Assessment of external root temperature during root canal irradiation by Nd:YAG andEr:YAG lasersDaphne Câmara Barcellos, Cláudio Antonio Talge Carvalho, Carlos Rocha Gomes Torres, César Rogério Pucci,Claudia Roberta Santos Azuma, and Eduardo Nunes Pugliesi Citation: Journal of Laser Applications 21, 119 (2009); doi: 10.2351/1.3184428 View online: http://dx.doi.org/10.2351/1.3184428 View Table of Contents: http://scitation.aip.org/content/lia/journal/jla/21/3?ver=pdfcov Published by the Laser Institute of America Articles you may be interested in Viability of Cladosporium herbarum spores under 157nm laser and vacuum ultraviolet irradiation, lowtemperature (10K) and vacuum J. Appl. Phys. 116, 104701 (2014); 10.1063/1.4894621 Mechanism of oxidative stress generation in cells by localized near-infrared femtosecond laser excitation Appl. Phys. Lett. 95, 233702 (2009); 10.1063/1.3273373 Three-dimensional finite element thermal analysis of dental tissues irradiated with Er,Cr:YSGG laser Rev. Sci. Instrum. 79, 093910 (2008); 10.1063/1.2953526 Effects of irradiated conditions of Er:yttritium–aluminum–garnet laser on tooth vibration J. Laser Appl. 16, 128 (2004); 10.2351/1.1710887 Detection of thermal acoustic radiation from laser-heated deep tissue Appl. Phys. Lett. 81, 3918 (2002); 10.1063/1.1521245

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Assessment of external root temperature during root canal irradiationby Nd:YAG and Er:YAG lasers

Daphne Câmara BarcellosDepartment of Restorative Dentistry, São José dos Campos School of Dentistry, São Paulo State University,SP, Brazil

Cláudio Antonio Talge CarvalhoDepartment of Restorative Dentistry, Endodontics Course, São José dos Campos School of Dentistry,São Paulo State University, SP, Brazil

Carlos Rocha Gomes Torres,a� César Rogério Pucci,Claudia Roberta Santos Azuma, and Eduardo Nunes PugliesiDepartment of Restorative Dentistry, São José dos Campos School of Dentistry, São Paulo State University,SP, Brazil

�Received 14 October 2008; accepted for publication 10 April 2009; published 23 July 2009�

Different types of laser have been widely studied for applicability in the oral health area. In theendodontic area, investigations with some types of laser have been conducted to establish safeparameters for clinical application in root canals. However, it has not been duly explained whetherthe temperature increase caused by laser irradiation could cause alteration in the temperature on theexternal surface of the root and, consequently, alterations in the cells of the periodontal ligament,causing resorption and even loss of the dental element. The proposal in this paper was to gauge theexternal root temperature in the apical and cervical regions of the roots of human teeth during rootcanal irradiation with Nd:yttrium aluminum garnet �YAG� and Er:YAG lasers using differentparameters. The novel approach of this paper is the use of the technique of laser applications alongthe total length of the root canal with series of repetitive irradiation, however, using time of 1 s ofirradiation associated with 1 s off to avoid cumulative thermal effects. Experimental results confirmthe accuracy of the parameters and exposure regimen obtained. All the parameters used in this paperare acceptable from a clinical as well as a biological point of view. © 2009 Laser Institute ofAmerica.

Key words: Lasers, root canal, surface, temperature

I. Introduction

The goal of scientific and technological advancements indentistry is to facilitate the professionals’ work and providepatients with safe and efficient treatment alternatives. Theintroduction of laser has aroused the interest of the studiousas it has wide applicability in the oral health area although inreality it is used very little by the majority of dentists in theirday to day work.

