Evaluation of various root canal irrigation methods in primary teeth: a systematic review
Primary teeth (PT) preservation is essential for maintaining proper oral function and aesthetics and facilitating the eruption of permanent teeth. Consequently, it is necessary to apply suitable treatment strategies for the conservation of PT with deep caries or traumatic dental events, among which root canal therapy is a frequently utilized method. A pulpectomy is a procedure in which the inflammatory or necrotic tissue of the pulp chamber and root canals is completely removed . Chemomechanical debridement is vital for removing microbiota, by-products, pulpal tissue, and organic/inorganic debris . Root canal irrigation complements mechanical instrumentation by ensuring that the root canal system is thoroughly disinfected and the smear layer (SL) is removed . This is crucial for eliminating microorganisms, dissolving organic debris, and enhancing disinfection. The complexity of root canal anatomy in PT, along with limited access and instrumentation challenges, necessitates effective irrigation techniques for optimal disinfection . However, during pulpectomy procedures, there is a risk of pushing infected debris into the periradicular area, which can lead to inflammation, pain, and delayed healing . Minimizing debris extrusion is vital for successful treatment in both primary and permanent teeth, especially since PT are more prone to extrusion due to their wider apical foramina, potentially causing damage to surrounding tissues and permanent tooth follicles . While all irrigation techniques lead to some degree of debris and irrigant extrusion, the extent is different. Efforts have been ongoing to improve irrigant delivery systems in endodontics, which are classified into those with and without irrigant activation. The activation and delivery of irrigation solutions are believed to improve their flow and distribution throughout the root canal system . Endodontic irrigant activation techniques include manual irrigation, heating (either internal or external), negative apical pressure (e.g., EndoVac by Kerr Endodontics and Dürr Dental), sonic techniques (e.g., EDDY by VDW and EndoActivator by Dentsply Maillefer), passive ultrasonic irrigation, and laser techniques . Each method offers distinct advantages for enhancing irrigation outcomes. Despite extensive use of conventional needle irrigation, it falls short in safely and effectively delivering large volumes of the irrigation solution throughout the entire root canal system, including hard-to-reach areas . Irrigation needles are designed as either side-vented needles (SVNs) or open-ended needles (OENs). SVNs reduce the risk of solution overflow to the periapical region and are considered more effective than OENs . The EndoVac system, a negative apical pressure system, safely delivers irrigants to apical and otherwise unreachable areas of the root canal,  showing superiority over conventional needle irrigation in terms of debridement efficacy, SL removal, and antimicrobial efficacy in permanent teeth . It also minimizes the risk of irrigant extrusion to the periapical area and reduces the chances of sodium hypochlorite (NaOCl) accidents . Various activation methods, particularly sonic and ultrasonic activation techniques, have undergone a thorough investigation . Passive ultrasonically activated irrigation creates microstreaming and secondary acoustic streaming around the file . Manual dynamic activation with files produces mechanical agitation, especially along the curved sections of the files,  whereas sonic activation firstly agitates at the file’s tip.  These techniques enhance intracanal fluid agitation, improving irrigant flow into less accessible areas of the root canal system and aiding in the cleaning of the main canal, thereby facilitating the filling of more lateral canals . Lastly, lasers, through the emission of photonic energy, can activate irrigant solutions, potentially increasing irrigation efficacy by reaching previously inaccessible parts of the tubular network . Various irrigation techniques aim to boost the effectiveness of antimicrobial agents and SL removal while reducing the apical extrusion of debris and irrigants to enhance treatment outcomes. However, there is no consensus on the most effective root canal irrigation technique for PT, and systematic evaluation and comparisons of these methods, specifically for PT, are currently missing. Accordingly, this systematic review seeks to fill the current knowledge gap by critically reviewing and synthesizing the literature on various root canal irrigation techniques for PT. It aims to guide clinicians in making evidence-based choices for irrigation methods, thereby improving treatment results and PT preservation. The review could also spotlight areas needing more research and the importance of establishing standardized protocols or guidelines for root canal irrigation in PT. 

This systematic review study was completed in accordance with the guidelines of the Preferred Reporting Items for Systematic Reviews and Meta-Analyses,  and its protocol was registered in PROSPERO (the ID number CRD42023458318). Review question The research question focused on the effectiveness of various root canal irrigation methods for PT. Using the PICO, the human PT and root canal irrigation techniques were considered the population and interventions (conventional needle irrigation, sonic irrigation, passive ultrasonic irrigation, laser-activated irrigation, and the like), respectively. In addition, routine or standard root canal irrigation was regarded as the control, and outcomes included the reduction of microorganisms, extrusion of debris from the apical foramen, removal of debris and SL, and postoperative pain (PP). Eligibility criteria The study included both clinical and laboratory articles. Therefore, eligible studies had to be aligned with the main research question. No restrictions were applied on language or publication date. There were several inclusion criteria for in vitro studies. They had to have investigated at least two irrigation techniques and have included children with PT as the study population. Moreover, the mechanical root canal preparation process had to be conducted alongside the irrigation technique in these studies. Additionally, they had to have evaluated outcomes such as reduced microbial load, SL removal, and debris extrusion. Some inclusion criteria were also followed for in vivo studies. They had to have examined at least two irrigation techniques, and the study population had to have included children and PT. Moreover, it was essential for them to evaluate outcomes such as PP and microbial load within the canal. On the other hand, the exclusion criteria were investigations that focused solely on the irrigant or filling material without addressing the technique, as well as studies that used laser or photodynamic therapy as a disinfection method before or after irrigation. Data sources and search strategy Search strategy This systematic review was conducted through an extensive electronic search until May 2023 by two independent experienced researchers (Z. M. & M. V.) by utilizing broad MeSH terms and keywords across several databases, including Web of Science, Scopus, PubMed, Cochrane Library (all databases), EMBASE, and Google Scholar. Additionally, ProQuest dissertation and theses were searched for grey literature. Table presents the strategy of the search. Furthermore, a hand search was performed on relevant journals and reference lists. All retrieved articles were transferred to EndNote software (version X8, Thomson Reuters, 2013, New York, USA). Study selection and data collection Selection of studies Initially, duplicated studies were excluded from the investigation. N. D. and Z. M. independently screened the titles and abstracts of the articles and extracted suitable studies relying on the inclusion and exclusion criteria. Data extraction Three authors (N. D., Z. M., & F. Kh.) reviewed the full texts of the selected articles. Data were collected for each study independently, including information on authors, publication year, country, sample size, and study characteristics such as sample selection, crown preparation, root canal shaping, intervention, comparison, follow-up period, examination scales, and outcomes. Any disagreement among the authors was resolved by the supervisor (M. V.). The corresponding authors were contacted to collect the missing data. Risk-of-bias assessment The QUIN assessment instrument was employed to evaluate the quality of the intended in vitro studies. Two researchers used a scoring system that included adequately specified (2–1 points), not specified (0 points), and not applicable (exempt from calculation). The total score determined the risk of bias, classified as low (> 70%), medium (50–70%), or high (< 50%) . The Cochrane risk-of-bias instrument (RoB 2.0)  was utilized for in vivo studies. The RoB 2.0 tool addresses bias across several domains. including bias due to deviations from intended interventions, bias in the selection of reported results, bias from randomization, bias in outcome measurement, bias from missing outcome data, and overall bias. Following the RoB 2.0, the risk of bias in each domain was categorized as low risk, high risk, or some concerns. One study was deemed to have a low risk of overall bias in case it had low risk in all domains. In case the study included some concerns in at least one domain while there was no high risk in any domain, it was considered to have some concerns overall. Another study was judged to be at high risk of overall bias in case it had a high risk in any one domain. Synthesis methods No meta-analysis was performed because of data heterogeneity and inconsistency in the diagnostic criteria and outcome measurements of the intended studies. 

The research question focused on the effectiveness of various root canal irrigation methods for PT. Using the PICO, the human PT and root canal irrigation techniques were considered the population and interventions (conventional needle irrigation, sonic irrigation, passive ultrasonic irrigation, laser-activated irrigation, and the like), respectively. In addition, routine or standard root canal irrigation was regarded as the control, and outcomes included the reduction of microorganisms, extrusion of debris from the apical foramen, removal of debris and SL, and postoperative pain (PP). 

The study included both clinical and laboratory articles. Therefore, eligible studies had to be aligned with the main research question. No restrictions were applied on language or publication date. There were several inclusion criteria for in vitro studies. They had to have investigated at least two irrigation techniques and have included children with PT as the study population. Moreover, the mechanical root canal preparation process had to be conducted alongside the irrigation technique in these studies. Additionally, they had to have evaluated outcomes such as reduced microbial load, SL removal, and debris extrusion. Some inclusion criteria were also followed for in vivo studies. They had to have examined at least two irrigation techniques, and the study population had to have included children and PT. Moreover, it was essential for them to evaluate outcomes such as PP and microbial load within the canal. On the other hand, the exclusion criteria were investigations that focused solely on the irrigant or filling material without addressing the technique, as well as studies that used laser or photodynamic therapy as a disinfection method before or after irrigation. 

