Efficacy of Laser-Activated Irrigation Versus Ultrasonic-Activated Irrigation: A Systematic Review

This study aimed to conduct a systematic review and critical analysis of the evidence pertaining to the efficacy of laser-activated irrigation (LAI) versus ultrasonic-activated irrigation (UAI) in mature permanent teeth. A comprehensive literature search was performed using PubMed and Google Scholar. Additionally, a hand search was performed to identify relevant studies related to UAI and LAI. The search covered all articles published from January 1997 to December 2021. The identified studies were screened for eligibility using the inclusion and exclusion criteria. The included articles were then subjected to data extraction and analysis. The search yielded 1,637 results. Of these, 23 articles were included in this systematic review. All included articles were assessed for the outcomes of antimicrobial efficacy, smear layer, and dentin debris removal. The majority of the articles reported the superiority of LAI over UAI. Within the confines of this systematic review, the current evidence mandates that LAI has superior efficacy over UAI in the elimination of microorganisms, dentin debris, and smear layer from the root canal system.


Introduction And Background
Endodontic treatment consists of thorough cleaning and disinfection of the root canal system to remove debris, microbial loads, and necrotic pulp tissue. Currently, mechanical instruments and disinfecting irrigants are used for this purpose [1].
When the root canal system is instrumented, dentin debris and an accumulated smear layer cover the canal walls [2]. The smear layer is a non-uniform, amorphous layer consisting of organic and inorganic components such as pathogenic organisms, their by-products, and parts of the odontoblastic process [3]. The smear layer has been shown to prevent both irrigants and sealants from penetrating the dentinal tubules [4]. This prevents proper cleaning and root canal filling. Consequently, chemical disinfection by irrigation is essential [5].
A syringe and a needle are frequently used in conjunction to irrigate the root canal. However, its effectiveness is constrained because the irrigant can only flow 1 mm past the tip of the needle [6,7]. This suggests that the irrigant frequently misses the apical region of the canal [8]. This encourages the continuation of biofilm and the survival of a large number of microflora, even after the chemomechanical preparation is deemed to be finished [9].
Additionally, Enterococcus faecalis and Porphyromonas gingivalis species have a 500-micron penetration limit in dentinal tubules and are the main causes of persistent periradicular pathosis [10]. Therefore, effective debridement and disinfection depend on the ability of the irrigant to penetrate sufficiently, especially in the untreated portions of the root canal [9].
To circumvent the disadvantages of syringe-needle irrigation, several more sophisticated techniques have been developed, including the use of ultrasonics and lasers. These are of utmost importance because they increase the effectiveness of irrigants [11][12][13]. Lasers can eliminate Candida albicans and highly resistant E. faecalis species in addition to cleaning and sterilizing the root canal dentin [14][15][16]. Laser-guided irrigation effectively removes the debris and smear layer from the root canal system by creating unstable vapor bubbles with a secondary cavitation effect [17]. The phenomena of cavitation and acoustic flow are produced by ultrasonic-guided irrigation and are beneficial for the more effective eradication of biofilm [18]. Ultrasonicstimulated irrigation has been shown to remove more debris and smear layer than conventional irrigation [19]. ultrasonic-activated irrigation (UAI) and the disinfection efficacy of various laser applications [20,21]. None of the systematic reviews attempted to compare the efficacy of laser-activated irrigation (LAI) and UAI. Hence, this study aimed to conduct a systematic review and critical analysis of the evidence pertaining to the efficacy of LAI versus UAI in mature permanent teeth.

Study Design
This systematic review is structured and adheres to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) standards [22]. The use of checklists in PRISMA is likely to raise reporting requirements for systematic reviews and provide transparency in the selection of papers for a systematic review.

