Dentinal Tubules Sealing by Means of Diode Lasers
(810 and 980nm): A Preliminary In Vitro Study
Monica Umana, DDS,1Daniel Heysselaer, DDS,1Marc Tielemans, DDS,1Philippe Compere, Ing, PhD2
Toni Zeinoun, DDS,3and Samir Nammour, DDS, PhD1
Objective: The aim of this study was to evaluate the effect on dentinal surfaces of diode lasers (810 and 980nm)
at different parameters. Materials and methods: Twenty-four caries-free human impacted wisdom teeth were
used. The crowns were sectioned transversely in order to expose the dentin. The smear layer was removed by a
1min application of ethylenediaminetetraacetic acid (EDTA). Each surface was divided into four quadrants
irradiated at a different output power setting for each kind of laser: 0.8, 1, 1.6, and 2 W (energy densities: 2547,
3184, 5092, and 6366J/cm2, irradiation speed 1mm/sec; optical fiber diameter: 200lm; continuous and non-
contact mode). Half of the samples were stained with a graphite paste. All specimens were sent for scanning
electron microscopic (SEM) analysis. Pulp temperature increases in additional 20 teeth were measured by a
thermocouple. Results: Diode laser irradiations at 0.8 and 1 W led to occlusion or narrowing of dentin tubules
without provoking fissures or cracks. The application of graphite paste increased the thermal effects in dentin.
Measurements of pulp temperature showed that irradiations at 0.8 and 1 W for a period of 10sec in continuous
mode increased pulp temperature (T £2?C). Conclusions: Diode lasers (810 and 980nm) used at 0.8 and 1 W for
10sec in continuous mode were able to seal the dentin tubules. These parameters can be considered harmless for
pulp vitality, and may be effective in the treatment of dentinal hypersensitivity.
to a stimulus that would not cause pain in a healthy
tooth under normal conditions. It is distinguished by an acute
pain of short duration from thedenuded dentin. Its etiology is
unknown,1and seems to be a consequence of the presence of
open dentin tubules on the exposed dentin surface.2Bra ¨nn-
stro ¨m’s hydrodynamic theory3states that the movement of
fluid in the dentin tubules stimulates the mechano-receptors
in or near the pulp, which is the reason that the tubules’ oc-
clusion reduces dentin permeability and, proportionally, de-
creases the degree of dentin hypersensitivity.4,5
Although many substances are available to treat dentin
hypersensitivity,6–9they have turned out to be ineffective
over the long term, and/or studies10,11have revealed con-
tradictory results. An ideal desensitizing agent should allow
occlusion of dentinal tubules without endangering the pulp,
should be relatively painless, easily applied, rapid, and
permanently effective, and should not discolor the teeth.6,7
The results from research regarding the effect of lasers on
the treatment of dentin hypersensitivity vary, and so do the
irradiation parameters, wavelengths, and application tech-
entin hypersensitivity is described as the response
niques.12In some studies, the dentin is irradiated at low
energy densities (*4J/cm)13,14with the aim of stimulating
the production of tertiary dentin by the odontoblasts. On the
contrary, several studies use higher energy densities in order
to provoke a dentinal melting and occlude dentinal tubules,
but this practice can induce significant thermal effects, if laser
parameters are inadequately controlled. Studies reported
that Nd:YAG, Er:YAG, CO2and diode lasers produce an
efficient desensitizing effect;7,15–18however, subsequent fur-
ther research seems necessary19to define the optimal irra-
diation conditions for harmlessness to pulp and tubule
The aim of our study was to evaluate the alterations in dentin
irradiated with diode laser beams (810 and 980nm) at different
parameters. We sought to establish the best laser parameter
settings to achieve a reduction in the diameter of dentin tubules
with the aim of finding a future clinical application for diode
lasers in the treatment of dentin hypersensitivity.
Materials and Methods
The approval of the local research ethics committee is not
required in our University for this kind of protocol.
1Department of Dental Sciences, Faculty of Medicine, University of Lie `ge, Quai Godfroid Kurth, Lie `ge, Belgium.
