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The solvent action of sodium hypochlorite on pulp tissue of extracted teeth
The solvent action of sodium hypochlorite on pulp tissue of extracted teeth E. Steve Senia, Major, USAF (DC),* P. James Marshall, M.#.,** and Samuel Rosen, Ph.D.,*** Columbus, Ohio OHIO STATE UNIVERSITY
D.M.D.,
COLLEGE OF DENTISTRY
In a study involving the mesia1 root canals of extracted human molars, sodium hypochlorite was found to be more effective than normal saline solution in clissolving pulp tissue and in cleaning the wider areas of the canals.
S
odium hypochlorite (NaOCl) was first recommended as an antiseptic solution by Henry Dakin .I During World War I, it was used extensively to irrigate wounds. Taylor and Austin 2*3 demonstrated the solvent action of NaOCl (Dakin’s solution) on nonvital tissue while noting that the solution was only mildly inflammatory to normal tissue. Walker4 and Grossman5 advocated the irrigation of root canals with a doublestrength chlorinated soda solution. Grossman and MeimarP found that sodium hypochlorite was a more effective pulp tissue solvent than potassium hydroxide, sulfuric acid, sodium hydroxide, hydrochloric acid, and papain. Lewis7 suggested the use of full-strength Cloroxt for treating root canals. Masterton found that sodium hypochlorite irrigation was superior to saline irrigation in the treatment of infected pulpless teeth and teeth with chronic periapical abscesses.Shih and associates9 found that full-strength Clorox irrigations sterilized artificially infected root canals in extracted human teeth but that diluted Clorox was not as efficient. Hagal studied the debridement of the mesial canals of mandibular molars and reported that they were inadequately cleaned and shaped 81.2 per cent This article is abstracted from a thesis submitted by the senior author in partial fulflllment of the requirements for the degree of Master of Science in the graduate school at Ohio State University. The views expressed herein are those of the authors and do not necessarily reflect the views of the United States Air Force or the Department of Defense. *Chairman, Department of Endodontics, David Grant USAF Medical Center, Travis Air Force Base, Calif. **Professor and Head, Department of Endodontics, Ohio State University College of Dentistry. *““Professor, College of Dentistry and Academic Faculty of Microbial and Cellular Biology, Ohio State University. iThe Clorox Company, Oakland, Calif.
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of the time. Gutierrez and GarciaI’ reported similar findings for anterior root canals. Because sodium hypochlorite dissolves nonvital tissue, it is generally believed that this solution, when used as an irrigant, dissolves nonvital pulp tissue within the root canal. The purpose of the present study was to evaluate the solvent action of Clorox (5.25 per cent NaOCl) in the canals of extracted human mandibular molars. MATERIALS AND METHODS Clorox was chosen as the source of sodium hypochlorite because of its common usage, availability, and low cost. The stock of Clorox was stored in a cool (ll” C.), dark place throughout the study. Periodic checks with a pH meter showed no change in the original pH of 11.7. The two mesial root casals of human mandibular molars were used to evaluate the tissue-solvent action of NaOCl in root canals that are difficult to shape and clean. When a communicating isthmus of pulp tissue was present between the canals, the effect of treatment on this tissue was also studied. Seventy-eight freshly extracted teeth were used. These were sealed in Petri dishes and stored in a freezer until needed. The crowns were removed by grinding on a model trimmer. Teeth with no pulp tissue in the chamber were discarded. The grinding was continued into the bifurcation area, and the roots were separated. The mesial root was examined to ensure that pulp tissue apparently filled both root canals at the point of separation from the crown and that a solid bridge of dentine was present between the two mesial root canals. Preliminary studies of cross sections of twenty-five mesial roots showed that in all cases pulp tissue was present to the apex. Both root canals were enlarged to the size of a No. 30 reamer, and all walls were filed with a No. 25 file. Each instrument used during treatment was extended to the apical foramen. If the point of the instrument could not be seen at the apical foramen with the aid of magnifying loupes, the root was discarded. During instrumentation, normal saline solution was used in both canals to flush out loose debris. The buccal or lingual root canal was selected at random for treatment with NaOCl, and the corresponding root surface was grooved longitudinally