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An unusual foreign body associated with an endodontically treated tooth: report of a case
J O U R N A L OF E N D O D O N T I C S I V O L 8, N O 9, SEPTEMBER 1982
An unusual foreign body associated with an endodontically treated tooth: report of a case Ralph Bellizzi, DDS, Ronald D. Woody, DDS; Edward O'Brien, MSc, DMD; and John Fraser, BDS, MDS
The use of amalgam as a restorative material in dentistry is axiomatic. Its use in endodontics as a retrofilling material is well documented. Studies dealing with the biocompatibility of amalgam indicate that it is well tolerated in soft tissue 14 and cell cultures, s Some authors 6 have suggested that amalgam may even be less irritating than gutta-percha. Silver amalgam is presently the preferred material in endodontic surgery that requires a retrograde filling. The use of zinc-containing alloy has been challenged by.Omnell 7 because it was believed to have resulted in the formation of a zinc-carbonate precipitate in association with a root canal containing a post. The zinc-carbonate combination was believed to have been responsible for the eventual failure of the case reported in the literature. However, other authors 811 have shown little if no difference between zinccontaining and zinc-free amalgam. Although not as popular today as in the past, two root canal sealers (Kerr and AH-26) contain precipitated silver for increased radiopacity. In 1960, Orban and Wentz 12 reported localized argyria after obturation using root canal cement that contained silver. Localized argyria has also been repoted by KirchoW 3 after surgical endodontic treatment in teeth containing silver cones. On occasion, we have seen soft tissue argyria in teeth that have undergone root resection, which were obturated with gutta-
percha using a silver-containing sealer. The following case report describes an intraosseous discoloration strongly suggestive of argyria. It was associated with chronic periapical inflammation in an endodontically treated tooth. The root canal sealer was suspected of being the causative factor. REPORT OF CASE A 35-year-old white woman was referred to the endodontic service for treatment of the maxillary left lateral incisor that was causing the patient some discomfort. The tooth had been opened one month previously on an emergency basis. The medical history was noncontributory. A diagnostic periapieal radiograph disclosed nothing significant about the maxillary left lateral incisor, but the radiograph did show previous endodontic therapy of the maxillary left and right central and right lateral incisors (Fig 1). However, several millimeters from the apex of the maxillary left central incisor, a radiopaque object was visible. At the time of the examination, the patient was asymptomatic. However, she reported a history of periodic sensitivity that involved the maxillary left central incisor. She was specific about this tooth and accompanied her description with a tapping of the tooth in question as well as digital pressure over the root apex. The dental history was significant. Endodontic therapy of
Fig l--Diagnostic radiograph. Maxillary left lateral incisor shows initial access. Left, central incisor with its associated foreign body located at root apex.
the root canals (Fig 1) had been performed four years before her current visit when she lived in England. Although she could not be specific about the diagnosis and therapy, she did report that she was told the maxillary left central incisor was infected. Treatment consisted of repeated visits in which dressing was placed in the tooth and changed several times. The root canal was finally obturated. After the final obturation, the patient continued to experience transient episodes of discomfort, but no discomfort persisted for any length of time. The
417
v
dental history showed no periapieal surgery, and no pathosis could be seen clinically. There was no history of any trauma in the anterior region. The patient was informed that a foreign body appeared to be associated with the maxillary left central incisor in the presence of periapical inflammatory disease. It was suggested that in addition to endodontic re-treatment of the left lateral incisor to alleviate discomfort, this lesion also be treated. Apical curettage was suggested. The patient said she would consider it after endodontic re-treatment of the incisor. In the intervening time, the maxillary left lateral incisor was cleaned, shaped, and obturated with gutta-percha using a conventional sealer (Fig 2). At that time, the patient still had not decided on therapy of the maxillary left central incisor. A follow-up examination was scheduled. Three weeks later, the patient was admitted and reported acute pain that centered on the maxillary left central incisor. There was no visible swelling but severe apical tenderness. The patient received a local anesthesic, and a full mucoperiosteal flap was reflected. There was a pathologic fenestration of the cortical bone overlying the root apex of the maxillary left central incisor. The apical third of the root was visible and appeared slate gray in color. The periapical lesion was attached to the root apex on the palatal aspect. It was enucleated without difficulty (Fig 3). Associated with the lesion was an intact gray-black foreign body. It was brittle and fragmented easily, except for a central core that was firm and remained intact (Fig 4). The lesion was submitted for histologic examination and X-ray dispersive analysis. The flap was sutured with no. 3-0 silk, and the patient was given another appointment. Three 418
I
Fig 2--Obturation of maxillary left lateral incisor with gutta-percha and conventional sealer.
