enamel and dentin biology.ppt

Dentin and enamel biology

1. In the name of creature

2. Enamel and Dentin
Biology
Dr.B.Behniafar
DDS, MDS of Aesthetic and Restorative Dentitry
ShahidSadoughiUniversity of Yazd
faculty of Dentistry

3. •Structures of Teeth:
Teeth are composed of (enamel, the pulp-dentin complex,Cementum).
Enamel and Dentin Biology

4. •Enamel formation; amelogenesis:
•by ameloblasts.
•originating from the embryonic germ layer (ectoderm).
•Enamel covers the anatomic crown
•varies in thickness: thicker at the incisal and
occlusal areas
•becomes progressively thinner until at the
cementoenamel junction (CEJ).
Enamel Biology

5. Enamel Biology
•The thickness also varies in each tooth:
2 mm at the incisal ridges of incisors,
2.3 to 2.5 mm at the cusps of premolars,
2.5 to 3 mm at the cusps of molars.

6. Enamel Biology
•Chemical structure:
enamel is a highly mineralized
crystalline structure.
Enamel
Mineraliz
ed
crystalls
(HA)
90-
92%
Organic
material
s
(matrix
proteins
)
1-2%
Water
4-12%

7. Enamel Biology
•enamel:
millions of enamel rods or prisms + rod Sheaths + cementing inter-rod
substance in some areas.
The spacingsare partially organic material
•The rods vary:
5 million for a mandibular incisor
12 million for a maxillary molar.
The rods are densely packed and intertwined in a wavy course
extends from the DEJ to the external surface of the tooth.

8. Enamel Biology

9. Enamel Biology
•Enamel; the hardestsubstance of the human body.
•Hardness varies according to:
Enamel location
decreases inwardly (lowest hardness at the DEJ)
•The density of enamel:
decreases from the surface to the DEJ.
Enamel is: rigid, strong and brittle
Enamel requires a dentin support to withstand masticatory forces.
Dentin is a more flexible (strong and resilient)
Dentin increases the fracture toughness

10. Enamel Biology
•Enamel rods in transverse section have;
1.rounded head or body section
2.tail section
•The rounded head portion of each prism (5 µm wide) lies
between the narrow tail portions (5 µm long) of two adjacent
prisms
•rounded head portion: incisal or occlusal direction;
•tail: cervically.

11. Enamel Biology
•The structural components of the enamel prism:
are millions of small, elongated apatite crystallites that vary in size
 and shape.
tightly packed in a distinct pattern of orientation (incresingthe strength)
The long axis of the apatite crystallites at the center of body:parallelto the
rod long axis
•the inclination of crystallites to the prism axis in
the tail region:
65 degrees
•the head of rod; dissolution process
•the tail regions and the periphery of the head: resistant
to acid attack.

12. Enamel Biology
•The HA crystallites:
irregular in shape
Average length of 160 nm
average width of 20 to 40 nm.
Composed of thousands of unit cells
have a highly ordered arrangement of atoms
A crystallite (300 unit cells long, 40 cells wide,
and 20 cells thick)
hexagonal configuration
prism sheath : an organic matrix surrounding individual crystals and is
organically rich rather than a structural entity.

13. Enamel Biology

14. Enamel Biology
•Gnarled enamel:
•Groups of enamel rods may entwine with adjacent groups of rods, and they
follow a curving irregular path toward the tooth surface.
•occurs near the cervical, incisaland occlusal areas
•Is not subject to fracture as much as is regular enamel.
•Resists to the pressure of bladed, hand-cutting instruments

15. Enamel Biology
•Hunter-Schregerbands:
•opticalappearance
•The changes in direction of enamel prisms that minimize fracture in the
axial direction
These bands: composed of alternate light and dark zones of varying widths
that have slightly different permeability and organic content.
Because the enamel rod orientation varies:
Hunter-Schregerbands in anterior teeth located near the incisal
surfaces.
Hunter-Schregerbands increase in numbers and areas of teeth, from
canines to premolars.

