Microleakage of a resin sealant after acid-etching, Er:YAG laser irradiation and air-abrasion of pits and fissures
Maria
Cristina Borsatto, DDS, MS, PhD; Silmara Aparecida Milori Corona , DDS, MS, PhD;Regina
Guenka Palma Dibb, DDS, MS, PhD; Renata Pereira Ramos, DDS; Jesus Djalma Pécora,
DDS, MS, PhD
Abstract; Introduction; Material and Methods; Results; Discussions; Conclusions; References
Objective:
The aim of this in vitro study was to assess microleakage underneath a
filled pit-and-fissure sealant bonded to occlusal surfaces treated by four
enamel etching techniques.
Summary
Background Data: There has been no report of a study assessing microleakage
of a pit-and-fissure sealant, comparing acid-etching, Er:YAG laser and
air-abrasion for treating enamel surface.
Methods:
Forty extracted human third molars were selected and randomly assigned into four
groups of ten teeth: group I, the occlusal surfaces were acid-etched; group II,
a very short pulsed Er:YAG laser was used to treat the surfaces; group III,
aluminum oxide air-abrasion was associated with acid-etching; group IV, Er:YAG
laser was associated with acid-conditioning. The surfaces were sealed and the
teeth were stored for 7 days in distilled water. Then, specimens were
thermocycled, immersed in a 0,2% Rhodamine solution, sectioned and analyzed for
leakage using an optical microscope connected to a video camera. The images were
digitized and a software allowed microleakage assessment in millimeters.
Results:
Statistical analysis showed that occlusal surfaces exclusively treated by Er:YAG
laser (group II) provided the less satisfactory marginal sealing and that
acid-etching (group I) was statistically similar to aluminum oxide air-abrasion
+ acid etching (group III) and to Er:YAG laser + acid-etching (group IV).
Conclusions:
The results suggest that complementing either air-abrasion or Er:YAG laser
irradiation with a subsequent acid-conditioning did not lessen microleakage at
enamel-sealant interface, comparing to acid-etched group. It was also observed
that treating enamel surface exclusively by Er:YAG laser resulted in the highest
degree of leakage.
The major
concern of modern Dentistry, mainly for the last decades, has become focused on
reducing patients' risk of caries, stimulating preventive measures and
preserving tooth structure, indicating, as often as possible, non-invasive
conservative techniques instead of proceeding an invasive healing treatment.
The resin
sealants undoubtedly contribute to preserve the integrity of occlusal surface
acting as an effective mechanical obstacle to plaque retention, therefore
reducing the incidence of fissure caries. However, the preventive benefit of
this treatment rely upon the ability of the material to promote an appropriate
sealing of pits, fissures or eventual anatomic defects and remain completely
intact and bonded to enamel surface, thus preventing marginal microleakage and
the consequent progression of a carious process underneath the sealant1,2,3,4.
Most recently,
the applicability of newer methods for preparing dental substrates, such as
laser irradiation and
air-abrasion, has been greatly developed. The effect of laser irradiation on
dental enamel and dentin, especially regarding to microleakage and bonding to
tooth structure, has been a research interest during the past quarter of a
century. Several types of lasers varying a number of parameters, including pulse
mode, irradiation time, frequency and energy outputs have been used on dental
hard tissue and the most promising wavelength has been the Er:YAG at 2.94
micrometers5. A great sort of investigations5,6,7,8, 9,10,11,12
have reported the ability of Er:YAG laser to cut or ablate tooth structure,
removal of carious lesion, cavity preparation and modification of dentin and
enamel surfaces before acid-etching technique for increasing bond strength.
Likewise, air-abrasion technology has been examined for potential applications
within dentistry. This technique employs a high speed stream of purified
aluminum oxide particles delivered by air pressure and has been reported as an
effective and safe alternative for treating and/or preparing dental substrate13,14,15,16,117
with increased patient comfort by reducing pressure, heat, vibration and noise,
usually associated with rotational methods18,19,20.
The use of
these methods for cleaning and treating pits and fissures prior to sealant
application, would produce an enhanced microretentive surface structure, result
in minimal loss of sound dental tissue and may be performed with or without a
subsequent standard 37% phosphoric acid-etching treatment. Nevertheless, there
are still few studies comparing the bonding of adhesive materials to enamel
surfaces treated by these techniques9.
