Lasers in Surgery and Medicine
Innovative Wavelengths in Endodontic Treatment
Ulrich Schoop, MD, DDS,1* Wolf Kluger, MD, DDS,1 Selma Dervisbegovic,1 Kawe Goharkhay, MD, DDS,1
Johann Wernisch, TD, PhD,2 Apostolos Georgopoulos, MD, PhD,3 Wolfgang Sperr, MD, DDS, PhD,1
and Andreas Moritz, MD, DDS, PhD1
Department of Conservative Dentistry, Dental School, Medical University of Vienna, A—1090 Vienna, Wahringer Straße
Institute for Applied and Technical Physics, Technical University of Vienna, A—1040 Vienna, Wiedner Hauptstraße
University Clinic for Internal Medicine I, Department of Infectious Diseases and Chemotherapy, A-1090 Vienna,
¨ ¨rtel 18-20, Austria
were capable of complete eradication of E. faecalis to
Background and Objectives: The sanitation of the root
a signiﬁcant extent. There was no signiﬁcant relation
canal system and the adjacent dentin has always been a key
between the temperature increase and the bactericidal
requirement for successful endodontics. In recent years,
various laser systems have provided a major contribution to
Conclusions: The present study demonstrates that both
this aim, namely the Nd:YAG-, the 810 nm Diode-, the
wavelengths investigated could be suitable for the disin-
Er:YAG-, and the Er,Cr:YSGG laser. Numerous studies
fection of even the deeper layers of dentin and equal the
could prove their efﬁciency within the endodontic proce-
results achieved by established wavelengths in state-of-
dure. Recently, two new wavelengths have been introduced
the-art endodontics. Lasers Surg. Med.
to the ﬁeld of oral laser applications: The KTP laser
ß 2006 Wiley-Liss, Inc.
emitting at 532 nm and the 980 nm diode laser. The present
in vitro investigation was performed to evaluate the effects
Key words: 980 nm diode; KTP laser; bacteria; endodon-
of these laser systems focusing on their antibacterial effect
tics; root canal
in deep layers of dentin and their impact on the root canal
Study Design/Materials and Methods: Two-hundred
A crucial step within endodontic therapy is the disinfec-
slices of root dentin with a thickness of 1 mm were obtained
tion of the root canal and the three-dimensional network of
by longitudinal cuts of freshly extracted human premolars.
dentinal tubules. From the infected pulpal tissue bacteria
The samples were steam sterilized and subsequently
penetrate into the deeper layers of root dentin and pro-
inoculated with a suspension of either Escherichia coli or
pagate a periapical inﬂammation with subsequent destruc-
Enterococcus faecalis. After the incubation, the samples
tion of the adjacent connective tissues [1–3]. The sanitation
were randomly assigned to the two different laser systems
of the root canal including the most distant areas of the
tested. Each laser group consisted of two different opera-
tubular system can be regarded as a major challenge in
tional settings and a control. The dentinal samples under-
today’s endodontics and is of great importance for the
went ‘‘indirect’’ laser irradiation through the dentin from
prolonged preservation of endodontically treated teeth.
the bacteria-free side and were then subjected to a classical
The local microenvironment favors the selection of
quantitative microbiologic evaluation. To assess the
relatively few bacterial species which can survive and
temperature increase during the irradiation procedure,
proliferate being out of reach of the host’s immune
additional measurements were carried out using a thermo-
response. Even rinsing solutions applied during conven-
couple. To assess the impacts on the root canal walls, 20
tional root canal treatment only partly affect those bacteria.
additional samples underwent laser irradiation at two
The pathogenic microorganisms are able to penetrate the
different settings and were subjected to scanning electron
root dentin up to a depth of more than 1 mm, whereas
disinfecting solutions only reach a depth around 100 mm
Results: Microbiology indicated that both laser systems
were capable of signiﬁcant reductions in both test strains.
At an effective output power of 1 W, E. coli was reduced by
Wolfgang Sperr is the head of Department of Conservative
at least 3 log steps in most of the samples by the tested Dentistry.
*Correspondence to: Ulrich Schoop, MD, DDS, Department of
wavelengths, with the best results for the KTP laser
Conservative Dentistry, Dental School, Medical University of
showing complete eradication of E. coli in 75% of the ¨
Vienna, Wahringerstr. 25a, 1090 Vienna, Austria.
samples. E. faecalis, a stubborn invader of the root canal, E-mail: firstname.lastname@example.org
Accepted 23 February 2006
showed minor changes in bacterial count at 1 W. Using the
Published online in Wiley InterScience
higher setting of 1.5 W, signiﬁcant reductions of E. coli were (www.interscience.wiley.com).
again observed with both laser systems, where the lasers DOI 10.1002/lsm.20331
ß 2006 Wiley-Liss, Inc.
