Root Surface Temperature Changes During Root Canal Laser Irradiation with Dual Wavelength Laser (940 and 2780 nm): A Preliminary Study

Abstract

Objective: This study aimed to evaluate the temperature changes on the root surface during root canal irradiation using 2780 nm erbium, chromium: yttrium, scandium, gallium, garnet (Er,Cr:YSGG) and 940 nm diode lasers in an alternating sequence. Materials and methods: Eighteen single-rooted human teeth were randomly divided into three groups (n = 6). Teeth were embedded in a resin block, and six thermocouples were introduced at different positions on the tooth surfaces, while immersed in a 37°C thermal bath during laser irradiation. The laser radial firing tip (RFT)2 was operated in helicoidal movements and withdrawn from the root canal in a coronal direction at a speed of 2 mm/sec. Group A was irradiated with the Er,Cr:YSGG laser (1.25 W, 25 mJ, 50 Hz, 50 μs pulse duration, 50% water, and 30% air spray); Group B was irradiated with the Er,Cr:YSGG laser (same settings) and a 940 nm diode (2 W, with 20% duty cycle), and Group C was irradiated with the Er,Cr:YSGG laser (same settings) and a 940 nm diode (2 W, 50% duty cycle). Results: The maximum temperature recorded was in the apical thirds of Groups A–C, resulting in increments of 8.35°C, 7.33°C, and 3.82°C, respectively. All measured temperatures were considerably below the critical value of 10°C. Conclusions: The alternate use of Er,Cr:YSGG and 940 nm diode lasers can be considered biologically safe to be used in endodontics.

Introduction

The main goal of a root canal treatment is the effective elimination of bacteria within the root canal system.^1
–3 Moreover, the root canal enlargement using hand and/or rotary instruments creates a smear layer, which is known to play an important role in endodontic outcomes by allowing the persistence of bacteria within dentinal tubules.^4,5 Consequently, different types of chemical irrigants have been tested to remove the smear layer and disinfect the root canal system. However, none of these irrigants is capable of completely rendering the root canal system free of smear layer and fully eliminate all bacterial load. In fact, some bacterial species such as Enterococcus faecalis were shown to be capable of penetrating up to 500 μm deep into the dentinal tubules, whereas the penetration depth of conventional chemical irrigants is known to be limited to 100–300 μm.^6
–8

Several studies demonstrate that lasers can be superior in comparison with other techniques regarding their debridement and disinfection properties.^{9

–18} However, when inappropriate laser parameters are used, they can produce high thermal increments, negatively affecting the surrounding periodontal tissues.^19–20

Thus, the primordial goal for using lasers in endodontics is to remove the smear layer and to disinfect the root canal system without exceeding a temperature rise of 10°C, above body temperature, for more than 1 min.²¹

Wide ranges of temperature analysis have been reported with regard to distinct diode lasers. Gutknecht et al. ²² evaluated the temperature rise in the periodontal surrounding tissues while using a 810 nm diode laser inside the root canal, using output powers of 0.6–1 and 1–1.5 W in continuous wave and 0.6–1 W in chopped mode with 10 msec pulse duration and 10 msec interval. Their results showed that none of the settings has increased the temperature of the surrounding tissues more than 7°C.

Hmud et al. ²³ assessed the thermal changes inside root canals and on root surfaces using 940 and 980 nm lasers with 4 W/10 Hz and 2.5 W/25 Hz, respectively, delivered by 200-μm fibers. The maximum temperature rise on root surfaces using these settings was 4°C. The authors of this study concluded that both 940 and 980 nm diode lasers could be safely used in endodontics.

Other studies evaluated the safety, bactericidal effects, and the ability for smear layer removal using erbium lasers in endodontics. George and Walsh²⁴ measured the temperature changes in teeth apical thirds while applying Er:YAG (4 W/20 Hz) and erbium, chromium: yttrium, scandium, gallium, garnet (Er,Cr:YSGG) (1.25 W/20 Hz) lasers using either conical side emitting or conventional bare fiber tips. Their results showed that, regardless of the fiber types, the temperature elevation was less than 2.3°C. Moreover, this study reported that conical fiber tips could be beneficial by minimizing the risks of thermal injury.

