It has long been established in endodontics that mechanical instrumentation of the canal system is insufficient for proper disinfection. Instead, a combined chemo-mechanical approach is needed whereby mechanical and chemical interactions occur with the pulp and dentin of a tooth.1-3 Infected dentin is removed and shaped with files while irrigating solutions chemically interact with the pulp and dentin to promote tissue dissolution and dentin disinfection. It is essential to mention that the chemical and mechanical interaction depends on the ability to make proper contact. An irrigating syringe is commonly used to deliver the solution into the canals. Files of different tapers, designs, and metals are constructed to maximize contact with the infected dentin. Limitations are present in both methods; the solution cannot reach the apex in smaller preparations, and dentin surfaces go untouched.4,5 Once contact is made, the irrigating solution should be properly agitated. In this article, we will point out the limitations of syringe irrigation and demonstrate why the agitation of these solutions is critical for enhanced disinfection of the root canal system. I will explain how the Waterlase iPlus (Er,Cr:YSGG), All Tissue Laser is an exceptional tool for enhanced irrigation with sodium hypochlorite in laser-assisted endodontics.
Before considering the agitation of sodium hypochlorite, let’s review some of its benefits. It is the most widely used irrigating solution in endodontics, and for a good reason. It has excellent antibacterial properties as it can dissolve necrotic and vital pulp tissue, organic components of dentin, and biofilm.6 Sodium hypochlorite, commonly known as bleach, comes very close to being an ideal irrigant. It has a long history and was even used in WWI as a 0.5% buffered solution, called “Dakin’s solution,” for irrigating contaminated wounds.7
So, what is an ideal irrigant for endodontic treatment? It should be antibacterial, tissue dissolving, non-irritating to the periapical tissues, have low surface tension, not stain the tooth, be stable in solution, be able to remove the smear layer, be able to penetrate dentin without adverse effects, have no negative impact on filling materials. Sodium hypochlorite checks off almost all these objectives. The limitations are that it irritates the periapical tissues, so we must be cautious not to push any out of the apex. It’s also ineffective in removing inorganic dentin debris or smear layer.8
Two crucial factors that improve the effectiveness of NaOCl are temperature and concentration. It is well known that heating NaOCl solution and increasing its percent concentration can enhance its effectiveness. A higher 8.25% NaOCl concentration has increased tissue dissolving capability, and if the NaOCl solution is refreshed, dentin does not decrease its efficacy.9 Commercially available sodium hypochlorite can come in various concentrations, including 8.25%, 6% and 5.25%.9 If diluting by half, you want to ensure that you know your starting and final concentrations when describing full or half strength to your dental assistants. In the same study, the authors mention how hydroxyl ions are released as NaOCl interacts with organic tissues and how hypochlorous acid and, ultimately, active chlorine, a potent oxidizing agent, leads to amino acid degradation, destruction of bacteria and their enzymes.9 All this bactericidal activity and more are sped up just by increased sodium hypochlorite concentration.
Another well-established fact about sodium hypochlorite is that its effects can be potentiated if the solution’s temperature is increased. It was demonstrated that a 1% NaOCl solution at 45° C has the same tissue dissolving capability as a 5.25% NaOCl solution at 20° C.10 Not only is the tissue dissolving power of NaOCl increased dramatically by just heating the solution, but its bactericidal properties against E. faecalis were also reported by the authors to increase by a factor of 100 with a 25°C rise in temperature.10 What’s more is that in another experimental heat study of an extracted tooth, a temperature of 100° C only raised the external root temperature by only a few degrees and therefore concluded that a rise to 45° C or even 60° C at which E. faecalis can be denatured, was below the threshold to cause bone necrosis.11
The discussion of increased concentrations and temperature of sodium hypochlorite makes for a proper introduction to the Er,Cr:YSGG laser (Waterlase iPlus All Tissue Laser). Since its wavelength of 2780 nm is absorbed explicitly by water molecules, it can convert light energy into kinetic energy in anything containing water. A hydrokinetic system is born where photomechanical and photothermal effects pervade. Since soft and hard tissues comprise most of our body parts, including teeth, the Er,Cr:YSGG can ablate tissue as its concentrated light energy is absorbed by the water molecules within these tissues. Upon activating specially designed end firing tips for the Waterlase iPlus, one can visualize hard tissue vaporizing right in front of your very eyes during access preparation on dentin and enamel and on soft tissue for gingivectomies.