Search strategy This systematic review was conducted through an extensive electronic search until May 2023 by two independent experienced researchers (Z. M. & M. V.) by utilizing broad MeSH terms and keywords across several databases, including Web of Science, Scopus, PubMed, Cochrane Library (all databases), EMBASE, and Google Scholar. Additionally, ProQuest dissertation and theses were searched for grey literature. Table presents the strategy of the search. Furthermore, a hand search was performed on relevant journals and reference lists. All retrieved articles were transferred to EndNote software (version X8, Thomson Reuters, 2013, New York, USA). 

This systematic review was conducted through an extensive electronic search until May 2023 by two independent experienced researchers (Z. M. & M. V.) by utilizing broad MeSH terms and keywords across several databases, including Web of Science, Scopus, PubMed, Cochrane Library (all databases), EMBASE, and Google Scholar. Additionally, ProQuest dissertation and theses were searched for grey literature. Table presents the strategy of the search. Furthermore, a hand search was performed on relevant journals and reference lists. All retrieved articles were transferred to EndNote software (version X8, Thomson Reuters, 2013, New York, USA). 

Selection of studies Initially, duplicated studies were excluded from the investigation. N. D. and Z. M. independently screened the titles and abstracts of the articles and extracted suitable studies relying on the inclusion and exclusion criteria. Data extraction Three authors (N. D., Z. M., & F. Kh.) reviewed the full texts of the selected articles. Data were collected for each study independently, including information on authors, publication year, country, sample size, and study characteristics such as sample selection, crown preparation, root canal shaping, intervention, comparison, follow-up period, examination scales, and outcomes. Any disagreement among the authors was resolved by the supervisor (M. V.). The corresponding authors were contacted to collect the missing data. 

Initially, duplicated studies were excluded from the investigation. N. D. and Z. M. independently screened the titles and abstracts of the articles and extracted suitable studies relying on the inclusion and exclusion criteria. 

Three authors (N. D., Z. M., & F. Kh.) reviewed the full texts of the selected articles. Data were collected for each study independently, including information on authors, publication year, country, sample size, and study characteristics such as sample selection, crown preparation, root canal shaping, intervention, comparison, follow-up period, examination scales, and outcomes. Any disagreement among the authors was resolved by the supervisor (M. V.). The corresponding authors were contacted to collect the missing data. 

The QUIN assessment instrument was employed to evaluate the quality of the intended in vitro studies. Two researchers used a scoring system that included adequately specified (2–1 points), not specified (0 points), and not applicable (exempt from calculation). The total score determined the risk of bias, classified as low (> 70%), medium (50–70%), or high (< 50%) . The Cochrane risk-of-bias instrument (RoB 2.0)  was utilized for in vivo studies. The RoB 2.0 tool addresses bias across several domains. including bias due to deviations from intended interventions, bias in the selection of reported results, bias from randomization, bias in outcome measurement, bias from missing outcome data, and overall bias. Following the RoB 2.0, the risk of bias in each domain was categorized as low risk, high risk, or some concerns. One study was deemed to have a low risk of overall bias in case it had low risk in all domains. In case the study included some concerns in at least one domain while there was no high risk in any domain, it was considered to have some concerns overall. Another study was judged to be at high risk of overall bias in case it had a high risk in any one domain. 

No meta-analysis was performed because of data heterogeneity and inconsistency in the diagnostic criteria and outcome measurements of the intended studies. 

