Enamel CONSERVATIVE DENTISTRY AND ENDODONTICS

ENAMEL
Presented by,
Swapnika.G.
(1 MDS)
Conservative Dentistry and Endodontics

• Introduction
• Functions of enamel
• Physical and chemical properties
• Surface structures of enamel
• Life cycle of ameloblasts and Amelogenesis
• Enamel adhesion
• Effect of bleaching on enamel
• Developmental disturbances of enamel
• Age changes and clinical considerations
• References
CONTENTS

INTRODUCTION
• Enamel is a protective covering of variable thickness over the entire surface of the
crown.
• Enamel is the hardest calcified tissue in the human body.
• The shape and contour of the cusps receive their final modeling in the enamel.
• The cells that are responsible for the formation of enamel (Ameloblasts) are lost as
the tooth erupts into the oral cavity, and hence can’t renew itself.
• To compensate this enamel undergoes complex structural organization and high
degree of mineralization.

FUNCTIONS OF ENAMEL
• Transfers occlusal load to the biomechanical unit.
• It prevents premature wearing of dentine.
• Prevents hypersensitivity of dentine.
• Protects pulp dentine complex from thermal, chemical and electrical substances.
• Provides aesthetics.
• Helps in maintain contacts, contours and vertical dimension.

PHYSICAL PROPERTIES
• Hardest calcified tissue- high content of mineral salts and crystalline arrangement.
• Modulus of elasticity and hardness- more at the surface than at the DEJ.
• Maximum thickness: 2-2.5mm
• Semi-permeable membrane.
• Specific gravity – 2.8
• Translucency- degree of calcification and homogenesity.
• Color : ranges from light yellow to bluish gray.
• Incisal areas may have a bluish tinge where the thin edge consists of only a double layer of
enamel and cervical areas show yellowish tinge because of thinness of the enamel.
Kumar GS. Orban's oral histology & embryology. Elsevier Health Sciences; 2014 Feb 10.

CHEMICAL PROPERTIES
ENAMEL
ORGANIC
COMPONENT
AMELOGENINS(90%)
NON AMELOGENINS
(10%)
Enamelin Ameloblastin Tuftelin
INORGANIC
COMPONENT(96%)
HYDROXYAPATITE
CRYSTALS
WATER(4%)

INORGANIC MATERIAL
• The inorganic material of enamel is hydroxyapatite.
• The crystals are hexagonal in cross section.
• The shape of the single crystal is rod with an equilateral
hexagon base.
• The crystals are arranged to form enamel rods or prisms.
• The core of the crystal are rich in Mg and carbonate.
• Water is present in the crystals and in between the crystals.

ENAMEL RODS
• Prisms- cylindrical in longitudinal section. (rods)
• Diameter averages 4 micro meters.
• DEJ to the surface of the tooth- tortuous.
• Length of most of the rods> thickness of enamel—oblique and wavy
course.
• Diameter of rods from DEJ to surface= 1:2 increase
DIRECTION OF RODS:
• Oriented at right angles to dentine.
• Wavy course from DEJ to enamel surface.

• Cross section—fish scale appearance.
• ARCADE outlines—near DEJ.
• KEYHOLE or PADDLE shaped prism— Longitudinal Sections
• Head is directed towards occlusal aspects and tail towards the
cervical aspect of the tooth.
• When enamel is cut longitudinally section passes through heads
of one row of rods and tails of the adjacent row.
• This produces an appearance rods separated from interrod
substance.
• 5 um breadth, 9 um length– rod measurement.
• Hydroxyapatite crystals– parallel to long axis of prisms, deviation-
40 degrees.
ULTRASTRUCTURE

ROD SHEATH
• The boundary between the rod and interrod substance is delimited by a narrow
space containing organic material.
• It is a thin peripheral layer.
• Darker than the rod.
• Relatively acid resistant.
• Less calcified and contains more organic matter
than the rod itself.
INTERPRISMATIC SUBSTANCE:
• Cementing rods together.
• Less calcified than the rod and more calcified than the rod sheath.

STRIATIONS
• Each enamel rod is built up of segments separated by dark lines that gives its
striated appearance.
• Become more visible by the action of acids.
• These rods are segmented because the enamel matrix is formed in a rhythmic
manner.
• In humans these segments seem to be uniform length of about 4 microns.

HUNTER SCHREGER BANDS
• The change in the direction of the rods is responsible for appearance of
the Hunter Schreger bands.
• Alternating dark and light bands of varying widths seen in longitudinal
sections under oblique reflected light.
• They originate at DEJ and ends at some distance from outer enamel
surface.
• The prisms which are cut longitudinally produce dark bands called
PARAZONES.
• The prisms cut transversely produce light bands called DIAZONES.
• The angle between these two is 40 degrees.

