Irrigant flow during photon-induced photoacoustic streaming (PIPS) using Particle Image Velocimetry (PIV)

Principle and antimicrobial efficacy of laser-activated irrigation: A narrative review

In the last two decades, the activation of root canal irrigants with pulsed lasers as an adjunct in root canal treatment has become increasingly popular. This narrative review explains the physical basics and the working mechanism of laser-activated irrigation (LAI), explores the parameters influencing LAI efficacy, considers historical evolutions in the field and summarizes laboratory and clinical evidence with emphasis on the antimicrobial action of LAI. Cavitation is the driving force behind LAI, with growing and imploding vapour bubbles around the laser tip causing various secondary phenomena in the irrigant, leading to intense liquid dynamics throughout the underlying root canal. High-speed imaging research has shown that laser wavelength, pulse energy, pulse length and fibre tip geometry are parameters that influence this cavitation process. Nevertheless, this has not resulted in standardized settings for LAI. Consequently, there is significant variability in studies assessing LAI efficacy, complicating the synthesis of results. Laboratory studies in extracted teeth suggest that, with regard to canal disinfection, LAI is superior to conventional irrigation and there is a trend of higher antimicrobial efficacy of LAI compared to ultrasonic activation. Clinical evidence is limited to trials demonstrating similar postoperative pain levels after LAI versus no activation or ultrasonic activation. Clinical evidence concerning the effect of LAI on healing of apical periodontitis as yet is scarce.

The influence of laser-activated irrigation on post-operative pain following root canal treatment: A systematic review

OBJECTIVES

Synthesise evidence on post-endodontic pain (PEP) in adult teeth undergoing primary root canal treatment with the adjunctive use of laser-activated irrigation (LAI) as compared with conventional needle irrigation (CNI) during the first post-operative week.

DATA

An electronic search was performed; no language constraints or restriction on the year of publication were applied.

SOURCES

Medline, Scopus, Cochrane and PubMed on 04 June 2023 STUDY SELECTION: Randomised clinical trials (RaCTs) that evaluated PEP after LAI of endodontic irrgants were included. Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines were used. PEP was analysed at various time intervals until 1 week after treatment, related to the type of LAI used and the need for analgesia.

REULTS

Of the 793 articles identified through the electronic database search, 6 RaCTs were included. Qualitative review was favoured over meta-analysis due to substantial methodological heterogeneity between studies. Five studies were at high risk for bias determined by the Cochrane Risk-of-Bias 2 tool. Diode LAI demonstrated superior efficacy to needle irrigation in reducing pain 6-48 h post-treatment. The impact of LAI by photon-induced photoacoustic streaming (PIPS) was unclear and no difference was observed between PIPS and needle irrigation. However, PIPS mitigated PEP better than manual dynamic activation, sonic and ultrasonic activation. There was no difference in analgesia intake between LAI and needle irrigation groups.

CONCLUSIONS

LAI may help reduce PEP in the first 48 h. Methodological standardisation of future RaCTs on LAI would be beneficial in allowing a more accurate review with the possibility of quantitative synthesis.

CLINICAL SIGNIFICANCE

This unique synthesis used stringent criteria to reduce confounding factors and provided valuable evidence regarding PEP with different types of LAI. It helps clinicians choose an appropriate LAI technique as compared with CNI and predicts a time frame for reducing PEP.

Phase-locked µPIV analysis of flow dynamics in a simulated root canal with different laser-activated irrigations

PURPOSE

To measure the dynamic characteristics of the flow field in a complex root canal model activated by two laser-activated irrigation (LAI) modalities at different activation energy outputs: photon-induced photoacoustic streaming (PIPS) and microshort pulse (MSP).

METHODS

A phase-locked micro-scale Particle Image Velocimetry (µPIV) system was employed to characterise the temporal variations of LAI-induced velocity fields in the root canal following a single laser pulse. The wall shear stress (WSS) in the lateral root canal was subsequently estimated from the phase-averaged velocity fields.

RESULTS

Both PIPS and MSP were able to generate the 'breath mode' of the irrigant current under all tested conditions. The transient irrigation flush in the root canal peaked at speeds close to 6 m/s. However, this intense flushing effect persisted for only about 2000 µs (or 3% of a single laser-pulse activation cycle). For MSP, the maximum WSS magnitude was approximately 3.08 Pa at an activation energy of E = 20 mJ/pulse, rising to 9.01 Pa at E = 50 mJ/pulse. In comparison, PIPS elevated the WSS to 10.63 Pa at E = 20 mJ/pulse.

CONCLUSION

Elevating the activation energy can boost the peak flushing velocity and the maximum WSS, thereby enhancing irrigation efficiency. Given the same activation energy, PIPS outperforms MSP. Additionally, increasing the activation frequency may be an effective strategy to improve irrigation performance further.

Can diode laser 810 nm decrease post endodontic pain in patients with asymptomatic necrotic maxillary incisors? A four-arm randomized controlled trial

AIM

To find the best method for applying the diode laser 810 nm to relieve post-endodontic pain on necrotic maxillary incisors with periapical lesions within a single-visit treatment.

METHODS

Eighty patients with a necrotic incisor, diagnosed with asymptomatic apical periodontitis, received standardized cleaning and shaping procedures, then divided randomly with a 1:1:1:1 allocation ratio into four groups: Group 1: control group with no laser application, Group 2: applying the diode laser as an irrigation activation system (IAS), Group 3: applying the diode laser from the buccal and palatal mucosa, Group 4: applying the diode laser as an IAS and from buccal and palatal mucosa. The postoperative pain was assessed using the visual analog scale (VAS) 1, 3, 7, and 14 days after the treatment. The mean values of the VAS score were statistically analyzed used Kruskal-Walis and Mann-Whitney U tests. The level of significance was set at a = 0.05.

RESULTS

During 14 days after treatment, there was a statistically significant difference between mean values of VAS scores in the four groups (P value < 0.05); Group 1 scored the highest score, whereas Group 4 showed the lowest one. Moreover, Group 4 showed favorable outcomes compared with Group 2 and Group 3 during the first three days after treatment.

CONCLUSION

Diode laser reduced postoperative pain after necrotic teeth with large-sized apical lesion treatment, whereas using diode laser either as an IAS or LLLT reduced the postoperative pain compared with the control group. Moreover, the usage of a diode laser in both previous techniques represents the best protocol for postoperative pain relief during 14 days of treatment.

CLINICAL RELEVANCE

The clinical significance of this study is to investigate the best method to reduce postoperative pain using diode lasers 810 nm; where the results of this study indicated that the more diode laser exposer in LLLT and IAS, the less postoperative pain after endodontic procedures.

Traditional and Recent Root Canal Irrigation Methods and Their Effectiveness: A Review

According to contemporary dental standards, the primary goal of endodontic therapy is the chemo-mechanical cleaning of the complex root canal system. Watering root canals with approved solutions and activating them are essential parts of this operation. This review outlines various irrigant activation methods for root canal therapy. Specifically, a comparison among the methods of manual dynamic activation, sonics (subsonic, sonic, and ultrasonic), internal heating, and lasers, was conducted. The results in this work were gathered using Scopus, Web of Science, Google Scholar, and PubMed databases by searching the following keywords: sodium hypochlorite, cleaning, activation, and irrigation methods. The present work concluded that the use of irrigant activation has a greater benefit than its absence. Regardless, it is impossible to point to a single effective activation method.

Biofilm Removal from In Vitro Narrow Geometries Using Single and Dual Pulse Er:YAG Laser Photoacoustic Irrigation

The disinfection and removal of biofilm from titanium dental implants remains a great challenge in oral medicine. Here we present results of novel photoacoustic irrigation laser modalities for biofilm removal in model geometries mimicking the peri-implant pocket. The efficacy of single pulse (Er:YAG-SSP) and dual pulse (Er:YAG-AutoSWEEPS) photoacoustic irrigation modalities were determined for Enterococcus faecalis biofilm decontamination from titanium surfaces in narrow cylindrical and square gap geometries. The density of bacteria as well as the number of live bacteria were determined prior and after different photoacoustic treatments. Both SSP and AutoSWEEPS photoacoustic irrigation techniques removed at least 92% of biofilm bacteria during the 10 s photoacoustic treatment. The effectiveness of cleaning was better in the narrow square gap geometry compared to the cylindrical geometry. The dual pulse Er:YAG-AutoSWEEPS photoacoustic irrigation showed better results compared to SSP modality. No chemical adjuvants were needed to boost the effectiveness of the photoacoustic irrigation in the saline solution. The results imply that photoacoustic irrigation is an efficient cleaning method for debridement and decontamination in narrow geometries and should be considered as a new therapeutic option for the treatment of peri-implant diseases.