with a No. 2 round bur for orientation. The apex was sealed with green stick compound in order to retain the irrigating solutions within the canals, and the root was mounted upright on a glass slide. The seventy-eight roots were divided into two groups for treatment. Group A One canal in each of sixty-one mesial roots was irrigated with full-strength Clorox (treatment canal), whereas the other canal of the same root was irrigated with normal saline solution (control canal). First, the control canal was irrigated intermittently with 1 cc. of normal saline solution. A 1 cc. disposable tuberculin syringe with a 26 gauge, s/s inch needle was used to dispense the irrigating solution. The solution in the canal was stirred and carried apically every 5 minutes by means of a No. 10 reamer. After 15 minutes, the canal was dried and
98 Senia, Marshall, and Rosen
Oral Surg. January, 1971
the occlusal opening was sealed with hot compound to a depth of approximately 3 mm. The treatment canal then was irrigated intermittently with 1 cc. fullstrength Clorox by the same methods as before. After I5 minutes the Clorox was removed by irrigation of the canal with normal saline solution, and the canal was then dried and sealed. The root was immediately embet&d in a clear plastic material* which was allowed to harden overnight. Group
B
Twenty-seven canals were treated individually with Clorox, as in Group A, except that the irrigating solution was applied for twice as long (30 minutes). All roots were embedded immediately after treatment and sectioned by the following technique: The occlusal end of the mesial root was secured to the head of a 3-inch bolt with green stick compound. A clear plastic tube larger than the bolt head was placed over the root and luted under the bolt head with compound. The clear plastic was poured into this mold and allowed to harden overnight. Excess plastic material was ground away to expose the apical foramina. The root cross sections were cut with a jeweler’s slotting sawt mounted on a converted drill press.$ A fine stream of water was directed to each side of the cutting blade for lubrication and cooling. Each root was cross sectioned 1 mm., 3 mm., and 5 mm. from the apex, and specimens 400 microns thick were obtained. Each specimen was removed from the embedding plastic with cotton pliers and stained differentially. It was immersed for 10 minutes in a 3 per cent solution of basic fuchsin (3 cc. of a saturated alcoholic solution in 97 cc. of distilled water). Any pulp tissue present was stained red. The section was transferred to water for 2 minutes to remove excess basic fuchsin and then blotted on bibulous paper. The section was placed in a concentrated solution of picrie acid (0.5 Gm. of chemically pure picric acid dissolved in 4 cc. of acetone) for 5 to 7 seconds and then removed and blotted. This counterstained the dentine yellow. The section was cleared for one second in a solution of equal parts acetone and xylene and then examined microscopically to verify the clearing and removal of excess picric acid stain. The sections were placed in xyltne for 5 minutes prior to mounting. All three cross sections from each root were mounted in balsam on a single glass slide and placed in a 50° C. oven at least 24 hours for hardening. The sections were examined microscopically at xl00 and the effect of treatment was evaluated. The contents of the isthmus between the canals were also recorded. Photomicrographs of typical findings were made (Figs. 1 and 2). RESULTS NaOCl applied
for
15 minutes
In thirty of the sixty-one canals treated with Clorox for 15 minutes and sectioned at the 1 mm. level (Table I), all the pulp tissue was removed. The other *Clear Cast, American Handicrafts Company, tCircular Tool Company, Providence, R. I. $Savage Cutlery, Inc., Hollywood, Calif.
Ft. Worth,
Texas.
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Pig. 1, Cross section of a mandibular molar condition of the canals. n, All tissue removed; (Original magnification, x11.)
action of sod&n
hypochlorite
99
root at 1 mm. from the apex showing the b, c, and d, some or no tissue remo ved.
Fig. 2. Cross section of a mandibular molar root at 5 mm. from the apex showing the condition of the isthmus. b, Small amount of tissue removed; c, large amount of ti 99218 removed. Note flute in canal (b). (Original magnification, x11.)
100
Senia, Marshall,
and Rosen
Table
I. Number of canals and various effect.s of treatment
Oral Burg. January, 1971
NaOCl Amount of tissqe removed at various level8
All Some or none Number of canals treated
Table
NaOCl
Saline (15 mindes) (15 minutes) (80 minzctes) 1 mm. ) 3 mm. ( 5 mm. 1 mm.13 mm.)5mm. 1 mm.\3 mm.15mm. 41 30 52 58 12 23 25 22 43 20 31 9 3 15 4 2 39 18 ii 1 ;i?