In endodontic area, investigations with different types oflaser have been conducted in an endeavor to establish safeparameters for clinical application in aiding canal prepara-tion, cleaning, and disinfection. It is known that root canalirradiation causes morphologic alterations in dentin.1–3 How-ever, it has not been duly explained whether the temperatureincrease caused by this irradiation could cause any alterationin the temperature on the external surface of the root,1,4–7

which could cause alterations in the cells of the periodontalligament, causing resorption and even loss of the dental ele-

ment. Various researchers8,9 have studied the level of tem-perature increase that the adjacent periradicular tissue couldbear without suffering any type of lesion. Excessive thermaleffects on the external surface of the root could cause a con-dition of necrosis of the cement and/or periodontal ligamentand alveolar bone and consequently root resorption orankylosis.10

The literature relates that temperature increase must notbe higher than 5 °C to prevent pulp tissue destruction11 andthat 47 °C in the periodontal ligament is the temperaturethreshold for the occurrence of morphologically evident bonetissue damage.12 Gutmann et al.13 in 1987 informed that tem-perature increase in the external region of roots with a maxi-mum recording of 11 °C for 60 s did not cause apparenthistologic damage to the adjacent periodontal ligament. Thetemperature level at the threshold of 7 °C was commonlyconsidered the highest biologically acceptable temperaturelimit for avoiding periodontal damage.14

The aim of this paper was to compare Er:YAG andNd:YAG lasers and endeavor to define safe parameters fortheir use inside root canals, in a clinical situation, withoutgenerating possible thermal effects on the adjacent periodon-tal tissue, which could cause the treatment to fail. The treat-

a�Present address: Av. Eng. Francisco José Longo, 777, Jardim São Dimas,São José dos Campos 12245-000, SP, Brazil; Tel: �55 �12� 3947 9048;Electronic mail: carlosrgt@fosjc.unesp.br

JOURNAL OF LASER APPLICATIONS VOLUME 21, NUMBER 3 AUGUST 2009

1042-346X/2009/21�3�/119/5/$25.00 © 2009 Laser Institute of America119

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ment pattern used in this paper for laser application was touse series of repetitive irradiation from the apex to the cer-vical regions along the full extent of the canal, however,modifying the technique of laser irradiation using the time of1 s of irradiation associated with 1 s off to avoid cumulativethermal effects.

II. Material and method

In this paper 40 uniradicular human teeth �incisors� ofpatients between 18 and 25 years old, extracted for periodon-tal or prosthetic reasons, were used. After extraction, theteeth were immersed in distilled water and kept in a freezerat −18 °C for a period not exceeding six weeks up to thetime they were used. The crowns were sectioned with carbo-rundum disks �Dentorium, Labordental, São Paulo, SP, Bra-zil� in a high speed lathe and the root size standardized at 15mm. The roots received biomechanical preparation, with theworking length determined at 1 mm to short of the apex, byperforming the serial instrumentation technique �classical�,with Kerr type endodontic files �Maillefer/Dentsply, Bal-laigues, Sweden� up to instrument 40 K-file, alternately irri-gating the canals with 1% sodium hypochlorite. To finalizebiomechanical preparation, scaled instrumentation was per-formed with progressive anatomical withdrawal until instru-ment 80 K-file.

Later, the roots were randomly divided into four groups,according to the laser to be used and for different irradia-tions:

�a� Group 1—Ten roots were irradiated by Nd:YAG laser:wavelength of 1064 nm, mean power of 1.5 W, pulsefrequency of 15 Hz, pulse duration of 100 �s, andpulse energy of 100 mJ.

�b� Group 2—Ten roots were irradiated by Nd:YAG laser:wavelength of 1064 nm, mean power of 2.1 W, pulsefrequency of 15 Hz, pulse duration of 100 �s, andpulse energy of 140 mJ.

�c� Group 3—Ten roots were irradiated by Er:YAG laser:wavelength of 2940 nm, mean power of 1.4 W, pulsefrequency of 10 Hz, pulse duration of 100 �s, andpulse energy of 140 mJ.

�d� Group 4—Ten roots were irradiated by Er:YAG laser:wavelength of 2940 nm, mean power of 1.6 W, pulsefrequency of 10 Hz, pulse duration of 100 �s, andpulse energy of 160 mJ.