Franzen et al. ²⁵ evaluated the extent of the bactericidal effect of an Er,Cr:YSGG laser with a very low power setting of 0.25 W/20 Hz in the root canal, using both microbiological and scanning electron microscope (SEM) analyses. This report showed that bacterial reduction was significant up to 500 μm deep into dentin, whereas SEM images revealed the absence of smear layer, open dentinal tubules, and no detectable signs of thermal damage.

Martins et al. (2013–2014)^26,27 performed a blind randomized clinical trial by analyzing the efficacy of the Er,Cr:YSGG laser and radial firing tips (RFT)2 (140 μs, 37.5 mJ, 20 Hz) and RFT3 (140 μs, 62.5 mJ, 20 Hz) versus the use of 3% sodium hypochlorite and interim calcium hydroxide paste in necrotic teeth with chronic apical periodontitis. They concluded that for single-rooted and premolar teeth, the laser-assisted protocol could achieve predictable endodontic outcomes.

Finally, Al-Karadaghi²⁸ investigated the radicular dentin permeability and degree of smear layer elimination comparing the Er,Cr:YSGG laser (1.25 W, 50 Hz, 50 μs, 60% water, and 30% air) and a dual wavelength Er,Cr:YSGG laser (same settings) in combination with a 940 nm diode laser (2 W, chopped mode) through 270 μm RFTs. Scanning electron micrographs of dual wavelength group showed a distinctive removal of smear layer, and dye penetration was significantly higher than that of the Er,Cr:YSGG laser group. They also suggested that the use of RFTs removes the smear layer in more homogenous pattern.

Aim

The aim of this study was to detect the temperature changes on root surfaces during the use of a dual wavelength laser (940 and 2780 nm) within the same endodontic protocol to combine the deep disinfection potential of near IR radiation at 940 nm with the cavitation abilities of the Er,Cr:YSGG laser for smear layer removal.

Material and Methods

Sample selection

This study used 18 human single-rooted teeth extracted for periodontal or orthodontic reasons. The approval to use these teeth for the experiment was obtained from the ethics committee of Iraq's Ministry of Health. Absence of carious lesions, pre-existing root canal treatments, and abnormal root canal anatomy was verified radiographically. The teeth were stored in normal saline containing 0.08% thymol to prevent dehydration and bacterial colonization. Samples were divided into three groups (n = 6), namely A–C. Five teeth per group were selected for the temperature measurements and one sample from each group was used for SEM examination.

Sample preparation

All crowns were dissected at the cemento–enamel junction; patency was verified with an ISO #8 K-file. The root canals were prepared and enlarged through a reciprocating technique (Reciproc; VDW GmbH, Munich, Germany) up to an ISO #0.25/0.08, with the working length 1 mm shorter than the root length. To simulate the clinical situation during laser procedures, the samples were embedded in a two-component polyurethane cast resin (ISO-PUR K 760), having a thermal conductivity (0.6 W/m K) similar to that of bone (0.58–1.2 W/m K).²⁹

Laser parameters and protocols

The laser setup for the first group was an Er,Cr:YSGG laser (1.25 W, 25 mJ, 50 Hz, 50 μs pulse duration, 50% water, and 30% air spray) without any adjunct diode laser irradiation. The laser setup for the second group consisted of an Er,Cr:YSGG laser whose pulses were alternated with pulses of a 940 nm diode laser operating with a duty cycle of 0.2 (pulse duration to pulse period ratio = 20%). The third group used an Er,Cr:YSGG laser whose pulses were alternated with those of the 940 nm diode laser with a duty cycle of 0.5 (pulse duration to pulse period ratio = 50%).