Study selection Figure depicts the Preferred Reporting Items for Systematic Reviews and the Meta-Analyses flow diagram, which displays the process of study selection. Overall, 2,381 records were identified through a search of five electronic databases. Following reviewing the titles and abstracts, the full texts of 195 studies were assessed in detail for inclusion. The reason for removing the review articles was that they focused on the irrigant type or the use of laser or photodynamic therapy. Ultimately, 17 studies—11 in vitro and 6 in vivo—were selected for analysis. The total sample size for the in vitro studies was 503 teeth, while the in vivo studies comprised 423 teeth. Basic features of the studies In vitro studies The features of the 11 intended in vitro studies are summarized in Table . Regarding their geographical distribution, five and three studies were conducted in Turkey and India, respectively, and the remaining three were performed in Iran, Lebanon, and Japan, respectively. In terms of the sample size, one study analyzed 15 teeth, while another examined 120 teeth. The average sample size of the other studies was 46 teeth. The majority of these studies focused on primary second molars, either from the mandible or maxilla, except for three studies that included first primary molars , maxillary canines , and other multi- and single-rooted PR  in addition to the second molar. In addition, two studies only used primary incisors . Intervention and control Studies included groups that compared conventional irrigation (OEN or SVN) for endodontic treatment in PT with sonic, ultrasonic, EndoVac, and laser activation methods. Only one study compared OENs and SVNs. In four studies, conventional irrigation was performed along with needle activation (agitation during irrigation). Outcomes The results investigated in the in vitro studies included microorganism reduction, SL removal, and debris extrusion from the apical area. Reduction of microorganisms ( Enterococcus faecalis) Five studies compared the conventional irrigation method (four studies without activation and one study with activation) with three methods of activating the irrigation material using sonic, EndoVac, and laser. In the study by Kodical et al. , the colony-forming units of E. faecalis in group 3 (laser-activated irrigation— 810 nm diode laser— with Aquatine Endodontic Cleanser) were reduced compared to group 2 (conventional irrigation with Aquatine Endodontic Cleanser); Nonetheless, such a difference was not significant ( P = 0.7). On the contrary, the findings of Yavagal et al.  revealed that 2.5% NaOCl activated by the 810 nm diode laser significantly reduced bacterial growth compared to conventional irrigation with a syringe. In the study performed by Korkut et al. , the second and third groups were only techniques for canal disinfection rather than different irrigation methods; thus, the first (conventional irrigation with 5% NaOCl) and fourth (5% NaOCl activation with Er:YAG laser) groups underwent comparison. The viable count of E. faecalis was significantly decreased in group 4 in comparison to group 1 ( P < 0.05). In the study by Forghani et al. , no significant differences were found in the number of colonies with or without sonic activation between different concentrations. The sonic activation of the 0.5% NaOCl solution could reduce the number of colonies (not statistically significant). Finally, in the study conducted by Buldur et al. , the subgroups using EndoVac demonstrated a greater reduction in bacterial colonies than the activation of the irrigant with a conventional needle (not statistically significant). Smear layer removal Eight studies were compared, including studies that used conventional needles (30G side-vented needle,  23G needle syringe,  and two studies that were not discussed),  as well as three studies without activation  and one study with irrigant activation . Further, one study compared the smear removal efficacy of OENs and DSVNs . Four studies of root canal irrigation in PT using a conventional needle have been compared, including one with a 30G SVN , another with a 23G needle syringe,  and two studies that were not discussed in this review . Additionally, three studies did not use activation , and one study employed irrigant activation . Moreover, one study compared the smear removal efficacy of an OEN with that of a DSVN. . According to the study by El Hashem et al. , SL and debris scores decreased from the apical to the coronal thirds of the root canal across all groups, including passive ultrasonic activation with Ultra-X, conventional needle, sonic activation with EQ-S, and mechanical activation with XP-endo Finisher groups. In all thirds, the control group (the conventional needle) represented the highest score for the SL and the remaining debris. No significant difference was observed between the XP-endo Finisher, Ultra-X, and EQ-S groups ( P > 0.05). Irrigation solution activation increased the removal of SL and debris in all canal thirds. The findings of a study by Korkut et al.  confirmed that Er:YAG laser-activated irrigation by photon-induced photoacoustic streaming (PIPS) led to greater removal of smear and debris from the root canal walls and a higher number of open tubules compared to conventional irrigation. According to the findings of a study performed by Buldur et al. , EndoVac was more influential in removing the SL from the apical third of the root canal system when compared to the conventional needle ( P < 0.05). The ozonated water + ethylenediaminetetraacetic acid (EDTA) regimen could provide SL removal comparable to that of NaOCl + EDTA. Toyota et al.  investigated the efficacy of SL removal and measured the amount of the remaining SL by observing the percentage of open dentinal tubules (POD) in the root canal. In the middle third of the root canal, active irrigation with ultrasonic and 5% NaOCl significantly increased the removal of the POD and the SL in comparison to the conventional needle. However, with 14% EDTA as the irrigant, no significant difference was found in SL removal between the two irrigation methods. In the apical third of the root, active irrigation with 14% EDTA and ultrasonic could significantly enhance SL and POD removal in comparison to other groups. Based on the findings of the study by Demirel et al. , experimental groups revealed significantly better SL removal in the coronal third of the root canal when compared to the control group, with a notable statistical significance ( P < 0.05). There was no significant difference in the use of 6% CA and 5% EDTA solutions when applied with either DSVNs or OENs ( P > 0.05). In the middle third, using 5% EDTA with DSVN, 6% CA with OEN, and 6% CA with DSVN showed statistically significant superior SL removal in comparison to the control group ( P < 0.05). Similarly, in the apical third, DSVN groups (using 6% CA and 5% EDTA) achieved significantly more influential SL removal than the control group ( P < 0.05). Moreover, the removal of SL was statistically more noticeable in the coronal third than in the apical third across all experimental groups ( P < 0.05). The findings confirm that the effectiveness of OENs and DSVNs for SL removal might be comparable, suggesting their similar effectiveness across different parts of the root canal. Apical extrusion of debris Two studies investigated the apical extrusion of debris following pulpectomy in primary molars, comparing the conventional needle irrigation technique (which activates the irrigant with an up-and-down movement of the needle) with two other root canal irrigation methods. The applied irrigants were the same across the compared groups. According to the findings of Gungor et al. , two root canal irrigation techniques were evaluated, along with two different instrumentation methods. It was revealed that all irrigation and instrumentation systems resulted in an assessable apical debris extrusion. Conversely, no statistically significant difference was found in debris extrusion between the irrigation methods ( P > 0.05). The total amount of debris extruded apically by the laser-activated irrigation (Er,Cr:YSGG laser system with optical fiber) was greater than that by the CNI (27G open-ended conventional needle). Venumbeka et al.  assessed the rate of irrigant extrusion and the depth of irrigant penetration into the dentin. According to their results, using the EndoVac system, the irrigation solution’s apical extrusion was significantly lower when compared to the manual irrigation system, namely, the DISPO VAN single-use syringe needle with a diameter of 0.50 mm ( P = 0.002). Additionally, greater irrigation penetration was obtained with the EndoVac system than with the manual irrigation system ( P = 0.000). The depth of irrigation penetration at 6 mm sections was higher than that at 4 mm and 2 mm sections for both irrigation systems ( P = 0.000). In vivo studies All six articles included randomized clinical trials in which various irrigation techniques were compared for the treatment of primary root canals (Table ). Three and two studies were conducted in India and Turkey, respectively, and one study was performed in Syria. A total of 503 PT from 351 participants with an age group of 3–9 years (average 6.5 years) were treated, including cases from two studies focusing only on maxillary primary molars , one study examining maxillary anterior teeth , two studies investigating primary molars , and one study that did not focus on the type of treated teeth) . The pulp status of the pulpectomized teeth was not mentioned only in one study . In the others, the pulp was necrotic or irreversibly inflamed. Intervention and control In the randomized controlled trials included in this systematic review study, the conventional endodontic syringe (without activation) was compared with three activation methods (sonic, ultrasonic, and Endovac). In addition, two studies only compared conventional open-end syringes with side-vented ones. Outcomes The results included PP reduction, pulpectomy outcomes, obturation quality, and antibacterial efficacy after different root canal irrigation protocols. Postoperative pain Three studies by Seshadri et al. , Topçuoğlu et al. , and Gümüş et al.  attempted to compare the effect of irrigation with SVNs and activation with sonic (Endoactivator) in PP after pulpectomy of the primary molar teeth with the conventional irrigation technique. Two studies compared PP with OENs and SVNs. In the study performed by Topçuoğlu et al. , PP was compared by applying a 4-point pain intensity scale at intervals of 6, 12, 24, 48, and 72 h. At the 6-, 12-, and 24-h time points, groups that irrigated with an OEN demonstrated more severe PP compared to those irrigated with a DSVN ( P < 0.05). There was no significant difference between the groups after 48 h, 72 h, and 1 week ( P > 0.05). However, Seshadri et al. also reported that based on the visual analog scale and the Wong-Baker faces pain scale, PP was higher in the OEN than the SEN group in all the investigated intervals (6, 24, 48, and 72 h). Nonetheless, this difference was only significant after 24 h ( P < 0.05). The study by Gümüş et al.  was in favor of the active sonic irrigation technique (EndoActivator™). Based on the five-face scale, in the intervals of 8, 24, 48, and 72 h and 1 week following treatment, lower PP was recorded in the three investigated times up to 48 h. No significant difference was observed between active irrigation with sonic and conventional endodontic syringes 72 h and 1 week after treatment. Pulpectomy outcomes and obturation quality Jain et al.  studied radiographic and clinical outcomes of pulpectomy in PT after 24 h, 1 week, 1 month, 6 months, and 12 months, with two irrigants, 1% NaOCl and 6% citric acid (CA), as well as two irrigation techniques, namely, active sonic (EndoActivator™) and conventional needle techniques. The quality of obturation was also assessed with postoperative radiographs. All groups could significantly alleviate pain within 24 h of pulpectomy ( P < 0.001). The overall radiographic and clinical success rates over one year were 97.7% and 98.86%, respectively. The maximum quantity of optimal fillings was found in the CA + Endoactivator group, though it was statistically insignificant. The Endoactivator could contribute to 18% of optimal obturation, regardless of the applied chelating agent. The least number of voids and void area was found by the combination of Endoactivator and chelating agent (Group 1); nonetheless, this was not statistically significant. The researchers concluded that the inclusion of Endoactivator and 6% citric acid as irrigation adjuncts could help achieve better obturation quality and earlier pain alleviation. Antibacterial efficacy The findings of the study by Ahmadi et al.  showed that Endovac could significantly reduce the bacterial colony count of E. faecalis with both types of irrigants (NaOCl 2.5% and CHX 2%) compared to conventional syringes in primary molar teeth. Likewise, Kharsa et al.  evaluated the antibacterial effectiveness of ultrasonically activated and non-activated (the 27G conventional needle) solutions and the gel form of CHX 2% in infected root canals of anterior PT. Unlike the aerobic bacteria, no statistical differences were observed in the mean percentage change of the decimal logarithm of the anaerobic bacterial colony count. For aerobic bacteria, the CHX 2% solution activated better than the inactivated and control (NaOCl 5.25%), and the CHX 2% gel activated better than the inactivated CHX 2% solution and control. Risk of bias of studies The QUIN tool’s scoring  indicated that among in vitro studies, four and eight represented a medium and low risk of bias, respectively. Among the articles with a medium-level risk of bias, the most frequent non-specified criteria were “operator details” and “detailed explanation of the sample size calculation”. Interestingly, some studies did not provide any information regarding randomization, blinding, or outcome assessor details. The assessment details of the QUIN tool are provided in Table . Based on ROB 2, six clinical studies were evaluated, three of which were deemed to have a low-level risk of bias. One study had a medium-level risk of bias, whereas two studies were categorized as high risk. Studies with a high-level risk of bias were found to have significant concerns in four domains, namely, deviation from intended interventions, the randomization process, outcome measurement, and missing outcomes. Additionally, the study that raised concerns in the randomization process was judged to have some concerns. Figures A and B present the results of the ROB 2 tool. 

Figure depicts the Preferred Reporting Items for Systematic Reviews and the Meta-Analyses flow diagram, which displays the process of study selection. Overall, 2,381 records were identified through a search of five electronic databases. Following reviewing the titles and abstracts, the full texts of 195 studies were assessed in detail for inclusion. The reason for removing the review articles was that they focused on the irrigant type or the use of laser or photodynamic therapy. Ultimately, 17 studies—11 in vitro and 6 in vivo—were selected for analysis. The total sample size for the in vitro studies was 503 teeth, while the in vivo studies comprised 423 teeth. 