Fig 3--Surgery site subsequent to removal or foreign material.
Fig 4--Foreign material that was removed. Firm cen tral core surrounded by small fragments which were easily displaced during sepa ration from periapical lesion
days later, the patient returned and the sutures were removed. The enucleated fragmented specimen obtained from the surgery site (Fig 4) was carbon-coated; it was then observed with a scanning electron microscope (ETEC Corp, Hayward, Calif) at 20 KV. Elemental components were identified using energy dispersive X-ray analysis ( O R T E C Energy Dispersive X-ray Analysis, Biomedical Research Electronics, Palo Alto, Calif) at magnifications of X40 and X200 with 200,000 counts on a 0 to 20 KeV Scan.
RESULTS A histologic diagnosis of granulation tissue with chronic inflammatory cells was recorded for the submitted specimen. A representative X-ray dispersive energy spectrum of the specimen at a magnification of X200 is shown in Figure 5. Significant amounts of zinc (La) 960, (Ka) 708, (K/3) 185 counts and silver (La) 1,216 counts were present. Lesser amounts of iodine (La) 622, (Ifl) 492 counts were also present in the specimen. After semiquantita-
JOURNAL OF ENDODONTICS ] VOL 8, NO 9, SEPTEMBER 1982
1400-
Ag(La)
Zn(Ka)
I(Lo)
rruJ 0
"l
'
2
!
f
3
ft'
5
I
6
' X-RAY , ENERGY , t,t,
keV
Fig 5--X-ray dispersive spectrum o/ enucleated specimen. tive analysis, silver and zinc were present by weight in approximately the same concentration, and iodine in about half the concentration of silver and zinc. Healing was uneventful and the patient remained asymptomatic. Six months later, the patient returned for a follow-up exar0ination. She had no symptom, and the teeth were restored with posts and crowns (Fig 6). DISCUSSION From the data accumulated, it appears that the foreign material surrounded by the granulation tissue at the apex of the maxillary left central incisor may have been either responsible for or contributed to the persistent chronic inflammation. How this material found its way to the apical region of the involved tooth is a mystery. To answer this question, we must, of necessity, approach it from the r~alm of speculation. At the time the maxillary left central incisor was being treated, the patient was residing in England. Her description of the treatment is similar to the technique in which iodoform pastes are used in root canal therapy, popular in Europe and South America.
Iodoform-containing material is not new to dentistry and can be traced to Rose TM in 1894. A popular form of iodoform paste was introduced by WalkoW s in 1928. A review of the use of iodoform paste can be found in Nicholl's text./6 It is interesting to note that the use of iodoform paste in necrotic cases, as indicated by Walkoff) 5 involved the widening of the apical foramen intentionally during preparation, and the insertion of the iodoform paste into and out of the root canal into the periapical region. This insertion was performed regardless of the state of the periapex. The paste can be used as the sole material for obturation or as an interim dressing. When used as an interim dressing, it is removed and replaced with a solid core obturating material after symptoms subside. In this case report, evidence suggests that an iodoform paste was used as an interim dressing. A strong possibility further suggests that during final obturation with a solid core material, that is, gutta-percha, or intentionally before the final filling, the contents of the root canal were extruded through the apex. The extruded material may have been a combination of a sealer using precipitated silver and possibly a
Fig 6 - - P a t i e n t on six-month recall. Teeth are restored with post and crown. Patient has been asymptomatic to date.
residue of iodoform paste, or a mixture, with pre-existing iodoform paste previously placed beyond the apex. Periapical inflammation resulting from the use of iodoform pastes has been reported by Friend and Browne 4 as well as Bell. 17 The inflammatory potential of necrotic pulp remnants, extruded root canal cements such as zinc oxideeugenol, iodoform paste, and cements containing precipitated silver suggests a plausible explanation for the persistant chronic periapical lesion described in this case report. Host response to iodoform sensitivities, although not elicited in the medical history, may also have been a hidden underlying factor. The elements shown in Figure 5 associated with the periapieal tissue as well as the existence of chronic inflammation seem to suggest a possible relationship that may have been responsible for or contributed to the persistent periapical inflammation. These findings would indicate that additional research into the toxicity of 419
JOURNAL OF ENDODONTICS ] VOL 8, NO 9, SEPTEMBER 1982
endodontic materials is w a r r a n t e d , as has recently been suggested. 1~
The opinions or assertions contained herein are the private ones of the authors and are not to be construed as official or as reflecting the views of the US Army.