RFTs; Biolase with 25 mm in length and 275 μm diameter (RFT2) were used. Each RFT was introduced inside the root canal, 1 mm short of working length and withdrawn in coronal direction with a speed of 2 mm/sec, performing helicoidal movements. Before each laser round, each canal was irrigated with 2 mL of distilled water at room temperature. All the parameters and protocols for the three Groups A–C are shown in Table 1. The alternating pulses emitted through the same laser tip during the laser device operation are illustrated in Fig. 1.

FIG. 1.

Schematic view of the alternating pulses of Er,Cr:YSGG and 940 nm diode lasers, emitted through one radial firing tip.

Table 1.

Laser Irradiation Parameters and Protocols Using RFT, Biolase, with 25 mm in Length and 275 μm Diameter (RFT2)

Group	Laser setting	Irradiation time
A, n = 6	(Step 1): Er,Cr:YSGG 2780 nm:	2 mm/sec
		Helicoidal movements
		Step 1: 3× irradiations
	Average power 1.25 W
	Peak power 500 W
	Energy per pulse 25 mJ
	Frequency 50 Hz
	Pulse duration 50 μs
	W/A^a 50/30
B, n = 6	(Step 1) + (Step 2): diode 940 nm:	2 mm/sec
		Helicoidal movements
	Average power 0.4 W	Step 2: 3× irradiations; (6× total)
	Peak power 2 W
	Delay^b 8 msec
	Pulse duration 4 msec
	Duty cycle 20%
C, n = 6	Step1 + Step 2 + Step 3: diode 940 nm:	2 mm/sec
		Helicoidal movements
	Average power 1 W	Step 2: 3× irradiations; (9× total)
	Peak power 2 W
	Delay 5 msec
	Pulse duration 10 msec
	Duty cycle 50%

W/A, water to air ratio.

Delay, the delay time after Er,Cr:YSGG pulse to start the diode pulse.

RFT, radial firing tip.

Temperature measurements

The temperature measurements were carried out using a digital thermometer (OM-USB-TC, OMEGA ENGINEERING, INC.) and six thermocouples (K-Type, model OMEGA 5TC-TT-36, 0.13 mm in diameter). Three thermocouples were placed on the cervical, middle, and apical thirds of the external root surface, whereas the remaining three thermocouples were placed in 0.5 mm diameter, 1 mm deep holes that were created on the root surfaces. Silicone heat conducting paste (ARCTIC, MX-2) was used to improve heat conduction from the root surface to the thermocouples. Radiographs were taken to verify the correct placement of the thermocouples (Fig. 2). The specimens were immersed in a 37°C thermal bath during laser irradiation. The temperature rises on the external tooth surfaces above the baseline temperature (37°C) were described as delta T (ΔT). The same operator performed the laser irradiation procedures.

FIG. 2.

Radiograph showing the position of all thermocouples.

Sample preparation for scanning electron microscope (pilot study)

After laser irradiation and for SEM imaging (XL 30ESEM; FEG Company), the coronal, middle, and apical thirds of one sample from each group were sectioned and examined.

Data analysis

ANOVA and post hoc Tukey tests were used to compare the groups regarding the temperature rise between the three groups as well as differences between the different areas (cervical, middle, and apical) within the same group.

Results

Temperature measurement results

The statistical results of the temperature rises and their distribution between the three groups and within the three different regions (cervical, middle, and apical) are shown in the box-plot graphs, (Fig. 3A–C). Within all groups, the mean temperature rise was highest in the apical thirds followed by the middle and cervical root thirds.

FIG. 3.

Box-plot graphs showing the results of the temperature rise in the cervical, middle, and apical regions for Groups A–C.

The mean, median, standard deviation, minimum, and maximum values of ΔT for Groups A–C in cervical, middle, and apical thirds are shown in Table 2. The mean values of ΔT in different areas (cervical, middle, and apical) within the same group were significantly different (p < 0.001; Table 3). Moreover, the mean values of ΔT between Groups A–C were also significantly different (p < 0.001; Table 4).

Table 2.