In vitro studies The features of the 11 intended in vitro studies are summarized in Table . Regarding their geographical distribution, five and three studies were conducted in Turkey and India, respectively, and the remaining three were performed in Iran, Lebanon, and Japan, respectively. In terms of the sample size, one study analyzed 15 teeth, while another examined 120 teeth. The average sample size of the other studies was 46 teeth. The majority of these studies focused on primary second molars, either from the mandible or maxilla, except for three studies that included first primary molars , maxillary canines , and other multi- and single-rooted PR  in addition to the second molar. In addition, two studies only used primary incisors . Intervention and control Studies included groups that compared conventional irrigation (OEN or SVN) for endodontic treatment in PT with sonic, ultrasonic, EndoVac, and laser activation methods. Only one study compared OENs and SVNs. In four studies, conventional irrigation was performed along with needle activation (agitation during irrigation). Outcomes The results investigated in the in vitro studies included microorganism reduction, SL removal, and debris extrusion from the apical area. Reduction of microorganisms ( Enterococcus faecalis) Five studies compared the conventional irrigation method (four studies without activation and one study with activation) with three methods of activating the irrigation material using sonic, EndoVac, and laser. In the study by Kodical et al. , the colony-forming units of E. faecalis in group 3 (laser-activated irrigation— 810 nm diode laser— with Aquatine Endodontic Cleanser) were reduced compared to group 2 (conventional irrigation with Aquatine Endodontic Cleanser); Nonetheless, such a difference was not significant ( P = 0.7). On the contrary, the findings of Yavagal et al.  revealed that 2.5% NaOCl activated by the 810 nm diode laser significantly reduced bacterial growth compared to conventional irrigation with a syringe. In the study performed by Korkut et al. , the second and third groups were only techniques for canal disinfection rather than different irrigation methods; thus, the first (conventional irrigation with 5% NaOCl) and fourth (5% NaOCl activation with Er:YAG laser) groups underwent comparison. The viable count of E. faecalis was significantly decreased in group 4 in comparison to group 1 ( P < 0.05). In the study by Forghani et al. , no significant differences were found in the number of colonies with or without sonic activation between different concentrations. The sonic activation of the 0.5% NaOCl solution could reduce the number of colonies (not statistically significant). Finally, in the study conducted by Buldur et al. , the subgroups using EndoVac demonstrated a greater reduction in bacterial colonies than the activation of the irrigant with a conventional needle (not statistically significant). Smear layer removal Eight studies were compared, including studies that used conventional needles (30G side-vented needle,  23G needle syringe,  and two studies that were not discussed),  as well as three studies without activation  and one study with irrigant activation . Further, one study compared the smear removal efficacy of OENs and DSVNs . Four studies of root canal irrigation in PT using a conventional needle have been compared, including one with a 30G SVN , another with a 23G needle syringe,  and two studies that were not discussed in this review . Additionally, three studies did not use activation , and one study employed irrigant activation . Moreover, one study compared the smear removal efficacy of an OEN with that of a DSVN. . According to the study by El Hashem et al. , SL and debris scores decreased from the apical to the coronal thirds of the root canal across all groups, including passive ultrasonic activation with Ultra-X, conventional needle, sonic activation with EQ-S, and mechanical activation with XP-endo Finisher groups. In all thirds, the control group (the conventional needle) represented the highest score for the SL and the remaining debris. No significant difference was observed between the XP-endo Finisher, Ultra-X, and EQ-S groups ( P > 0.05). Irrigation solution activation increased the removal of SL and debris in all canal thirds. The findings of a study by Korkut et al.  confirmed that Er:YAG laser-activated irrigation by photon-induced photoacoustic streaming (PIPS) led to greater removal of smear and debris from the root canal walls and a higher number of open tubules compared to conventional irrigation. According to the findings of a study performed by Buldur et al. , EndoVac was more influential in removing the SL from the apical third of the root canal system when compared to the conventional needle ( P < 0.05). The ozonated water + ethylenediaminetetraacetic acid (EDTA) regimen could provide SL removal comparable to that of NaOCl + EDTA. Toyota et al.  investigated the efficacy of SL removal and measured the amount of the remaining SL by observing the percentage of open dentinal tubules (POD) in the root canal. In the middle third of the root canal, active irrigation with ultrasonic and 5% NaOCl significantly increased the removal of the POD and the SL in comparison to the conventional needle. However, with 14% EDTA as the irrigant, no significant difference was found in SL removal between the two irrigation methods. In the apical third of the root, active irrigation with 14% EDTA and ultrasonic could significantly enhance SL and POD removal in comparison to other groups. Based on the findings of the study by Demirel et al. , experimental groups revealed significantly better SL removal in the coronal third of the root canal when compared to the control group, with a notable statistical significance ( P < 0.05). There was no significant difference in the use of 6% CA and 5% EDTA solutions when applied with either DSVNs or OENs ( P > 0.05). In the middle third, using 5% EDTA with DSVN, 6% CA with OEN, and 6% CA with DSVN showed statistically significant superior SL removal in comparison to the control group ( P < 0.05). Similarly, in the apical third, DSVN groups (using 6% CA and 5% EDTA) achieved significantly more influential SL removal than the control group ( P < 0.05). Moreover, the removal of SL was statistically more noticeable in the coronal third than in the apical third across all experimental groups ( P < 0.05). The findings confirm that the effectiveness of OENs and DSVNs for SL removal might be comparable, suggesting their similar effectiveness across different parts of the root canal. Apical extrusion of debris Two studies investigated the apical extrusion of debris following pulpectomy in primary molars, comparing the conventional needle irrigation technique (which activates the irrigant with an up-and-down movement of the needle) with two other root canal irrigation methods. The applied irrigants were the same across the compared groups. According to the findings of Gungor et al. , two root canal irrigation techniques were evaluated, along with two different instrumentation methods. It was revealed that all irrigation and instrumentation systems resulted in an assessable apical debris extrusion. Conversely, no statistically significant difference was found in debris extrusion between the irrigation methods ( P > 0.05). The total amount of debris extruded apically by the laser-activated irrigation (Er,Cr:YSGG laser system with optical fiber) was greater than that by the CNI (27G open-ended conventional needle). Venumbeka et al.  assessed the rate of irrigant extrusion and the depth of irrigant penetration into the dentin. According to their results, using the EndoVac system, the irrigation solution’s apical extrusion was significantly lower when compared to the manual irrigation system, namely, the DISPO VAN single-use syringe needle with a diameter of 0.50 mm ( P = 0.002). Additionally, greater irrigation penetration was obtained with the EndoVac system than with the manual irrigation system ( P = 0.000). The depth of irrigation penetration at 6 mm sections was higher than that at 4 mm and 2 mm sections for both irrigation systems ( P = 0.000). In vivo studies All six articles included randomized clinical trials in which various irrigation techniques were compared for the treatment of primary root canals (Table ). Three and two studies were conducted in India and Turkey, respectively, and one study was performed in Syria. A total of 503 PT from 351 participants with an age group of 3–9 years (average 6.5 years) were treated, including cases from two studies focusing only on maxillary primary molars , one study examining maxillary anterior teeth , two studies investigating primary molars , and one study that did not focus on the type of treated teeth) . The pulp status of the pulpectomized teeth was not mentioned only in one study . In the others, the pulp was necrotic or irreversibly inflamed. Intervention and control In the randomized controlled trials included in this systematic review study, the conventional endodontic syringe (without activation) was compared with three activation methods (sonic, ultrasonic, and Endovac). In addition, two studies only compared conventional open-end syringes with side-vented ones. Outcomes The results included PP reduction, pulpectomy outcomes, obturation quality, and antibacterial efficacy after different root canal irrigation protocols. Postoperative pain Three studies by Seshadri et al. , Topçuoğlu et al. , and Gümüş et al.  attempted to compare the effect of irrigation with SVNs and activation with sonic (Endoactivator) in PP after pulpectomy of the primary molar teeth with the conventional irrigation technique. Two studies compared PP with OENs and SVNs. In the study performed by Topçuoğlu et al. , PP was compared by applying a 4-point pain intensity scale at intervals of 6, 12, 24, 48, and 72 h. At the 6-, 12-, and 24-h time points, groups that irrigated with an OEN demonstrated more severe PP compared to those irrigated with a DSVN ( P < 0.05). There was no significant difference between the groups after 48 h, 72 h, and 1 week ( P > 0.05). However, Seshadri et al. also reported that based on the visual analog scale and the Wong-Baker faces pain scale, PP was higher in the OEN than the SEN group in all the investigated intervals (6, 24, 48, and 72 h). Nonetheless, this difference was only significant after 24 h ( P < 0.05). The study by Gümüş et al.  was in favor of the active sonic irrigation technique (EndoActivator™). Based on the five-face scale, in the intervals of 8, 24, 48, and 72 h and 1 week following treatment, lower PP was recorded in the three investigated times up to 48 h. No significant difference was observed between active irrigation with sonic and conventional endodontic syringes 72 h and 1 week after treatment. Pulpectomy outcomes and obturation quality Jain et al.  studied radiographic and clinical outcomes of pulpectomy in PT after 24 h, 1 week, 1 month, 6 months, and 12 months, with two irrigants, 1% NaOCl and 6% citric acid (CA), as well as two irrigation techniques, namely, active sonic (EndoActivator™) and conventional needle techniques. The quality of obturation was also assessed with postoperative radiographs. All groups could significantly alleviate pain within 24 h of pulpectomy ( P < 0.001). The overall radiographic and clinical success rates over one year were 97.7% and 98.86%, respectively. The maximum quantity of optimal fillings was found in the CA + Endoactivator group, though it was statistically insignificant. The Endoactivator could contribute to 18% of optimal obturation, regardless of the applied chelating agent. The least number of voids and void area was found by the combination of Endoactivator and chelating agent (Group 1); nonetheless, this was not statistically significant. The researchers concluded that the inclusion of Endoactivator and 6% citric acid as irrigation adjuncts could help achieve better obturation quality and earlier pain alleviation. Antibacterial efficacy The findings of the study by Ahmadi et al.  showed that Endovac could significantly reduce the bacterial colony count of E. faecalis with both types of irrigants (NaOCl 2.5% and CHX 2%) compared to conventional syringes in primary molar teeth. Likewise, Kharsa et al.  evaluated the antibacterial effectiveness of ultrasonically activated and non-activated (the 27G conventional needle) solutions and the gel form of CHX 2% in infected root canals of anterior PT. Unlike the aerobic bacteria, no statistical differences were observed in the mean percentage change of the decimal logarithm of the anaerobic bacterial colony count. For aerobic bacteria, the CHX 2% solution activated better than the inactivated and control (NaOCl 5.25%), and the CHX 2% gel activated better than the inactivated CHX 2% solution and control. 

