Basic Research—Technology
Comparison of Smear Layer Removal Using the Nd:YAG Laser, Ultrasound, ProTaper Universal System, and CanalBrush Methods: An In Vitro Study Grasiele Assis da Costa Lima, DDS, MSc,* Carlos Menezes Aguiar, DDS, PhD,* Andrea Cruz C^ amara, DDS, PhD,* Luiz Carlos Alves, PhD,† F abio Andre Brayner dos Santos, PhD,† and Aline Elesb~ ao do Nascimento, PhD‡ Abstract Introduction: The aim of this study was to compare the efficacy of the Nd:YAG laser, ultrasound, the ProTaper Universal system (Dentsply Maillefer, Ballaigues, Switzerland), and the CanalBrush (Coltene Whaledent, Langenau, Germany) methods for the removal of the smear layer from the apical third of root canals. Methods: Fifty distal root canals from extracted human mandibular first molars were instrumented up to ProTaper Universal F5 and divided randomly into 5 groups (n = 10) according to the following final irrigation agitation techniques: no agitation (control), ProTaper Universal file, ultrasound, CanalBrush, and Nd:YAG laser. Specimens were observed under a scanning electron microscope. The presence of the smear layer was evaluated using a 3-grade scoring system. The data were analyzed with Cohen kappa, Kruskal-Wallis, and Mann-Whitney U tests. A level of significance of .05 was adopted. Results: The ultrasound group performed significantly better than the rest of the groups; 56.6% of the specimens revealed no smear layer, 44.4% showed the presence of a moderate smear layer, and no heavy smear layers were observed. In the Nd:YAG laser group, 30% of the specimens presented with no smear layer, 70% showed the presence of a moderate smear layer, and no heavy smear layers were observed. In contrast, a heavy smear layer was observed on the surfaces of the root canals in the CanalBrush (23.4%), ProTaper Universal (13.4%), and control (86.6%) groups. Statistically significant differences were observed (P < .05). Conclusions: None of the agitation methods completely removed the smear layer. However, the ultrasound method performed significantly better followed by the Nd:YAG laser, the CanalBrush, and the ProTaper Universal system. Agitation of the irrigant improved smear layer removal in the apical third of the canal. (J Endod 2015;-:1–5)
Key Words EDTA, laser, smear layer, sodium hypochlorite, ultrasound
I
nstrumentation of the root canal is associated with disadvantages such as the formation of a smear layer (1). The presence of a smear layer prevents the penetration of intracanal disinfectant into the dentinal tubules and prevents complete adaptation of obturation materials to the dentinal walls. The smear layer acts as a physical barrier, which may reduce dentin permeability and delay medications from accessing infected dentinal tubules. Additionally, bacteria remaining in dentinal tubules after root canal preparation may be sealed by the smear layer (2, 3). To date, no single irrigant has been shown to be capable of dissolving both the organic and inorganic parts of the dentin (2). A final irrigation sequence with a chelating agent, such as EDTA, and sodium hypochlorite (NaOCl) is recommended to remove inorganic as well as organic components of the smear layer (4, 5). Throughout the history of endodontics, endeavors have continuously been made to develop more effective irrigant delivery and agitation systems for root canal irrigation. These systems might be divided into 2 broad categories: manual agitation techniques and machine-assisted agitation devices (6). To enhance the dispersal of the irrigant and to activate it, sonic and ultrasonic techniques have been investigated and developed. The use of ultrasonics employs an acoustic streaming effect, and it has been shown that the use of a small oscillating file is able to transport irrigants into the apical parts of the root canal. This could be beneficial for transporting chelating agents and improving smear layer removal in the apical root canal (4). Recent studies have shown that ultrasonic activation of irrigants can provide an advantage over conventional needle and syringe irrigation for root canal debridement (7). Lasers have been proposed as an alternative to