2Unit of Ultra-structural Morphology, Laboratory of Evolutive and Functional Morphology, Lie `ge, Belgium.
3Department of Dental Sciences, Faculty of Medicine, University of Lie `ge, Quai Lie `ge, Belgium.
Photomedicine and Laser Surgery
Volume 31, Number 7, 2013
ª Mary Ann Liebert, Inc.
Twenty-four caries free adult (18–25 years of age) human
impacted wisdom teeth extracted by surgery were kept in
balanced salt solution20at 4?C during 1 week. The external
surfaces were cleaned using a scaler, and, immediately, teeth
were sectioned transversely at the mid-level of the crowns at
a low speed (300rpm) using a precision sectioning 20 LC
diamond blade (Isomet?Low Speed Saw, Buehler?Ltd.,
Lake Bluff, IL) in order to totally expose the dentin. The
exposed dentinal surfaces of these discs were polished with
Soft-Lex discs 3M Espe (coarse-grit disc and medium-grit)
using a handpiece speed of 12,000rpm for 20sec. Then they
were rinsed with cool water and dried with a 5sec air blast.21
Each exposed dentinal surface was divided into four
quadrants with a 10mm long, standard grit diamond bur
(C4, 10mm long, standard grit, Crosstech Diamond Instru-
ments Ltd., Thailand) under cooling water.
The smear layer was removed by a 1min application of
18% ethylenediaminetetraacetic acid (EDTA) (Ultradent
Products, Inc, USA). Teeth were rinsed with distilled water
and immediately irradiated at different energy densities for
each kind of laser.
The first group was irradiated with the 810nm diode
(Elexxion Claros Nano, Germany), whereas we used the
980nm diode laser (Biolitec, Germany) for the second group.
The parameters used for both groups were the following:
continuous, tangential, noncontact mode (the distance between
the optical fiber and the irradiated surface was 1mm), deliv-
ered energy densities per second 2547, 3184, 5092, and 6366J/
cm2for the following output power settings: 0.8, 1, 1.6, and
2 W. The optical fiber diameter was 200lm. Irradiation speed
was 1mm/sec. Specimens were placed on a flat surface; the
optical fiber was moved by the operator tangentially (45 de-
gree angle) at *1mm/sec speed. The tangency of irradiation
and the speed were controlled and appreciated by the operator
with possible human error.
Half of the specimens of each group were stained with a
graphite paste obtained by mixing distilled water and fine
grain (particle size 25–50lm) graphite powder (Pressol,
Nuremberg, Germany) as an enhancer. Subsequently, these
samples were carefully rinsed with distilled water in order to
eliminate the residual graphite that could be easily removed
because its particle size is larger than average diameter of
Scanning electron microscopy (SEM) analysis
The specimens were dehydrated in blue silicon (with a
humidity indicator) at room temperature. At that point, they
were attached to aluminum stubs and metallized with a
layer of gold (25nm thick), using vacuum evaporation in a
metallizer (model SCD 005, Bautec, Berlin, Germany).22The
samples were analyzed by SEM (Jeol JSM 840-A, Japan) and
were observed under 1500x magnification.
Pulp temperature increase measurements
To assess temperature variations, 20 additional teeth were ir-
the other half were irradiated by a 980nm diode laser. Five
measurements – with and without graphite paste – were per-
densities per second were 2547, 3184, 5092, and 6366J/cm2.
Scanning speed was 1mm/sec. Continuous and noncontact
modes were used for 10sec.
We followed the protocol used in previous studies for the
measurements of pulp temperature increase during laser ir-
radiation.23–29The thickness of the dentin between the ex-
posed dentinal surfaces and the pulp roof was 1mm, and
this measurement was further confirmed by radiography
complemented by a millimeter grid.
