- Email: [email protected]
Debris Removal from the Mesial Root Canal System of Mandibular Molars with Laser-activated Irrigation
Basic Research—Technology
Debris Removal from the Mesial Root Canal System of Mandibular Molars with Laser-activated Irrigation Stamatina Passalidou, DDS, MSc, Filip Calberson, DDS, MSc, Mieke De Bruyne, DDS, MSc, PhD, Roeland De Moor, DDS, MSc, PhD, and Maarten August Meire, DDS, MSc, PhD Abstract Introduction: The purpose of this study was to compare in vitro the canal and isthmus debridement of manualdynamic, passive ultrasonic, and laser-activated irrigation with an Er:YAG laser in mesial roots of human mandibular molars. Methods: Fifty extracted mandibular molars with an isthmus were embedded in resin and sectioned axially 4 mm from the apex. The teeth were reassembled with guide pins and bolts, and the mesial canals were instrumented up to a ProTaper F2 rotary file (Dentsply Maillefer, Ballaigues, Switzerland). Teeth were randomly assigned to the following irrigant activation groups (n = 10): conventional needle irrigation (NI), manualdynamic irrigation with a ProTaper F2 gutta-percha cone, ultrasonically activated irrigation using a size 20 Irrisafe (Satelec Acteon, Merignac, France), and laser-activated irrigation (LAI) with an Er:YAG laser and a conical 400-mm fiber tip in the canal entrance or a 600-mm tip over the canal entrance. Root cross-sectional images were taken before and after final irrigation, and the area occupied by debris in the main canal and the isthmus was determined using image analysis software. Differences in debris before and after activation were statistically compared within and across groups. Results: Significant reductions in debris levels were observed in all groups, except for NI and manual-dynamic irrigation (canal only). None of the methods rendered the canal systems debris free. In the canal, LAI with an Er:YAG laser and a 600-mm tip over the canal entrance removed significantly more debris than NI. In the isthmus, LAI with an Er:YAG laser and a conical 400-mm fiber tip in the canal entrance removed significantly more debris than NI. Conclusions: Within the limitations of this in vitro study, canal and isthmus cleanliness significantly improved after irrigant activation. (J Endod 2018;-:1–5)
Key Words Er:YAG laser, isthmus, laser-activated irrigation, PIPS, root canal irrigation, ultrasonically activated irrigation
I
rrigation of the root caSignificance nal with antimicrobial Many irrigant activation techniques have been solutions is paramount to described, with great variation in the working thorough cleaning and mechanism and efficacy. This study found all disinfection of the root catested activation methods to aid in debriding the nal system. The irrigants mesial root canals of mandibular molars. flush away debris, clean the noninstrumented areas of the root canals, remove the smear layer, and disinfect the canal space (1– 3). The traditional syringe needle method of irrigation often fails in adequate delivery and penetration of irrigant solutions within the complex 3-dimensional microstructure of the canal system because the fluid penetration in the apical third and beyond the main canal is limited (4). Therefore, irrigant activation techniques have been suggested to improve their distribution in the canal system and increase irrigation effectiveness (5). An isthmus is a challenging area to debride because of its confined dimensions, deep extension, and frequent clogging with hard and soft tissue debris during instrumentation with rotary NiTi instruments (6). This may result in remaining pulpal tissue, debris, or microorganisms, yielding potential for treatment failure (7). The incidence of an isthmus is high (54.8%) in the mesial root of mandibular molars, particularly in sections 3–5 mm from the apex (8, 9). Different irrigant activation techniques have been proposed. Manual dynamic irrigation (MDI) involves the vertical movement of a well-fitting gutta percha within the instrumented canal, improving displacement and exchange of irrigant. MDI has been proven to result in better root canal cleaning than conventional needle irrigation (NI) and is considered simple and cost-effective (10, 11). Ultrasonically activated irrigation (UAI) implies the activation of irrigant by a noncutting, ultrasonically oscillating instrument placed in the center of the canal after its shaping (12). Although cavitation effects have been observed with UAI (13), its main cleaning action is attributed to acoustic microstreaming. UAI has been shown to be more effective than conventional irrigation in cleaning root canal extensions (14). Some studies have specifically shown a significantly cleaner isthmus when UAI is used in comparison with syringe irrigation (15). Laser-activated irrigation (LAI) is another method of irrigant activation. With LAI, the tip of an erbium laser is activated within a canal brim full of irrigant. The effect of LAI is based solely on cavitation. The radiation emitted by erbium lasers is strongly absorbed by water or water-based root canal irrigants (16). Pulsed laser operation results in expanding and imploding vapor bubbles at the fiber tip, resulting in considerable
From the Department of Restorative Dentistry and Endodontology, Dental School, Ghent, Belgium. Address requests for reprints to Dr Roeland De Moor, Department of Restorative Dentistry and Endodontology, Dental School, Ghent University, Ghent University Hospital, De Pintelaan 185/P8, B-9000 Ghent, Belgium. E-mail address: [email protected] 0099-2399/$ - see front matter Copyright ª 2018 American Association of Endodontists. https://doi.org/10.1016/j.joen.2018.06.007
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Basic Research—Technology
Figure 1. Specimen preparation. (A) A mandibular molar with an isthmus based on cone-beam computed tomographic imaging. (B) The specimen embedded in resin. (C) The specimen after the placement of bolts and guide pins in predrilled shafts. (D) The specimen after sectioning and reconstruction.
fluid movement inside the canal (17), shock waves in the fluid at the point of collapse (18), and secondary cavitation that can cause acoustic streaming. In the photon-induced photoacoustic streaming approach, a conical fiber tip on a pulsed Er:YAG laser is used with low pulse energies (10 or 20 mJ) and a very short pulse length (50 microseconds), resulting in high peak powers and hence more efficient cavitation generation. Although the fiber tip originally was held in the canal entrance, the tip position has been changed to the pulp chamber. It is currently unclear which LAI approach better cleans the isthmus and how LAI compares with UAI in canal and isthmus debridement. Therefore, the aim of the present study was to compare in vitro the canal and isthmus debridement of syringe irrigation, MDI, UAI, and 2 LAI approaches.
