- Email: [email protected]
Tissue Dissolution by a Novel Multisonic Ultracleaning System and Sodium Hypochlorite
Basic Research—Technology
Tissue Dissolution by a Novel Multisonic Ultracleaning System and Sodium Hypochlorite Markus Haapasalo, DDS, PhD,* Zhejun Wang, DDS, PhD,* Ya Shen, DDS, PhD,* Allison Curtis, MSc,† Payal Patel, BSc,† and Mehrzad Khakpour, PhD† Abstract Introduction: This study aimed to evaluate the effectiveness of a novel Multisonic Ultracleaning System (Sonendo Inc, Laguna Hills, CA) in tissue dissolution in comparison with conventional irrigation devices. Methods: Pieces of bovine muscle tissue (68 2 mg) were placed in 0.7-mL test tubes (height: 23.60 mm, inner diameter: 6.00 mm, outer diameter: 7.75 mm) and exposed to 5 minutes of irrigation by different devices. Endodontic devices included the Multisonic Ultracleaning System, the Piezon Master 700 (EMS, Dallas, TX) ultrasonic system with agitation, the EndoVac negative-pressure irrigation system (SybronEndo, Orange, CA), and a conventional positive-pressure 27-G irrigation needle at a flow rate of 10 mL/min. The systems were tested with 0.5%, 3%, and 6% sodium hypochlorite (NaOCl) at room temperature (21 C) as well as 40 C. Irrigation with sterile water was used as a control. The mass of tissue specimens was measured and recorded before and after the use of each device, and if the specimen was completely dissolved visually within 5 minutes, the dissolution time was recorded. The rate of tissue dissolution (%/s) was then calculated. Results: The Multisonic Ultracleaning System had the fastest rate of tissue dissolution (P < .05), at 1.0% 0.1% per second using 0.5% NaOCl, 2.3% 0.9% per second using 3% NaOCl, and 2.9% 0.7% per second using 6% NaOCl. This tissue dissolution rate was more than 8 times greater than the second fastest device tested (P < .01), the Piezon Master 700 ultrasonic system, which resulted in a tissue dissolution rate of 0.328% 0.002% per second using 6% NaOCl at 40 C. For all irrigation devices tested, the rate of tissue dissolution increased with a higher concentration and temperature of the NaOCl solution. Conclusions: The novel Multisonic Ultracleaning System achieved a significantly faster tissue dissolution rate when compared with the other systems examined in vitro. (J Endod 2014;-:1–4)
Key Words Irrigation, Multisonic Ultracleaning, sodium hypochlorite, tissue dissolution, ultrasonic
I
rrigation of the root canal system during treatment potentially has several important functions; it removes loose tissue debris from the canal, kills planktonic and biofilm microbes, and dissolves inorganic and organic tissue (1–8). Sodium hypochlorite (NaOCl) is the most popular irrigating solution because it has many of the desired characteristics of a root canal irrigant (9, 10), and it is the only clinically acceptable irrigant capable of dissolving organic tissue. It is known that the effectiveness of organic tissue dissolution by NaOCl is dependent on concentration and temperature of the NaOCl solution (4). Studies have also shown that agitation helps improve the tissue-dissolving activity of NaOCl (11, 12). Interestingly, although the role of agitation is recognized, Stojicic et al (12) reported that the increase in tissue dissolution by NaOCl was the same whether agitation was done using pipetting, EndoActivator (Dentsply, Tulsa, OK), or ultrasound. One explanation for the equal performance by devices such as ultrasound and EndoActivator is that although ultrasound causes acoustic streaming that may reach the peripheral areas of the root canal system, the theoretically more effective cavitation outcome can only be detected a few micrometers from the ultrasonic instrument (12–15). Recently, a novel technology, the Multisonic Ultracleaning System (Sonendo Inc, Laguna Hills, CA), has been developed for cleaning of the root canal system. The system is designed to develop a broad spectrum of waves within the solution to clean soft tissue and bacteria inside root canals. The goal of the present study was to compare the (organic) tissue-dissolving effectiveness of the Multisonic Ultracleaning System with conventional methods of irrigation using NaOCl in concentrations ranging from 0.5% to 6% and at different temperatures (21 C and 40 C) of the irrigating solution.