Focused Research Question
The clinical question was formulated according to PICOS, and was as follows: "Which irrigation activation method, between the laser-activated irrigation and ultrasonic-activated irrigation, is more effective in terms of root canal disinfection, smear layer removal, debris removal, or cleanliness in human-extracted teeth?." The population (P) considered here were mature permanent extracted teeth; the intervention (I) was irrigant activation methods; the comparison (C) was between UAI and LAI methods; the outcome (O) assessed were root canal disinfection, smear layer removal, debris removal, or cleanliness in human extracted teeth; and the study design (S) considered were all in vitro studies.

Literature Search
To find all relevant articles pertaining to UAI and LAI, a thorough literature search was conducted utilizing two electronic databases and a manual search. PubMed and Google Scholar were consulted by using the following search strategy: "(ultrasonic-activated irrigation) AND (laser-activated irrigation) AND (antimicrobial efficacy) OR (biofilm removal) OR (smear layer removal) OR (cleanliness) OR (debris removal)." All articles published from January 1997 to December 2021 were included in the search process.
All identified reports were located, recovered, and entered into bibliographic software (Rayyan). Records with duplicates were eliminated. All in vitro studies published in the English language were included in the systematic review. After removing duplicate entries, the published title and abstracts were first evaluated for relevancy using the inclusion and exclusion criteria. The full texts of these pertinent studies were then acquired, reviewed, and ultimately decided to be included in the systematic review. The search process is depicted in Figure 1.

Inclusion Criteria
In vitro studies comparing LAI and UAI and assessing antimicrobial efficiency, smear layer removal, debris removal, or cleanliness on fully formed non-endodontically treated human mature permanent teeth were included, as were publications exclusively in the English language with full text available in hard copy or soft copy.

Exclusion Criteria
Studies that did not use either activation technique; studies that did not assess antimicrobial effectiveness, smear layer removal, debris removal, or cleanliness; laboratory studies using resin models, bovine root models, and endodontically treated teeth; and animal studies were excluded. Randomized control trials, case reports, reviews, and studies unrelated to the subject of the current study were also excluded.

Data Extraction and Analysis
Two reviewers each extracted the data independently. Mutual evaluation of the first 30 articles served as the calibration process. Initial screening was done on all titles and abstracts using the inclusion and exclusion criteria. Subsequently, complete texts of these selected studies were acquired for a second round of screening. To resolve any disagreements, reviewers got together for a meeting and discussion. Studies that passed the second round of screening were sent in for data extraction. The data gathered included the year of study, author, sample size, master apical file, irrigation instrument, wavelength, time, irrigant used, evaluation method, evaluation criteria, presence or absence of isthmus, and results. All 23 relevant articles were suitable for the systematic review (  MAF = master apical file; Er,Cr:YSGG = erbium, chromium-doped yttrium-scandium-gallium and garnet; NaOCl = sodium hypochlorite; LAI = laseractivated irrigation; PUI = passive ultrasonic irrigation; Er:YAG = erbium-doped yttrium aluminum garnet; EDTA = ethylenediamine tetraacetic acid; UAI = ultrasonic-activated irrigation; PIPS = photon-induced photoacoustic streaming; Nd:YAG = neodymium-doped yttrium aluminum garnet; SEM = scanning electron microscope; CFU = colony-forming units; WL = working length; CLSM = confocal laser scanning microscope; SWEEPS = shockwave-enhanced emission photoacoustic streaming

Systematic Review
The search resulted in 1,637 articles. Eliminating duplicates and non-relevant articles resulted in 118 articles. After screening their titles and abstracts, 86 studies were excluded. In total, 32 articles were considered relevant and searched for full-text availability. Finally, the full texts of 23 articles were procured and studied in detail. After studying the full text of these 23 articles, all studies qualified for this systematic review [9,13,.
Antimicrobial efficacy was the only outcome of the study in seven reports [9,13,27,31,37,39,40]. Smear layer removal was the only outcome of the investigation in five reports [29,30,32,36,43]. Debris removal was the only outcome of the investigation in nine reports [23][24][25]28,34,35,38,41,42]. Both antimicrobial efficacy and smear layer removal were the outcomes of investigation in one report [33]. Both smearing layer removal and debris removal were the outcomes of an investigation in one report [26].
Despite the fact that the other four studies found no appreciable distinction between the two approaches [28,35,38,42].