2 SCHOOP ET AL.
[4,5]. In addition, bacteria like Enterococcus faecalis have then cut from the upper and medium third of the dentin
adjacent to the root canal. The sample size was chosen in
the capability to form intra- and extraradicular bioﬁlms,
order to simulate the irradiation conditions of prepared root
which makes them even harder to control [6–8]. These facts
canals in complete and intact teeth. To remove the smear
are often responsible for those cases, which are therapy
layer resulting from the cutting procedure, the specimens
resistant from the beginning or end up as long-term failures
were immersed in an ultrasonic bath with ethylenediami-
after accomplished endodontic treatment.
netetraacetic acid for 4 minutes, followed by three washes
The introduction of lasers in endodontics helped to
in physiological saline solution for a period of 2 minutes
overcome the problem of the insufﬁcient penetration depth
each. The samples were stored in physiological saline
of disinfecting agents. This new method dramatically
solution at a temperature of 48C until further use.
improves the effectiveness and success rate of root canal
treatment. In general, dental lasers provide greater acces-
sibility of formerly unreachable parts of the tubular Bacterial Inoculation
network due to their better penetration into dentinal
The samples were steam sterilized (Melatronic 23,
tissues [9–11]. Scientiﬁc research was ﬁrst conducted with
Melag, Berlin, Germany) at 1348C for 10 minutes to remove
the Nd:YAG [12–15] and the diode lasers [16–19], which
all preexisting bacteria. Previous investigations  did
gained widespread acceptance in the ﬁelds of laser-assisted
not show alterations of the physical nature of the samples.
endodontics. For both wavelengths, a high disinfecting
Chemical alterations, particularly of the organic com-
capability was reported. Lasers suitable for the preparation
pounds of the dentinal tissues, cannot be excluded but
of dental hard substances like the Er:YAG and the
have to be accepted due to the necessity of a complete
Er,Cr:YSGG underwent further development resulting in
sterilization of the samples. However, this factor does not
delivery systems also usable for root canal application. The
affect the comparability of the samples. Following this step,
according investigations indicate that these laser systems
they were inoculated with 2 ml of either of the two test
exhibit satisfying bactericidal abilities thus constituting
strains, Escherichia coli (ATCC 25922) or E. faecalis (ATCC
relatively new additions to the spectrum of lasers used in
29212) on one side by means of a micropipette. The initial
inoculum was 108 CFU/ml, standardized by the same
In a comprehensive study  four different laser
dilution series which was used for the investigation of the
systems, namely the Nd:YAG-, the Diode-, the Er:YAG-,
actual samples. Incubation at 378C for 4 hours was carried
and the Er,Cr:YSGG lasers, were compared under stan-
out to allow the propagation of the bacteria into the dentinal
dardized conditions. The study came to the conclusion that
tubules, as described in a previous scanning electron
all four tested wavelengths were able to disinfect the root
microscopic evaluation .
canal dentin to a high extent and constitute valuable tools
in up-to-date endodontics.
In the meantime, new wavelengths have been estab-
Two different laser systems were applied during the
lished in dentistry. The diode wavelength of 810 nm has
been complemented by a diode device emitting at 980 nm. In
As a diode laser the ‘‘MDL 10’’ device (Vision GmbH,
addition, the KTP laser emitting at 532 nm, representing a
Goxe, Germany) was used. Emitting at a wavelength of
frequency-doubled Nd:YAG device, has been introduced
980 nm, the laser can be operated in CW mode with an
mainly for tooth-bleaching procedures. The abbreviation
output power up to 2.5 W and in pulsed mode with a
‘‘KTP’’ stands for ‘‘Kalium-Titanyl-Phosphat’’ meaning
repetition rate up to 1,000 Hz.