The Results of Mean, Median, Standard Deviation, Minimum, and Maximum Values of (ΔT) for Groups A–C

	ΔT_Cervical (1 mm)	ΔT_Middle (1 mm)	ΔApical (1 mm)	ΔT_Cervical (surface)	ΔT_Middle (surface)	ΔT_Apical (surface)
Group A
Mean	−1.43	0.03	0.83	−0.93	0.18	0.38
Median	−1.06	0.03	0.65	−0.46	0.10	0.09
SD	1.74	0.55	0.81	1.15	0.46	0.53
Minimum	−6.64	−1.40	−0.23	−3.58	−1.05	−0.73
Maximum	0.48	1.27	3.83	0.35	1.43	1.74
Group B
Mean	−1.50	0.85	1.79	−1.17	0.63	1.93
Median	−1.24	0.51	1.55	0.83	0.35	1.66
SD	1.68	1.07	1.56	1.45	1.07	1.70
Minimum	−5.23	−1.01	−0.48	−5.64	−1.20	−0.70
Maximum	0.85	3.84	7.34	2.00	3.93	6.72
Group C
Mean	−3.96	−0.49	1.71	−4.56	0.22	1.54
Median	−4.79	−0.51	0.90	−5.45	0.02	1.15
SD	2.26	1.26	1.95	2.42	1.21	1.49
Minimum	−7.66	−2.46	−0.32	−7.68	−1.57	−0.25
Maximum	0.18	3.74	8.36	0.16	4.22	7.47

Table 3.

Comparison Between the Mean Values of ΔT in Cervical, Middle, and Apical Thirds Within Each Group (A–C)

	Mean ΔT	SD	Significance (p)
Group A
Cervical	−0.93	1.15	All differences are significant (p < 0.001)
Middle	0.18	0.46
Apical	0.38	0.53
Group B
Cervical	−1.17	1.45	All differences are significant (p < 0.001)
Middle	0.63	1.07
Apical	1.93	1.70
Group C
Cervical	−4.56	2.42	All differences are significant (p < 0.001)
Middle	0.22	1.21
Apical	1.54	1.49

Table 4.

Comparison Between the Mean Values of Δt Between the Three Main Groups A–C

Variables	Groups	Mean	SD	Significance, p < 0.001
ΔT_Cervical (1 mm)	A	−1.43	1.74	A × B
	B	−1.50	1.68	A × C
	C	−3.96	2.26	B × C
ΔT_Middle (1 mm)	A	0.03	0.55	A × B
	B	0.85	1.07	A × C
	C	−0.49	1.26	B × C
ΔT_Apical (1 mm)	A	0.83	0.81	A × B
	B	1.79	1.56	A × C
	C	1.71	1.95	B × C
ΔT_Cervical (surface)	A	−0.93	1.15	A × B
	B	−1.17	1.45	A × C
	C	−4.56	2.42	B × C
ΔT_Middle (surface)	A	0.18	0.46	A × B
	B	0.63	1.07	A × C
	C	0.22	1.21	B × C
ΔT_Apical (surface)	A	0.38	0.53	A × B
	B	1.93	1.70	A × C
	C	1.54	1.49	B × C

In all samples, the recorded thermal changes were below the critical value of 10°C. The highest increase in temperature was measured in one specimen from Group C (8.36°C), which lasted for 10 sec. The highest temperature rises (ΔT_Max) of all Groups A–C are expressed in Table 5. A representative example for a single measurement (i.e., from Group C) is shown in Fig. 4.

FIG. 4.

Typical thermal measurement of one specimen in Group C.

Table 5.

The Highest ΔT_Max of All the Groups (Groups A–C), and Time Required for the Temperature to Start Dropping

Group	ΔT_Max (C°)	Time (seconds)
A	8.36	10
B	7.34	8
C	3.83	31

Scanning electron microscopy results

SEM micrographs were taken for each third (cervical, middle, and apical) in one specimen from each group. No cracking, fissuring, or sign of thermal side effects were observed in any of these samples.

In Group A (Er,Cr:YSGG laser), the smear layer removal and open dentinal tubules could be detected in both the cervical and middle thirds. However, in the apical third, some dentinal tubules were obliterated with smear layer, indicating insufficient debridement in this area (Fig. 5A–C).