the conventional approach to cleaning and disinfecting. Various types of lasers have been investigated in an attempt to develop improved treatment methods, and the performance of lasers that are used in the field of dentistry has been increasing (8). The CanalBrush (Coltene Whaledent, Langenau, Germany) is an endodontic microbrush. This highly flexible microbrush is molded entirely from polypropylene and might be used manually with a rotary action. However, it is more efficacious when attached to a contra-angle handpiece running at 600 rpm (6). The aim of this study was to compare the efficacy of the Nd:YAG laser, ultrasound, the ProTaper Universal system (Dentsply Maillefer, Ballaigues, Switzerland), and the
From the *Department of Prosthetics and Oral and Facial Surgery, Faculty of Dentistry, Federal University of Pernambuco, Recife, Brazil; †Department of Parasitology, Aggeu Magalh~aes Research Center, Fiocruz, Recife, Brazil; and ‡Department of Biology, Catholic University of Pernambuco, Recife, Brazil. Address requests for reprints to Dr Grasiele Assis da Costa Lima, Rua Sebasti~ao Alves, 74, Parnamirim, Recife, PE 51020-150, Brazil. E-mail address: gaga_lima@ hotmail.com 0099-2399/$ - see front matter Copyright ª 2015 American Association of Endodontists. http://dx.doi.org/10.1016/j.joen.2014.11.004
JOE — Volume -, Number -, - 2015
Smear Layer Removal
1
Basic Research—Technology CanalBrush for the removal of the smear layer from the apical third of root canals. The null hypothesis was that there would be no difference in smear layer removal between the Nd:YAG laser, ultrasound, the ProTaper Universal system, and CanalBrush methods.
Materials and Methods Selection and Preparation of the Samples Fifty freshly intact distal canals of human mandibular first molars (length 20–21 mm, straight, with a single root canal) checked by radiographs and with complete apex formation that were extracted for orthodontic reasons from patients aged 16–18 years obtained from the tooth bank of the Department of Prosthetics and Oral and Facial Surgery of the Federal University of Pernambuco were selected with the approval of the Ethics in Research Committee of the University’s Center of Health Sciences. The teeth were stored in 10% formalin until use. Coronal access was achieved, and the distal root was separated from the mesial root with the aid of a carborundum disc (KG Sorensen, Barueri, Brazil). The mesial root was returned to the tooth bank, and the distal root was washed in running water for 20 seconds and left to dry at room temperature. The specimens were decoronated with a diamond disc (KG Sorensen) under water coolant to obtain a standardized root length of 15 mm. To determine the working length (WL), a #10 K-file (Dentsply Maillefer) was inserted into the distal canal until it was visible at the apical foramen. The WL was calculated to be 1 mm less than the length obtained with this initial file. To simulate the clinical situation, each apex was sealed with sticky wax (Wilson, Sao Paulo, Brazil). Biomechanical Preparation of the Root Canals All root canals were instrumented with the ProTaper Universal system using an electric motor (Endo-Pro Torque; Driller Dental, Sao Paulo, Brazil) at a speed of 300 rpm as follows: 1. An SX file was used to one half of the WL 2. An S1 file was used up to 4 mm short of the apex 3. S1 and S2 files were used to the full WL F1, F2, F3, F4, and F5 files were used to the full WL. A single operator instrumented all root canals. The instruments were replaced after 10 uses. Freshly prepared 1% NaOCl solution (Farmacia Escola Carlos Dumont de Andrade, Recife, Brazil) was used for root canal irrigation. For irrigation of the root canal, a 3-mL FCF syringe system (FCF, Sao Paulo, Brazil) with a 30-G needle (Injecta, Diadema, Brazil) was used. After each instrument change, the root canals were rinsed with 3 mL of the irrigating solution. During the irrigation procedures, the irrigator tips were placed 1 mm from the WL and then moved backwards and forwards. Subsequently, the root canals were irrigated with 10 mL distilled water to avoid the prolonged effects of the NaOCl solution.
