Noor.doc

J Bagh College Dentistry Vol. 27(1), March 2015 The effect of

Pedodontics, Orthodontics and Preventive Dentistry 182

The effect of ER: YAG laser on enamel resistance to caries
during orthodontic treatment: An in vitro study

Noor M.H. Garma, B.D.S., M.Sc. (1)
Esraa S. Jasim, B.D.S., M.Sc. (1)

ABSTRACT
Background: One common undesirable side effect of orthodontic treatment with fixed appliances is the
development of incipient caries lesions around brackets, particularly in patients with poor oral hygiene. Different
methods have been used to prevent demineralization; the recent effort to improve the resistance against the
demineralization is by the application of lasers.
Materials and method: Thirty human premolars extracted for orthodontic purposes were used to test the effect of two
energy level of ER-YAG laser on enamel resistance to demineralization. The brackets were bonded on the teeth and
all the labial surface excluding 2 mm area gingival to the brackets were painted with acid resistance varnish. Three
groups were generated. The first group was the control group (A) with no treatment was performed. In the second
(group B) and third (group C) groups; teeth were irradiated by ER-YAG laser of 200, 60 mj energy respectively. All the
teeth were individually subjected to acid challenge cycle for 30 days. After debonding longitudinal sections were
taken and examined under stereomicroscope. The enamel demineralization evaluation was done by taking the
average of three depths at the centre of the artificial lesion. Also the enamel surface was classified by an
experienced investigator according to acid etch pattern. Comparisons of the average depth values of the groups
were performed with ANOVA and LSD tests. The statistical significance level was set at p ≤ 0.05.
Results: The results revealed that average lesion depth was significantly deeper at the control group than the laser
groups, and it was significantly deeper in group (B) with 200 mj than in group (C) with 60 mj. Enamel surfaces showed
deeper pits and craters than in control group.
Conclusions: The decrease in artificial caries lesion depth associated with use of the two laser energy level support
the ER-YAG laser as a tool to increase enamel resistance to demineralization and white spot lesion prevention.
Key words: Demineralization, ER-YAG, laser. (J Bagh Coll Dentistry 2015; 27(1):182-188).

INTRODUCTION
One of the most difficult problems in

orthodontic treatment with fixed appliances is the
control of enamel demineralization around the
brackets. (1) Fixed orthodontic appliances
complicate the removal of food debris that results
in the accumulation of plaque. Several studies
have found an increased amount of plaque around
orthodontic appliances. (2) Plaque bacteria produce
organic acids that cause the dissolution of calcium
and phosphate ions from the enamel surface. This
dissolution can cause white spots or early carious
lesions to form in as little as 4 weeks. (3,4)
Significant increase in the prevalence and severity
of enamel demineralization after orthodontic
treatment when compared with untreated control
subjects.

The prevalence of white spot lesions in
orthodontic patients has been reported between
2% and 96 %.(5-6) Sognnaes and Stern (7) were the
first to advocate the potential of lasers to decrease
enamel solubility and increase caries resistance.
Since that study, several studies have been
conducted with different laser systems: argon,
Nd:YAG, Er:YAG, Er,Cr:YSSG, and carbon
dioxide lasers.(8-13) It is well clear that with
available technology, only erbium family lasers
(Er:YAG and Er,Cr:YSGG) are suitable for this
purpose.
(1)Lecturer. Department of Orthodontics. College of Dentistry,
University of Baghdad.

The wavelength of Er: YAG laser is highly
absorbed by water and hydroxyapatite (14) making
it suitable for both hard and soft tissue ablation.
Several factors may act together to achieve this
reduction in caries susceptibility of lased enamel.

The most likely mechanism for caries
resistance is through the creation of microspaces
within lased enamel. During demineralization,
acid solutions penetrate into the enamel and result
in release of calcium, phosphorus and fluoride
ions. In sound enamel, these ions diffuse into the
acid solutions and are released into the oral
environment. With lased enamel, the microspaces
created by laser irradiation, trap the released ions
and act as sites for mineral re-precipitation within
the enamel structure. Thus, lased enamel has an
increased affinity for calcium, phosphate and
fluoride ions. (8)

There are contradictory reports about the effect
of Er: YAG laser on decreasing enamel solubility.
Cecchini et al. (9) used an Er:YAG laser with
different parameters of irradiation and reported
that lower energies (subablative dose) decreased
enamel solubility. Hossain et al. (16) reported an
increase in the calcium to phosphorus ratio during
laser irradiation, which resulted in caries
inhibition showed improvement in crystalline
structure and had the lowest mineral dissolution
compared to control and phosphoric acid-etched
specimens. Another study showed that Er: YAG
laser treatment reduced the carbonate content and