Within the pulp chamber and root canal orifice, the use of radial firing tips, which are also available for the Er,Cr:YSGG, provide for a 360° “donut-shaped” irradiating pattern that focuses light energy peripherally in the direction of dentinal tubules within a canal or on the external root surface and inner soft tissue aspect of a periodontal pocket. This radial pattern is very effective in the simultaneous debridement and detoxification of periodontal pockets in the soft tissue gingival surfaces and the hard tissue external root surfaces. It is optimally designed to irradiate all canal surfaces at once on an axial plane depending on the depth of placement of the tip during root canal treatment. When placed in the canal with sodium hypochlorite solution, these radial firing tips form the hydrokinetic system in which light energy is converted into mechanical energy via a photoacoustic effect that generates vapour bubbles. These vapour bubbles are instantly formed and then collapse to form shockwaves. The shockwaves represent the mechanical portion of the photomechanical effect that, in turn, results in shear forces. The turbulent, robust acoustic streaming and cavitation effects created by the Waterlase iPlus can increase the fluid velocity of the irrigating solution, dislodging dentin debris and smear layer and disrupting biofilm. Essentially, a fluid pump is created that allows for these elements to be propelled outward into the orifice for removal.12,13 At the same time, because vapour bubbles are being formed, the solution is warmed within the canal, which enhances its effect.
Let’s now discuss some limitations of syringe irrigation. The needle tip gauge or size, its design and placement within the canal are all critical factors that influence the ability of the irrigating solution to reach the apex. Unfortunately, the pendulum on syringe irrigation has been swinging back and forth for various reasons. Do we modify our canal preparation at the expense of tooth structure to fit our current technologies? Or do we adapt our instruments and devices to perform a more effective and efficient root canal treatment that offers the chance of conservation of dentin?
Is our goal to open canal apices to a 35/06 or a 40/04 preparation to achieve the proper oscillation of ultrasonic tips (per several studies) or to allow for adequate needle tip placement for syringe irrigation?4,13,14 Even with the use of an EndoVac unit which has shown better results than syringe irrigation, ISO sizes of 35 or greater are advocated for proper needle placement at the apex.15 The next question is, why do we need to instrument so broadly? Since the Waterlase iPlus can generate cavitation and powerful shockwaves through the entire canal system, you may consider smaller apical sizes and place more emphasis on biofilm disruption and depth of penetration into dentinal tubules. Boutsioukis et al. found that irrigating solutions cannot penetrate up to the working length in root canals prepared to apical size 20/06 or 25/06 taper; instead, a 30/06 preparation is necessary.4 With an Er: YAG 2940 nm, which belongs to the same class of erbium lasers as the Waterlase iPlus, the most outstanding bacterial killing efficiency occurred with laser assisted irrigation at 150-μm deep into dentin in all 3 root segments tested compared to ultrasonics, and syringe irrigation.
Let’s take another example from a “skinny” 25/02 preparation size. Again, laser-activated irrigation was more effective at 20/02 than 25/06 syringe irrigation for biofilm disruption in artificial root canal blocks.17 Waterlase radial firing tips: RFT2 and RFT3 come in 200- and 300-micron diameters, respectively. The RFT2 tip can reach deeply into the canal, although mid-root, orifice, and chamber are advocated for placement.16 The versatility and ease of placement of the Waterlase endodontic radial firing tips into the canals is perhaps the reason why it showed the most effective killing of E. faecalis and C. Albican biofilm compared to two other lasers, the Er: YAG and Nd: YAG.18 In this study, the authors speculated that the Waterlase produced more agitation deeper into the canal.18 While these are in vitro models, and much care needs to be taken when extrapolating results to in vivo situations, we can observe some interesting findings.