Effect of SWEEPS and PIPS techniques on dye extrusion in photodynamic therapy procedure after root canal preparation

AIM

The aim of this study is to measure and compare the amount of apical extrusion of the methylene blue as photosensitizer using Laser-activated irrigation(LAI) techniques (SWEEPS, PIPS) and photodynamic therapy (PDT).

MATERIALS AND METHODS

40 single-rooted premolar teeth were selected and their root canals were cleaned and prepared. The photosensitizer, Methylene blue (MB), was used as dye which applied inside the root canals and the access cavities. Then the teeth were randomly allocated to 4 groups. Different techniques (SWEEPS, PIPS, PDT) were used in 3 groups. One group received no activation. Data related to the concentration of the extruded methylene blue was measured using ultraviolet and visible (UV-Vis) absorption spectroscopy. Absorption peak intensity of MB in the wavelength of 668 nm was considered as the concentration index according to Beer Lambert law. Taking into account the normal distribution of this data, one-way ANOVA analysis was used to evaluate the effects of the independent variables on the amount of apical extrusion of the irrigant.

RESULTS

Based on the results of ANOVA analysis, there was no significant difference between the amounts of apical extrusion of MB between different groups (p = 0.628) CONCLUSION: Using SWEEPS and PIPS techniques, despite diffusion of the photosensitizer, didn't lead to any difference in the amount of apical extrusion. Therefore, these LAI techniques can be used safely for root canal irrigation.

Efficiency of diode laser in control of post-endodontic pain: a randomized controlled trial

OBJECTIVES

As post-endodontic pain control is one of the main targeted addressed in endodontics, our aim was delignated to compare two different methods for low-level laser application utilizing diode laser: low-level laser therapy (LLLT) and laser-activated irrigation (LAI) in the control of post-endodontic pain.

MATERIALS AND SUBJECTS

A total of 180 patients received single-visit root canal treatment; they were randomly allocated into 3 equal groups. Group I received LAI, group II received LLLT, and group III served as control with normal root canal treatment and mock laser intervention (ML group). Postoperative pain was recorded using visual analogue scale (VAS) after 24, 48, and 72 h. Data were tabulated and statistically analyzed.

RESULTS

At 24 h, there was a statistically significant difference between median pain scores in the three groups (P value < 0.001) with ML group scored highest score followed by LAI and then LLLT group. At 48 h, there was a statistically significant difference between the three groups (P value < 0.001), with ML group scoring highest median pain scores while LLLT and LAI showed statistical insignificant scores. At 72 h, there was no statistically significant difference between the 3 groups (P value = 0.179).

CONCLUSION

LLLT is superior to LAI and ML group in the control of immediate postoperative pain after 24 h while after 48 h both LAI and LLLT were equally effective, but they still showed significant differences when compared to ML group.

CLINICAL RELEVANCE

Diode laser can be used by clinicians as it decreases the post-endodontic pain in patients with symptomatic apical periodontitis undergoing endodontic treatment.

Advances in the Role of Sodium Hypochlorite Irrigant in Chemical Preparation of Root Canal Treatment

Irrigation of root canal system is of great significance to the success of endodontic treatment, where sodium hypochlorite (NaOCl) is the most widely used irrigant in chemical preparation. NaOCl functions by eliminating bacterial biofilms and dissolving organic tissue, which may vary according to several factors such as the microbiology of root canal infection and the concentration of the irrigant. It has been proposed that the effectiveness of NaOCl could be enhanced via several methods, including heating the irrigant, applying in conjunction with certain reagents, or activating by agitation techniques. Despite its antibacterial and tissue-dissolving capacities, NaOCl should be used with caution to avoid detrimental effect due to its cytotoxicity and negative effect on dentin properties. In this narrative review, we discussed the factors that affect the properties of NaOCl, the methods to improve its efficacy, and the side effects that might occur in clinical practice.

Isthmus morphology influences debridement efficacy of activated irrigation: A laboratory study involving biofilm mimicking hydrogel removal and high-speed imaging

AIM

Little is known about the influence of isthmus morphology on the debridement efficacy of activated irrigation. The aim of this study was to investigate the influence of isthmus morphology on the debridement efficacy of laser-activated irrigation (LAI), EDDY and needle irrigation (NI), and to explain the methods of isthmus cleaning by LAI and EDDY.

METHODOLOGY

Four root canal models (apical diameter: 0.30 mm, taper: 0.06, curvature: 23°, length: 20 mm) were produced by CAD-CAM with different isthmus morphologies: long-wide (4 mm; 0.4 mm), long-narrow (4 mm; 0.15 mm), short-wide (2 mm; 0.4 mm) and short-narrow (2 mm; 0.15 mm). The isthmuses were filled with a hydrogel containing dentine debris. The canals were filled with irrigant and models were assigned to the following irrigation protocols (n = 240): needle irrigation (NI) with a 30G needle, Eddy, and LAI (2940 nm Er:YAG-laser, 15 Hz, 40 mJ, SWEEPS, tip at the canal entrance). Standardized images of the isthmuses were taken before and after irrigation, and the amount of removed hydrogel was determined using image analysis software and compared across groups using Kruskal-Wallis test followed by Dunn's multiple comparison. Visualization of the isthmus during activation was achieved using a high-speed camera. The pattern and speed of the flow in the isthmus as well as transient and stable cavitation were analysed using imaging software.

RESULTS

Laser-activated irrigation, EDDY and NI removed more hydrogel in short-wide isthmuses than in narrow isthmuses (p < .001). LAI and EDDY removed more hydrogel than NI in every isthmus configuration (p < .001). EDDY showed eddies and stable cavitation, and LAI showed transient cavitation at each pulse, and pulsed horizontal flow with the highest particle speed in closed short isthmuses.

CONCLUSIONS

Isthmus morphology influences debridement in all irrigation groups. Short-wide isthmuses were the easiest to clean while narrow isthmuses were the most challenging to clean. Width seems to be a more critical anatomical parameter than length. LAI and EDDY resulted in the greatest biofilm removal and performed better than NI. EDDY produced eddies and stable cavitation in the isthmus, and LAI showed transient cavitation and pulsed horizontal flow.

Effect of different irrigation activation techniques on irrigation penetration into the simulated lateral canals

This study, in which a hundred human teeth with single straight canal were used, focused on the evaluation of contrast solution penetration ability into the simulated lateral canals activated by XP-endo Finisher (XPF), EDDY, Nd:YAG, and Er:YAG laser systems with three different observation methods. The root canals were prepared up to X4 at working length using the ProTaper Next system. The teeth were decalcified and simulated lateral canals were created with #8 K-file at 2, 4, and 6 mm levels. Then the teeth were cleared using methyl salicylate and divided into 5 equal groups according to irrigation activation techniques (CSI, XPF, EDDY, Nd:YAG, and Er:YAG laser). After the contrast solution was activated, images of the simulated lateral canals were obtained by a dental microscope, digital radiography, and CBCT. The contrast solution penetration scores at the 2, 4, and 6 mm levels according to irrigation activation techniques and observation methods were analyzed statistically using Kruskal-Wallis non-parametric analysis of variance Bonferroni test post hoc comparisons. With the other 2 parameters are ignored, the highest and lowest contrast solution penetration were observed at 6 and 2 mm simulated lateral canal levels (p < 0.05), in Er:YAG irrigation activation and CSI technique (p < 0.05), and in direct visual and digital radiographic observation method (p < 0.05), respectively. Within the limits of this study, it was determined that the contrast solution penetration into the simulated lateral canals decreased from the coronal to the apical and achieved with the most effective Er:YAG laser activation technique. In addition, direct visual observation was found to be the best method for the assessment of contrast solution penetration.