II. Number of isthmuses and various effects of treatment NC&Of3
Amount, of tissue removed at various levels
None Some Number of isthmuses treated
NaOCl
Saline (15 minutes) (15 minutes) (30 mhwtes) 1 mm. (3 mm. 15 mm. 1 mm.~.?mm.15mm. 1 mm.~3mm.~5mm. 17 15 10 0 i 1; 2 24 30 9 11 28 20 8 4 9 -G 26 38 20 G-G lo 28 39
thirty-one treated canals showed varying amounts of tissue removed. Of the sixty-one untreated control canals, twenty-two showed all the pulp tissue removed and the other thirty-nine canals showed varying amounts of tissue removed. There was no significant difference in results between the treated and untreated control canals. The effect of Clorox on the tissue in the isthmus was greater than the effect of the normal saline solution control. An isthmus with tissue present was observed next to the treated canal in twenty-six of the sixty-one specimens (Table II). Fifteen of the twenty-six treated isthmuses showed no tissue removed, and eleven showed some tissue removed. An isthmus with tissue present was observed next to the untreated control canal in twenty-eight of the sixty-one specimens. Twenty-four of the twenty-eight showed no t.issue removed, and four showed some tissue removed. There was more tissue removed from the treated isthmuses than from the untreated isthmuses. This difference was statistically significant : P < 0.05, x2 = 3.97, d.f. = 1. Fifty-two of the sixty-one canals treated with Clorox for 15 minutes and sectioned at the 3 mm. level (Table I) showed all the pulp tissue removed. The other nine treatment canals showed varying amounts of tissue removed. Fortythree of the sixty-one untreated control canals showed all the pulp tissue removed. The other eighteen showed varying amounts of tissue removed. There was no significant difference in results between the treated and untreated control canals. The effect of Clorox on the tissue in the isthmus was greater than the effect of the normal saline solution control. An isthmus with tissue present was observed next to the treated canal in thirty-eight of the sixty-one specimens (Table II). Ten of the thirty-eight showed no tissue removed, and twenty-eight showed some tissue removed. An isthmus with tissue present was observed next to the untreated control canal in thirty-nine of the sixty-one specimens. Thirty of the thirty-nine showed
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no tissue removed, and nine showed some tissue removed. The effect of treatment on isthmus tissue was statistically significant: P < 0.001, x2 = 17.55, d.f. = 1. Fifty-eight of the sixty-one canals treated with Clorox for 15 minutes and sectioned at the 5 mm. level (Table I) showed all the pulp tissue removed. The other three treatment canals showed varying amounts of tissue removed. Fortyone of the sixty-one untreated canals showed all the pulp tissue removed. The other twenty showed varying amounts of tissue removed. The effect of treatment in removing pulp tissue from the root canal at this level was statistically significant: P < 0.001, x2 = 13.8, d.f. = 1. The effect of Clorox on the tissue in the isthmus was greater than the control effect. On the treatment side of the root, an isthmus of tissue was present in twenty of the sixty-one specimens (Table II). All twenty of the specimens showed some tissue removed. On the control side of the root, an isthmus of tissue was present in twentysix of the sixty-one specimens. Seventeen of the twenty-six showed no tissue removed, and nine showed some tissue removed. The effect of treatment was statistically significant: P < 0.001, x2 = 18.0, d.f. = 1. NaOCl
applied
for 30 minutes
When twenty-seven canals were treated with full-strength Clorox for a longer period of time (30 minutes) and sectioned at the 1 mm. level, twelve showed all of the pulp tissue removed (Table I). The other fifteen canals showed some or no tissue removed. An isthmus with tissue present was observed next to the treated (30 minutes) canals in fourteen of the twenty-seven specimens (Table II). Nine of the fourteen isthmuses showed no tissue removed, and five showed some tissue removed. When twenty-seven canals were treated for 30 minutes and sectioned at the 3 mm. level, twenty-three showed all the pulp tissue removed (Table I). The other four canals showed some or no tissue removed. An isthmus with tissue present was observed next to the treated (30 minutes) canals in twenty of the twenty-seven specimens (Table II). One of the isthmuses showed no tissue removed, and nineteen showed some tissue removed. When twenty-seven canals were treated for 30 minutes and sectioned at the 5 mm. level, twenty-five showed all of the pulp tissue removed (Table I). The other two canals showed some or no tissue removed. An isthmus with tissue present was observed next to the treated (30 minutes) canals in ten of the twenty-seven specimens (Table II). Two of the isthmuses showed no tissue removed, and eight showed some tissue removed. When each result of the 30-minute Clorox treatment experiment was compared with its 15-minute Clorox treatment counterpart, no significant difference was noted. DISCUSSION
Full-strength Clorox did not appear to be very effective in removing pulp tissue which remained after instrumentation. To obtain the maximum effect for the tissue-dissolving properties of NaOCl,
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Se&a, Marshall,
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Oral January,
