0099-2399/92/1812-0605/$03.00/0 JOURNAL OF ENDODONTICS Copyright © 1992 by The American Association of Endodontists
Printed in U.S.A.
VOL. 18, NO. 12, DECEMBER1992
Efficacy of Several Concentrations of Sodium Hypochlorite for Root Canal Irrigation J. Craig Baumgartner, DDS, PhD, and Paul R. Cuenin, DDS, MS
either a needle or with an ultrasonic device in the middle third of root canals. Both the instrumented and the uninstrumented surfaces of root canal walls were examined using a scanning electron microscope.
Sodium hypochlorite (NaOCl) has been recommended for irrigation during root canal preparation. This investigation used scanning electron microscopy to examine instrumented and uninstrumented surfaces in the middle third of root canals following the use of several concentrations of NaOCI (5.25%, 2.5%, 1.0%, and 0~.5%). NaOCI was delivered with either an endodontic irrigation needle or an ultrasonic device. All of the concentrations of NaOCI with either delivery system were very effective in flushing out loose debris from the root canals. A smear layer with some exposed dentinal tubules was seen on all instrumented surfaces regardless of concentration of NaOCI or irrigation device. NaOCI in concentrations of 5.25%, 2.5%, and 1% completely removed pulpal remnants and predentin from the uninstrumented surfaces. Although 0.5% NaOCI removed the majority of pulpal remnants and predentin from the uninstrumented surfaces, it left some fibrils on the surface.
MATERIALS AND METHODS Matched pairs of single canal bicuspids that had been extracted for orthodontic purposes were used in this study. Paired teeth have been previously used to compare irrigation regimens (2). Following extraction, the teeth were stored in sterile saline and refrigerated at 4"C. Saline was used for storage to avoid any effect that a fixative might have on dissolution of the organic tissue by NaOC1. Two pairs of teeth were used as controls. A horizontal groove was placed in the facial surface of all teeth just below the cervical line for identification purposes and the crowns of the teeth were amputated at the cervical line. Longitudinal grooves were placed in the facial and lingual surfaces of each root to facilitate their fracture with orthodontic wire cutters. All superficial grinding debris was carefully removed from the surface of the root under running tap water with a soft brush prior to treatment of the root canal system. The control teeth received no irrigation of the root canal system. Pulpal tissue was left in the root canal of one tooth in each control pair while the other tooth had the pulpal tissue extirpated using a #15 K-type file (Kerr, Romulus, MI) with no additional instrumentation. The roots of the control teeth were fractured into longitudinal halves using wire cutters and immediately placed into 2% glutaraldehyde (Polysciences, Inc., Warrinton, PA) with 0.2 M cacodylate buffer (pH 7.4) (Kodak, Rochester, NY) and refrigerated. In preparation for scanning electron microscopic evaluation, the fractured roots were fixed with 1% osmium tetroxide (Polysciences). The specimens were dehydrated using a graded series of alcohol and critical-point dried by immersion in hexamethyldisilizane (Polysciences) for 5 min before air drying at room temperature. The two halves of each root were then mounted on a single stub and prepared for scanning electron microscopic (AMRAY 1645; AMRAY, Bedford, MA) evaluation by sputter coating with gold-palladium. Four experimental groups, which each contained four pairs of bicuspids, were used to evaluate the debridement capabilities of four concentrations of NaOC1 (5.25%, 2.5%, 1.0%, and 0.5%). Similarly to the control teeth, each experimental
Numerous solutions have been recommended for use as root canal irrigants. Research and clinical experience have shown that NaOC1 has several properties that contribute to effective chemomechanical debridement of a root canal system. NaOC1 acts as a lubricant for instrumentation and can flush loose debris from root canals (1, 2). NaOC1 is an effective antimicrobial agent with the capability of detoxifying the root canal system (3). In addition, NaOC1 is effective in dissolving both vital and nonvital tissue (4-6). Studies have shown that both the antibacterial and tissue-dissolving capabilities of 5.25% NaOC1 decrease when it is diluted (3-5). Recent studies have shown that ultrasonic energy increases the debridement and antimicrobial capabilities of NaOC1 (7, 8). Sp~mgberg et al. (9) recommended 0.5% NaOC1 for acceptably noncytotoxic levels. Others have found only a minimal irritant effect for higher concentrations in animal models (10); however, severe sequelae have been reported when 5.25% NaOC1 is injected into human periapical tissue (11). The purpose of this study was to describe the debridement capabilities of several concentrations of NaOC1 delivered with
605
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tooth had a horizontal notch placed on the facial surface of the root, the crown was amputated, and longitudinal grooves were placed in the roots to facilitate fracture following treatment of the root canal system. After rinsing the superficial grinding debris from the root surface, the root length was measured and the roots were placed into pieces of rubber tubing so that 2 to 3 m m of the coronal portion of each root protruded from the tubing. The apical portion of the tubing was then filled with Impregum (Premier Dental Products Co., Norristown, PA) to prevent irrigation through the apical foramen of the experimental roots. The bulk of the pulpal tissue was extirpated using a #15 K-type file. The root canals were then instrumented 1 mm short of the measured root length using sequential K-type files, #10 through #50. Great care was taken to instrument only one side of the root canal. Two of the four pairs in each group were instrumented on the facial surface while the other two pairs were instrumented on the lingual surface. The half of the root canal not instrumented served as the "uninstrumented" half of the root canal. The amount of irrigant used in each root canal was carefully controlled. A total of 30 ml of NaOC1 