Materials and Methods Solutions NaOCl solutions in concentrations of 0.5%, 3%, and 6% were tested. A stock solution of 8.5% NaOCl (Clorox Bleach; Clorox, Oakland, CA) was obtained from the manufacturer. The amount of available chlorine was verified for each experiment by an iodine/thiosulfate titration method as previously described (16). The 0.5%, 3%, and 6% NaOCl solutions were prepared by diluting the 8.5% stock solution in sterile water. The solutions were brought to room temperature before use. The solutions for the experiments were used either at room temperature (21 C) or heated to 40 C using a temperature-controlled water bath (Haake B3; Thermo Electron Corp, Waltham, MA) with the exception of the Multisonic Ultracleaning System. The solution was stored in a 1-L glass bottle placed inside a water bath. The temperature of the
From the *Division of Endodontics, Department of Oral Biological and Medical Sciences, Faculty of Dentistry, The University of British Columbia, Vancouver, Canada; and †Sonendo Inc, Laguna Hills, California. Address requests for reprints to Dr Markus Haapasalo, Division of Endodontics, Oral Biological and Medical Sciences, UBC Faculty of Dentistry, 2199 Wesbrook Mall, Vancouver, BC, Canada V6T 1Z3. E-mail address: [email protected] 0099-2399/$ - see front matter Copyright ª 2014 American Association of Endodontists. http://dx.doi.org/10.1016/j.joen.2013.12.029
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Basic Research—Technology solutions was confirmed using a thermometer and maintained automatically by the water bath. For the Multisonic Ultracleaning System, solution was placed in the unit at room temperature but automatically dispensed out of the handpiece tip at 40 C for all samples. As a negative control, sterilized water (Sterile Water for Irrigation, Baxter, Deerfield, IL) irrigation was also tested.
Equipment Endodontic devices tested included the Multisonic Ultracleaning System, Piezon Master 700 (EMS, Dallas, TX) ultrasonic system with agitation, EndoVac negative-pressure irrigation system (SybronEndo, Orange, CA) with the 28-G (0.32 mm) Microcannula EndoVac needle, and a conventional positive-pressure 27-G irrigation needle (Appli-Vac, Vista, Racine, WI). The 27-G needle was attached by a luer lock connection to 3-stop color-coded Tygon ST tubing (Ismatec, WertheimMondfeld, Germany), whereas the EndoVac needle was attached to the titanium finger piece and tubing provided. A digitally controlled peristaltic pump (Reglo Digital MS-2/8, Ismatec) was used to deliver the irrigant from the needles at precise flow rates. The peristaltic pump was calibrated before using each irrigation needle to ensure an accurate flow rate by measuring the mass of the solution delivered through the pump in a specified period of time. The needle flow rates were calibrated again with each set of irrigating conditions to ensure fidelity. Multisonic Ultracleaning System The Multisonic Ultracleaning System is a novel type of root canal cleaning system that consists of a console and handpiece, which externally resembles a dental handpiece. During use, the tip of the handpiece is placed 1 mm above the pulp chamber floor. The handpiece tip never enters the canal orifices at any point of the procedure. The system is operated from a touch screen control panel that regulates the high speed flow of irrigating solution from the central unit to the handpiece, where it hits a metal impingement plate at the end of the tip and creates a spray that is released from the tip at approximately 45 mL/min at a temperature of approximately 40 C. As opposed to the other systems tested, the console is built to degas the irrigation solutions. When the Multisonic Ultracleaning System is used, the pulp chamber of the tooth is sealed from the oral cavity, preventing the possibility of NaOCl mist spreading around the working area. The handpiece itself has a builtin 5-point vented suction system that collects the excess NaOCl from the pulp chamber. Tissue Dissolution The same type of fresh bovine meat was used for the tissue sample in the experiment. Before use, it was kept frozen at 15 C in standard packaging to retain moisture. As the surface area of the sample is likely to have an impact on tissue dissolution, each sample had similar size and shape. Frozen tissue was thus cut into equal-sized pieces of 4 4 2 mm using a stainless steel blade. Tissue specimen mass was then measured before treatment using a calibrated electronic balance (FX-300; A&D Company Ltd, Tokyo, Japan). Six parallel samples per group were included. There was no significant difference in the sample mass used for each group, with an average initial mass of 68 2 mg. For the experiment, the samples were threaded onto a thin steel wire and then positioned in the middle of a 0.7-mL glass vial (SKS, Watervliet, NY). The testing was performed with irrigating solutions at room temperature and at 40 C. The temperature of the solutions was confirmed before each use with a thermometer (Fisher Scientific, Ottawa, Ontario, Canada). 2
Haapasalo et al.
For all devices tested, tips and needles were immersed in the vial containing irrigating solutions to a distance of 10 mm from the tissue specimen. For ultrasonic irrigation, the ultrasound energy (power setting at grade III, Piezon Master 700, EMS) in endo mode alternated between on and off every 15 seconds for the 5-minute period. Ultrasonic agitation was performed with and without continuous flow of irrigant solutions at a flow rate of 10 mL/min. Degassed NaOCl has not been used with the conventional methods of canal irrigation. However, in order to evaluate the possible role of degassing of hypochlorite on the tissue dissolution, additional experiments were performed with the conventional irrigation equipment as described previously but by using degassed NaOCl instead of the nondegassed solution. If tissue was completely dissolved as judged visually in less than 5 minutes, the time (seconds) it took to dissolve the tissue was recorded. For all other specimens, the samples were blotted dry with a paper towel after 5 minutes of exposure, and the tissue mass was recorded.