What seems to be expected in the more conservative canal preparation sizes is that effective contact and enhancement of the sodium hypochlorite solution is produced by laser activating the irrigating solution. It’s that photomechanical, hydrokinetic effect again, or simply put the agitation. The agitation is also slightly warmed owing to the laser photothermal effects. Even outside teeth, disruption of biofilm contained in infected wounds through laser-induced vapour nanobubbles has shown antibiotics to be much more effective at killing the bacteria within them.19
Agitation of irrigating solutions may be the key to the increased penetration depth of the solutions to reach deeper into dentinal tubules, isthmuses, and lateral canals.20-22 We already know from in vitro studies that a 6% sodium hypochlorite solution can penetrate dentin up to 300 microns after a 20-minute exposure time. By comparison, a 1% solution penetrated 77 microns within the first 2 minutes. The authors in the same study remarked that the effect, which varied by changing concentration and exposure time, could have been amplified further with agitation, which was not conducted.23 Also important is the sequence of our use of irrigating solutions. For example, pretreatment with 10% EDTA followed by 1% Triton X-100, a tensioactive agent, and then 5% sodium hypochlorite created an infection free zone of up to 130 microns into dentin which was lacking if 5% NaOCl was used first followed by 10% EDTA.24 Knowledge of the depth of penetration of our irrigating solutions is essential since we need to reach deeply into these dentinal tubules and lateral canals where bacteria can reside. After all, we know that bacteria can penetrate between 300–500 microns into dentinal tubules.25-26
Agitation is significant for tissue dissolution, depth of penetration of irrigating solutions, and enhanced disinfection. Although sonic and ultrasonic devices promote agitation, laser-activated irrigation creates a more adequate and potent version. In a study of pulpal tissue dissolution, the pulp from 53 intact third molars was removed, aggregated, and weighed. Samples were equally distributed to 4 groups and one control. The groups were as follows: manual agitation with gutta-percha points, ultrasonic activation, photodynamic therapy with diode, and laser-activated irrigation with the Waterlase. The percentage change in weight loss of the tissue sample was most remarkable for the Waterlase at 85%, followed by the ultrasonic unit at 35% change.27
Look at these two root canal treatments: #13 and #18 (#25 and #37, respectively) completed in a single visit. While lateral canals and apical deltas may be easier to fill in long-standing necrotic cases, these two examples of vital cases using the Waterlase iPlus with the RFT2 tip offer a glimpse of more predictable debridement and filling of these ramifications. There is no doubt that lasers will provide a new chapter in our quest for sterilization of the canal(s) and better 3-dimensional fills of root anatomy. Sodium hypochlorite is still our preferred irrigating solution. In this article, I’ve discussed how the Waterlase iPlus can effectively potentiate sodium hypochlorite solution so that it can reach the apex, apical deltas, lateral canals, and deeper inside dentinal tubules. It does so by maximal agitation, even in smaller preparation sizes, to offer better disinfection and debridement of the canal. So next time you place a syringe needle inside the canal, think about how lasers can make your root canal treatment more efficient for you and your patient.
Oral Health welcomes this original article.
- Byström A, Sundqvist G. Bacteriologic evaluation of the efficacy of mechanical root canal instrumentation in endodontic therapy. Scand J Dent Res. 1981 Aug;89(4):321-8.
- Byström A, Sundqvist G. Bacteriologic evaluation of the effect of 0.5 percent sodium hypochlorite in endodontic therapy. Oral Surg Oral Med Oral Pathol. 1983 Mar;55(3):307-12.
- Bystrom A, Sundqvist G. The antibacterial action of sodium hypochlorite and EDTA in 60 cases of endodontic therapy. Int Endod J. 1985;18:35.
- Boutsioukis C, Gutierrez N. Syringe Irrigation in Minimally Shaped Root Canals Using 3 Endodontic Needles: A Computational Fluid Dynamics Study. JOE 2021 47, 1487-1495.
- Peters OA, Schönenberger K, Laib A. Effects of four Ni-Ti preparation techniques on root canal geometry assessed by micro computed tomography. Int Endod J. 2001 Apr;34(3):221-30.
