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ORIGINAL ARTICLE
Year : 2020  |  Volume : 10  |  Issue : 1  |  Page : 28-32

Evaluation of temperature rise on the external root surface during the application of laser in root canals: An in vitro study


Department of Conservative Dentistry and Endodontics, King George's Medical University, Lucknow, Uttar Pradesh, India

Date of Submission23-Jan-2019
Date of Decision19-Feb-2019
Date of Acceptance28-May-2019
Date of Web Publication27-Dec-2019

Correspondence Address:
Prof. Rakesh Kumar Yadav
Department of Conservative Dentistry and Endodontics, King George's Medical University, Lucknow, Uttar Pradesh
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/sej.sej_13_19

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  Abstract 

Background: Laser systems play an eminent role in endodontic treatment; however, some parameters should be investigated so that damage to the periodontal tissues can be prevented. Hence, in this context, the purpose of this study was to evaluate the temperature rises during the application of different power levels of neodymium-doped yttrium aluminum garnet (Nd:YAG) laser and erbium-doped yttrium aluminum garnet (Er:YAG) laser to the external root surface of permanent teeth.
Materials and Methods: Sixty mandibular single-rooted premolars were selected and prepared chemomechanically. Nd:YAG laser (Group I) activated irrigation was performed in 30 teeth and remaining 30 received Er:YAG laser (Group II) treatment at three different power levels (1, 1.5, and 2.0 Watt), applied to 10 samples from each group. Type K thermocouple wire, along with a digital calibrated thermometer, was used to measure the temperature changes on the external root surface. Data were assessed with unpaired Student's t-test and two-way ANOVA.
Results: With increasing power levels, temperature of external root surface also increased to some extent in both the groups. For apical third, at power level of 1.5 and 2 Watt, the difference in mean temperature between the two groups was found to be significant (6.30°C and 7.75°C; P = 0.005 and 9.11°C and 10.05°C; P = 0.036), whereas for middle third region, it was found that at power level of 2 Watt, the difference in mean temperature between the two groups was significant (6.69°C and 7.91°C; P = 0.007).
Conclusion: Both Nd:YAG laser and Er:YAG laser at various power levels lead to rise in temperature on the external root surface, but the temperature changes in all the tested groups remained below the critical threshold.

Keywords: Erbium-doped yttrium aluminum garnet laser, neodymium-doped yttrium aluminum garnet laser, root canal, root surface, temperature rise


How to cite this article:
Verma A, Yadav RK, Tikku AP, Chandra A, Shakya VK. Evaluation of temperature rise on the external root surface during the application of laser in root canals: An in vitro study. Saudi Endod J 2020;10:28-32

How to cite this URL:
Verma A, Yadav RK, Tikku AP, Chandra A, Shakya VK. Evaluation of temperature rise on the external root surface during the application of laser in root canals: An in vitro study. Saudi Endod J [serial online] 2020 [cited 2020 Apr 2];10:28-32. Available from: http://www.saudiendodj.com/text.asp?2020/10/1/28/274181


  Introduction Top


After the advent of ruby laser by Maimman in 1960, the use of lasers as an alternative or as an adjunct has been extensively investigated in dentistry. In endodontics, different laser systems as new alternative disinfection modalities have been investigated in detail by several researchers.[1],[2],[3],[4],[5] Owing to the various parameters such as laser wavelength, power levels, and pulse repetition rate, laser energy can concentrate and cause thermal damages that are mainly governed by photoabsorptive properties of tissue being irradiated.[6]

Among the various laser systems available in current times, the erbium-doped yttrium aluminum garnet (Er:YAG) laser and neodymium-doped yttrium aluminum garnet (Nd:YAG) laser have been used as a viable means of photothermal disinfection of root canal.[7] The wavelength of Er:YAG laser (2940 nm) is well absorbed by water and hydroxyapatite crystals, which leads to better ablation of dental hard tissues, and as far as Nd:YAG laser (1064 nm) is concerned, it is poorly absorbed by water, and moreover, the Nd:YAG when enters the biological tissue, instead of getting absorbed, it gets scattered.[8] Due to irradiation, there is increase in the tissue's volume due to steam pressure of the vaporized water from the tissue. This results in microexplosions leading to formation of microparticles of organic and inorganic tissue.[9],[10] However, both these events are governed by important factors such as wavelength, beam diameter, pulse duration, pulse repetition rate, optical properties of tissue, and energy density.[4],[5]

Better disinfection and hard tissue ablation can be achieved with increased energy levels as it has been demonstrated in various studies. Laser system is found to be effective in removing the smear layer along with NaOCl and ethylenediaminetetraacetic acid irrigation without significant additional loss of mineral content.[11] However, with the increasing energy levels, the chances of damaging adjacent periodontal tissue also increase.[12],[13]

In an attempt to keep the benefits of laser irradiation in endodontics while minimizing the potential damages to the adjacent periodontium, the purpose of this in vitro study was to evaluate the temperature changes on the root's middle and apical thirds during Nd:YAG and Er:YAG laser irradiation at various power levels. Null hypothesis-temperature rise on the external root surface by application of laser with different power levels during root canal irrigation does not have any damaging effect on periodontium.