Final Irrigation Procedures After biomechanical preparation of the root canals, the specimens were divided randomly into 5 groups of 10 teeth each. Except for the negative control group, to remove the smear layer, the root canals were subjected to a final rinse with 1 mL 17% EDTA (Farmacia Dermatologe, Rio Grande do Sul, Brazil) using an FCF syringe system with a 30-G needle, which was placed 1 mm from the WL. The groups were as follows: 1. Group 1 (n = 10): Negative control; no final rinse and no additional agitation of the irrigant were performed. 2
da Costa Lima et al.
2. Group 2 (n = 10): File activation; the solution was activated with the F5 file of the ProTaper Universal system placed at the WL, with slight in-and-out movements for 30 seconds. 3. Group 3 (n = 10): CanalBrush; the irrigant was activated with a medium-sized CanalBrush placed in a slow-speed handpiece set at 600 rpm and advanced to the WL. A circumferential motion was made for 30 seconds. 4. Group 4 (n = 10): Ultrasound activation; the solution was activated by ultrasound following the method proposed by Jiang et al (9). A TR20 ultrasound tip (GNATUS, Sao Paulo, Brazil) was used, driven by using the GNATUS Jet Sonic device (GNATUS) at a frequency of 30 KHz and an amplitude of 30 mm. The ultrasound tip was moved up and down 3 mm from the WL for 30 seconds. 5. Group 5 (n = 10): Nd:YAG laser agitation; the solution was agitated with a laser. A Nd:YAG laser with a wavelength of 1064 nm (Fotona, Madrid, Spain) was used for laser irradiation according to the methodology of Moon et al (10). The standardized settings were 150 mJ/ pulse and 10 Hz (average power = 1.5 W) delivered into a 320-mm flexible endodontic fiber. During irradiation, the laser fiber was used with constant motion in the apical-coronal direction and kept 3 mm from the WL. The laser fiber was inserted and withdrawn 4 times for 5 seconds each with 10-second intervals in between. After EDTA agitation, the specimens in all groups were irrigated for 60 seconds with 1 mL 1% NaOCl followed by a final rinse with 5 mL 0.9% sterile saline solution. The root canals were then dried with absorbent F5 paper points (Dentsply, Rio de Janeiro, Brazil), and the specimens were stored in 1.5 mL Eppendorf tubes (HXT, Jiangsu, China).
Evaluation by Scanning Electron Microscopy The teeth were grooved along the buccal and lingual surfaces by using a diamond disc (KG Sorensen) at low speed and split longitudinally with a chisel and mallet into 2 halves. For each specimen, the half containing the most visible part of the apex was placed in a 2% glutaraldehyde solution for 24 hours. The other half of each tooth was discarded. The fixed specimens were rinsed 3 times with a sodium cacodylate-buffered solution (0.1 mol/L, pH = 7.2), incubated in osmium tetroxide for 1 hour, dehydrated with ascending concentrations of ethyl alcohol (30%–100%), and placed in a desiccator for at least 24 hours. Each specimen was mounted on an aluminum stub, coated with 25 mm gold palladium, and examined under a scanning electron microscope (JEOL-5600 LV; JEOL, Tokyo, Japan). The photomicrographs were taken from the apical thirds of the root canals between 0.5 mm and 5 mm from the apical foramen at a magnification of 2000. The photomicrographs were analyzed by 3 examiners who were specialists in endodontics and were blind to group status. Each examiner scored the presence or absence of a smear layer in the apical third following the method described by Torabinejad et al (11) in which a score of 1 indicated no smear layer (no smear layer on the surface of the root canals; all tubules were clean and open), a score of 2 indicated a moderate smear layer (no smear layer on the surface of root canal, but tubules contained debris), and a score of 3 indicated a heavy smear layer (smear layer covered the root canal surface and the tubules). Before scoring, the 3 examiners assessed the first 20 specimens together for calibration purposes. The results were tabulated and submitted to statistical analysis. Statistical Analysis of the Data The categoric data were summarized by means of absolute frequency and relative percentages, and the numeric data were summarized JOE — Volume -, Number -, - 2015
Basic Research—Technology by means of the usual descriptive statistics of location and dispersion. The agreement between the 3 examiners regarding the presence or absence of a smear layer in the apical third of the root canal was evaluated with Cohen kappa. Comparisons between groups were analyzed statistically using the Kruskal-Wallis nonparametric analysis of variance and MannWhitney U tests (12). A level of significance of .05 was adopted for all tests, with a 95% confidence interval. The Statistical Package for the Social Sciences, version 13 (SPSS, Chicago, IL) was used.