irrigant was used for each root canal with both the 27-gauge blunt endodontic needles (Sherwood Medical, St. Louis, MO) and the Cavi-Endo (P105 insert; Dentsply, York, PA) ultrasonic delivery system. A preliminary study determined that the ultrasonic device at full power delivered 3 ml of fluid in 10 s. With each pair of experimental roots, one root had the irrigant delivered to within 2 to 3 mm of the apex with the endodontic needle and the other root had the irrigant delivered to within 2 to 3 m m of the apex with the ultrasonic device. Three milliliters of NaOCI was used to irrigate the root canal following pulp extirpation and again after the use of each instrument from #10 through #50. A total of 30 ml of NaOC1 was used in each root canal. Each root canal was left flooded with irrigant during the instrumentation phase. The total time that the NaOC1 solution was present in the root canal system was carefully controlled at 12 min. A final irrigation with 3 ml of sterile water delivered with a 27-gauge needle was used in each experimental root canal to stop any further chemical activity of the NaOC1 solutions. The roots of the experimental teeth were immediately fractured into halves and placed into 2% glutaraldehyde with 0.2 M cacodylate buffer (pH 7.4) and refrigerated. The experimental specimens were later prepared for scanning electron microscopic evaluation as previously described for the control teeth. A standardized series of photomicrographs of each root canal was taken for comparative purposes. A photomicrograph was taken at x150 in the middle third of each root canal showing a representative junction between the instrumented and the uninstrumented sides. Next, photomicrographs were taken in the same area at x500 and x4000 on both the instrumented and the uninstrumented sides of the root canal. Evaluation of the scanning electron micrographs focused on the amount of superficial debris, the nature of the smear layer on the instrumented side, and the characteristics of the surface on the uninstrumented surface of the root canal. RESULTS The macroscopic nature of the extirpated pulp was consistently a gelatinous intact mass of tissue that was easily removed
from the root canal. Histopathological examination of the tissue revealed complete necrosis demonstrated by loss of cellular architecture and extensive autolysis. The root canals of the control teeth without pulp extirpation displayed a large bulk of tissue that could be seen macroscopically. The nature of the tissue was not well defined at ×500 with the scanning electron microscope. At x4000, the pulpal tissue was clearly seen to be a mass of interwoven fibers associated with a few cells (Fig. 1). When the pulp was extirpated, the surface of the walls appeared to be relatively free of superficial debris at ×500. At ×4000, masses of pulpal tissue and superficial fibers could be clearly seen on the canal walls. The fibrils of the predentin could not be clearly observed at x500. The fibers making up the predentin could be observed around the orifices of dentinal tubules at ×4000 (Fig. 1). In the experimental teeth, the junction between the instrumented and the uninstrumented surfaces of each root canal was well defined. There was minimal or no evidence of superficial debris on either the instrumented or the uninstrumented surfaces of the root canals. There was no apparent difference in the appearance of the amorphous smear layer associated with the different concentrations of NaOC1 or with the delivery system used. However, the smear layer was not totally intact. In some places, exposed dentinal tubules could be seen on the instrumented surface (Figs. 2 to 5). Exposed dentinal tubules were present whether the irrigant was delivered with the needle or the ultrasonic device for each of the concentrations of NaOC1 (Figs. 2 to 5). Scanning electron micrographs revealed that the pulpal remnants and predentin had been removed on the uninstrumented side of the root canals. The uninstrumented surfaces were composed of fields of mineralized globular dentin (calcospherites) (Figs. 4 and 5). Because there was no difference in the results on the uninstrumented side of the root canals using 5.25%, 2.5%, and 1% NaOC1, only scanning electron micrographs of the 1% concentration are shown in this article. With the exception of 0.5 % NaOC1, neither the concentration (5.25%, 2.5%, and 1%) of NaOC1 nor the delivery device (needle or ultrasonic) made any difference in removing pulpal debris and predentin from the uninstrumented surfaces of the root canal. With 0.5% NaOC1, some fibrils could be observed at both x500 and x4000 on the surface of the calcospherites (Figs. 4 and 5). These fibrils were on the surface of the mineralized dentin and extended over to adjacent calcospherites. DISCUSSION This study used a scanning electron microscope to observe the effect of irrigating root canals with four concentrations of NaOC1 and two delivery methods under controlled conditions. This model system has been previously used to show that the smear layer occurs only on instrumented surfaces of root canals and to compare the efficacy of different irrigants on both the instrumented and the uninstrumented surfaces (2). Previous studies have related the efficacy of flushing loose superficial debris from a root canal to the volume of irrigant and to the extent of apical position of the needle (1). Irrigation with 3 ml of NaOC1 after each instrument in this study did an excellent job of removing superficial debris whether deliv-
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FIG 1. Control specimens before and after pulp extirpation. A (original magnification ×500) (bar = 10 ~zm),A mass of pulp tissue in the exposed root canal. B (original magnification x4000) (bar = 10 #m), The pulp tissue is composed of a mass of interwoven fibers. C (original magnification ×500), Wall of root canal following pulp extirpation showing exposed dentinal tubules. D (original magnification x4000) (bar = 10 #m), The surface of the root canal wall following pulp extirpation is covered with pulpal remnants and uncalcified predentin fibers which surround the dentinal tubules.