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Pedodontics, Orthodontics and Preventive Dentistry 183

modified the organic matrix, thus providing
caries-preventive effect on enamel. (17) However,
some studies did not find any significant
difference between Er:YAG-lased and non-lased
groups with respect to the enamel
demineralization. (18,19) Apel et al. (20) observed
that Er:YAG laser was unable to achieve any
notable reduction in acid solubility of dental
enamel. Some authors concluded that the
application of sub-ablative erbium lasers solely
for preventive caries treatment does not seem to
be sensible under the conditions they studied.
(20,21) Ahrari et al. (12) found in their study that
Er:YAG laser does not reduce enamel
demineralization when exposed to acid challenge,
these conflicting findings brought up the demand
to conduct this study for more basic data about
Er:YAG laser role against enamel
demineralization.

MATERIALS AND METHODS

Thirty human premolars extracted for
orthodontic purposes were selected for this study.
In transillumination examination, the selected
teeth should have healthy enamel on the buccal
surface, without attrition, fracture, restoration,
congenital anomalies and structural defects. There
was no history of chemical substance application
such as hydrogen peroxide for these teeth.

After cleaning the teeth from blood and debris,
they were placed in thymol containing water for
inhibiting bacterial growth until their use. The
buccal enamel surfaces of the teeth were pumiced
for 10 seconds, washed for 30 seconds, and dried
for 10 seconds with a moisture-free air spray.
Before etching, a self-adhesive tape with a cut-out
window the size of the bracket base was applied
to each tooth to prevent etching and sealing of
enamel areas that would later not be covered by
the bracket. Conventional etching was performed
with 37% phosphoric acid for 15 seconds
followed by rinsing for 30 seconds and drying for
10 second.

All the teeth were bonded with Edgewise
premolar metal brackets with light cured
composite Resilience ® (Ortho technology Co.,
USA). The bracket was placed gently onto the
centre of the labial surface using a clamping
tweezers and pressed firmly into place. The
adhesive tape and the excess adhesive were
carefully removed, followed by light-curing for 3
seconds from the mesial and distal sides flash
Max 2 light cure unit (CSM dental Aps,
Denmark) at a distance of 2mm and a 45º angle to
the surface. Acid-resistant varnish was applied to
each tooth by leaving a 2-mm rim of exposed
sound enamel surrounding the bracket gingivally

and left to set overnight. The teeth were allocated
into three groups (n=10) according to the caries
prevention way :
Group A: Control group with no caries prevention

method .
Group B: Lased with 200 mj energy and 4 Hz

frequency of Er:YAG laser at a distance
of 12mm with water for 20 seconds, the
beam diameter at the focal area was 1.0
mm .

Group C: Teeth lased with 60 mj energy and 2 Hz
frequency of Er:YAG laser at a distance
of 4mm with water for 20 seconds, The
beam diameter at the focal area was 1.0
mm.

Lasing method of the teeth in group B and C
was done by using Kavo laser unit (2060) (Figure
1A). The teeth were placed in plastic jar cover
filled with heavy body dough (Figure 1B) and the
buccal surface facing the laser handpiece which
had been fixed in a special holder designed for
this purpose at the recommended distance (Figure
1C).

The laser source was fixed while the teeth
moved laterally beneath with a uniform motion.
Each tooth was placed separately in deionized
water in a 10 ml plastic jar labeled with tooth
group and number until they were subjected to the
demineralization process. Without removing the
brackets, all the teeth were challenged by
submerging in a demineralizing solution (0.075
M/L acetic acid, 1.0 m M/L calcium chloride, 2.0
M/L m potassium phosphate) at 37°C, the pH was
adjusted to 4.3 by pH meter for 17 hour and
remineralizing solution (150 m M/L potassium
chloride, 1.5 m M/L calcium nitrate 0.9m M/L
potassium phosphate) at 37°C, the pH was
adjusted to 7 for 7 hour, this procedure were
repeated for 30 days.