Data Analysis The rate of tissue dissolution was calculated according to the following equation: % Percent Tissue Mass Loss Rate of Tissue Dissolution ¼ s Recorded Time The values for each device and irrigant tested were expressed as a mean rate of tissue dissolution standard deviation. The mean tissue dissolution rates for all irrigation solution concentrations and temperatures using the different devices/irrigation methods were compared using univariate analysis of variance followed by the post hoc test (Games-Howell test) for multiple comparisons (SPSS Inc, Chicago, IL). Differences in mean tissue dissolution rates were considered statistically significant if the P value was less than .05.
Results The rate of tissue dissolution for the devices tested using sterile water and different concentrations of NaOCl at room temperature and 40 C are shown in Figures 1 and 2. The fastest rate of tissue dissolution was obtained with the Multisonic Ultracleaning System, which dissolved the tissue specimen at a rate of 1.0% 0.1% per second using 0.5% NaOCl, 2.3% 0.9% per second using 3% NaOCl, and 2.9% 0.7% per second using 6% NaOCl. These rates were significantly faster (P < .05) than any other device tested. None of the other irrigation protocols were able to dissolve the complete specimen in 5 minutes. These average rates of tissue dissolution ranged from 0.04% 0.01% per second to 0.328% 0.002% per second depending on temperature and NaOCl concentration. The rate of tissue dissolution increased when the temperature of the NaOCl solution (P < .05) was increased. Degassing of NaOCl for the conventional irrigation systems did not enhance tissue dissolution (data not shown). When sterile water was used for irrigation instead of NaOCl, the Multisonic Ultracleaning System dissolved the tissue at a rate of 0.16% 0.02% per second. Using the other irrigation systems with water did not result in a rate of tissue dissolution that allowed for a significant loss of tissue over the 5-minute procedure.
Discussion Several different types of experimental designs have been used in previous research measuring the effectiveness of soft tissue dissolution by different irrigating solutions and/or irrigating systems. An in vitro model like the present one has been used in many studies (10, 12, 17). This type of model is not supposed to provide detailed JOE — Volume -, Number -, - 2014
Basic Research—Technology
Figure 1. The rate of tissue dissolution (%/s) at room temperature using the Multisonic Ultracleaning System and other conventional irrigation devices. Different letters indicate statistically significant differences between groups (P < .05). ND, not done.
recommendations for clinical protocols, but it has several advantages when the comparative effectiveness of different systems is being evaluated in a standardized setting. There are limitations of the present model, including the size and geometry of the measurement vial, the fixed distance of 10 mm from the tip of the endodontic device to the tissue, and the type of tissue used. Nevertheless, 10 mm was a safe distance to prevent the tissue from dislodging from the wire, which allowed for an accurate post-treatment tissue mass measurement for all devices tested. The vial geometry and size could be altered to reflect different root canal sizes or the distance from the tissue specimen, and the tip of the endodontic device could be varied to determine the role this distance plays in tissue-dissolution capabilities. Optimally, necrotic human pulp tissue should be used for this type of testing (18). However, because of the limited availability and size of human pulp, this is not practical, especially when a large number of groups are tested. Bovine muscle tissue is easily available, has a fairly uniform composition, and can be cut into pieces of predetermined size and
shape. Not only can the initial mass be standardized (68 2 mg in the present study), but the shape and surface area are also similar for all specimens, which is likely to be a factor when chemical dissolution of tissue is measured. The small standard deviations for the average tissue dissolution rates are an indication of the reproducibility of these results. The tissue-dissolution effects achieved with the Multisonic Ultracleaning System using any of the 3 NaOCl concentrations (0.5%, 3%, and 6%) was significantly superior when compared with all other irrigation protocols and systems evaluated (P < .05). Although the standard deviations appear higher in the Multisonic Ultracleaning data presented in Figures 1 and 2, this is an expected result. The Multisonic Ultracleaning System achieved complete tissue mass loss for every sample tested, making the time recorded the main component that affected the variability of the rate of tissue mass loss. Because the tissue was completely dissolved for all samples in a short period of time, any small difference in time recorded would have a greater effect on the variability
Figure 2. The rate of tissue dissolution (%/s) at 40 C using the Multisonic Ultracleaning System and other conventional irrigation devices. Different letters indicate statistically significant differences between groups (P < .05). ND, not done.
