consist of cementum & dentine

1. Chemical
Composition of The
Teeth

2. 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

3. The relations of the main dental tissues

4. 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) - > 90% inorganic

6.  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

8. Mineral composition:
 Most reliable analysis obtained by
heating tissue to 105°C 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

10. The structure of the inorganic fraction:
i. The main constituent is the crystalline
form of calcium phosphate known as
apatite with some amorphous calcium
phosphate (except probably in
enamel)

11. ii. 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
iii. Apatites belong to the hexagonal
system of crystals*
*(Hexagonal crystal system. The hexagonal system has four crystallographic
axes consisting of three equal horizontal, or equilateral axes at 120ₒ
degrees to each other, as well as one vertical axis which is perpendicular
to the other three. This vertical axis can be longer or shorter than the
horizontal axes.)

12. The system has the following forms:
Prism
Pinacoid
Dipyramid
Ditrigonal Pyramid
Trigonal Prism
Ditrigonal Prism.

13. The crystal structure of hydroxyapatite

14. iv. 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 60°C, so if view
along the longitudinal axis, the calcium
atoms in the two triangles would appear as
a second hexagon

15. The crystal structure of hydroxyapatite

16. v. 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

17. vi. 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.

18.  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

19. The crystal structure of hydroxyapatite

20. vii. 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

22. Fluoride
Dental caries is a continuous process of demineralization and
remineralization of the enamel and fluoride plays a key role in this
process through its action at the plaque enamel interface. It is now
accepted that the primary mode of action of fluoride is post-eruptive*.
The post-eruptive action of fluoride has resulted in new methods of
delivering fluoride.
Fluoride is a mineral
Fluoride ion comes from the element fluorine
Fluorine is 17th most abundant element in the earths crust
Never encountered in its free state in nature
Exits only in combination with other elements as a fluoride compound
At the time of tooth eruption, enamel is not quite completely mineralized and
will undergo what is called the post-eruptive period (topical effect) that will take
approximately two years. Throughout this enamel maturation period, fluoride
continues to accumulate in the outer surfaces of the enamel. This fluoride is
derived from the saliva, as well as exposure to fluoride-containing products
such as food and beverages. Most of the fluoride incorporated into the
developing enamel occurs during what is now called the pre-eruptive (systemic
effect) period of enamel formation, but also occurs topically during the post-
eruptive period of enamel maturation.

23. How does it work?
Changes the crystalline structure of
enamel to make it less soluble.
Suppresses cariogenic bacteria in
dental plaque (Streptococcus
mutans).
Acts on the enamel surface to
inhibit bacterial adhesion

24. Nature of tooth mineral
{ Ca10-x(Na)x(PO4)6-y(CO3)z(OH)2-u(F)u}
Highly substituted carbonated apatite
Most soluble
Ca10(PO4)6(OH)2
hydroxyapatite (less soluble)
Ca10(PO4)6(F)2 = fluoroapatite
Least soluble

25. Mechanism of action
Recent evidences
shows that the main
effect of fluoride in
caries prevention
are
POST ERUPTIVE
Through Topical
effect
OLD concept :
That major inhibitory
effect was thought to
be due to its
incorporation in
tooth mineral during
the development of
the tooth prior to
eruption

26. Source: Featherstone , 1999

27. Mechanism of action
Only when fluoride is
concentrated into a new
crystal surface during Re-
mineralization, it is
sufficient to alter solubility
beneficially.

28. Mechanism of action
If fluoride is present in the plaque
fluids at the time that bacteria
generate acids, it will travel with the
acid down into the subsurface of
the tooth, adsorb to the crystal
surface and protect it from being
dissolved.

29. viii. Biological apatite are non-stoichiometric*:
 Pure synthetic apatite has Ca:P ratio of
2.15
 Ratio is lower in bone and teeth
 Two properties of apatite explain the
variation in nature
*Relating to or denoting quantities of reactants in simple integral ratios, as
prescribed by an equation or formula.
Stoichiometry measures these quantitative relationships, and is used to
determine the amount of products and reactants that are produced or needed
in a given reaction. Describing the quantitative relationships among
substances as they participate in chemical reactions is known as
reaction stoichiometry.

30. a. Adsorption:
e.g. adsorption of excess phosphate as (HPO4
-)
on the crystal surface, and of citrate, CO3
2-,
HCO3
- and magnesium as (MgOH)+ as well
b. 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

32. ix. The more general formula for biologically
formed apatite is Ca10-x (HPO4)x (PO4)6-x (OH) 2-x .
XH2O (where x is between 0 and 2, and normally
a fractional number)
x. Another likely component with apatite is Octa-
Calcium Phosphate (OCP): Ca8 H2 (PO4)6 .5H2O
i.e. Ca8 (HPO4)2 (PO4)4.5H2O [Ca:P=1.33], thus
explaining the lower Ca:P ratio in nature

33. 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

34. 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 (pointed end with two curves).
 Crystallites within rods are oriented in a
cuspal-cervical direction in the tail end, but
perpendicular to this direction in the head
end

36.  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

38.  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

39. Note:
These changes in direction produce the
optical phenomenon known as the
Hunter Schreger bands

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

41. Minor inorganic constituents of
enamel and dentine
a. Higher concentration on the surface
of enamel than within (F, Pb, Zn, Fe,
Sb, Mn, Cl, Se)
b. Lower concentration on surface than
within (Na, Mg, CO32-)
c. Distribution approximately uniform (K,
Sr, Cu, Al)

42.  Concentrations range from a few ppm to
<0.01 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

43.  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

44. 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

46. Organic Matter of Dentine
1. Collagen:
a. Higher in the outer third (composite)
b. Contains chondroitin sulphate (CS)
c. OH-lysine higher than in skin
d. Is linked to a phospho-protein through
an oligosaccharide

47. 2. Non collagen matrix:
a. Approx. 20 components
b. 2 large molecules: a glycoprotein
containing sialic acid*, and a
proteoglycan containing CS. Both have
phosphoserine
c. Serum albumin and immunoglobulins
are also present
• Sialic acid is a generic term for the N- or O-substituted derivatives of neuraminic acid, a
monosaccharide with a nine-carbon backbone. It is also the name for the most common
member of this group, N-acetylneuraminic acid (Neu5Ac or NANA).
• Sialic acids are a diverse family of sugar units with a nine-carbon backbone that are
typically found attached to the outermost ends of these chains. Given their location and
ubiquitous distribution, sialic acids can mediate or modulate a wide variety of
physiological and pathological processes.

48. 3. Lipids:
a. Some is bound to, or trapped by, the
mineral matter
b. F, MAG, DAG, lecithin and cardiolipin are
not bound (Monoacyl & Diacyl Glycerols)
c. Cholesterol, its esters and TAG are partially
bound
4. Citrate

50. Organic Matter of Enamel
A. Protein
1. Outer and inner enamel
2. Consist of peptides of MW <3500
3. High in ser, pro, and gly
4. Standing in acid becomes insoluble
5. Contains bound carbohydrates
(hexoses, fucose and xylolose)
6. High content leads to reduction in
spread of caries
Soluble Insoluble
- Inner enamel
- Larger
- High in gly & leu

51. 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

52. The relations of the main dental tissues

53. 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
Cementum situated around a human molar

54.  Both contain collagen fibers of the
periodontal membrane embeded
 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 throughout life
 Amount & arrangement is influenced by
occlusal stress