A 5 minute wash with distilled and deionized
water was done between the demineralizing and
remineralizing phases and at the end of the
process. Each tooth cycled separately in
individual containers and each solution was
changed periodically every day throughout the 30
days procedure. After completing the
demineralization procedure, the brackets were
removed with straight bracket removing pliers
(Orthotechnology Co., USA), then each tooth
immersed in 0.5 % methylene blue solution for 24
hours. After that, each tooth was rinsed in tap
water and air dried. (22)

Ground sections of approximately 100 µm of
thickness were made in a coronal-apical direction
right by the cusp edge so that each tooth was
sectioned longitudinally by using water-cooled
low speed saw of a hard-tissue microtome.

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Pedodontics, Orthodontics and Preventive Dentistry 184

Sections were carefully washed and placed in
labeled Petri dishes and were oriented
longitudinally on glass cover slides, and then the
sections were examined under stereomicroscope
with maximum illumination. Lesion depth was
measured by taking the average of three
representative measurements from the surface to
the depth of the lesion that were 100 µm apart in
the center of the carious lesion. One examiner
performed all the measurements. Figure 2
illustrates a lesion depth measurement.

The enamel surface was classified by an

experienced investigator, according to Ibrahim et
al (23) into:
Type I - Preferential dissolution of the prism cores

resulting in a honey-comb-like
appearance.

Type II - Preferential dissolution of the prism
peripheries creating a cobble stone-like
appearance.

Type III - A mixture of type I and type II patterns.

Type IV - Pitted enamel surfaces as well as
structures that look like unfinished
puzzles, maps or networks.

Type V - Flat, smooth surfaces.

RESULTS

The means values and standard deviation for
the groups of this study are summarized in table 1.
The results showed that the lowest mean value of
the groups of this study was for the group C
(group in which the samples was treated with 60
mJ Er:YAG laser) while the highest mean value
of the groups of this study was for the group A
(Control group).

ANOVA test was performed to identify the
presence of statistically significant differences for
all group of this study; the result showed that
there was high statistically significant difference
among these groups.

LSD test was performed to identify the
differences between each paired group. The
results showed the group A has high statistical
significant as compared with group B and group C
while the group B has high statistical significant
as compared with group C, when P value ≤ 0.05.

Table 1: The means values and standard
deviation for the groups of this study

Groups Mean(µm) S.D.
Group A 18.7 ±2.2
Group B 14.3 ±0.63
Group C 10.6 ±0.84

Histopathological study:

The histopathological examination revealed
that the lesion mass difference between the three
groups is more significant and well demarcated in
the control group. It became smaller in group B
and surrounded by remineralized enamel and it
even smaller in group C with more remineralized
enamel structure, as shown in figures 3a, 4a, 5a.

Difference in the types of enamel surface
pattern in tested groups:

Group A has 60% of type IV of enamel
surface, 20% of type III of enamel surface and
20% of type V of enamel surface while the group
B has 40% of type I of enamel surface, 20% of
type II of enamel surface, 20% of type III of
enamel surface and 20% of type V of enamel
surface while the group C has 60% of type II of
enamel surface, 20% of type III of enamel surface
and 20% of type V of enamel surface. Figures 3b,
4b, 4c and 5b, 5c illustrate the enamel surface
pattern for the three groups.

Figure 1: A, Kavo laser unit (2060)
providing ER-YAG laser. B, the teeth
were placed in plastic jar cover filled
with heavy body dough. C, the buccal

surface facing the laser handpiece
which had been fixed in a special

holder at the recommended distance

Figure 2: Magnified view of
longitudinal section of demineralized

lesion illustrate lesion depth
measurement

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Pedodontics, Orthodontics and Preventive Dentistry 185

DISCUSSION

The strongly absorbed laser energy in the
enamel is converted to heat that boils water
abruptly. The boiled water forms high-pressure
steam that leads to the ablation process when the
pressure exceeds the ultimate strength of the
tooth. During the ablation process, water
evaporates explosively with tooth particles. The
ablated materials and their successive recoil force
create craters on the surface and the irradiated
surface becomes a flaky structure with an
irregularly serrated and microfissured
morphology. (16) Some researchers suggested that
the caries protective effect of laser light has been
attributed to the heat produced during laser

irradiation which can cause changes in the
chemical and crystalline structure of the enamel.
(16,20,21,24) On the other hand, this surface
morphology of irradiated enamel may be
vulnerable to acid attack and mineral loss (27) and
may be sites of high risk for bacterial
accumulation creating favorable conditions for the
development of carious lesions. (18)

