未治疗及治疗失败感染根管微生物定植模式研究
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摘要
目的：通过扫描电镜和光学显微镜在原位上观察未治疗及治疗失败的无症状感染根管中微生物的形态、分布和相对位置来初步了解微生物在这二者中的定植模式及其异同，并初步探讨微生物与牙髓治疗失败的关系，为临床上治疗失败根管的再治疗提供参考。
材料与方法：新鲜拔除的18颗无症状并伴有根尖部病损的离体牙牙根，其中未治疗牙根6颗、根管治疗失败和塑化治疗失败的牙根各6颗。2.5％戊二醛固定24小时后，将牙根在颊舌向沿牙齿长轴劈开成两半，一半用于扫描电镜观察；另一半脱钙后切片，分别用HE染色(观察细胞)和Brown & Brenn染色(观察微生物)后在光学显微镜下观察。
结果：(1)所有未治疗组被检根管均被微生物感染，在根管壁的大部分区域均能找到稠密的微生物，不同根管和同一根管的不同部位，微生物的构成存在差异，常由多种细菌(球菌、多种杆菌)构成致密复杂的生物膜。细菌侵入牙本质小管的深度通常在100μm以内，某些样本中可侵入约300μm深。根尖周组织中以慢性炎细胞浸润为主，未见有微生物。(2)根管治疗失败组中3例在根管中发现有细菌，主要为球菌，1例仅发现真菌。微生物形态较单一，菌落分布均散在。细菌可侵入牙本质小管中，侵入深度在100μm以内。5例样本根尖周组织有慢性炎细胞浸润，1例为疤痕组织，均未见微生物。(3)塑化治疗失败组中2例在根管中发现有细菌，主要为球菌，2例仅发现真菌。微生物形态较单一，菌落分布均散在。细菌可侵入牙本质小管中，侵入深度在100μm以内。4例样本根尖周组织有慢性炎细胞浸润，2例为疤痕组织，均未见微生物。
结论：(1)未治疗组中根管微生物的定植模式为多种细菌混合感染，微生物形成稠密而结构复杂的生物膜。(2)塑化治疗失败组和根管治疗失败组根管中微生物的量明显减少。其定植模式为：形态上单一的细菌构成孤岛状的小
菌落，以分散的形式存在，球菌为最常见的微生物。(3)根尖周组织的炎症
可能与微生物在根管中的持续存在有关，根尖周组织以疤痕形式愈合的情况
可能与其根管为无菌状态有关。(4)塑化治疗失败根管中，单一真菌感染出
现的几率较高。(5)根尖周组织中没有发现有微生物存在的证据。
Objective: To study the morphology, distribution and relative position of microorganisms in situ in untreated and fail-treated root canal using scanning electron microscopy and light microscopy.
Methods: 18 recently extracted roots were studied. They were divided into three groups. The roots on group 1 were untreated. Group 2 were failed in root canal therapy. Group 3 were failed in resinfying therapy. Each group had six roots. All cases demonstrated evidence of periapical radiolucencies. The root was split into two halves along the gena-lingua axis. One half was studied under scanning electron microscopy. The other half was observed under light microscopy for histology and microorganisms.
Results: (1) Microorganisms were found in all untreated roots. However, the patterns of microbial colonization were different in individual roots and varied in different areas of the same root. The microbial colonization in root canals was made up of cocci and/or bacilli that often blended together in a community. The depth of the invasion of bacteria in dental tube was about 100 um. However, in some roots we did find that it could be up to 300um. Infiltration of chronic inflammation cell was discovered in periapical tissues with no microorganism observed. (2) In the group that failed in the root canal therapy, bacteria, mostly cocci were found in 3 cases and fungus was found in one case solely. The invasion of bateria was within 100um. Colonies can be found dispersedly in dental tubes with unitary morphology. Chronic inflammation cell infiltration was discovered in the perapical tissue of 5 specimens. Scar tissue was found in one specimens. No microorganism was found in the perapical tissue. (3) In the grou
p that failed in resinfying therapy, cocci were found mostly in 2 cases and fugi were found solely in the other 2 cases. The invasion of bateria was within 100um. Colonies can be found dispersedly in dental tubes with unitary morphology. Chronic inflammation cell infiltration was discovered in the perapical tissue of 3 specimens, and scar
tissue was found in 2 specimens. No microorganism was found in the perapical
tissue.