Methods Tooth Selection Extracted human mandibular molars were subjected to conebeam computed tomographic imaging (Promax 3D; Planmeca, Helsinki, Finland), in order to explore the presence of an isthmus in the mesial root. All the teeth had completed root formation and had been extracted for reasons unrelated to the current study. The sample collection and study methodology were approved by the institutional ethics committee (project no. EC/2018/0543). Tooth imaging continued until 50 teeth with an isthmus were identified. Specimen Preparation The experimental setup is a modification of the protocol as described by Klyn et al (19). After standard access cavity preparation, cusps were flattened to obtain stable reference points. Coronal interferences in both mesial canals were removed with ProTaper Universal Sx and S1 instruments (Dentsply Maillefer, Ballaigues, Switzerland). Then, the working length was established by subtracting 1 mm from the length at which the tip of an ISO10 file was just visible at the apical foramen. A glide path was made with an ISO 15 K-file. The apex of each root was 2
Passalidou et al.
then sealed with flowable composite resin (Filtek Supreme; 3M ESPE, St Paul, MN). Each tooth was then embedded in transparent resin (Orthocryl; Dentaurum BVBA, Antwerp, Belgium), resulting in cubical specimens with 25-mm edges. Four cylindrical holes were drilled in the resin, parallel to the long axis of the tooth. The blocks were then sectioned axially at 4 mm from the apex using a low-speed saw (Isomet; Buehler, Dusseldorf, Germany). Standardized high-resolution images of the coronal surface of the apical section were then taken using a digital single-lens reflex camera (Nikon D300; Nikon Corp, Tokyo, Japan) with a macrolens (Medical Nikkor 120 mm f/4.0, Nikon Corp) mounted on a platform with an adjustable stage for positioning of the sections. The slices were reassembled and fixated with the help of guide pins and metal bolts in the predrilled shafts (Fig. 1A–D).
Canal Preparation The mesial roots were then prepared with rotary instruments (ProTaper Universal) up to a ProTaper F2 file. The instrument sequence was S1, S2, F1, and F2. The canals were rinsed with 1 mL sodium hypochlorite (NaOCl) 2.5% after each file using a 3-mL syringe and a 27-G needle (Monoject; Tyco Healthcare, Mansfield, MA). After drying with paper points, the specimens were disassembled, and images of the coronal surface of each section were taken as described previously. These images comprised the postpreparation images. Final Irrigation Teeth were then randomly assigned to 1 of 5 groups (n = 10) representing different irrigant activation methods: 1. Conventional NI with 4 mL 2.5% NaOCl using a 27-G endodontic needle (Monoject). The needle was moved up and down in the canal with a flow rate of approximately 0.3 mL/s. 2. MDI: a ProTaper F2 gutta-percha cone was inserted to the working length. A total of 100 push-pull strokes were performed manually in 1 minute. The canal was then irrigated with 4 mL 2.5% NaOCl JOE — Volume -, Number -, - 2018
Basic Research—Technology using a 30-G irrigating needle (Appli-Vac; Vista Dental Products, Racine, WI). 3. UAI: a noncutting #20 file (Irrisafe; Satelec Acteon, Merignac, France) driven by an ultrasonic device (Suprasson Pmax Newtron, Satelec Acteon) was used in the canal for 3 20 seconds at 50% power. The file was prebent to allow insertion up to the working length minus 1 mm. In between each 20-second cycle, the canal was rinsed with 1 mL NaOCl and finally with 2 mL. 4. LAI400: a 2.940-nm Er:YAG laser (AT Fidelis; Fotona, Ljubljana, Slovenia) equipped with a handpiece (R14-PIPS, Fotona) holding a conical 400-mm-diameter fiber (XPulse 400/14, Fotona) was used to activate the irrigant. The fiber tip was placed in the canal entrance and activated for 3 20 seconds. The pulse energy was 20 mJ, the frequency was 20 Hz, and the pulse length was 50 microseconds. In between each 20-second cycle, the canal was rinsed with 1 mL NaOCl and finally with 2 mL. 5. LAI600: the same laser and handpiece were used to hold a conical 600-mm-diameter fiber (XPulse 600/14; Fotona). This time the tip of the fiber was placed in the pulp chamber over the canal
entrance. The remainder was identical to that performed in the LAI400 group. The root canals were dried with paper points, and images of the sections were taken as described previously.