SUMMARY E v a l u a t i o n w i t h histologic and X ray dispersive analysis was p e r f o r m e d on a foreign body associated with an a r e a of periapical i n f l a m m a t i o n . Evidence indicated the foreign body resulted from the e x t r u s i o n of root canal filling materials, and the persistent chronic periapical i n f l a m m a t i o n m a y have been related to the combined interaction of the individual material constituents. A d d i t i o n a l research in biocompatibility and toxic potential of endodontic materials is advocated.
CONCLUSION T h e possibility that certain materials used in endodontics can contribute to persistent periapieal i n f l a m m a t i o n w h e n they e x t r u d e beyond the apex has been suggested. T h i s p r e l i m i n a r y report indicates that sealers that e x t r u d e beyond the a p e x m a y have contributed to the persistent inflamm a t i o n in this ease. Also, resistance and allergic responses should not be r u l e d out.
420
Dr. Bellizzi, former director of the endodontic residency training program, Madigan Army Medical Center, is currently chief endodontics, 87th Medical Detachment (DS), APO New York 09105. Dr. Woody is chief, fixed prosthetics, US Army Dental Activity, Ft Lewis, Wash. Dr. O'Brien is a parttime faculty member, dental materials, University of British Columbia, and is in private practice. Dr. Fraser is a parttime faculty member in the department of endodontics, University of British Columbia, and has a private endodontic practice in Vancouver, BC. Requests for reprints should be directed to Dr. Bellizzi.
References I. Mitchell, D.F. The irrational qualities of dental materials. JADA 59:954, 1959. 2. Dixon, D.M., and Rickert, U. Tissue tolerance to foreign material. JADA 20:1458, 1933. 3. Sperber, G.H. Biological reaction to experimental dental amalgam. J Dent Res 45:99, 1966. 4. Friend, L.A., and Browne, R.M. Tissue reactions to some root filling materials. Br Dent J 125:291, 1968. 5. Keresztesi, K., and Kellner, G. The biological effect of root filling materials. Int Dent J 16:222, 1966. 6. Feldman, G., and Nyborg, H. Tissue reactions to filling materials. Comparison between gutta-percha and silver amalgam implanted in rabbit. Odontol Revy 13:1, 1962. 7. Omnel, K-A. Electrolytic precipitation of
zinc carbonate in the jaw. Oral Surg 12:846, 1959. 8. Martin, L.R., and others. Histologie response of rat connective tissue to zinc-contain. ing amalgam. J Endod 2:25, 1976. 9. Zarmer, R.J.; James, G.A.; and Butch, B.S. Bone tissue response to zinc polycarboxylate cement and zinc free amalgam. J Endod 2:203, 1976. 10. Marcotte, L.R.; Dowson, J.; and Rowe, N.H. Apical healing with retrofilling materials amalgam and gutta-percha. J Endod 1:63, 1975. 11. Liggett, W., and others. Light microscopy, scanning electron microscopy, and microprobe analysis of bone response to zinc and non-zinc amalgam implants. Oral Surg 49:254, 1980. 12. Orban, B.J., and Wentz, F.M. Atlas of clinical pathology of the oral mucous membrane. St Louis, C. V. Mosby Co, 1960, p 133. 13. Kirchoff, D.A. Localized argyria after a surgical endodontic procedure. Oral Surg 32:613, 1971. 14. Rose, C. The treatment of teeth with diseased pulp. Dent Cosmos 36:358, 1894. 15. Walkoff, O. Mein system der medicamentosen behandlung schwerer grkrankungen der zahnpulpa und des periodontiums. Berlin, Meusser, 1928 (Quoted by Castagnola, L., and Orlay, H.G.) Br Dent J 93:93, 1952. 16. Nicholls, E. Endodontics, ed 2. Bristol, John Wright & Sons LTD, 1977. 17. Bell, J.W. Kri 1 paste. N Z Dent J 65:96, 1969. 18. Spfingberg, L.S. In vitro assessment of the toxicity of endodontic materials. Int Endod J 14:27, 1981.