16. Enamel Biology

17. Enamel Biology
•Factors providing strength by resisting, distributing impact
forces:
The orientation of the enamel rod heads and tails
the gnarling of enamel rods

18. Enamel Biology
•Enamel tufts;
•hypo mineralized structures of the enamel rods and the inter-rod substance
•project between adjacent groups of enamel rods from the DEJ.
•They arise in dentin
•extend into enamel in the direction of the long axis of the crown
•may spread dental caries.

19. Enamel Biology
•Enamel lamellae;
•thin, leaf-like faults between enamel rod groups
•extend from the enamel surface toward the DEJ
•sometimes extending into dentin
•contain mostly organic material
•weak area: entry of bacteria and dental caries.

20. Enamel Biology
•Incremental striae of Retzius;
•Enamel rods are formed linearly by successive apposition of enamel in
discrete increments.
•Growth rings; variations in structure and mineralization
•The striae of Retzius In horizontal sections;
•appear as concentric circles.
•In vertical sections;
•the lines traverse the cuspal and incisal areas in a symmetric arc pattern
•descending obliquely to the cervical region and terminating at the DEJ.
•When these circles are incomplete at the enamel surface, a series of
alternating grooves, called imbrication lines of Pickerill,are formed.
•The elevations between the grooves are called perikymata;
•these are continuous around a tooth and usually lie parallel to the CEJ and
each other.

21. Enamel Biology

22. Enamel Biology
•Prismless Enamel;
•A structureless outer layer of enamel about 30 µm thick.
•Often at the cervical area and less often on cusp tips.
•No prism outlines are visible
•All of the apatite crystals are parallel to one another and perpendicular to
the striae of Retzius.
•More heavily mineralized.

23. Enamel Biology
•Anatomic Faults;
•Microscopic circular depressions where the enamel rods end.
•The concavities vary in depth and shape
•contribute to the adherence of plaque
•Resulting in caries attack, especially in young individuals.
•The dimpled surface anatomy of the enamel, gradually wears smooth with
age.

24. Enamel Biology
•Enamel is incapable of repairing itself: because the ameloblast cell
degenerates after the formation of the enamel rod.
•The final act of the ameloblast : secretion of a membrane covering the end
of the enamel rod (Nasmyth's membrane, or primary enamel cuticle)
•It covers the newly erupted tooth and is worn away by mastication and
cleaning.
•The membrane is replaced by an organic deposit called the pellicle;from
salivary proteins.

25. DEJ
•The interface of enamel and dentin ( dentinoenameljunction, or DEJ) is
scalloped or wavy in outline
•The crest of the waves penetrating toward enamel
•The rounded projections of enamel fit into the shallow depressions of
dentin.
•Contributing to: firm attachment between dentin and enamel.
•DEJ: hypermineralizedzone approximately 30 µm thick.
Enamel
Dentin

26. Pulp-Dentin complex
•Specialized connective tissue of mesodermal origin, formed from the dental
papilla of the tooth bud
•dental pulp
•four functions:
•(1) formative or developmental
•(2) nutritive
•(3) sensory or protective (only pain responses in dentin)
•(4) defensive or reparative

27. Dentin Biology
•Dentin formation
•Dentinogenesis; by odontoblasts.
•their cell bodies are in the pulp cavity
•their long, slender cytoplasmic cell processes (Tomes fibers) extend well (100-200
µm) into the tubules in the mineralized dentin.
•Enamel spindles:
•Odontoblasticprocesses occasionally cross the DEJ into enamel
•They may serve as painreceptors, explaining the enamel sensitivity experienced by
some patients during tooth preparation.