Results Intraexaminer and Interexaminer Agreement Good agreement was shown between examiners 1 and 3 (k = 0.683) and examiners 2 and 3 (k = 0.721). Excellent agreement was shown between examiners 1 and 2 (k = 0.824), with a significance set at .05. This suggests that there was good to excellent reliability and reproducibility among the examiners (12), with values $0.60 for the different groups. The distribution of smear layer scores is presented in Table 1. The ultrasound group (group 4) performed significantly better than the rest of the groups with respect to smear layer removal in the apical third of root canal. A full 56.6% of the specimens revealed no smear layer (score 1), whereas 44.4% showed the presence of a moderate smear layer (score 2). No instance of a heavy smear layer (score 3) was observed. In the Nd:YAG laser group (group 5), 30% of the specimens presented no smear layer, 70% revealed the presence of a moderate smear layer, and no heavy smear layer was observed. In contrast, a heavy smear layer was observed on the surfaces of the root canals in the CanalBrush (group 3: 23.4%), ProTaper Universal (group 2:13.4%), and control (group 1: 86.6%) groups. The Kruskal-Wallis test revealed a statistically significant difference between the groups (P < .001), showing that the groups exhibited different degrees of capacity for smear layer removal in the apical third of the root canal. Table 2 shows the means and standard deviations of the groups. The Mann-Whitney U test for the comparison of the groups revealed statistically significant differences (P < .05) in all cases except between groups 2 and 3 (P = .321). All activation groups showed significantly lower smear layer scores than group 1. Groups 2 and 3 had similar smear layer scores, which were higher than groups 4 and 5. The null hypothesis was rejected. Figure 1A–F shows representative photomicrographs of each group.
Discussion After mechanical preparation, an amorphous, irregular layer known as the smear layer is formed on root canal walls. Possible deleterious effects may occur if the smear layer is not removed during root canal treatment. Microorganisms remaining in the smear layer after the instrumentation of an infected root canal space can survive and reinfect the canal. The smear layer has also been shown to hinder the penetraTABLE 1. Distribution of Smear Layer Scores Group (n = 10) 1 2 3 4 5
Score
Agitation technique
1 (%)
2 (%)
3 (%)
Control ProTaper Universal Canalbrush Ultrasound Laser
0 (0) 0 (0) 0 (0) 17 (56.6) 9 (30)
4 (13.4) 26 (86.6) 23 (76.6) 13 (44.4) 21 (70)
26 (86.6) 4 (13.4) 7 (23.4) 0 (0) 0 (0)
1, no smear layer; 2, moderate smear layer; 3, heavy smear layer.
