2. Acid Etching
Etching of dental surface with an
acid to remove the smear layer and
open enamel tubules, increase
retention of resin sealant, and
promote mechanical retention.
3. Development
A concept of etching enamel surfaces
with phosphoric acid, first proposed by
Buonocore in1955 to increase the
bond strength between the composite
resin and etched enamel.
4. Mechanism of Action
The irregular enamel surface created
by dissolving hydroxyapatite crystals
permits penetration of the fluid
adhesive components and this
penetration provides micromechanical
retention. Acid etching of enamel
appears to improve retention by
selectively eroding certain
hydroxyapatite formations and
facilitating penetration by the
development of resin tags.
6. Types of Acid Etching
According to Silverstone et al there are 5 types
of acid etching pattern:
1. Type 1: preferential dissolution of prism
cores, resulting in honey comb like
appearance.
2. Type II: preferential dissolution of prism
peripheries, giving cobblestone like
appearance.
3. Type III: a mixture of type I and II pattern.
4. Type VI: pitted enamel surfaces as well as
structures that look like unfinished puzzle,
maps or networks.
5. Type V: flat, smooth surface
7.
8.
9. Acid etching removes approximately 10 µm
of enamel surface and creates a
morphologically porous layer (5 µm to 50 µm
deep).
The low-viscosity fluid resin contacts the
surface and is attracted to the interior of
these microporosities created by capillary
attraction.
Resin tags are formed into microporosities
of conditioned enamel that after adequate
polymerization, provide a resistant, long-
lasting bond by micromechanical interlocking
with this tissue.
10. Effects of Important Variables on
Bond Strength
Differences among Teeth
Differences in bond strength are generally
not observed among different teeth.
Likewise, no differences in bond strength
are observed between lingual and buccal
surfaces.
11. Effects of Fluoride
Teeth with a higher concentration of
fluoride are more resistant to acid etching
than normal teeth and may require an
extended etching time.
Bond strengths to a group of severely
and moderately fluorotic teeth, were
about 40 % lower than bond strengths to
normal teeth,
Group of mildly to moderately fluorotic
teeth from young adults showed similar
bond strengths when compared to
normal teeth.
12. Type and Concentration of
Acid
In restorative dentistry the highest
possible bond strength to tooth structure
is desirable.
In contrast, the orthodontic bond
strength must be sufficient to retain the
brackets but low enough to allow easy
clean-up of adhesive when the case is
completed and the brackets are
removed.
13. Factors which are affecting acid
etching of enamel include:
1. Type of the acid
2. Concentration of the acid
3. The time of etching.
Etching with 10 % or 37 % phosphoric acid
produces the highest bond strengths to
enamel.
The use of 10 % maleic acid for etching
results in a lower bond strength
No etching yields a very low bond strength.
No differences in bond strengths are
observed when enamel is etched with
phosphoric acid ranging in concentration
from 2 % to 37 %.
14. Duration of Etching
No differences in bond strength are
detected between 15-second and 60-
second etching with 37 % phosphoric
acid; however, shorter etching times
cause less enamel damage on
debonding.
Decreasing etching time between 30 and
10 seconds does not affect bond
strength(11 Mpa) or location of failure
site
Whereas etching for 0 or 5 seconds
reduces bond strength (less than 3 MPa)
15. Etching vs. Not Etching
Resin composite does not bond well to
unetched enamel
However, hybrid ionomer orthodontic
cements have bond strengths to moist,
unetched enamel ranging from 8 to 25
MPa.
Hybrid ionomer orthodontic cements
presently bond better to moist, unetched
enamel than to sandblasted metal
brackets. Once their bond strength to
metal brackets is improved, these
cements could be used in a non-acid-
16. Comparison of relative properties of cements
and adhesives used for orthodontic bonding
and banding
Cement / Adhesive Bond Strength to Bond Strength to
Enamel Metal Brackets
Resin composite High Medium – high
Hybrid ionomer Medium – high Low-medium
17. Use of Pumice with or without
Fluoride
Pumice is used to clean the enamel
surface before acid etching and
bonding.
However, bond strength appears to be
unaffected whether pumice is used or
not.