ered with an endodontic irrigation needle or the ultrasonic device. Studies have suggested that ultrasonic endodontic procedures remove the smear layer more effectively than conventional methods while other studies found that ultrasound had little effect on the removal of the smear layer (12-14). After ultrasonic irrigation of root canals for 2 rain with 3% NaOC1, Ciucchi et al. (15) found that 27% of the observed surfaces were smear free in the middle third. In this study, the smear layers on the instrumented portion of the root canals appeared to be very similar irrespective of the concentration of the NaOC1 or the delivery system. Some exposed dentinal tubules could be seen in the smear layer whether the irrigant was delivered with the needle or the ultrasonic device (Figs. 2 to 5). The smear layer was only on the instrumented surface and consisted of an amorphous layer of material. The amorphous smear material has been shown to be on the surface of instrumented root canals and to extend into dentinal tubules under the surface layer (16). The smear layer resulting from instrumentation of a root canal is believed to consist of particles of calcified tissue with organic material such as pulp tissue, bacteria, and blood products (16). The use of NaOC1
for root canal irrigation may dissolve the organic components and leave a smear layer of mineralized tissue. Studies have shown that NaOCI in combination with EDTA is effective in removing the smear layer and that the combination of irrigants was more effective as an antimicrobial than NaOCI by itself (2, 17). The removal of the smear layer may allow the NaOC1 to penetrate into dentinal tubules or other confined areas protected by the smear layer. The efficacy of NaOC1 for the dissolution of organic tissue has been related to its concentration (3) Harrison and Hand (3) showed that dilution of 5.25% NaOCI resulted in a significant decrease in its ability to dissolve necrotic tissue. In this investigation, examination of scanning electron micrographs of uninstrumented surfaces could not detect any difference in the removal of pulpal remnants and predentin in the middle third of the root canals with 5.25%, 2.5%, of 1% NaOC1 delivered with either a needle or an ultrasonic device. Although most pulpal remnants and predentin were removed, 0.5% NaOCI delivered with either a needle or the ultrasonic device left what appeared to be a few fibrils from predentin on the surface. These could only be seen at ×500 and x4000. The position of these fibrils was consistent with what would
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FiG 2. NaOCl (1%) irrigation using an endodontic needle. A (original magnification x150), Junction (arrow) between the instrumented (I) and uninstrumented (U) halves of the root canal wall. B (original magnification x500) (bar = 10 #m) and C (original magnification x40O0) (bar = 10 #m), The uninstrumented half of the root canal wall showing fields of exposed calcospherites. All of the pulpal remnants and uncalcified predentin have been removed by the chemical action of NaOCI. D (original magnification ×500) (bar = 10 Cm) and E (original magnification x4000) (bar = 10 ~m), The instrumented half of the root canal with some exposed dentinal tubules seen in the amorphous smear layer.
be expected if remnants of organic predentin on the surface of the calcified dentin did not undergo complete dissolution. Ultrasonic endodontic procedures have been shown to increase the dissolving and disinfecting potential of NaOC1
solutions (8). The effectiveness of low concentrations of NaOCI may be improved by using larger volumes of irrigant, by frequent exchange of irrigant, or by the presence of replenished irrigant in the canals for longer periods of time; Clini-
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FiG 3. NaOCI (1%) irrigation using an endosonic device. A (original magnification x 150), Junction (arrow) between the instrumented (I) and uninstrumented (U) halves of the root canal wall. B (original magnification x500) (bar = 10 #m) and C (original magnification x4000) (bar = 10 #m), The instrumented half of the root canal with some exposed dentinal tubules seen in the amorphous smear layer. D (original magnification x500) (bar = 10 #m) and E (original magnification x4000) (bar = 10 #m), The uninstrumented half of the root canal wall showing fields of exposed calcospherites. All of the pulpal remnants and uncalcified predentin have been removed by the chemical action of NaOCI.
cians and investigators should keep in mind that the size of the root canals and crown removal in this study made irrigation much easier than what is usually found clinically. It seems probable that there, would be a greater amount of organic residue present following irrigation of longer, nar-
rower, or more convoluted root canals which impede the delivery of the irrigant. Sodium hypochlorite does not penetrate well into confined areas of a root canal system (18, 19). Perhaps the fluid movement that occurs with ultrasonics may help carry the irrigant into uninstrumented areas and contrib-
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FIG 4. NaOCI (0.5%) irrigation using an endodontic needle. A (original magnification x150), Junction (arrow) between the instrumented (I) and uninstrumented (U) halves of the root canal wall. B (original magnification x500) (bar = 10 #m) and C (original magnification x4000) (bar -- 10 #m), The uninstrumented half of the root canal wall showing fields of exposed calcospherites with some fibrils of what appears to be remnants of predentin on the surface. D (original magnification x500) (bar = 10 #m) and E (original magnification x4000) (bar = 10 #m), The uninstrumented half of the root canal with some exposed dentinal tubules seen in the amorphous smear layer.