The pulp chamber was filled with a thermoconductor paste
(Prosilican thermal compound: warme Leitpaste WPN 10;
Austerlitz electronic, Nuremberg 1, Germany). It was injected
by a Lentulo compactor into the cameral pulp cavity to ensure
optimal contact and maximal thermal conduction between the
sensor tip of the thermocouple probe and the roof of the
cameral pulp. The thermal conductivity of the paste amoun-
ted to 0.4 cal s-1m-1K-1. This is comparable to the ther-
mal conductivity of soft tissues (0.2 – 0.5 cal s-1m-1K-1
depending upon hydration).30
The temperature at the roof of the cameral pulp and that
of the room were compared in order to record the variations
of temperature (D T?C).
A type K thermocouple was used (Model TM – 946, 4
channels, Lutron, Taiwan), with an accuracy of 0.01?C.
One thermocouple probe was placed in close contact with
the roof of the cameral pulp. A second probe was placed
at room temperature to compare temperature changes
at the roof of the cameral pulp with changes in room
Once the base pulp temperature became stable after 30sec,
we started measuring the temperature variations. Pulp
temperature was recorded every second for 180sec after the
end of the irradiation. Five records were repeated for each
The considered temperatures (Dt) were calculated as the
difference between recorded temperatures at the roof of the
cameral pulp (Tcp) and recorded room temperatures (TRT):
Dt=Tcp - TRT.
The mean of recorded temperatures (Dt) and the standard
deviation for each irradiation condition were calculated.
lased dentin (control) treated only with ethylenediaminete-
traacetic acid (EDTA) (18%). The dentin is not covered by the
smear layer. The tubules are open. Magnification: 1500·.
Scanning electron microscopic (SEM) view of un-
2 UMANA ET AL.
Normality tests were performed using the Kolmogorov and
Smirnov (KS) test.
The nonirradiated control group presented open tubules,
absence of the smear layer, and a regular aspect, which is a
standard pattern of dentin treated with EDTA29,30(Fig. 1).
SEM analysis of the irradiated dentin surface showed
surface structural changes caused by laser irradiation.
A narrowing of the dentinal tubules was observed at
delivered output powers of 0.8–1.6 W for 810nm diode
laser (Figs. 2 and 3) and 0.8–1 W for 980nm diode laser
The dentin showed melting areas and a total occlusion of
tubules at 2 W for 810nm diode laser (Fig. 3) and at 1.6–2 W
for 980nm diode laser (Fig. 5). At 2 W, 980nm diode laser
irradiation provoked some areas of dentinal ablation and
destruction (Fig. 5).
Samples stained with graphite paste
The graphite absorbed the laser beam intensely. This ab-
sorption generated an important source of heat and in-
creased the effect of the diode beam. Therefore, the dentin
surfac2e presented areas of fusion, melting, and cracks.
At 0.8–1 W, 810nm diode laser irradiation reduced the
diameter of the dentinal tubules (Fig. 6). Higher output
powers (1.6 and 2 W) produced dentinal melting, craters,
and loss of substance (Fig. 7).
At 0.8–1 W, 980nm diode laser irradiation, the dentinal
surface appeared irregular and scaly with a total occlusion of
dentinal tubules (Fig. 8). At higher output powers (1.6 and
2 W), melted dentinal areas with loss of substances were
noticed (Fig. 9).
A znarrowing of dentinal tubules can be noted (arrows). Magnification: 1500·.
Scanning electron microscopic (SEM) views of treated dentin by diode laser (810nm) at (a) 0.8 W and (b) 1 W.
A narrowing of dentinal tubules can be noted at 1.6 W (arrow), whereas at 2 W, some tubules are completely occluded
(arrow). Magnification: 1500·.
Scanning electron microscopic (SEM) views of treated dentin by diode laser (810nm) at (a) 1.6 W and (b) 2 W.
DETINAL TUBULES SEALING BY MEANS OF DIODE LASERS3
Measurements of temperature
After 10sec of irradiation (1mm/sec; power range: 1–2
W), the means and standard deviations of temperature
increases at the roof of the cameral pulp were between
0.8–2.30?C and 0.4–1.3?C, respectively, for the irradiation
using a diode laser (980nm) with and without graphite. The
cameral pulp temperature rise ranged from 1.7?C to 3.5?C
and from 0.9?C to 2?C, respectively, for the diode laser
(810nm) irradiations with and without graphite.