Retreatability of calcium silicate-based root canal sealer using reciprocating instrumentation with different irrigation activation techniques in single-rooted canals

This study analysed the bioceramic sealer cleaning ability of two chemo-mechanical systems in intact and restored teeth. Thirty-two single-rooted teeth were used, and half of them restored with a pre-endodontic composite restoration (PCR). All samples were instrumented with a size 40 Reciproc Blue file and filled with BioRoot RCS. Canals were retreated using the R40 and then R50 Reciproc Blue. The samples were divided into four experimental groups (n = 8): intact teeth/passive ultrasonic irrigation (PUI) (G1), intact teeth/shock wave-enhanced emission photoacoustic streaming (SWEEPS) (G2), PCR/PUI (G3) and PCR/SWEEPS (G4). The samples were scanned by micro-CT before and after retreatment, and the volume of remaining filling material was evaluated. The minor percentage of residues were observed in G2, with a volume of 0.447 ± 0.356% of the endodontic space (P < 0.001). The Reciproc/SWEEPS technique showed the better performance in intact teeth compared with PUI technique. Pre-endodontic restoration did not significantly affect the effectiveness of sealer removal.

Comparison of Er:YAG laser and ultrasonic in root canal disinfection under minimally invasive access cavity

The disinfection of root canal through minimally invasive access cavity remains questionable. This in vitro study compared the effectiveness of three disinfection measures including conventional irrigation, ultrasonic assisted irrigation, and erbium:yttrium-aluminum-garnet (Er:YAG) laser assisted irrigation through conventionally or minimally invasive access. Sixty-six extracted maxillary first molars were randomly divided into group 1 conventionally invasive access group (CIA) and group 2 computer-guided minimally invasive access group (MIA). Each group was further randomly divided into three subgroups, (A) conventional irrigation (CI), (B) passive ultrasonic agitation (PUI), and (C) Er:YAG laser activated irrigation (LAI). Enterococcus faecalis (E. faecalis) infection model was established inside all root canals after instrumentation was performed up to ProTaper Universal F2. After various disinfection methods, microbial samples were collected from root canals by paper tip method and cultured, and colony forming units (CFU) values of each sample were calculated. Then the root canals were enlarged to the size of F3, after which dentin debris was collected from the F3 file. After dilution and culturing, the CFU value was calculated for each group. Two-way analysis of variance (ANOVA) was performed to test the interaction. The results revealed a significant antagonism (F = 3.394, P = 0.043). The bacterial CFU counts of group B and group C were significantly less than that of group A (P < 0.05), and there was no significant difference between group B and C (P > 0.05). Additionally, group 2A was better than group 1A (P < 0.05); there was no significant difference between group 1B and group 2B, group 1C and group 2C (P > 0.05). Comparison of the bacterial CFU counts in dentin debris after disinfection, the results revealed a significant antagonism (F = 7.224, P = 0.002), and group C had the least. The disinfection effect of Er:YAG laser or ultrasonic assisted computer-guided minimally invasive access is similar to conventionally invasive access, and Er:YAG laser is better than ultrasonic in removing bacteria from dentinal tubules and is easy to operate, which is more suitable for minimally invasive root canal treatment.

Revascularization of an Immature Permanent Tooth with Periapical Periodontitis Using Concentrated Growth Factor Assisted by Erbium Laser (2940 nm) Irrigation: A Case Report

Revascularization has been incorporated into endodontic practice and become a viable treatment alternative for immature teeth with pulp necrosis. Thorough disinfection of the root canal is a key factor for successful revascularization. An erbium: yttrium–aluminium–garnet (Er: YAG) laser has been proved advantageous for efficient root canal disinfection. This article reports one case of periapical periodontitis caused by a fractured occlusal tubercle. Revascularization assisted by Er: YAG laser irrigation was carried out with long-term follow up. During the process of treatment, we opened drainage to relieve the acute symptoms first. The necrotic pulp was removed, and then the root canal was rinsed with 0.5% sodium hypochlorite (NaOCl) solution assisted by Er: YAG laser irrigation, dried, and filled with a triple-antibiotic paste. After two weeks, the intracanal medication was removed, and 9 mL of whole vein blood was taken from the patient to prepare concentrated growth factor (CGF) after failing to induce enough blood into the canal system by over-instrumenting. The newly prepared CGF was transferred into the root canal. A 3 mm mineral trioxide aggregate (MTA) was placed directly on the thrombus of the CGF and then restored with glass-ionomer cement (GIC). The case was followed up for more than four years to record the clinical symptoms and imaging manifestations. Er: YAG irrigation is an efficient root canal disinfection protocol with the advantages of easy operation and minimal risk, which might be applicable to the revascularization of necrotic immature permanent teeth.

A critical analysis of research methods and experimental models to study irrigants and irrigation systems

Irrigation plays an essential role in root canal treatment. The purpose of this narrative review was to critically appraise the experimental methods and models used to study irrigants and irrigation systems and to provide directions for future research. Studies on the antimicrobial effect of irrigants should use mature multispecies biofilms grown on dentine or inside root canals and should combine at least two complementary evaluation methods. Dissolution of pulp tissue remnants should be examined in the presence of dentine and, preferably, inside human root canals. Micro-computed tomography is currently the method of choice for the assessment of accumulated dentine debris and their removal. A combination of experiments in transparent root canals and numerical modeling is needed to address irrigant penetration. Finally, models to evaluate irrigant extrusion through the apical foramen should simulate the periapical tissues and provide quantitative data on the amount of extruded irrigant. Mimicking the in vivo conditions as close as possible and standardization of the specimens and experimental protocols are universal requirements irrespective of the surrogate endpoint studied. Obsolete and unrealistic models must be abandoned in favour of more appropriate and valid ones that have more direct application and translation to clinical Endodontics.

Er:YAG laser-induced cavitation can activate irrigation for the removal of intraradicular biofilm

We investigated the biofilm removal effects of laser activated irrigation (LAI) using a pig model, focusing on the impact of the fiber tip position, and used a high-speed camera to observe the occurrence and positioning of the cavitation associated with laser irradiation. A total of 16 roots of deciduous mandibular second premolars from 4 pigs were used. After a pulpectomy, the canals were left open for 2 weeks and sealed for 4 weeks to induce intraradicular biofilm. Root canal irrigation was then performed with Er:YAG laser activation. The fiber tip was inserted at two different positions, i.e., into the root canal in the intracanal LAI group and into the pulp chamber in the coronal LAI group. Intracanal needle irrigation with saline or 5% NaOCl was utilized in the positive control and conventional needle irrigation (CNI) groups. SEM and qPCR were carried out to evaluate treatment efficacy. Statistical analysis was performed using ANOVA and a Tukey–Kramer post-hoc test for qPCR and with a Steel–Dwass test to compare the SEM scores, with α = 0.05. A high-speed camera was used to observe the generation of cavitation bubbles and the movement of the induced bubbles after laser irradiation. The intracanal and coronal LAI groups showed significantly lower amounts of bacteria than either the positive control or CNI groups. There was no significant difference found between the intracanal and coronal LAI groups. SEM images revealed opened dentinal tubules with the destruction of biofilm in both LAI groups. High-speed camera images demonstrated cavitation bubble production inside the root canal after a single pulse irradiation pulse. The generated bubbles moved throughout the entire internal multi-rooted tooth space. Coronal LAI can generate cavitation in the root canal with a simply placed fiber inside the pulp chamber, leading to effective biofilm removal. This method could thus contribute to the future development of endodontic treatments for refractory apical periodontitis caused by intraradicular biofilm.

Influence of sodium hypochlorite concentration on cavitation effect and fluid dynamics induced by photon-induced photoacoustic streaming (PIPS): A visualization study

PURPOSE

The aim of the present study was to visualize and compare the cavitation effect and fluid dynamics induced by photon-induced photoacoustic streaming (PIPS) using sodium hypochlorite (NaOCl) with different concentrations as irrigant.

METHODS

Forty artificial root canals were prepared using MTWO Niti file up to size #25/.06. The canals were randomly divided into four groups (n = 10/group). High-speed camera was used to visualize and compare the cavitation effect induced by PIPS in the artificial root canals containing saline or NaOCl. Fluid velocity and Reynolds number of saline, 1%-, 2.5%- and 5.25% NaOCl irrigants induced by PIPS in the apical region were calculated using TEMA 2D software while the fluid motions were recorded.

