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Year : 2016  |  Volume : 4  |  Issue : 2  |  Page : 48-52

Smear layer removal and ultramorphological changes of root canal dentin induced by erbium, chromium: Yttrium-scandium-gallium-garnet laser

1 Department of Restorative Dentistry, College of Dentistry, Ajman University of Science and Technology, Ajman, UAE
2 Department of Oral and Craniofacial Health Science, University of Sharjah, Sharjah, UAE
3 Department of Oral Surgery, College of Dentistry, Ajman University of Science and Technology, Ajman, UAE

Date of Web Publication21-Apr-2016

Correspondence Address:
Dr. Musab H Saeed
Department of Restorative Dentistry, Ajman University of Science and Technology, P. O. Box 346, Ajman
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/2321-4619.180998

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Aim: Using SEM & EDX analysis to evaluate: 1. The ability of Er;Cr;YSSG laser irradiation to the remove of smear layer from the root canal walls compared to the conventional EDTA/NaOCl irrigation technique 2. The effect of Er;Cr;YSSG laser irradiation on ultra morphologic characteristics and on the inorganic contents of root canal dentine. Materials and Methods: 18 single rooted freshly extracted human premolars) were chemomechanically prepared using protaper rotary nickel titanium (Ni-Ti) instruments (Dentsply maillefer) up to size 40/60 (F4) between each instruments 2 ml of 2.5% NaOcl were used. Samples were divided into two groups (n=8): Group A: 5 ml of 17% EDTA for 1 minute. Group B: Irradiation with Er;Cr;YSSG laser. Two teeth were used as a positive control (presence of smear layer). Teeth sections were evaluated by using the SEM and the EDX analysis. Results: It has been found that more than 70% of the examined samples in EDTA group showed significant removal of the smear layer in coronal, middle and apical third of the examined teeth. In Er;Cr;YSGG group, the coronal portion showed complete removal of the smear layer but with destruction of the inner wall of the dentin. In apical portion more than 87.5% of the samples showed the persistence of the smear layer in that region after laser treatment. When evaluating the degree of erosion, the highest degree was noted in the samples treated with Er,Cr;YSGG. Laser irradiation has less effect on the mineral contents of the root canal walls. Conclusions: The findings of the present study suggest that the use of Er;Cr;YSGG laser irradiation alone is significantly less effective in removing the apical third smear layer than the golden standard irrigation with 2.5% NaOCl and 17% EDTA.

Keywords: Erbium, chromium: yttrium-scandium-gallium-garnet, ethylenediaminetetraacetic acid, laser, smear layer

How to cite this article:
Alhadi D, Al-Rawi NH, Jaber FM, Agah M, Saeed MH. Smear layer removal and ultramorphological changes of root canal dentin induced by erbium, chromium: Yttrium-scandium-gallium-garnet laser. J Res Dent 2016;4:48-52

How to cite this URL:
Alhadi D, Al-Rawi NH, Jaber FM, Agah M, Saeed MH. Smear layer removal and ultramorphological changes of root canal dentin induced by erbium, chromium: Yttrium-scandium-gallium-garnet laser. J Res Dent [serial online] 2016 [cited 2020 Aug 7];4:48-52. Available from: http://www.jresdent.org/text.asp?2016/4/2/48/180998

  Introduction Top

The smear layer contains organic and inorganic particles of dentin, remnants of pulp tissue, microorganisms, endotoxins, and blood cells. It has been found between smear layer removal and improved periapical healing.[1] Different methods have been used to remove the smear layer include chemical agents, ultrasonics, and laser irradiations.[1]

The use of ethylenediaminetetraacetic acid (EDTA) and sodium hypochlorite (NaOCl) solution has gained wide acceptance and has been advocated as an effective irrigation regimen to remove organic and inorganic remnants of smear layer.[2] Still number of studies have been reported that use of EDTA alone or in combination with NaOCl can cause excessive erosion throughout the dentinal structure.[3] It can also have a detrimental effect on the major inorganic components of dental hard tissue (calcium [Ca] and phosphorus [P]) and is capable of decreasing the Ca/P ratio of the root canal dentin significantly.[4],[5] Which in turn changes the permeability, microhardness, and solubility of root canal dentin and may also adversely affect the sealing ability and adhesion of resin-based cements and root canal sealers.[6],[7] Recently, lasers have been proposed as an alternative method for disinfecting root canals and removing smear layer and debris.[2],[3]

The use of dental laser devices can be advantageous for root canal procedures; dental lasers can provide better access to formerly unreachable parts of the root canal system.[8],[9] Recently, it has been claimed that most laser wavelengths can remove the smear layer, number of studies using the erbium: yttrium-aluminum-garnet (Er: YAG) laser, demonstrated optimal removal of the smear layer without melting, charring, or recrystallization associated with other laser types.[1],[10],[11]