Conclusions: (1) Severe infection occurs in untreated root canals. The pattern of
microbial colonization is characterized as climax community. (2) The pattern of
microbial colonization in failed-treated root canals of root canal therapy and
resinfying therapy dramatically differ from that of the untreated, which can be
characterized as unitary morphology, smaller dispersed islet-like colonies. (3) The
continuant existence of microorganisms is due to the failure of root canal therapy
and resinfying therapy. (4) In the asymptomatic infected root canals of failure
treatments, the coccus is the mostly common microorganism. (5) The eukaryotic
microorganism is related to the chronicle continuant infection and its reoccurrence.
(6) It is possible that little microorganisms exist in the perapical tissue of
asymptomatic infected root canals.
材料与方法：新鲜拔除的18颗无症状并伴有根尖部病损的离体牙牙根，其中未治疗牙根6颗、根管治疗失败和塑化治疗失败的牙根各6颗。2.5％戊二醛固定24小时后，将牙根在颊舌向沿牙齿长轴劈开成两半，一半用于扫描电镜观察；另一半脱钙后切片，分别用HE染色(观察细胞)和Brown & Brenn染色(观察微生物)后在光学显微镜下观察。
结果：(1)所有未治疗组被检根管均被微生物感染，在根管壁的大部分区域均能找到稠密的微生物，不同根管和同一根管的不同部位，微生物的构成存在差异，常由多种细菌(球菌、多种杆菌)构成致密复杂的生物膜。细菌侵入牙本质小管的深度通常在100μm以内，某些样本中可侵入约300μm深。根尖周组织中以慢性炎细胞浸润为主，未见有微生物。(2)根管治疗失败组中3例在根管中发现有细菌，主要为球菌，1例仅发现真菌。微生物形态较单一，菌落分布均散在。细菌可侵入牙本质小管中，侵入深度在100μm以内。5例样本根尖周组织有慢性炎细胞浸润，1例为疤痕组织，均未见微生物。(3)塑化治疗失败组中2例在根管中发现有细菌，主要为球菌，2例仅发现真菌。微生物形态较单一，菌落分布均散在。细菌可侵入牙本质小管中，侵入深度在100μm以内。4例样本根尖周组织有慢性炎细胞浸润，2例为疤痕组织，均未见微生物。
结论：(1)未治疗组中根管微生物的定植模式为多种细菌混合感染，微生物形成稠密而结构复杂的生物膜。(2)塑化治疗失败组和根管治疗失败组根管中微生物的量明显减少。其定植模式为：形态上单一的细菌构成孤岛状的小
菌落，以分散的形式存在，球菌为最常见的微生物。(3)根尖周组织的炎症
可能与微生物在根管中的持续存在有关，根尖周组织以疤痕形式愈合的情况
可能与其根管为无菌状态有关。(4)塑化治疗失败根管中，单一真菌感染出
现的几率较高。(5)根尖周组织中没有发现有微生物存在的证据。
Objective: To study the morphology, distribution and relative position of microorganisms in situ in untreated and fail-treated root canal using scanning electron microscopy and light microscopy.
Methods: 18 recently extracted roots were studied. They were divided into three groups. The roots on group 1 were untreated. Group 2 were failed in root canal therapy. Group 3 were failed in resinfying therapy. Each group had six roots. All cases demonstrated evidence of periapical radiolucencies. The root was split into two halves along the gena-lingua axis. One half was studied under scanning electron microscopy. The other half was observed under light microscopy for histology and microorganisms.
Results: (1) Microorganisms were found in all untreated roots. However, the patterns of microbial colonization were different in individual roots and varied in different areas of the same root. The microbial colonization in root canals was made up of cocci and/or bacilli that often blended together in a community. The depth of the invasion of bacteria in dental tube was about 100 um. However, in some roots we did find that it could be up to 300um. Infiltration of chronic inflammation cell was discovered in periapical tissues with no microorganism observed. (2) In the group that failed in the root canal therapy, bacteria, mostly cocci were found in 3 cases and fungus was found in one case solely. The invasion of bateria was within 100um. Colonies can be found dispersedly in dental tubes with unitary morphology. Chronic inflammation cell infiltration was discovered in the perapical tissue of 5 specimens. Scar tissue was found in one specimens. No microorganism was found in the perapical tissue. (3) In the grou
p that failed in resinfying therapy, cocci were found mostly in 2 cases and fugi were found solely in the other 2 cases. The invasion of bateria was within 100um. Colonies can be found dispersedly in dental tubes with unitary morphology. Chronic inflammation cell infiltration was discovered in the perapical tissue of 3 specimens, and scar
tissue was found in 2 specimens. No microorganism was found in the perapical
tissue.