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Basic Research—Technology of the rate of tissue mass loss, contributing to the higher standard deviations compared with the other devices tested. Regardless of this variability, the rate of tissue dissolution for the Multisonic Ultracleaning System with 6% NaOCl was 2.9% 0.7% per second, which was more than 8 times faster than the rate of tissue dissolution with the Piezon Master 700 Ultrasonic System. Interestingly, the Multisonic Ultracleaning System used with water instead of NaOCl had a tissue dissolution rate of 0.16% 0.02% per second, making it equally effective as needle irrigation with 2% NaOCl at 40 C and a 45-mL/min flow rate (data not shown). The Multisonic Ultracleaning System uses a high flow rate of approximately 45 mL/min for NaOCl irrigation, and the solution is at a temperature of 40 C when it is released from the handpiece into the pulp chamber. In an effort to understand the possible mechanisms responsible for the fast tissue-dissolution time using the Multisonic Ultracleaning System, an experimental group with similar parameters (40 C, 45 mL/min) was tested with needle irrigation. It should be noted that a 45-mL/min flow rate cannot be achieved with 25-G to 30-G needles; therefore, a size 19-G (0.91-mm) (Monoject; Kendall Healthcare, Mansfield, MA) needle was used even though no clinical relevance could be identified. In addition, positive-pressure needle irrigation at 45 mL/min in the canal, even if possible, is likely to be a safety risk with regard to apical pressure and possible extrusion of NaOCl into the periapical tissue (19, 20). As expected, using these needle irrigation conditions, regardless of the NaOCl concentration, did not result in a significant additional loss of tissue mass over the 5-minute period compared with other conventional methods (data not shown). Thus, the high flow rate and elevated temperature of the NaOCl alone cannot explain the superior performance of the Multisonic Ultracleaning System. It has been reported that air in the liquid can cushion the implosive effects of cavitation (21). Therefore, it is possible that degassing the NaOCl solution by the Multisonic Ultracleaning System facilitates the effects of cavitation if present. The results indicate that some form of physical energy generated by the Multisonic Ultracleaning System may be responsible for the fast effect beyond what can be achieved by optimizing the flow rate, concentration, and temperature of NaOCl. Whether cavitation created by the Multisonic Ultracleaning System in the liquid explains the superior performance of the system remains to be clarified in future studies. A concern in a clinical situation when high flow rates are used is the possibility of high apical pressure and extrusion of the solution through the apical foramen (22). Control experiments with the Multisonic Ultracleaning System using colored liquid and transparent teeth have shown that the irrigating solution circulates in all canals instantly up to the level of the apical foramen but does not penetrate/extrude through the apical foramen (data not shown). In conclusion, the Multisonic Ultracleaning System used with NaOCl at different concentrations dissolved tissue at a significantly faster rate when compared with the conventional irrigation devices examined under the conditions in the present study. For future studies, changes in the present model setup may allow us to determine the effect that the different components, including the size of the measurement vial, distance of the endodontic device tip from the tissue specimen, and type of tissue, have on the rate of tissue dissolution.
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Acknowledgments Supported by Sonendo Inc and start-up funds provided by the Faculty of Dentistry, University of British Columbia, Canada. One of the authors (M.H.) has commercial interest in the tested product. Three authors are employees of Sonendo Inc.
References 1. Cunningham WT, Balekjian AY. Effect of temperature on collagen-dissolving ability of sodium hypochlorite endodontic irrigant. Oral Surg Oral Med Oral Pathol 1980; 49:175–7. 2. Cunningham WT, Joseph SW. Effect of temperature on the bactericidal action of sodium hypochlorite endodontic irrigant. Oral Surg Oral Med Oral Pathol 1980; 50:569–71. 3. Sedgley CM, Nagel AC, Hall D, et al. Influence of irrigant needle depth in removing bioluminescent bacteria inoculated into instrumented root canals using real-time imaging in vitro. Int Endod J 2005;38:97–104. 4. Gutarts R, Nusstein J, Reader A, et al. In vivo debridement efficacy of ultrasonic irrigation following hand-rotary instrumentation in human mandibular molars. J Endod 2005;31:166–70. 5. van der Sluis LW, Gambarini G, Wu MK, et al. The influence of volume, type of irrigant and flushing method on removing artificially placed dentine debris from the apical root canal during passive ultrasonic irrigation. Int Endod J 2006;39:472–6. 6. Zehnder M. Root canal irrigants. J Endod 2006;32:389–98. 7. Gu LS, Kim JR, Ling J, et al. Review of contemporary irrigant agitation techniques and devices. J Endod 2009;35:791–804. 8. Haapasalo M, Shen Y, Qian W, et al. Irrigation in endodontics. Dent Clin North Am 2010;54:291–312. 9. Rosenfeld EF, James GA, Burch BS. Vital pulp tissue response to sodium hypochlorite. J Endod 1978;4:140–6. 10. Turkun M, Cengiz T. The effects of sodium hypochlorite and calcium hydroxide on tissue dissolution and root canal cleanliness. Int Endod J 1997;30:335–42. 11. Moorer WR, Wesselink PR. Factors promoting the tissue dissolving capability of sodium hypochlorite. Int Endod J 1982;15:187–96. 12. Stojicic S, Zivkovic S, Qian W, et al. Tissue dissolution by sodium hypochlorite: effect of concentration, temperature, agitation, and surfactant. J Endod 2010; 36:1558–62. 