Evaluation Method Each picture was analyzed using imaging software (SigmaScan Pro; Systat Software, San Jose, CA, and Adobe Photoshop CS5; Adobe Systems Inc, San Jose, CA). The outline of the root canal and the isthmus was traced as well as the area occupied by debris within the canal or within the isthmus. These areas were quantified by counting the number of pixels. The debris percentage was calculated as the ratio between the debris area and the total canal or isthmus area. The debris difference was defined as debris percentage before activation minus debris percentage after activation. Statistical analysis was performed using SPSS Statistics Version 23.0 (IBM, Armonk, USA). One-way analysis of variance (ANOVA) was used to compare the debris differences across the different activation groups. Because the debris percentages before
Figure 2. Representative images of the sections showing canals and isthmuses (A) before instrumentation, (B) after instrumentation, and (C) after irrigant activation with a (1) 27-G needle, (2) MDI, (3) UAI, (4) LAI400, and (5) LAI600.
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Basic Research—Technology TABLE 1. The Mean Debris Percentages (Standard Deviation) in the Canal Area before and after Irrigant Activation (n = 10) Group
Mean debris % pre
Mean debris % post
Difference (%)
NI MDI LAI400 LAI600 UAI
22.5 (16.4) 27.0 (12.9) 24.7 (13.7) 29.6 (20.5) 26.4 (13.6)
18.9 (11.4) 17.4 (9.5) 5.7 (8.1)* 3.3 (4.5)* 5.5 (5.9)*
3.6 (12.4)a 9.6 (18.6)a,b 19.1 (12.8)a,b 26.3 (18.5)b 20.9 (13.1)a,b
LAI400, laser-activated irrigation with a conical 400-mm fiber tip in the canal entrance; LAI600, laseractivated irrigation with a 600-mm tip over the canal entrance; MDI, manual dynamic irrigation; NI, needle irrigation; UAI, ultrasonic-activated irrigation. Different superscript letters indicate significant debris differences between groups. *A significant difference in debris percentage before and after activation.
and after irrigant activation were not normally distributed in all groups, the Wilcoxon test was used to compare these data across the groups. The significance level was set at .05.
Results The presence of an isthmus was confirmed in all specimens. Before activation, mean debris levels in the isthmus (60.3%) were significantly higher than those in the canal (26.0%). Representative section images from all groups are shown in Figure 2A–C.
Main Canal Table 1 shows the mean debris percentages in the canal before and after irrigant activation in the different groups. No significant differences in debris percentage before activation were observed between groups (P > .05). When comparing debris levels before and after activation, statistically significant differences were noted in the UAI, LAI 400, and LAI600 groups (Wilcoxon test, P < .05) but not the NI and MDI groups (P > .05). Statistically significant differences in debris difference were observed only between NI and LAI600 (1-way analysis of variance, post hoc Tukey test, P > .05). Isthmus Table 2 shows the mean debris percentages in the isthmus before and after irrigant activation in the different groups. No significant differences in isthmus debris percentage before activation were observed between groups (ANOVA, P > .05). When comparing debris levels before and after activation, statistically significant differences were noted in all groups (Wilcoxon test, P < .05). Statistically significant differences in debris difference were observed only between NI and LAI400 (1-way ANOVA, post hoc Games-Howell test, P < .05). TABLE 2. The Mean Debris Percentages (Standard Deviation) in the Isthmus Area before and after Irrigant Activation (n = 10) Group
Mean debris % pre
Mean debris % post
Difference (%)
NI MDI LAI 400 LAI 600 UAI
53.3 (36.3) 58.0 (28.3) 65.2 (26.1) 62.8 (36.6) 62.1 (25.3)
34.6 (23.8)* 31.3 (23.5)* 6.4 (7.9)* 15.9 (30.8)* 34.7 (29.4)*
18.7 (16.6)a 26.8 (26.8)a,b 58.8 (25.9)b 46.9 (43.5)a,b 27.4 (23.1)a,b
LAI400, laser-activated irrigation with a conical 400-mm fiber tip in the canal entrance; LAI600, laseractivated irrigation with a 600-mm tip over the canal entrance; MDI, manual dynamic irrigation; NI, needle irrigation; UAI, ultrasonic-activated irrigation. Different superscript letters indicate significant debris differences between groups. *A significant difference in debris percentage before and after activation.
