Advancements in Endodontic Irrigation Techniques

The goal of endodontic treatment is to treat or prevent apical periodontitis. This requires mechanical instrumentation and antibacterial irrigation, commonly called chemomechanical canal preparation. It is impossible to sterilize the canal, but the goal is to reduce the bacterial load to a sublevel from which the body can heal.¹ Endodontic instrumentation is estimated to leave 35% of the canal walls untouched.²

Hard tissue debris and bacteria and their by-products can remain in complex anatomy, such as isthmuses, lateral canals, and untouched dentin walls. Bacteria can penetrate dentin tubules up to 0.3 mm.³ Recent research has focused on introducing irrigation into these hard-to-reach areas via adjunctive irrigation techniques.

Needle/​Manual Irrigation

Root canals are typically instrumented using an endodontic file and copious irrigation with sodium hypochlorite in a standard Luer-lock syringe and a side-venting blunted needle. The needle is often inserted until just before binding or within 2 mm of the root apex.⁴ The alternative method is to use the master apical cone and hydraulically pump it slowly up and down a few times to encourage the solution into the apical third. Most irrigation studies use standard needle irrigation as a benchmark to compare other methods.⁵

Sonic and Ultrasonic Irrigation

Sonic activation uses a smooth, noncutting polymer tip placed into the canal close to the working length and activated, causing vibration and fluid movement into hard-to-reach areas of the canal system.⁶ Finishing files are designed as an alternative to sonic activation. A smooth polymer file is run in a slow-speed handpiece at 700 to 900 rpm to agitate irrigation solution and transport debris coronally via a specialized flute design.⁷ Inadvertent damage to the dentin walls has not been observed with sonic activation.⁸

Passive ultrasonic irrigation is an ultrasonically activated file transmitting acoustic energy to a liquid irrigant within the canal system.⁹ Ultrasonic devices oscillate at a 25 to 30 kHz frequency vs sonic, which operates at a lower frequency of 1 to 6 kHz.¹⁰

The term passive does not describe the irrigation process but rather the file’s noncutting action. A small noncutting file or smooth wire is placed in the center of a previously shaped canal and ultrasonically activated to agitate the irrigant. As the file ultrasonically oscillates, it creates multiple eddies of fluid motion along the file. Each eddy flows in the opposite direction of its immediate neighbor. Slower moving secondary eddies form outside the primary ones, aiding in fluid movement from the apex to the coronal aspect.

The streaming patterns close to the file cause irrigant fluid movement, producing shear stress against the root canal walls and aiding in debris removal.¹¹ Streaming velocity depends on the file’s diameter, taper, and cross-sectional shape,¹² with the highest streaming velocities noted at the file tip.¹³

So which is better — sonic or ultrasonic activation? Research results are mixed. Both sonic and ultrasonic activation render root canal walls significantly cleaner than manual syringe irrigation.¹⁴ If comparing sonic to ultrasonic, however, ultrasonic tends to do better, likely due to increased oscillation. However, some studies have not shown a statistically significant difference between sonic and ultrasonic irrigation.⁵

Laser-Assisted Irrigation

Lasers are widely used in dentistry with hard and soft tissue applications. The erbium: yttrium aluminum garnet (Er:Yag) emits a wavelength of 2,940 nm. The erbium chromium: yttrium scandium gallium garnet (Er,Cr:YSGG) emits a wavelength of 2,780 nm. The Er:YAG laser wavelength coincides with the absorption peak of water and hydroxyapatite, making it ideal for use during root canal therapy.¹⁵

In water, the laser pulse forms large vapor bubbles, which expand and then implode. The bubbles may expand up to 1,600 times their original volume; this increases pressure and drives fluid movement. When the bubble implodes after 100 to 200 microseconds, the underpressure forces fluid back into the canal, inducing a rebound secondary cavitation.¹⁶

The secondary cavitation bubbles are much smaller compared to the first vapor bubble. When the secondary cavitation bubbles collapse, even smaller bubbles form and disappear repeatedly. This phenomenon allows the operator to keep the laser tip in the chamber yet activate irrigation in the apical segment.¹⁷ This makes it a promising tool to enhance disinfection by mechanically removing debris, biofilm, and infected tissue while minimizing thermal damage to surrounding structures.

Nanoparticles

Nanomaterials are natural or manufactured materials containing particles in which more than 50% of the particles have an external dimension of 1 to 100 nm. They have unique physicochemical properties (eg, ultrasmall size, relatively large surface area, and increased chemical reactivity). The increased surface-to-volume ratio means more atoms are present near the surface.¹⁸

Nanoparticles are classified by their composition, usually either naturally occurring or synthetic. They can be further categorized as organic or inorganic. They come in many shapes, such as particles, spheres, tubes, rods, etc. A functionalized nanoparticle has a core of 1 material and additional molecules or proteins bonded to its surface or encapsulated within the particle. They can be functionalized with peptides, drugs, or photosensitizers.¹⁹

Few known mechanisms exist by which nanoparticles can act on microorganisms to assist in removing biofilms within endodontic canals. Positively charged nanoparticles can attack negatively charged microorganisms, accumulating on the bacterial cell surface. This upsets the bacterial cell wall, increasing permeability and interrupting bacterial cell activities. Nanoparticles can cause the release of reactive oxygen species, causing oxidative stress on the microbe and, ultimately, disrupting the cell membrane. Protein-bound nanoparticles can interrupt the amino acids’ oxidative process, causing the degradation of proteins and inactivating microbe enzymes.

While nanoparticles show promise in enhancing endodontic disinfection, thorough research is ongoing to ensure their safety, biocompatibility, and long-term effects on dental tissues.²⁰ Striking the right balance between effective microbial control and minimal cytotoxicity is crucial for successfully integrating nanoparticles into routine endodontic practice. Undoubtedly, the future of endodontics is headed in the “nanodirection.”²¹

Conclusion

The evolution of endodontic irrigation techniques has greatly enhanced the efficacy and precision of root canal treatment. Sonic and ultrasonic irrigation methods offer efficient debridement and debris removal through acoustic streaming and cavitation, ensuring thorough cleaning of complex root canal systems. With its targeted and selective water interaction, laser irrigation provides a promising avenue for disinfection and debris removal while minimizing damage to surrounding tissues. Integrating nanoparticles in irrigation solutions or obturation materials also holds immense potential for enhancing antimicrobial efficacy and promoting tissue healing. As the field continues to advance, the synergistic combination of these techniques promises to elevate the standard of care in endodontics, facilitating better outcomes and improved patient satisfaction.

References

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From Decisions in Dentistry. May/June 2025;11(3):20-21.