13. Ahmad M, Pitt Ford TJ, Crum LA. Ultrasonic debridement of root canals: acoustic streaming and its possible role. J Endod 1987;13:490–9. 14. Cameron JA. The synergistic relationship between ultrasound and sodium hypochlorite: a scanning electron microscope evaluation. J Endod 1987;13:541–5. 15. Lumley PJ, Walmsley AD, Laird WR. Streaming patterns produced around endosonic files. Int Endod J 1991;24:290–7. 16. Macedo RG, Wesselink PR, Zaccheo F, et al. Reaction rate of NaOCl in contact with bovine dentine: effect of activation, exposure time, concentration and pH. Int Endod J 2010;43:1108–15. 17. Okino LA, Siqueira EL, Santos M, et al. Dissolution of pulp tissue by aqueous solution of chlorhexidine digluconate and chlorhexidine digluconate gel. Int Endod J 2004; 37:38–41. 18. Hasselgren G, Olsson B, Cvek M. Effects of calcium hydroxide and sodium hypochlorite on the dissolution of necrotic porcine muscle tissue. J Endod 1988; 14:125–7. 19. Tinaz AC, Alacam T, Uzun O, et al. The effect of disruption of apical constriction on periapical extrusion. J Endod 2005;31:533–5. 20. Mitchell RP, Baumgartner JC, Sedgley CM. Apical extrusion of sodium hypochlorite using different root canal irrigation systems. J Endod 2011;37:1677–81. 21. Budris A, Mayleben PA. Effects of entrained air, NPSH margin, and suction piping on cavitation in centrifugal pumps. Proceedings of the 15th International Pump Users Symposium. Houston: Turbomachinery Laboratory; 1998:99–108. 22. de Sermeno RF, da Silva LA, Herrera H, et al. Tissue damage after sodium hypochlorite extrusion during root canal treatment. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2009;108:e46–9.
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Tissue Dissolution by a Novel Multisonic Ultracleaning System and Sodium Hypochlorite Markus Haapasalo, DDS, PhD,* Zhejun Wang, DDS, PhD,* Ya Shen, DDS, PhD,* Allison Curtis, MSc,† Payal Patel, BSc,† and Mehrzad Khakpour, PhD† Abstract Introduction: This study aimed to evaluate the effectiveness of a novel Multisonic Ultracleaning System (Sonendo Inc, Laguna Hills, CA) in tissue dissolution in comparison with conventional irrigation devices. Methods: Pieces of bovine muscle tissue (68 2 mg) were placed in 0.7-mL test tubes (height: 23.60 mm, inner diameter: 6.00 mm, outer diameter: 7.75 mm) and exposed to 5 minutes of irrigation by different devices. Endodontic devices included the Multisonic Ultracleaning System, the Piezon Master 700 (EMS, Dallas, TX) ultrasonic system with agitation, the EndoVac negative-pressure irrigation system (SybronEndo, Orange, CA), and a conventional positive-pressure 27-G irrigation needle at a flow rate of 10 mL/min. The systems were tested with 0.5%, 3%, and 6% sodium hypochlorite (NaOCl) at room temperature (21 C) as well as 40 C. Irrigation with sterile water was used as a control. The mass of tissue specimens was measured and recorded before and after the use of each device, and if the specimen was completely dissolved visually within 5 minutes, the dissolution time was recorded. The rate of tissue dissolution (%/s) was then calculated. Results: The Multisonic Ultracleaning System had the fastest rate of tissue dissolution (P < .05), at 1.0% 0.1% per second using 0.5% NaOCl, 2.3% 0.9% per second using 3% NaOCl, and 2.9% 0.7% per second using 6% NaOCl. This tissue dissolution rate was more than 8 times greater than the second fastest device tested (P < .01), the Piezon Master 700 ultrasonic system, which resulted in a tissue dissolution rate of 0.328% 0.002% per second using 6% NaOCl at 40 C. For all irrigation devices tested, the rate of tissue dissolution increased with a higher concentration and temperature of the NaOCl solution. Conclusions: The novel Multisonic Ultracleaning System achieved a significantly faster tissue dissolution rate when compared with the other systems examined in vitro. (J Endod 2014;-:1–4)
Key Words Irrigation, Multisonic Ultracleaning, sodium hypochlorite, tissue dissolution, ultrasonic
I
rrigation of the root canal system during treatment potentially has several important functions; it removes loose tissue debris from the canal, kills planktonic and biofilm microbes, and dissolves inorganic and organic tissue (1–8). Sodium hypochlorite (NaOCl) is the most popular irrigating solution because it has many of the desired characteristics of a root canal irrigant (9, 10), and it is the only clinically acceptable irrigant capable of dissolving organic tissue. It is known that the effectiveness of organic tissue dissolution by NaOCl is dependent on concentration and temperature of the NaOCl solution (4). Studies have also shown that agitation helps improve the tissue-dissolving activity of NaOCl (11, 12). Interestingly, although the role of agitation is recognized, Stojicic et al (12) reported that the increase in tissue dissolution by NaOCl was the same whether agitation was done using pipetting, EndoActivator (Dentsply, Tulsa, OK), or ultrasound. One explanation for the equal performance by devices such as ultrasound and EndoActivator is that although ultrasound causes acoustic streaming that may reach the peripheral areas of the root canal system, the theoretically more effective cavitation outcome can only be detected a few micrometers from the ultrasonic instrument (12–15). Recently, a novel technology, the Multisonic Ultracleaning System (Sonendo Inc, Laguna Hills, CA), has been developed for cleaning of the root canal system. The system is designed to develop a broad spectrum of waves within the solution to clean soft tissue and bacteria inside root canals. The goal of the present study was to compare the (organic) tissue-dissolving effectiveness of the Multisonic Ultracleaning System with conventional methods of irrigation using NaOCl in concentrations ranging from 0.5% to 6% and at different temperatures (21 C and 40 C) of the irrigating solution.