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Discussion This study sought to quantify debris removal using different final irrigation protocols from both the canals and isthmus of mesial roots of mandibular molars. The model that was used in this study was based on the K-Kube described by Klyn et al (19). The combination of guide pins and tightening bolts provided the necessary repositioning precision and compressive force to the tooth slices, allowing investigation of root cross sections at the different stages of root canal preparation and irrigation. Although the K-Kube requires cutting of the tooth specimen, it offers the advantage of evaluating both hard and soft tissue debris, which is not possible with (nondestructive) micro–computed tomographic analysis. This model also provides a closed system, a prerequisite to study irrigation protocols (20). When comparing debris levels before and after activation, UAI and LAI resulted in significantly improved cleaning in the canal area compared with syringe irrigation and MDI. In the isthmus area, improved canal cleaning was determined in all activation groups. The results of this study indicate that after chemomechanical canal preparation, additional canal system debridement can be obtained with activation techniques, confirming the role of these additional activation steps. In the present study, the differences between the experimental groups were not statistically significant. The only significant differences were between the LAI and the control (NI) groups. When considering the present results, the great variation in the preoperative debris percentages is notable. These great deviations could explain the lack of significant differences between groups. The debris score variations were especially in the isthmi, a finding also confirmed in other studies (19, 21). This variation in preoperative debris levels can have to do with the presence or absence of an (intact) pulp at the beginning of the experiment, with the soft pulp tissue facilitating accumulation of hard tissue debris in canal extensions/isthmi in comparison with a pulpless tooth. Root canal system anatomy can also play a role, with a wide isthmus and a limited intercanal distance acting as factors promoting flushing of debris. No attempts were made to control these factors in the present study. The degree of debris reduction with LAI in both the canal and isthmus area is in accordance with previous in vitro studies in which LAI with erbium lasers has been shown to be more effective than syringe/needle-based irrigation in terms of debris removal from artificial root canal irregularities (22–25). No statistically significant differences in debris removal between LAI or UAI were obtained in the present study, neither for the canal nor the isthmus area. Other studies comparing LAI with UAI in isthmi, canal extensions, or irregularities came to a similar conclusion (24, 26). However, other investigations found LAI to be significantly better than UAI in removing dentinal debris in an artificial groove in the canal wall (25, 27). The lasing conditions of the 50-microsecond pulse duration, the 20-mJ pulse energy, and conical fiber tip delivery, as used in this experiment, represent the photon-induced photo acoustic streaming approach. In this approach, the combination of a conical tip and very short pulses produce profound irrigant dynamics, whereas the low pulse energy produces minimal thermal effects (18, 28). When comparing the 2 LAI protocols, no statistically significant differences were observed. More studies are needed to compare the efficacy of LAI with these 2 approaches. In the main canals, MDI did not result in a significant reduction in debris level, whereas in the isthmus debris reduction was significant. These results suggest that MDI works better when a lateral “escape way” for the debris is available, which is the case in an (open) isthmus, and not in a dead-ending canal extension. Both Susin et al (29) and
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Basic Research—Technology Parente et al (30) hypothesized that the irrigant displacement could be hindered by a relatively close adaptation of the gutta-percha cone to the canal wall, resulting in the debris settling back into the canal system after removal of the gutta-percha cone. In the present study, the greatest debris reductions were obtained with the LAI protocols. However, these results were not significantly different from the other activation groups, probably because of great variation in preoperative debris levels. Nevertheless, in many studies involving LAI, LAI cleaning results were either better than those of UAI or other activation techniques (23–25, 27); or the results did not differ significantly from these groups, while net outcome were better (26). This trend suggests LAI possesses a stronger activation action. It is hypothesized that this is because of the violent fluid dynamics caused by the expanding and imploding bubbles at the fiber tip of the Er:YAG laser. This physical process appears to be more vigorous than acoustic fluid agitation with ultrasound and other activation techniques. Within the limitations of this in vitro study, it can be concluded that canal and isthmus cleanliness significantly improved after the final irrigation regimen in each group.
Acknowledgments The authors deny any conflicts of interest related to this study.
References 1. Mader CL, Baumgartner JC, Peters DD. Scanning electron microscopic investigation of the smeared layer on root canal walls. J Endod 1984;10:477–83. 2. Paque F, Boessler C, Zehnder M. Accumulated hard tissue debris levels in mesial roots of mandibular molars after sequential irrigation steps. Int Endod J 2011;44:148–53. 3. Peters OA, Schonenberger K, Laib A. Effects of four Ni-Ti preparation techniques on root canal geometry assessed by micro computed tomography. Int Endod J 2001;34: 221–30. 4. Ram Z. Effectiveness of root canal irrigation. Oral Surg Oral Med Oral Pathol 1977; 44:306–12. 5. Gu LS, Kim JR, Ling J, et al. Review of contemporary irrigant agitation techniques and devices. J Endod 2009;35:791–804. 6. Paque F, Laib A, Gautschi H, et al. Hard-tissue debris accumulation analysis by highresolution computed tomography scans. J Endod 2009;35:1044–7. 7. Nair PN, Henry S, Cano V, et al. Microbial status of apical root canal system of human mandibular first molars with primary apical periodontitis after “one-visit” endodontic treatment. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2005;99:231–52. 8. Teixeira FB, Sano CL, Gomes BP, et al. A preliminary in vitro study of the incidence and position of the root canal isthmus in maxillary and mandibular first molars. Int Endod J 2003;36:276–80. 9. de Pablo OV, Estevez R, Peix Sanchez M, et al. Root anatomy and canal configuration of the permanent mandibular first molar: a systematic review. J. Endod 2010;36: 1919–31. 10. Huang TY, Gulabivala K, Ng YL. A bio-molecular film ex-vivo model to evaluate the influence of canal dimensions and irrigation variables on the efficacy of irrigation. Int Endod J 2008;41:60–71.