The features of the 11 intended in vitro studies are summarized in Table . Regarding their geographical distribution, five and three studies were conducted in Turkey and India, respectively, and the remaining three were performed in Iran, Lebanon, and Japan, respectively. In terms of the sample size, one study analyzed 15 teeth, while another examined 120 teeth. The average sample size of the other studies was 46 teeth. The majority of these studies focused on primary second molars, either from the mandible or maxilla, except for three studies that included first primary molars , maxillary canines , and other multi- and single-rooted PR  in addition to the second molar. In addition, two studies only used primary incisors . Intervention and control Studies included groups that compared conventional irrigation (OEN or SVN) for endodontic treatment in PT with sonic, ultrasonic, EndoVac, and laser activation methods. Only one study compared OENs and SVNs. In four studies, conventional irrigation was performed along with needle activation (agitation during irrigation). Outcomes The results investigated in the in vitro studies included microorganism reduction, SL removal, and debris extrusion from the apical area. Reduction of microorganisms ( Enterococcus faecalis) Five studies compared the conventional irrigation method (four studies without activation and one study with activation) with three methods of activating the irrigation material using sonic, EndoVac, and laser. In the study by Kodical et al. , the colony-forming units of E. faecalis in group 3 (laser-activated irrigation— 810 nm diode laser— with Aquatine Endodontic Cleanser) were reduced compared to group 2 (conventional irrigation with Aquatine Endodontic Cleanser); Nonetheless, such a difference was not significant ( P = 0.7). On the contrary, the findings of Yavagal et al.  revealed that 2.5% NaOCl activated by the 810 nm diode laser significantly reduced bacterial growth compared to conventional irrigation with a syringe. In the study performed by Korkut et al. , the second and third groups were only techniques for canal disinfection rather than different irrigation methods; thus, the first (conventional irrigation with 5% NaOCl) and fourth (5% NaOCl activation with Er:YAG laser) groups underwent comparison. The viable count of E. faecalis was significantly decreased in group 4 in comparison to group 1 ( P < 0.05). In the study by Forghani et al. , no significant differences were found in the number of colonies with or without sonic activation between different concentrations. The sonic activation of the 0.5% NaOCl solution could reduce the number of colonies (not statistically significant). Finally, in the study conducted by Buldur et al. , the subgroups using EndoVac demonstrated a greater reduction in bacterial colonies than the activation of the irrigant with a conventional needle (not statistically significant). Smear layer removal Eight studies were compared, including studies that used conventional needles (30G side-vented needle,  23G needle syringe,  and two studies that were not discussed),  as well as three studies without activation  and one study with irrigant activation . Further, one study compared the smear removal efficacy of OENs and DSVNs . Four studies of root canal irrigation in PT using a conventional needle have been compared, including one with a 30G SVN , another with a 23G needle syringe,  and two studies that were not discussed in this review . Additionally, three studies did not use activation , and one study employed irrigant activation . Moreover, one study compared the smear removal efficacy of an OEN with that of a DSVN. . According to the study by El Hashem et al. , SL and debris scores decreased from the apical to the coronal thirds of the root canal across all groups, including passive ultrasonic activation with Ultra-X, conventional needle, sonic activation with EQ-S, and mechanical activation with XP-endo Finisher groups. In all thirds, the control group (the conventional needle) represented the highest score for the SL and the remaining debris. No significant difference was observed between the XP-endo Finisher, Ultra-X, and EQ-S groups ( P > 0.05). Irrigation solution activation increased the removal of SL and debris in all canal thirds. The findings of a study by Korkut et al.  confirmed that Er:YAG laser-activated irrigation by photon-induced photoacoustic streaming (PIPS) led to greater removal of smear and debris from the root canal walls and a higher number of open tubules compared to conventional irrigation. According to the findings of a study performed by Buldur et al. , EndoVac was more influential in removing the SL from the apical third of the root canal system when compared to the conventional needle ( P < 0.05). The ozonated water + ethylenediaminetetraacetic acid (EDTA) regimen could provide SL removal comparable to that of NaOCl + EDTA. Toyota et al.  investigated the efficacy of SL removal and measured the amount of the remaining SL by observing the percentage of open dentinal tubules (POD) in the root canal. In the middle third of the root canal, active irrigation with ultrasonic and 5% NaOCl significantly increased the removal of the POD and the SL in comparison to the conventional needle. However, with 14% EDTA as the irrigant, no significant difference was found in SL removal between the two irrigation methods. In the apical third of the root, active irrigation with 14% EDTA and ultrasonic could significantly enhance SL and POD removal in comparison to other groups. Based on the findings of the study by Demirel et al. , experimental groups revealed significantly better SL removal in the coronal third of the root canal when compared to the control group, with a notable statistical significance ( P < 0.05). There was no significant difference in the use of 6% CA and 5% EDTA solutions when applied with either DSVNs or OENs ( P > 0.05). In the middle third, using 5% EDTA with DSVN, 6% CA with OEN, and 6% CA with DSVN showed statistically significant superior SL removal in comparison to the control group ( P < 0.05). Similarly, in the apical third, DSVN groups (using 6% CA and 5% EDTA) achieved significantly more influential SL removal than the control group ( P < 0.05). Moreover, the removal of SL was statistically more noticeable in the coronal third than in the apical third across all experimental groups ( P < 0.05). The findings confirm that the effectiveness of OENs and DSVNs for SL removal might be comparable, suggesting their similar effectiveness across different parts of the root canal. Apical extrusion of debris Two studies investigated the apical extrusion of debris following pulpectomy in primary molars, comparing the conventional needle irrigation technique (which activates the irrigant with an up-and-down movement of the needle) with two other root canal irrigation methods. The applied irrigants were the same across the compared groups. According to the findings of Gungor et al. , two root canal irrigation techniques were evaluated, along with two different instrumentation methods. It was revealed that all irrigation and instrumentation systems resulted in an assessable apical debris extrusion. Conversely, no statistically significant difference was found in debris extrusion between the irrigation methods ( P > 0.05). The total amount of debris extruded apically by the laser-activated irrigation (Er,Cr:YSGG laser system with optical fiber) was greater than that by the CNI (27G open-ended conventional needle). Venumbeka et al.  assessed the rate of irrigant extrusion and the depth of irrigant penetration into the dentin. According to their results, using the EndoVac system, the irrigation solution’s apical extrusion was significantly lower when compared to the manual irrigation system, namely, the DISPO VAN single-use syringe needle with a diameter of 0.50 mm ( P = 0.002). Additionally, greater irrigation penetration was obtained with the EndoVac system than with the manual irrigation system ( P = 0.000). The depth of irrigation penetration at 6 mm sections was higher than that at 4 mm and 2 mm sections for both irrigation systems ( P = 0.000). 

Studies included groups that compared conventional irrigation (OEN or SVN) for endodontic treatment in PT with sonic, ultrasonic, EndoVac, and laser activation methods. Only one study compared OENs and SVNs. In four studies, conventional irrigation was performed along with needle activation (agitation during irrigation). 