JOE — Volume -, Number -, - 2015
TABLE 2. Comparisons between Groups according to Smear Layer Removal Mean ± SD Comparison
First group
Second group
P value*
Group 1 group 2 Group 1 group 3 Group 1 group 4 Group 1 group 5 Group 2 group 3 Group 2 group 4 Group 2 group 5 Group 3 group 4 Group 3 group 5 Group 4 group 5
2.87 0.35 2.87 0.35 2.87 0.35 2.87 0.35 2.13 0.35 2.13 0.35 2.13 0.35 2.23 0.43 2.23 0.43 1.43 0.50
2.13 0.35 2.23 0.43 1.43 0.50 1.70 0.47 2.23 0.43 1.43 0.50 1.70 0.47 1.43 0.50 1.70 0.47 1.70 0.47
Comparison of Smear Layer Removal Using the Nd:YAG Laser, Ultrasound, ProTaper Universal System, and CanalBrush Methods: An In Vitro Study Grasiele Assis da Costa Lima, DDS, MSc,* Carlos Menezes Aguiar, DDS, PhD,* Andrea Cruz C^ amara, DDS, PhD,* Luiz Carlos Alves, PhD,† F abio Andre Brayner dos Santos, PhD,† and Aline Elesb~ ao do Nascimento, PhD‡ Abstract Introduction: The aim of this study was to compare the efficacy of the Nd:YAG laser, ultrasound, the ProTaper Universal system (Dentsply Maillefer, Ballaigues, Switzerland), and the CanalBrush (Coltene Whaledent, Langenau, Germany) methods for the removal of the smear layer from the apical third of root canals. Methods: Fifty distal root canals from extracted human mandibular first molars were instrumented up to ProTaper Universal F5 and divided randomly into 5 groups (n = 10) according to the following final irrigation agitation techniques: no agitation (control), ProTaper Universal file, ultrasound, CanalBrush, and Nd:YAG laser. Specimens were observed under a scanning electron microscope. The presence of the smear layer was evaluated using a 3-grade scoring system. The data were analyzed with Cohen kappa, Kruskal-Wallis, and Mann-Whitney U tests. A level of significance of .05 was adopted. Results: The ultrasound group performed significantly better than the rest of the groups; 56.6% of the specimens revealed no smear layer, 44.4% showed the presence of a moderate smear layer, and no heavy smear layers were observed. In the Nd:YAG laser group, 30% of the specimens presented with no smear layer, 70% showed the presence of a moderate smear layer, and no heavy smear layers were observed. In contrast, a heavy smear layer was observed on the surfaces of the root canals in the CanalBrush (23.4%), ProTaper Universal (13.4%), and control (86.6%) groups. Statistically significant differences were observed (P < .05). Conclusions: None of the agitation methods completely removed the smear layer. However, the ultrasound method performed significantly better followed by the Nd:YAG laser, the CanalBrush, and the ProTaper Universal system. Agitation of the irrigant improved smear layer removal in the apical third of the canal. (J Endod 2015;-:1–5)
Key Words EDTA, laser, smear layer, sodium hypochlorite, ultrasound
I
nstrumentation of the root canal is associated with disadvantages such as the formation of a smear layer (1). The presence of a smear layer prevents the penetration of intracanal disinfectant into the dentinal tubules and prevents complete adaptation of obturation materials to the dentinal walls. The smear layer acts as a physical barrier, which may reduce dentin permeability and delay medications from accessing infected dentinal tubules. Additionally, bacteria remaining in dentinal tubules after root canal preparation may be sealed by the smear layer (2, 3). To date, no single irrigant has been shown to be capable of dissolving both the organic and inorganic parts of the dentin (2). A final irrigation sequence with a chelating agent, such as EDTA, and sodium hypochlorite (NaOCl) is recommended to remove inorganic as well as organic components of the smear layer (4, 5). Throughout the history of endodontics, endeavors have continuously been made to develop more effective irrigant delivery and agitation systems for root canal irrigation. These systems might be divided into 2 broad categories: manual agitation techniques and machine-assisted agitation devices (6). To enhance the dispersal of the irrigant and to activate it, sonic and ultrasonic techniques have been investigated and developed. The use of ultrasonics employs an acoustic streaming effect, and it has been shown that the use of a small oscillating file is able to transport irrigants into the apical parts of the root canal. This could be beneficial for transporting chelating agents and improving smear layer removal in