Conclusions: (1) Severe infection occurs in untreated root canals. The pattern of
microbial colonization is characterized as climax community. (2) The pattern of
microbial colonization in failed-treated root canals of root canal therapy and
resinfying therapy dramatically differ from that of the untreated, which can be
characterized as unitary morphology, smaller dispersed islet-like colonies. (3) The
continuant existence of microorganisms is due to the failure of root canal therapy
and resinfying therapy. (4) In the asymptomatic infected root canals of failure
treatments, the coccus is the mostly common microorganism. (5) The eukaryotic
microorganism is related to the chronicle continuant infection and its reoccurrence.
(6) It is possible that little microorganisms exist in the perapical tissue of
asymptomatic infected root canals.
引文
1. Sundqvist G. Associations between microbial species in dental root canal infections. Oral Microbial Immunol 1992; 7: 257-62.
2. Siqueira JF Jr. tratamento das infectces endodrnticas. Rio de Janeiro: MEDSI, 1997. p. 31-32.
3. Baumgartner and Falkler. Bacteria in the apical 5 mm of infected root canals. J. Endod. 1991; 17: 380-383.
4. Strindberg LZ. The dependence of the results of pulp therapy on certain factors: an analytical study base on radiographic and clinical follow-up examinations. Acta Odont Scand 1956; 14: (supplement 21): 1-175.
5. Grahnén H. Hansson L. The prognosis of pulp and root canal therapy: a clinical and radiographic follow-up examination. Odontol Revy 1961; 12:146-65.
6. Seltzer S, Bender IB, Turkenkopf S. Factors affecting successful repair after root canal therapy. J Am Dent Assoc 1963; 67: 651-662.
7. Storms JL. Factors that influence the success of endodontic treatment. J Can Dent Assoc 1969; 35: 83-97.
8. Kerekes K, Tronstad L. Long-term results of endodontic treatment performed with a standardized technique. J Endod 1979; 5: 83-90.
9. Molven O. The frequency, technical standard and results of endodontic therapy. Norske Tannlaegeforenings Tidende 1976; 86: 142-147.
10. Molven O, Halse A. Success rates for gutta-percha and Kloroperka N-Φ root fillings made by undergraduate students: radiographic findings after 10-17 years. Int Endod J 1998; 21: 243-50.
11. Sjgren U, Hgglund B, Sundqvist G, Wing K. Factors affecting the long-term results of endodontic treatment. J Endod 1990; 16: 498-504.
12. Sundqvist et al. Microbiologic analysis of teeth with failed endodontic treatment and the outcome of conservative re-treatment. Oral Surg. Oral Pathol. Oral Radiol. Endod. 1998; 85: 86-93.
13．王效平．塑化治疗后牙慢性根尖周病10年后临床观察[J]．现代口腔医学杂志，1998；12(4)：271～272．
14．赵皿，张翠贤，谢欣梅．液体充填治疗尖周炎180例临床报告。中华口腔科杂志 1979；14：183-184，
15. Jose F.Siqueira et. Al. Pattern of microbial colonization in primary root canal infections. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2002; 93: 174-178.
16. Pashley DH. Clinical consideration in microleakage. J endodontic 1990; 16: 70-77.
17. Peters LB, Wesseling PR, Buijs JF, van Winkelhoff AJ, Viable bacteria in toot dentinal tubules of teeth with apical periodontitis. J Endod 2001; 27: 76-81.
18. Love RM. Bacterial penetration of the root canal of intact incisor teeth after a simulated traumatic injury. Endod Dent Traumatol 1996a; 12: 289-293.
19. Delivanis PD, Fan VSC. The localization of blood-borne bacterial in instrumented unfilled and overinstrumented canals. J Endodont 1984; 19: 521-524.