The second device used was a ‘‘SmartLite’’ KTP laser
The present study was performed to evaluate the
(Deka, Calenzano, Italy). It represents a frequency-doubled
bactericidal effect of these novel wavelengths and to
Nd:YAG laser and emits at a wavelength of 532 nm (visible
compare their effectiveness to the other lasers tested in
green). This laser can be operated in pulsed (up to 16 Hz) or
the study cited above . Following an identical study
CW mode at an output power up to 3 W.
design, the devices were evaluated with regard to their
Each laser was equipped with a proprietary ﬂexible
effectiveness in the deep layers of dentin simulated by
waveguide and ﬁber tip with a diameter of 400 mm and was
indirect irradiation through dentin slices. This bacteriolo-
operated in pulsed mode with a repetition rate of 15 Hz
gical evaluation was complemented by scanning electron
without any water spray or air cooling. The lasers were
microscopy and temperature measurements.
adjusted for an effective average output power of 1 W and
1.5 W measured directly on the ﬁber tip using a wattmeter
MATERIALS AND METHODS
(Field Master, Coherent, Auburn) before each irradiation
Sample Preparation cycle. This procedure ensured stable and standardized
irradiation schemes for each sample.
Human premolars were cut into 1-mm thick longitudinal
sections using a diamond-coated band saw (‘‘Trennschleif
System,’’ Exakt, Norderstedt, Germany) under continuous
water irrigation. The teeth had been freshly extracted for After incubation, the samples in both groups were
orthodontic purposes and were obviously free from carious divided into nine subgroups, consisting of 20 specimens
lesions. One hundred eighty slices measuring 2Â6 mm were each. Eight of these subgroups underwent laser irradiation;
INNOVATIVE WAVELENGTHS 3
the last group of 20 samples served as a control group for meter (TMG-1 device, manufactured by the Technical
each test strain and remained untreated. University of Vienna, Vienna, Austria). The average value
The following irradiation procedure was used with both and the standard deviation of the ﬁve measurements per
lasers: the specimens were irradiated from the side oppos- laser/setting were calculated subsequently.
ing the inoculated area in contact mode under constant
Scanning Electron Microscopy
scanning movement of the optical ﬁber at an angle of
15 degrees to the surface. The irradiated area thus showed Additional 20 samples were subdivided in four groups
a cone-shaped outline resulting in a ﬂuence of 6.7 J/cm2 for (two lasers at 1 and 1.5 W each) and prepared as described
the samples irradiated at 1 W and 10 J/cm2 for the samples above (except for the bacteriological procedure). The
irradiated at 1.5 W. One lasing cycle comprised ﬁve samples were then submitted to scanning electron micro-
irradiations of 5 seconds each, with 15 seconds intervals. scopy in order to evaluate the morphological changes
The irradiation was done by hand and always by the same induced by laser irradiation. The specimen were assessed
investigator to ensure the comparability between the using an environmental scanning electron microscope
sample groups within the actual study and the preceding (ESEM XL30, Philips, Eindhoven, The Netherlands) work-
investigation . No water or air cooling were used with ing with mild subpressure and without sputtering of the
any device. samples, thus facilitating the assessment of native samples
and the minimization of artifacts. Figures were made at
100-fold, 500-fold, and 1,000-fold magniﬁcation.
Upon irradiation, the specimens were placed into sterile
Eppendorf tubes and 100 ml of physiological saline solution RESULTS
were added. Each tube was then vortexed for 1 minute to
remove the bacteria from the dentin and the dentinal
Table 1 shows the results of the bacteriologic test
tubules. The extracted ﬂuid was diluted in log 10 steps.
regarding E. coli and E. faecalis.
Twenty microliters of each dilution were applied to culture
Samples are rated in log steps of the colony counts
plates (sheep agar plates, Bio Merieux, Marcy I’Etoile,
(CFU/ml), the laser device applied, and the speciﬁc
France) and incubated for 24 hours at 378C. The colonies
were then counted and the total number of bacteria (colony
The results of the control group of both test strains
forming units per milliliter of the extraction ﬂuid) was
showed colony counts ranging between 106 and 107 CFU/ml
assessed. The lowest detection level of bacteria was
5Â102 CFU/ml. demonstrating a decrease of 1–2 log steps through the
inoculation and incubation process.
Temperature Measurements As far as E. coli is concerned, both wavelengths succeeded
To assess the thermal impacts of the different wave- in a major reduction of the test bacterium even at the lower
lengths and their possible inﬂuence on the bactericidal setting of 1 W. At the higher power setting (1.5 W), the
effect, temperature measurements were carried out. For impact is even more considerable, yielding 3–4 log steps.
this purpose, ﬁve samples were used for each laser and Both lasers are equally effective in killing these bacteria.
power setting. The dentin slices were mounted on an even In comparison, both devices encountered greater difﬁ-
culties in eliminating the gram-positive E. faecalis. At 1 W
thermocouple using a silicon-based heat-conductive com-
pound (Dow Corning 340 Heat Sink Compound, Dow the KTP laser was capable of removing the germ to an
Corning, Midland, Michigan). During the irradiation extent of 1–4 log steps, whereas the 980 nm diode laser
procedure, which was carried out in the same way as the showed a reduction of only 1–2 log steps in the majority of
irradiation of the inoculated samples, the maximum the samples.
temperature increase (starting from a room temperature An increase in effective irradiation power to 1.5 W
of 218C) was recorded by the means of a digital thermo- strongly improved the bactericidal effect of the lasers used.
