Effect on apical intracanal dentin after laser irradiation: A microleakage and scanning electron microscopic evaluation

Shachi Goenka; Vivek Hegde

doi:10.4103/0976-2868.106664

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ORIGINAL ARTICLE

Year : 2012 | Volume : 6 | Issue : 2 | Page : 61-65

Effect on apical intracanal dentin after laser irradiation: A microleakage and scanning electron microscopic evaluation

Shachi Goenka, Vivek Hegde
Department of conservative dentistry and endodontics, Rangoonwala Dental College and Research Centre, Pune, Maharashtra, India

Date of Web Publication

31-Jan-2013

Correspondence Address:
Shachi Goenka
6 - Rukmani Nagar, Opposite Head Post Office, Shri Ram Goenka Marg, Akola, Maharashtra
India

Source of Support: None, Conflict of Interest: None

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DOI: 10.4103/0976-2868.106664

Abstract

Aim: The purpose of this in vitro study was to evaluate the effect of neodymium:Yttrium aluminum garnet (Nd:YAG) laser and diode laser irradiation on intracanal dentin surface by scanning electron microscopic (SEM) analysis, and its interference in the apical seal of filled canals. Materials and Methods: After endodontic treatment procedures, 60 single-rooted teeth were randomly assigned to four groups. In the negative control group (n = 15), no additional treatment was performed and teeth were filled with laterally condensed gutta-percha; in the Nd:YAG laser-treated group (n = 15) and in the diode laser-treated groups (n = 15), the root canals were irradiated with
Nd:YAG laser -1.5 W/Diode laser 810 nm - 2 W /Diode laser 980 nm - 2 W } using 200 micron fiber
before filling, as described for the control group. Two specimens of each group were prepared for SEM analysis to evaluate the presence and extent of morphological changes and removal of debris; the other specimens were immersed in 2% rhodamine B for 72 h at 37°C for evaluation of the linear dye leakage at the apical third. Results: Laser groups showed significantly less linear leakage as compared to the control group.

Keywords: Diode laser, neodymium:yttrium aluminum laser, scanning electron microscopic

How to cite this article:
Goenka S, Hegde V. Effect on apical intracanal dentin after laser irradiation: A microleakage and scanning electron microscopic evaluation. J Dent Lasers 2012;6:61-5

How to cite this URL:
Goenka S, Hegde V. Effect on apical intracanal dentin after laser irradiation: A microleakage and scanning electron microscopic evaluation. J Dent Lasers [serial online] 2012 [cited 2023 Jun 9];6:61-5. Available from: http://www.jdentlasers.org/text.asp?2012/6/2/61/106664

Introduction

The fundamental part in endodontic therapy is the removal of inorganic and organic debris, followed by the appropriate filling of the canal space in order to seal it off from the surrounding oral tissues. The main purpose of this last step is to achieve a complete seal that prevents bacterial leakage and a further recontamination of root canal dentin in the entire root canal system, particularly in the apical third. Apical leakage has been proven as an important reason for root canal treatment failure, and its occurrence is generally associated with deficient smear layer removal. ^[1],[2],[3]

A number of studies have demonstrated that the traditional method for root canal preparation produces a significant amount of smear layer that can adhere on the dentinal walls, obliterating the dentinal tubules. It thus reduces dentinal permeability and hinders penetration of intracanal drugs into dentin, even when chemical irrigation is used combined with mechanical instrumentation. It has been claimed that the incidence of leakage is significantly reduced in the absence of smear layer and that smear layer removal is capable of enhancing seal ability, and hence increasing resistance to bacterial penetration. ^[4]

New techniques that may result in higher success rates have recently been developed and the use of lasers in endodontics appears as an interesting adjunct to root canal treatment. Neodymium: Yttrium-aluminum-garnet (Nd:YAG) laser can be absorbed by mineral structures, like phosphates and carbonate hydroxyapatite, and disrupts crystal structures by thermochemical action. The morphological changes are characterized by melting and resolidification processes on dentin surface, which can improve the sealing ability and reduce dentinal permeability. ^[5] It has been verified that the use of Nd:YAG laser in combination with hand filing could produce clean root canals without smear layer and tissue remnants. ^[6],[7] Nd:YAG laser was found to be capable of sealing the root canal wall dentin by deposition of glass-like materials and significantly reduced dentin permeability. More recently, it was also reported that high-level lasers were capable of improving apical seal, thus preventing microorganisms from invading the periradicular tissues. ^{[8],[9],[10],[11],[12]}