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there must be maximum surface contact with the tissue being treated. The pulp tissue remaining after instrumentation was attached to the canal walls or sheltered within an isthmus. Thus, not all surfaces of the pulp tissue were exposed simultaneously to the solvent action of NaOCl. Without direct contact with NaOCl, the deeper protected tissues were dissolved more slowly and less completely. The volume of solution used for irrigation (1 CL) may seem to be inadequate when compared to those usually employed clinically (5 cc. per treatment), but in this study all the solution entered only one canal. One drop from the syringe filled the entire canal, and there were approximately forty to fifty drops per cubic centimeter. Even with this amount of solution exchanged, complete cleaning was not achieved. The effectiveness of NaOCl within the root canal is further limited by the very small amount of solution that can be present in a narrow root canal at the 1 and 3 mm. levels. There is also the difficulty of adequately exchanging the solution in this area. It is almost impossible to drive a fluid into a confined space with a sharp-pointed instrument. Effervescence probably decreases the effectiveness of NaOCl within the root canal when bubbles rather than the NaOCl (which is the actual tissue solvent) occupy the limited space available. This action also may prevent fresh solution from reaching the apical areas of the root canal by mechanically pushing the new solution away from the apex. Thus, all three factors (limited surface contact, volume, and exchange of solution), either individually or together, may limit the effectiveness of NaOCl as a tissue solvent at the 1 mm. and 3 mm. levels. It is more effective at the 5 mm. level, where the canal is wider and a greater volume and exchange of solution are possible. Under clinical conditions, in which the irrigating needle seldom enters narrow canals for fear of binding, the mixing and circulation of the treatment solution would be even less. Irrigation was accomplished with 26 gauge needles in this study. This size is smaller than those normally used in clinical practice. Smaller needles would pass even further into the canal and thus, hopefully, would result in better exchange and better cleaning. However, the use of a needle with a very fine lumen is not practical clinically because of crystallization of the NaOCl solution in the lumen during the course of treatment. Under the conditions of this study, insufficient treatment time was not a limiting factor, since increasing irrigation time from 15 to 30 minutes did not significantly change the results. Mechanical preparation of the root canals by standard techniques was inadequate in most cases, even when access was ideal. It appears to be almost impossible to clean narrow and curved ro’ot canals in the apical 5 mm. The flutes and canal wall deviations reported by Hagal and Gutierrez and Garcia,ll and considered to be mechanically untreatable, were also seen. SUMMARY
This study evaluated the solvent effect of sodium hypochlorite in the mesial root canals of extracted human mandibular molars.
on pulp tissue
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The two canals of each mesial root were prepared in a standard manner. One of the root canals was treated with full-strength Clorox, while the other was irrigated with normal saline solution as a control. Both 15- and 30- minute irrigation times were used. Cross sections of the roots were made at 1 mm., 3 mm., and 5 mm. levels from the apex and, after staining, were examined microscopically at x100. The contents of the root canals were evaluated, and when an isthmus of pulp tissue was present between the two , canals this area was also evaluated. CONCLUSIONS 1. Clorox was generally more effective than normal saline solution in dissolving human pulp tissue. However, there was no significant difference in the cleaning effect of Clorox in the root canals at the 1 mm. and 3 mm. levels. At the 5 mm. level, Clorox cleaned more effectively than did normal saline solution,’ and this difference was statistically significant. 2. Where an isthmus was found between the two canals, more pulp tissue was dissolved by Clorox than by normal saline solution. This difference was statistically significant at all three levels. 3. Clorox was more effective in the larger diameters of the root canals than in the smaller apical constrictions. 4. The canals in the mesial roots of lower human molars were not adequately debrided and cleaned in the apical 5 mm. by standard endodontic techniques. 5. The value of sodium hypochlorite as an irrigating agent for dissolving pulp tissue in the apical 3 mm. of narrow root canals is questionable. REFERENCES 1. Dakin,
2. 3. 4. 5. 6. ii: 9. 10. 11.
H. D.: On the Use of Certain Antiseptic Substances in the Treatment of Infected Wounds, Brit. Med. J. 2: 318-320, 1915. Taylor, H. D., and Austin, J. H.: The Solvent Action of Antiseptics on Necrotic Tissue, J. Exp. Med. 27: 155, 1918. Austin, J. H., and Taylor, H. D.: Behavior of Hypochlorite Solution in Contact With Necrotic and Normal Tissues In Vivo, J. Exp. Med. 27: 624, 1918. Walker, A.: A Definite and Dependable Therapy for Pulpless Teeth, J. Amer. Dent. Ass. 23: 1418, 1936. Grossman, L. I.: Root Canal Therapy, ed. 1, Philadelphia, 1940, Lea & Febiger, p. 141. Grossman, L. I., and Meiman, B.: Solution of Pulp Tissue by Chemical Agents, J. Amer. Dent. Ass. 28: 223, 1941. Lewis, P.: Sodium Hypochlorite Root Canal Therapy, J. Fla. Dent. Sot. 24: 10, 1954. Masterton, J. B.: Chemical Debridement in the Treatment of Infected Pulpless Teeth and Chronic Periapical Abscess, Dent. Pm& 15: 162-170, 1965. Shih, M., Marshal!, F. J., and Rosen, S.: Bacterial Efficiency of Sodium Hypochlorite as an Endodontic Irrlgant, ORAL &so. 29: 613-619, 1970. Haga, C. S.: Microscopic Measurements of Root Canal Preparations Following Instrumentation, J. Brit. Endo. Sot. 2: 41-46, 1968. Gutierrez, J. H., and Garcfa, J.: Microscopic and Macrosoopic Investigation on Results of Mechanical Preparation of Root Canals, ORAL &JRG. 25: 108-115, 1968.