FIG. 5.

(A–C) Scanning electron microscopy of Group A cervical, middle and apical thirds (1000×).

In Group B (Er,Cr:YSGG and diode 940 nm 2 W, 20% duty cycle), SEM images did not reveal any significant morphological alteration in comparison with Group A in the cervical and middle thirds (where the ablation pattern was nonhomogeneous) and only partial removal of smear layer could be observed. In the apical third, a heavy smear layer covered the root canal walls and only a small number of open dentinal tubules could be detected (Fig. 6A–C).

FIG. 6.

(A–C) Scanning electron microscopy of Group B cervical, middle and apical thirds (1000×).

In Group C (Er,Cr:YSGG and diode 940 nm 2 W, 50% duty cycle), a uniform smear layer removal along the three areas of the root canal wall (cervical, middle, and apical) could be detected (Fig. 7A–C). The dentinal tubules were completely uncovered and the intratubular dentin was more ablated than the peritubular dentin (Fig. 8).

FIG. 7.

(A–C) Scanning electron microscopy of Group C cervical, middle and apical thirds (1000×).

FIG. 8.

Scanning electron microscopy of Group C apical third (5000×).

Discussion

In our study, a dual wavelength protocol was used to fulfill the goal of removing the smear layer along with bacterial eradication within the root canal system.^30–31 The Er,Cr:YSGG laser, at a wavelength of 2780 nm, has been shown to be able to remove the smear layer because of the high absorption coefficients in hydroxyapatite and water molecules.^32
–34 The 940 nm diode wavelength is transmitted through the dentin and is able to penetrate deeper into the dentinal tubules, improving the disinfection properties.^35,36

We aimed to compare the temperature rise in human teeth, induced by the alternating use of the Er,Cr:YSGG laser and the 940 nm diode laser. The pattern of temperature changes is shown in Fig. 4. Each peak value corresponded to the rapid temperature rise and the passage of the optical fiber near the thermocouples. Then temperature dropped firmly as the fiber was moved away. The negative ΔT values are attributed to the water spray effect, as well as the use of irrigants, which were at room temperature of 21°C.

Although most of the temperature changes between the three groups and between different areas within the same group were significantly different (p < 0.001), the highest increase in temperature was 8.36°C for 10 sec, which is lower than the physiological limit of 10°C.²¹ Therefore, these statistical significant differences may be considered clinically irrelevant.

Our results are in accordance with a recent study that evaluated the temperature elevation on the external root surface and subsurfaces during root canal treatment using a dual wavelength laser Er,Cr:YSGG (1.25 W, 50 Hz, 50 μs, 60% water, and 30% air) and a 940 nm diode laser (2 W, pulsed mode). It was concluded that within the limits of an in vitro study, the alternative use of a dual wavelength laser can be considered safe for endodontic purposes.³⁷

With regard to the differences in temperature elevation between the different areas within the same group, the highest temperature rises were consistently measured at the apical thirds. This can be attributed to the fact that the dentin thickness in this area is thinner, which makes it the most susceptible region to display thermal damages.³⁸ In fact, previous studies reported that temperature elevation in both external root surfaces and their surrounding tissues is highly influenced by the anatomy of teeth (i.e., shape and size),³⁹ and the heat flux on the root surface is not only related to the laser power but also to the canal surface area.⁴⁰ Our results may confirm such findings.