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11. Jiang LM, Lak B, Eijsvogels LM, et al. Comparison of the cleaning efficacy of different final irrigation techniques. J Endod 2012;38:838–41. 12. van der Sluis LW, Versluis M, Wu MK, et al. Passive ultrasonic irrigation of the root canal: a review of the literature. Int Endod J 2007;40:415–26. 13. Macedo RG, Verhaagen B, Fernandez Rivas D, et al. Sonochemical and high-speed optical characterization of cavitation generated by an ultrasonically oscillating dental file in root canal models. Ultrason Sonochem 2014;21:324–35. 14. Jiang LM, Verhaagen B, Versluis M, et al. The influence of the ultrasonic intensity on the cleaning efficacy of passive ultrasonic irrigation. J Endod 2011;37:688–92. 15. Gutarts R, Nusstein J, Reader A, et al. In vivo debridement efficacy of ultrasonic irrigation following hand-rotary instrumentation in human mandibular molars. J Endod 2005;31:166–70. 16. Meire MA, Poelman D, De Moor RJ. Optical properties of root canal irrigants in the 300-3,000-nm wavelength region. Lasers Med Sci 2014;29:1557–62. 17. Blanken J, De Moor RJ, Meire M, et al. Laser induced explosive vapor and cavitation resulting in effective irrigation of the root canal. Part 1: a visualization study. Lasers Surg Med 2009;41:514–9. 18. Gregorcic P, Jezersek M, Mozina J. Optodynamic energy-conversion efficiency during an Er:YAG-laser-pulse delivery into a liquid through different fiber-tip geometries. J Biomed Opt 2012;17:075006. 19. Klyn SL, Kirkpatrick TC, Rutledge RE. In vitro comparisons of debris removal of the EndoActivator system, the F file, ultrasonic irrigation, and NaOCl irrigation alone after hand-rotary instrumentation in human mandibular molars. J Endod 2010;36: 1367–71. 20. Tay FR, Gu LS, Schoeffel GJ, et al. Effect of vapor lock on root canal debridement by using a side-vented needle for positive-pressure irrigant delivery. J Endod 2010;36: 745–50. 21. Howard RK, Kirkpatrick TC, Rutledge RE, et al. Comparison of debris removal with three different irrigation techniques. J. Endod 2011;37:1301–5. 22. Lloyd A, Uhles JP, Clement DJ, et al. Elimination of intracanal tissue and debris through a novel laser-activated system assessed using high-resolution microcomputed tomography: a pilot study. J Endod 2014;40:584–7. 23. de Groot SD, Verhaagen B, Versluis M, et al. Laser-activated irrigation within root canals: cleaning efficacy and flow visualization. Int Endod J 2009;42:1077–83. 24. De Moor RJ, Meire M, Goharkhay K, et al. Efficacy of ultrasonic versus laseractivated irrigation to remove artificially placed dentin debris plugs. J Endod 2010;36:1580–3. 25. Arslan H, Capar ID, Saygili G, et al. Effect of photon-initiated photoacoustic streaming on removal of apically placed dentinal debris. Int Endod J 2014;47: 1072–7. 26. Verstraeten J, Jacquet W, De Moor RJ, et al. Hard tissue debris removal from the mesial root canal system of mandibular molars with ultrasonically and laseractivated irrigation: a micro-computed tomography study. Lasers Med Sci 2017; 32:1965–70. 27. De Moor RJ, Blanken J, Meire M, et al. Laser induced explosive vapor and cavitation resulting in effective irrigation of the root canal. Part 2: evaluation of the efficacy. Lasers Surg Med 2009;41:520–3. 28. Olivi G, DiVito E. Advanced laser-activated irrigation: PIPS technique and clinical protocols. In: Olivi G, de Moor RJ, DiVito E, eds. Lasers in Endodontics: Scientific Background and Applications. London, UK: Springer; 2016. 29. Susin L, Liu Y, Yoon JC, et al. Canal and isthmus debridement efficacies of two irrigant agitation techniques in a closed system. Int Endod J 2010;43:1077–90. 30. Parente JM, Loushine RJ, Susin L, et al. Root canal debridement using manual dynamic agitation or the EndoVac for final irrigation in a closed system and an open system. Int Endod J 2010;43:1001–12.
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Debris Removal from the Mesial Root Canal System of Mandibular Molars with Laser-activated Irrigation Stamatina Passalidou, DDS, MSc, Filip Calberson, DDS, MSc, Mieke De Bruyne, DDS, MSc, PhD, Roeland De Moor, DDS, MSc, PhD, and Maarten August Meire, DDS, MSc, PhD Abstract Introduction: The purpose of this study was to compare in vitro the canal and isthmus debridement of manualdynamic, passive ultrasonic, and laser-activated irrigation with an Er:YAG laser in mesial roots of human mandibular molars. Methods: Fifty extracted mandibular molars with an isthmus were embedded in resin and sectioned axially 4 mm from the apex. The teeth were reassembled with guide pins and bolts, and the mesial canals were instrumented up to a ProTaper F2 rotary file (Dentsply Maillefer, Ballaigues, Switzerland). Teeth were randomly assigned to the following irrigant activation groups (n = 10): conventional needle irrigation (NI), manualdynamic irrigation with a ProTaper F2 gutta-percha cone, ultrasonically activated irrigation using a size 20 Irrisafe (Satelec Acteon, Merignac, France), and laser-activated irrigation (LAI) with an Er:YAG laser and a conical 400-mm fiber tip in the canal entrance or a 600-mm tip over the canal entrance. Root cross-sectional images were taken before and after final irrigation, and the area occupied by debris in the main canal and the isthmus was determined using image analysis software. Differences in debris before and after activation were statistically compared within and across groups. Results: Significant reductions in debris levels were observed in all groups, except for NI and manual-dynamic irrigation (canal only). None of the methods rendered the canal systems debris free. In the canal, LAI with an Er:YAG laser and a 600-mm tip over the canal entrance removed significantly more debris than NI. In the isthmus, LAI with an Er:YAG laser and a conical 400-mm fiber tip in the canal entrance removed significantly more debris than NI. Conclusions: Within the limitations of this in vitro study, canal and isthmus cleanliness significantly improved after irrigant activation. (J Endod 2018;-:1–5)
Key Words Er:YAG laser, isthmus, laser-activated irrigation, PIPS, root canal irrigation, ultrasonically activated irrigation
I