  Materials and Methods Top


The research protocol of this study was approved by the Institutional Ethical Committee of King George's Medical University, Lucknow, Uttar Pradesh, India (Reg.#: ECR/262/Inst/UP/2013/RR-16 and Ref. Code: 96th ECMIIB Thesis/P2). Sixty mandibular single-rooted mandibular premolars, freshly extracted for orthodontic reasons, were selected. Each sample was numbered sequentially from 1 to 60, and the samples were randomly divided into two groups by biased coin method. Before the study, informed consent was obtained from the patient and their family. Until used, all the teeth were stored in 0.1% thymol at 4°C. All the teeth were checked radiographically and standardized to fulfill following characteristics: straight roots at least 11 mm long, single canal with no resorption or calcification and completely formed apex.

All the sample teeth were washed thoroughly using normal saline to remove any residual thymol. Access opening was done with endoaccess bur and endo-z bur (DENTSPLY Tusla OK) with a high-speed handpiece. A No. 15 K file (Dentsply-Maillefer, Ballaigues, Switzerland) was introduced into the canal until it appeared at the apical foramen. 1 mm was subtracted from this length and considered as working length. The root canals were shaped with ProTaper (DENTSPLY Tulsa OK, USA) Rotary Ni-Ti instruments using the crown-down method with an electric motor (X-Smart, Dentsply-Maillefer). After enlarging the coronal third with Sx file, the middle thirds were shaped with S1 and S2 files followed by final preparation with F1, F2, and F3 file till the working length. Between each instrument change, 1 ml of 3% NaOCl was used for irrigation. Final irrigation was done with 10 ml of distill water, and the canals were dried with paper points.

All the teeth were embedded in self-cure acrylic resin block with the help of mold, to form a test apparatus and fix the roots. Two holes (1 mm in diameter) were drilled in the test apparatus, one at 2 mm from the apex (apical third) and another at 5 mm from the apex (middle third). These holes were drilled to provide access to the thermocouple wire to the external root surface [Figure 1].
Figure 1: Schematic diagram of in vitro model

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Laser irradiation

Two types of laser systems were applied to the root canals Nd:YAG laser (Group I) system (FIDELIS ORIGINAL ARTICLE, Fontana, Slovenia) and Er:YAG laser (Group II) system (FIDELIS ORIGINAL ARTICLE, Fontana, Slovenia). The ten root canals for each experimental group were irradiated at 1, 1.5, and 2 Watt power of Nd:YAG and Er:YAG lasers, respectively. Before laser irradiation, each canal was filled with 1 ml of distill water. During laser irradiation, endodontic fiber optic cable of 200 mm was used in repetitive pulse mode. Each canal was continuously irradiated from apical foramen to the canal orifice in a circular motion for 20 s. Laser irradiation was performed in cycles of 5 s with 5 s recovery time. Each root canal was irradiated four times (total 20 s).

The study was performed in a temperature-controlled room, and the baseline temperature of all samples was standardized at 25°C. Digital thermometer with K-type thermocouple wire with temperature range of − 58°F–1832°F was used to measure the temperature. Temperature alterations were calculated by subtracting the highest value recorded during intracanal irradiation and the initial value of 25°C.

Operator and evaluator both were two different endodontists. The operator performed laser-activated irrigation, whereas evaluator was the one who noted down the temperature rise during laser application.

Statistical analysis

A statistical comparison between two treatment procedures at various power levels was done, and the data were summarized as in mean ± standard deviation (SD). Unpaired Student's t-test and two-way ANOVA were applied to detect significant effects of groups and power levels. P < 0.05 was considered statistically significant. SPSS version 18 software (SPSS Inc., Chicago, IL) was used for analysis.


  Results Top


The mean values along with SD of both the groups (Group I – Nd:YAG laser and Group II – Er:YAG Laser) together with their statistical comparison are presented in [Table 1] and [Figure 2].
Table 1: Comparison of temperature rise (°C) between the groups for apical and middle third region

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Figure 2: Comparison of temperature rise (°C) between the groups for apical third region (a) and temperature rise (°C) between the groups for the middle third region (b)

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On comparing the temperature rise (°C) between the groups for apical third region, it was found that at power level of 1 Watt, the difference in mean temperature rise between the two groups was not found to be significant (P = 0.250). At power level of 1.5 and 2 Watt, the difference in mean temperature rise between the two groups was found to be statistically significant, i.e., P = 0.005 and P = 0.036, respectively.

On comparing the temperature rise (°C) between the groups for middle third region, it was found that at power level of 1 and 1.5 Watt, the difference in mean temperature rise between the two groups was not significant, i.e., P = 0.087 and P = 0.152, respectively, whereas at power level of 2 Watt, the difference in mean temperature between the two groups was statistically significant (P = 0.007).