Use of a fluoridated pumice or paste
with varying fluoride concentrations
also does NOT affect bond strength or
location of bond failures.
18. Iatrogenic Effects of
Etching
1. Fracture and cracking of enamel upon
debonding.
2. Increased surface porosity - possible
staining.
3. Loss of acquired fluoride in outer 10 µm
of enamel surface.
4. Loss of enamel during etching about 10
±20 µm of enamel.
5. Resin tags retained in enamel -
possible discoloration of resin.
6. Rougher surface if over-etched.
19. Crystal-Growing Solutions
A proposed alternative to etching enamel for retention
of an adhesive is to grow crystals on the enamel
surface, this technique is called crystal bonding.
Potential advantages of crystal bonding include:
1. Easier debonding
2. Less residual adhesive left on the tooth
3. Less damage to enamel.
Crystal bonding involves application to enamel of a
poly (acrylic acid) solution containing sulfate ions,
which causes growth of calcium sulfate dihydrate
crystals on the enamel surface. These crystals in turn
retain the adhesive.
Since crystal bonding produces bond strengths of
60±80 % of the bond strength obtained with acid
etching, it is not yet considered a practical technique.
20. Acidic Primers(Self Etching
Primer)
Another alternative to etching enamel
with phosphoric acid is to use an
acidic primer of the type used to bond
restorative composites to enamel and
dentin. Although these primers are
expensive, comparable bond
strengths are found.
21. Air Abrasion
Air abrasion, also referred to as micro-
etching, is a technique in which
particles of aluminum oxide are
propelled against the surface of
enamel by high air pressure, causing
abrasion of the surface.
Bond strengths to air-abraded enamel
are only about 50 % of those to acid-
etched enamel.
Air abrasion could be an alternative to
pumicing the teeth before etching.
22. Laser Etching
The application of laser energy to an
enamel surface causes localized melting
and ablation.
Removal of enamel (etching) results
primarily from the micro-explosion of
entrapped water in the enamel and some
melting of the hydroxyapatite crystals.
Laser etching of enamel by a
neodymium-yttrium-aluminum garnet
(Nd:YAG) laser typically produces lower
bond strengths than does acid etching.
23. Moisture-Resistant Primers
An alternative to bonding to dry enamel
is to apply a moisture-resistant primer to
etched enamel that has been
contaminated with moisture or saliva.
This type of primer is a hydrophilic
methacrylate monomer that will wet
enamel contaminated with saliva or
moisture.
The bond strength of a resin composite
adhesive applied to enamel primed with
the moisture-resistant primer is similar to
that of resin composite adhesive applied
to etched, dry enamel.
24. Chlorhexidine
Chlorhexidine can be applied on the teeth
and over orthodontic appliances during
treatment to reduce bacterial colonization.
Bond strength is not affected if the
chlorhexidine is applied after bonding has
been completed or as a prophylactic paste on
enamel before etching.
Bond strength is reduced if the chlorhexidine
is applied as a layer on etched enamel or on
the sealant before the adhesive is applied.
A chlorhexidine-containing primer did not
significantly affect bond strength.
25. Bleaching
Teeth recently have significantly lower
bond strengths to resin composites.
The bleach produces oxygen, which
inhibits free radical polymerization of
resin composites.
Research has shown that orthodontic
brackets can be placed after use of
carbamide peroxide bleaching with no
adverse effect on bond strength.
26.
27. References
1. http://www.angle.org/doi/pdf/10.2319/120605-
426R.1
2. http://www.forp.usp.br/bdj/Bdj9(1)/t0191/t0191.
html
3. http://www.angle.org/doi/pdf/10.2319/120605-
426R.1
4. http://www.danielathys.com.br/downloads/enam
el_acid_etching_-_a_review.pdf
5. http://www.jaypeejournals.com/eJournals/Show
Text.aspx?ID=3128&Type=FREE&TYP=TOP&I
N=_eJournals/images/JPLOGO.gif&IID=241&is
PDF=YES
6. Orthodontic Material Scientific and Clinical
Aspects, William A. Brantley and Theodore
Eliades (2001).