RESULTS

Visualization profile revealed that NaOCl presented a stronger cavitation effect and fluid dynamics than saline during PIPS activation. In the apical region, 1% NaOCl group presented the highest average velocity of 3.868 m/s, followed by 2.5% NaOCl group (3.685 m/s), 5.25% NaOCl group (2.353 m/s) and saline group (1.268 m/s), corresponding to Reynolds number of 1653.173, 1572.196, 995.503 and 477.692. Statistically higher fluid velocity was calculated in 1% and 2.5% NaOCl groups compared to saline group, respectively (p < 0.05).

CONCLUSIONS

The application of NaOCl and its concentration significantly influence the cavitation effect and fluid dynamics during PIPS activation. 1% and 2.5% NaOCl groups presented a more violent fluid motion in the apical region when activated by PIPS.

Efficacy of five irrigation techniques in removing calcium hydroxide from simulated S-shaped root canals

Background/purpose

Calcium hydroxide [Ca(OH)₂], a wildly used intracanal medicament, should be completely removed from the root canal before obturation to avoid negative effects on the treatment. This study evaluated the effectiveness of conventional needle irrigation (CNI), passive ultrasonic activation (PUI), photon-induced photoacoustic streaming (PIPS), XP-endo Finisher (XP) and EDDY for the removal of Ca(OH)₂ from S-shaped root canal.

Materials and methods

Eighty-four S-shaped root canals in resin blocks were prepared using Protaper Gold up to size #25/0.08 and filled with Ca(OH)₂. Five groups were established according to the removal techniques (n = 16): CNI, PUI, PIPS, XP and EDDY group. The positive and negative control group (n = 2) were also established. Sodium hypochlorite 3% was used as the irrigant. Digital radiographs were used to measure the remaining Ca(OH)₂. Statistical analysis of the data was performed by using the Kruskal–Wallis test, followed by Dunn's post hoc test with Bonferroni correction (α = 0.05).

Results

All the tested techniques completely removed Ca(OH)₂ from the straight portion and coronal curve of the S-shaped root canal in 100% of cases. Regarding the apical curve, PUI, EDDY, PIPS and XP removed significantly more Ca(OH)₂ than CNI (P < 0.05), with no significant differences among these four groups (P > 0.05). The complete clearance of Ca(OH)₂ from the apical curve was observed in 75%, 62.5%, 56.3%, 43.8% and 0% of cases of PUI, EDDY, PIPS, XP and CNI group, respectively.

Conclusion

Irrigant activation enhanced Ca(OH)₂ removal from the apical region of the S-shaped root canal. CNI was significantly less effective than all activation techniques.

An experimental intraradicular biofilm model in the pig for evaluating irrigation techniques

BACKGROUND

We established an in vivo intraradicular biofilm model of apical periodontitis in pigs in which we compared the efficacy of different irrigant activation techniques for biofilm removal.

METHODS

Twenty roots from the deciduous mandibular second premolar of 5 male pigs were used. After pulpectomy, canals were left open for 2 weeks and then sealed for 4 weeks to enable the development of an intracanal biofilm. The intraradicular biofilms was evaluated using SEM and bacterial 16S rRNA gene-sequencing. To investigate the efficacy of biofilm removal, root canal irrigations were performed using conventional needle, passive ultrasonic, subsonic, or laser-activated irrigation. Real-time PCR was conducted to quantitate the remaining biofilm components. Statistical analysis was performed using ANOVA followed by a Tukey kramer post-hoc test with α = 0.05.

RESULTS

The pulp exposure model was effective in inducing apical periodontitis and SEM analysis revealed a multi-layer biofilm formation inside the root canal. 16S rRNA sequence analysis identified Firmicutes, Bacteroidetes, and Fusobacteria as the predominant bacterial phyla components, which is similar to the microbiome profile seen in humans. None of the tested irrigation techniques completely eradicated the biofilm components from the root canal, but the subsonic and laser-activated irrigation methods produced the lowest bacterial counts (p < 0.05).

CONCLUSIONS

An experimental intraradicular biofilm model has been successfully established in pigs. Within the limitations of the study, subsonic or laser-activated irrigation demonstrated the best biofilm removal results in the pig system.

Effect of Optimized Irrigation With Photon-Induced Photoacoustic Streaming on Smear Layer Removal, Dentin Microhardness, Attachment Morphology, and Survival of the Stem Cells of Apical Papilla

BACKGROUND AND OBJECTIVES

This study aimed to evaluate the effect of optimized irrigation with photon-induced photoacoustic streaming (PIPS) activation of different irrigants (distilled water or ethylenediaminetetraacetic acid [EDTA]) on smear layer removal, dentin microhardness, attachment morphology, and survival of stem cells of the apical papilla (SCAP) in an organotypic root canal model.

STUDY DESIGN/MATERIALS AND METHODS

A total of 144 standardized root segments were randomly allocated into 6 groups for irrigation: (i) NaOCl group, (ii) NaOCl + EDTA group, (iii) NaOCl + PIPS (distilled water) group, (iv) NaOCl + PIPS (EDTA) group, (v) NaOCl + EDTA + PIPS (distilled water) group, and (vi) NaOCl + EDTA + PIPS (EDTA) group. Each group was divided into four subgroups for assessment: (i) dentin cleanliness; (ii) dentin microhardness; (iii) cell attachment morphology; and (iv) viable SCAP quantification.

RESULTS

Compared with the control groups, the NaOCl + EDTA + PIPS (EDTA) group showed higher efficiency in smear layer removal and in increasing SCAP viability with more stretched cellular morphology. There were no statistically significant differences in either smear layer removal effect, dentin microhardness, attachment morphology, or survival of SCAP among the other groups when optimized with PIPS (distilled water or EDTA) (P > 0.05).

CONCLUSIONS

Our findings indicated that irrigation optimized with PIPS activation of EDTA for 40 seconds was conducive to smear layer removal without additional dentin microhardness decrease. Additionally, this irrigation created more cell-friendly dentin conditioning than other approaches, which was beneficial for the attachment and survival of SCAP. Lasers Surg. Med. © 2021 Wiley Periodicals LLC.

Efficacy of Laser Photoacoustic Streaming in Paediatric Root Canal Disinfection - An Ex-Vivo Study

Background

Various techniques have been employed to enhance the root canal disinfection rate using sodium hypochlorite (NaOCl) as an irrigant. Photon initiated photo-acoustic streaming using lasers is a newer method of endodontic disinfection.

Aim

The aim of this study is to evaluate and compare the efficacy of photo-initiated photoacoustic streaming and conventional irrigation technique using 2.5% NaOCl for root canal disinfection in primary teeth.

Setting and Design

Laboratory setting and ex-vivo design.

Materials and Methods

Twenty extracted primary teeth were selected in which Enterococcus faecalis incubation was done in the root canals and bacterial counts were obtained before the intervention. The teeth were randomly allocated into two groups. Group I samples were irrigated with conventional syringe method using 2.5% NaOCl and Group II samples were irrigated using photon-initiated photo-acoustic streaming method with erbium-doped yttrium aluminum garnet laser (wavelength - 2940 nm). Postintervention samples were obtained, and bacterial colony count was done. Wilcoxon Signed- Ranks Test and Mann-Whitney test were applied to test the intragroup and intergroup differences in the bacterial counts.

Results

Postintervention results showed no bacterial growth in the canals irrigated using Laser (P = 0.004) whereas, fewer bacterial colonies were observed in NaOCl group (P = 0.005). There was statistically significantly higher reduction in E. faecalis counts in Laser Activated irrigation (LAI) group compared to NaOCl group (P < 0.05).

Conclusion

Total elimination of E. faecalis counts was obtained by the use of laser activated NaOCl irrigation in the infected root canals, hence, it can be considered as an effective method for pediatric endodontic disinfection.

Postoperative pain after ultrasonically and laser-activated irrigation during root canal treatment: a randomized clinical trial

AIM

To compare the intensity of postoperative pain after primary root canal treatment of asymptomatic teeth when using ultrasonically (UAI) or laser-activated irrigation (LAI).

