Activated Irrigation in Endodontics

Research into endodontic outcomes shows that disinfection of the root canal system via cleaning and irrigation is a significant parameter of success.³ As per Vertucci,⁴ the nature of the canal system is not uniform and there is a high prevalence of accessory canals that cannot be instrumented by endodontic files. This has been documented in various studies that analyze treated teeth in cross section⁵ or with micro computed tomography.⁶ It has been noted that effective endodontic ­irrigation requires both adequate penetration of the irrigant³ and suf­ficient volume.⁷

One of the most cited papers on irrigation in endodontics is by Zehnder,⁸ who commented on the potential of newer approaches to traditional irrigation — activation of the irrigation fluid — to improve debridement of the canal system. Increasing the turbulence of the irrigant can improve penetration of the fluid to enhance antibacterial action.⁹ Common methods include shaking the irrigant with a file or activator tip, and use of ultrasonic and sonic tips running at a frequency to cause a hydrodynamic effect or microcavitation in the fluid. Lasers can also be used to achieve a similar effect (Figure 1). Bubbles created by these energy transfer techniques will form and collapse within the irrigant and the pressure waves will lead to shear stress along the root canal walls, which can effectively remove biofilm. This explosion and implosion of bubbles in the energized irrigant has been shown to increase fluid penetration and contact with canal walls, thereby improving cleaning efficacy.¹⁰

Lasers were first used in endodontics in 1971,¹¹ with Nd:YAG, Er:YAG, diode and CO₂ laser technologies initially used for irradiating root canals by way of heat absorption and the photodamaging effects to bacteria. The Er:YAG was found to be the more effective of the lasers utilized.^11,12 The protocol introduces a laser fiber tip into the prepared root canal to the apical region to create the desired effect. This method has limitations when faced with the curved nature of canals and not being able to introduce the tip to the apical area in a narrower canal. Another disadvantage when used in a dry state is the effect on tooth structure and potential for over-enlargement or ledging of the root canal.¹³

CANAL CLEANING EFFICIENCY

Laser-activated irrigation has since moved toward introducing the tip at an earlier stage in root canal treatment, and applying the laser to the irrigant solution to aid in cleaning the canal system (Figures 2A and 2B).¹⁴ The radiation emitted by the laser is absorbed by fluid molecules and there is an activation of the irrigant through what is described as a “transient cavitation” effect.¹⁵ Regarding cleaning efficiency, studies have shown laser-activated irrigation significantly reduces bacteria levels, with some papers demonstrating greater efficacy than other means of activation.^16–19 Although there is a benefit in more effective cleaning — including smear layer removal — the disadvantage (as seen with any method of irrigant activation) is the potential for apical extrusion of the irrigant.²⁰

Studies have since investigated placement of the laser tip, and whether it is advantageous to move the tip close to the apex (as in previous approaches) or if placement more coronally creates sufficient irrigant activation.^21,22 A video setup constructed by Blanken et al²¹ to assess the dynamics of laser-activated irrigant showed bubble formation, with bubble expansion and subsequent collapse within the fluid due to the resulting turbulence. It was noted that bubble implosion resulting from laser activation forms secondary cavitation bubbles. In a comparison between free water and a root canal model, the authors reported that bubble formation, collapse and resultant secondary bubbles enhanced the effect. The study showed that a more coronally placed laser tip has the potential for significant irrigant activation.

Laser irradiation of the irrigant will heat the fluid and boil it to vapor in 1 microsecond. This creates the bubble, which expands. Further laser emission passes through the vapor bubble and evaporates the fluid in front of it, causing more expansion, as described by the Moses effect.²³ This pushes the fluid toward the canal walls. As the laser stops, the vapor bubble shrinks and collapses, which causes shock waves within the irrigant. During this rapid irrigant flow, the rebound effect of pressure changes leads to the formation of secondary bubbles, which collapse and form smaller bubbles. This results in dynamic movement of the irrigant in what has been described as acoustic streaming.²²

Matsumoto et al²² demonstrated that in a narrower root canal space the initial bubble cannot expand as much, which leads to increased streaming of the cavitation bubbles; however, there may be less energy in the shock waves created. In this study, the laser tip was not placed at a close distance to the apex and the cavitation bubbles were still able to reach the apical region. This may have applications in situations where ultrasonic activation is limited, such as in narrow canals — where laser activation may work without pre-enlarging the canal system. This can allow a more minimally invasive approach to endodontics, as the laser tip can be placed in the pulp chamber and a fully prepared or enlarged root canal is not necessary.^22,24,25