the apical root canal (4). Recent studies have shown that ultrasonic activation of irrigants can provide an advantage over conventional needle and syringe irrigation for root canal debridement (7). Lasers have been proposed as an alternative to the conventional approach to cleaning and disinfecting. Various types of lasers have been investigated in an attempt to develop improved treatment methods, and the performance of lasers that are used in the field of dentistry has been increasing (8). The CanalBrush (Coltene Whaledent, Langenau, Germany) is an endodontic microbrush. This highly flexible microbrush is molded entirely from polypropylene and might be used manually with a rotary action. However, it is more efficacious when attached to a contra-angle handpiece running at 600 rpm (6). The aim of this study was to compare the efficacy of the Nd:YAG laser, ultrasound, the ProTaper Universal system (Dentsply Maillefer, Ballaigues, Switzerland), and the
From the *Department of Prosthetics and Oral and Facial Surgery, Faculty of Dentistry, Federal University of Pernambuco, Recife, Brazil; †Department of Parasitology, Aggeu Magalh~aes Research Center, Fiocruz, Recife, Brazil; and ‡Department of Biology, Catholic University of Pernambuco, Recife, Brazil. Address requests for reprints to Dr Grasiele Assis da Costa Lima, Rua Sebasti~ao Alves, 74, Parnamirim, Recife, PE 51020-150, Brazil. E-mail address: gaga_lima@ hotmail.com 0099-2399/$ - see front matter Copyright ª 2015 American Association of Endodontists. http://dx.doi.org/10.1016/j.joen.2014.11.004
JOE — Volume -, Number -, - 2015
Smear Layer Removal
1
Basic Research—Technology CanalBrush for the removal of the smear layer from the apical third of root canals. The null hypothesis was that there would be no difference in smear layer removal between the Nd:YAG laser, ultrasound, the ProTaper Universal system, and CanalBrush methods.
Materials and Methods Selection and Preparation of the Samples Fifty freshly intact distal canals of human mandibular first molars (length 20–21 mm, straight, with a single root canal) checked by radiographs and with complete apex formation that were extracted for orthodontic reasons from patients aged 16–18 years obtained from the tooth bank of the Department of Prosthetics and Oral and Facial Surgery of the Federal University of Pernambuco were selected with the approval of the Ethics in Research Committee of the University’s Center of Health Sciences. The teeth were stored in 10% formalin until use. Coronal access was achieved, and the distal root was separated from the mesial root with the aid of a carborundum disc (KG Sorensen, Barueri, Brazil). The mesial root was returned to the tooth bank, and the distal root was washed in running water for 20 seconds and left to dry at room temperature. The specimens were decoronated with a diamond disc (KG Sorensen) under water coolant to obtain a standardized root length of 15 mm. To determine the working length (WL), a #10 K-file (Dentsply Maillefer) was inserted into the distal canal until it was visible at the apical foramen. The WL was calculated to be 1 mm less than the length obtained with this initial file. To simulate the clinical situation, each apex was sealed with sticky wax (Wilson, Sao Paulo, Brazil). Biomechanical Preparation of the Root Canals All root canals were instrumented with the ProTaper Universal system using an electric motor (Endo-Pro Torque; Driller Dental, Sao Paulo, Brazil) at a speed of 300 rpm as follows: 1. An SX file was used to one half of the WL 2. An S1 file was used up to 4 mm short of the apex 3. S1 and S2 files were used to the full WL F1, F2, F3, F4, and F5 files were used to the full WL. A single operator instrumented all root canals. The instruments were replaced after 10 uses. Freshly prepared 1% NaOCl solution (Farmacia Escola Carlos Dumont de Andrade, Recife, Brazil) was used for root canal irrigation. For irrigation of the root canal, a 3-mL FCF syringe system (FCF, Sao Paulo, Brazil) with a 30-G needle (Injecta, Diadema, Brazil) was used. After each instrument change, the root canals were rinsed with 3 mL of the irrigating solution. During the irrigation procedures, the irrigator tips were placed 1 mm from the WL and then moved backwards and forwards. Subsequently, the root canals were irrigated with 10 mL distilled water to avoid the prolonged effects of the NaOCl solution.
