Potential of an Er:YAG Laser in the Removal of Calcium Hydroxide from Root Canals

Abstract

Objective: The purpose of this study was to assess the calcium hydroxide (CH) removal potential of an Er:YAG laser in combination with ethylenediaminetetraacetic acid (EDTA) and sodium hypochlorite (NaOCl) irrigation. Backround data: Removal of the CH dressing prior to the root canal filling is mandatory, as its remnants may mechanically block the apical area of the root canal system and also have an effect on the texture, viscosity, working time, penetration, and adhesion of root canal sealers. However, the removal of CH from the canal space is challenging, because it should ideally be placed deep and densely, so that its biological effects can be exerted in close proximity to the appropriate tissues. Methods: In this study, the mandibular premolar teeth were embedded in acrylic blocks and sectioned longitudinally through the canal, forming two halves following shaping of the root canals with ProTaper (Maillefer, Ballaigues, Switzerland) rotary instruments. The teeth were reassembled after standard grooves created onto canal walls were filled with CH. In group 1, conventional irrigation was performed with 10 mL of 17% EDTA and 10 mL of 5% NaOCl, and in goup 2, Er:YAG laser following conventional irrigation was performed. Images of the grooves taken before and after irrigation were scored and the Mann–Whitney U test was used to statistically evaluate the results. Results: The percentage of CH score reduction was 46.30% in group 1 and 60.58% in group 2. No significant difference was found between two groups (p>0.05). Conclusions: The laser did not improve the removal of CH during conventional root canal irrigation performed with NaOCl and EDTA under the conditions of current study.

Introduction

T here is no doubt that bacteria and/or their byproducts play a key role in the initiation and perpetuation of pulpo-periapical pathology.¹ The elimination of bacteria from the root canal system depends upon mechanical instrumentation in combination with copious irrigation and antibacterial medicaments.² Non-setting paste in the form of calcium hydroxide (CH) is a user-friendly and cost=effective intracanal medicament. Its antibacterial effect on most of the strains identified in root canal infections has been well-documented.^3
–5 The CH powder is mixed routinely with water or saline; carried to the working length with a lentulo spiral and left in the root canal system for 1–4 weeks.^2,6 Removal of the CH dressing prior to the root canal filling is mandatory, as its remnants may mechanically block the apical area of the root canal system⁷ and also have an effect on the texture,⁸ viscosity,⁸ working time,⁹ penetration,¹⁰ and adhesion¹¹ of root canal sealers.¹⁰ However, the removal of CH from the canal space is challenging, because it should ideally be placed deep and densely, so that its biological effects can be exerted in close proximity to the appropriate tissues.⁶

A variety of techniques have been recommended for removing CH from the root canal system.^2,7,10,12,13 The most frequently described method is the instrumentation of the root canal with a master apical file in combination with copious irrigation of sodium hypochlorite (NaOCl) and ethylenediaminetetraacetic acid (EDTA).^2,8,10 EDTA has the ability to chelate residues and make them easier to remove by irrigation.^8,12 However, hand filing and irrigation alone have been found to be inadequate for the complete remove of all of the CH.^4,13 Irregularities of the root canal system may be inaccessible for conventional irrigation procedures, and CH may remain in these extensions.¹⁴

Recently, laser irradiation has been presented as an alternative method in endodontics.¹⁵ The effects of lasing were tested for pulp capping,¹⁶ on the adhesion of endodontic sealers,^17,18 the sealing ability of pulp capping materials,¹⁹ inflammatory processes,²⁰ evaluating the blood flow in dental pulp, elimination of bacteria,²¹ removal of the smear layer,²² and cleaning root canal walls.^15,23 The results of these studies stated that the Nd:YAG laser is more effective in the sterilization of root canals, whereas the Er:YAG laser is highly recommended for hard tissue applications.^15,23 The Er:YAG laser is particularly used for the removal of the smear layer and could also be effective for removal of aqueous materials, such as CH, from the dentin wall surface.^23,24 Nevertheless, until recently the influence of Er:YAG laser irradiation in the removal of CH has not been evaluated.

Therefore, the aim of this study was to evaluate the effectiveness of EDTA and NaOCl irrigation with and without the use of an Er:YAG laser to remove CH.

Methods

Single-rooted mandibular premolar teeth, extracted for periodontal reasons, were used in the current study. Teeth with caries, internal or external resorptions, cracks, and incomplete apices were excluded. Buccolingual and mesiodistal radiographs were taken to eliminate the teeth with variations in root canal configurations. Only the teeth with a single canal and classified as a Vertucci I root canal configuration were included. Forty-six teeth were selected.