An unusual foreign body associated with an endodontically treated tooth: report of a case Ralph Bellizzi, DDS, Ronald D. Woody, DDS; Edward O'Brien, MSc, DMD; and John Fraser, BDS, MDS
The use of amalgam as a restorative material in dentistry is axiomatic. Its use in endodontics as a retrofilling material is well documented. Studies dealing with the biocompatibility of amalgam indicate that it is well tolerated in soft tissue 14 and cell cultures, s Some authors 6 have suggested that amalgam may even be less irritating than gutta-percha. Silver amalgam is presently the preferred material in endodontic surgery that requires a retrograde filling. The use of zinc-containing alloy has been challenged by.Omnell 7 because it was believed to have resulted in the formation of a zinc-carbonate precipitate in association with a root canal containing a post. The zinc-carbonate combination was believed to have been responsible for the eventual failure of the case reported in the literature. However, other authors 811 have shown little if no difference between zinccontaining and zinc-free amalgam. Although not as popular today as in the past, two root canal sealers (Kerr and AH-26) contain precipitated silver for increased radiopacity. In 1960, Orban and Wentz 12 reported localized argyria after obturation using root canal cement that contained silver. Localized argyria has also been repoted by KirchoW 3 after surgical endodontic treatment in teeth containing silver cones. On occasion, we have seen soft tissue argyria in teeth that have undergone root resection, which were obturated with gutta-
percha using a silver-containing sealer. The following case report describes an intraosseous discoloration strongly suggestive of argyria. It was associated with chronic periapical inflammation in an endodontically treated tooth. The root canal sealer was suspected of being the causative factor. REPORT OF CASE A 35-year-old white woman was referred to the endodontic service for treatment of the maxillary left lateral incisor that was causing the patient some discomfort. The tooth had been opened one month previously on an emergency basis. The medical history was noncontributory. A diagnostic periapieal radiograph disclosed nothing significant about the maxillary left lateral incisor, but the radiograph did show previous endodontic therapy of the maxillary left and right central and right lateral incisors (Fig 1). However, several millimeters from the apex of the maxillary left central incisor, a radiopaque object was visible. At the time of the examination, the patient was asymptomatic. However, she reported a history of periodic sensitivity that involved the maxillary left central incisor. She was specific about this tooth and accompanied her description with a tapping of the tooth in question as well as digital pressure over the root apex. The dental history was significant. Endodontic therapy of
Fig l--Diagnostic radiograph. Maxillary left lateral incisor shows initial access. Left, central incisor with its associated foreign body located at root apex.
the root canals (Fig 1) had been performed four years before her current visit when she lived in England. Although she could not be specific about the diagnosis and therapy, she did report that she was told the maxillary left central incisor was infected. Treatment consisted of repeated visits in which dressing was placed in the tooth and changed several times. The root canal was finally obturated. After the final obturation, the patient continued to experience transient episodes of discomfort, but no discomfort persisted for any length of time. The
417
v
dental history showed no periapieal surgery, and no pathosis could be seen clinically. There was no history of any trauma in the anterior region. The patient was informed that a foreign body appeared to be associated with the maxillary left central incisor in the presence of periapical inflammatory disease. It was suggested that in addition to endodontic re-treatment of the left lateral incisor to alleviate discomfort, this lesion also be treated. Apical curettage was suggested. The patient said she would consider it after endodontic re-treatment of the incisor. In the intervening time, the maxillary left lateral incisor was cleaned, shaped, and obturated with gutta-percha using a conventional sealer (Fig 2). At that time, the patient still had not decided on therapy of the maxillary left central incisor. A follow-up examination was scheduled. Three weeks later, the patient was admitted and reported acute pain that centered on the maxillary left central incisor. There was no visible swelling but severe apical tenderness. The patient received a local anesthesic, and a full mucoperiosteal flap was reflected. There was a pathologic fenestration of the cortical bone overlying the root apex of the maxillary left central incisor. The apical third of the root was visible and appeared slate gray in color. The periapical lesion was attached to the root apex on the palatal aspect. It was enucleated without difficulty (Fig 3). Associated with the lesion was an intact gray-black foreign body. It was brittle and fragmented easily, except for a central core that was firm and remained intact (Fig 4). The lesion was submitted for histologic examination and X-ray dispersive analysis. The flap was sutured with no. 3-0 silk, and the patient was given another appointment. Three 418
I
Fig 2--Obturation of maxillary left lateral incisor with gutta-percha and conventional sealer.