Unlike bare fibers, which deliver the laser beam in a forward direction, the RFT fibers such as those used in this experiment have the advantage of delivering the laser beam in a radial pattern, decreasing the possibility of any thermal damage to the surrounding tissues.^24,41 The tip of the laser fiber might also lead to a higher temperature rise in the apical area, since it comes closer to the canal walls because of the tapered shape of the root canal; this supports why the fiber should be constantly moved in a helicoidal motion.^33,42

Blood circulation in an in vivo situation must be taken into consideration as it will enhance thermal conductivity of the periodontal tissues. Saunder⁴³ demonstrated that in an in vivo situation, the body's recovery from temperature elevation is faster than in an in vitro situation. Most in vitro studies measured the root surface temperature from a baseline temperature of room temperature or human body temperature.^44,45 In this study, the samples were immersed in a water bath stabilized at 37°C to simulate the in vivo situation. In fact, a drop in temperature was observed during temperature measurement between the laser radiation rounds; this observation is similar to those from previous studies.⁴⁶

In addition, the water spray during laser irradiation is an important factor in the cavitation effects promoted by the Er,Cr:YSGG laser and its effects on smear layer removal.^34,47 This was confirmed by the morphological evaluation in our study. In Group A (Er,Cr:YSGG, 1.25 W) and Group B (Er,Cr:YSGG, 1.25 W and 940 nm diode, 2 W, 20% duty cycle), the smear layer was removed. However, some areas showed inefficient cleanliness, specifically in the apical third, where the smear layer occluded the dentinal tubules. This can be explained by the fact that the root canal is constricted in the apical third, where most of the debris is produced during conventional root canal instrumentation.⁵

In Group C (Er,Cr:YSGG, 1.25 W and diode 940 nm, 2 W, 50% duty cycle), the SEM images presented a different pattern, showing uniform smear layer removal along the entire root canal wall and open dentinal tubules. The increased irradiation time (nine laser cycles) may have influenced the superior results of this group, as an effective removal of the smear layer could be noticed even at the apical third (Fig. 8).

Based on the results of this preliminary study, it can be expected that this dual wavelength laser (2780 and 940 nm) protocol can be safely tested in clinical studies, possibly offering a new contribution to endodontic treatment.

Conclusions

Based on the conditions of this study, it can be concluded that the alternate use of the Er,Cr:YSGG (1.25 W, 25 mJ, 50 Hz, W/A: 50/30) and the 940 nm diode (peak power 2 W, duty cycle 50%) lasers is safe regarding its thermal assurance. Further studies with regard to smear layer removal, root canal surface morphology, and microbiological tests are recommended.

Footnotes

Author Disclosure Statement

No competing financial interest exits.

References

Walton

, Rivera

. Cleaning and shaping. In: Principle and Practice of Endodontics. Walton

, Torabinejad

(eds.). Philadelphia, PA: W.B. Saunders Company, 2002, p. 207.

Baumgartner

. Endodontic microbiology. In: Principle and Practice of Endodontics. Walton

, Torabinejad

(eds.). Philadelphia, PA: W.B. Saunders Company, 2002; pp. 283–287.

Bansal

, Gupta

. Smear layer in endodontics. Indian J Dental Sci, 2009; 1:67–68.

Hülsmann

, Hahn

. Complications during root canal irrigation–literature review and case reports. Int Endod J, 2000; 33:186–193.

Mader

, Baumgartner

, Peters

. Scanning electron microscopic investigation of the smeared layer on root canal walls. J Endod, 1984; 10:77–83.

Love

, Jenkinson

. Invasion of dentinal tubules by oral bacteria. Oral Biol Med, 2002; 13:171–183.

Horiba

, Maekawa

, Matsumoto

, Nakamura

. A study of the distribution of endotoxin in the dentinal wall of infected root canals. J Endod, 1990; 16:331–334.

Wong

, Cheung

. Extension of bactericidal effect of sodium hypochlorite into dentinal tubules. J Endod, 2014; 40:825–829.

Moritz

, Schoop

, Goharkhay

, Jakolitsch

, Kluger

, Wernisch

. The bactericidal effect of Nd:YAG, Ho:YAG and Er:YAG laser irradiation in the root canal. Laser Med Surg, 1999; 17:161–164.

10.

Goodis

, White

, Marshal

Jr , Yee

, Fuller

, Gee

, Marshal

. Evaluation of the Nd:YAG laser in the root canal sterilization. J Dent Res, 1992; 4:556–571.

11.

Rooney

, Midda

, Leeming

. A laboratory investigation of the bactericidal effect of the Nd:YAG laser. Br Dent J, 1994; 176:61–64.