METHODOLOGY

In this superiority randomized clinical trial (ClinicalTrials.gov ID: NCT03981237) with parallel design, fifty-six patients with an asymptomatic tooth in need of primary root canal treatment were enrolled. After chemo-mechanical canal preparation using rotary instruments and NaOCl irrigation, teeth were randomly assigned to two groups and patients were blinded to the final irrigation protocol. In the UAI group (n = 28), 60s activation with an Irrisafe tip was done per canal. In the LAI group (n = 28), NaOCl was activated with a pulsed Er:YAG (2940 nm) laser, equipped with a conical tip, with settings of 50 µs, 20 mJ at 15 Hz for 60 s. Patients recorded their pain intensity 6, 24, 48 and 72 h after treatment on a 100 mm visual analogue scale (VAS), as well as their analgesic consumption. Pain levels and incidence were compared across groups using the Mann-Whitney U-test and chi-square test.

RESULTS

Overall, mean postoperative pain intensity was low, with the majority of patients having no or minimal pain 24 h postoperatively. At 6 h postoperatively, pain intensity and incidence were significantly higher in the UAI group compared to the LAI group (P < 0.05). For the other time intervals, no significant differences in postoperative pain incidence or intensity were found. The frequency of analgesic intake did not differ significantly between the two groups. Neither of the activation methods resulted in any adverse effects.

CONCLUSIONS

Ultrasonically and laser-activated irrigation resulted in low and comparable levels of postoperative pain in asymptomatic patients receiving primary root canal treatment.

Efficacy of different irrigation technique in simulated curved root canals

The aim of this study was to assess the influence of the canal curvature on the efficacy of sonically, ultrasonically, and laser-activated irrigation in removing a biofilm-mimicking hydrogel (BMH) from simulated canal irregularities. Transparent resin blocks containing a curved root canal (40° or 60°) were used as test models. A 4-mm groove at 1 mm from the apex was filled with BMH. Five different irrigation procedures were performed (n=20): needle irrigation (NI), EndoActivator (EA), Eddy, ultrasonically activated irrigation (UAI) (Irrisafe), and laser-activated irrigation (LAI) using a pulsed erbium laser (PIPS approach). All protocols were executed for 3×20s. Images of the groove were taken before and after irrigation, and the percentage BMH removal was calculated using image analysis software. In the 40° canal curvature model, the highest BMH removal was observed for UAI (99.9%), yielding a significantly better removal than that of EA (57.2%) and NI (53.8%), but not of LAI (96.8%) and Eddy (99.4%). In the 60° canal curvature model, UAI removed 99.5%, which resulted in significantly greater hydrogel removal than all other groups (P < 0.05). The difference between LAI (82.5%) and Eddy (78.1%) was not statistically significant, but both were more effective than EA (13.5%) and NI (7.3%). Canal curvature negatively affects the cleaning efficacy of different irrigation methods. The effect was most pronounced for the sonic techniques, while this was not the case for UAI. This could be ascribed to the prebent ultrasonic tip. Despite the position of the laser tip at the orifice level, fluid streaming during LAI resulted in substantial BMH removal beyond the curve.

Photoacoustic removal of Enterococcus faecalis biofilms from titanium surface with an Er:YAG laser using super short pulses

Biofilms that grow on implant surfaces pose a great risk and challenge for the dental implant survival. In this work, we have applied Er:YAG photoacoustic irrigation using super short pulses (Er:YAG-SSP) to remove biofilms from the titanium surfaces in the non-contact mode. Mature Enterococcus faecalis biofilms were treated with saline solution, chlorhexidine, and hydrogen peroxide, or photoacoustically with Er:YAG-SSP for 10 or 60 s. The number of total and viable bacteria as well as biofilm surface coverage was determined prior and after different treatments. Er:YAG-SSP photoacoustic treatment significantly increases the biofilm removal rate compared to saline or chemically treated biofilms. Up to 92% of biofilm-covered surface can be cleaned in non-contact mode during 10 s without the use of abrasives or chemicals. In addition, Er:YAG-SSP photoacoustic irrigation significantly decreases the number of viable bacteria that remained on the titanium surface. Within the limitations of the present in vitro model, the ER:YAG-SSP seems to constitute an efficient therapeutic option for quick debridement and decontamination of titanium implants without using abrasives or chemicals.

Comparison of Needle, Ultrasonic, and Laser Irrigation for the Removal of Calcium Hydroxide from Mandibular Molar Root Canals

Objective: This study aimed to compare the efficacy of conventional needle irrigation (CI), ultrasonically activated irrigation (UAI), photon-induced photoacoustic streaming (PIPS), and shock wave-enhanced emission photoacoustic streaming (SWEEPS) in removing calcium hydroxide [Ca(OH)₂] from root canals of mandibular molars using microcomputed tomography. Background: Various adjunctive irrigation strategies have been recommended to improve the removal of Ca(OH)₂. No reports have evaluated the SWEEPS laser-activated method for the removal of Ca(OH)₂ from root canals of mandibular molars. Materials and methods: Forty mandibular molars were instrumented and filled with Ca(OH)₂. Four irrigation groups (CI, UAI, PIPS, and SWEEPS) were established. The volume of root canals and Ca(OH)₂ and the Ca(OH)₂ volume reduction percentage (%Rd) were calculated. Data were analyzed by one-way analysis of variance and Kruskal-Wallis analysis of variance. Results: The residual Ca(OH)₂ in the apical third was higher than that in the cervical and middle thirds in all groups (p < 0.05). Comparison of the %Rd of Ca(OH)₂ in mesial canals revealed that PIPS and SWEEPS removed more Ca(OH)₂ than CI and UAI in the cervical third (p < 0.05). The middle third of the mesial canals and the cervical and middle thirds of the distal canals did not show significant differences among groups (p > 0.05). Significant differences in the %Rd of Ca(OH)₂ were noted between CI and other groups in the apical third of mesial and distal canals (p < 0.05). No group demonstrated complete removal of Ca(OH)₂. Conclusions: UAI and laser-activated irrigation significantly improved Ca(OH)₂ removal in the apical third of mesial and distal canals. No agitation technique could completely remove Ca(OH)₂.

Determination of Optimal Separation Times for Dual-Pulse SWEEPS Laser-Assisted Irrigation in Different Endodontic Access Cavities

Background and Objectives

The purpose of this ex vivo study is to investigate whether it is possible to pre‐determine and set the optimal separation times for the SWEEPS Er:YAG laser pulses pair during laser‐assisted irrigation of endodontic root canals based on known lateral dimensions of the endodontic access cavities of different types of teeth.

Study Design/Materials and Methods

As the optimal SWEEPS laser pulse pair separation for enhanced shockwave generation depends on the life‐cycle of a single‐pulse bubble, measurements of the oscillation time T_B of the Er:YAG laser‐generated bubble were made in 23 different endodontic access cavities of different types of teeth progressively widened in three different steps, into larger cavities, for a total of 69 cavities of different shapes and sizes. Different fiber‐tip geometries (flat and radial), laser pulse energies (10 mJ and 20 mJ) and depth of fiber‐tip insertion (2 mm and 4 mm) were also investigated. The obtained data were then analyzed using the reported relationship between the bubble oscillation time and the diameter of a cylindrically shaped cavity.

Results

A good fit to the relation analogue for ideal cylindrical cavities was found by taking the characteristic diameter of the access cavity to be represented by the cavity diameter either in the mesiodistal (D_min) or buccolingual (D_max) direction, or alternatively by the average of the two diameters (D_ave). The best fit was obtained for D_min (R² = 0.73) followed in order by D_ave (R² = 0.71) and D_max (R² = 0.63).

Conclusion

In spite of the endodontic cavities being non‐cylindrical and of varied shape and size, the bubble oscillation time T_B and the corresponding optimal SWEEPS separation time can be well predicted using a single characteristic dimension of the access cavity. This finding enables a simple and practical method for determining optimal conditions for shock wave generation and enhanced photodynamic streaming in differently shaped and sized root canals, leading to improved treatment efficacy and safety of root canal irrigation. Lasers Surg. Med. 2020. © 2020 The Authors. Lasers in Surgery and Medicine published by Wiley Periodicals LLC

Characteristics of the Irrigant Flow in a Simulated Lateral Canal Under Two Typical Laser-Activated Irrigation Regimens

BACKGROUND AND OBJECTIVES

Photon-induced photoacoustic streaming (PIPS) and shockwave-enhanced emission photoacoustic streaming (SWEEPS) are two promising laser-activated irrigation (LAI) methods for root canal irrigation. Their performance in driving irrigant flush in a complex root canal system will be evaluated by microscale particle image velocimetry (μPIV) measurement and will be compared with that of ultrasonic-activated irrigation (UAI).

