Chemical Composition of The Teeth

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Chemical Composition of The Teeth
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The main dental tissues

• Teeth are made of
• Enamel Dentine Cementum
• Enamel and dentine have different composition
• Cementum and dentine are very similar in
  composition

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The relations of the main dental tissues
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Composition of dental tissues

• Dental tissues are made of Organic matter
  minerals water
• Different of constituents depending on
  calculation of proportions by weight or volume
• Enamel contains very little organic matter (
  1.3 of dry weight or 1.1 of wet tissues, but
  3 of the actual volume) - gt 90 inorganic

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• Dentine contains more organic matter ( 20 of
  dry weight, or 21 of wet tissues, but 28 of
  the actual volume), while the inorganic part is
  72 of wet weight, or 48 actual volume
• Cementum is similar to dentine in composition

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Mineral composition

• Most reliable analysis obtained by heating tissue
  to 105C to evaporate water prior to analysis
• The most predominant mineral is calcium followed
  by phosphorus, and finally magnesium
• Ca and P are more in enamel
• Mg and CO2 are more in dentine

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The structure of the inorganic fraction

• The main constituent is the crystalline form of
  calcium phosphate known as apatite with (except
  probably in enamel) some amorphous calcium
  phosphate

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1. Apatites are a crystalline form having the
   general formula Ca10 (Po4)6 X2, and the most
   widely distributed type is hydroxy apatite (HA)
   where x is OH
2. Apatites belong to the hexagonal system of
   crystals

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The crystal structure of hydroxyapatite
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• Calcium in the apatite structure (two types)
• A- columnar calcium forms a series of hexagons
• B- hexagonal calcium lie within the hexagons,
  and the ions are arranged in triangles placed
  parallel to each other with adjacent triangles
  rotated through 60C, so if viewed along the
  longitudinal axis, the calcium atoms in the two
  triangles would appear as a second hexagon

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The crystal structure of hydroxyapatite
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• Phosphate in the apatite structure
• phosphates are placed in two tetrahedra
  (each consisting of one phosphorus atom with four
  oxygen atoms) between pairs of calcium ions in
  the outer hexagon , so that one phosphorus and
  three oxygen atoms are above the plane of the
  calcium ions (the fourth oxygen atom being below
  the plane) and the other phosphate is arranged in
  the reverse way

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The crystal structure of hydroxyapatite
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• The hydroxyl ions in the apatite structure
• OH- are placed inside the triangles formed
  by the calcium ions.
• The O is either slightly above, or an equal
  distance below the plane of the calcium
  triangles.
• There is no room to accommodate two OH
  group pointing towards each other (-OH---
  ---HO-) in adjacent calcium triangles.

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• They must either be arranged in an ordered
  column i.e. (OH- OH- OH- .) along the axis or
  in disordered column with the direction
  reversed at various places.
• The latter is supported by evidence, resulting
  in voids or vacancies where space prevents an OH
  group being placed

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The crystal structure of hydroxyapatite
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• Fluoride in the apatite structure
• Fluoride can enter the vacancies, so that
  it occupies a central position in the same plane
  as calcium ions
• In addition, it can replace OH ions
• The resulting crystal is more stable and
  less soluble than apatite without fluoride

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• Biological apatite are non-stoichiometric
• Pure synthetic apatite has CaP ratio of 2.15
• Ratio is lower in bone and teeth
• Two properties of apatite explain the variation
  in nature

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• Adsorption
• e.g. adsorption of excess phosphate as
  (HPO4-) on the crystal surface, and of citrate,
  CO32-, HCO3- and magnesium as (MgOH) as well
• Ion exchange
• e.g. substitution of Calcium by sodium and
  magnesium, or H3O for two adjacent calcium, or
  even absence of some calcium and the addition of
  one H to PO4 3 to give HPO42- and the absence
  of OH- to maintain electrical balance

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• The more general formula for biologically formed
  apatite is Ca10-x (HPO4)x (PO4)6-x (OH) 2-x .XH2O
  (where x is between o and 2, and normally a
  fractional number)
• Another likely component with apatite is Octa
  Calcium Phosphate (OCP)
• Ca8 H2 (PO4)6 .5H2O
• i.e. Ca8 (HPO4)2 (PO4)4.5H2O CaP1.33,
  thus explaining the lower CaP ratio in nature

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The crystallinity of apatite

• Biologically formed crystals are not perfect
• Fluoride presence in environment during crystal
  formation improves crystallinity
• Magnesium and carbonate inhibit crystal growth
  and lead to formation of crystals with poor
  crystallinity