TABLE 1. Bacterial Counts of E. coli and E. faecalis: For Each Power Setting and Laser Applied the Number of
Specimens With the According Range of CFU/ml Is Indicated
E. coli CFU/ml E. faecalis CFU/ml
103 104 105 106 107 103 104 105 106 107
Control 12 8 12 8
Diode 980nm, 1 W 11 7 2 1 5 13 1
Diode 980nm, 1.5 W 15 4 1 4 2 8 6
KTP, 1 W 10 8 2 4 6 4 6
KTP, 1.5 W 15 5 10 5 4 1
4 SCHOOP ET AL.
TABLE 2. Temperature Measurements
Device 1W 1.5 W
3.8 Æ 0.48C 4.7 Æ 0.28C
980 nm diode
4.1 Æ 0.28C 5.5 Æ 0.48C
The averages and standard deviations have been calculated
from ﬁve individual measurements per laser and power
A reduction of E. faecalis below the detection level was
observed in 50% of the samples irradiated with the KTP
laser. On the other hand, the diode laser yielded a bacterial
reduction by up to 4 log steps in a considerable number of
samples. Fig. 2. Environmental scanning electron microscopic picture
of a dentin slice. 980 nm diode laser, 1.5 W. Magniﬁcation Â
Table 2 presents the results of the temperature measure-
ments. All the measurements were carried out at a room
temperature of 218C, thus they refer to an initial sample
dentinal surface, including melting, recrystallisation, and
temperature of 218C. For instance, the value 3.88C stands
the formation of micro cracks (Fig. 4).
for a temperature rise to 24.88C. While the diode laser
showed the lower temperature increases at both power
settings, the temperature rise caused by the KTP device
only slightly exceeds those values.
The persistence of bacteria in the three-dimensional
Environmental Scanning Electron Microscopy tubular network of root dentin can be regarded as the main
The diode laser irradiation at 1W seems to have little cause for the failure of an endodontic treatment [2,3]. The
impact on the sample surface. Dentinal tubules remain pathogenic ﬂora is usually constituted of approximately
open and no signs of melting can be discerned (Fig. 1). equal portions of gram-negative and gram-positive bacteria
When the irradiation power is raised to 1.5 W, ﬁrst signs [24,25], sustaining the periapical inﬂammatory process.
of melting and recrystallisation can be seen, ﬁrst of all in The removal of these bacteria and their toxins is an
the lower right corner of the picture (Fig. 2). indispensable prerequisite for a successful endodontics.
KTP laser irradiation at an output power of 1 W shows During conventional root canal treatment with chemo-
major morphological changes of the dentinal surface. The mechanical methods, infected pulp tissue, and layers of root
majority of the tubules appears to be sealed due to melting canal dentin can only be removed to a certain extent. While
and recrystallisation of the hard tissues (Fig. 3). root canal morphology limits the extent of mechanical
At an output power of 1.5 W, the KTP laser irradiation preparation, chemical irrigants are only effective in dentin
results in an almost complete transformation of the layers directly adjacent to the canal wall. As shown by
Fig. 1. Environmental scanning electron microscopic picture Fig. 3. Environmental scanning electron microscopic picture
of a dentin slice. 980 nm diode laser, 1 W. Magniﬁcation Â 1000. of a dentin slice. KTP laser, 1 W. Magniﬁcation Â 1000.
INNOVATIVE WAVELENGTHS 5
bactericidal potential of Er,Cr:YSGG laser regarding E. coli
and E. faecalis for the ﬁrst time in a controlled in vitro
study. In order to facilitate a direct comparison between the
four laser systems tested in the study, the authors decided
to operate all devices (including the Er:YAG and
Er,Cr:YSGG lasers) without any air or water cooling.
The present study was carried out to evaluate two
wavelengths recently introduced to the ﬁelds of dentistry,
namely the 980 nm diode- and the KTP lasers. To allow for a
comparison between the lasers tested in the present and the
preceding study, the same study design for the bacteriologic
tests was pursued, including identical average power
output and ﬂuence values.