STUDY DESIGN/MATERIALS AND METHODS

A μPIV system with 7 μm fluorescent tracer particles was adopted to measure two-dimensional (2D) velocity fields around the junction region, with a size of 1.8 mm × 1.5 mm, between one main canal and one lateral canal in an endodontic training block, which was driven by SWEEPS (Er:YAG laser) operating at 15 Hz and 20 mJ. The flow field driven by PIPS (Er:YAG laser) at the same frequency and energy, as well as by UAI (with non-cutting insert) operating at 40% unit power, was also measured for a direct comparison.

RESULTS

It was found that both SWEEPS and PIPS can activate a so-called "breath mode" during the irrigation. Namely, the induced irrigant flush presented a back-and-forth oscillation along both the main canal and the lateral one. The maximum flow speed in the lateral canal was observed to be up to 10 m/s in the SWEEPS modality, while reduced to around 7 m/s in the PIPS modality. The penetration length in the lateral canal in both modalities was estimated to be larger than 1 mm. In comparison, the flow field induced by UAI was characterized as irregular vortical structures, the maximum flow speed in the lateral canal was 0.15 m/s and significantly lower than LAI (P < 0.01), and the penetration length was less than 300 μm and lower than LAI (P < 0.05).

CONCLUSION

Compared to UAI, PIPS, and SWEEPS are more capable of delivering the irrigant deeper into the lateral canal. Furthermore, the back-and-forth flush in the breath mode is ideal for removing debris during irrigation. Lasers Surg. Med. © 2020 Wiley Periodicals LLC.

The Efficiency of the Er: YAG Laser and PhotonInduced Photoacoustic Streaming (PIPS) as an Activation Method in Endodontic Irrigation: A Literature Review

In the field of endodontics, lasers have been used for a long time for the optimization of Endodontic irrigation in particular. The laser-activated irrigation (LAI) technique is based on the photomechanical effects of the lasers at low settings. They create specific cavitation phenomena and acoustic streaming in intracanal fluids. More recently, a new technique with a Er:YAG laser has been used with sub-ablative energy (20 mJ, 15 Hz) and ultra-short pulses (50 µs). This leads to intracanal cavitation and shockwaves as a result of photoacoustic and photomechanical effects. This phenomenon is called photon-induced photoacoustic streaming (PIPS). PIPS and Laser activated irrigation are described in the literature as a revolutionary and powerful method to activate the irrigant; however, systematic literature on this topic is missing. This review compares the literature on Er:YAG LAI and PIPS on endodontic irrigation with other irrigation methods. An article search was performed on the PubMed database using a series of keywords related to endodontic irrigation, including Er:YAG LAI and PIPS; 59 articles were selected for the review according to the inclusion and exclusion criteria. No in vivo study was found. The Er:YAG LAI and PIPS outperformed other methods in 33 of the 59 articles. There was a great variety in the study designs including bacterial incubation time, laser parameters, irrigation protocols, and irrigating solution used. The evidence suggests that the Er:YAG LAI and PIPS are promising in canal disinfection as well as debris and smear layer removal. However, the large variety in the study methods makes the results less significant. Further studies are needed to better evaluate the efficiency of these techniques, especially in vivo studies.

Measurement of Simulated Debris Removal Rates in an Artificial Root Canal to Optimize Laser-Activated Irrigation Parameters

BACKGROUND AND OBJECTIVES

To compare temporal rates of debris removal from an artificial root canal for three laser-assisted irrigation modalities single-pulse super short pulse (SSP), and two dual-pulse X-SWEEPS and AutoSWEEPS, and for two fiber-tip (FT) geometries flat and radial, and to evaluate the dependence of the debris flushing rate on the delay between the SWEEPS laser pulse pair.

STUDY DESIGN/MATERIALS AND METHODS

Laser-assisted irrigation was performed with a pulsed Er:YAG laser operating in single-pulse SSP and dual-pulse SWEEPS laser modalities. The laser energy was delivered to the water-filled model access cavity through a FT with either a flat or radial ending. The X-SWEEPS modality delivered pairs of laser pulses separated by a fixed adjustable delay, while with the AutoSWEEPS modality the delay was automatically and repeatedly swept between 200 and 600 microseconds. The debris removal rate was determined with the use of a digital camera by measuring the rate at which a simulated debris was being flushed out of the artificial root canal.

RESULTS

The simulated debris removal rate of the AutoSWEEPS modality is almost three times higher compared with that of the SSP modality. Further, the flat FT outperforms the radial FT by a factor of more than five in the case of SSP, and by more than 10 with AutoSWEEPS. The X-SWEEPS flushing rate exhibits strong dependence on the delay between the SWEEPS pulse pair, with the highest removal rate measured to be more than seven times higher in comparison with SSP.

CONCLUSION

Dual-pulse laser irrigation modalities (AutoSWEEPS and X-SWEEPS) exhibit significantly higher simulated debris removal rates in comparison with the standard single-pulse SSP laser-assisted irrigation. As opposed to the previously reported dependence of pressure generation on FT geometry, the flat FT's simulated debris removal rate significantly outperforms the radial FT. © 2020 The Authors. Lasers in Surgery and Medicine published by Wiley Periodicals LLC.

Effect of Pulse Energy, Pulse Frequency, and Tip Diameter on Intracanal Vaporized Bubble Kinetics and Apical Pressure During Laser-Activated Irrigation Using Er:YAG Laser

Objective: Er:YAG laser-activated irrigation (LAI) is an effective method of root canal cleaning, but irrigant extrusion from the apical foramen has been a concern. We aimed to analyze the effects of pulse energy, pulse frequency, and laser tip diameter on intracanal vapor bubble kinetics and periapical pressure generation during LAI with Er:YAG laser. Background: Irrigant vapor bubble kinetics are one of indices of root canal cleaning efficacy. However, few studies have compared laser pulse conditions to vapor bubble kinetics, in relation to periapical pressure. Methods: A plastic root canal model (apical diameter 0.50 mm, 6% taper, 20 mm long) was filled with distilled water, and LAI with Er:YAG laser (Erwin AdvErl Unit; 30, 50, or 70 mJ; 10, or 20 pulses per second; laser tip R200T or R600T) was performed with the end of the tip fixed at 15 mm from the root apex. The number, maximum diameter, and velocity of vapor bubbles were analyzed by high-speed video imaging. Pressure generated outside the apical foramen was measured with a pressure sensor. Results: Vapor bubble count and maximum diameter increased significantly with pulse energy, pulse frequency, and tip diameter. Vapor bubble velocity increased significantly with pulse frequency, but not with pulse energy or tip diameter. Periapical pressure increased significantly with pulse energy, pulse frequency, and tip diameter. Conclusions: The pulse frequency was the single factor that significantly affected all the examined parameters (the number, diameter, and velocity) of vapor bubble kinetics together with the periapical pressure.

Characteristics of Bubble Oscillations During Laser-Activated Irrigation of Root Canals and Method of Improvement

BACKGROUND AND OBJECTIVES

Laser-activated irrigation of dental root canals is being increasingly used as its efficacy has been shown to be superior compared with conventional techniques. The method is based on laser-initiated localized fluid evaporation and subsequent rapid bubble expansions and collapses, inducing microfluid flow throughout the entire volume of the cavity. The irrigation efficacy can be further improved if optimally delayed "SWEEPS" double laser pulses are delivered into the canal. This study aims to show that the irrigation efficacy, as measured by the induced pressure within the canal, is related to the double pulse delay, with the maximal pressure generated at an optimal delay. The second aim is to find a method of determining the optimal delay for different cavity dimensions and/or laser parameters.

STUDY DESIGN/MATERIALS AND METHODS

Experiments were made in transparent models of root canals where Er:YAG laser (λ = 2.94 μm, pulse duration t_p  = 25 or 50 microseconds, and pulse energies up to E_L  = 40 mJ) was used with a combination of cylindrical and conical fiber-tip geometries (diameters 400 and 600 µm). High-speed photography (60,000 fps) and average pressure measurements inside the canal were used for process characterization.

RESULTS

The results show that a pressure amplification of more than 1.5 times occurs if the laser pulse delay approximately coincides with the bubble oscillation time. Correlations between normalized oscillation time and canal diameter for a wide range of laser pulse energies (R²  = 0.96) and between the average pressure within the canal and the bubble oscillation periods (R²  = 0.90) were found. A relationship between the bubble oscillation time and the diameter of the treated cavity was found depending on the bubble oscillation time in an infinite fluid reservoir.