Wang et al. ^[13] verified smear layer removal resulting in cleaner root canal walls by treating the dentin with NaOCl and 980-nm diode laser with 5 W. Dentin irrigated with NaOCl/ethylenediaminetetraacetic acid (EDTA) and subsequently irradiated with 980-nm diode laser has been described as presenting absent or modified smear layer, cracks, and some melted areas. ^[14],[15] These surface alterations in dentin after irradiation with 980-nm diode laser can be directly correlated with changes in apical leakage, ^[13] dentin permeability, ^[15] and adhesion of root canal sealers. ^[16] The morphological changes in dentin walls caused by 980-nm diode laser irradiation could improve the sealing ability of endodontic sealers. ^[16]

The thermal effects are among the most important points to be considered in laser root canal irradiation using diode 810 nm, as the temperature could rise to critical levels, with deleterious effects to the tissues surrounding the tooth. The temperature can rise 10°C above the body temperature for less than 1 min, without resulting in damage to periodontal tissue. ^[17],[18] Numerous effects have been reported after laser therapy by irradiation of the interior of the root canal, including removal of the smear layer and morphological changes such as opening or closing of dentinal tubules, fusion and recyrstallization of the dentin. ^[17],[19]

The purpose of this study was to evaluate the effect of different lasers' irradiation on the intracanal dentin surface by scanning electron microscopic (SEM) analysis and its interference in the apical leakage of filled root canals.

Materials and Methods

Sixty human maxillary incisors were obtained and radiographs were taken to verify the presence of any anomaly in the pulp chamber or root canal. The teeth had their crowns sectioned at the cemento-enamel junction, and root canal preparation was carried out using K-files and RC Help (Prime Dental Products Pvt Ltd, India) combined with 5.2% NaOCl. The working length of each root canal was then established 1.0 mm short of the apical foramen and apical preparation was made using 25 no. K-file, followed by Rotary Protaper (Dentsply, Maillefer, Ballaigues, Switzerland). A final flush was done using 15 ml of 17% EDTA (Desmear). After instrumentation, teeth were randomly assigned into four groups: A negative control group, i.e., Group I (n = 15), which received no treatment before root filling; Group II Nd:YAG laser-treated group (n = 15), Group III diode 810-nm laser-treated group (n = 15), and Group IV Diode 980-nm laser-treated group (n = 15), which were irradiated with laser before root filling. Five specimens of each group were prepared for SEM analysis and the other 10 were prepared for dye penetration test.

Specimen treatment

Root canals of the control group were filled with gutta-percha and AH Plus sealer (Dentsply, DeTrey, GmbH, Konstanz, Germany) using lateral condensation technique immediately after instrumentation. The endodontic sealer was mixed according to the manufacturer's instructions and placed into the canal with a master gutta-percha cone. The master cone was fitted to the working length and lateral condensation was then carried out using accessory gutta-percha cones. The excess of gutta-percha was removed with a heated plugger and the remaining filling material was vertically condensed with a cold plugger. In the laser-treated groups, the root canal walls were irradiated with Nd:YAG 1064 nm (Fotona, Fotona Fidelis III ,combination of Er:YAG and Nd:YAG laser, Slovenia), diode 810 nm (Fotona XD - 2 810nm, Slovenia), and diode 980 nm (Mickro Scientific Instruments - Sunny,India) at the following parameters:

Irradiation was executed by introducing the fiberoptic cable along the entire length of the root canal, irradiating all the dentinal walls from apical to cervical region, with helicoidal movements at a speed of 1 mm/s. This procedure was repeated four times. The specimens were kept at room temperature for 20 s between each irradiation to prevent the temperature rise from exceeding the accepted allowance. After laser irradiation, root canals were filled as described for the control group.

Scanning electron microscopic analysis

Five roots of each group were prepared for SEM analysis, in order to verify the apical surface morphology with and without laser irradiation. The teeth were split in the buccolingual direction and then examined with a scanning electron microscope. The dentin surface located 3 mm short of the apex and equidistant from lateral walls was analyzed for the presence and extension of morphological changes and removal of debris.

Dye penetration

The remaining specimens were externally coated with two layers of nail polish, except for apical 2 mm, and were immersed in 2% rhodamine B for 72 h at 37°C and 100% humidity. Thereafter, they were thoroughly rinsed in running water and cut longitudinally. For analysis of dye penetration, images of each root half were taken with a digital camera attached to a stereomicroscope under the same magnification. Linear dye penetration was measured by a single operator, blinded regarding groups, using Image J 1.41 software. Data were subjected to statistical analysis using Kolmogorov-Smirnov test for normality, and then the Student's t-test for independent variables was used at a significance level of 5%.

Results

SEM analysis of dentin surface

Root dentin irrigated with irrigants presented typical pattern with flat surface, no smear layer, and open dentinal tubules. The laser irradiation resulted in absence of smear layer and partially obliterated dentinal tubules, suggesting an initial melting process [Figure 1], [Figure 2], [Figure 3], [Figure 4].