Pulp temperature recordings showed that the samples ir-
radiated by 810nm diode laser at 2 W (with graphite) pre-
sented the highest values, 3.26–0.251?C (higher than the
safety level of 3 ?C for pulp injury).
Tables 1 and 2 show the mean, minimal, and maximal
values of pulp temperature increase for each group.
All samples in each group passed the normality test (KS)
with a p value>0.05.
Diode lasers provide an abundance of available wave-
lengths in the visible and infrared spectrum. Near infrared
(NIR) lasers are characterized by a high absorption in chro-
mophore found in soft tissue. For this study, we selected the
810 and 980nm wavelengths, the most commonly used
wavelengths in dentistry, especially in endodontics and
periodontics.12,31They can be modulated in continuous wave
(CW) or pulsed mode.12,31
The wavelength of a laser determines its level of absorption
and interaction with the tissue. The absorption coefficient is a
measure of the level of absorption that occurs in a specific
tissue by a specific wavelength. A high absorption coefficient
means that less energy is needed to get the same local heating
effect.12The coefficient la (cm-1) characterizes the absorption.
The absorption coefficients of diode lasers in dental tissues are
low: *0.1cm-1in dentin and 10cm-1in the pulp.32
of the dentinal tubules can be noted (arrow). At 1 W, some tubules are occluded (arrow). Magnification: 1500 and 1200·.
W, some tubules are completely occluded (arrow), whereas at 2 W, some areas with dentinal ablation can be noted (arrows).
Scanning electron microscopic (SEM) views of treated dentin by diode laser (980nm) at (a) 1.6 W and (b) 2 W. At 1.6
4 UMANA ET AL.
W and (b) 1 W, a narrowing of dentinal tubules can be noted (arrows). Magnification: 1500·.
Scanning electron microscopic (SEM) views of treated and graphite-stained dentin by diode laser (810nm). At (a) 0.8
treated and graphite-stained dentin by diode laser (810nm)
at (a) 1.6 W and (b) 2 W. Some tubules are completely oc-
cluded, whereas some areas with dentinal ablation can be
noted (narrows). Magnification: 1500·.
Scanning electron microscopic (SEM) views of
treated and graphite-stained dentin by diode laser (980nm)
at (a) 0.8 W and (b) 1 W. The tubules are completely oc-
cluded, whereas multiple areas with dentinal ablation can be
noted at 1 W (arrow). Magnification: 1500·.
Scanning electron microscopic (SEM) views of
DETINAL TUBULES SEALING BY MEANS OF DIODE LASERS5
A laser wavelength of between 800 and 980nm is poorly
absorbed in water and hydroxyapatite.12,32This low ab-
sorption in dental tissues allows propagation, scattering, or
diffused transmission of the laser radiation through the
dentin, and important thermal effects.32–34The energy ab-
sorbed by the dentin surface provokes a sufficient increase in
temperature to obtain a melting effect and reduce or close the
In our research, the chosen parameters were selected after
prior tests. According to literature, diode lasers are able to
seal dentinal tubules in a far lesser degree than other lasers
(Er; Cr: YSGG, and CO2) with negligible effects on desensi-
tization.35A previous study showed that the irradiation of
980nm diode laser in dentin at different output powers and
delivery modes produced changes that ranged from smear
layer removal to dentine fusion.36,37
Continuous wave mode was employed because it is easier
for the operator to scan the whole dentin surface in this way.
Nevertheless, pulsed mode can also be useful because it
enables the target tissue to cool between successive pulses,
but this should be the objective of future studies. We selected
the noncontact mode to protect the optical fiber from the
graphite paste. The tangentially mode (45 degree angle) was
preferred in the aim to avoid a direct pulp exposure by the
part of the beam not absorbed by dentin.