20. Cheung GSP, Ho MWM. Microbial flora of root canal-treated teeth associatedwith asymptomatic periapical radiolucent lesions. Oral Microbiol Immunol 2001; 16: 332-337.
21. H. H. Hancock, Ⅲ, Asgeir Sigurdsson. Bacteria isolated after unsuccessful endodontic treatment in a North American population. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2001; 91: 579-586.
22. Lin LM. et al. Clinical, radiographyic, and histopathological study of endodontic treatment failures. Oral Surg. Oral Pathol. Oral Radiol. Endod. 1991; 71: 603-611.
23. Siqueira JF Jr. Tratamento das Infecces Endodnticas. Rio de Janeiro: Medsi.
24. Saunders WP, Saunders EM Coronal leakage as a cause offailure in root-canal therapy: a review. Endodontics and Dental Traumatology 1994; 10: 105-108.
25. Madison S, Swanson K, Chiles SA. An evaluation of coronal microleakage in endodontically treated teeth. Part Ⅱ. Sealer types. Journal of Endodontics 1987; 13: 109-112.
26. Madison S, Wilcox LR. An evaluation of coronal microleakage in endodontically treated teeth. Part Ⅱ. In vivo study. Journal of Endodontics
1988; 14: 455-458.
27. Marshall FJ, Massler M. The sealing of pulpess teeth evaluated by radioisotopes. Journal of Dental Medicine 1961; 16:172-174.
28. Sundqvist G, Figdor D. Endodontic treatment of apical periodontitis. In: Φ rstavik D, Pitt Ford TR, editors. Essential endodontology. Oxford: Blackwell; 1998. p. 242-277.
29. Molander A, Reit C, Dahlén G, Kvist. Microbiological status of root-filled teeth with apical periodontitis. International Endodontic Journal 1998; 31: 1-7.
30. Barbosa SV, Araki K, Spangberg LSW. Cytotoxicity of some modified root canal and their leachable components. Oral Surgery, Oral Medicine, Oral Pathology and Endodontics 1993; 75: 357-361.
31. Spanberg LSW. Instruments, materials and devices. In: Cohen S, Burns RC. Acta Odontologica Scandinavica 1998; 14(suppl, 21): 1-175.
32. Lopes HP, Siqueira JF Jr. (1999) Endododtia: Biologia E Técnica. Rio de Janeiro: Medsi.
33. Lin LM, Skribner JE, Gaengler P. Factors associated with endodontics treatment failures. Jorunal of Endodontics 1992; 18: 625-627.
34. Sjgren U, Figdor D, Persson S, Sundqvist G. Influence of infection at the time of root filling on the outcome of endodontic treatment of teeth with apical periodontitis. International Endodontic Journal 1997; 30: 297-306.
35. Simon JHS, Chimenti RA, Mintz CA. Clinical significance of the pulse granuloma. Jorunal of Endodontics 1982; 6: 116-119.
36. Koppang HS, Koppang R, Solheim T, Aarnes H, Stolen SO. Cellulose fibers from endodontic paper points as an etiological factor in postendodontic periapical granulomas and cysts. Jorunal of Endodontics 1989; 15: 369-372.
37. Yusuf H. The significance of the presence of foreign material periapically as a cause of fallure of root treatment. Oral Surgery, Oral Medicine, Oral Pathology and Endodontics 1982; 54: 566-574.
38．王嘉德，陈理珍，毛秀萍．牙髓塑化治疗后根管内及根尖孔附近的塑化情况。华西口腔医学杂志 1989；1：41-42．
39．赵皿，张翠贤，谢欣梅．液体充填治疗尖周炎180例临床报告。中华口腔
科杂志 1979；14：183-184．，
40．吴民凯，王满恩．对实验动物牙根管内酚醛树脂体积变化的观察。中华口腔科杂志 1983；18：226-228．
41. Orstavik D, Haapadalo M. Disinfection bu endodontic irrigants and dressings of experimentally infected dentinal tubules. Endod Dent Traumatol 1990; 6: 142-149.
42. Perez F, Calas P, Falguerolles A, Mautette A. Migration of a Streptococcus sanguis strain through the root dentinal tubules. J Endod 1993; 19: 297-301.