Figure 1: Group I: Control - Dentinal surface free of smear layer and with open dentinal tubules

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Figure 2: Group II: Nd YAG - Dentin fusion and resolidification with no smear layer or debris

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Figure 3: Group III: Diode 810 nm - Melting

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Figure 4: Group IV: Diode 980 nm - Melting and fusion of dentinal tubules and decrease in tubule diameter seen

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Apical microleakage

[Table 1] shows the mean values and standard deviation of apical infiltration (mm) for each group. There was statistically significant difference (P < 0.05) for both tested factors: Irrigating solution and laser irradiation.

Table 1: Between group comparison of Linear Leakage Score (Statistical comparison)

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Student's t-test showed that the laser-treated groups presented significantly less linear dye leakage (1.0 ± 0.41 mm) than the control group (1.68 ± 0.45 mm) (P = 0.0002). SEM analysis of control group showed the surface free of smear layer and open dentinal tubules. In the laser-treated groups, an irregular and non-uniform surface with dentin fusion and resolidification without smear layer and debris was observed. Areas with some dentinal tubules overlapping the fused dentin areas could also be observed. Melting and fusion of dentinal tubules was seen. Melting and decrease in tubule diameter was seen.

Discussion

Proper seal of the apical region is an important issue in preventing leakage and possible reinfection of root canal system. In this way, the importance of smear layer elimination to improve the success rate of filled teeth has already been established. ^[1],[2] Due to laser wavelength and the flexible conductors, Nd:YAG laser can be used to stop bleeding after pulpectomy or apicoectomy to improve disinfection of root canals, ^[20],[21] and to remove smear layer and seal dentinal tubules, thus reducing dentinal permeability. ^[8],[22] In the present study, the laser-treated group showed lower values of dye penetration than the control group. The smear layer was probably fused and resolidificated together with root canal dentin after treatment with Nd:YAG laser, acting as a single substrate. This outcome is in agreement with the results reported in other studies that investigated the occurrence of melting and recrystallization of smear layer using this type of laser. ^[5] The influence of Nd:YAG laser on apical seal when used before root canal filling with different resin-based cements has also been studied. It has been found that Nd:YAG was able to reduced the marginal permeability, regardless of the type of root canal filling material used. ^[12] Goya et al. ^[8] demonstrated by SEM that Nd:YAG laser irradiation combined with black ink increases the removal of smear layer and reduces apical leakage following filling significantly. After the laser treatment, the smear layer was melted or had evaporated and leakage was observed in 20% of the specimens.

Park et al. ^[10] investigated the effect of Nd:YAG laser irradiation on apical leakage of filled root canals using an electrochemical method. The electrical resistance between standard and experimental electrodes in the canals was measured over a period of 10 days. This method could provide quantitative measurements of apical leakage and the opportunity to study leakage over a continuous time period. Although irradiated specimens showed less leakage than the control specimens, as found in our study, increasing apical leakage over time was observed in all groups. This result suggests that laser can prevent apical leakage to a certain degree although it is difficult to completely inhibit its occurrence.

As a rule, the irradiation of diode lasers is poorly absorbed by hard dental tissues, and thus allows propagation, scattering, or diffused transmission of light through dentin. ^{[13],[14],[21],[23],[24],[25],[26],[27]} However, Marchesan et al. ^[24] observed sparse lava-like areas of dentin fusion after irradiation with 3 W with the same laser of this study, in root canals irrigated with water, suggesting that diode laser at 980 nm has good interaction with the dentin tissue. Overall, this study showed that the application of 980-nm diode laser on intraradicular dentin resulted in ultrastructural alterations ranging from modifying smear layer to initial melting, and these effects were intensified with the increase of power. However, these alterations were not able to improve apical sealing, regardless of the power and irrigating solution used during the biomechanical preparation. Sealing capacity is one of the main aspects of the quality of root canal sealer. ^[28],[29]

Moritz et al. ^[30] determined that irradiation with a diode laser in two subsequent sessions resulted in almost complete elimination of bacteria and suggested that the diode laser could be considered equal to the Nd:YAG laser in endodontic treatment. While the number of colony-forming units per milliliter (CFU/ml) represented a close estimate of viable bacteria inside the root canal system, our results indicated no statistical difference between Nd:YAG and diode laser irradiation concerning the number of viable bacteria inside the root canal system.

Whatever type of laser is applied, the laser's capacity to disinfect root canals is principally a result of the heating effect. Physically, disinfection results from converting radiant energy into thermal energy inside tissues within very short timeframes.

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