ute to better debridement of narrower and more complex root canal systems. The chemical removal of organic tissue by NaOC1 is by the release of hypochlorous acid which reacts with insoluble proteins to form soluble polypeptides, amino acids, and other by-products (20). With regular exchange of
the irrigant, the efficacy of the chemical reaction may be enhanced. Frequent exchange of the irrigant and the use of large quantities of irrigant should not only remove superficial debris but also replenish the chemical activity of NaOC1 which is depleted by reacting with organic tissue. In this study, a
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FIG 5. NaOCI (0.5%) irrigation using an endosonic device. A (original magnification x150), Junction (arrow) between the instrumented (I) and uninstrumented (U) halves of the root canal wall. B (original magnification x500) (bar = 10 um) and C (original magnification x4000) (bar = 10 #m), The instrumented half of the root canal with some exposed dentinal tubules seen in the amorphous smear layer. D (original magnification x500) (bar = 10 um) and E (original magnification x4000) (bar = 10 #m), The uninstrumented half of the root canal wall showing fields of exposed calcospherites with some fibrils of what appears to be remnants of predentin on the surface.
relatively small volume ofirrigant was used in the root canals for only 12 rain. If NaOC1 is often replenished and allowed to remain in the root canal system for a longer period of time, more complete chemical removal of organic debris would be expected to take place.
It is believed that thorough debridement before sealing the root canal system is a key to long-term successful endodontic therapy. This study demonstrates the efficacy of NaOCI for the physical removal of superficial debris from root canal
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surfaces and the chemical removal of organic pulpal debris and predentin from uninstrumented areas of a root canal. The opinions contained herein are the private views of the authors and are not to be construed as official or as reflecting the views of the Department of the Army or the Department of Defense. Dr. Baumgartner is former chief, Microbiology Branch, United States Army Institute of Dental Research, Walter Reed Army Medical Center, Washington, DC and chairman, Department of Endodontology, School of Dentistry, Oregon Health Sciences University, Portland, OR. Dr. Cuenin is chief, Oral Pathology, United States Army Institute of Dental Research, Walter Reed Army Medical Center. Address requests for reprints to Dr. J. Craig Baumgartner, School of Dentistry, OHSU, 611 SW Campus Dr., Portland OR 97201.
References 1. Abou-Rass M, Piccinino MV. The effectiveness of four clinical irrigation methods on the removal of root canal debris. Oral Surg 1982;54:323-8. 2. Baumgartner JC, Mader CL. A scanning electron microscopic evaluation of four root canal irrigation regimens. J Endodon 1987;4:147-57. 3. Harrison JW, Hand RE. The effect of dilution and organic matter on the antibacterial property of 5.25% sodium hypochlorite. J Endodon 1981;7: 128-32. 4. Koskinen KP, Stenvall H, Uitto V. Dissolution of bovine pulp tissue by endodontic solutions. Scand J Dent Res 1980;88:406-11. 5. Hand RE, Smith ML, Harrison JW. Analysis of the effect of dilution on the necrotic tissue dissolution property of sodium hypochlorite. J Endodon 1978;4:60-4. 6. Rosenfeld EF, James GA, Burch BS. Vital pulp response to sodium hypochlorite. J Endodon 1978;4:140-6.
Journal of Endodontics 7. Cameron JA. The synergistic relationship between ultrasound and sodium hypochlorite. J Endodon 1987;13:541-5. 8. Sjogren U, Sunqvist G. Bacteriologic evaluation of ultrasonic root canal instrumentation. Oral Surg 1987;63:366-70. 9. Spangberg L, Engstrom B, Langland K. Biologic effects of dental materials. III. Toxity and antimicrobial effect of endodontic antiseptics in vitro. Oral Surg 1973;36:856-71. 10. Th6 S. Reactions of guinea pig subcutaneous connective tissue following exposure to sodium hypochlorite. Oral Surg 1980;49:460-6. 11. Sabala C, Powell S. Sodium hypochlorite injection into periapical tissues. J Endodon 1989;15:490-2. 12. Langeland K, Liao K, Pascon E. Work-saving devises in endodontics: efficacy of sonic and ultrasonic techniques. J Endodon 1985;11:499-510. 13. Cymerman J, Jerome L, Moodnik R. A scanning electron microscope study comparing the efficacy of hand instrumentation with ultrasonic instrumentation of the root canal. J Endodon 1983;9:327-31. 14. Cameron J. The use of ultrasonics in the removal of the smear layer: a scanning electron microscope study. J Endodon 1983;9:289-92. 15. Ciucchi B, Khettabi M, Holtz J. The effectiveness of different endodontic irrigation procedures on the removal of the smear layer: a scanning electron microscopic study. Int Endod J 1989;22:21-8. 16. Mader CL, Baumgartner JC, Peters DD. Scanning electron microscopic investigation of the smeared layer on root canal walls. J Endodon 1984;10: 477-83. 17. Goldman L, Goldman M, Cavaleri R, Bogis J, Lin P. The efficacy of several endodontic irrigating solutions: a scanning electron microscopic study. J Endodon 1982;8:487-92. 18. Senia E, Marshall F, Rosen S. The solvent action of sodium hypochlorite on pulp tissue of extracted teeth. Oral Surg 1971 ;31:96-103. 19. McComb D, Smith D. A preliminary scanning electron microscopic study of root canals after endodontic procedures. J Endodon 1975;1:238-42. 20. Baumgartner JC, Ibay AC. The chemical reactions of irrigants used for root canal debridement. J Endodon 1987;13:47-51.
You M i g h t Like to K n o w Another bug, yet!! A variety of Escherichia coli which produces verocytotoxin is receiving increasing attention (Com Dis Rep 1991 ;1:35). Identified in 1971 and as a significant pathogen in 1982, it has been responsible for several recent outbreaks of hemorrhagic colitis in the United States and Canada. It is most commonly associated with improperly handled and undercooked beef products. Zachariah Yeomans
Printed in U.S.A.