INCREMENTAL LINES OF RETZIUS AND
PERIKYMATA
• Appears as brownish bands in ground sections.
• They illustrate the incremental pattern of the enamel, that is, the
successive apposition of layers of enamel during formation of the
crown.
• In longitudinal sections– surround tip of dentin.
• In transverse sections— concentric circles.
• Perikymata are the transverse wave like grooves, believed to be the
external manifestation of the striae of Retzius.
• They are continuous around a tooth and usually lie parallel to each
other and to CEJ.

PRISMLESS ENAMEL OTHER SURFACE
STRUCTURES
• Structureless enamel– 30um
• All deciduous and 70% permanent
teeth.
• Cervical areas of teeth.
• Hydroxyapetite crystals are parelllel
to one another and perpendicular
to striae of Retzius.
• More mineralized than enamel
beneath.
• Pits- 1-1.5um- ends of ameloblasts.
• Enamel caps-small elevations-10-
15um- enamel mineralization on non-
mineralizable debris.
• Enamel brochs-Larger elevations.

ENAMEL CUTICLE NEONATAL LINE
• A delicate membrane called Nasmyth’s
membrane.
• Primary enamel cuticle.
• Covers entire crown of newly erupted tooth.
• Secreted by ameloblasts when enamel
formation is completed.
• Basal lamina found beneath epithelia.
• Soon disappears due to masticatory forces.
• Erupted enamel- pellicle- precipitate of
salivary proteins.
• Accentuated incremental
line of Retzius.

ENAMEL LAMELLAE ENAMEL TUFTS
• Thin leaf like structures that extend from enamel
surface towards DEJ.
• Sometimes penetrates dentine.
• More organic less mineral content.
• Seen in transverse ground sections.
• Arise at DEJ and reach into enamel to
about 1/5 to 1/3 of its thickness.
• Ground sections– grass like.
• Seen in transverse sections.

ENAMEL SPINDLES
• Odontoblastic processes that pass across the DEJ into
enamel.
• Since many are thickened at their end they have been
termed as spindles.
• Direction of odontoblastic process and spindles
corresponds to the original direction of ameloblasts.
• Before hard substances were formed.
• Direction- at right angles to dentin.
• Ground sections– dark in transmitted light.

GNARLED ENAMEL DEJ
• Over the cusps of teeth the rods
appear twisted around each other in a
seemingly complex arrangement and
this optical appearance known as
gnarled enamel.
GNARLED ENAMEL

LIFE CYCLE OF AMELOBLASTS
MORPHOGENIC STAGE
ORGANISING STAGE
FORMATIVE STAGE
MATURATIVE STAGE
PROTECTIVE STAGE
DESMOLYTIC STAGE
POST
SECRETORY
PRE
SECRETORY
SSECRETORY

MORPHOGENIC STAGE
• Before ameloblasts are fully differentiated and produce
enamel, they interact with adjacent mesenchymal cells,
determining the shape of the DEJ.
• Cells are short and columnar, with large oval nuclei that
almost fill the cell body.
• During ameloblasts differentiation, terminal bars appear
concomitantly with migration of mitochondria to the
basal region of the cell.

ORGANISING STAGE
• Characterized by change in the appearance of the cells of IEE.
• They become longer and the nucleus free zones at the distal ends of
the cells become almost as long as the proximal parts containing the
nuclei.
• Reversal of functional polarity takes place.
• Clear cell free zone between the IEE and dental papilla disappears.
• Thus epithelial cells come into close contact with the connective tissue
cells of the pulp., which differentiate into odontoblasts.
• During terminal phase of organizing stage dentine formation begins.
• First appearance of the dentine is the critical phase of the life cycle of
IEE.

FORMATIVE STAGE
• Ameloblasts enter into formative stage after the first layer of
dentine is formed.
• Cells retain the same length and arrangement.
• Changes in the organization and number of cytoplasmic
organelles are related to initiation of SECRETION of enamel
matrix.
• Earliest change is development of blunt cell processes on
the ameloblast surface and penetrate the basal lamina and
enter predentine.

MATURATIVE STAGE
• Full mineralization of enamel forms after most if the
thickness of the enamel matrix has been formed in the
occlusal parts of the crown and incisal areas.
• Ameloblasts are slightly reduced in length and closely attach
to enamel matrix.
• Ameloblasts display microvilli at their distal proximities and
cytoplasmic vacuoles containing material resembling
enamel matrix are present.
• These structures indicate absorptive function of these cells.

PROTECTIVE STAGE
• The enamel has completely developed, and has fully
calcified, the Ameloblasts cease to be arranged in a well-
defined layer.
• Cells then form a stratified epithelial covering of enamel,
the so-called reduced enamel epithelium.
• The function of REE is that of protecting the mature
enamel by separating it from the connective tissue until
tooth erupts.
• If connective tissue comes in contact with the enamel,
anomalies may develop.