12.

Hardee

, Miserendino

, Kos

, Walia

. Evaluation of the antibacterial effects of the intra-canal Nd:YAG laser irradiation. J Endod, 1994; 20:377–380.

13.

Fegan

, Steinman

. Comparative evaluation of the antibacterial effect of intra canal Nd:YAG laser irradiation. J Endod, 1995; 21:415–417.

14.

Gutknecht

, Moritz

, Conrads

, Sievert

, Lambert

. Bactericidal effect of the Nd:YAG Laser in in-vitro root canals. J Clin Laser Med Surg, 1996; 14:77–80.

15.

Gutknecht

, Moritz

, Conrads

, Lampert

. The diode laser and its bactericidal effect in the root canal. Endodontics, 1997; 3:217–222.

16.

Gutknecht

, Moritz

, Burghardt

, Lampert

. The efficiency of root canal disinfection using a holmium-yttrium-garnet laser. J Clin Laser Med Surg, 1997; 15:75–78.

17.

Gutknecht

, Wilkert Walter

, Lampert

. Bactericidal effect of the CO2 laser in the root canal. SPIE Proc, 1998; 3248:62–167.

18.

Schoop

, Moritz

, Goharkhay

. Die Anwedung des Er:YAG lasers in der endodontic. Stomatologie, 1999; 96:23–27.

19.

Spangberg

. Instruments, materials and devices. In: Pathways of the Pulp. Cohen

, Burns

(eds.). Missouri: Mosby, 2002, p. 565.

20.

Bahcall

, Howard

, Miserendino

, Walia

. Preliminary investigation of the histological effects of laser endodontic treatment on the periradicular tissues in dogs. J Endod, 1992; 18:47–51.

21.

Ramskold

, Fong

, Stromberg

. Thermal effects and antibacterial properties of energy levels required to sterilize stained root canals with an Nd:YAG laser. J Endod, 1997; 23:96–100.

22.

Gutknecht

, Franzen

, Meister

, Vanweersch

, Mir

. Temperature evolution on human teeth root surface after diode laser assisted endodontic treatment. Lasers Med Sci, 2005; 20:99–103.

23.

Hmud

, Kahler

, Walsh

. Temperature changes accompanying near infrared diode laser endodontic treatment of wet canals. J Endod, 2010; 36:908–911.

24.

George

, Walsh

. Thermal effects from modified endodontic laser tips used in the apical third of root canals with Er:YAG and E,Cr:YSGG lasers. Photomed Laser Surg, 2010; 28:161–165.

25.

Franzen

, Esteves-Oliveira

, Meister

, Wallerang

, Vanweersch

, Lampert

. Gutknecht N. Decontamination of deep dentin by means of E,Cr:YSGG laser irradiation. Lasers Med Science, 2009; 24:75–80.

26.

Martins

, Carvalho

, Vaz

, Capelas

, Martins

, Gutknecht

. Efficacy of Er,Cr:YSGG laser with endodontical radial firing tips on the outcome of endodontic treatment: blind randomized controlled clinical trial with six-month evaluation. Photomed Laser Surg, 2012. DOI:10.1007/s10103-012-1172-6.

27.

Martins

, Carvalho

, Pina-Vaz

, Capelas

, Martins

, Gutknecht

. Outcome of Er,Cr:YSGG laser-assisted treatment of teeth with apical periodontitis: a blind randomized clinical trial. Photomed Laser Surg, 2014; 32:3–9.

28.

Al-Karadaghi

, Franzen

, Jawad

, Gutknecht

. Investigations of radicular dentin permeability and ultra-structural changes after irradiation with Er,Cr:YSGG laser and dual wavelength (2780 and 940 nm) laser. Lasers Med Sci, 2015, DOI 10.1007/s10103-015-1757-y.

29.

Jakubinek

, Samarasekera

, White

. Elephantivory: a low thermal conductivity, high strength nanocomposite. J Mater Res, 2006; 21:287–292.