Considering
the importance of sealant integrity, the purpose of this in vitro study was to assess the microleakage of a filled pit-and
fissure sealant comparing four enamel etching techniques.
Forty sound human third molars, extracted within a six-month period and stored in saline solution, were selected, cleaned with a water/pumice slurry in dental prophylactic cup and carefully rinsed to remove the residual debris from pits and fissures. The apices were sealed with a light-cured composite resin and the teeth were randomly assigned into four groups of ten specimens each.
Group
I, the occlusal surfaces were etched with a 37% phosphoric acid gel (Gel Etchant,
Kerr Corporation) for 30 seconds, rinsed with air/water spray for 20 seconds and
gently air-dried.
Group II, the occlusal surfaces were treated by a very short pulsed Er:YAG laser (Fotona-Fidelis-USA) emitted at a wavelength of 2.94 mm, with density energy of 120 mJ and frequency of 4Hz under water spray coolant for 30 seconds. The diameter of the laser at the enamel surface was 1.0 mm and a flexible fiber delivery system held in a handpiece was used.
Group
III, the enamel surfaces were prepared by the handpiece of the air-abrasive
system (Kreativ Mach 4.1- New Image), with a 0,011-inch nozzle opening, using a
27,5mm aluminum oxide particles stream at 60 psi air pressure for 10 seconds.
The treatment was accomplished at a distance of approximately 2mm at a 45°
angle with the occlusal surface. Following air-abrasion, the teeth were rinsed,
dried and the occlusal surfaces were etched with a 37% phosphoric acid gel for
30 seconds, rinsed for 20 seconds and gently dried with compressed air.
Group IV, the surfaces were treated by the Er:YAG laser associated with a sequent phosphoric acid-etching for 30 seconds.
A
uniform layer of a filled resin pit-and-fissure sealant (Fluroshield, Dentsply)
was applied over treated surfaces from the central fissure upon the cusp height
in order to prevent voids, air entrapment and bubbles. The material was then
polymerized for 20 seconds using a visible light-curing unit with an output of
400 mW/cm2 (XL 3000, 3M Dental Products).
The
specimens were subjected to a thermocycling regimen of 500 cycles between 5° C
and 55° C waterbaths. Dwell time was 1 minute, with a 3-second transfer time
between baths. In preparation for dye penetration test, the specimens were dried
superficially, entirely sealed with epoxy resin and two coats of nail varnish -
excepting the occlusal surface and a 1 mm-window around the enamel/sealant
interface – and immersed in a 0,2% Rhodamine for 24 hours. Then, the epoxy
resin and nail varnish were removed with a sharp instrument and the specimens
were rinsed, dried and included in chemically activated acrylic resin. After
polymerization, the teeth were sectioned longitudinally in a buccolingual
direction with a diamond saw in the sectioning machine Minitom (Struers A/S)
providing four to five cuts of 1.0 mm thick for each tooth. The sections were
initially thinned in a polishing machine (Politriz,
Struers A/S) using sandpapers from n. 180 to 600 and then manually smoothed with
water sandpapers n. 1000 and n. 1200 to obtain a flattened surface and a final
thickness of approximately 0.25 mm.
The cuts were
identified, carefully fixed on microscopic slides and analyzed for leakage
separately, by viewing them under a x2.5 magnification optical microscope (Axioskope
- Zeiss) connected to a color video camera (TK-1270, JVC). The images obtained
were transmitted to a personal computer and after digitization they were
analyzed using the KS300-v2.0 software
(Kontron Elektronik) which allows a standardized assessment and a quantitative
measurement of microleakage in millimeters. Dye penetration was evaluated along
enamel/sealant interface for both buccal and lingual cusp heights. The
percentage of infiltration in relation to the extension of the sealant over the
fissure was also determined. The data were submitted to statistical analysis
using the Kruskal-Wallis test.
Table 1
illustrates the means of dye penetration along enamel/sealant interface for the
experimental groups.
Analyzing the
results, it was observed that group II (occlusal surface treated exclusively by
Er:YAG laser) showed statically significant difference (p<0,01) when compared
with the other groups, providing the less satisfactory marginal sealing.
Group I (acid-etching)
showed statistical similarity with group III (air-abrasion plus acid-etching)
and group IV (Er:YAG laser plus with acid-etching). However, only groups I and
III completely sealed occlusal fissures.