Erbium, chromium: Yttrium-scandium-gallium-garnet (Er, Cr: YSGG) laser is a member of the erbium family. It is a water-absorbing infrared laser that has the potential to clean root canals in different output powers of 1–3 W.[12] This hard laser systems are approved by the Food and Drug Administration for cleaning, shaping, and enlarging the root canal as well as for use in osseous, apical, and periodontal surgery.[13],[14] The Er, Cr: YSGG laser can remove calcified hard tissues by emitting a beam of infrared energy at 2.78 μm that works in combination with a water spray. Similar to Er: YAG laser, the Er, Cr: YSGG laser has been also shown to activate and improve the ability of EDTA with Cetavlon in smear layer removal from the root canal wall.[15],[16] A recent study has also shown that the Er, Cr: YSGG laser has a considerable effect on bacterial reduction within dentinal tubules of roots infected with Enterococcus faecalis.[17]

Using the scanning electron microscope (SEM) and the energy dispersive X-ray (EDX), the aim of this study is to evaluate:

  • The removal of smear layer using (Er, Cr: YSGG) laser irradiation compared to the conventional EDTA/NaOCl irrigation technique
  • The effect of (Er, Cr: YSGG) laser irradiation on ultramorphological characteristics and on the inorganic contents of root canal dentine.

  Materials and Methods Top

Eighteen freshly extracted human mature single rooted permanent premolar teeth were selected for the experiment, after obtaining the ethical clearance from the Institutional Review Board of College of Dentistry, Ajman University of Science and Technology (RD-03 19/1/2014). All the teeth were evaluated radiographically and under a stereomicroscope to verify the presence of single canal, mature apex, and absence of any resorption. The teeth with caries, cracks, and dilacerations were excluded from the study.

Teeth were then decoronated using a high-speed diamond bur to obtain a uniform root length of 14 mm. The pulp tissue was extirpated using barbed broach (Dentsply-Maillefer, Switzerland) and the working length was established by inserting a number 10 K file into each root canal. The samples were then chemo-mechanically prepared using ProTaper rotary nickel–titanium instruments (Dentsply Maillefer) with Tri Auto ZX device up to size 40/.06 (F4). Between each instrument, 2 mL of 2.5% NaOCl was used.

Samples were then divided into two groups; experimental (A and B): Eight teeth each and a group of two teeth were used as a positive control.

Irrigation procedure

Irrigation was performed using a 27 gauge side vented needle (Appli-Vac, Vi Vista Dental Products, and the USA). The needle was placed within 1–2 mm of the working length in each canal. Canals were then irrigated with 2 ml of 2.5% NaOCl for 1 min between each instrument change. Two teeth were finally irrigated with 5 ml of sterile saline for 5 min and used as a positive control (for the presence of smear layer).

For Group A, canals received a final flush of 5 ml of 17% EDTA (Merck, Darmstadt, Germany) for 1 min.

Laser irradiation

For Group B, teeth received no EDTA treatment. The canals filled with distilled water then subjected for irradiation with Er; Cr; YSGG laser. The laser unit (Waterlase Millennium, Biolase Technology, San Clemente, CA) set at WL of 2.78 nm with an output power of 1.25 W, pulse frequency of 50 Hz, 24% water pressure, and 34% air pressure. A 200 µm radial diameter fiber optic tip (RFT2 Endolase, Biolase Technology, Inc.) inserted 1 mm away from the apex was activated and moved from the apical to coronal along the working length at speed of (2 mm/s) for a total of 7 s. This step was repeated twice for each sample.

This was followed by a flush of 5 ml of distilled water for 1 min to remove any remnants of irrigating solutions and the canals were then dried with sterile paper points.

All the prepared teeth were then longitudinally grooved using a diamond disk (Diatec Swiss Dental, Switzerland) to obtain a total of 34 halves.

Scanning electron microscope and energy dispersive X-ray analysis

Samples from both groups were irrigated with 5 ml of distilled water for 1 min and subsequently dehydrated at 120°C in a hot air oven for 30 min. Specimens were then mounted on aluminum stubs, sputter-coated with gold, and introduced into the vacuum chamber of an SEM (LEO 440i, Tokyo, Japan). Photomicrographs of the root canal walls were then taken at 2 mm, 7 mm, and 12 mm depth from the apex. Apical, middle, and coronal thirds were specified accordingly.

The photomicrographs were evaluated by two independent evaluators who were unaware of the experimental groups to which the samples belonged. To guide examiners during morphological and ultrastructural analyses, scores were established based on images obtained by the SEM.

The amount of smear layer was graded between 1 and 4 according to the method described by Rome et al.[18] as shown in [Table 1].
Table 1: Grading criteria for the presence of smear layer

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EDX analysis of the same samples was done under EDX analyzer (Oxford Inc., Concord, MA, USA) to assess the Ca, P, and Mg content and to determine the Ca/P ratio.

Statistical analysis

The Kappa analysis showed excellent reliability (0.9) between the evaluators.

For the whole sample Wilcoxon signed rank test was used to evaluate the smear layer score, then paired t-test was used to evaluate the smear layer (P < 0.01 was considered statistically significant) and the mineral contents at coronal, middle, and apical third of tested sample. (P < 0.05 was considered statistically significant).