However, while comparing average temperature rise, according to unpaired t- test, the difference in mean temperature between the two groups was not found to be significant. [Table 2] and [Figure 3] show that the temperature changes seen in both the tested groups remained below the critical threshold of 11°C for 5 min or 13°C for 1 min.[12],[14]
Table 2: Comparison of average (middle and apical) temperature rise (°C) between the groups

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Figure 3: Comparison of average (middle and apical) temperature rise (°C) between the groups

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As far as intragroup comparison is concerned, whenever power level was raised, there was highly significant rise in mean temperature difference seen in both the groups [Table 3] and [Figure 4].
Table 3: Intragroup comparison of temperature rise (°C) between the various power level pairs using Tukey post hoc test

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Figure 4: Intragroup comparison of temperature rise (°C) between the various power level pairs using Tukey post hoc test

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  Discussion Top


In the field of endodontics, lasers are serving as an important tool, and over a short period, it has gained significant interest of researchers.[14] To evaluate the safety and effectiveness of laser irradiation in endodontics, various investigations have been done.[4],[12],[15] Temperature rising over the root surface beyond a particular threshold can be detrimental for surrounding periodontium. A temperature rise of 47°C for 1 min is considered to be tolerable threshold for bone.[16],[17] That means approximately 10°C increase in temperature for 1 min can be well tolerated. However, temperature rise of 11°C for 5 min or 13°C for 1 min is the critical threshold for periodontium.[16],[18]

In the present study, the temperature rise at the apical area was 4.47°C, 6.30°C, and 9.11°C at three different power levels (1, 1.5, and 2 Watt, respectively) with the use of Nd:YAG laser and 4.02°C, 7.75°C, and 10.05°C with the use of Er:YAG laser at respective power levels.

Similarly, the temperature rise at the middle third was 2.02°C, 4.49°C, and 6.69°C at three different power levels (1, 1.5, and 2 Watt, respectively) with the use of Nd:YAG laser and 2.52°C, 5.04°C, and 7.91°C with the use of Er:YAG laser at respective power levels. However, the temperature rise for all the test groups remained below the critical threshold of 11°C for 5 min and 13°C for 1 min.[16],[18]

Maximum temperature rise was observed with 2 Watt power level at the apical third, which almost approached the critical threshold. This can be explained as the apical third of root has least dentin thickness, and dentin acts as thermal insulator and helps in better transmission of heat.[12] Hence, while irradiating the apical third, proper care should be taken to avoid any irreversible thermal damage to the periodontium.

In another study, Scaini et al[19] evaluated temperature changes on the root's external surface during Er:YAG laser irradiation with different pulse repetition rates (6, 8, 10, and 15 Hz) and observed that increased pulse repetition rates resulted in more temperature rise on external root surface, regardless of the root third assessed and the highest temperature change (14.63°C) was seen with a high pulse repetition rate of 15 Hz. In our study Er:YAG laser was used at 15 Hz and 75 mJ with varying power levels, maximum temperature rise on the root surface was observed at apical third (10.05°C) which almost approached critical threshold whereas temperature rise was found to be 6.69°C at the middle third. Similarly, in a study, Lan [20] evaluated temperature elevation on the root surface during Nd:YAG laser irradiation at various energy outputs and pulse repetition rate and concluded that the temperature elevation will not exceed 10°C on the root surface if the Nd:YAG laser energy output is below 100 mJ at 20 pulses/s, 80 mJ at 25 pulses/s, and 60 mJ at 30 pulses/s, respectively, for 15 s, and in our study, the energy levels as well as the pulse repetition rates were kept below 100 mJ and 20 Hz, respectively. Similarly, Valério et al.[21] concluded that the duration of the laser pulse of Nd:YAG increased the temperature of the primary enamel but was not influenced by different pulse durations during irradiation. In a study, Khouja et al.[22] demonstrated safe use of 808 nm diode laser at 1 Watt at continuous wave mode and at 5 Watt at pulsed mode for two cycles of 30 s. Sheima'a et al.[23] did temperature elevation investigations on the external root surface during irradiation with 940 nm diode laser and found that continuous-wave mode of diode laser led to temperature rise of 6.7°C in apical portion, whereas with pulsed mode, the temperature rise was 8.5°C.

The greatest energy concentration occurred in axial direction instead of lateral dissipation because the fiber optic tip delivered energy frontally and not laterally, and this could be a possible reason for higher temperature rise at the apical third of root. Other factors such as angle of incidence and amount of energy loss can also be the possible cause of variation in temperature rise.[20]

The possible limitation of this study is that the current model does not represent clinical cases where the teeth are embedded in bony socket and temperature rise may be different.


  Conclusion Top


Both Nd:YAG laser and Er:YAG laser at various power levels lead to rise in temperature on external root surface, but the temperature changes in both the tested groups remained below the critical threshold. Hence, lasers can be a better treatment option when used within safe yet effective power levels. However, more similar studies are required for final conclusion.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

 
  References Top

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    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4]
 
 
    Tables

  [Table 1], [Table 2], [Table 3]



 

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