DESMOLYTIC STAGE
• The reduced enamel epithelium proliferates and
seems to induce atrophy of the connective tissues
separating it from oral epithelium.
• Epithelial cells elaborate enzymes that are able to
destroy connective tissue fibers by desmolysis.
• Premature degeneration of the reduced enamel
epithelium may prevent the eruption of a tooth.

AMELOGENESIS
Amelogenesis or enamel formation is a two step process.
Organic matrix formation
Mineralization
• Amelogenin a component of enamel matrix proteins, undergo extracellular
degradation by proteolytic enzymes and break into smaller low molecular weight
fragments.
• These are suggested to have specific function in regulating crystal growth.

TOMES PROCESS
• The surfaces of the ameloblasts facing the developing enamel are not
smooth.
• There is an interdigitation of the cells and enamel rods that they
produce.
• This is a result of the fact that the long axes of the ameloblasts are not
parallel to the long axes of the rods.
• The projections of the ameloblasts into the enamel matrix have been
named as Tome’s processes.
• The junctional complexes which form at the distal end are called distal
terminal bars.
• These terminal bars separate the Tome’s processes from the cell
proper.

ENAMEL ADHESION
• Acid etching transforms the smooth enamel into an irregular surface and increases its
surface free energy.
• The formation of resin microtags within the enamel surface is the fundamental mechanism
of resin-enamel adhesion. (micromechanical)
TYPE- 1 TYPE- II TYPE- III
Roberson T, Heymann HO, Swift Jr EJ. Sturdevant's art and science of operative dentistry. Elsevier Health Sciences; 2006 Apr 13.
Anusavice KJ, Shen C, Rawls HR, editors. Phillips' science of dental materials. Elsevier Health Sciences; 2012 Sep 27.

50% conc monocalcium phosphate monohydrate rinsed off.
<27% conc dicalciumphosphate monohydrate cannot be rinsed, adhesion
interference
Barkmeier WW, et al: Effects of 15 vs 60 second enamel acid conditioning on adhesion and morphology, Oper Dent 11:111-116, 1986.
• An etching time of 60 seconds permanent enamel using 30% to 40% phosphoric acid.
• For primary enamel– 45-60 seconds
• Severe fluorosed teeth– 75-90 sec (fluorosis index=4)

RETENTIVE FEATURES PLACED IN ENAMEL
• Partial bevel- for cast metal restorations
• Short bevel- for cast metal restorations
• Skirt preperations: Skirts are thin extensions
of the facial or lingual proximal margins of
the cast metal onlay that extend from the
primary flare to a termination just past the
transitional line angle of the tooth.
• Bevelling the composite restorations.
Marzouk MA, Simonton AL, Gross RD. Operative dentistry. Modern theory and practice, 1st ed. St Louise-Tokyo, Ishiyahu EuroAmerica Inc.
1985.

EFFECT OF BLEACHING ON ENAMEL
• In office extracoronal bleaching- gel with 25% to 38% H2O2.
• The light source can be a laser (e.g., argon, CO2), halogen, plasma
arc, or light-emitting diodes (LED).
• For professional at home bleaching- 3% to 7.5% H2O2 or 10 to 22%
carbamide peroxide, especially those with 10% carbamide peroxide.
• Several investigators reported alteration of enamel surfaces
associated with bleaching treatments, including shallow depression,
increased porosity, and slight erosion.
• Associated with products using acidic pre rinse or gels of low pH.
Ingle JI, Bakland LK, Baumgartner JC, editors. Ingle's endodontics 6. Pmph usa; 2008.

75 volunteers were distributed according to the bleaching technique (n=25):
(a) at-home: 10%HP (Opalescence GO) for 15 days of continuous use (1 hour per day);
(b) in-office: 40%HP (Opalescence Boost) in three clinical sessions (40 minutes each session);
(c) combined: one initial session with 40%HP, and the rest with 10%HP for 15 days of
continuous use.
Clinical evaluations and Ca and P concentration collections were obtained before, during
bleaching treatment, and 15 days after conclusion of treatment.
RESULTS:
• The in-office technique presented the lowest tooth sensitivity.
• All techniques resulted in lower Ca and P concentrations in enamel at each time point,
compared with the baseline concentrations.
• Calcium concentrations did not differ significantly among the treatments (P= 0.9360).
• Phosphorus concentration at the 8th day was higher for the in-office technique group (P<
0.05).
Dourado AP, Carlos NR, Amaral FL, França FM, Turssi CP, Basting RT. At-home, in-office and combined dental bleaching techniques
using hydrogen peroxide: Randomized clinical trial evaluation of effectiveness, clinical parameters and enamel mineral content.
American journal of dentistry. 2019 Jun;32(3):124-32.