  Results Top

Scanning electron microscope evaluation of smear layer

According to Rome et al.[18] scoring criteria, a highly significant reduction in smear layer was observed in EDTA Group (A) when compared with the Er, Cr: YSGG Group (B) (P < 0.0) [Table 2].
Table 2: Standard error of mean results for the presence of smear layer within the tested groups

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Dentinal changes

When evaluating the degree of erosion [Figure 1]a, more than one-third of the specimens (30%) had erosion in the inner dentin layer for samples treated with EDTA alone. Teeth treated with Er, Cr: YSGG alone demonstrated erosion in nearly all tested samples (100%).
Figure 1: SEM of middle third; Er Cr –YSGG sample (a) showing intertubular dentin break and (b) showing erosions (Original magnification 2000X)

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For the intertubular dentin changes in term of cracks [Figure 1]b and conjugation, the minimal changes were observed in teeth treated with EDTA-treated group when compared with Er, Cr: YSGG treated group (12.5% and 42%, respectively).

Energy dispersive X-ray findings

Regarding mineral analysis, EDX analyzer was aimed toward the center of the SEM image of all tested sample. [Table 3] highlights the Ca, P, and Mg levels in coronal, middle, and apical thirds of the root canal. No significant difference in calcium content was found in the coronal and middle third, when teeth irrigated with EDTA Group (A) was compared with Er, Cr: YSGG treated Group (B). However, calcium contents increased in the apical portion of Er, Cr: YSGG treated group. Mg levels showed a significant reduction in content in a coronal and middle portion of Er, Cr: YSGG treated group when compared with EDTA-treated group (P < 0.05). Ca/P ratio was not significantly altered between both groups [Table 3].
Table 3: Mineral content values and calcium/phosphorus ratio of the tested groups

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  Discussion Top

This study was carried out to compare the ability of Er, Cr: YSGG and 17% EDTA to remove the smear layer from root canal walls, as well as to examine their effects on dentin structure using SEM and measuring the mineral contents (Ca, P, and Mg) using EDX.

With regards to smear layer, all tested groups have shown certain extent of smear layer removal, especially in the middle and coronal part of the root surface [Figure 2] and [Figure 3]. Within the EDTA-treated group, results of this study showed most of the root surfaces in coronal, middle, and apical thirds had marked smear layer removal (70%). These findings were in agreement with number of previous studies.[3],[12],[19]
Figure 2: Scanning electron microscope of coronal, middle, and apical third of ethylenediaminetetraacetic acid-treated group showing removal of the smear layer. (×2000)

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Figure 3: Scanning electron microscope of a coronal, middle, and apical third of erbium, chromium: yttrium-scandium-gallium-garnet laser treated group. Presence of smear layer at the apical third. (×2000)

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On the other hand, Er, Cr: YSGG laser irradiation removed the smear layer to lesser extent than that of 17% EDTA specially in the apical third where 33.3% of remained smear layer was on score 4 with excessive ablation in nearly all tested sample. A recent study used Er, Cr: YSGG laser at two different output powers (1.5 and 2.5W) has also shown some reduction in the smear layer in the apical, middle, and coronal sections of the root canal but less debris removal efficiency compared to EDTA.[12] Regarding melting and ablative effect of laser irradiation, our study is in disagreement with other studies which did not observe this melting and ablative effect on the tested samples.[16],[20]

The smear layer removal action of EDTA is attributed to its chelation action on the root canal dentin.[1] While Lasers vaporize tissues in the main canal, remove smear layer, and eliminate residual tissue in the apical portion of root canals.[21],[22] The effectiveness of lasers depends on many factors including the power level, the duration of exposure, the absorption of light in the tissues, the geometry of the root canal, and the tip-to-target distance.[23],[24]

When erosive effect of EDTA was compared with that of Er, Cr: YSGG, it was found that the significant higher erosive effect of Er, Cr: YSGG laser compared to the EDTA group. (100% vs. 30%).

Regarding the mineral contents, previous studies have shown that 17% EDTA can demineralize the inorganic parts of dentin.[25] This finding was consistent with that of this study especially at apical part with the Ca andP content where markedly reduced when compared with that in middle and coronal thirds.

In agreement with a pervious study,[26] our study showed that Er, Cr: YSGG laser irradiation in less effect in terms of mineral loss in coronal, middle, and apical third. An exception is for the Ca mineral content in apical third which was more than that found in other portion of other groups. This increase in calcium contents in apical group could be due to formation of calcium phosphate substrate, which might produce a mechanical obstruction.

  Conclusions Top

The findings of this study suggest that the use of Er, Cr: YSGG laser irradiation alone is significantly less effective in removing the smear layer than the golden standard irrigation with 2.5% NaOCl and 17% EDTA mainly at the apical part of the root canal walls. In addition, sever erosions have been noticed in the root canal walls within the Er, Cr: YSGG laser irradiated group. Laser irradiation showed minimal loss of the mineral contents of the root canal walls compared to EDTA irrigation with no significant difference in Ca/P ratios.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

  References Top

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Gordon W1, Atabakhsh VA, Meza F, Doms A, Nissan R, Rizoiu I, et al. 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.  Back to cited text no. 17
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  [Figure 1], [Figure 2], [Figure 3]

  [Table 1], [Table 2], [Table 3]


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