Pathogenesis of apical periodontitis and the causes of endodontic failures. Crit Rev.

By Nair PN

Date: 02/2006
Journal: Oral Biol Med

Apical periodontitis is a sequel to endodontic infection and manifests itself as the host defense response to microbial challenge emanating from the root canal system.

• It is viewed as a dynamic encounter between microbial factors and host defenses at the interface between infected radicular pulp and periodontal ligament that results in local inflammation, resorption of hard tissues, destruction of other periapical tissues, and eventual formation of various histopathological categories of apical periodontitis, commonly referred to as periapical lesions.

•The treatment of apical periodontitis consists of eradicating microbes or substantially reducing the microbial load from the root canal and preventing reinfection by orthograde root filling.

• The treatment has a remarkably high degree of success. Nevertheless, endodontic treatment can fail.

• Most failures occur when treatment procedures, mostly of a technical nature, have not reached a satisfactory standard for the control and elimination of infection.

•There are root canal regions that cannot be cleaned and obturated with existing equipments, materials, and techniques, and thus, infection can persist.

• In very rare cases, there are also factors located within the inflamed periapical tissue that can interfere with post-treatment healing of the lesion.

Causes of Endodontic Failures:

•Inadequate aseptic control, poor access cavity design, missed canals, inadequate instrumentation, and leaking temporary or permanent fillings (Sundqvist and Figdor, 1998).

•Even when the highest standards are met and the most careful procedures followed, failures still occur, because of the anatomical complexity of the root canal system (Hess, 1921)

•There are factors beyond the root canals, within the inflamed periapical tissue, that can interfere with post-treatment healing of the lesion.

•(A) INTRARADICULAR INFECTION

•(B) ENDODONTIC FLORA OF ROOT-CANAL-TREATED TEETH

•(C) EXTRARADICULAR ACTINOMYCOSIS

•(D) OTHER EXTRARADICULAR INFECTIONS

•(E) CYSTIC APICAL PERIODONTITIS

•(F) FOREIGN-BODY REACTIONS

(A)INTRARADICULAR INFECTION

•It has been suggested that intraradicular infection can also remain within the innermost portions of infected dentinal tubules that serve as a reservoir for endodontic re-infection that might interfere with periapical healing (Shovelton, 1964).

•A histobacteriological study, with the use of serial-step-sectioning and special bacterial stains, found bacteria in the root canals of 14% of the 66 specimens examined (Andreasen and Rud, 1972a).

•(B) ENDODONTIC FLORA OF ROOT-CANAL-TREATED TEETH

•Predominantly Gram-positive cocci, rods, and filaments.

•By culture techniques, species belonging to the genera Actinomyces, Enterococcus, and Propionibacterium (previously Arachnia) are frequently isolated from such root canals  (Möller, 1966)

•Repeated reporting of Enterococcus faecalis (Möller, 1966). It is resistant to most of the intracanal medicaments, particularly to calcium hydroxide dressings (Byström et al., 1985), due to its ability to regulate internal pH with an efficient proton pump (Evans et al., 2002).

•E. faecalis can survive prolonged starvation (Figdor et al., 2003). It can grow as a mono-infection in treated canals in the absence of synergistic support from other bacteria (Fabricius et al., 1982b).

•studies have shown the presence of yeast in canals of root-filled teeth with unresolved apical periodontitis.

• Candida albicans is the most frequently isolated fungus from root-filled teeth with apical periodontitis (Molander et al., 1998)

•(C) EXTRARADICULAR ACTINOMYCOSIS

•Because of the ability of the actinomycotic organisms to establish extraradicularly, they can perpetuate the inflammation at the periapex, even after orthograde root canal treatment. Therefore, periapical actinomycosis is important in endodontics (Sundqvist and Reuterving, 1980).

•A. israelii and P. proprionicum are consistently isolated and characterized from the periapical tissue of teeth which did not respond to proper conventional endodontic treatment (Happonen, 1986).

•The intertwining filamentous colonies are often called “sulphur granules” because of their appearance as yellow specks in exudate

•The properties that enable these bacteria to establish in the periapical tissues are not fully understood, but appear to involve their ability to build cohesive colonies that enable them to escape the host defense system (Figdor et al., 1992).

•(D) OTHER EXTRARADICULAR INFECTIONS

Extraradicular infections do occur in:

•Acute apical periodontitis lesions (Nair, 1987)

•Periapical actinomycosis (Sundqvist )

•Association with pieces of infected root dentin that may be displaced into the periapex during root canal instrumentation (Holland et al., 1980) or cut from the rest of the root by massive apical resorption (Valderhaug, 1974)

•Infected periapical cysts, particularly in periapical pocket cysts with cavities open to the root canal (Nair, 1987).

Except for these special situations, the long-standing idea that solid granuloma generally do not harbor micro-organisms is still valid.

•(E) CYSTIC APICAL PERIODONTITIS

•A great majority of the cystic lesions should heal to account for the ‘high success rate’ after endodontic treatment and the reported ‘high histopathological incidence’ of radicular cysts. Since orthograde endodontic treatment removes much of the infectious material from the root canal and prevents re-infection by obturation, a periapical pocket cyst may heal after conventional endodontic therapy (Simon, 1980; Nair et al., 1993, 1996).

•A true cyst is self-sustaining (Nair et al., 1993) by virtue of its tissue dynamics and independent of the presence or absence of irritants in the root canal (Simon, 1980).

•Therefore, true periapical cysts, particularly those containing cholesterol crystals, are less likely to be resolved by conventional endodontic therapy (Nair, 1998a, 2003a)

•(F) FOREIGN-BODY REACTIONS

•(1) Cholesterol crystals

•(2) Foreign bodies

•(a) Gutta percha

•(b) Plant materials

•(c) Other foreign materials

•(G) SCAR-TISSUE HEALING

All these factors, microbial infection persisting in the apical portion of the root canal system is the major cause of endodontic failures in properly treated cases (Nair et al., 1990a; Sjögren,1996; Figdor, 2002).Failures due to extraradicular actinomycosis, cystic lesions, foreign-body reaction, and scar-tissue healing are rare.

All these factors, microbial infection persisting in the apical portion of the root canal system is the major cause of endodontic failures in properly treated cases (Nair et al., 1990a; Sjögren,1996; Figdor, 2002).Failures due to extraradicular actinomycosis, cystic lesions, foreign-body reaction, and scar-tissue healing are rare.