rrigation of the root caSignificance nal with antimicrobial Many irrigant activation techniques have been solutions is paramount to described, with great variation in the working thorough cleaning and mechanism and efficacy. This study found all disinfection of the root catested activation methods to aid in debriding the nal system. The irrigants mesial root canals of mandibular molars. flush away debris, clean the noninstrumented areas of the root canals, remove the smear layer, and disinfect the canal space (1– 3). The traditional syringe needle method of irrigation often fails in adequate delivery and penetration of irrigant solutions within the complex 3-dimensional microstructure of the canal system because the fluid penetration in the apical third and beyond the main canal is limited (4). Therefore, irrigant activation techniques have been suggested to improve their distribution in the canal system and increase irrigation effectiveness (5). An isthmus is a challenging area to debride because of its confined dimensions, deep extension, and frequent clogging with hard and soft tissue debris during instrumentation with rotary NiTi instruments (6). This may result in remaining pulpal tissue, debris, or microorganisms, yielding potential for treatment failure (7). The incidence of an isthmus is high (54.8%) in the mesial root of mandibular molars, particularly in sections 3–5 mm from the apex (8, 9). Different irrigant activation techniques have been proposed. Manual dynamic irrigation (MDI) involves the vertical movement of a well-fitting gutta percha within the instrumented canal, improving displacement and exchange of irrigant. MDI has been proven to result in better root canal cleaning than conventional needle irrigation (NI) and is considered simple and cost-effective (10, 11). Ultrasonically activated irrigation (UAI) implies the activation of irrigant by a noncutting, ultrasonically oscillating instrument placed in the center of the canal after its shaping (12). Although cavitation effects have been observed with UAI (13), its main cleaning action is attributed to acoustic microstreaming. UAI has been shown to be more effective than conventional irrigation in cleaning root canal extensions (14). Some studies have specifically shown a significantly cleaner isthmus when UAI is used in comparison with syringe irrigation (15). Laser-activated irrigation (LAI) is another method of irrigant activation. With LAI, the tip of an erbium laser is activated within a canal brim full of irrigant. The effect of LAI is based solely on cavitation. The radiation emitted by erbium lasers is strongly absorbed by water or water-based root canal irrigants (16). Pulsed laser operation results in expanding and imploding vapor bubbles at the fiber tip, resulting in considerable
From the Department of Restorative Dentistry and Endodontology, Dental School, Ghent, Belgium. Address requests for reprints to Dr Roeland De Moor, Department of Restorative Dentistry and Endodontology, Dental School, Ghent University, Ghent University Hospital, De Pintelaan 185/P8, B-9000 Ghent, Belgium. E-mail address: [email protected] 0099-2399/$ - see front matter Copyright ª 2018 American Association of Endodontists. https://doi.org/10.1016/j.joen.2018.06.007
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Figure 1. Specimen preparation. (A) A mandibular molar with an isthmus based on cone-beam computed tomographic imaging. (B) The specimen embedded in resin. (C) The specimen after the placement of bolts and guide pins in predrilled shafts. (D) The specimen after sectioning and reconstruction.
fluid movement inside the canal (17), shock waves in the fluid at the point of collapse (18), and secondary cavitation that can cause acoustic streaming. In the photon-induced photoacoustic streaming approach, a conical fiber tip on a pulsed Er:YAG laser is used with low pulse energies (10 or 20 mJ) and a very short pulse length (50 microseconds), resulting in high peak powers and hence more efficient cavitation generation. Although the fiber tip originally was held in the canal entrance, the tip position has been changed to the pulp chamber. It is currently unclear which LAI approach better cleans the isthmus and how LAI compares with UAI in canal and isthmus debridement. Therefore, the aim of the present study was to compare in vitro the canal and isthmus debridement of syringe irrigation, MDI, UAI, and 2 LAI approaches.
Methods Tooth Selection Extracted human mandibular molars were subjected to conebeam computed tomographic imaging (Promax 3D; Planmeca, Helsinki, Finland), in order to explore the presence of an isthmus in the mesial root. All the teeth had completed root formation and had been extracted for reasons unrelated to the current study. The sample collection and study methodology were approved by the institutional ethics committee (project no. EC/2018/0543). Tooth imaging continued until 50 teeth with an isthmus were identified. Specimen Preparation The experimental setup is a modification of the protocol as described by Klyn et al (19). After standard access cavity preparation, cusps were flattened to obtain stable reference points. Coronal interferences in both mesial canals were removed with ProTaper Universal Sx and S1 instruments (Dentsply Maillefer, Ballaigues, Switzerland). Then, the working length was established by subtracting 1 mm from the length at which the tip of an ISO10 file was just visible at the apical foramen. A glide path was made with an ISO 15 K-file. The apex of each root was 2
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then sealed with flowable composite resin (Filtek Supreme; 3M ESPE, St Paul, MN). Each tooth was then embedded in transparent resin (Orthocryl; Dentaurum BVBA, Antwerp, Belgium), resulting in cubical specimens with 25-mm edges. Four cylindrical holes were drilled in the resin, parallel to the long axis of the tooth. The blocks were then sectioned axially at 4 mm from the apex using a low-speed saw (Isomet; Buehler, Dusseldorf, Germany). Standardized high-resolution images of the coronal surface of the apical section were then taken using a digital single-lens reflex camera (Nikon D300; Nikon Corp, Tokyo, Japan) with a macrolens (Medical Nikkor 120 mm f/4.0, Nikon Corp) mounted on a platform with an adjustable stage for positioning of the sections. The slices were reassembled and fixated with the help of guide pins and metal bolts in the predrilled shafts (Fig. 1A–D).