EVOLVING APPROACHES

Laser-activated irrigation has evolved to include photon induced photoacoustic streaming (PIPS) and shock wave enhanced emission photoacoustic streaming (SWEEPS) technologies designed to enhance the effectiveness of laser-activated irrigation. The PIPS protocol calls for use of a special laser tip that is stripped and altered from end firing to radial firing.²⁶ The resulting energy is emitted in multiple directions, which reportedly achieves more effective activation of the fluid — and without the potential apical extrusion of irrigants.²⁷ This technology uses extremely low levels of energy, which leads to faster bubble collapse and a greater secondary cavitation effect, with short bursts of peak power of around 400 to 1000 watts. A study by Olivi¹³ demonstrated a temperature rise in the apical region of only 1.5^o C after 40 seconds of use, which reduces the potential for thermal damage. Research by Peters et al²⁸ showed the PIPS protocol to be effective in root canal disinfection.

A further literature search into PIPS yields positive results. Orinola-Zapata et al²⁹ report PIPS significantly improved biofilm removal compared to a standard needle, sonic activation or passive ultrasonic activation. Lloyd et al³⁰ used micro computed tomography to analyze the canal volume and debris removal using the PIPS method, and reported 2.6 times greater efficacy of debris removal than standard needle irrigation. Pedulla et al³¹ showed the effectiveness of the PIPS protocol in debris removal with sterile water, with or without a laser; however, the authors could not show a significant difference with sodium hypochlorite. In regard to bacterial reduction, a study of colony forming unit levels by Olivi et al³² showed significant reduction of Enterococcus faecalis using PIPS. This was also noted in systematic reviews by Sadik et al³³ and Al-Aqeedi et al.³⁴ A modified PIPS protocol was considered by Golob et al,³⁵ who cycled between sodium hypochlorite and ethylenediaminetetraacetic acid, and lowering the energy level from 20 mJ to 10 mJ. Despite lower energy, this did not lessen the effect of PIPS in reducing bacterial levels within the canal.

The SWEEPS protocol was developed to improve the photoacoustic streaming of irrigants with PIPS (Figure 3).³⁶ Based on a technique used with ultrasound to break kidney stones, it uses specially timed laser pulses to maximize bubble formation and collapse during irrigant activation, increasing the cleaning and debriding effects of the resulting shock waves. A study that examined bubble dynamics showed deeper penetration of bubbles with the SWEEPS protocol compared to PIPS. This finding confirmed the work of Meire et al,³⁷ who used shorter pulses of laser irradiation to improve debris removal.

CONCLUSION

Regardless of the modality used, activated irrigation has been shown to increase the efficacy of root canal cleaning, and is evolving into the standard of care in endodontic treatment. Activation by laser has the potential to be clinically relevant because it supports minimally invasive therapy. There is a trend in endodontics toward smaller access and apical sizes³⁸ and preserving as much tooth structure as possible, while still achieving adequate disinfection of root canals. Continued positive results in published studies may strengthen the evidence base for laser-activated irrigation.

While it is not possible to conclude there are proven benefits for laser-activated irrigation surpassing other methods, this is a developing area of endodontic disinfection that may hold promise for the future.

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KEY TAKEAWAYS

• With the goal improved tooth survival, the future of endodontics is moving toward more minimally invasive, restorative-driven root canal therapy.
• Effective endodontic irrigation requires both adequate penetration of the irrigant³ and sufficient volume.⁷
• Increasing the turbulence of the irrigant can improve penetration of the fluid to enhance antibacterial action,⁹ and this has led to the development of various irrigant activation technologies.
• Common methods of activation include shaking the irrigant with a file or activator tip, use of ultrasonic and sonic tips running at a frequency to cause a hydrodynamic effect or microcavitation in the fluid, and laser activation.
• The explosion and implosion of bubbles in the energized irrigant increases fluid contact with canal walls, thereby improving cleaning efficiency.¹⁰
• Regardless of the modality used, activated irrigation has been shown to increase the efficacy of root canal cleaning, and is evolving into the standard of care in endodontic treatment.

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REFERENCES

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The author has no commercial conflicts of interest to disclose.