Materials and Methods Solutions NaOCl solutions in concentrations of 0.5%, 3%, and 6% were tested. A stock solution of 8.5% NaOCl (Clorox Bleach; Clorox, Oakland, CA) was obtained from the manufacturer. The amount of available chlorine was verified for each experiment by an iodine/thiosulfate titration method as previously described (16). The 0.5%, 3%, and 6% NaOCl solutions were prepared by diluting the 8.5% stock solution in sterile water. The solutions were brought to room temperature before use. The solutions for the experiments were used either at room temperature (21 C) or heated to 40 C using a temperature-controlled water bath (Haake B3; Thermo Electron Corp, Waltham, MA) with the exception of the Multisonic Ultracleaning System. The solution was stored in a 1-L glass bottle placed inside a water bath. The temperature of the
From the *Division of Endodontics, Department of Oral Biological and Medical Sciences, Faculty of Dentistry, The University of British Columbia, Vancouver, Canada; and †Sonendo Inc, Laguna Hills, California. Address requests for reprints to Dr Markus Haapasalo, Division of Endodontics, Oral Biological and Medical Sciences, UBC Faculty of Dentistry, 2199 Wesbrook Mall, Vancouver, BC, Canada V6T 1Z3. E-mail address: [email protected] 0099-2399/$ - see front matter Copyright ª 2014 American Association of Endodontists. http://dx.doi.org/10.1016/j.joen.2013.12.029
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Basic Research—Technology solutions was confirmed using a thermometer and maintained automatically by the water bath. For the Multisonic Ultracleaning System, solution was placed in the unit at room temperature but automatically dispensed out of the handpiece tip at 40 C for all samples. As a negative control, sterilized water (Sterile Water for Irrigation, Baxter, Deerfield, IL) irrigation was also tested.
Equipment Endodontic devices tested included the Multisonic Ultracleaning System, Piezon Master 700 (EMS, Dallas, TX) ultrasonic system with agitation, EndoVac negative-pressure irrigation system (SybronEndo, Orange, CA) with the 28-G (0.32 mm) Microcannula EndoVac needle, and a conventional positive-pressure 27-G irrigation needle (Appli-Vac, Vista, Racine, WI). The 27-G needle was attached by a luer lock connection to 3-stop color-coded Tygon ST tubing (Ismatec, WertheimMondfeld, Germany), whereas the EndoVac needle was attached to the titanium finger piece and tubing provided. A digitally controlled peristaltic pump (Reglo Digital MS-2/8, Ismatec) was used to deliver the irrigant from the needles at precise flow rates. The peristaltic pump was calibrated before using each irrigation needle to ensure an accurate flow rate by measuring the mass of the solution delivered through the pump in a specified period of time. The needle flow rates were calibrated again with each set of irrigating conditions to ensure fidelity. Multisonic Ultracleaning System The Multisonic Ultracleaning System is a novel type of root canal cleaning system that consists of a console and handpiece, which externally resembles a dental handpiece. During use, the tip of the handpiece is placed 1 mm above the pulp chamber floor. The handpiece tip never enters the canal orifices at any point of the procedure. The system is operated from a touch screen control panel that regulates the high speed flow of irrigating solution from the central unit to the handpiece, where it hits a metal impingement plate at the end of the tip and creates a spray that is released from the tip at approximately 45 mL/min at a temperature of approximately 40 C. As opposed to the other systems tested, the console is built to degas the irrigation solutions. When the Multisonic Ultracleaning System is used, the pulp chamber of the tooth is sealed from the oral cavity, preventing the possibility of NaOCl mist spreading around the working area. The handpiece itself has a builtin 5-point vented suction system that collects the excess NaOCl from the pulp chamber. Tissue Dissolution The same type of fresh bovine meat was used for the tissue sample in the experiment. Before use, it was kept frozen at 15 C in standard packaging to retain moisture. As the surface area of the sample is likely to have an impact on tissue dissolution, each sample had similar size and shape. Frozen tissue was thus cut into equal-sized pieces of 4 4 2 mm using a stainless steel blade. Tissue specimen mass was then measured before treatment using a calibrated electronic balance (FX-300; A&D Company Ltd, Tokyo, Japan). Six parallel samples per group were included. There was no significant difference in the sample mass used for each group, with an average initial mass of 68 2 mg. For the experiment, the samples were threaded onto a thin steel wire and then positioned in the middle of a 0.7-mL glass vial (SKS, Watervliet, NY). The testing was performed with irrigating solutions at room temperature and at 40 C. The temperature of the solutions was confirmed before each use with a thermometer (Fisher Scientific, Ottawa, Ontario, Canada). 2
Haapasalo et al.
