1. Factors playing role in achieving
adhesive bonds
WETTABILITY
Wettability of a liquid is characterised by the contact angle
between the liquid and the solid as measured within liquid
Categories of wettability include
Mostly non wetting >90 degrees
Absolutely no wetting 180 degrees
Mostly wetting <90 degrees
Absolute wetting 0 degrees
Contact angles of water on a A)clean glass slab, B) on acrylic surface C) on teflon
The smaller the contact angle between an
adhseive and an adherent the better the ability
of an adhesive to flow into and fill in
irregularities within the surface of adherent.
2. SURFACE ENERGY
• The energy on the surface per unit
area is referred to as the surface
energy (in mJ/m2) or surface tension
(in mN/m).
• No attraction is expected when the
surface molecules of the attracting
substances are separated by distances
greater than 0.7 nm (0.0007 μm).
• Wettability can be enhanced by
increasing the surface energy of the
substrates.
• Contaminants lower the surface
energy of the substrate.
3. ENAMEL ADHESION
• Enamel is composed of a hard solid crystalline structure-hydroxyapatite
(HAp) with strong intermolecular forces, high-energy surface, besides
water and organic material.
• Acid etching transforms the smooth enamel into an irregular surface and
increases its surface free energy.
• When a fluid resin-based material is applied to the irregular etched
surface, the resin penetrates into the surface aided by capillary action.
• Monomers in the material polymerize, and the material becomes
interlocked with the enamel surface
• The formation of resin microtags within the enamel surface is the
fundamental mechanism of resin-enamel adhesion.
4. Enamel etching results in three different
micromorphologic patterns.
TYPE I
This pattern involves
the dissolution of
prism cores without
dissolution of prism
peripheries
TYPE II
This pattern is the
opposite of type I: The
peripheral enamel is
dissolved,but the cores
are left intact.
TYPE III
It includes areas that
resemble the other
patterns and areas
whose topography is
not related to enamel
prism morphology
Sturdvent’s art and science of operative dentistry 6th edition
5. • Enamel etching removes about
10um of enamel .This creates
microporosities 5 to 50 μm deep
Etching also increases the surface
energy
Which ensures that:
• That resin monomers will readily
wet
the surface
• And will Infiltrate into microtags
• And polymerize to form resin tags
Resin tags formed are around 6um
in diameter and 10-20 um in length.
Macrotags (white stars) are formed
circularly between the longitudinally
sectioned enamel prism (black arrows)
peripheries.
Microtags (black stars) are formed at
the cores of the enamel prisms.
6. Enamel etchants
• Phosphoric acid at a concentration between 30% and
50% , typically 37% is preferred for 15 secs.
• Application of 50% phosphoric acid results in
formation of a monocalcium phosphate
monohydrate precipitate on the etched surface
which inhibits further dissolution.
• Concentrations less than 27% may create a
dicalcium phosphate monohydrate precipitate,
however, which cannot be removed easily and
consequently may interfere with adhesion.
7. Other enamel etchants
• Ethylene Diamine Tetraacetic Acid – Strong decalcifying agent,
promotes only low bond strength to enamel, as EDTA does no etch
preferentially.
• Pyruvic acid: 10% buffered with glycine to a pH 2.2, promotes high
bond strengths to enamel, but is impractical because of its instability.
• Sulphuric acid: 2% used for 30 seconds has shown to be as effective as
H3PO4; High H2SO4 concentration produce heavy crystal deposits
which interfere with bonding and cannot be washed away easily.
• Inorganic acids
• Nitric acid – 2.5% concentration.
• Organic Acids :
• Citric acid 10%
• Maleic acid 10%
• Oxalic acid : 1.6% - 3.5%
8. • LASER ETCHING
• Continuous vaporization and microexplosion due to
vapourisation of water trapped within the
hydroxyapatite matrix.
• Eg. CO2 and Nd:YAG
9. DENTIN ADHESION
• Dentin is intrinsically humid, and less hard than
enamel, with low intermolecular forces and low-energy
surfaces.
• The dentin is different from enamel, as it has smear
layer, organic contents and presence of fluid inside the
dentinal tubules.
• In addition, the density of dentinal tubules
varies with dentinal depth and, as well as the
water content of dentin, is lowest in
superficial dentin and highest in deep
dentin.
• In superficial dentin, which contains
fewer tubules, the permeation of resin into
intertubular dentin will be responsible for
most of the bond strength.
10. • In deep dentin, dentinal tubules are more in number: the
intratubular permeability of resins will be responsible for higher
bond strength.
• Dentin is also a substrate that undergoes change with age in an
asymmetrical physiological aging process, leading to an increase of
dentin thickness and decrease in dentin permeability.
• Furthermore, sclerotic and carious dentin suffers structural changes
that result in a higher mineralization and a consequently reduced
permeability.
• Unlike dentin, enamel can be dried easily: so bonding process to
enamel is different from that of dentin.
Classification review of dental adhesive systems: from the IV generation to the universal type Eshrak
Sofan, PhD, Afrah Sofan, PhD, Gaspare Palaia,, PhD, Gianluca Tenore, MD, DDS, Umberto Romeo,
MD, DDS, and Guido Migliau, MD, DDS, 2017:VIII(1):1-17
