1.Secretory ameloblasts (Tomes’ process) & DEJ delineate/indicate
the position of the enamel space
2.Secreted amelogenin assembles, forming supramolecular structural
framework
3.Ca & P transport by ameloblasts result in supersaturated solution -
crystal nucleation by pre-existing dentine or non-amelogenin matrix
molecules
4.Control of crystal growth, morphology & orientation by matrix i.e
amelogenin nanospheres
5.Cessation of initial crystallite growth by degradation of matrix ; and
final maturation involves rapid crystal growth concomitant with
controlled protein processing, degradation & loss
14. How is acidity neutralised in the enamel
maturation stage?
• A- Carbonic anhydrase II expression by smooth ended ameloblasts
starts , producing HCO3- to neutralise the acidity generated
• B- ruffle ended ameloblasts secreting carbonic anhydrase which
produces HCO3-.
• C- It is not neutralised
• D- along the c-axis
15. How is acidity neutralised in the enamel
maturation stage?
• A- Carbonic anhydrase II expression by smooth ended ameloblasts
starts , producing HCO3- to neutralise the acidity generated
• B- ruffle ended ameloblasts secreting carbonic anhydrase which
produces HCO3-.
• C- It is not neutralised
• D- along the c-axis
16. Which of these statements is correct?
• A- CO32- substitutes for OH-, or PO43- and Mg2+ substitutes
for Ca2+ =has a destabilising effect.
• B-Mg- substitutes for OH- or PO43, and, CO32+ substitutes
for Ca2+ =has a destabilising effect.
• C-CO32- substitutes for OH- or PO43- and Mg2+ substitutes
for Ca2+ =has a stabilising effect.
17. Which of these statements is correct?
• A- CO32- substitutes for OH- or PO43- and Mg2+ substitutes
for Ca2+ has a destabilising effect.
• B-Mg- substitutes for OH- or PO43, and, CO32+ substitutes
for Ca2+ has a destabilising effect.
• C-CO32- substitutes for OH- or PO43- and Mg2+ substitutes
for Ca2+ has a stabilising effect.