The crowns and the coronal parts of the teeth were removed to standardize all of the specimens as having 12-mm-long roots. The working length was established 1 mm short of the length where the file exited the apical foramen. The root canals were shaped with ProTaper rotary canal instruments (Maillefer, Ballaigues, Switzerland) to a size F3. A single operator instrumented all of the teeth. Between each instrument, the canals were irrigated with 2 mL of 5% NaOCl. Irrigation was performed using disposable plastic syringes with 27-gauge needles. The needle was placed 1 mm short of the working length during irrigation. To remove the smear layer, root canals were irrigated with 10 mL of 17% EDTA at the end of shaping. This procedure was followed by a final rinse with 10 mL of 5% NaOCl. The root canals were dried with paper points (Diadent, Diadent Group International, Burnaby BC, Canada). The teeth were embedded in acrylic blocks following placement of a ball of dental wax on the tip of each tooth to prevent acrylic leakage into the root canal. The buccolingual diameters of the teeth were measured at the widest point with a Boley gauge (Hu-Friedy Inc., Chicago, IL). The teeth were radomized into two groups (n=21 teeth each) based on this measurement, while saving four teeth with a median value in diameter for the control group. The acrylic blocks were split longitudinally in the buccolingual direction with a diamond saw (Isomet Buehler, Ltd, Lake Bluff, IL) through the canal, forming two halves.

Artificial standardized grooves of 4 mm in length were then created in one canal wall using a scalpel. The groove was 0.2 mm wide, 0.5 mm deep, and located 2–6 mm from the apex. The root canals were filled with CH paste (Ultracal XS®, Ultradent products, South Jordan, UT) using paper points. The two teeth from the control group were kept for a negative control and received no CH treatment. The blocks were reassembled with plastic wires, and sections were isolated with sticky wax and stored for 1 week at 37°C in 100% relative humidity. One week later, the root halves were separated and images of the canals with a groove were taken under×40 magnification using a stereomicroscope (Olympus SZX7, E330-12 Tokyo, Japan) immediately before irrigation. Photographs were calibrated with the help of the Analysis-LS professional FNE program. This step was followed by reassembling the two root halves using plastic wires, and isolation of sections with sticky wax was repeated.

In group I (n=21), the root canals were irrigated with 10 mL of %5 NaOCl and 10 mL of 17% EDTA, respectively. During the irrigation procedures, the canals were recapitulated with the master apical file. This procedure was followed by a final rinse of 10mL of 5% NaOCl. The teeth in group 2 (n=21), were also irrigated with the same procedures as the samples in group 1. However, roots in group 2 were irradiated with an Er:YAG laser (Versawave by HOYA ConBio, Fremont, CA) before final irrigation with 10mL of 5% NaOCl. The teeth were irradiated at a wavelength of 2.94 um, with an output of 1.5 W, a pulse energy of 100 mJ, and a pulse frequency of 15 Hz. During irradiation, the fiber tip with a 0.2 mm diameter was introduced into the canal 1 mm from the working length, parallel to the canal wall, and in contact with the wall. The fiber optic was used in a continous spiral motion from the apex to the canal entrance with three exposures of 10 sec each. Between each exposure, lasing was paused for 15 sec. During the lasing procedure, the teeth were kept constantly wet with water coolant spray. The roots kept for a positive control received calcium hydroxide but no irrigation was performed. After irrigation, the root halves were seperated. The grooves were examined under a stereomicroscope under×40 magnification, to evaluate the amount of residual CH. Images of each half of the canal with a groove were taken by using the same method described previously, prior to testing. The quantity of CH in the groove before and after irrigation was scored by three precalibrated blinded examiners. The amount of the CH in the groove was evaluated according to the criteria determined by Van der Sluis et al.¹² The specimens were scored as follows:

Score 0: The groove is empty (Fig. 1A)

Score 1: Less than half of the groove is filled with CH (Fig. 1B)

Score 2: More than half of the groove is filled with CH (Fig. 1C)

Score 3: The groove is filled completely with CH (Fig. 1D)

FIG. 1.

(A) Score 0: The groove is empty. (B) Score 1: Less than half of the groove is filled with calcium hydroxide (CH). (C) Score 2: More than half of the groove is filled with CH. (D) Score 3: The groove is filled completely with CH.

The percentage of score reduction was calculated as follows: \documentclass{aastex}\usepackage{amsbsy}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{bm}\usepackage{mathrsfs}\usepackage{pifont}\usepackage{stmaryrd}\usepackage{textcomp}\usepackage{portland,xspace}\usepackage{amsmath,amsxtra}\pagestyle{empty}\DeclareMathSizes{10}{9}{7}{6} \begin{document} \begin{align*} \hbox{percentage of score reduction} = ({score \ before \ irrigation} \\ \quad - {score \ after \ irrigation}) \times \it 100 \ \hbox{score before irrigation} \end{align*} \end{document}

Removal of CH from the standardized grooves was scored by three blinded examiners, based on the scale described previously.

Statistical measurements

An inter-rater reliability analysis using the κ statistic was performed to determine the consistency among the examiners in determining the score of CH removal. The Mann–Whitney U test was used to compare the outcomes of the laser group (group 1) and the conventional group (group 2). The significance level was established at 5%.