VOL. 18, NO. 12, DECEMBER1992
Efficacy of Several Concentrations of Sodium Hypochlorite for Root Canal Irrigation J. Craig Baumgartner, DDS, PhD, and Paul R. Cuenin, DDS, MS
either a needle or with an ultrasonic device in the middle third of root canals. Both the instrumented and the uninstrumented surfaces of root canal walls were examined using a scanning electron microscope.
Sodium hypochlorite (NaOCl) has been recommended for irrigation during root canal preparation. This investigation used scanning electron microscopy to examine instrumented and uninstrumented surfaces in the middle third of root canals following the use of several concentrations of NaOCI (5.25%, 2.5%, 1.0%, and 0~.5%). NaOCI was delivered with either an endodontic irrigation needle or an ultrasonic device. All of the concentrations of NaOCI with either delivery system were very effective in flushing out loose debris from the root canals. A smear layer with some exposed dentinal tubules was seen on all instrumented surfaces regardless of concentration of NaOCI or irrigation device. NaOCI in concentrations of 5.25%, 2.5%, and 1% completely removed pulpal remnants and predentin from the uninstrumented surfaces. Although 0.5% NaOCI removed the majority of pulpal remnants and predentin from the uninstrumented surfaces, it left some fibrils on the surface.
MATERIALS AND METHODS Matched pairs of single canal bicuspids that had been extracted for orthodontic purposes were used in this study. Paired teeth have been previously used to compare irrigation regimens (2). Following extraction, the teeth were stored in sterile saline and refrigerated at 4"C. Saline was used for storage to avoid any effect that a fixative might have on dissolution of the organic tissue by NaOC1. Two pairs of teeth were used as controls. A horizontal groove was placed in the facial surface of all teeth just below the cervical line for identification purposes and the crowns of the teeth were amputated at the cervical line. Longitudinal grooves were placed in the facial and lingual surfaces of each root to facilitate their fracture with orthodontic wire cutters. All superficial grinding debris was carefully removed from the surface of the root under running tap water with a soft brush prior to treatment of the root canal system. The control teeth received no irrigation of the root canal system. Pulpal tissue was left in the root canal of one tooth in each control pair while the other tooth had the pulpal tissue extirpated using a #15 K-type file (Kerr, Romulus, MI) with no additional instrumentation. The roots of the control teeth were fractured into longitudinal halves using wire cutters and immediately placed into 2% glutaraldehyde (Polysciences, Inc., Warrinton, PA) with 0.2 M cacodylate buffer (pH 7.4) (Kodak, Rochester, NY) and refrigerated. In preparation for scanning electron microscopic evaluation, the fractured roots were fixed with 1% osmium tetroxide (Polysciences). The specimens were dehydrated using a graded series of alcohol and critical-point dried by immersion in hexamethyldisilizane (Polysciences) for 5 min before air drying at room temperature. The two halves of each root were then mounted on a single stub and prepared for scanning electron microscopic (AMRAY 1645; AMRAY, Bedford, MA) evaluation by sputter coating with gold-palladium. Four experimental groups, which each contained four pairs of bicuspids, were used to evaluate the debridement capabilities of four concentrations of NaOC1 (5.25%, 2.5%, 1.0%, and 0.5%). Similarly to the control teeth, each experimental
Numerous solutions have been recommended for use as root canal irrigants. Research and clinical experience have shown that NaOC1 has several properties that contribute to effective chemomechanical debridement of a root canal system. NaOC1 acts as a lubricant for instrumentation and can flush loose debris from root canals (1, 2). NaOC1 is an effective antimicrobial agent with the capability of detoxifying the root canal system (3). In addition, NaOC1 is effective in dissolving both vital and nonvital tissue (4-6). Studies have shown that both the antibacterial and tissue-dissolving capabilities of 5.25% NaOC1 decrease when it is diluted (3-5). Recent studies have shown that ultrasonic energy increases the debridement and antimicrobial capabilities of NaOC1 (7, 8). Sp~mgberg et al. (9) recommended 0.5% NaOC1 for acceptably noncytotoxic levels. Others have found only a minimal irritant effect for higher concentrations in animal models (10); however, severe sequelae have been reported when 5.25% NaOC1 is injected into human periapical tissue (11). The purpose of this study was to describe the debridement capabilities of several concentrations of NaOC1 delivered with
605
606
Journal of Endodontics
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tooth had a horizontal notch placed on the facial surface of the root, the crown was amputated, and longitudinal grooves were placed in the roots to facilitate fracture following treatment of the root canal system. After rinsing the superficial grinding debris from the root surface, the root length was measured and the roots were placed into pieces of rubber tubing so that 2 to 3 m m of the coronal portion of each root protruded from the tubing. The apical portion of the tubing was then filled with Impregum (Premier Dental Products Co., Norristown, PA) to prevent irrigation through the apical foramen of the experimental roots. The bulk of the pulpal tissue was extirpated using a #15 K-type file. The root canals were then instrumented 1 mm short of the measured root length using sequential K-type files, #10 through #50. Great care was taken to instrument only one side of the root canal. Two of the four pairs in each group were instrumented on the facial surface while the other two pairs were instrumented on the lingual surface. The half of the root canal not instrumented served as the "uninstrumented" half of the root canal. The amount of irrigant used in each root canal was carefully controlled. A total of 30 ml of NaOC1 irrigant was used for each root canal with both the 