Canal Preparation The mesial roots were then prepared with rotary instruments (ProTaper Universal) up to a ProTaper F2 file. The instrument sequence was S1, S2, F1, and F2. The canals were rinsed with 1 mL sodium hypochlorite (NaOCl) 2.5% after each file using a 3-mL syringe and a 27-G needle (Monoject; Tyco Healthcare, Mansfield, MA). After drying with paper points, the specimens were disassembled, and images of the coronal surface of each section were taken as described previously. These images comprised the postpreparation images. Final Irrigation Teeth were then randomly assigned to 1 of 5 groups (n = 10) representing different irrigant activation methods: 1. Conventional NI with 4 mL 2.5% NaOCl using a 27-G endodontic needle (Monoject). The needle was moved up and down in the canal with a flow rate of approximately 0.3 mL/s. 2. MDI: a ProTaper F2 gutta-percha cone was inserted to the working length. A total of 100 push-pull strokes were performed manually in 1 minute. The canal was then irrigated with 4 mL 2.5% NaOCl JOE — Volume -, Number -, - 2018
Basic Research—Technology using a 30-G irrigating needle (Appli-Vac; Vista Dental Products, Racine, WI). 3. UAI: a noncutting #20 file (Irrisafe; Satelec Acteon, Merignac, France) driven by an ultrasonic device (Suprasson Pmax Newtron, Satelec Acteon) was used in the canal for 3 20 seconds at 50% power. The file was prebent to allow insertion up to the working length minus 1 mm. In between each 20-second cycle, the canal was rinsed with 1 mL NaOCl and finally with 2 mL. 4. LAI400: a 2.940-nm Er:YAG laser (AT Fidelis; Fotona, Ljubljana, Slovenia) equipped with a handpiece (R14-PIPS, Fotona) holding a conical 400-mm-diameter fiber (XPulse 400/14, Fotona) was used to activate the irrigant. The fiber tip was placed in the canal entrance and activated for 3 20 seconds. The pulse energy was 20 mJ, the frequency was 20 Hz, and the pulse length was 50 microseconds. In between each 20-second cycle, the canal was rinsed with 1 mL NaOCl and finally with 2 mL. 5. LAI600: the same laser and handpiece were used to hold a conical 600-mm-diameter fiber (XPulse 600/14; Fotona). This time the tip of the fiber was placed in the pulp chamber over the canal
entrance. The remainder was identical to that performed in the LAI400 group. The root canals were dried with paper points, and images of the sections were taken as described previously.
Evaluation Method Each picture was analyzed using imaging software (SigmaScan Pro; Systat Software, San Jose, CA, and Adobe Photoshop CS5; Adobe Systems Inc, San Jose, CA). The outline of the root canal and the isthmus was traced as well as the area occupied by debris within the canal or within the isthmus. These areas were quantified by counting the number of pixels. The debris percentage was calculated as the ratio between the debris area and the total canal or isthmus area. The debris difference was defined as debris percentage before activation minus debris percentage after activation. Statistical analysis was performed using SPSS Statistics Version 23.0 (IBM, Armonk, USA). One-way analysis of variance (ANOVA) was used to compare the debris differences across the different activation groups. Because the debris percentages before
Figure 2. Representative images of the sections showing canals and isthmuses (A) before instrumentation, (B) after instrumentation, and (C) after irrigant activation with a (1) 27-G needle, (2) MDI, (3) UAI, (4) LAI400, and (5) LAI600.
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Basic Research—Technology TABLE 1. The Mean Debris Percentages (Standard Deviation) in the Canal Area before and after Irrigant Activation (n = 10) Group
Mean debris % pre
Mean debris % post
Difference (%)
NI MDI LAI400 LAI600 UAI
22.5 (16.4) 27.0 (12.9) 24.7 (13.7) 29.6 (20.5) 26.4 (13.6)
18.9 (11.4) 17.4 (9.5) 5.7 (8.1)* 3.3 (4.5)* 5.5 (5.9)*
3.6 (12.4)a 9.6 (18.6)a,b 19.1 (12.8)a,b 26.3 (18.5)b 20.9 (13.1)a,b
LAI400, laser-activated irrigation with a conical 400-mm fiber tip in the canal entrance; LAI600, laseractivated irrigation with a 600-mm tip over the canal entrance; MDI, manual dynamic irrigation; NI, needle irrigation; UAI, ultrasonic-activated irrigation. Different superscript letters indicate significant debris differences between groups. *A significant difference in debris percentage before and after activation.
and after irrigant activation were not normally distributed in all groups, the Wilcoxon test was used to compare these data across the groups. The significance level was set at .05.
Results The presence of an isthmus was confirmed in all specimens. Before activation, mean debris levels in the isthmus (60.3%) were significantly higher than those in the canal (26.0%). Representative section images from all groups are shown in Figure 2A–C.