Results

Initially, a total of 46 teeth were included in the study, with four being used as controls. Fourty-two were randomly allocated into two groups based on buccopalatal diameters. The Student t test indicated no difference in the buccopalatal diameters of group 1 (6.79±0.62 mm) and group 2 (6.9±0.7 mm).

The inter-rater agreement for the assesors on the score of residual CH was κ=0.82, (p<0.05).

The percentage of CH score reduction was 46.46% in group 1 and 62.77% in group 2. Whereas the amount of residual CH was more when using the conventional removal technique, no significant difference was found between the two calcium hydroxide removal methods (p>0.05) (Table 1).

Table 1.

The Percentages of Score Reductıon of Resıdual CH After Irrıgatıon Using NaOCl and EDTA Wıth (Group 2) or Wıthout (Group 1) Laser Enhancement

	N	Mean (%)	SD	SEM
Group 1	21	46.46	40.66	8.66
Group 2	21	62.77	30.85	6.9

CH, calcium hydroxide; NaOCl, sodium hypochlorite; EDTA, ethylenediaminetetraacetic acid.

Discussion

CH is a highly recommended root canal medicament.^3
–5 Its removal prior to the placement of a permenant root canal fillling is necessary, as remnants may have a negative impact on the sealing ability of root canal sealers.^8

–11 However, the removal of this material from the root canal has not been completely achieved.^2,4,13,25

Previous studies have used various qualitative^26

–30 and quantitative^31

–35 methodologies, such as scoring remnants within the canals,^26

–30 measuring the areas occupied by remnants using computer programs,^33,34 calculating the volume of remaining material by CT.³⁵ The groove model, which is a qualitative and established methodology,^{12,25,36

–42} was preferred in the current study, as the primary goal was to provide an initial insight about the presence–absence of efficacy of laser application on removal of CH. It was designed to imitate the irregularities that root canal instruments are unable to access, which also seems to be similar to the clinical situation of the apical portion of the canal.¹²

The effects of irrigation solutions can be improved by some additional interventions, such as the use of larger volumes,⁴³ a patency file,² rotary files,¹³ passive ultrasonic irrigation,⁴⁴ and laser.³⁰ The effects of lasers on caries prevention,⁴⁵ inflammatory process,²⁰ fusion of root fractures,⁴⁶ direct pulp capping,^16,19 microorganisms,³ adhesive properties of root canal sealers,¹⁸ surface characteristics of dentin,²⁴ debris, and smear layer reduction within the root canal,^22,30,47,48 have been investigated in the field of endodontics. In the current investigation, irrigation was performed with or without Er:YAG laser irradiation. The coefficient of water absorbtion for the Er:YAG laser is 10 times more than the CO₂ laser and 15,000–20,000 times more than the Nd:YAG laser. Less tissue degeneration and no carbonization were observed when used in combination with water.¹⁵ Er:YAG laser irradiaton energy is selectively absorbed by water molecules and hydrous organic components of biological tissues. This procedure causes water evaporation and produces internal pressures in hard tissues, resulting in microexplosions and mechanical tissue collapse. This is called “ablation” and it removes calcified tissue with minimal thermal effects.²⁴ There is no consensus on ablative settings of Er:YAG laser to be used within the canals. A variety of parameters have been described in the literature regarding power and duration that have been used during Er:YAG laser-activated irrigation of the root canals.^{22,30,49
–51} The Er:YAG laser had been previously found to vaporize organic tissues and reduce the smear layer^15,47,48 without melting, charring, recristalization, and exposing the dentinal tubules.¹⁵ A major concern considered during choosing parameters was sensitivity of periradicular bone tissue to heat. Maximum increase without any damage to periradicular bone was reported to be 47°C⁵² for 1 min, which corresponds to a 10°C increase in the human body. Although no measurements regarding temperature were performed in our study, the parameters 100 mJ and a pulse frequency of 15 Hz were lower than the ones reported to be safe^53,54 in terms of the temperature increase. The findings of the current study showed that Er:YAG laser irradiation had no significant effect on the removal of CH. However, results could be different if the duration of laser irradiation was increased from 30 to 60 sec³⁰ or the tip was located 2 mm from the apex.⁵¹ On the other hand, the ablation effect attributed to this type of laser depends upon water within the material to be removed.¹⁵ The only ingredient in Ultracal®XS in addition to CaO powder is known to be barium sulphate. Although it is marketed as an “aqueous mix,” premixed products may increase the retention of the material;⁴ therefore, the present results would have been different if the CH had been mixed with distilled water. However, laser application seems to be promising. New studies are required with novel designed tips at various application times as well as with different types of CH pastes prepared with various vehicles, to determine the effect of Er:YAG laser on the removal of CH from the root canals.

Conclusions

It can be concluded that laser did not improve the removal of CH during conventional root canal irrigation performed with NaOCl and EDTA under the conditions of current study.

Footnotes

Author Disclosure Statement

No conflicting financial interests exist.

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