The advantage of etching with phosphoric acid
is the high level of bracket bond strength
achieved. On the other hand, the loss of mineral
crystals, essentially the acid-protecting barrier, is
inevitable (16), therefore; this research used the
laser around the bracket to test its potential to
increase acid resistance of enamel and prevention

Figure4: A, Photomicrograph of enamel treated with 200 mj Er:YAG laser shows reminerlized
enamel (RE) and underneath it a focal deminerlized lesion (arrow) X4. B, View for pereferal

dissolution of prism cores shows as a honey-comb like appearance (type I) .X 4. C, pitted enamel
prisms (arrows) with deep craters (arrows heads).X4

A B C

Figure 3: A, Photomicrograph view for surface enamel of control group, showed
dark demineralization zone extends to dentine enamel junction (arrow head). B,
longitudinal ground section shows extension of lesion (arrow) with rough pitted

enamel. X4

A B

Figure 5: A, Photomicrograph of enamel surface treated with 60 mj Er:YAG laser shows
remineralization zone as a focal translucent area .A small demineralized lesion (arrow) was

detected.X4. B, View for enamel prisms placed side by side, prism sheath shows form of
ring(arrows). As Cobbl stone form (type III). X10. C, Magnifying view for prism sheath shows thick

sides with deep craters (arrows). X20

A B B

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Pedodontics, Orthodontics and Preventive Dentistry 186

of white lesion hazards while keeping the
advantage of high shear bond strength of
conventional acid etch.

It has been reported that caries preventive
effects induced by Er:YAG laser treatment have
been shown to depend on number of factors: the
energy density of the laser, the irradiation time,
the focal distance, and the irrigation conditions.
(9,11,15,18,20,24,26,27) Both ablative and subablative
doses have been tested to try to decrease the acid
solubility of enamel. The ablation threshold of
the Er:YAG laser is also a controversial topic: it
varies between 7 and 18.6 J/cm2 in the literature.
(26,28,29)

Apel et al (18) suggested Er:YAG laser with
energy densities below the ablation threshold, this
is not to ablate or melt the surface but to change
its structure or chemical composition attempting
to increase its acid resistance. Liu et al. (24)
assessed the optimal laser energy range between
100 and 200 mJ for the laser induced caries
prevention with Er:YAG laser without water
cooling and concluded that caries prevention
might be achieved by using Er:YAG laser if the
optimal ranges of laser parameters were chosen.
Altan et al (13) preferred a subablative dose in his
study utilized 100 mJ per pulse (12.73 J/cm2) with
water spray surface cooling and obtained positive
results in accordance with the results of Hsu et al.
(30) who presented marked caries inhibition using
subablative laser parameters.

Also Cecchini et al. (9) evaluated the different
settings of Er:YAG laser on enamel acid
resistance and reported that lower energies (60-80
mJ) caused a significant reduction in enamel
solubility. The temperature increase in pulpal
tissue caused by laser irradiation with ablative
doses should be considered. From this point of
view, White and Goodish (31) determined the safe
limits for pulpal health to be 1 W and 10 Hz. By
considering the whole, we preferred a subablative
dose (60-200) mj in this study with water cooling
to simulate the clinical situation. Both wave
length energy showed that there is a marked
reduction in the depth of the artificial carious
lesion concomitants with Er: YAG laser
irradiation, and this reduction was greater in
group C (60 mj), there was a 24% reduction in
mean lesion depth in group B and 44% reduction
in group C in comparison with the control group
and these significant results are in agreement with
researches use subablative energies discussed
above yet it can't be comparatively analyzed with
them as different laser parameter were used.

Another aspect affecting the generated results
is the method for assessing demineralization in
ER:YAG laser studies making the comparison
with other researches even more difficult. While

the present study results were contradictory to that
of Ahrari et al (12) who observed a non increase of
the enamel resistance to demineralization utilizing
300 mJ of laser beam which was directed
manually at 1 mm distance.

Also Ulkur et al (32) stated that 80mJ
irradiation with 200 µs pulse duration and pulse
frequency of 2Hz was found ineffective against
enamel demineralization. Also this research
disagreed with Rodrı´guez-Vilchis et al (33) who
reported that the acid resistance of enamel due to
subablative ER: YAG laser irradiation did not
increase significantly compared to control.

In the present study, a lower depth of Caries
lesion in the acidic solution of irradiated groups
showed that enamel acid resistance was increased
under the experimental conditions employed.

