10 February 2023

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Innovative root canal irrigation strategy in minimally invasive endodontics

Study evaluated antimicrobial efficacy

Lara Figini

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Endodontic irrigation is an essential step in root canal treatment. Current irrigation techniques are based on the use of sodium hypochlorite but do not guarantee success in eliminating microorganisms from the root canal.

Minimally invasive endodontic treatment focuses on the preservation of structural dentin to enhance fracture resistance as well as the long-term survival of endodontically treated teeth. However, there are limitations associated with conservative preparation as many conventional irrigation strategies rely on larger preparations for optimal fluid dynamics and antibacterial effect. Hence the need to develop irrigation methods compatible with minimally prepared canals.

Antimicrobial photodynamic therapy (APDT) has shown potential efficacy in endodontics in both in vitro and in vivo treatment. This technique involves the application of a photosensitizing solution (PS), which binds to the bacteria, and upon activation with low light energy source, highly reactive oxygen is produced which causes bacterial cell death.

APDT acts on several targets in a bacterium, including the cell wall and plasmids, as well as having the ability to cause DNA damage and produce enzyme inactivation. However, APDT has limitations including limited penetration of PS into dentinal tubules and complex anatomies, reduced yield of reactive oxygen in a hypoxic environment, and uneven distribution of light energy throughout the root canal system.

Microbubble emulsions are produced from an oxygen carrier and an oxidizer and have been proposed as an application to complement and enhance the effects of APDT.

Microbubbles have been optimized to enhance the antimicrobial efficacy of APDT by elevating reactive oxygen availability and increased light distribution within complex root canal structures. The activated microbubbles produce a viscous flow within the canal to improve the shear wall stresses of the instruments, essential to fulfilling the physical requirement of root canal irrigation. The activation of the micro bubbles also results in a rapid release of single oxygen into the environment which leads to improved antibacterial efficacy.

Materials and methods

In a study published in December 2022 in the Journal of Endodontics, the authors evaluated the antimicrobial efficacy of a new irrigation strategy using synchronized photodynamic microbubble activation (SYMPA) in a single minimally prepared canal. Single-channel mandibular incisors were inoculated with Enterococcus faecalis for three weeks and randomly assigned to one of four groups according to the irrigation protocols:

• Group 1: control group (irrigation with saline solution): the canal was instrumented with WaveOne Gold Primary (25.07v), under irrigation of 6.5 ml of saline solution during preparation.
• Group 2: conventional needle irrigation (CI): the canal was instrumented with WaveOne Gold Primary (25.07v), under irrigation of 4.5 ml 6% NaOCl during preparation and a final rinse was performed with 1 ml of 5% sodium thiosulfate and 1 ml of saline solution.
• Group 3: Ultrasound-assisted irrigation (IU): the canal was instrumented with WaveOne Gold Primary (25.07v), under irrigation of 3 ml of 6% NaOCl. Ultrasonic activation was performed using size 15.02 titanium EndoUltra (Vista, USA) tips according to the manufacturer's instructions. Ultrasonic activation of 0.5 ml 6% NaOCl 3x20 sec was performed and the final rinse was performed with 1 ml 5% sodium thiosulfate and 1 ml saline.
• Group 4: irrigation with SYMPA, canal instrumented with WaveOne Gold Small (20.07v), under irrigation of 3 ml 6% NaOCl during preparation, SYMPA applied and final rinsing with 1 ml 5% sodium thiosulfate and 1 ml of saline solution.

SYMPA is a two-step technique:

• Step 1: Photosensitization: 0.5 ml of photosensitizer was applied and activated for 15 seconds with an S-tip (S-Tip) to distribute the solution inside the canal. After photosensitization, the solution was activated with both light and S-tip alternately.
• Step 2: Microbubble Emulsion Activation: 0.5ml of microbubble emulsion was applied into the canal and activated with the S-tip for 1 minute followed by activation with both light and S-tip for 1 minute alternately.

The groups 1, 2 and 3 were instrumented up to instrument 25.07v (WaveOne Gold Primary) and the SYMPA group was minimally primed up to instrument 20.07v (WaveOne Gold Small, Dentsply Sirona, Tulsa, OK). The apical 5mm was resected for microbiological evaluation using culture techniques (colony forming units (CFU)), ATP-based viability testing (relative luminescent units (RLU)), and calculation of the percentage of viable bacteria) and laser scanning confocal microscopy (CLSM).

Results

The microbiological CFU calculation of group three and group four SYMPA was reduced compared to the control group and the group two CI. The ATP-based vitality test (RLU) provided significantly reduced data for the third IU group and the four SYMPA group compared to the control group. The percentage of live bacteria was significantly lower in IU, SYMPA, compared to control and CI. Although a higher microbial reduction was observed in SYMPA than in UI, there was no statistical significance between the two groups.

Conclusions

From the data of this study, researchers concluded that SYMPA in minimally prepared canals has significant antimicrobial efficacy. The new SYMPA irrigation method could be an effective disinfection strategy for minimally prepared root canals.

Clinical implications

Application of SYMPA in a conservatively prepared root canal preparation has valid antimicrobial efficacy against E. faecalis biofilm in vitro. The S-shaped tip of the SYMPA is flexible and fully illuminates the root canal during shaking. It's therefore predictable that this strategy works effectively in curved canals. Furthermore, photo-oxidation and photosensitizer potential were found to be significantly higher when mixed with microbubbles, indicating increased single oxygen production. This SYMPA irrigation strategy could be an effective disinfection strategy for minimally prepared root canals. This enhanced strategy applied to a minimally prepared canal is beneficial as it allows the clinician to perform minimally invasive endodontics without compromise disinfection.

Christine Teed, Hebatullah Hussein, Anil Kishen. “Synchronized microbubble-photodynamic activation to disinfect minimally prepared root canals.” Journal of Endodontics. December 2022 https://doi.org/10.1016/j.joen.2022.12.003