28. Dentin Biology
•Dentin formation:
Immediately before enamel formation.
Begins: subjacent to the cusp tip or incisalridge and gradually spreads to the apex
of the root
It continues after tooth eruption and throughout the life of the pulp
•Predentin:
The most recently formed layer of dentin: is always on the pulpal surface .
unmineralizedzone of dentin
immediately next to the cell bodies of odontoblasts

29. Dentin Biology
•Primary Dentin:
•The dentin forming the initial shape of the tooth
•Completed 3 years after tooth eruption (permanent teeth).
•The dentinal tubules : small canals extending the entire width of dentin
•Cytoplasmic cell process (Tomes fiber) inside the tubules
•Peri-tubular dentin:
more mineralized dentin lining each tuble
•Intertubulardentin:
dentin between each tubule

30. Dentin Biology

31. Dentin Biology
•The course of the dentinal tubules:
•Crown:slight S-curve
•Incisalridges, cusps, and root areas : straighter
•The ends of the tubules are perpendicular to the DEJ
•Canaliculi:small lateral openings along the tubule walls
•Anastomosingnetwork: Near the DEJ, the tubules divide into
several terminal branches,formingan intercommunication.

32. Dentin Biology
•Secondary Dentin:
1.After the primary dentin
2.dentin deposition continues at a reduced rate
3.without obvious external stimuli,
4.physiologic secondary dentin
5.the rate and amount, vary considerably among individuals
6.the tubules take a slightly different directional pattern in contrast to primary
dentin
7.forms on all internal aspects of the pulp cavity
8.in the pulp chamber, in multi-rooted teeth, it tends to be thicker on the
roof and floor

33. Dentin Biology
•Tertiary dentin:
•moderate stimuli are applied to dentin,
•such as caries, attrition, and some operative procedures
•the affected odontoblasts may die.
•Replacement odontoblasts (termed secondary odontoblasts) of pulpal origin
•Forming reparative dentin
•localized dentin deposit on the wall of the pulp cavity immediately subjacent to the
area on the tooth that has received the injury
•(a dentin deposit underneath the affected tubules)
•highly atubular
•structurally different from the primary and secondary dentin.

34. Dentin Biology
•Sclerotic dentin:
•results from aging or mild irritation (e.g.,slowly advancing caries)
•causing a change in the compositionof the primary dentin
•The peri-tubular dentin becomes wider
•filling the tubules with calcified material
•harder, denser, less sensitive dentin and more protective of the pulp against
subsequent irritations.
•physiologic dentin sclerosis;
•Sclerosis resulting from aging
•reactive dentin sclerosis;
•sclerosis resulting from a mild irritation
•often radiographically in the form of a more radiopaque (lighter) area in the S-shape
of the tubules.

35. Dentin Biology
•Human dentin (by volume):
•50%inorganic material
•30% organic material(90% type I collagen and 10% noncollagenous
proteins)
•Enamel> Dentin mineralization >cementum or bone
•Age: The mineral content of dentin increases
•The mineral phase:
•hydroxyapatite crystallites
•smaller than enamel crystallites
•having a length of 20 to 100 nm
•widthof about 3 nm < size seen in bone and cementum

36. Dentin Biology

37. Dentin Biology
•Dentin usually is distinguished from enamel by:
(1) color and opacity,
(2) reflectance,
(3) hardness,
(4) Sound
Dentin is normally yellow-white and slightly darker than enamel.
In older patients; dentin is darker
becomes brown or black when it has been exposed to:
oral fluids,
old restorative materials,
slowly advancing caries.

38. Dentin Biology
•Dentin surfaces compare to Enamel:
•opaque and dull,
•being less reflective to light than similar enamel surfaces (shiny).
•Dentin is softer than enamel
•greater yield to the pressure of a sharp explorer tine,
•explorer tends to catch and hold in dentin.

39. Dentin Biology
•Sensitivity:
•Stimulation of odontoblasts and their processes during operative procedures,
even
•Physical, thermal, chemical,bacterial, and traumatic stimuli: pain receptor
mechanism
•hydrodynamic theory; rapid movements of fluid within the dentinal tubules.

40. Dentin Biology
•Permeability:
•Coronal dentin > root dentin
•Depending on the remaining dentin thickness (length and diameter of the
tubules)
•Deep dentin is a less effective pulpal barrier (tubules are shorter, more
•numerous, and larger in diameter closer to the pulp)

41. Thank’s for your
attention