CONCLUSIONS

The bubble oscillation time within a constrained volume can be determined based on the known oscillation time in infinite space, which offers a fast and simple solution for optimization of the laser parameters. These findings enable determination of optimal conditions for shock wave generation, and improvement of root canal irrigation at the same dose of laser energy input, leading to improved treatment efficacy and safety. Lasers Surg. Med. © 2020 The Authors. Lasers in Surgery and Medicine published by Wiley Periodicals, Inc.

Efficacy of the photon-initiated photoacoustic streaming combined with different solutions on Enterococcus faecalis in the root canals

This study aimed to evaluate the efficacy of different irrigation solutions used in photon-initiated photoacoustic streaming (PIPS) or conventional needle irrigation (CNI) for eradication of Enterococcus faecalis from artificial root canals. Altogether, 240 artificial root canal samples were included. The models were split and incubated for 2 days to allow formation of E. faecalis biofilm. The models were randomly divided into two groups (n = 120): CNI and laser-activated irrigation (LAI). Each group was divided into six subgroups according to different irrigation solutions: distilled water, 1% sodium hypochlorite (NaOCl), 2% NaOCl, 5.25% NaOCl, MTAD, and chlorhexidine, respectively. After irrigation, half of the samples (n = 10) were assessed immediately, and the other half of the samples (n = 10) were incubated for 6 hr. Bacterial suspensions were obtained from all samples before and after irrigation, and after incubation, and were quantified adenosine 5'-triphosphate (ATP) assay kit. The biofilms were examined using fluorescent microscopy and analyzed by Image Pro Plus software. Significant reduction of ATP, average fluorescence density after irrigation, and growth after incubation was obtained in LAI group than in CNI group (p < .05). LAI can improve bacteriostasis effect of 2% NaOCl (p < .05). PIPS improved the antibacterial effect of the 2% NaOCl used in root canal therapy.

In Vitro Effect of Er:YAG Laser on Different Single and Mixed Microorganisms Being Associated with Endodontic Infections

Objective: The purpose of this in vitro study was to evaluate the antimicrobial effect of activated irrigation with different modes of erbium-doped yttrium aluminum garnet (Er:YAG) laser application on microorganisms related to secondary endodontic infection. Background: Er:YAG laser has been recommended as an adjuvant tool for root canal disinfection during endodontic treatment. Materials and methods: Laser-activated irrigation (LAI) with 300 or 600 μm tips were tested with or without intermittent irrigation with 0.9% sodium chloride (NaCl) solution against different microorganisms (five single strains and dual species (Streptococcus gordonii combined with Actinomyces oris or Fusobacterium nucleatum) in root canals after 3 days of incubation. In a 21-day infection model, LAI was used together with intermittent rinsing with sodium hypochlorite (NaOCl) against the dual-species mixtures; here the incidence of microbial regrowth after up to 7 days was monitored. Results: In the 3-day root infection model, LAI protocols did not show any significant reduction of the microbial load when compared with manual irrigation with saline solution. In the 21-day infection, S. gordonii combined with A. oris were not detectable anymore after applying the LAI protocol with a 600 μm tip (30 mJ/10 pps) up to 7 days after treatment. Conclusions: Application of LAI with a 600 μm tip by using an Er:YAG laser might be advantageous in treatment of endodontic infections.

Efficacy and Safety of Photon Induced Photoacoustic Streaming for Removal of Calcium Hydroxide in Endodontic Treatment

Calcium hydroxide removal from the root canal by photon induced photoacoustic streaming (PIPS) compared to needle irrigation and irrigation using sonic activation was investigated. Additionally, safety issues regarding apical extrusion were addressed. In endodontic treatment temporary intracanal medication like calcium hydroxide should be completely removed for long term success. For analysis, 60 artificial teeth were prepared, filled with calcium hydroxide, and divided into four groups. The teeth were assigned to needle irrigation, irrigation using a sonic device, PIPS with a lower energy setting (10 mJ, 15 Hz), or PIPS with a higher energy setting (25 mJ/40 Hz). For comparison the weight of each tooth was measured before and after calcium hydroxide incorporation, as well as after removing calcium hydroxide using the four different methods. Regarding safety issues another 24 samples were filled with stained calcium hydroxide and embedded in 0.4% agarose gel. Color changes in the agarose gel due to apical extrusion were digitally analysed using Photoshop. No significant differences were found for calcium hydroxide removal between the two laser groups. Sonic assisted removal and needle irrigation resulted in significant less calcium hydroxide removal than both laser groups, with significantly more calcium hydroxide removal in the ultrasonic group than in the needle irrigation group. For apical extrusion the higher laser (25 mJ/40 Hz) group resulted in significant higher color changes of the periapical gel than all other groups. PIPS with the setting of 10 mJ/15 Hz achieved almost complete removal of calcium hydroxide without increasing apical extrusion of the irrigation solution.

Amplification of pressure waves in laser-assisted endodontics with synchronized delivery of Er:YAG laser pulses

When attempting to clean surfaces of dental root canals with laser-induced cavitation bubbles, the resulting cavitation oscillations are significantly prolonged due to friction on the cavity walls and other factors. Consequently, the collapses are less intense and the shock waves that are usually emitted following a bubble’s collapse are diminished or not present at all. A new technique of synchronized laser-pulse delivery intended to enhance the emission of shock waves from collapsed bubbles in fluid-filled endodontic canals is reported. A laser beam deflection probe, a high-speed camera, and shadow photography were used to characterize the induced photoacoustic phenomena during synchronized delivery of Er:YAG laser pulses in a confined volume of water. A shock wave enhancing technique was employed which consists of delivering a second laser pulse at a delay with regard to the first cavitation bubble-forming laser pulse. Influence of the delay between the first and second laser pulses on the generation of pressure and shock waves during the first bubble’s collapse was measured for different laser pulse energies and cavity volumes. Results show that the optimal delay between the two laser pulses is strongly correlated with the cavitation bubble’s oscillation period. Under optimal synchronization conditions, the growth of the second cavitation bubble was observed to accelerate the collapse of the first cavitation bubble, leading to a violent collapse, during which shock waves are emitted. Additionally, shock waves created by the accelerated collapse of the primary cavitation bubble and as well of the accompanying smaller secondary bubbles near the cavity walls were observed. The reported phenomena may have applications in improved laser cleaning of surfaces during laser-assisted dental root canal treatments.

Activation of Alkaline Irrigation Fluids in Endodontics

In conventional endodontic treatment, alkaline solutions of sodium hypochlorite (NaOCl) and ethylenediaminetetraacetic acid (EDTA) are used in combination to disinfect the root canal system and to eliminate debris and smear layers. An important concept that has emerged over recent years is the use of active physical methods for agitating these fluids to improve their penetration within areas that are not reached by endodontic instruments and to accelerate the chemical actions of these alkaline fluids against planktonic microorganisms, biofilms, soft tissue remnants and smear layers. Ultrasonic agitation and more recently pulsed lasers have emerged as two promising methods for activating endodontic irrigation fluids. Ultrasonic agitation with piezoelectric devices employs a moving tip, while laser agitation uses a stationary tip. Both methods cause cavitation, followed by implosions and shear forces which assist with debridement. Fluid streaming further enhances the activity of the fluids. While agitation enhances performance of irrigants, extrusion of fluids from the root canal during activation is a hazard that must be controlled.

Erbium:Yttrium Aluminum Garnet Laser-Activated Sodium Hypochlorite Irrigation: A Promising Procedure for Minimally Invasive Endodontics

OBJECTIVE

This study was to evaluate the potential of Erbium:Yttrium Aluminum Garnet laser-activated sodium hypochlorite irrigation (Er:YAG + NaOCl) for minimally invasive endodontics (MIE).

BACKGROUND DATA

Er:YAG laser irradiation can dramatically enhance the penetration of NaOCl, which may be a promising protocol for MIE.