It
has been reported that the treatment with Er:YAG laser would create surfaces
that appear similar to acid-etched surfaces21,22. Other investigations23,24 have
shown that when bonding composite to tooth structure, the Er:YAG laser alone or
combined with acid-etching produces a surface with bonding strength equal or
better than that produce by acid-etching alone. However, Eduardo et al25
observed that composite resin shear bond strength to enamel was superior for
acid-etched group comparing to the group prepared by Er:YAG laser, once the
morphological alterations created on enamel surface by laser irradiation were
not sufficient to effectively bond composite to dental surface.
The
findings of the present study disclosed that preparing pits and fissures
exclusively by Er:YAG laser did not result in optimal penetration of sealant
into etched enamel. The laser irradiation alone was not able to produce a
high-quality, dye penetration-resistant interface and therefore the laser group
provided the highest degree of microleakage. Although the laser mechanism has
not been yet well cleared up, a suitable explanation for such performance would
be that the laser does not create, on enamel surface, the uniform
microporosities characteristics of the acid conditioning and instead promotes a
disorganized destruction of enamel prisms, possibly due to its great ability to
remove substance. Additionally, the laser alone promotes an incomplete etching
of the enamel surface resulting from the difficulty to obtain an uniform pulse
administration. The morphological observation of lased surfaces by scanning
electron microscope (SEM) reveals an irregular ablation pattern (Figure 1) and
the existence of non-conditioned areas (Figure 2). The resultant microretentions
clearly differs from acid-etching pattern and this irregular microstructure
would lead to a decreased marginal sealing. The association of acid-etching
following Er:YAG laser irradiation may ensure a complete surface conditioning
and optimize the adhesion of resin sealant to pits and fissures. A previous
investigation10, also reported non-etched areas on enamel surfaces treated by Er:YAG
laser and, analyzing the composite resin bond strength to enamel, found that
laser conditioned surfaces provided statistically inferior results to those
treated by other techniques.
However,
in this investigation, when a subsequent 37% phosphoric acid-conditioning was
accomplished, the marginal integrity of the sealant was considerably enhanced.
These observations are consistent with those of a previous study26, which stated
that a complete surface etching is only performed when the Er:YAG laser is used
in association with conventional acid-etching technique.
The
air-abrasion has been reported for tooth preparation27,28,29, and depending on
the air stream pressure and aluminum oxide particles size, creates a roughened
enamel surface30. Nevertheless, it has been demonstrated that the air-abrasive
treatment results in a irreversible removal of both organic and inorganic
components of the enamel matrix producing a smoother and less retentive surface,
likely due to the minimal etching effects of air abrasion. Conversely, the
standard acid solutions promote a selective dissolution of just the inorganic
components of the enamel matrix; the organic component remains intact, leading
to a more appropriately microretentive surface31. Several authors29,32,33,34
observed that the air abrasion technique does not eliminate the need of
acid-etching and moreover the association of treatments might increase
considerably the adhesion to dental substrate, due to the macroscopical
superficial alterations and microscopical irregularities created. Although
air-abrasion produces a roughened surface, there is not an effective penetration
of sealant into abraded enamel surface and the bonded resin material lacks the
seal obtained with acid-etching32, thus showing an unsatisfactory clinical
performance.
Supported
by these observations, in the research conducted, the air-abrasive system was
used combined with a subsequent phosphoric acid-conditioning and it was observed
that the association of these techniques provided similar satisfactory marginal
sealing to that of acid-etched group. These results were also found in previous
microleakage studies8,29
Further
investigation focusing on the long-term effect of ultrastructural changes
observed in enamel and dentin substrate treated by laser or air-abrasive system
may lead to improved microleakage prevention as well as to a more widespread
applicability of these new technologies in clinical practice.
Based
on the findings of this study, and within the limitations of an in vitro
investigation, it seems appropriate to conclude that:
1.
Complementing either air-abrasion with aluminum oxide particles or Er:YAG laser
irradiation with a subsequent phosphoric acid-conditioning did not result in
less microleakage at enamel-sealant interface, comparing to acid-etched group.
2.
When pits and fissures where exclusively treated by Er:YAG laser the highest
degree of infiltration was observed.
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