Written by Karl F. Woodmansey, DDS Friday, 30 September 2005 19:00
Thorough chemo-mechanical debridement of root canal systems is critical for successful endodontic treatment. With antimicrobial and proteolytic properties, sodium hypochlorite is an effective and efficient endodontic irrigant. This article introduces a simple technique to increase the debridement efficacy of sodium hypochlorite by intracanal heating of the solution with a heat source.
Techniques have been reported to enhance the efficacy of sodium hypochlorite irrigant, including circulating greater volumes of irri-gant and preheating the irrigant.1-3 Sedgely, et al demonstrated the advantages of adequate irrigant volumes delivered to within the apical 1-mm of root canal preparations.1 Cunningham and Joseph2 found that sterility was achieved in significantly less time with body temperature (37Â°C) sodium hypochlorite solution than with a room temperature (22°C) solution.
Heating sodium hypochlorite enhances its tissue solubility and debridement proper-ties.3,4 Abou-Ross and Oglesby3 compared tissue dissolution times of rat connective tissues with 2.6% and 5.25% sodium hypochlorite solutions at both 23°C and 60°C. They found that both the higher concentration and the higher temperature sodium hypochlorite solutions significantly reduced tissue dissolution times. Their tests evaluated both fresh and necrotic rat connective tissues, and determined that necrotic tissue required significantly more time for dissolution.
Because no studies have reported the efficacy of sodium hypochlorite at temperatures above 60°C, the author performed a simple bench test to evaluate the solvent ability of sodium hypochlorite at high temperatures. Samples of simulated pulpal tissue were immersed in 300 mL of 6% sodium hypochlorite (Ultra Clorox Regular Bleach, Clorox) until fully dissolved. Sections (0.6 g) of John Morrell Franks (John Morrell) were used as the simulated dental pulp tissue. On average, boiling disintegrated the samples 210 times faster (2 minutes versus 420 minutes) than immersion in room temperature sodium hypochlorite. The agitation of the boiling solution appeared to facilitate the decomposition.
Chemical reaction rates accelerate with increases in temperature, pressure, and concentration. Since intracanal pressure cannot be readily increased, only the irrigant concentration or temperature can be increased to speed chemical debridement. Concentra- tions of sodium hypochlorite greater than 6% are not readily available. Frequent replenishment and mechanical agitation of the intracanal solution ensure that the solution's effective concentration remains as efficient as possible.
Increased irrigant temperatures can be achieved by preheating solutions prior to irrigation or with intracanal placement of heated instruments. Preheated solutions have limited usefulness due to their rapid equilibration to a temperature between body temperature and room temperature.4 Abou-Ross and Oglesby3 speculated that heated instruments might be able to heat sodium hypochlorite solutions clinically in teeth.
The author advocates intracanal heating of sodium hypochlorite irrigant using a System B Heat Source (SybronEndo). With a System B Heat Source, the clinician is able to produce and maintain precisely controlled, preselected temperatures in the tips of an attached Buchanan System B Plugger (SybronEndo). The newer Elements Obtu-ration Unit (SybronEndo) is similarly capable of heating Buchanan System B Pluggers.
After routine cleaning and shaping of the root canal system, a Buchanan System B Plugger is verified to fit passively to within 3 mm of the apex, and the System B Heat Source is set to a power setting of 10 and a temperature of 200°C. The canal and chamber of the tooth are flooded with sodium hypochlorite irrigant. With high-volume evacuation (HVE) placed adjacent to the tooth, the plugger is reinserted into the flooded canal, and the heat is activated for 3 to 5 seconds. As the sodium hypochlorite is rapidly heated beyond its boiling point, the irrigant vigorously bubbles from the canal orifice. The vapor and residue are removed by the HVE.
The canal is visually inspected, and the process is repeated until only minimal irrigant persists. The canal's dryness can then be ensured with a paper point. Through an operating microscope, the practitioner will note thorough canal debridment.
Caution must be exercised to prevent overheating of the tooth's periodontal ligament (PDL). Exterior root surface temperatures exceeding 47°C for more than 1 minute are considered to jeopardize the health of the PDL.5 Although no measurements have been made with heated intracanal solutions, studies with System B heated condensation of gutta-percha have demonstrated negligible increases in the temperature of root surfaces.6
For the Continuous Wave of Conden-sation technique with the System B Heat Source, Buchanan recommends heating the plugger for less than 4 seconds for safety.7 When Hosoya, et al8 used intracanal heated Buchanan Pluggers to dry canals, 2 applications of 200°C for 5 seconds were separated by a 5-second cooling interval. In general, to minimize the risk of PDL overheating with this irrigation technique, the Buchanan System B Plugger must remain passive and not be wedged against the canal walls. The plugger should only be heated in 3- to 5-second bursts and not continuously activated.
Most chemical reactions accelerate with increasing temperature. The irrigation technique presented here is thought to be effective because of the in-creased kinetic energy and the vigorous boiling motion of the irrigant solution. Empirically, canals irrigated with this technique appear well debrided when viewed through an operating microscope. Further re-search is in progress to compare this technique with traditional irrigation techniques.
1. 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.
2. Cunningham WT, Joseph SW. Effect of temperature on the bactericidal action of sodium hypochlorite endodontic irrigant. Oral Surg Oral Med Oral Pathol. 1980;50:569-571.
3. Abou-Rass M, Oglesby SW. The effects of temperature, concentration and tissue type on the solvent ability of sodium hypochlorite. J Endod. 1981;7:376-377.
4. Cunningham WT, Balekjian AY. Effect of temperature on collagen-dissolving ability of sodium hypochlorite endodontic irrigant. Oral Surg Oral Med Oral Pathol. 1980;49:175-177.
5. Eriksson AR, Albrektsson T. Temperature threshold levels for heat-induced bone tissue injury: a vital-microscopic study in the rabbit. J Prosthet Dent. 1983;50:101-107.
6. Romero AD, Green DB, Wucherpfennig AL. Heat transfer to the periodontal ligament during root obturation procedures using an in vitro model. J Endod. 2000;26(2):85-87.
7. Buchanan SL. The continuous wave of obturation technique: â€œcenteredâ€ condensation of warm gutta percha in 12 seconds. Dent Today. Jan 1996;15:60-67.
8. Hosoya N, Nomura M, Yoshikubo A, et al. Effect of canal drying methods on the apical seal. J Endod. 2000;26:292-294.
The author acknowledges Jeffery M. Hamling, DDS, MS, for his development of this technique and for his inspiration to publish this manuscript.
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