For all devices tested, tips and needles were immersed in the vial containing irrigating solutions to a distance of 10 mm from the tissue specimen. For ultrasonic irrigation, the ultrasound energy (power setting at grade III, Piezon Master 700, EMS) in endo mode alternated between on and off every 15 seconds for the 5-minute period. Ultrasonic agitation was performed with and without continuous flow of irrigant solutions at a flow rate of 10 mL/min. Degassed NaOCl has not been used with the conventional methods of canal irrigation. However, in order to evaluate the possible role of degassing of hypochlorite on the tissue dissolution, additional experiments were performed with the conventional irrigation equipment as described previously but by using degassed NaOCl instead of the nondegassed solution. If tissue was completely dissolved as judged visually in less than 5 minutes, the time (seconds) it took to dissolve the tissue was recorded. For all other specimens, the samples were blotted dry with a paper towel after 5 minutes of exposure, and the tissue mass was recorded.
Data Analysis The rate of tissue dissolution was calculated according to the following equation: % Percent Tissue Mass Loss Rate of Tissue Dissolution ¼ s Recorded Time The values for each device and irrigant tested were expressed as a mean rate of tissue dissolution standard deviation. The mean tissue dissolution rates for all irrigation solution concentrations and temperatures using the different devices/irrigation methods were compared using univariate analysis of variance followed by the post hoc test (Games-Howell test) for multiple comparisons (SPSS Inc, Chicago, IL). Differences in mean tissue dissolution rates were considered statistically significant if the P value was less than .05.
Results The rate of tissue dissolution for the devices tested using sterile water and different concentrations of NaOCl at room temperature and 40 C are shown in Figures 1 and 2. The fastest rate of tissue dissolution was obtained with the Multisonic Ultracleaning System, which dissolved the tissue specimen at a rate of 1.0% 0.1% per second using 0.5% NaOCl, 2.3% 0.9% per second using 3% NaOCl, and 2.9% 0.7% per second using 6% NaOCl. These rates were significantly faster (P < .05) than any other device tested. None of the other irrigation protocols were able to dissolve the complete specimen in 5 minutes. These average rates of tissue dissolution ranged from 0.04% 0.01% per second to 0.328% 0.002% per second depending on temperature and NaOCl concentration. The rate of tissue dissolution increased when the temperature of the NaOCl solution (P < .05) was increased. Degassing of NaOCl for the conventional irrigation systems did not enhance tissue dissolution (data not shown). When sterile water was used for irrigation instead of NaOCl, the Multisonic Ultracleaning System dissolved the tissue at a rate of 0.16% 0.02% per second. Using the other irrigation systems with water did not result in a rate of tissue dissolution that allowed for a significant loss of tissue over the 5-minute procedure.
Discussion Several different types of experimental designs have been used in previous research measuring the effectiveness of soft tissue dissolution by different irrigating solutions and/or irrigating systems. An in vitro model like the present one has been used in many studies (10, 12, 17). This type of model is not supposed to provide detailed JOE — Volume -, Number -, - 2014
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Figure 1. The rate of tissue dissolution (%/s) at room temperature using the Multisonic Ultracleaning System and other conventional irrigation devices. Different letters indicate statistically significant differences between groups (P < .05). ND, not done.