Discussion
During endodontic therapy, it might be challenging to completely remove biofilms, pathogenic organisms, necrotic tissue, and hard tissue debris from the root canal complex. Because of the complicated structure of root canal architecture, it is hard to reach every area, leaving some unattended. The root canal abnormalities, fins, and isthmuses are filled with a smear layer caused by mechanical instrumentation, which compromises the effectiveness of cleaning and disinfection [44]. Irrigation plays a vital role in cleaning and disinfecting the root canal complex, including fins and isthmuses [45].
In this study, the effectiveness of removing biofilm, smear layer, and dentin debris from the root canal system using LAI and UAI was compared. The results show that irrigation with laser activation is superior to irrigation with ultrasonic activation. However, a moderate level of evidence showed no distinction between irrigation that was activated by a laser and irrigation that was activated by ultrasonic.
As a novel method of agitating intracanal disinfectants, LAI has recently gained popularity. Its result causes cavitation. By powerfully assimilating the laser energy, laser radiation causes temporary cavitation in the irrigant via optical breakdown [46,47]. A well-known method of LAI is photon-induced photoacoustic streaming (PIPS), which uses a fiber tip to pulse at incredibly low energies to convey energy into the solution while only slightly raising dental temperature [48]. It intensifies fluid exchange and the removal of debris by producing vapor bubbles with secondary cavitation effects [17,24]. In clinical use, UAI is undoubtedly the most common method of irrigant activation. Its principal cleaning action is accredited to acoustic microstreaming [49]. In prepared canals, acoustic microstreaming can produce sufficient shear forces to clear the debris.
The study approaches used in the included papers showed considerable variation. The authors demonstrated the methodological differences in the master apical file (MAF), irrigation time, irrigant, and irrigant concentrations after reviewing the included articles. As a result, depending on these factors, the effectiveness of these two strategies may change. It is significant to remember that these variables may affect the findings of the investigation. It is important to stress that the authors of the included research used variable laser parameters with various irrigants, as well as their concentrations and durations of action ( Table 1). There were noticeable differences in the ultrasonic devices and their power settings, ultrasonic tips, and irrigation times in the included studies. These variations may have led to conflicting evidence in some comparisons.
This review had certain restrictions. The diversity of the studies included was the first drawback. Therefore, it was inappropriate to perform a meta-analysis [50]. The second drawback was that in vitro research was used to obtain the results of the included studies. A well-designed experimental in vitro investigation, however, may also result in effective treatments for medical issues. The lack of standardized assessment criteria for the evaluation of debris remains and subsequent cleanliness made cross-study comparisons problematic due to the varied evaluation procedures utilized in the investigations.
To conclude, out of the 23 publications that were included, more articles favored LAI in terms of antibacterial effectiveness, smear layer removal, and dentin debris removal from the root canal system. The results of this analysis are relevant to clinical practice because irrigation is a necessary method for removing biofilm, smear layer, and dentin debris from the root canal system during endodontic treatments.

Conclusions
Within the confines of this systematic review, the current evidence mandates that LAI has superior efficacy over UAI in the elimination of microorganisms, dentin debris, and smear layer from the root canal system. Studies of superior methodologic standards are needed to examine the effectiveness of LAI and UAI for the removal of microorganisms, dentin debris, and smear layer from the root canal system as the results were expressed from moderately high-standard studies.

Conflicts of interest:
In compliance with the ICMJE uniform disclosure form, all authors declare the following: Payment/services info: All authors have declared that no financial support was received from any organization for the submitted work. Financial relationships: All authors have declared that they have no financial relationships at present or within the previous three years with any organizations that might have an interest in the submitted work. Other relationships: All authors have declared that there are no other relationships or activities that could appear to have influenced the submitted work.