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- Dakin HD. On the use of certain antiseptic substances in treatment of infected wounds. Br Med J. 1915 2:318–20.
- Cohen’s Pathways of the Pulp 10th edition. 2011 Hargreaves KM, Cohen S, Berman LH. pp- 246.
- Cullen JK, Wealleans JA, Kirkpatrick TC, Yaccino JM. The effect of 8.25% sodium hypochlorite on dental pulp dissolution and dentin flexural strength and modulus. J Endod. 2015 41:920-4.
- Sirtes G, Waltimo T, Schaetzle M, Zehnder M. The effects of temperature on sodium hypochlorite short-term stability, pulp dissolution capacity, and antimicrobial efficacy. J Endod. 2005 31:669-671.
- Bartolo A, Koyess E, Camilleri J, Micallef C. Model assessing thermal changes during high temperature root canal irrigation. Healthc Technol Lett. 2016 Aug 5;3(3):247-251.
- De Moor RJ, Blanken JW, Meire M, Verdaasdonk RM. Laser Induced Explosive Vapor and Cavitation Resulting in Effective Irrigation of the Root Canal. Part 2: Evaluation of the Efficacy. Lasers Surg Med. 2009 Sep;41(7):520-3.
- De Moor RJ, Meire M, Goharkhay K, Moritz A, Vanobbergen J. Efficacy of ultrasonic versus laser-activated irrigation to remove artificially placed dentin debris plugs. J Endod. 2010 36:1580–3.
- Hsieh YD, Gau CH, Kung Wu SF, Shen EC, Hsu PW, Fu E: Dynamic recording of irrigating fluid distribution in root canals using thermal image analysis. Int Endod J. 2007 40:11.
- Baumgartner JC, Nielsen B. Comparison of the EndoVac System to Needle Irrigation of Root canals. J Endod. 2010 Mar; 36(3):509-11.
- Wen C, Kong Y, Zhao J, Li Y, Shen Y, Yang Y, Jiang Q. Effectiveness of photon-initiated photoacoustic streaming in root canal models with different diameters or tapers. BMC Oral Health. 2021 21:307.
- Kasic’ S, Knezovic’ M, Beader N, Gabric’ D, Malcˇ i c ’ A, Baraba A. Efficacy of Three Different Lasers on Eradication of Enterococcus faecalis and Candida albicans Biofilm in Root Canal System Photomedicine and Laser Surgery. 2017 35(7): 372-377.
- Teirlinck, E., Xiong, R., Brans, T. et al. Laser-induced vapor nanobubbles improve drug diffusion and efficiency in bacterial biofilms. Nat Commun 9, 4518 (2018).
- Pereira TC, Boutsioukis C, Dijkstra RJB, Petridis X, Versluis M, de Andrade FB et al. Biofilm removal from a simulated isthmus and lateral canal during syringe irrigation at various flow rates: a combined experimental and Computational Fluid Dynamics approach. International Endod J. 2021 Mar 54(3):427-438.
- Anastasios Retsas, DDS, MSc, Rene J. B. Dijkstra, Ing, Luc van der Sluis, DDS, PhD, Christos Boutsioukis, DDS, MSc, PhD. Antibiofilm Effect of Ultrasonic Activation Protocols. June 2022 JOE 48;6.
- Swimberghe R, Tzourmanas R, De Moor RJG, Braekmans K, Coenye T, Meire A. Explaining the working mechanism of laser activated irrigation and its action on microbial biofilms: A high speed imaging study. Int Endod J. 2022 Dec;55 (12):1372-1384.
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About the Author
Fernando J. Meza graduated in 2002 from the University of Connecticut School of Dental Medicine. Before dental school, he attended Vanderbilt University and completed a B.A. in Psychology. Dr. Meza received his Certificate in Endodontics from Temple School of Dentistry in 2004. During residency, Dr. Meza researched the Biolase Waterlase All Tissue Laser to explore the disinfecting capabilities of the laser on bacterially infected roots. In July 2007, he published his research in the Journal of the American Dental Association (JADA). In addition, Dr. Meza has lectured for Biolase in hands-on courses and provided in-office training to endodontists in the USA and Canada.