The results investigated in the in vitro studies included microorganism reduction, SL removal, and debris extrusion from the apical area. Reduction of microorganisms ( Enterococcus faecalis) Five studies compared the conventional irrigation method (four studies without activation and one study with activation) with three methods of activating the irrigation material using sonic, EndoVac, and laser. In the study by Kodical et al. , the colony-forming units of E. faecalis in group 3 (laser-activated irrigation— 810 nm diode laser— with Aquatine Endodontic Cleanser) were reduced compared to group 2 (conventional irrigation with Aquatine Endodontic Cleanser); Nonetheless, such a difference was not significant ( P = 0.7). On the contrary, the findings of Yavagal et al.  revealed that 2.5% NaOCl activated by the 810 nm diode laser significantly reduced bacterial growth compared to conventional irrigation with a syringe. In the study performed by Korkut et al. , the second and third groups were only techniques for canal disinfection rather than different irrigation methods; thus, the first (conventional irrigation with 5% NaOCl) and fourth (5% NaOCl activation with Er:YAG laser) groups underwent comparison. The viable count of E. faecalis was significantly decreased in group 4 in comparison to group 1 ( P < 0.05). In the study by Forghani et al. , no significant differences were found in the number of colonies with or without sonic activation between different concentrations. The sonic activation of the 0.5% NaOCl solution could reduce the number of colonies (not statistically significant). Finally, in the study conducted by Buldur et al. , the subgroups using EndoVac demonstrated a greater reduction in bacterial colonies than the activation of the irrigant with a conventional needle (not statistically significant). Smear layer removal Eight studies were compared, including studies that used conventional needles (30G side-vented needle,  23G needle syringe,  and two studies that were not discussed),  as well as three studies without activation  and one study with irrigant activation . Further, one study compared the smear removal efficacy of OENs and DSVNs . Four studies of root canal irrigation in PT using a conventional needle have been compared, including one with a 30G SVN , another with a 23G needle syringe,  and two studies that were not discussed in this review . Additionally, three studies did not use activation , and one study employed irrigant activation . Moreover, one study compared the smear removal efficacy of an OEN with that of a DSVN. . According to the study by El Hashem et al. , SL and debris scores decreased from the apical to the coronal thirds of the root canal across all groups, including passive ultrasonic activation with Ultra-X, conventional needle, sonic activation with EQ-S, and mechanical activation with XP-endo Finisher groups. In all thirds, the control group (the conventional needle) represented the highest score for the SL and the remaining debris. No significant difference was observed between the XP-endo Finisher, Ultra-X, and EQ-S groups ( P > 0.05). Irrigation solution activation increased the removal of SL and debris in all canal thirds. The findings of a study by Korkut et al.  confirmed that Er:YAG laser-activated irrigation by photon-induced photoacoustic streaming (PIPS) led to greater removal of smear and debris from the root canal walls and a higher number of open tubules compared to conventional irrigation. According to the findings of a study performed by Buldur et al. , EndoVac was more influential in removing the SL from the apical third of the root canal system when compared to the conventional needle ( P < 0.05). The ozonated water + ethylenediaminetetraacetic acid (EDTA) regimen could provide SL removal comparable to that of NaOCl + EDTA. Toyota et al.  investigated the efficacy of SL removal and measured the amount of the remaining SL by observing the percentage of open dentinal tubules (POD) in the root canal. In the middle third of the root canal, active irrigation with ultrasonic and 5% NaOCl significantly increased the removal of the POD and the SL in comparison to the conventional needle. However, with 14% EDTA as the irrigant, no significant difference was found in SL removal between the two irrigation methods. In the apical third of the root, active irrigation with 14% EDTA and ultrasonic could significantly enhance SL and POD removal in comparison to other groups. Based on the findings of the study by Demirel et al. , experimental groups revealed significantly better SL removal in the coronal third of the root canal when compared to the control group, with a notable statistical significance ( P < 0.05). There was no significant difference in the use of 6% CA and 5% EDTA solutions when applied with either DSVNs or OENs ( P > 0.05). In the middle third, using 5% EDTA with DSVN, 6% CA with OEN, and 6% CA with DSVN showed statistically significant superior SL removal in comparison to the control group ( P < 0.05). Similarly, in the apical third, DSVN groups (using 6% CA and 5% EDTA) achieved significantly more influential SL removal than the control group ( P < 0.05). Moreover, the removal of SL was statistically more noticeable in the coronal third than in the apical third across all experimental groups ( P < 0.05). The findings confirm that the effectiveness of OENs and DSVNs for SL removal might be comparable, suggesting their similar effectiveness across different parts of the root canal. Apical extrusion of debris Two studies investigated the apical extrusion of debris following pulpectomy in primary molars, comparing the conventional needle irrigation technique (which activates the irrigant with an up-and-down movement of the needle) with two other root canal irrigation methods. The applied irrigants were the same across the compared groups. According to the findings of Gungor et al. , two root canal irrigation techniques were evaluated, along with two different instrumentation methods. It was revealed that all irrigation and instrumentation systems resulted in an assessable apical debris extrusion. Conversely, no statistically significant difference was found in debris extrusion between the irrigation methods ( P > 0.05). The total amount of debris extruded apically by the laser-activated irrigation (Er,Cr:YSGG laser system with optical fiber) was greater than that by the CNI (27G open-ended conventional needle). Venumbeka et al.  assessed the rate of irrigant extrusion and the depth of irrigant penetration into the dentin. According to their results, using the EndoVac system, the irrigation solution’s apical extrusion was significantly lower when compared to the manual irrigation system, namely, the DISPO VAN single-use syringe needle with a diameter of 0.50 mm ( P = 0.002). Additionally, greater irrigation penetration was obtained with the EndoVac system than with the manual irrigation system ( P = 0.000). The depth of irrigation penetration at 6 mm sections was higher than that at 4 mm and 2 mm sections for both irrigation systems ( P = 0.000). 

All six articles included randomized clinical trials in which various irrigation techniques were compared for the treatment of primary root canals (Table ). Three and two studies were conducted in India and Turkey, respectively, and one study was performed in Syria. A total of 503 PT from 351 participants with an age group of 3–9 years (average 6.5 years) were treated, including cases from two studies focusing only on maxillary primary molars , one study examining maxillary anterior teeth , two studies investigating primary molars , and one study that did not focus on the type of treated teeth) . The pulp status of the pulpectomized teeth was not mentioned only in one study . In the others, the pulp was necrotic or irreversibly inflamed. Intervention and control In the randomized controlled trials included in this systematic review study, the conventional endodontic syringe (without activation) was compared with three activation methods (sonic, ultrasonic, and Endovac). In addition, two studies only compared conventional open-end syringes with side-vented ones. Outcomes The results included PP reduction, pulpectomy outcomes, obturation quality, and antibacterial efficacy after different root canal irrigation protocols. Postoperative pain Three studies by Seshadri et al. , Topçuoğlu et al. , and Gümüş et al.  attempted to compare the effect of irrigation with SVNs and activation with sonic (Endoactivator) in PP after pulpectomy of the primary molar teeth with the conventional irrigation technique. Two studies compared PP with OENs and SVNs. In the study performed by Topçuoğlu et al. , PP was compared by applying a 4-point pain intensity scale at intervals of 6, 12, 24, 48, and 72 h. At the 6-, 12-, and 24-h time points, groups that irrigated with an OEN demonstrated more severe PP compared to those irrigated with a DSVN ( P < 0.05). There was no significant difference between the groups after 48 h, 72 h, and 1 week ( P > 0.05). However, Seshadri et al. also reported that based on the visual analog scale and the Wong-Baker faces pain scale, PP was higher in the OEN than the SEN group in all the investigated intervals (6, 24, 48, and 72 h). Nonetheless, this difference was only significant after 24 h ( P < 0.05). The study by Gümüş et al.  was in favor of the active sonic irrigation technique (EndoActivator™). Based on the five-face scale, in the intervals of 8, 24, 48, and 72 h and 1 week following treatment, lower PP was recorded in the three investigated times up to 48 h. No significant difference was observed between active irrigation with sonic and conventional endodontic syringes 72 h and 1 week after treatment. Pulpectomy outcomes and obturation quality Jain et al.  studied radiographic and clinical outcomes of pulpectomy in PT after 24 h, 1 week, 1 month, 6 months, and 12 months, with two irrigants, 1% NaOCl and 6% citric acid (CA), as well as two irrigation techniques, namely, active sonic (EndoActivator™) and conventional needle techniques. The quality of obturation was also assessed with postoperative radiographs. All groups could significantly alleviate pain within 24 h of pulpectomy ( P < 0.001). The overall radiographic and clinical success rates over one year were 97.7% and 98.86%, respectively. The maximum quantity of optimal fillings was found in the CA + Endoactivator group, though it was statistically insignificant. The Endoactivator could contribute to 18% of optimal obturation, regardless of the applied chelating agent. The least number of voids and void area was found by the combination of Endoactivator and chelating agent (Group 1); nonetheless, this was not statistically significant. The researchers concluded that the inclusion of Endoactivator and 6% citric acid as irrigation adjuncts could help achieve better obturation quality and earlier pain alleviation. Antibacterial efficacy The findings of the study by Ahmadi et al.  showed that Endovac could significantly reduce the bacterial colony count of E. faecalis with both types of irrigants (NaOCl 2.5% and CHX 2%) compared to conventional syringes in primary molar teeth. Likewise, Kharsa et al.  evaluated the antibacterial effectiveness of ultrasonically activated and non-activated (the 27G conventional needle) solutions and the gel form of CHX 2% in infected root canals of anterior PT. Unlike the aerobic bacteria, no statistical differences were observed in the mean percentage change of the decimal logarithm of the anaerobic bacterial colony count. For aerobic bacteria, the CHX 2% solution activated better than the inactivated and control (NaOCl 5.25%), and the CHX 2% gel activated better than the inactivated CHX 2% solution and control. 