27-gauge blunt endodontic needles (Sherwood Medical, St. Louis, MO) and the Cavi-Endo (P105 insert; Dentsply, York, PA) ultrasonic delivery system. A preliminary study determined that the ultrasonic device at full power delivered 3 ml of fluid in 10 s. With each pair of experimental roots, one root had the irrigant delivered to within 2 to 3 mm of the apex with the endodontic needle and the other root had the irrigant delivered to within 2 to 3 m m of the apex with the ultrasonic device. Three milliliters of NaOCI was used to irrigate the root canal following pulp extirpation and again after the use of each instrument from #10 through #50. A total of 30 ml of NaOC1 was used in each root canal. Each root canal was left flooded with irrigant during the instrumentation phase. The total time that the NaOC1 solution was present in the root canal system was carefully controlled at 12 min. A final irrigation with 3 ml of sterile water delivered with a 27-gauge needle was used in each experimental root canal to stop any further chemical activity of the NaOC1 solutions. The roots of the experimental teeth were immediately fractured into halves and placed into 2% glutaraldehyde with 0.2 M cacodylate buffer (pH 7.4) and refrigerated. The experimental specimens were later prepared for scanning electron microscopic evaluation as previously described for the control teeth. A standardized series of photomicrographs of each root canal was taken for comparative purposes. A photomicrograph was taken at x150 in the middle third of each root canal showing a representative junction between the instrumented and the uninstrumented sides. Next, photomicrographs were taken in the same area at x500 and x4000 on both the instrumented and the uninstrumented sides of the root canal. Evaluation of the scanning electron micrographs focused on the amount of superficial debris, the nature of the smear layer on the instrumented side, and the characteristics of the surface on the uninstrumented surface of the root canal. RESULTS The macroscopic nature of the extirpated pulp was consistently a gelatinous intact mass of tissue that was easily removed
from the root canal. Histopathological examination of the tissue revealed complete necrosis demonstrated by loss of cellular architecture and extensive autolysis. The root canals of the control teeth without pulp extirpation displayed a large bulk of tissue that could be seen macroscopically. The nature of the tissue was not well defined at ×500 with the scanning electron microscope. At x4000, the pulpal tissue was clearly seen to be a mass of interwoven fibers associated with a few cells (Fig. 1). When the pulp was extirpated, the surface of the walls appeared to be relatively free of superficial debris at ×500. At ×4000, masses of pulpal tissue and superficial fibers could be clearly seen on the canal walls. The fibrils of the predentin could not be clearly observed at x500. The fibers making up the predentin could be observed around the orifices of dentinal tubules at ×4000 (Fig. 1). In the experimental teeth, the junction between the instrumented and the uninstrumented surfaces of each root canal was well defined. There was minimal or no evidence of superficial debris on either the instrumented or the uninstrumented surfaces of the root canals. There was no apparent difference in the appearance of the amorphous smear layer associated with the different concentrations of NaOC1 or with the delivery system used. However, the smear layer was not totally intact. In some places, exposed dentinal tubules could be seen on the instrumented surface (Figs. 2 to 5). Exposed dentinal tubules were present whether the irrigant was delivered with the needle or the ultrasonic device for each of the concentrations of NaOC1 (Figs. 2 to 5). Scanning electron micrographs revealed that the pulpal remnants and predentin had been removed on the uninstrumented side of the root canals. The uninstrumented surfaces were composed of fields of mineralized globular dentin (calcospherites) (Figs. 4 and 5). Because there was no difference in the results on the uninstrumented side of the root canals using 5.25%, 2.5%, and 1% NaOC1, only scanning electron micrographs of the 1% concentration are shown in this article. With the exception of 0.5 % NaOC1, neither the concentration (5.25%, 2.5%, and 1%) of NaOC1 nor the delivery device (needle or ultrasonic) made any difference in removing pulpal debris and predentin from the uninstrumented surfaces of the root canal. With 0.5% NaOC1, some fibrils could be observed at both x500 and x4000 on the surface of the calcospherites (Figs. 4 and 5). These fibrils were on the surface of the mineralized dentin and extended over to adjacent calcospherites. DISCUSSION This study used a scanning electron microscope to observe the effect of irrigating root canals with four concentrations of NaOC1 and two delivery methods under controlled conditions. This model system has been previously used to show that the smear layer occurs only on instrumented surfaces of root canals and to compare the efficacy of different irrigants on both the instrumented and the uninstrumented surfaces (2). Previous studies have related the efficacy of flushing loose superficial debris from a root canal to the volume of irrigant and to the extent of apical position of the needle (1). Irrigation with 3 ml of NaOC1 after each instrument in this study did an excellent job of removing superficial debris whether deliv-
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FIG 1. Control specimens before and after pulp extirpation. A (original magnification ×500) (bar = 10 ~zm),A mass of pulp tissue in the exposed root canal. B (original magnification x4000) (bar = 10 #m), The pulp tissue is composed of a mass of interwoven fibers. C (original magnification ×500), Wall of root canal following pulp extirpation showing exposed dentinal tubules. D (original magnification x4000) (bar = 10 #m), The surface of the root canal wall following pulp extirpation is covered with pulpal remnants and uncalcified predentin fibers which surround the dentinal tubules.