Fig 3--Surgery site subsequent to removal or foreign material.
Fig 4--Foreign material that was removed. Firm cen tral core surrounded by small fragments which were easily displaced during sepa ration from periapical lesion
days later, the patient returned and the sutures were removed. The enucleated fragmented specimen obtained from the surgery site (Fig 4) was carbon-coated; it was then observed with a scanning electron microscope (ETEC Corp, Hayward, Calif) at 20 KV. Elemental components were identified using energy dispersive X-ray analysis ( O R T E C Energy Dispersive X-ray Analysis, Biomedical Research Electronics, Palo Alto, Calif) at magnifications of X40 and X200 with 200,000 counts on a 0 to 20 KeV Scan.
RESULTS A histologic diagnosis of granulation tissue with chronic inflammatory cells was recorded for the submitted specimen. A representative X-ray dispersive energy spectrum of the specimen at a magnification of X200 is shown in Figure 5. Significant amounts of zinc (La) 960, (Ka) 708, (K/3) 185 counts and silver (La) 1,216 counts were present. Lesser amounts of iodine (La) 622, (Ifl) 492 counts were also present in the specimen. After semiquantita-
JOURNAL OF ENDODONTICS ] VOL 8, NO 9, SEPTEMBER 1982
1400-
Ag(La)
Zn(Ka)
I(Lo)
rruJ 0
"l
'
2
!
f
3
ft'
5
I
6
' X-RAY , ENERGY , t,t,
keV
Fig 5--X-ray dispersive spectrum o/ enucleated specimen. tive analysis, silver and zinc were present by weight in approximately the same concentration, and iodine in about half the concentration of silver and zinc. Healing was uneventful and the patient remained asymptomatic. Six months later, the patient returned for a follow-up exar0ination. She had no symptom, and the teeth were restored with posts and crowns (Fig 6). DISCUSSION From the data accumulated, it appears that the foreign material surrounded by the granulation tissue at the apex of the maxillary left central incisor may have been either responsible for or contributed to the persistent chronic inflammation. How this material found its way to the apical region of the involved tooth is a mystery. To answer this question, we must, of necessity, approach it from the r~alm of speculation. At the time the maxillary left central incisor was being treated, the patient was residing in England. Her description of the treatment is similar to the technique in which iodoform pastes are used in root canal therapy, popular in Europe and South America.
Iodoform-containing material is not new to dentistry and can be traced to Rose TM in 1894. A popular form of iodoform paste was introduced by WalkoW s in 1928. A review of the use of iodoform paste can be found in Nicholl's text./6 It is interesting to note that the use of iodoform paste in necrotic cases, as indicated by Walkoff) 5 involved the widening of the apical foramen intentionally during preparation, and the insertion of the iodoform paste into and out of the root canal into the periapical region. This insertion was performed regardless of the state of the periapex. The paste can be used as the sole material for obturation or as an interim dressing. When used as an interim dressing, it is removed and replaced with a solid core obturating material after symptoms subside. In this case report, evidence suggests that an iodoform paste was used as an interim dressing. A strong possibility further suggests that during final obturation with a solid core material, that is, gutta-percha, or intentionally before the final filling, the contents of the root canal were extruded through the apex. The extruded material may have been a combination of a sealer using precipitated silver and possibly a
Fig 6 - - P a t i e n t on six-month recall. Teeth are restored with post and crown. Patient has been asymptomatic to date.
residue of iodoform paste, or a mixture, with pre-existing iodoform paste previously placed beyond the apex. Periapical inflammation resulting from the use of iodoform pastes has been reported by Friend and Browne 4 as well as Bell. 17 The inflammatory potential of necrotic pulp remnants, extruded root canal cements such as zinc oxideeugenol, iodoform paste, and cements containing precipitated silver suggests a plausible explanation for the persistant chronic periapical lesion described in this case report. Host response to iodoform sensitivities, although not elicited in the medical history, may also have been a hidden underlying factor. The elements shown in Figure 5 associated with the periapieal tissue as well as the existence of chronic inflammation seem to suggest a possible relationship that may have been responsible for or contributed to the persistent periapical inflammation. These findings would indicate that additional research into the toxicity of 419
JOURNAL OF ENDODONTICS ] VOL 8, NO 9, SEPTEMBER 1982
endodontic materials is w a r r a n t e d , as has recently been suggested. 1~
The opinions or assertions contained herein are the private ones of the authors and are not to be construed as official or as reflecting the views of the US Army.