The roots were irradiated by the lasers with differentparameters. For groups 1 and 2, Nd:YAG Pulse Master 600IQ laser �American Dental Technologies, TX, USA� wasused, which emits a wavelength of 1.064 �m; and forgroups 3 and 4, Er:YAG laser model Kavo Key Laser 3�Kavo Dental GmbH, Biberach, Germany� was used, whichemits a wavelength of 2940 nm. The laser irradiation param-eters were adjusted according to Table I.

Nd:YAG and Er:YAG laser applications were performedby introducing the quartz fiber optic �320 �m� until it en-tered up to the apex of the root canal, which was floodedwith physiological solution sodium chloride �NaCl� of 0.9%�w/v�.15 Then one examiner performed the procedure of ac-

tivating the laser and rotating the fiber to make spiralmovements16 from the apex to the coronal part of the root.To make the laser application, the technique was modified:four series of repetitive irradiation were performed along thetotal length of the root canal using a 1 s of laser irradiationswitched on, with 1 s resting time �1 s ON–1 s OFF�, expo-sure regimen, totaling 9 s per series �5 s switched ON with 4s OFF�. At the end of each cycle, the fiber optic was againpositioned at the apex, and a new series of irradiation wasperformed without a time interval between the cycles, attain-ing a total irradiation time of 45 s for each specimen. The useof resting times was necessary to avoid cumulative thermaleffects.17

To verify the temperature increase in the external sur-faces of the roots, a pair of thermoelectric appliances, type Tthermocouples �Ecil Met Tec Ltda, Piedade, São Paulo, Bra-zil� were placed in the most apical and coronal regions withan application of thermal paste �Votorantim, São Paulo, SP,Brazil�. The thermoelectric appliances displayed the tem-perature readings with a precision of �0.02 °C. Throughoutthe entire irradiation and temperature gauging process, thespecimens were fixed in a device made of utility wax toavoid any interference in the temperature �Fig. 1�. The mea-surements were based on a room temperature of 24 °C. Thevalues of temperature increase were monitored continuouslythroughout the period of irradiation. On conclusion of thelaser application, the highest temperature increase value�maximum peak� in degrees Celsius was recorded.

TABLE I. Laser and irradiation parameters used for each group.

Group LaserWavelength

�nm�

Meanpower�W�

Pulsefrequency

�Hz�

Pulseduration

��s�

Pulseenergy�mJ�

1 Nd:YAG 1064 1.5 15 100 1002 Nd:YAG 1064 2.1 15 100 1403 Er:YAG 2940 1.4 10 100 1404 Er:YAG 2940 1.6 10 100 160

44..33ººCC

FIG. 1. Representative outline of the gauging of external root temperaturecanal during the irradiation.

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The maximum, minimum, and the mean temperature in-crease expressed in degrees Celsius were obtained and com-pared among the different groups.

III. Results

Figure 2 shows a box plot with reference to the tempera-ture data attained by the laser irradiations. Table II shows theresults of maximum and minimum temperature values, andmean temperature increase expresses the values in degreesCelsius obtained in the apical region for all groups. Whenanalyzing mean temperature increase values, group 2, inwhich Nd:YAG laser was used at mean power of 2.1 W,showed highest temperature increase �3.13 °C�. Group 3, inwhich the root was irradiated with Er:YAG at mean power of1.4 W, presented the lowest temperature increase �2.13 °C�.The maximum temperature obtained was 6.7 °C presented ingroup 2.

Table III shows the results of maximum and minimumtemperature values, and mean temperature increase expressesthe values in degrees Celsius obtained for all groups in thecervical region. When analyzing mean temperature increasevalues, group 2, in which Nd:YAG Laser was used at meanpower of 2.1 W, showed highest temperature increase�2.83 °C�. Group 3, in which the root was irradiated withEr:YAG at mean power of 1.4 W, presented the lowest tem-perature increase �1.90 °C�. The maximum temperature ob-tained was 4.9 °C, presented in group 2.