30.

Aktener

, Bilkay

. Smear layer removal with different concentrations of EDTA-ethylenediamine mixtures. J Endod, 1993; 19:228–231.

31.

Beer

, Buchmair

, Wernisch

, Georgopoulos

, Moritz

. Comparison of two diode lasers on bactericidity in root canals—an in vitro study. Lasers Med Sci, 2012; 27:361–364.

32.

Varella

, Pileggi

. Obturation of root canal system treated by Cr, Er: YSGG laser irradiation. J Endod, 2007; 33:1091–1093.

33.

Silva

, Guglielmi

, Meneguzzo

, Aranha

, Bombana

, de Paula Eduardo

. Analysis of permeability and morphology of root canal dentin after Er, Cr:YSGG laser irradiation. Photomed Laser Surg, 2010; 28:103–108.

34.

De Moor

, Blanken

, Meire

, Verdaasdonk

. Laser induced explosive vapor and cavitation resulting in effective irrigation of the root canal. Part 2: evaluation of the efficacy. Lasers Surg Med, 2009; 41:520–523.

35.

Schoop

, Kluger

, Dervisbegovic

. Innovative wavelengths in endodontic treatment. Lasers Surg Med, 2006; 38:624–630.

36.

Gutknecht

, Franzen

, Schippers

, Lampert

. Bactericidal effect of a 980-nm diode laser in the root canal wall dentin of bovine teeth. J Clin Laser Med Surg, 2004; 22:9–13.

37.

Al-Karadaghi

, Gutknecht

, Jawad

, Vanweersch

, Franzen

. Evaluation of temperature elevation during root canal treatment with dual wavelength laser: 2780 nm Er,Cr:YSGG and 940 nm diode. Photomed Laser Surg, 2015; 9:460–466.

38.

Aoki

, Mizutani

, Takasaki

. Current status of clinical laser applications in periodontal therapy. Gen Dent, 2008; 56:674–689.

39.

Lipski

. Root surface temperature rises during root canal obturation in vitro by the continuous wave of condensation technique using system B heat source. Oral Surg Oral Med Oral Pathol Oral Radiol Endod, 2005; 99:505–510.

40.

Lipski

. In vitro infrared thermographic assessment of root surface temperatures generated by high temperature thermo-plasticized injectable gutta percha obturation technique. J Endo, 2006; 32:438–441.

41.

Gordon

, Atabakhsh

, Meza

, Doms

, Nissan

, Rizoiu

. The antimicrobial efficacy of the erbium, chromium:yttrium-scandium-gallium-garnet laser with radial emitting tips on root canal dentin walls infected with Enterococcus faecalis. J Am Dent Assoc, 2007; 138:992–1002.

42.

Özer

, Basaran

. Evaluation of micro leakage of root canal fillings irradiated with different output powers of erbium, chromium:yttrium-scandiumgallium- garnet laser. Aust Endod J, 2013; 39:8–14.

43.

Saunders

. In vivo findings associated with heat generation during thermo mechanical compaction of gutta percha. 2. Histological response to temperature elevation on the external surface of the root. Int Endo J, 1990; 23:268–274.

44.

Lee

, Jeng

, Lin

, Shoji

, Lan

. Thermal effect and morphological changes induced by Er:YAG laser with two kinds of fiber tips to enlarge the root canals. Photomed Laser Surg, 2004; 22:191–197.

45.

Labossière

, Pitts

, Johnson

. An investigation of the heat induced during ultrasonic post removal. J Endo, 2007; 33:1222–1226.

46.

Glockner

, Rumpler

, Ebeleseder

, Städtler

. Intra pulpal temperature during preparation with the Er: YAG laser compared to the conventional burr. J Clin Laser Med Surg, 1998; 16:153–157.

47.

Yamazaki

, Goya

, Yu

, Kimura

, Matsumoto

. Effects of erbium, chromium: YSGG laser irradiation on root canal walls: a scanning electron microscopic and thermo graphic study. J Endod, 2001; 27:9–12.