ered with an endodontic irrigation needle or the ultrasonic device. Studies have suggested that ultrasonic endodontic procedures remove the smear layer more effectively than conventional methods while other studies found that ultrasound had little effect on the removal of the smear layer (12-14). After ultrasonic irrigation of root canals for 2 rain with 3% NaOC1, Ciucchi et al. (15) found that 27% of the observed surfaces were smear free in the middle third. In this study, the smear layers on the instrumented portion of the root canals appeared to be very similar irrespective of the concentration of the NaOC1 or the delivery system. Some exposed dentinal tubules could be seen in the smear layer whether the irrigant was delivered with the needle or the ultrasonic device (Figs. 2 to 5). The smear layer was only on the instrumented surface and consisted of an amorphous layer of material. The amorphous smear material has been shown to be on the surface of instrumented root canals and to extend into dentinal tubules under the surface layer (16). The smear layer resulting from instrumentation of a root canal is believed to consist of particles of calcified tissue with organic material such as pulp tissue, bacteria, and blood products (16). The use of NaOC1
for root canal irrigation may dissolve the organic components and leave a smear layer of mineralized tissue. Studies have shown that NaOCI in combination with EDTA is effective in removing the smear layer and that the combination of irrigants was more effective as an antimicrobial than NaOCI by itself (2, 17). The removal of the smear layer may allow the NaOC1 to penetrate into dentinal tubules or other confined areas protected by the smear layer. The efficacy of NaOC1 for the dissolution of organic tissue has been related to its concentration (3) Harrison and Hand (3) showed that dilution of 5.25% NaOCI resulted in a significant decrease in its ability to dissolve necrotic tissue. In this investigation, examination of scanning electron micrographs of uninstrumented surfaces could not detect any difference in the removal of pulpal remnants and predentin in the middle third of the root canals with 5.25%, 2.5%, of 1% NaOC1 delivered with either a needle or an ultrasonic device. Although most pulpal remnants and predentin were removed, 0.5% NaOCI delivered with either a needle or the ultrasonic device left what appeared to be a few fibrils from predentin on the surface. These could only be seen at ×500 and x4000. The position of these fibrils was consistent with what would
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FiG 2. NaOCl (1%) irrigation using an endodontic needle. A (original magnification x150), Junction (arrow) between the instrumented (I) and uninstrumented (U) halves of the root canal wall. B (original magnification x500) (bar = 10 #m) and C (original magnification x40O0) (bar = 10 #m), The uninstrumented half of the root canal wall showing fields of exposed calcospherites. All of the pulpal remnants and uncalcified predentin have been removed by the chemical action of NaOCI. D (original magnification ×500) (bar = 10 Cm) and E (original magnification x4000) (bar = 10 ~m), The instrumented half of the root canal with some exposed dentinal tubules seen in the amorphous smear layer.
be expected if remnants of organic predentin on the surface of the calcified dentin did not undergo complete dissolution. Ultrasonic endodontic procedures have been shown to increase the dissolving and disinfecting potential of NaOC1
solutions (8). The effectiveness of low concentrations of NaOCI may be improved by using larger volumes of irrigant, by frequent exchange of irrigant, or by the presence of replenished irrigant in the canals for longer periods of time; Clini-
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FiG 3. NaOCI (1%) irrigation using an endosonic device. A (original magnification x 150), Junction (arrow) between the instrumented (I) and uninstrumented (U) halves of the root canal wall. B (original magnification x500) (bar = 10 #m) and C (original magnification x4000) (bar = 10 #m), The instrumented half of the root canal with some exposed dentinal tubules seen in the amorphous smear layer. D (original magnification x500) (bar = 10 #m) and E (original magnification x4000) (bar = 10 #m), The uninstrumented half of the root canal wall showing fields of exposed calcospherites. All of the pulpal remnants and uncalcified predentin have been removed by the chemical action of NaOCI.
cians and investigators should keep in mind that the size of the root canals and crown removal in this study made irrigation much easier than what is usually found clinically. It seems probable that there, would be a greater amount of organic residue present following irrigation of longer, nar-
rower, or more convoluted root canals which impede the delivery of the irrigant. Sodium hypochlorite does not penetrate well into confined areas of a root canal system (18, 19). Perhaps the fluid movement that occurs with ultrasonics may help carry the irrigant into uninstrumented areas and contrib-
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FIG 4. NaOCI (0.5%) irrigation using an endodontic needle. A (original magnification x150), Junction (arrow) between the instrumented (I) and uninstrumented (U) halves of the root canal wall. B (original magnification x500) (bar = 10 #m) and C (original magnification x4000) (bar -- 10 #m), The uninstrumented half of the root canal wall showing fields of exposed calcospherites with some fibrils of what appears to be remnants of predentin on the surface. D (original magnification x500) (bar = 10 #m) and E (original magnification x4000) (bar = 10 #m), The uninstrumented half of the root canal with some exposed dentinal tubules seen in the amorphous smear layer.
ute to better debridement of narrower and more complex root canal systems. The chemical removal of organic tissue by NaOC1 is by the release of hypochlorous acid which reacts with insoluble proteins to form soluble polypeptides, amino acids, and other by-products (20). With regular exchange of
the irrigant, the efficacy of the chemical reaction may be enhanced. Frequent exchange of the irrigant and the use of large quantities of irrigant should not only remove superficial debris but also replenish the chemical activity of NaOC1 which is depleted by reacting with organic tissue. In this study, a
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FIG 5. NaOCI (0.5%) irrigation using an endosonic device. A (original magnification x150), Junction (arrow) between the instrumented (I) and uninstrumented (U) halves of the root canal wall. B (original magnification x500) (bar = 10 um) and C (original magnification x4000) (bar = 10 #m), The instrumented half of the root canal with some exposed dentinal tubules seen in the amorphous smear layer. D (original magnification x500) (bar = 10 um) and E (original magnification x4000) (bar = 10 #m), The uninstrumented half of the root canal wall showing fields of exposed calcospherites with some fibrils of what appears to be remnants of predentin on the surface.
relatively small volume ofirrigant was used in the root canals for only 12 rain. If NaOC1 is often replenished and allowed to remain in the root canal system for a longer period of time, more complete chemical removal of organic debris would be expected to take place.