Final Irrigation Procedures After biomechanical preparation of the root canals, the specimens were divided randomly into 5 groups of 10 teeth each. Except for the negative control group, to remove the smear layer, the root canals were subjected to a final rinse with 1 mL 17% EDTA (Farmacia Dermatologe, Rio Grande do Sul, Brazil) using an FCF syringe system with a 30-G needle, which was placed 1 mm from the WL. The groups were as follows: 1. Group 1 (n = 10): Negative control; no final rinse and no additional agitation of the irrigant were performed. 2
da Costa Lima et al.
2. Group 2 (n = 10): File activation; the solution was activated with the F5 file of the ProTaper Universal system placed at the WL, with slight in-and-out movements for 30 seconds. 3. Group 3 (n = 10): CanalBrush; the irrigant was activated with a medium-sized CanalBrush placed in a slow-speed handpiece set at 600 rpm and advanced to the WL. A circumferential motion was made for 30 seconds. 4. Group 4 (n = 10): Ultrasound activation; the solution was activated by ultrasound following the method proposed by Jiang et al (9). A TR20 ultrasound tip (GNATUS, Sao Paulo, Brazil) was used, driven by using the GNATUS Jet Sonic device (GNATUS) at a frequency of 30 KHz and an amplitude of 30 mm. The ultrasound tip was moved up and down 3 mm from the WL for 30 seconds. 5. Group 5 (n = 10): Nd:YAG laser agitation; the solution was agitated with a laser. A Nd:YAG laser with a wavelength of 1064 nm (Fotona, Madrid, Spain) was used for laser irradiation according to the methodology of Moon et al (10). The standardized settings were 150 mJ/ pulse and 10 Hz (average power = 1.5 W) delivered into a 320-mm flexible endodontic fiber. During irradiation, the laser fiber was used with constant motion in the apical-coronal direction and kept 3 mm from the WL. The laser fiber was inserted and withdrawn 4 times for 5 seconds each with 10-second intervals in between. After EDTA agitation, the specimens in all groups were irrigated for 60 seconds with 1 mL 1% NaOCl followed by a final rinse with 5 mL 0.9% sterile saline solution. The root canals were then dried with absorbent F5 paper points (Dentsply, Rio de Janeiro, Brazil), and the specimens were stored in 1.5 mL Eppendorf tubes (HXT, Jiangsu, China).
Evaluation by Scanning Electron Microscopy The teeth were grooved along the buccal and lingual surfaces by using a diamond disc (KG Sorensen) at low speed and split longitudinally with a chisel and mallet into 2 halves. For each specimen, the half containing the most visible part of the apex was placed in a 2% glutaraldehyde solution for 24 hours. The other half of each tooth was discarded. The fixed specimens were rinsed 3 times with a sodium cacodylate-buffered solution (0.1 mol/L, pH = 7.2), incubated in osmium tetroxide for 1 hour, dehydrated with ascending concentrations of ethyl alcohol (30%–100%), and placed in a desiccator for at least 24 hours. Each specimen was mounted on an aluminum stub, coated with 25 mm gold palladium, and examined under a scanning electron microscope (JEOL-5600 LV; JEOL, Tokyo, Japan). The photomicrographs were taken from the apical thirds of the root canals between 0.5 mm and 5 mm from the apical foramen at a magnification of 2000. The photomicrographs were analyzed by 3 examiners who were specialists in endodontics and were blind to group status. Each examiner scored the presence or absence of a smear layer in the apical third following the method described by Torabinejad et al (11) in which a score of 1 indicated no smear layer (no smear layer on the surface of the root canals; all tubules were clean and open), a score of 2 indicated a moderate smear layer (no smear layer on the surface of root canal, but tubules contained debris), and a score of 3 indicated a heavy smear layer (smear layer covered the root canal surface and the tubules). Before scoring, the 3 examiners assessed the first 20 specimens together for calibration purposes. The results were tabulated and submitted to statistical analysis. Statistical Analysis of the Data The categoric data were summarized by means of absolute frequency and relative percentages, and the numeric data were summarized JOE — Volume -, Number -, - 2015
Basic Research—Technology by means of the usual descriptive statistics of location and dispersion. The agreement between the 3 examiners regarding the presence or absence of a smear layer in the apical third of the root canal was evaluated with Cohen kappa. Comparisons between groups were analyzed statistically using the Kruskal-Wallis nonparametric analysis of variance and MannWhitney U tests (12). A level of significance of .05 was adopted for all tests, with a 95% confidence interval. The Statistical Package for the Social Sciences, version 13 (SPSS, Chicago, IL) was used.