Until now, little is known about the impacts of these
wavelengths on endodontics. Romanos et al. tested the
980 nm diode laser for its ability to remove periodontal
Fig. 4. Environmental scanning electron microscopic picture
pocket epithelium in vitro . The objective of another
of a dentin slice. KTP laser, 1.5 W. Magniﬁcation Â 1000.
in vitro study performed by Gutknecht et al. was to assess
the bactericidal effect of the 980 nm wavelength on bovine
teeth . Using comparatively high power settings, the
authors were able to eliminate bacteria within the bovine
Kouchi et al. , bacteria are able to invade the periluminal
dentin to a signiﬁcant extent.
dentin up to a depth of 1,000 mm, whereas the penetration
In an early in vitro study Tewﬁk et al. demonstrated the
depth of chemical disinfectants is limited to a range about
impacts of the KTP laser on root canal walls  and
130 mm . Due to this lack in penetration depth of the
described the laser to produce an increased permeability of
bactericidal agents, pathogenic bacteria survive and con-
the root canal dentin by enlarging and cracking the oriﬁces
stitute the reason for therapy resistant cases and long-term
of the dentinal tubules. Another in vitro study addressed
failures in endodontic treatment.
the use of the KTP laser as an adjunct to scaling and root
With the introduction of lasers to the ﬁelds of conserva-
planning . The authors drew the conclusion that the
tive dentistry, the endodontic procedure was enriched by a
KTP laser could be applied without endangering the dental
multitude of new treatment methods dramatically improv-
pulp or sound periodontal tissues if it is applied at
ing the chance for a successful treatment outcome. Lasers
reasonable settings. In another study, Nammour et al.
showed to be feasible and effective tools for the cleaning and
performed temperature measurements on root surfaces
disinfection of the root canal system. This holds true for the
while irradiating root canals in vitro . Though the
Nd:YAG laser which has been assessed for its application in
authors applied energy settings up to 4 W, the temperature
endodontic therapy by many authors [12–15,26,27] as well
rise on the root surface did not exceed critical values as long
as for the diode laser [16–19]. In contrast to chemical
as cooling times of 1 second were heeded. A study by
irrigants, these lasers are extremely effective in deep layers
Machida et al. focused on the inﬂuence of the KTP laser on
of dentin. An explanation for this effect was given by
the root canal surface and the extent of the temperature
Vaarkamp et al.  and Odor et al. . Their ﬁndings
increase at the root surface in vitro . Using scanning
suggest that the dentinal tubules act as light conductors
electron microscopy, the authors found out that KTP laser
propagating the laser light even to remote areas of the root
irradiation facilitated the removal of smear layer from the
root canal surface. Thermography revealed the harmless-
Another laser system proposed for endodontic therapy is
ness of the procedure in reference to the temperature rise
the Er:YAG laser, up to that time established as a device for
on the root surface.
hard tissue preparation [28–32]. The applicability of this
The highest temperature rise yielded in the present
laser for endodontic purposes has been described by Hibst
study was 5.58C. One must bear in mind that the
et al.  and Schoop et al. [21,22]. Another wavelength
measurements have been carried out on isolated dentin
mainly used for the preparation of dental hard substances
slices instead of intact human teeth. Due to the lack of heat
is the Er,Cr:YSGG laser [33,34,35] which has recently been
used for endodontic purposes as well [36,37]. conduction into a greater volume, the slices should
represent a rather ‘‘supercritical’’ sample shape compared
In a comprehensive study, Schoop et al. compared the
to complete teeth. In the examination cited above  the
bactericidal abilities of these four different laser devices in
authors utilized intact extracted human teeth and yielded a
endodontics . To facilitate a statement on the bacter-
highest temperature rise below 78C on the root surface
icidal effects in deeper layers of dentin, the authors
when using a maximum energy of 4 W. This temperature
inoculated dentin slices with two different test strains
rise was regarded to be harmless for periodontal tissues
and irradiated from the side opposing the inoculation site.
by the authors. The temperature rise produced in the
The study revealed that all tested wavelengths were able to
present study was quite lower, even though thin dentin
disinfect the dentin samples to a high extent, showing
slices have been used instead of complete teeth. It stands
the best results for the Er:YAG laser and illustrating the
6 SCHOOP ET AL.
to reason that this temperature rise should not produce any
adverse effects when the tested laser systems are applied
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INNOVATIVE WAVELENGTHS 7
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