It is believed that thorough debridement before sealing the root canal system is a key to long-term successful endodontic therapy. This study demonstrates the efficacy of NaOCI for the physical removal of superficial debris from root canal
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surfaces and the chemical removal of organic pulpal debris and predentin from uninstrumented areas of a root canal. The opinions contained herein are the private views of the authors and are not to be construed as official or as reflecting the views of the Department of the Army or the Department of Defense. Dr. Baumgartner is former chief, Microbiology Branch, United States Army Institute of Dental Research, Walter Reed Army Medical Center, Washington, DC and chairman, Department of Endodontology, School of Dentistry, Oregon Health Sciences University, Portland, OR. Dr. Cuenin is chief, Oral Pathology, United States Army Institute of Dental Research, Walter Reed Army Medical Center. Address requests for reprints to Dr. J. Craig Baumgartner, School of Dentistry, OHSU, 611 SW Campus Dr., Portland OR 97201.
References 1. Abou-Rass M, Piccinino MV. The effectiveness of four clinical irrigation methods on the removal of root canal debris. Oral Surg 1982;54:323-8. 2. Baumgartner JC, Mader CL. A scanning electron microscopic evaluation of four root canal irrigation regimens. J Endodon 1987;4:147-57. 3. Harrison JW, Hand RE. The effect of dilution and organic matter on the antibacterial property of 5.25% sodium hypochlorite. J Endodon 1981;7: 128-32. 4. Koskinen KP, Stenvall H, Uitto V. Dissolution of bovine pulp tissue by endodontic solutions. Scand J Dent Res 1980;88:406-11. 5. Hand RE, Smith ML, Harrison JW. Analysis of the effect of dilution on the necrotic tissue dissolution property of sodium hypochlorite. J Endodon 1978;4:60-4. 6. Rosenfeld EF, James GA, Burch BS. Vital pulp response to sodium hypochlorite. J Endodon 1978;4:140-6.
Journal of Endodontics 7. Cameron JA. The synergistic relationship between ultrasound and sodium hypochlorite. J Endodon 1987;13:541-5. 8. Sjogren U, Sunqvist G. Bacteriologic evaluation of ultrasonic root canal instrumentation. Oral Surg 1987;63:366-70. 9. Spangberg L, Engstrom B, Langland K. Biologic effects of dental materials. III. Toxity and antimicrobial effect of endodontic antiseptics in vitro. Oral Surg 1973;36:856-71. 10. Th6 S. Reactions of guinea pig subcutaneous connective tissue following exposure to sodium hypochlorite. Oral Surg 1980;49:460-6. 11. Sabala C, Powell S. Sodium hypochlorite injection into periapical tissues. J Endodon 1989;15:490-2. 12. Langeland K, Liao K, Pascon E. Work-saving devises in endodontics: efficacy of sonic and ultrasonic techniques. J Endodon 1985;11:499-510. 13. Cymerman J, Jerome L, Moodnik R. A scanning electron microscope study comparing the efficacy of hand instrumentation with ultrasonic instrumentation of the root canal. J Endodon 1983;9:327-31. 14. Cameron J. The use of ultrasonics in the removal of the smear layer: a scanning electron microscope study. J Endodon 1983;9:289-92. 15. Ciucchi B, Khettabi M, Holtz J. The effectiveness of different endodontic irrigation procedures on the removal of the smear layer: a scanning electron microscopic study. Int Endod J 1989;22:21-8. 16. Mader CL, Baumgartner JC, Peters DD. Scanning electron microscopic investigation of the smeared layer on root canal walls. J Endodon 1984;10: 477-83. 17. Goldman L, Goldman M, Cavaleri R, Bogis J, Lin P. The efficacy of several endodontic irrigating solutions: a scanning electron microscopic study. J Endodon 1982;8:487-92. 18. Senia E, Marshall F, Rosen S. The solvent action of sodium hypochlorite on pulp tissue of extracted teeth. Oral Surg 1971 ;31:96-103. 19. McComb D, Smith D. A preliminary scanning electron microscopic study of root canals after endodontic procedures. J Endodon 1975;1:238-42. 20. Baumgartner JC, Ibay AC. The chemical reactions of irrigants used for root canal debridement. J Endodon 1987;13:47-51.
You M i g h t Like to K n o w Another bug, yet!! A variety of Escherichia coli which produces verocytotoxin is receiving increasing attention (Com Dis Rep 1991 ;1:35). Identified in 1971 and as a significant pathogen in 1982, it has been responsible for several recent outbreaks of hemorrhagic colitis in the United States and Canada. It is most commonly associated with improperly handled and undercooked beef products. Zachariah Yeomans