METHODS

Extracted human teeth were contaminated with Enterococcus faecalis for 4 weeks. The infected canals were then shaped to different apical terminal working widths (ATWW, 15#/0.04, 20#/0.04, 25#/0.04, 30#/0.04, and 40#/0.04) and treated with either Er:YAG + NaOCl (0.3 W, 20 sec) or NaOCl alone. Then, the ATWW were fixed at 15#/0.04, and the canals were treated with Er:YAG + NaOCl at 0.3 W for 40 and 60 sec, or at 0.5 and 1.0 W for 20 sec. Finally, bacterial reductions were evaluated using the cell count method.

RESULTS

Er:YAG + NaOCl showed a higher disinfection efficacy at each ATWW compared with NaOCl alone (p < 0.001). The maximum bacterial reduction was 99.9% for the 40#/Er:YAG + NaOCl group and 93.6% for the 40#/NaOCl group. To achieve similar disinfection efficacy, the Er:YAG + NaOCl group needed a smaller ATWW than the NaOCl group. At a fixed ATWW, increasing the output power of the Er:YAG laser was more effective than increasing the radiation time to improve the disinfection efficacy of Er:YAG + NaOCl. The 15#/Er:YAG + NaOCl group reached the maximum bacterial reduction of 99.2% when the Er:YAG laser was activated at 1.0 W for 20 sec.

CONCLUSIONS

The 15#/Er:YAG + NaOCl with the Er:YAG laser irradiation at 1.0 W for 20 sec may be considered a promising procedure for MIE.

Comparison of sodium hypochlorite extrusion by five irrigation systems using an artificial root socket model and a quantitative chemical method

OBJECTIVES

This is to compare the volumes of irrigant apically extruded by five irrigation systems in an artificial socket model simulating clinical conditions.

MATERIALS AND METHODS

Twenty extracted human single-rooted teeth were enlarged to size 40/04 and then embedded in silicone impression material. The root canal space was irrigated with nominal 3% sodium hypochlorite (NaOCl) using standard needle irrigation (SNI) with a 30-gauge notched needle, EndoActivator (EA), XP Endo Finisher (XP Endo), EndoVac (EV), and photon-induced photoacoustic streaming (PIPS). Extruded NaOCl was collected, reacted with taurine to form taurine-monochloramine, and absorbance of taurine-monochloramine was measured at 252 nm using a spectrophotometer. The five irrigation systems were compared with repeated measures ANOVA and pairwise comparisons.

RESULTS

The EV group had very low extrusion (mean ± SD = 0.12 ± 0.2 μL) and differed significantly from the other four groups (P ≤ 0.001). Larger volumes of irrigant were extruded in the other irrigation groups. There were no significant differences in the extruded volumes among the SNI (7.4 ± 3.4 μL), EA (7.0 ± 6.1 μL), and XP Endo (7.8 ± 4.1 μL) groups (P = 1). The PIPS group had the highest mean extruded volume (12.9 ± 6.8 μL) and differed significantly from SNI (P = 0.030), EV (P < 0.0005), and EA (P = 0.02), but not XP Endo (P = 0.154).

CONCLUSION

Under the in vitro conditions of this study, irrigant extrusion appears unavoidable unless negative pressure irrigation such as EV is used. PIPS extrudes more irrigant than other systems, while SNI, EA, and XP Endo extrude similar volumes of irrigant.

CLINICAL RELEVANCE

The findings help clinicians select the optimal irrigation system to avoid irrigant extrusion.

Removal of calcium hydroxide from Weine Type II systems using photon-induced photoacoustic streaming, passive ultrasonic, and needle irrigation: a microcomputed tomography study

Objective

This study compared the effectiveness of Er:YAG laser-activated irrigation (PIPS), passive ultrasonic irrigation (PUI) with EndoUltra and standard needle irrigation (SNI) in the removal of calcium hydroxide [Ca(OH)2] from the mesial roots of Weine Type II mandibular molars.

Material and Methods

Thirty mandibular molars were screened by µCT for the presence of mesial roots with complex intra-canal anatomy and a common apical foramen. The teeth were enlarged to a standardized 25/.06 preparation and filled with Ca(OH)2 paste. Specimens were divided into three groups (n=10) according to the technique used for Ca(OH)2 removal: PIPS, at 15 Hz and 20 mJ using a 9 mm long, 600 µm diameter tip; PUI using a 15/.02 tip; and SNI (30 Ga. side-vented needle). Equal volumes of 8.25% NaOCl and 17% EDTA were used in all groups. µCT was used to measure the initial amount of Ca(OH)2 present and to assess the residual volume of Ca(OH)2 following each irrigation protocol. Data were analyzed using Tukey HSD and Kruskal-Wallis tests (α=5%).

Results

The mean volume of Ca(OH)2 before removal was significantly higher in the coronal third than in the middle and apical third (p<0.001). Ca(OH)2 was similarly removed from the coronal and middle thirds with the three methods used (p>0.05). PIPS (median 0%; IQR: 0-0) showed significant higher Ca(OH)2 removal in the apical third than PUI (median 100%, IQR: 85-100) and SNI (median 47%; IQR: 16-72) (p<0.001).

Conclusions

PIPS laser-activation was more effective for the removal of Ca(OH)2 from mesial roots of mandibular molars with Weine Type II canal configurations than PUI with EndoUltra and SNI.

Wavelength dependence of photon-induced photoacoustic streaming technique for root canal irrigation

Laser-enhanced irrigation of complex root canals appears to be a very promising technique to improve the outcome of root canal treatment. This applies, in particular, if the technique can be effective at very low laser energies in irrigating not only the main canal but also the small lateral canals. This is important in order to avoid potential undesirable effects at higher laser energies such as temperature increase, dentin ablation, or extrusion of irrigating solution beyond the apical foramen. An improved understanding of the role of laser parameters, such as laser wavelength and pulse duration, in irrigation of lateral canals is therefore desired in order to optimize treatment efficacy. The influence of laser wavelength and pulse duration on cavitation phenomena was studied using shadow photography and a method of measuring fluid flow in lateral canals based on tracking of movements of small air bubbles naturally forming in liquid as a result of laser agitation. A simulated model of a root canal including a narrow lateral canal designed to represent typical root canal morphology was used for the water flow measurements. The following three laser wavelengths with relatively high absorption in water were studied: Er:YAG (2.94  μm), Er,Cr:YSGG (2.73  μm), and Nd:YAP (1.34  μm). Among the three wavelengths studied, the Er:YAG laser wavelength was found to be the most effective in formation of cavitation bubbles and in generating fluid motions within narrow lateral canals. A comparison between the shadow photography and fluid motion data indicates that it is the bubble’s radius and not the bubble’s volume that predominantly influences the fluid motion within lateral canals. Based on the results of our study, it appears that effective minimally invasive laser-assisted irrigation can be performed with low Er:YAG laser pulse energies below 10 mJ.

Efficacy of 4 Irrigation Protocols in Killing Bacteria Colonized in Dentinal Tubules Examined by a Novel Confocal Laser Scanning Microscope Analysis

INTRODUCTION

The aim of this study was to determine the efficiency of 4 irrigation systems in eliminating bacteria in root canals, particularly in dentinal tubules.

METHODS

Roots of human teeth were prepared to 25/04, autoclaved, and inoculated with Enterococcus faecalis for 3 weeks. Canals were then disinfected by (1) standard needle irrigation, (2) sonically agitating with EndoActivator, (3) XP Endo finisher, or (4) erbium:yttrium aluminum garnet laser (PIPS) (15 roots/group). The bacterial reduction in the canal was determined by MTT assays. For measuring live versus dead bacteria in the dentinal tubules (4 teeth/group), teeth were split open and stained with LIVE/DEAD BackLight. Coronal, middle, and apical thirds of the canal dentin were scanned by using a confocal laser scanning microscope (CLSM) to determine the ratio of dead/total bacteria in the dentinal tubules at various depths.

RESULTS

All 4 irrigation protocols significantly eliminated bacteria in the canal, ranging from 89.6% to 98.2% reduction (P < .001). XP Endo had the greatest bacterial reduction compared with other 3 techniques (P < .05). CLSM analysis showed that XP Endo had the highest level of dead bacteria in the coronal, middle, and apical segments at 50-μm depth. On the other hand, PIPS had the greatest bacterial killing efficiency at the 150-μm depth in all 3 root segments.

CONCLUSIONS

XP Endo appears to be more efficient than other 3 techniques in disinfecting the main canal space and up to 50 μm deep into the dentinal tubules. PIPS appears to be most effective in killing the bacteria deep in the dentinal tubules.