Reprint reqwsts to: E. Steve Senia, Major, USAF (DC) Department of Endodontics David Grant USAF Medical Center Travis Air Force Base, Calif. 94535
D.M.D.,
COLLEGE OF DENTISTRY
In a study involving the mesia1 root canals of extracted human molars, sodium hypochlorite was found to be more effective than normal saline solution in clissolving pulp tissue and in cleaning the wider areas of the canals.
S
odium hypochlorite (NaOCl) was first recommended as an antiseptic solution by Henry Dakin .I During World War I, it was used extensively to irrigate wounds. Taylor and Austin 2*3 demonstrated the solvent action of NaOCl (Dakin’s solution) on nonvital tissue while noting that the solution was only mildly inflammatory to normal tissue. Walker4 and Grossman5 advocated the irrigation of root canals with a doublestrength chlorinated soda solution. Grossman and MeimarP found that sodium hypochlorite was a more effective pulp tissue solvent than potassium hydroxide, sulfuric acid, sodium hydroxide, hydrochloric acid, and papain. Lewis7 suggested the use of full-strength Cloroxt for treating root canals. Masterton found that sodium hypochlorite irrigation was superior to saline irrigation in the treatment of infected pulpless teeth and teeth with chronic periapical abscesses.Shih and associates9 found that full-strength Clorox irrigations sterilized artificially infected root canals in extracted human teeth but that diluted Clorox was not as efficient. Hagal studied the debridement of the mesial canals of mandibular molars and reported that they were inadequately cleaned and shaped 81.2 per cent This article is abstracted from a thesis submitted by the senior author in partial fulflllment of the requirements for the degree of Master of Science in the graduate school at Ohio State University. The views expressed herein are those of the authors and do not necessarily reflect the views of the United States Air Force or the Department of Defense. *Chairman, Department of Endodontics, David Grant USAF Medical Center, Travis Air Force Base, Calif. **Professor and Head, Department of Endodontics, Ohio State University College of Dentistry. *““Professor, College of Dentistry and Academic Faculty of Microbial and Cellular Biology, Ohio State University. iThe Clorox Company, Oakland, Calif.
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of the time. Gutierrez and GarciaI’ reported similar findings for anterior root canals. Because sodium hypochlorite dissolves nonvital tissue, it is generally believed that this solution, when used as an irrigant, dissolves nonvital pulp tissue within the root canal. The purpose of the present study was to evaluate the solvent action of Clorox (5.25 per cent NaOCl) in the canals of extracted human mandibular molars. MATERIALS AND METHODS Clorox was chosen as the source of sodium hypochlorite because of its common usage, availability, and low cost. The stock of Clorox was stored in a cool (ll” C.), dark place throughout the study. Periodic checks with a pH meter showed no change in the original pH of 11.7. The two mesial root casals of human mandibular molars were used to evaluate the tissue-solvent action of NaOCl in root canals that are difficult to shape and clean. When a communicating isthmus of pulp tissue was present between the canals, the effect of treatment on this tissue was also studied. Seventy-eight freshly extracted teeth were used. These were sealed in Petri dishes and stored in a freezer until needed. The crowns were removed by grinding on a model trimmer. Teeth with no pulp tissue in the chamber were discarded. The grinding was continued into the bifurcation area, and the roots were separated. The mesial root was examined to ensure that pulp tissue apparently filled both root canals at the point of separation from the crown and that a solid bridge of dentine was present between the two mesial root canals. Preliminary studies of cross sections of twenty-five mesial roots showed that in all cases pulp tissue was present to the apex. Both root canals were enlarged to the size of a No. 30 reamer, and all walls were filed with a No. 25 file. Each instrument used during treatment was extended to the apical foramen. If the point of the instrument could not be seen at the apical foramen with the aid of magnifying loupes, the root was discarded. During instrumentation, normal saline solution was used in both canals to flush out loose debris. The buccal or lingual root canal was selected at random for treatment with NaOCl, and the corresponding root surface was grooved longitudinally with a No. 2 round bur for orientation. The apex was sealed with green stick compound in