43. Perez F, Rochd T, Lodter J-P, Calas P, Michel G. In vitro study of the penetration of three bacterial strains into root dentine. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 1993; 76: 97-103.
44. Berkiten M, Okar I, Berkiten R. In vitro study of the penetration of Streptococcus Sanguis and Prevotella intermedia strains into human dentinal tubules. J Endod 2000; 26: 263-269.
45. Shovelton DS. The presence and distribution of microorganisms within non-vital teeth. Br Dent J 1964; 117: 101-107.
46. Gutierrez JH, Jofre A, Villena E Scanning electron microscope study on the action of endodontic irrigants on bacteria invading the dentinal tubules. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 1990; 69:491-501.
47. Sen et al. Observation of bacteria and fungi in infected root canals and dentinal tubules by SEM. Endod. Dent. Traumatol. 1995; 11: 6-9.
48. Kühn, A.: Histologische Studien ǜber pathologische Vernderungen des Paradentiums, imbesonderen über die Herkunft des Epithels in Zahnwurzelzysten, über An-und Abbauvorgnge am Aleveolarknochen und Zement sowie über den Bakteriengehalt von Zahnwurzelgranulomen, Dtsch. Zahnheilkld. 1930; 76: 3-45.
49. Kronfeld, R.: Histopathology of the Teeth, ed. 2, Philadelphia, Lea and Febiger 1939, p. 209-211.
50. Grossman, L. I.: Bacteriologic status of Periapical Tissue in 150 Cases of Infected Pulpless Teeth, J. Dent. Rex. 1959; 38: 101-104.
51. Grossman, L. I.: Endodontic Practice, ed. 8, Philadelphia, Lea and Febiger
1974, P. 85.
52. Siqueira JF Jr, Araǘjo MCP, Filho PFG, Fraga RC, Saboia Dantas CJ. Histological evaluation of the effectiveness of five instrumentation technisques for cleaning the apical third of root canals. Journal of Endodontics 1997; 23: 499-502.
53. Nair PNRLight and electron microscopic studies of root canal flora and periapical lesions. Journal of Endodontics 1987; 13: 29-39.
54. Füsun Tanriverdi et al. An in vitro test model for investigation of disinfection of dentel tubules infected with Enterococcus faecalis. Braz Dent J 1997; 8(2): 67-72.
2. Siqueira JF Jr. tratamento das infectces endodrnticas. Rio de Janeiro: MEDSI, 1997. p. 31-32.
3. Baumgartner and Falkler. Bacteria in the apical 5 mm of infected root canals. J. Endod. 1991; 17: 380-383.
4. Strindberg LZ. The dependence of the results of pulp therapy on certain factors: an analytical study base on radiographic and clinical follow-up examinations. Acta Odont Scand 1956; 14: (supplement 21): 1-175.
5. Grahnén H. Hansson L. The prognosis of pulp and root canal therapy: a clinical and radiographic follow-up examination. Odontol Revy 1961; 12:146-65.
6. Seltzer S, Bender IB, Turkenkopf S. Factors affecting successful repair after root canal therapy. J Am Dent Assoc 1963; 67: 651-662.
7. Storms JL. Factors that influence the success of endodontic treatment. J Can Dent Assoc 1969; 35: 83-97.
8. Kerekes K, Tronstad L. Long-term results of endodontic treatment performed with a standardized technique. J Endod 1979; 5: 83-90.
9. Molven O. The frequency, technical standard and results of endodontic therapy. Norske Tannlaegeforenings Tidende 1976; 86: 142-147.
10. Molven O, Halse A. Success rates for gutta-percha and Kloroperka N-Φ root fillings made by undergraduate students: radiographic findings after 10-17 years. Int Endod J 1998; 21: 243-50.
11. Sjgren U, Hgglund B, Sundqvist G, Wing K. Factors affecting the long-term results of endodontic treatment. J Endod 1990; 16: 498-504.
12. Sundqvist et al. Microbiologic analysis of teeth with failed endodontic treatment and the outcome of conservative re-treatment. Oral Surg. Oral Pathol. Oral Radiol. Endod. 1998; 85: 86-93.