The action mechanism of the diode laser (980nm) in
dentin substrate is approximately similar to the Nd:YAG
laser (1064nm). As both systems are in the NIR portion of the
electromagnetic spectrum,38part of the energy is absorbed
by the mineral structures of dentin such as phosphate and
carbonate, disarranging the crystalline arrangement because
of thermochemical ablation and provoking melting of the
dentin tissue.39,40These transformations are more intense
when higher parameters are used.41SEM analysis was used
to verify ultrastructural changes of the irradiated dentine.
Oral tissues contain several chromophores: hemoglobin,
melanin, and other pigmented proteins and (carbonated)
hydroxyapatite. The absorption coefficients for the listed
chromophores with regard to the wavelengths used in
dental lasers is variable. Generally, pigmented tissues will
better absorb visible or NIR wavelengths, whereas un-
pigmented tissues absorb longer wavelengths. Diode lasers
are more absorbed in melanin and other pigments than in
In the present study, it was found that the diode laser
beam absorption could be highly increased in a pigmented
surface. We stained half of the samples with a graphite paste
(graphite powder and water). The application of graphite
paste enhances the effects of the diodes on the dentin surface.
It provokes an important increase of temperature to reduce or
close the dentinal tubules by a melting effect, but it can also
provoke cracks and destruction at highest energy densities.
The wavelength of 980nm was absorbed the most by
water but the 810nm had a greater absorption in melanin.
The higher absorption by dentinal water of the 980nm diode
laser may explain its lower pulp temperature increase com-
pared with the 810nm diode laser.42–44
treated and graphite-stained dentin by diode laser (980nm)
at (a) 1.6 W and (b) 2 W. The tubules are completely oc-
cluded, whereas many areas with dentinal ablation can be
noted (arrows). Magnification: 1500·.
Scanning electron microscopic (SEM) views of
Table 1. Pulp Temperature Increase Following
Different Diode Laser (980nm) Irradiation Settings
1 W 1 W – G* 1.6 W 1.6 W – G* 2 W 2 W – G*
G*, dentinal surface smeared with graphite.
Table 2. Pulp Temperature Increase Following
Different Diode Laser (810nm) Irradiation Settings
1 W –
1.6 W –
G* 2 W
2 W –
0.9000 1.7000 1.4000
1.0000 1.9000 1.7000
0.9800 1.8200 1.5330
0.0447 0.0837 0.1528
G*, dentinal surface smeared with graphite.
6UMANA ET AL.
A 2.5?C temperature threshold for the survival of the
pulp tissue was established in classical study of Zach
and Cohen.45Nowadays, an increase in temperature of
3?C is deemed to be the maximum ceiling to not produce
irreversible pulpal damage.46
On the one hand, the temperature measurements revealed
that 810 and 980nm diode laser irradiation up to 2 W cannot
be dangerous to the pulp tissues, but on the other hand, the
application of graphite produces temperature elevations,
which could exceed the safety level for irradiation by the
810nm diode laser.
This in vitro study provides an approximate assessment of
the temperature increase at the level of the pulp roof. The
degree of water content in dentin is certainly different from
in in vivo conditions. The laser beam was stopped at the
surface of the exposed dentin and the thermocouple was
placed at a 1mm distance from it. The possibility of elec-
tromagnetic interference of lasers on the thermocouple is an
inherent difficulty of this type of in vitro measurement of
Our preliminary in vitro study aimed to verify the possi-
bility of narrowing or occluding dentinal tubules by means
of diode lasers 810 and 980nm.
Nevertheless, as demonstrated by other authors,19further
clinical studies need to be conducted in order to confirm
these in vitro results before definitive conclusions can be
drawn and before use in the treatment of dentin hypersen-
Our results confirmed that 810 and 980nm diode laser
irradiation (0.8–1 W, continuous mode, irradiation speed:
1mm/sec for 10sec, laser fiber diameter: 200lm) can lead to
dentinal melting and to the narrowing of dentinal tubules.
Higher energy densities (1.6–2 W) produce an important
destruction of the dentinal surface and hence damage the
The application of a chromophore (graphite paste) en-
hances the thermal effects of the diodes on the dentin surface;
it increases the areas of fusion and destruction at high energy
densities (1.6–2 W).
Author Disclosure Statement
No competing financial interests exist.
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