IV. Discussion

The laser properties that allow it to be used in the endo-dontic area include the ability of laser energy to vaporize thenecrotic pulp, enhance dentinal wall cleaning �removal of thesmear layer�, reduce or increase dentin permeability, promoteablation of dentin, and reduce the bacteria in the root canal.In this paper, the Nd: YAG and Er: YAG laser parameterschosen for cleaning and disinfecting root canals are in agree-ment with the findings in the literature. Takeda et al.,18

Takeda et al.,19 and Takeda et al.20 reported that the use oflaser irradiation at power of 1 and 2 W is effective for clean-ing and removing the smear layer throughout the extent ofthe root canal and for maintaining the dentinal canaliculiopen. Matsuoka et al.21 reported that laser irradiation at pa-rameters of 1, 2, and 3 W are effective for cleaning the apicalregion of root canals. Cecchini et al.22 stated that the use oflaser irradiation at a power of 1.2 W is effective for cleaningand disinfecting root canals.

Abed et al.23 reported that the application of output en-ergies of up to 160 mJ could be beneficial without majornegative side effects, such as burning or carbonization on theroot surface. However, according to the results of this paper,it can be noted that groups 2 and 3 had the same pulse energy�140 mJ� but in group 2 there was a result of higher tempera-ture increase in the external root �3.13 °C� due to highermean power �2.1 W�. Group 2 in which Nd:YAG laser wasused, also showed the highest temperature increase �6.7 °C�,

± Std. Dev.± Std. Err.Mean

Categorized Plot for Variable: TEMPER

TemperatureIncrease(Deg-C)

LOCAL: apical

0,5

1,5

2,5

3,5

4,5

5,5

Group 1 Group 2 Group 3 Group 4

LOCAL: cervical

Group 1 Group 2 Group 3 Group 4

FIG. 2. Box-plot with reference to the temperature data attained by the laser irradiations.

TABLE II. Results of temperature variation in the apical region of allgroups.

Group LaserPmean

�W�

Apical�°C� Mean temperature

increase�°C�Minimum Maximum

1 Nd:YAG 1.5 1.3 4.3 2.352 Nd:YAG 2.1 1.4 6.7 3.133 Er:YAG 1.4 1.7 2.8 2.134 Er:YAG 2.6 1.8 2.8 2.32

TABLE III. Results of temperature variation in the cervical region of allgroups.

Group LaserPmean

�W�

Cervical�°C� Mean temperature

increase�°C�Minimum Maximum

1 Nd:YAG 1.5 1.1 3.8 2.192 Nd:YAG 2.1 1.1 4.9 2.833 Er:YAG 1.4 1.0 3.2 1.904 Er:YAG 2.6 1.4 3.1 2.37

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very close to the temperature of 7 °C, which is commonlyconsidered the highest biologically acceptable temperaturelimit for avoiding periodontal damage.14 It can be concludedthat the external root temperature increase depends moststrongly on the mean power of the laser, contradicting thefindings of Abed et al.23

Ramsköld et al.4 in 1997 verified that Nd:YAG laserwith a mean power of 3 W, in various 15 s applicationsfollowed by 15 s intervals, was used without causing thermaldamage to the surrounding tissues; however, many repeatedirradiations are required to achieve root canal sterilization.Lan5 recorded the changes on the external surface of the rootduring Nd:YAG laser irradiation inside the canal and notedthat the rise in temperature did not exceed 10 °C when amean power of 2 W was applied. Machida et al.2 evaluatedthe thermal and microstructural alterations resulting fromroot canal preparation with laser with power of 3 W andfound it was capable of removing residues and the smearlayer from the root canal walls without exceeding the ther-mal tolerance threshold of the periapical tissues. Cecchini etal.3 showed that the removal of the smear layer was efficientthroughout the entire extent of the root canal, mainly withthe laser at mean power of 1.2 W and that the temperatureincrease varied from 2–4 °C.

In Figure 2, it can be noted that Er:YAG laser presentedlower mean temperature increase values on the external sur-face of the root than the Nd:YAG laser. Nd:YAG laser iscapable of removing tissue by photothermal effect, where thelight energy is absorbed and converted into heat, causingvaporization and burning of the tissue by heating.24 Thus, theuse of Nd: YAG laser in hard tissues of teeth requires hightemperatures to reach the melting temperature of these tis-sues, which can cause thermal damage to subjacent tissues.