order to retain the irrigating solutions within the canals, and the root was mounted upright on a glass slide. The seventy-eight roots were divided into two groups for treatment. Group A One canal in each of sixty-one mesial roots was irrigated with full-strength Clorox (treatment canal), whereas the other canal of the same root was irrigated with normal saline solution (control canal). First, the control canal was irrigated intermittently with 1 cc. of normal saline solution. A 1 cc. disposable tuberculin syringe with a 26 gauge, s/s inch needle was used to dispense the irrigating solution. The solution in the canal was stirred and carried apically every 5 minutes by means of a No. 10 reamer. After 15 minutes, the canal was dried and
98 Senia, Marshall, and Rosen
Oral Surg. January, 1971
the occlusal opening was sealed with hot compound to a depth of approximately 3 mm. The treatment canal then was irrigated intermittently with 1 cc. fullstrength Clorox by the same methods as before. After I5 minutes the Clorox was removed by irrigation of the canal with normal saline solution, and the canal was then dried and sealed. The root was immediately embet&d in a clear plastic material* which was allowed to harden overnight. Group
B
Twenty-seven canals were treated individually with Clorox, as in Group A, except that the irrigating solution was applied for twice as long (30 minutes). All roots were embedded immediately after treatment and sectioned by the following technique: The occlusal end of the mesial root was secured to the head of a 3-inch bolt with green stick compound. A clear plastic tube larger than the bolt head was placed over the root and luted under the bolt head with compound. The clear plastic was poured into this mold and allowed to harden overnight. Excess plastic material was ground away to expose the apical foramina. The root cross sections were cut with a jeweler’s slotting sawt mounted on a converted drill press.$ A fine stream of water was directed to each side of the cutting blade for lubrication and cooling. Each root was cross sectioned 1 mm., 3 mm., and 5 mm. from the apex, and specimens 400 microns thick were obtained. Each specimen was removed from the embedding plastic with cotton pliers and stained differentially. It was immersed for 10 minutes in a 3 per cent solution of basic fuchsin (3 cc. of a saturated alcoholic solution in 97 cc. of distilled water). Any pulp tissue present was stained red. The section was transferred to water for 2 minutes to remove excess basic fuchsin and then blotted on bibulous paper. The section was placed in a concentrated solution of picrie acid (0.5 Gm. of chemically pure picric acid dissolved in 4 cc. of acetone) for 5 to 7 seconds and then removed and blotted. This counterstained the dentine yellow. The section was cleared for one second in a solution of equal parts acetone and xylene and then examined microscopically to verify the clearing and removal of excess picric acid stain. The sections were placed in xyltne for 5 minutes prior to mounting. All three cross sections from each root were mounted in balsam on a single glass slide and placed in a 50° C. oven at least 24 hours for hardening. The sections were examined microscopically at xl00 and the effect of treatment was evaluated. The contents of the isthmus between the canals were also recorded. Photomicrographs of typical findings were made (Figs. 1 and 2). RESULTS NaOCl applied
for
15 minutes
In thirty of the sixty-one canals treated with Clorox for 15 minutes and sectioned at the 1 mm. level (Table I), all the pulp tissue was removed. The other *Clear Cast, American Handicrafts Company, tCircular Tool Company, Providence, R. I. $Savage Cutlery, Inc., Hollywood, Calif.
Ft. Worth,
Texas.
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Pig. 1, Cross section of a mandibular molar condition of the canals. n, All tissue removed; (Original magnification, x11.)
action of sod&n
hypochlorite
99
root at 1 mm. from the apex showing the b, c, and d, some or no tissue remo ved.
Fig. 2. Cross section of a mandibular molar root at 5 mm. from the apex showing the condition of the isthmus. b, Small amount of tissue removed; c, large amount of ti 99218 removed. Note flute in canal (b). (Original magnification, x11.)
100
Senia, Marshall,
and Rosen
Table
I. Number of canals and various effect.s of treatment
Oral Burg. January, 1971
NaOCl Amount of tissqe removed at various level8
All Some or none Number of canals treated
Table
NaOCl
Saline (15 mindes) (15 minutes) (80 minzctes) 1 mm. ) 3 mm. ( 5 mm. 1 mm.13 mm.)5mm. 1 mm.\3 mm.15mm. 41 30 52 58 12 23 25 22 43 20 31 9 3 15 4 2 39 18 ii 1 ;i?
