Griffith University Oral Biology 2 1009 DOH Enamel Dr. Mahmoud Bakr Lecturer in General Dental Practice B.D.S, M.D.S (Cairo University), ADC (Australia) Member of the Australian Dental Association (ADA), the Australian Biology Institute Inc. (ABI) and the Egyptian Dental Union (EDU)
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Griffith University Oral Biology 2 1009 DOH
Enamel
Dr. Mahmoud Bakr
Lecturer in General Dental Practice
B.D.S, M.D.S (Cairo University), ADC (Australia)
Member of the Australian Dental Association (ADA),
the Australian Biology Institute Inc. (ABI) and the
Egyptian Dental Union (EDU)
Learning objectives: After completing this lecture you should be able to:
1- Name, classify, identify and describe the
structure and function of the components of
Enamel.
2- Describe age related changes to Enamel and their
effects.
3- By observing the histological details of cells and
tissues, you should be able to use a microscope to
identify different histological structures of
Enamel and understand the histological processes
involved in preparing slides.
• All Microscopic images are taken from the
Digital Library of the Oral Biology
Department (Cairo University).
INTRODUCTION
ENAMEL
-Makes up the outside layer of anatomical crown of a tooth
-Covers and protects the dentin of the crown
-Firmly attached to the underlying dentin at the dentinoenamel junction and meets the cementum at the cementoenamel junction
-The hardest and most mineralized substance of the body
-Has no way to regenerate itself
2-THICKNESS
5-PERMEABILITY
1-COLOUR
4-BRITTLNESS
3-HARDNESS
PHYSICAL PROPERTEIS
1- Colour: 1 - COLOUR
YELLOWISH WHITE TO GRAYISH WHITE
: DEPENDS ON
1- DEGREE OF CALCIFICATION
2- HOMOGENOUSITY OF THE ENAMEL CRYSTALS.
SO:
TRANSLUCENT E. YELLOWISH TEETH
OPAQUE E.
GREYISH TEETH
2-Thickness 2 - THICKNESS
- 2 – 2.5 mm. at the cusp tips.
- Thinning down to
Feather edge at the cervical line of the tooth
2 - THICKNESS
Thin enamel is
present at the
bottom of the pits
and fissures of the
crown surface
dentin
enamel
3 – HARDNESS
IT IS THE HARDEST
CALCIFIED TISSUE IN THE
BODY
DUE TO:
1- HIGH CONTENT OF THE
MINERAL SALTS
2- ITS CRYSTALLINE
ARRANGEMENT.
- ENAMEL OF THE
PERMANENT TEETH
IS HARDER THAN
THAT OF DECIDUOUS
ONES
+
-
+
+
3 – HARDNESS
-1 - IS GREATEST AT THE
AND SURFACE
DECREASED TOWARD
DEJ.
2 - IT IS GREATER AT THE
AND INCISAL CUSPS
RIDGE AND DECREASES
CERVICALTOWARD THE
LINE.
3- It is the hardest tissue of
the body
+
-
+
+
+
-
-
4- Brittleness: 4 - BRITTLENESS
-Very brittle due to large amount of minerals
-Dentin, which is less mineralized and less brittle, compensates
for enamel and is necessary as a support for enamel
-If this supportive layer of dentin is destroyed by caries or
improper cavity preparation, the unsupported enamel fractures
5- PERMEABILITY - IT ACTS AS A SEMIPERMEABLE MEMBRANE FOR CERTAIN IONS THROUGH PORES BETWEEN THE CRYSTALS.
-PER. IS MAINLY FROM
SALIVA TO OUTER
LAYER OF ENAMEL, BUT
LESS FROM THE PULP
TO THE INNER ENAMEL
LAYER ACROSS THE
DENTIN.
CHEMICAL PROPERTIES
water organic inorg
2% 1-2% 95-96% By
weight
10-12% 88-90% By
volume
INORGANIC
ORGANIC
a- Inorganic material of enamel:
CALCIUM PHOSPHATE
( HYDROXY APATITE)
CRYSTALS
3 Ca3 (PO4)2 . Ca (OH)2
-Most crystals are regularly
hexagonal in cross section.
(VERY LARGE) -
-They are 70 nm. in width,
25 nm. in thickness
length may reach to 0.1 micron
INORGANIC MATERIAL 96 %
Various ions if present during enamel formation or in
the environment of fully formed enamel may replace
•Influx of mineral ions into the present partially mineralized matrix occurs in relation to ruffled- ended cells
•Withdrawal of organic matrix from the maturing enamel occur mainly in the ruffled- ended cells as well as through passing between the leaky distal junctions of the smooth-ended cells
After complete Enamel matrix
formation and maturation
Ameloblasts become squeezed
as a layer of Reduced Enamel
Epithelium which protects Enamel
from resorption by cells from
Dental Sac.
5– Protective stage:
5– PROTECTIVE STAGE
REDUCED DENTAL
EPITHELIUM
PRIMARY ENAMEL CUTICLE
Reduced Enamel Epithelium (with
Ameloblasts being a part of it) secrets
desmolytic enzymes for elimination of
Dental sac and allowing fusion between
Reduced Enamel Epithelium and Oral
Epithelium.
This allows eruption of the tooth without
bleeding.
It is called Primary Enamel Cuticle which is
the last product of Ameloblasts.
6– DESMOLYTIC STAGE
ENAMEL
REDUCED DENTAL
EPITHELIUM
TOOTH ERUPTION
GINGIVAL
EPITHELIUM
still fusing with
E.CUTICLE
will wear away
THE BEGINNING OF MINERALIZATION OF THE
ENAMEL MATRIX DOES NOT AWAIT THE
COMPLETION OF ITS FORMATION.
AMELOGENESIS
A–SECRETORY
PHASE
B- MATURATION
PHASE
A-- Secretory phase:
Beginning of secretion End of secretion
STIPPLED MATERIAL OF ENAMEL
1- Stippled material secretion:
STRATUM INTERMEDIUM
AMELOBLASTS
ENAMEL MATRIX
MANTLE DENTIN
Secretory ameloblast
The first hydroxyapatite crystals formed interdigitate with the crystals of dentin.