In the randomized controlled trials included in this systematic review study, the conventional endodontic syringe (without activation) was compared with three activation methods (sonic, ultrasonic, and Endovac). In addition, two studies only compared conventional open-end syringes with side-vented ones. 

The results included PP reduction, pulpectomy outcomes, obturation quality, and antibacterial efficacy after different root canal irrigation protocols. Postoperative pain Three studies by Seshadri et al. , Topçuoğlu et al. , and Gümüş et al.  attempted to compare the effect of irrigation with SVNs and activation with sonic (Endoactivator) in PP after pulpectomy of the primary molar teeth with the conventional irrigation technique. Two studies compared PP with OENs and SVNs. In the study performed by Topçuoğlu et al. , PP was compared by applying a 4-point pain intensity scale at intervals of 6, 12, 24, 48, and 72 h. At the 6-, 12-, and 24-h time points, groups that irrigated with an OEN demonstrated more severe PP compared to those irrigated with a DSVN ( P < 0.05). There was no significant difference between the groups after 48 h, 72 h, and 1 week ( P > 0.05). However, Seshadri et al. also reported that based on the visual analog scale and the Wong-Baker faces pain scale, PP was higher in the OEN than the SEN group in all the investigated intervals (6, 24, 48, and 72 h). Nonetheless, this difference was only significant after 24 h ( P < 0.05). The study by Gümüş et al.  was in favor of the active sonic irrigation technique (EndoActivator™). Based on the five-face scale, in the intervals of 8, 24, 48, and 72 h and 1 week following treatment, lower PP was recorded in the three investigated times up to 48 h. No significant difference was observed between active irrigation with sonic and conventional endodontic syringes 72 h and 1 week after treatment. Pulpectomy outcomes and obturation quality Jain et al.  studied radiographic and clinical outcomes of pulpectomy in PT after 24 h, 1 week, 1 month, 6 months, and 12 months, with two irrigants, 1% NaOCl and 6% citric acid (CA), as well as two irrigation techniques, namely, active sonic (EndoActivator™) and conventional needle techniques. The quality of obturation was also assessed with postoperative radiographs. All groups could significantly alleviate pain within 24 h of pulpectomy ( P < 0.001). The overall radiographic and clinical success rates over one year were 97.7% and 98.86%, respectively. The maximum quantity of optimal fillings was found in the CA + Endoactivator group, though it was statistically insignificant. The Endoactivator could contribute to 18% of optimal obturation, regardless of the applied chelating agent. The least number of voids and void area was found by the combination of Endoactivator and chelating agent (Group 1); nonetheless, this was not statistically significant. The researchers concluded that the inclusion of Endoactivator and 6% citric acid as irrigation adjuncts could help achieve better obturation quality and earlier pain alleviation. Antibacterial efficacy The findings of the study by Ahmadi et al.  showed that Endovac could significantly reduce the bacterial colony count of E. faecalis with both types of irrigants (NaOCl 2.5% and CHX 2%) compared to conventional syringes in primary molar teeth. Likewise, Kharsa et al.  evaluated the antibacterial effectiveness of ultrasonically activated and non-activated (the 27G conventional needle) solutions and the gel form of CHX 2% in infected root canals of anterior PT. Unlike the aerobic bacteria, no statistical differences were observed in the mean percentage change of the decimal logarithm of the anaerobic bacterial colony count. For aerobic bacteria, the CHX 2% solution activated better than the inactivated and control (NaOCl 5.25%), and the CHX 2% gel activated better than the inactivated CHX 2% solution and control. 

The QUIN tool’s scoring  indicated that among in vitro studies, four and eight represented a medium and low risk of bias, respectively. Among the articles with a medium-level risk of bias, the most frequent non-specified criteria were “operator details” and “detailed explanation of the sample size calculation”. Interestingly, some studies did not provide any information regarding randomization, blinding, or outcome assessor details. The assessment details of the QUIN tool are provided in Table . Based on ROB 2, six clinical studies were evaluated, three of which were deemed to have a low-level risk of bias. One study had a medium-level risk of bias, whereas two studies were categorized as high risk. Studies with a high-level risk of bias were found to have significant concerns in four domains, namely, deviation from intended interventions, the randomization process, outcome measurement, and missing outcomes. Additionally, the study that raised concerns in the randomization process was judged to have some concerns. Figures A and B present the results of the ROB 2 tool. 

To the best of our knowledge, this is the first systematic review study of articles that have investigated different irrigation protocols of the PT root canal system. This study evaluated various techniques for irrigating PT canals, reviewing 11 in vitro and 6 in vivo studies. However, a meta-analysis was impossible due to data heterogeneity. In vitro studies Microorganisms are the leading causative agents in the infections of the dental pulp and periapical regions . The process of sterilizing the root canal is vital for the achievement of successful outcomes in root canal therapies for deciduous teeth, especially during the stages of root development or resorption . E. faecalis is frequently found in resistant or failed root canal treatments, making up 40% of initial endodontic infections . It is commonly used as a model organism in research on endodontic procedures for primary molars. The effectiveness of an irrigation method in pulpectomy procedures can be assessed by measuring the reduction in E. faecalis populations . The antimicrobial efficacy of irrigation methods in laboratory contexts is determined by several key factors, including the anatomical complexity of root canals, the detailed parameters of the testing protocol (e.g., irrigant type, concentration, and exposure duration), and various procedural elements such as contact time, volume, application rate, and technique. These variables collectively influence the overall effectiveness of antibacterial treatments . The studies by Korkut et al. , Kodical et al. , and Yavagal et al.  demonstrated that laser-activated irrigation methods generally resulted in greater reductions in E. faecalis populations compared to traditional techniques. However, Kodical’s study  did not show statistically significant reductions. These variations are primarily due to differences in the irrigants and laser types used. Kodical et al.  utilized hypochlorous acid with a diode laser (810 nm), while Korkut et al.  applied 5% NaOCl with an Er:YAG laser (2940 nm) and PIPS activation. The diode laser combined with NaOCl was more effective than hypochlorous acid due to its thermal bactericidal action. The Er:YAG laser with NaOCl showed a synergistic effect through photomechanical mechanisms, further enhancing bacterial reduction . No significant difference was found in E. faecalis reduction between sonic activation (Endoactivator) and apical negative pressure (Endovac) methods. While Endoactivator did not significantly outperform conventional irrigation using 2.5% NaOCl, Endovac demonstrated statistically significant bacterial reduction . This discrepancy may be attributed to the type of teeth used in the studies, single-rooted teeth (primary incisors)  are easier to clean due to simpler canal systems, while multi-rooted teeth (such as second primary molars)  with more complex anatomies may benefit more from acoustic activation, which can enhance cleaning efficiency compared to syringe irrigation. Moreover, Endovac led to lower apical extrusion and more irrigant penetration into the dentinal tubules compared to conventional syringe methods (with manual agitation) in primary molar teeth . Positive pressure irrigation techniques (closed-end needles and laser-activated irrigation) tend to cause more apical extrusion compared to negative pressure techniques . PT have larger apical foramina compared to permanent teeth due to natural root resorption, making it easier for cleaning materials to extrude into the periapical tissue during treatment . Extruded debris in primary dentition is significant since the negative impacts of the microorganisms, the apical extrusion from necrotic debris, and various irrigants, such as chlorhexidine and NaOCl, can be harmful to stem cells . Additionally, root canal cleaning agents can cause changes in tooth development, such as underdevelopment, changes in crown shape, or root growth stop . The SL removal is crucial for improving the long-term outcomes of pulpectomy in PT exhibiting initial symptoms of peri-radicular lesions and pulpal necrosis.  The SL, a composite of organic and inorganic debris on the dentin and other surfaces post-instrumentation, impedes irrigation solution penetration, serves as a bacterial substrate, and obstructs the interface between fillings and the root canal wall . Achieving a hermetic seal of resorbable fillings to the dentinal tubules and canal walls is essential for clinical success. Studies have shown that SL removal significantly enhances the chance of successful root canal treatment in PT over 24 months . According to the articles included in this systematic review study, active irrigation methods, as compared to conventional syringe needle irrigation, result in greater removal of the SL and debris, particularly in the apical third of the root canal . This finding becomes more significant when using non-chelating irrigants.  On the other hand, using chelating agents such as EDTA can cause erosion of root dentin, necessitating caution in their application . Several studies on permanent teeth corroborate this finding ; however, SL removal appears to be easier in PT.  During the irrigation of the conventional syringe needle, the irrigating solution may not deeply penetrate the apical part of the root canal due to inadequate mechanical flushing action and high surface tension . Active irrigation, precise filing close to the apex, and adequate enlargement of the root canal are essential for enhancing SL removal. In vivo studies The results of clinical trials showed the difference in PP reduction between irrigation protocols. However, a statistically significant difference was still notable comparing non-sonic versus sonic activation until 48 h,  SVNs versus OENs until 24 h  and SVNs versus OENs until 72 h . It might be important to consider superior techniques regarding PP, especially for children, because the experience of pain may negatively affect patients and their families’ cooperation and trust in dental procedures. Furthermore, it increases the need for analgesic intake after treatment. It is noteworthy that the pain assessment in studies is conducted by self-report tools, which may lead to some bias in reporting pain by respondents. The status of treated pulps could be another factor. Irrigants containing infectious debris of necrotic root canals can provoke severe inflammatory reactions if extruded apically. Nonetheless, this hypothesis cannot be undoubtedly concluded due to the scarcity of studies. Two studies evaluated the antibacterial efficacy of different irrigation protocols . The results of Kharsa’s study  showed a significant decrease in aerobic colonies with ultrasonic activation. It should be mentioned that the rationale of active irrigation to increase chemical access to hard-to-reach areas may be less important in anterior PT with wider and straighter root canals compared to primary molars with complicated root canal anatomy. However, Endovac could significantly decrease the quantity of bacterial colonies in primary molar teeth,  which may indicate that Endovac is more effective compared to ultrasonic activation. Another clinical study by Jain et al.  revealed that using active irrigation could enhance obturation quality, although the difference was not statistically meaningful. Effective removal of debris should be carefully followed due to the importance of an optimal filling to inhibit the reinfection of root canals. Thus, active irrigation methods could be beneficial. As mentioned earlier, the main limitation of this review study was the heterogeneity of irrigation protocols in both in vitro and in vivo studies, which inhibited further statistical analysis. In other words, available studies are not conclusive regarding the irrigation of the PT root canal system. Hence, researchers suggest more studies in both laboratory and clinical settings. 