II. Number of isthmuses and various effects of treatment NC&Of3
Amount, of tissue removed at various levels
None Some Number of isthmuses treated
NaOCl
Saline (15 minutes) (15 minutes) (30 mhwtes) 1 mm. (3 mm. 15 mm. 1 mm.~.?mm.15mm. 1 mm.~3mm.~5mm. 17 15 10 0 i 1; 2 24 30 9 11 28 20 8 4 9 -G 26 38 20 G-G lo 28 39
thirty-one treated canals showed varying amounts of tissue removed. Of the sixty-one untreated control canals, twenty-two showed all the pulp tissue removed and the other thirty-nine canals showed varying amounts of tissue removed. There was no significant difference in results between the treated and untreated control canals. The effect of Clorox on the tissue in the isthmus was greater than the effect of the normal saline solution control. An isthmus with tissue present was observed next to the treated canal in twenty-six of the sixty-one specimens (Table II). Fifteen of the twenty-six treated isthmuses showed no tissue removed, and eleven showed some tissue removed. An isthmus with tissue present was observed next to the untreated control canal in twenty-eight of the sixty-one specimens. Twenty-four of the twenty-eight showed no t.issue removed, and four showed some tissue removed. There was more tissue removed from the treated isthmuses than from the untreated isthmuses. This difference was statistically significant : P < 0.05, x2 = 3.97, d.f. = 1. Fifty-two of the sixty-one canals treated with Clorox for 15 minutes and sectioned at the 3 mm. level (Table I) showed all the pulp tissue removed. The other nine treatment canals showed varying amounts of tissue removed. Fortythree of the sixty-one untreated control canals showed all the pulp tissue removed. The other eighteen showed varying amounts of tissue removed. There was no significant difference in results between the treated and untreated control canals. The effect of Clorox on the tissue in the isthmus was greater than the effect of the normal saline solution control. An isthmus with tissue present was observed next to the treated canal in thirty-eight of the sixty-one specimens (Table II). Ten of the thirty-eight showed no tissue removed, and twenty-eight showed some tissue removed. An isthmus with tissue present was observed next to the untreated control canal in thirty-nine of the sixty-one specimens. Thirty of the thirty-nine showed
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no tissue removed, and nine showed some tissue removed. The effect of treatment on isthmus tissue was statistically significant: P < 0.001, x2 = 17.55, d.f. = 1. Fifty-eight of the sixty-one canals treated with Clorox for 15 minutes and sectioned at the 5 mm. level (Table I) showed all the pulp tissue removed. The other three treatment canals showed varying amounts of tissue removed. Fortyone of the sixty-one untreated canals showed all the pulp tissue removed. The other twenty showed varying amounts of tissue removed. The effect of treatment in removing pulp tissue from the root canal at this level was statistically significant: P < 0.001, x2 = 13.8, d.f. = 1. The effect of Clorox on the tissue in the isthmus was greater than the control effect. On the treatment side of the root, an isthmus of tissue was present in twenty of the sixty-one specimens (Table II). All twenty of the specimens showed some tissue removed. On the control side of the root, an isthmus of tissue was present in twentysix of the sixty-one specimens. Seventeen of the twenty-six showed no tissue removed, and nine showed some tissue removed. The effect of treatment was statistically significant: P < 0.001, x2 = 18.0, d.f. = 1. NaOCl
applied
for 30 minutes
When twenty-seven canals were treated with full-strength Clorox for a longer period of time (30 minutes) and sectioned at the 1 mm. level, twelve showed all of the pulp tissue removed (Table I). The other fifteen canals showed some or no tissue removed. An isthmus with tissue present was observed next to the treated (30 minutes) canals in fourteen of the twenty-seven specimens (Table II). Nine of the fourteen isthmuses showed no tissue removed, and five showed some tissue removed. When twenty-seven canals were treated for 30 minutes and sectioned at the 3 mm. level, twenty-three showed all the pulp tissue removed (Table I). The other four canals showed some or no tissue removed. An isthmus with tissue present was observed next to the treated (30 minutes) canals in twenty of the twenty-seven specimens (Table II). One of the isthmuses showed no tissue removed, and nineteen showed some tissue removed. When twenty-seven canals were treated for 30 minutes and sectioned at the 5 mm. level, twenty-five showed all of the pulp tissue removed (Table I). The other two canals showed some or no tissue removed. An isthmus with tissue present was observed next to the treated (30 minutes) canals in ten of the twenty-seven specimens (Table II). Two of the isthmuses showed no tissue removed, and eight showed some tissue removed. When each result of the 30-minute Clorox treatment experiment was compared with its 15-minute Clorox treatment counterpart, no significant difference was noted. DISCUSSION
Full-strength Clorox did not appear to be very effective in removing pulp tissue which remained after instrumentation. To obtain the maximum effect for the tissue-dissolving properties of NaOCl,
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Se&a, Marshall,
and Rosen
Oral January,
8urg. 1971
there must be maximum surface contact with the tissue being treated. The pulp tissue remaining after instrumentation was attached to the canal walls or sheltered within an isthmus. Thus, not all surfaces of the pulp tissue were exposed simultaneously to the solvent action of NaOCl. Without direct contact with NaOCl, the deeper protected tissues were dissolved more slowly and less completely. The volume of solution used for irrigation (1 CL) may seem to be inadequate when compared to those usually employed clinically (5 cc. per treatment), but in this study all the solution entered only one canal. One drop from the syringe filled the entire canal, and there were approximately forty to fifty drops per cubic centimeter. Even with this amount of solution exchanged, complete cleaning was not achieved. The effectiveness of NaOCl within the root canal is further limited by the very small amount of solution that can be present in a narrow root canal at the 1 and 3 mm. levels. There is also the difficulty of adequately exchanging the solution in this area. It is almost impossible to drive a fluid into a confined space with a sharp-pointed instrument. Effervescence probably decreases the effectiveness of NaOCl within the root canal when bubbles rather than the NaOCl (which is the actual tissue solvent) occupy the limited space available. This action also may prevent fresh solution from reaching the apical areas of the root canal by mechanically pushing the new solution away from the apex. Thus, all three factors (limited surface contact, volume, and exchange of solution), either individually or together, may limit the effectiveness of NaOCl as a tissue solvent at the 1 mm. and 3 mm. levels. It is more effective at the 5 mm. level, where the canal is wider and a greater volume and exchange of solution are possible. Under clinical conditions, in which the irrigating needle seldom enters narrow canals for fear of binding, the mixing and circulation of the treatment solution would be even less. Irrigation was accomplished with 26 gauge needles in this study. This size is smaller than those normally used in clinical practice. Smaller needles would pass even further into the canal and thus, hopefully, would result in better exchange and better cleaning. However, the use of a needle with a very fine lumen is not practical clinically because of crystallization of the NaOCl solution in the lumen during the course of treatment. Under the conditions of this study, insufficient treatment time was not a limiting factor, since increasing irrigation time from 15 to 30 minutes did not significantly change the results. Mechanical preparation of the root canals by standard techniques was inadequate in most cases, even when access was ideal. It appears to be almost impossible to clean narrow and curved ro’ot canals in the apical 5 mm. The flutes and canal wall deviations reported by Hagal and Gutierrez and Garcia,ll and considered to be mechanically untreatable, were also seen. SUMMARY
This study evaluated the solvent effect of sodium hypochlorite in the mesial root canals of extracted human mandibular molars.