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The size, shape and orientation of crystals

• The rods or prisms are the anatomical unit of
  enamel
• They are 5µm in diameter and extending through
  its full thickness
• They are shaped like a key hole with a round head
  or, in some places, a fish tail
• The tails of one row fit between the heads of the
  next, so that the heads are towards the cusp.
• Crystallites within rods are oriented in a
  cuspal-cervical direction in the tail end, but
  perpendicular to this direction in the head end

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• Each row of prisms is inclined to its neighbors
  by 2
• In the outer third the rows of prisms are
  parallel and roughly perpendicular to the enamel
  surface

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• The outer surface of enamel frequently lacks the
  normal arrangement of rods (or prisms) but is
  arranged either in continuous layers parallel to
  the surface or as onion like curves
• This prism-less layer is usually 20-30µm thick,
  and present in deciduous truths and 70 of
  permanent teeth, although it did not cover the
  whole of the surface in most teeth, probably
  because it was worn a way by abrasion
• The apatite crystals in this layer are arranged
  almost at right angles to enamel surface in
  contrast to those within the prisms

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• Note
• These changes in direction produce the optical
  phenomenon known as the Hunter Schreger bands

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• The crystals in enamel are 10x larger than
  those of bone or dentine i.e. smaller surface
  area/unit weight

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Minor inorganic constituents of enamel and
dentine

1. Higher concentration on the surface of enamel
   than within (F, Pb, Zn, Fe, Sb, Mn, Cl, Se)
2. Lower concentration on surface than within (Na,
   Mg, CO32-)
3. Distribution approximately uniform (K, Sr, Cu, Al)

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• Concentrations range from a few ppm to lt0.01 ppm.
• Only strontium, F and Zn reach or exceed conc.
  Of 100 ppm through out the teeth
• Ions that attach readily to apatite crystals tend
  to increase in parts of teeth which are exposed
  mostly to body fluid i.e. outer enamel, outer
  cementum and inner dentine

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• Ions that dissolve out from crystals easily, will
  tend to decrease in the above parts
• Sodium concentration of enamel is higher than
  that of any other tissue in the body
• Magnesium rises in concentration from about 0.45
  in outer enamel to 2 in inner dentine

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Factors affecting the composition of enamel and
dentine

1. Position in tooth already discussed
2. Type of tooth e.g. F on surface of enamel is
   higher in incisors than in molars-opposite for
   proteins
3. Effect of age increase in F and Sr with age.
   Some may decrease or increase due to decreased
   permeability

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Organic Matter of Dentine

• Collagen
• Higher in the outer third
• Contains chondroitin sulphate
• OH-lysine higher than in skin
• Is linked to a phospho protein through an oligo
  saccharide

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• Non collagen matrix
• Approx. 20 components
• 2 large molecules a glycoprotein containing
  sialic acid, and a proteoglycan containing CS.
  Both have phosphoserine
• Serum albumin and immunoglobulins are also present

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• Lipids
• Some is bound to, or trapped by, the mineral
  matter
• F.a., MAG, DAG, lecithin and cardiolipin are not
  bound
• Cholesterol, its esters and TAG are partially
  bound
• Citrate

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Organic Matter of Enamel

• A. Protein

• Inner enamel
• Larger
• High in gly leu

Insoluble
Soluble

• Outer and inner enamel
• Consist of peptides of MW lt3500
• High in ser, pro, and gly
• Standing in acid becomes insoluble
• Contains bound carbohydrates
• (hexoses, fucose and xylolose)
• High content leads to reduction in
• spread of caries

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• B. Lipids similar to dentine. Give strong
  staining reaction in early caries due to release
  from minerals
• C. Citrate higher on the surface and near the
  amelo-dentinal junction than in the middle
• D. Lactate similar distribution, but lower
  concentration

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The relations of the main dental tissues
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10- Cementum
Primary (Cell-free)
Secondary (Cell-containing)

• Contains cells Lacunae with
• canaliculi is Lamellated also
• Covers the apical two- thirds of
• the root

• A series of lamellae parallel to
• direction of root
• present on the coronal third of
• the root

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• Both contain collagen fibers of the periodontal
  membrane embedded
• Similar composition to dentine but lower ash
  content (Ca P)
• Formed intermittently by cementoblasts, lying
  between the edge of the periodontal membrane, and
  a thin layer of uncalcified pre cementum
• Continued formation through out life
• Amount arrangement is influenced by occlusal
  stress