DEVELOPMENTAL DISTURBANCES OF ENAMEL
AMELOGENESIS IMPERFECTA:
• A developmental disturbance in the structure of the enamel.
• Etiology : a genetic autosomal defective gene linked to the locus DXS85 at
Xp22.
• This is identified as a general location of human gene for amelogenin., a
principle protein in developing enamel.
• Hypoplastic : characterized by deficiency in the quality of enamel. Clinically
manifested as pits or grooves on the enamel surface.
• Hypocalcified : characterized by enamel that is insufficiently mineralized,
appearing clinically as soft and discolored, easy to remove.
• Hypomaturative : associated with abnormalities during the maturation of
enamel formation, giving the enamel an opaque and chalky appearance.Shafer WG, Hine MK, Levy BM, Rajendran R, Sivapathasundharam B. A textbook of oral pathology. Philadelphia: Saunders; 1983 Sep 20.

ENVIRONMENTAL ENAMEL HYPOPLASIA
• May be defined as incomplete or defective formation of the organic enamel matrix.
• A number of factors, each capable of producing injury to ameloblasts may give rise to
this condition.
• Rickets during the time of tooth formation is most common known cause of enamel
hypoplasia.
• Deficiencies of vitamin A and C also been named as causes for enamel hypoplasia.
• Vit – D deficiency causes pitting type of enamel defects.
NUTRITIONAL DEFICIENCIES
Shafer WG, Hine MK, Levy BM, Rajendran R, Sivapathasundharam B. A textbook of oral pathology. Philadelphia: Saunders; 1983 Sep 20.

CONGENITAL SYPHILLIS
• This hypoplasia involves maxillary and mandibular central incisors and first
molars.
• Characteristic shape of upper central incisor is “SCREW-DRIVER” shaped
incisors. (Hutchinson’s teeth).
• The incisal edge is usually notched.
• Molars are referred as mulberry molars.
measles, chickenpox and scarlet fever
Pitting type – CI, LI, CUSPIDS, MOLARS

FLUOROSIS
• Mottled enamel
• 0.9 to 1.0 ppm.
• Chronic ingestion of fluoride in
drinking water leads to dental fluorosis.
• Appears as a hypocalcified lesions on
the surface of enamel.
Peter S. Essentials of preventive and community dentistry. Arya (Medi) Publishing House; 2009.

AGE CHANGES AND CLINICAL CONSIDERATIONS
MICROSCOPIC CHANGES:
• Loss of Perikymata - generalized loss of rod ends
- more on buccal and lingual
- height of contour
- anterior teeth than posterior
• Localized increase in elements such as nitrogen and fluorine – darker color.
• Increase in the size of the crystal reduces permeability.
• Increase in the organic content of enamel.

MACROSCOPIC CHANGES
ATTRITION:
It is a mechanical wear of the incisal or occlusal tooth structure
as a result of functional or parafunctional movements of the
mandible.
ABRASION:
It is defined as an abnormal tooth structure loss resulting from
direct frictional forces between the teeth and external objects
or from frictional forces between contacting teeth in the
presence of an abrasive medium.

EROSION
• Progressive loss of dental tissue by chemical processes not involving bacteria.
• EXTRINSIC : Contact with acidic media, food.
• INTRINSIC : gastric acids regurgitated into esophagus and mouth.

REFERENCES
• Kumar GS. Orban's oral histology & embryology. Elsevier Health Sciences; 2014 Feb 10.
• Ten Cate AR, Nanci A. Ten Cate's oral histology: development, structure, and function.
Elsevier; 2013.
• Shafer WG, Hine MK, Levy BM, Rajendran R, Sivapathasundharam B. A textbook of oral
pathology. Philadelphia: Saunders; 1983 Sep 20.
• Roberson T, Heymann HO, Swift Jr EJ. Sturdevant's art and science of operative
dentistry. Elsevier Health Sciences; 2006 Apr 13.
• Anusavice KJ, Shen C, Rawls HR, editors. Phillips' science of dental materials. Elsevier
Health Sciences; 2012 Sep 27.
• Phillips RW. Skinner's science of dental materials. Philadelphia: Saunders; 1973.

• Barkmeier WW, et al: Effects of 15 vs 60 second enamel acid conditioning on adhesion
and morphology, Oper Dent 11:111-116, 1986.
• Marzouk MA, Simonton AL, Gross RD. Operative dentistry. Modern theory and
practice, 1st ed. St Louise-Tokyo, Ishiyahu EuroAmerica Inc. 1985.
• Ingle JI, Bakland LK, Baumgartner JC, editors. Ingle's endodontics 6. Pmph usa; 2008.
• Peter S. Essentials of preventive and community dentistry. Arya (Medi) Publishing
House; 2009.

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Enamel CONSERVATIVE DENTISTRY AND ENDODONTICS

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