recommendations for clinical protocols, but it has several advantages when the comparative effectiveness of different systems is being evaluated in a standardized setting. There are limitations of the present model, including the size and geometry of the measurement vial, the fixed distance of 10 mm from the tip of the endodontic device to the tissue, and the type of tissue used. Nevertheless, 10 mm was a safe distance to prevent the tissue from dislodging from the wire, which allowed for an accurate post-treatment tissue mass measurement for all devices tested. The vial geometry and size could be altered to reflect different root canal sizes or the distance from the tissue specimen, and the tip of the endodontic device could be varied to determine the role this distance plays in tissue-dissolution capabilities. Optimally, necrotic human pulp tissue should be used for this type of testing (18). However, because of the limited availability and size of human pulp, this is not practical, especially when a large number of groups are tested. Bovine muscle tissue is easily available, has a fairly uniform composition, and can be cut into pieces of predetermined size and
shape. Not only can the initial mass be standardized (68 2 mg in the present study), but the shape and surface area are also similar for all specimens, which is likely to be a factor when chemical dissolution of tissue is measured. The small standard deviations for the average tissue dissolution rates are an indication of the reproducibility of these results. The tissue-dissolution effects achieved with the Multisonic Ultracleaning System using any of the 3 NaOCl concentrations (0.5%, 3%, and 6%) was significantly superior when compared with all other irrigation protocols and systems evaluated (P < .05). Although the standard deviations appear higher in the Multisonic Ultracleaning data presented in Figures 1 and 2, this is an expected result. The Multisonic Ultracleaning System achieved complete tissue mass loss for every sample tested, making the time recorded the main component that affected the variability of the rate of tissue mass loss. Because the tissue was completely dissolved for all samples in a short period of time, any small difference in time recorded would have a greater effect on the variability
Figure 2. The rate of tissue dissolution (%/s) at 40 C using the Multisonic Ultracleaning System and other conventional irrigation devices. Different letters indicate statistically significant differences between groups (P < .05). ND, not done.
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Basic Research—Technology of the rate of tissue mass loss, contributing to the higher standard deviations compared with the other devices tested. Regardless of this variability, the rate of tissue dissolution for the Multisonic Ultracleaning System with 6% NaOCl was 2.9% 0.7% per second, which was more than 8 times faster than the rate of tissue dissolution with the Piezon Master 700 Ultrasonic System. Interestingly, the Multisonic Ultracleaning System used with water instead of NaOCl had a tissue dissolution rate of 0.16% 0.02% per second, making it equally effective as needle irrigation with 2% NaOCl at 40 C and a 45-mL/min flow rate (data not shown). The Multisonic Ultracleaning System uses a high flow rate of approximately 45 mL/min for NaOCl irrigation, and the solution is at a temperature of 40 C when it is released from the handpiece into the pulp chamber. In an effort to understand the possible mechanisms responsible for the fast tissue-dissolution time using the Multisonic Ultracleaning System, an experimental group with similar parameters (40 C, 45 mL/min) was tested with needle irrigation. It should be noted that a 45-mL/min flow rate cannot be achieved with 25-G to 30-G needles; therefore, a size 19-G (0.91-mm) (Monoject; Kendall Healthcare, Mansfield, MA) needle was used even though no clinical relevance could be identified. In addition, positive-pressure needle irrigation at 45 mL/min in the canal, even if possible, is likely to be a safety risk with regard to apical pressure and possible extrusion of NaOCl into the periapical tissue (19, 20). As expected, using these needle irrigation conditions, regardless of the NaOCl concentration, did not result in a significant additional loss of tissue mass over the 5-minute period compared with other conventional methods (data not shown). Thus, the high flow rate and elevated temperature of the NaOCl alone cannot explain the superior performance of the Multisonic Ultracleaning System. It has been reported that air in the liquid can cushion the implosive effects of cavitation (21). Therefore, it is possible that degassing the NaOCl solution by the Multisonic Ultracleaning System facilitates the effects of cavitation if present. The results indicate that some form of physical energy generated by the Multisonic Ultracleaning System may be responsible for the fast effect beyond what can be achieved by optimizing the flow rate, concentration, and temperature of NaOCl. Whether cavitation created by the Multisonic Ultracleaning System in the liquid explains the superior performance of the system remains to be clarified in future studies. A concern in a clinical situation when high flow rates are used is the possibility of high apical pressure and extrusion of the solution through the apical foramen (22). Control experiments with the Multisonic Ultracleaning System using colored liquid and transparent teeth have shown that the irrigating solution circulates in all canals instantly up to the level of the apical foramen but does not penetrate/extrude through the apical foramen (data not shown). In conclusion, the Multisonic Ultracleaning System used with NaOCl at different concentrations dissolved tissue at a significantly faster rate when compared with the conventional irrigation devices examined under the conditions in the present study. For future studies, changes in the present model setup may allow us to determine the effect that the different components, including the size of the measurement vial, distance of the endodontic device tip from the tissue specimen, and type of tissue, have on the rate of tissue dissolution.
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Acknowledgments Supported by Sonendo Inc and start-up funds provided by the Faculty of Dentistry, University of British Columbia, Canada. One of the authors (M.H.) has commercial interest in the tested product. Three authors are employees of Sonendo Inc.
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