However, this effect was more evident for
Group C than group B; this can be explained
through that the increased enamel resistance to
caries associated with lower energy could be
compensated by the decreased irradiation distance
since more laser effect can be achieved with less
distance. The described irradiation distances
ranged from contact mode to 17 mm working
distance, on focused and/or defocused modes.

Regarding the Er:YAG laser settings advised
for dental treatment, the laser irradiation distance
is an important parameter, for being directly
related to the laser ablation ability and surface
morphology. (28,34)

Thus, depending on the established irradiation
distance, the incident energy on dental surface
increases the ablation depth or amplifies the
irradiated site. (34) In fact, the dispersion of the
energy occurs when the active tip is far off the
substrate, causing a little amplification of the spot
size (diameter of the beam) and consequently
higher is the irradiated area, decreasing the
performance of the laser on the tissue (35). the
histopathological finding of lesion size difference
between the three groups certainly support the
mean lesion depth difference between the three
groups discussed above, while the etching
patterns were observed to vary between the
examined teeth of the same group on contrast to
the finding of Cehreli and Altay (36) who stated
that all the samples within a group were found to
be similar in the extent of surface irregularity. All
the three groups showed rough and irregular
enamel surface with craters but only the control
group enamel showed deeper pitting with type IV
dissolution, making the irradiated enamel superior
from this point of view.

Within the limitations of this study, Er: YAG
laser with subablative energy was found to be an

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Pedodontics, Orthodontics and Preventive Dentistry 187

effective factor to fight white lesion associated
with orthodontic brackets.

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الملخص
الحاص رات، وبخاص ة واحد من اآلثار الجانبیة الشائعھ الغیر المرغوب فیھا خالل المعالجة التقویمیة مع األجھزة الثابتة ھو نمو تسوس االسنان أألول ي ح ول :خلفیة

.تحسین المقاومة ضد تحلل المینا ھو استعمال اللیزروقد استخدمت أسالیب مختلفة لمنع تحلل المینا، الجھود الحدیثھ ل. في المرضى الذین یعانون من سوء صحة الفم
لی زر عل ى مقاوم ة ER-YAGاستخدمت ثالثون من ضواحك اإلنسان المقلوعة ألغراض تقویم األسنان الختبار تأثیر اثن ین م ن مس توى طاق ةال :المواد والطریقة

. مم من الجانب اللثوي للحاصرات تم طالئھ بواس طھ ط الء مق اوم للحموض ھ 2ء مساحة تم تثبیت الحاصرات على األسنان وكل السطح الشفوي باستثنا. المینا للتحلل
االس نان ;)ج(والمجموعھ الثالث ھ ) ب(في المجموعة الثانیة . ، وقد اجریت بدون عالج)أ(وكانت المجموعة األولى ھي مجموعة السیطرة . تم إنشاء ثالث مجموعات

. یوم ا 30جمیع األسنان تعرض ت بش كل ف ردي ل دورة التح دي الحمض یة لم دة . ملي جول على التوالي 60ل وطاقة ملي جو 200بطاقة ER-YAGأشعت باللیزر
ثالث ة أعم اق ف ي مرك ز التس وس تقییم تحلل المین ا ت م ع ن طری ق أخ ذ متوس ط . stereomicroscopeبعد ازالت الحاصرات أخذت مقاطع طولیة وتم فحصھا تحت

ق یم عم ق المجموع ات ت م اجرائھ ا م ع اختب ارات المقارن ات لمتوس ط . ینا تم تصنیفھ بواسطة باحث ذو خبرة وفقا لنمط الحفر الحمض یة كذالك سطح الم. االصطناعي
ANOVA وLSD . اخذ مستوى الداللة اإلحصائیة عندP ≤ 0.05.
) ب(رة من مجموعات اللیزر، وھي أعم ق بكثی ر ف ي المجموع ة أظھرت النتائج أن متوسط عمق التسوس االصطناعي كان أعمق بكثیر في مجموعة السیط :النتائج

.سطوح المینا أظھرت تخدشات وحفر أعمق مما كانت علیھ في مجموعة السیطرة, ملي جول 60) ج(ملي جول مما كانت علیھ في المجموعة 200
لی زر مم ا دع م اس تخدام اللی زر ك أداة لزی ادة ER-YAGطاق ة ال انخفاض عمق التسوس االصطناعي لالس نان الم رتبط باس تخدام اثن ین م ن مس توى :االستنتاجات

.مقاومة المینا للتحلل والوقایھ من آفة البقع البیضاء
.اللیزر, ER-YAGتحلل المینا، :الكلمات الرئیسیة