Er:YAG laser has an action mechanism known as thephotomechanical effect, with most of the incident energy be-ing consumed and only a small fraction resulting in heatingof the remaining tissue, as opposed to the photothermalmechanism of Nd:YAG laser.25 The action mechanism ofEr:YAG laser can also be called the photoablation effect,which consists of microexplosion and vaporization of harddentin tissue, reducing cumulative thermal effects.24 How-ever, according to the findings of this paper, even when usingthe photomechanical effect, Er:YAG laser produces heatingof the irradiated tissue thus raising the external temperatureof the root. Bornstein26 stated that the application of laser ata wavelength in the range of 3 �m, corresponding to that ofEr:YAG laser, generates heat when applied to hard tissues,induces the breakdown of the links of the �OH-� group ofhydroxyapatite, as well as heating the layer of water on thesurface of the crystal structure of tissues.

All high-intensity lasers deliver a large amount of en-ergy. If it is allowed to remain for a long time, it interactswith the target tissue by causing extensive thermal effectsonly in this tissue. To prevent a high temperature increasefrom occurring in the periodontal ligament, it is essential forthe laser to be applied in cycles of application interspersedwith resting time. Thus, this paper modified the technique ofirradiation in the root canal with the aim of minimizing thetemperature increase in the external root and, consequently,

damage to subjacent tissues. The technique consisted of atreatment cycle of switching on to allow 1 s of laser irradia-tion and switching off to allow 1 s of rest �1 s ON–1 s OFF�.This treatment may have contributed to all the parameterspresenting a mean temperature increase in �3.04 °C and thetemperature increase at the root surface remaining below7 °C, demonstrating the level of thermal alteration duringNd:YAG and Er:YAG laser irradiation, which the subjacenttissues were physiologically capable of tolerating.12–14 Con-firming the results of this paper, Nammour et al.17 in 2004related that in endodontic treatments, the use of laser irradia-tion needs to be alternated with pauses to avoid cumulativethermal effects since the time factor contributes to tempera-ture increase and to recovery of the adjacent structures as theheat is dispersed through blood circulation.

Figure 2 also showed that a higher temperature increasewas expected in the most apical region; nevertheless, theanalysis of variance statistical test showed that no statisti-cally significant differences were found with regard the tem-perature increase between the most apical and most coronalregions. In the apical part of the roots there is only a thinlayer of dentin and cement among the root canal, periodontalligaments, and surrounding alveolar bone. Therefore, areawill be more susceptible to thermal damage. Saunders,27 in1990 studying temperature increase in the root, found thatthere was no statistically significant difference between thetemperature increases recorded in vitro and that measured invivo. However, these temperature rises being dissipated morerapidly in vivo than in vitro are capable of being caused bythe refreshing effect of microvasculation of the periodontalmembrane.28

Safe parameters for clinical application in aiding canalpreparation, cleaning, and disinfection depend most stronglyon the mean power of the laser and time of laser irradiations.The critical characteristics that determine the extent of per-iradicular tissue damage can be controlled by the clinician.The use of laser irradiation at safe mean power, alternatedwith long pauses between irradiation cycles, can avoid thecumulative thermal effects on the periradicular tissue.

V. Conclusion

The experimental results confirm the accuracy of the pa-rameters and technique obtained. This paper suggests thatNd:YAG laser irradiation with a power of 2.1 W in rootcanals presented the greatest heating of the external root sur-face, thus may contribute to causing thermal injuries to pe-riodontal tissue and must be used with greater caution. How-ever, all the parameters using in this paper are acceptablefrom a clinical as well as biological point of view.

The novel approach of this paper, use of pulse irradiationassociated with pulse off, may be necessary to avoid cumu-lative thermal effects on the adjacent periradicular tissue.Additional studies should be conducted to ascertain the tem-perature increase in the root surfaces when using Nd:YAGand Er:YAG lasers.

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