Main Canal Table 1 shows the mean debris percentages in the canal before and after irrigant activation in the different groups. No significant differences in debris percentage before activation were observed between groups (P > .05). When comparing debris levels before and after activation, statistically significant differences were noted in the UAI, LAI 400, and LAI600 groups (Wilcoxon test, P < .05) but not the NI and MDI groups (P > .05). Statistically significant differences in debris difference were observed only between NI and LAI600 (1-way analysis of variance, post hoc Tukey test, P > .05). Isthmus Table 2 shows the mean debris percentages in the isthmus before and after irrigant activation in the different groups. No significant differences in isthmus debris percentage before activation were observed between groups (ANOVA, P > .05). When comparing debris levels before and after activation, statistically significant differences were noted in all groups (Wilcoxon test, P < .05). Statistically significant differences in debris difference were observed only between NI and LAI400 (1-way ANOVA, post hoc Games-Howell test, P < .05). TABLE 2. The Mean Debris Percentages (Standard Deviation) in the Isthmus Area before and after Irrigant Activation (n = 10) Group
Mean debris % pre
Mean debris % post
Difference (%)
NI MDI LAI 400 LAI 600 UAI
53.3 (36.3) 58.0 (28.3) 65.2 (26.1) 62.8 (36.6) 62.1 (25.3)
34.6 (23.8)* 31.3 (23.5)* 6.4 (7.9)* 15.9 (30.8)* 34.7 (29.4)*
18.7 (16.6)a 26.8 (26.8)a,b 58.8 (25.9)b 46.9 (43.5)a,b 27.4 (23.1)a,b
LAI400, laser-activated irrigation with a conical 400-mm fiber tip in the canal entrance; LAI600, laseractivated irrigation with a 600-mm tip over the canal entrance; MDI, manual dynamic irrigation; NI, needle irrigation; UAI, ultrasonic-activated irrigation. Different superscript letters indicate significant debris differences between groups. *A significant difference in debris percentage before and after activation.
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Discussion This study sought to quantify debris removal using different final irrigation protocols from both the canals and isthmus of mesial roots of mandibular molars. The model that was used in this study was based on the K-Kube described by Klyn et al (19). The combination of guide pins and tightening bolts provided the necessary repositioning precision and compressive force to the tooth slices, allowing investigation of root cross sections at the different stages of root canal preparation and irrigation. Although the K-Kube requires cutting of the tooth specimen, it offers the advantage of evaluating both hard and soft tissue debris, which is not possible with (nondestructive) micro–computed tomographic analysis. This model also provides a closed system, a prerequisite to study irrigation protocols (20). When comparing debris levels before and after activation, UAI and LAI resulted in significantly improved cleaning in the canal area compared with syringe irrigation and MDI. In the isthmus area, improved canal cleaning was determined in all activation groups. The results of this study indicate that after chemomechanical canal preparation, additional canal system debridement can be obtained with activation techniques, confirming the role of these additional activation steps. In the present study, the differences between the experimental groups were not statistically significant. The only significant differences were between the LAI and the control (NI) groups. When considering the present results, the great variation in the preoperative debris percentages is notable. These great deviations could explain the lack of significant differences between groups. The debris score variations were especially in the isthmi, a finding also confirmed in other studies (19, 21). This variation in preoperative debris levels can have to do with the presence or absence of an (intact) pulp at the beginning of the experiment, with the soft pulp tissue facilitating accumulation of hard tissue debris in canal extensions/isthmi in comparison with a pulpless tooth. Root canal system anatomy can also play a role, with a wide isthmus and a limited intercanal distance acting as factors promoting flushing of debris. No attempts were made to control these factors in the present study. The degree of debris reduction with LAI in both the canal and isthmus area is in accordance with previous in vitro studies in which LAI with erbium lasers has been shown to be more effective than syringe/needle-based irrigation in terms of debris removal from artificial root canal irregularities (22–25). No statistically significant differences in debris removal between LAI or UAI were obtained in the present study, neither for the canal nor the isthmus area. Other studies comparing LAI with UAI in isthmi, canal extensions, or irregularities came to a similar conclusion (24, 26). However, other investigations found LAI to be significantly better than UAI in removing dentinal debris in an artificial groove in the canal wall (25, 27). The lasing conditions of the 50-microsecond pulse duration, the 20-mJ pulse energy, and conical fiber tip delivery, as used in this experiment, represent the photon-induced photo acoustic streaming approach. In this approach, the combination of a conical tip and very short pulses produce profound irrigant dynamics, whereas the low pulse energy produces minimal thermal effects (18, 28). When comparing the 2 LAI protocols, no statistically significant differences were observed. More studies are needed to compare the efficacy of LAI with these 2 approaches. In the main canals, MDI did not result in a significant reduction in debris level, whereas in the isthmus debris reduction was significant. These results suggest that MDI works better when a lateral “escape way” for the debris is available, which is the case in an (open) isthmus, and not in a dead-ending canal extension. Both Susin et al (29) and
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Basic Research—Technology Parente et al (30) hypothesized that the irrigant displacement could be hindered by a relatively close adaptation of the gutta-percha cone to the canal wall, resulting in the debris settling back into the canal system after removal of the gutta-percha cone. In the present study, the greatest debris reductions were obtained with the LAI protocols. However, these results were not significantly different from the other activation groups, probably because of great variation in preoperative debris levels. Nevertheless, in many studies involving LAI, LAI cleaning results were either better than those of UAI or other activation techniques (23–25, 27); or the results did not differ significantly from these groups, while net outcome were better (26). This trend suggests LAI possesses a stronger activation action. It is hypothesized that this is because of the violent fluid dynamics caused by the expanding and imploding bubbles at the fiber tip of the Er:YAG laser. This physical process appears to be more vigorous than acoustic fluid agitation with ultrasound and other activation techniques. Within the limitations of this in vitro study, it can be concluded that canal and isthmus cleanliness significantly improved after the final irrigation regimen in each group.
Acknowledgments The authors deny any conflicts of interest related to this study.
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