13．王效平．塑化治疗后牙慢性根尖周病10年后临床观察[J]．现代口腔医学杂志，1998；12(4)：271～272．
14．赵皿，张翠贤，谢欣梅．液体充填治疗尖周炎180例临床报告。中华口腔科杂志 1979；14：183-184，
15. Jose F.Siqueira et. Al. Pattern of microbial colonization in primary root canal infections. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2002; 93: 174-178.
16. Pashley DH. Clinical consideration in microleakage. J endodontic 1990; 16: 70-77.
17. Peters LB, Wesseling PR, Buijs JF, van Winkelhoff AJ, Viable bacteria in toot dentinal tubules of teeth with apical periodontitis. J Endod 2001; 27: 76-81.
18. Love RM. Bacterial penetration of the root canal of intact incisor teeth after a simulated traumatic injury. Endod Dent Traumatol 1996a; 12: 289-293.
19. Delivanis PD, Fan VSC. The localization of blood-borne bacterial in instrumented unfilled and overinstrumented canals. J Endodont 1984; 19: 521-524.
20. Cheung GSP, Ho MWM. Microbial flora of root canal-treated teeth associatedwith asymptomatic periapical radiolucent lesions. Oral Microbiol Immunol 2001; 16: 332-337.
21. H. H. Hancock, Ⅲ, Asgeir Sigurdsson. Bacteria isolated after unsuccessful endodontic treatment in a North American population. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2001; 91: 579-586.
22. Lin LM. et al. Clinical, radiographyic, and histopathological study of endodontic treatment failures. Oral Surg. Oral Pathol. Oral Radiol. Endod. 1991; 71: 603-611.
23. Siqueira JF Jr. Tratamento das Infecces Endodnticas. Rio de Janeiro: Medsi.
24. Saunders WP, Saunders EM Coronal leakage as a cause offailure in root-canal therapy: a review. Endodontics and Dental Traumatology 1994; 10: 105-108.
25. Madison S, Swanson K, Chiles SA. An evaluation of coronal microleakage in endodontically treated teeth. Part Ⅱ. Sealer types. Journal of Endodontics 1987; 13: 109-112.
26. Madison S, Wilcox LR. An evaluation of coronal microleakage in endodontically treated teeth. Part Ⅱ. In vivo study. Journal of Endodontics
1988; 14: 455-458.
27. Marshall FJ, Massler M. The sealing of pulpess teeth evaluated by radioisotopes. Journal of Dental Medicine 1961; 16:172-174.
28. Sundqvist G, Figdor D. Endodontic treatment of apical periodontitis. In: Φ rstavik D, Pitt Ford TR, editors. Essential endodontology. Oxford: Blackwell; 1998. p. 242-277.
29. Molander A, Reit C, Dahlén G, Kvist. Microbiological status of root-filled teeth with apical periodontitis. International Endodontic Journal 1998; 31: 1-7.
30. Barbosa SV, Araki K, Spangberg LSW. Cytotoxicity of some modified root canal and their leachable components. Oral Surgery, Oral Medicine, Oral Pathology and Endodontics 1993; 75: 357-361.
31. Spanberg LSW. Instruments, materials and devices. In: Cohen S, Burns RC. Acta Odontologica Scandinavica 1998; 14(suppl, 21): 1-175.
32. Lopes HP, Siqueira JF Jr. (1999) Endododtia: Biologia E Técnica. Rio de Janeiro: Medsi.
33. Lin LM, Skribner JE, Gaengler P. Factors associated with endodontics treatment failures. Jorunal of Endodontics 1992; 18: 625-627.
34. Sjgren U, Figdor D, Persson S, Sundqvist G. Influence of infection at the time of root filling on the outcome of endodontic treatment of teeth with apical periodontitis. International Endodontic Journal 1997; 30: 297-306.
35. Simon JHS, Chimenti RA, Mintz CA. Clinical significance of the pulse granuloma. Jorunal of Endodontics 1982; 6: 116-119.
36. Koppang HS, Koppang R, Solheim T, Aarnes H, Stolen SO. Cellulose fibers from endodontic paper points as an etiological factor in postendodontic periapical granulomas and cysts. Jorunal of Endodontics 1989; 15: 369-372.
37. Yusuf H. The significance of the presence of foreign material periapically as a cause of fallure of root treatment. Oral Surgery, Oral Medicine, Oral Pathology and Endodontics 1982; 54: 566-574.
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