on pulp tissue
Volume Number
31 1
Solvent
action of sodium hypochlorite
103
The two canals of each mesial root were prepared in a standard manner. One of the root canals was treated with full-strength Clorox, while the other was irrigated with normal saline solution as a control. Both 15- and 30- minute irrigation times were used. Cross sections of the roots were made at 1 mm., 3 mm., and 5 mm. levels from the apex and, after staining, were examined microscopically at x100. The contents of the root canals were evaluated, and when an isthmus of pulp tissue was present between the two , canals this area was also evaluated. CONCLUSIONS 1. Clorox was generally more effective than normal saline solution in dissolving human pulp tissue. However, there was no significant difference in the cleaning effect of Clorox in the root canals at the 1 mm. and 3 mm. levels. At the 5 mm. level, Clorox cleaned more effectively than did normal saline solution,’ and this difference was statistically significant. 2. Where an isthmus was found between the two canals, more pulp tissue was dissolved by Clorox than by normal saline solution. This difference was statistically significant at all three levels. 3. Clorox was more effective in the larger diameters of the root canals than in the smaller apical constrictions. 4. The canals in the mesial roots of lower human molars were not adequately debrided and cleaned in the apical 5 mm. by standard endodontic techniques. 5. The value of sodium hypochlorite as an irrigating agent for dissolving pulp tissue in the apical 3 mm. of narrow root canals is questionable. REFERENCES 1. Dakin,
2. 3. 4. 5. 6. ii: 9. 10. 11.
H. D.: On the Use of Certain Antiseptic Substances in the Treatment of Infected Wounds, Brit. Med. J. 2: 318-320, 1915. Taylor, H. D., and Austin, J. H.: The Solvent Action of Antiseptics on Necrotic Tissue, J. Exp. Med. 27: 155, 1918. Austin, J. H., and Taylor, H. D.: Behavior of Hypochlorite Solution in Contact With Necrotic and Normal Tissues In Vivo, J. Exp. Med. 27: 624, 1918. Walker, A.: A Definite and Dependable Therapy for Pulpless Teeth, J. Amer. Dent. Ass. 23: 1418, 1936. Grossman, L. I.: Root Canal Therapy, ed. 1, Philadelphia, 1940, Lea & Febiger, p. 141. Grossman, L. I., and Meiman, B.: Solution of Pulp Tissue by Chemical Agents, J. Amer. Dent. Ass. 28: 223, 1941. Lewis, P.: Sodium Hypochlorite Root Canal Therapy, J. Fla. Dent. Sot. 24: 10, 1954. Masterton, J. B.: Chemical Debridement in the Treatment of Infected Pulpless Teeth and Chronic Periapical Abscess, Dent. Pm& 15: 162-170, 1965. Shih, M., Marshal!, F. J., and Rosen, S.: Bacterial Efficiency of Sodium Hypochlorite as an Endodontic Irrlgant, ORAL &so. 29: 613-619, 1970. Haga, C. S.: Microscopic Measurements of Root Canal Preparations Following Instrumentation, J. Brit. Endo. Sot. 2: 41-46, 1968. Gutierrez, J. H., and Garcfa, J.: Microscopic and Macrosoopic Investigation on Results of Mechanical Preparation of Root Canals, ORAL &JRG. 25: 108-115, 1968.
Reprint reqwsts to: E. Steve Senia, Major, USAF (DC) Department of Endodontics David Grant USAF Medical Center Travis Air Force Base, Calif. 94535