SUMMARY E v a l u a t i o n w i t h histologic and X ray dispersive analysis was p e r f o r m e d on a foreign body associated with an a r e a of periapical i n f l a m m a t i o n . Evidence indicated the foreign body resulted from the e x t r u s i o n of root canal filling materials, and the persistent chronic periapical i n f l a m m a t i o n m a y have been related to the combined interaction of the individual material constituents. A d d i t i o n a l research in biocompatibility and toxic potential of endodontic materials is advocated.
CONCLUSION T h e possibility that certain materials used in endodontics can contribute to persistent periapieal i n f l a m m a t i o n w h e n they e x t r u d e beyond the apex has been suggested. T h i s p r e l i m i n a r y report indicates that sealers that e x t r u d e beyond the a p e x m a y have contributed to the persistent inflamm a t i o n in this ease. Also, resistance and allergic responses should not be r u l e d out.
420
Dr. Bellizzi, former director of the endodontic residency training program, Madigan Army Medical Center, is currently chief endodontics, 87th Medical Detachment (DS), APO New York 09105. Dr. Woody is chief, fixed prosthetics, US Army Dental Activity, Ft Lewis, Wash. Dr. O'Brien is a parttime faculty member, dental materials, University of British Columbia, and is in private practice. Dr. Fraser is a parttime faculty member in the department of endodontics, University of British Columbia, and has a private endodontic practice in Vancouver, BC. Requests for reprints should be directed to Dr. Bellizzi.
References I. Mitchell, D.F. The irrational qualities of dental materials. JADA 59:954, 1959. 2. Dixon, D.M., and Rickert, U. Tissue tolerance to foreign material. JADA 20:1458, 1933. 3. Sperber, G.H. Biological reaction to experimental dental amalgam. J Dent Res 45:99, 1966. 4. Friend, L.A., and Browne, R.M. Tissue reactions to some root filling materials. Br Dent J 125:291, 1968. 5. Keresztesi, K., and Kellner, G. The biological effect of root filling materials. Int Dent J 16:222, 1966. 6. Feldman, G., and Nyborg, H. Tissue reactions to filling materials. Comparison between gutta-percha and silver amalgam implanted in rabbit. Odontol Revy 13:1, 1962. 7. Omnel, K-A. Electrolytic precipitation of
zinc carbonate in the jaw. Oral Surg 12:846, 1959. 8. Martin, L.R., and others. Histologie response of rat connective tissue to zinc-contain. ing amalgam. J Endod 2:25, 1976. 9. Zarmer, R.J.; James, G.A.; and Butch, B.S. Bone tissue response to zinc polycarboxylate cement and zinc free amalgam. J Endod 2:203, 1976. 10. Marcotte, L.R.; Dowson, J.; and Rowe, N.H. Apical healing with retrofilling materials amalgam and gutta-percha. J Endod 1:63, 1975. 11. Liggett, W., and others. Light microscopy, scanning electron microscopy, and microprobe analysis of bone response to zinc and non-zinc amalgam implants. Oral Surg 49:254, 1980. 12. Orban, B.J., and Wentz, F.M. Atlas of clinical pathology of the oral mucous membrane. St Louis, C. V. Mosby Co, 1960, p 133. 13. Kirchoff, D.A. Localized argyria after a surgical endodontic procedure. Oral Surg 32:613, 1971. 14. Rose, C. The treatment of teeth with diseased pulp. Dent Cosmos 36:358, 1894. 15. Walkoff, O. Mein system der medicamentosen behandlung schwerer grkrankungen der zahnpulpa und des periodontiums. Berlin, Meusser, 1928 (Quoted by Castagnola, L., and Orlay, H.G.) Br Dent J 93:93, 1952. 16. Nicholls, E. Endodontics, ed 2. Bristol, John Wright & Sons LTD, 1977. 17. Bell, J.W. Kri 1 paste. N Z Dent J 65:96, 1969. 18. Spfingberg, L.S. In vitro assessment of the toxicity of endodontic materials. Int Endod J 14:27, 1981.