Microorganisms are the leading causative agents in the infections of the dental pulp and periapical regions . The process of sterilizing the root canal is vital for the achievement of successful outcomes in root canal therapies for deciduous teeth, especially during the stages of root development or resorption . E. faecalis is frequently found in resistant or failed root canal treatments, making up 40% of initial endodontic infections . It is commonly used as a model organism in research on endodontic procedures for primary molars. The effectiveness of an irrigation method in pulpectomy procedures can be assessed by measuring the reduction in E. faecalis populations . The antimicrobial efficacy of irrigation methods in laboratory contexts is determined by several key factors, including the anatomical complexity of root canals, the detailed parameters of the testing protocol (e.g., irrigant type, concentration, and exposure duration), and various procedural elements such as contact time, volume, application rate, and technique. These variables collectively influence the overall effectiveness of antibacterial treatments . The studies by Korkut et al. , Kodical et al. , and Yavagal et al.  demonstrated that laser-activated irrigation methods generally resulted in greater reductions in E. faecalis populations compared to traditional techniques. However, Kodical’s study  did not show statistically significant reductions. These variations are primarily due to differences in the irrigants and laser types used. Kodical et al.  utilized hypochlorous acid with a diode laser (810 nm), while Korkut et al.  applied 5% NaOCl with an Er:YAG laser (2940 nm) and PIPS activation. The diode laser combined with NaOCl was more effective than hypochlorous acid due to its thermal bactericidal action. The Er:YAG laser with NaOCl showed a synergistic effect through photomechanical mechanisms, further enhancing bacterial reduction . No significant difference was found in E. faecalis reduction between sonic activation (Endoactivator) and apical negative pressure (Endovac) methods. While Endoactivator did not significantly outperform conventional irrigation using 2.5% NaOCl, Endovac demonstrated statistically significant bacterial reduction . This discrepancy may be attributed to the type of teeth used in the studies, single-rooted teeth (primary incisors)  are easier to clean due to simpler canal systems, while multi-rooted teeth (such as second primary molars)  with more complex anatomies may benefit more from acoustic activation, which can enhance cleaning efficiency compared to syringe irrigation. Moreover, Endovac led to lower apical extrusion and more irrigant penetration into the dentinal tubules compared to conventional syringe methods (with manual agitation) in primary molar teeth . Positive pressure irrigation techniques (closed-end needles and laser-activated irrigation) tend to cause more apical extrusion compared to negative pressure techniques . PT have larger apical foramina compared to permanent teeth due to natural root resorption, making it easier for cleaning materials to extrude into the periapical tissue during treatment . Extruded debris in primary dentition is significant since the negative impacts of the microorganisms, the apical extrusion from necrotic debris, and various irrigants, such as chlorhexidine and NaOCl, can be harmful to stem cells . Additionally, root canal cleaning agents can cause changes in tooth development, such as underdevelopment, changes in crown shape, or root growth stop . The SL removal is crucial for improving the long-term outcomes of pulpectomy in PT exhibiting initial symptoms of peri-radicular lesions and pulpal necrosis.  The SL, a composite of organic and inorganic debris on the dentin and other surfaces post-instrumentation, impedes irrigation solution penetration, serves as a bacterial substrate, and obstructs the interface between fillings and the root canal wall . Achieving a hermetic seal of resorbable fillings to the dentinal tubules and canal walls is essential for clinical success. Studies have shown that SL removal significantly enhances the chance of successful root canal treatment in PT over 24 months . According to the articles included in this systematic review study, active irrigation methods, as compared to conventional syringe needle irrigation, result in greater removal of the SL and debris, particularly in the apical third of the root canal . This finding becomes more significant when using non-chelating irrigants.  On the other hand, using chelating agents such as EDTA can cause erosion of root dentin, necessitating caution in their application . Several studies on permanent teeth corroborate this finding ; however, SL removal appears to be easier in PT.  During the irrigation of the conventional syringe needle, the irrigating solution may not deeply penetrate the apical part of the root canal due to inadequate mechanical flushing action and high surface tension . Active irrigation, precise filing close to the apex, and adequate enlargement of the root canal are essential for enhancing SL removal. 

The results of clinical trials showed the difference in PP reduction between irrigation protocols. However, a statistically significant difference was still notable comparing non-sonic versus sonic activation until 48 h,  SVNs versus OENs until 24 h  and SVNs versus OENs until 72 h . It might be important to consider superior techniques regarding PP, especially for children, because the experience of pain may negatively affect patients and their families’ cooperation and trust in dental procedures. Furthermore, it increases the need for analgesic intake after treatment. It is noteworthy that the pain assessment in studies is conducted by self-report tools, which may lead to some bias in reporting pain by respondents. The status of treated pulps could be another factor. Irrigants containing infectious debris of necrotic root canals can provoke severe inflammatory reactions if extruded apically. Nonetheless, this hypothesis cannot be undoubtedly concluded due to the scarcity of studies. Two studies evaluated the antibacterial efficacy of different irrigation protocols . The results of Kharsa’s study  showed a significant decrease in aerobic colonies with ultrasonic activation. It should be mentioned that the rationale of active irrigation to increase chemical access to hard-to-reach areas may be less important in anterior PT with wider and straighter root canals compared to primary molars with complicated root canal anatomy. However, Endovac could significantly decrease the quantity of bacterial colonies in primary molar teeth,  which may indicate that Endovac is more effective compared to ultrasonic activation. Another clinical study by Jain et al.  revealed that using active irrigation could enhance obturation quality, although the difference was not statistically meaningful. Effective removal of debris should be carefully followed due to the importance of an optimal filling to inhibit the reinfection of root canals. Thus, active irrigation methods could be beneficial. As mentioned earlier, the main limitation of this review study was the heterogeneity of irrigation protocols in both in vitro and in vivo studies, which inhibited further statistical analysis. In other words, available studies are not conclusive regarding the irrigation of the PT root canal system. Hence, researchers suggest more studies in both laboratory and clinical settings. 

Based on the findings of this in vitro study, the techniques of cleaning the PT canal, which is accompanied by the activation of the irrigant, cause a significant reduction in E. faecalis inside the canal. Among the different activation techniques, the laser has shown positive results. In addition to the irrigation technique, the type of irrigant is highly important in the removal of the SL. The use of chelating agents reduces the importance of the irrigation technique, especially in the apical third. It seems that activating the irrigant with ultrasonic has a positive effect on removing the SL and debris inside the canal. Regarding the extrusion of debris, the studies are very few and inconclusive; however, Endovac caused less extrusion and more penetration of the irrigant into the tubules. According to clinical studies, PP with side vent syringes was less than open-end, and the activation of irrigant with sonic activation was effective in reducing PP. The number of clinical studies that demonstrated the antibacterial effects of the type of irrigation technique is few and inconclusive. 

Supplementary Material 1. 