Results Intraexaminer and Interexaminer Agreement Good agreement was shown between examiners 1 and 3 (k = 0.683) and examiners 2 and 3 (k = 0.721). Excellent agreement was shown between examiners 1 and 2 (k = 0.824), with a significance set at .05. This suggests that there was good to excellent reliability and reproducibility among the examiners (12), with values $0.60 for the different groups. The distribution of smear layer scores is presented in Table 1. The ultrasound group (group 4) performed significantly better than the rest of the groups with respect to smear layer removal in the apical third of root canal. A full 56.6% of the specimens revealed no smear layer (score 1), whereas 44.4% showed the presence of a moderate smear layer (score 2). No instance of a heavy smear layer (score 3) was observed. In the Nd:YAG laser group (group 5), 30% of the specimens presented no smear layer, 70% revealed the presence of a moderate smear layer, and no heavy smear layer was observed. In contrast, a heavy smear layer was observed on the surfaces of the root canals in the CanalBrush (group 3: 23.4%), ProTaper Universal (group 2:13.4%), and control (group 1: 86.6%) groups. The Kruskal-Wallis test revealed a statistically significant difference between the groups (P < .001), showing that the groups exhibited different degrees of capacity for smear layer removal in the apical third of the root canal. Table 2 shows the means and standard deviations of the groups. The Mann-Whitney U test for the comparison of the groups revealed statistically significant differences (P < .05) in all cases except between groups 2 and 3 (P = .321). All activation groups showed significantly lower smear layer scores than group 1. Groups 2 and 3 had similar smear layer scores, which were higher than groups 4 and 5. The null hypothesis was rejected. Figure 1A–F shows representative photomicrographs of each group.
Discussion After mechanical preparation, an amorphous, irregular layer known as the smear layer is formed on root canal walls. Possible deleterious effects may occur if the smear layer is not removed during root canal treatment. Microorganisms remaining in the smear layer after the instrumentation of an infected root canal space can survive and reinfect the canal. The smear layer has also been shown to hinder the penetraTABLE 1. Distribution of Smear Layer Scores Group (n = 10) 1 2 3 4 5
Score
Agitation technique
1 (%)
2 (%)
3 (%)
Control ProTaper Universal Canalbrush Ultrasound Laser
0 (0) 0 (0) 0 (0) 17 (56.6) 9 (30)
4 (13.4) 26 (86.6) 23 (76.6) 13 (44.4) 21 (70)
26 (86.6) 4 (13.4) 7 (23.4) 0 (0) 0 (0)
1, no smear layer; 2, moderate smear layer; 3, heavy smear layer.
JOE — Volume -, Number -, - 2015
TABLE 2. Comparisons between Groups according to Smear Layer Removal Mean ± SD Comparison
First group
Second group
P value*
Group 1 group 2 Group 1 group 3 Group 1 group 4 Group 1 group 5 Group 2 group 3 Group 2 group 4 Group 2 group 5 Group 3 group 4 Group 3 group 5 Group 4 group 5
2.87 0.35 2.87 0.35 2.87 0.35 2.87 0.35 2.13 0.35 2.13 0.35 2.13 0.35 2.23 0.43 2.23 0.43 1.43 0.50
2.13 0.35 2.23 0.43 1.43 0.50 1.70 0.47 2.23 0.43 1.43 0.50 1.70 0.47 1.43 0.50 1.70 0.47 1.70 0.47
