Microbiology

Illustrated the role of pulpal inflammation to apical periodontitis.

Germ-free rats did not develop apical periodontitis following pulpal exposures, whereas conventional rats with normal oral flora rapidly developed apical pathology.

Moller = Monkeys

Sundqvist = Humans

Both found bacteria in necrotic pulps with apical periodontitis but not in necrotic pulps without apical disease.

Asserts that localized or generalized infection can result from dissemination of bacteria and toxic byproducts from a focus of infection.

Weston Price - 1925

Easlick - pointed out the fallacies in Price’s research methods, including the inadequate use of controls, large amounts of bacteria in the cases presented, and contamination of root canal–treated teeth studied during extraction.  Doing so, he effectively refuted the associations between endodontically treated teeth and systemic disease.

Fish - described the encapsulation of infections into the so-called “Zones of Fish”: Infection, Contamination, Irritation, Stimulation extending outward concentrically.  If the nidus of infection is removed, the body can recover, providing a basis for the success of root canal therapy

Certain species are unable to grow outside of physiologic conditions.

It is difficult to take a truly anaerobic sample for growth in culture.

Polymerase Chain Reaction - amplifies DNA, which can subsequently be sequenced to identify the presence of known and novel species.

Fluorescent In Situ Hybridization and DNA Checkerboard Analysis - allow detection of vast libraries of known species. Molecular techniques are also useful in the detection of nonbacterial infection sources. They can be used to identify the DNA from fungal infections, including candida, and viruses, including viruses in the herpes family.

Gram Positive Bacteria

• Labeled as such due to the affinity of the crystal violet dye for their thick peptidoglycan cell walls.
• Gram-positive bacteria include those in the Streptococcus, Peptostreptococcus, Enterococcus, Lactobacillus, Eubacterium, and Actinomyces genera.

Gram Negative Bacteria

• Have a lesser affinity for the crystal violet stain due to the presence of a cell wall containing lipopolysaccharide (LPS), often referred to as endotoxin.
• LPS is important in the progression of pulpal and periapical inflammation.
• Gram-negative bacteria include those in the Fusobacterium, Treponema, Prevotella, Porphyromonas, Tannerella, Dialister, Campylobacter, and Veillonella genera.

Dwyer and Torabinejad found that LPS stimulates cytokine production by macrophages.

When the body’s physiologic microbiome is interrupted, or pathogenic microbes enter normally sterile tissues such as the dental pulp, the balance shifts, and pathogenic infection can occur.

Regardless of the means of pulp inoculation, endodontic infections are polymicrobial. Both culture-based and molecular methods confirm this finding.

Bergenholtz

Proposed that microcracks caused by traumatic injuries allow ingress of bacteria to infect an already compromised, inflamed pulp.

Gier and Mitchell

• Proposed anachoresis as another means of infection.
• Anachoresis is the homing of bacteria to traumatized, unexposed pulps.

Delivanis, PD. Localization of blood-borne bacteria in instrumented unfilled root canals. Oral Surg Oral Med Oral Pathol 1981.

Effectively disproved anachoresis.

Defined biofilms as microbial-derived, sessile communities characterized by cells irreversibly attached to a substratum or interface or to one other, embedded in a self-produced matrix of extracellular polymeric substances, and exhibiting an altered phenotype with respect to growth rate and gene transcription compared with their planktonic counterparts.

• Qualities unique to biofilms:
• Metabolic diversity
• Concentration gradient
• Genetic exchange
• Quorum sensing

Metabolic diversity allows for a sharing of nutritional sources and waste products and results in greater overall survival.

Concentration gradient created by the mere density of the biofilm community allows for greater physical and chemical resistance to antimicrobials and immune responses.

Genetic exchange by the microbiota in close proximity allows for sharing of favorable virulence factors.

Quorum sensing serves as a communication method among the microbial community and permits the members to act as a group and increase effectiveness of their actions.

Yes

• Shindell
• Historical

No

• Tronstad et al.
• Sunde et al.
• Haapasaolo et al.
• Sassone et al.
• Sabeti and Slots.

Tronstad et al performed one of the first culture studies demonstrating the presence of bacteria, particularly anaerobes, in extraradicular infections.

Sunde et al (2000) confirmed the findings of Tronstad by using molecular techniques and noted the presence of certain species in periapical infections, in particular Aggregatibacter actinomycetemcomitans and Tannerella forsythia.

Haapasalo et al cultured anaerobic bacteria in sinus tracts.

Sassone et al reported a higher prevalence of Porphyromonas gingivalis and Fusobacterium nucleatum when a sinus tract was present.

Sabeti and Slots reported the presence of human cytomegalovirus and Epstein-Barr virus in apical periodontitis.

Andreasen demonstrated that periapical healing could occur despite pulpal necrosis in traumatically lunated teeth without bacterial contamination.

Wittgow and Sabiston found that 64% of teeth with pulpal necrosis were infected.

Bergenholtz found that teeth with pulpal necrosis AND periapical lesions were more often infected.

Streptococcus, Enterococcus, Prevotella, and Porphyromonas species.

Streptococcus

• Gram positive
• Generally facultative anaerobic bacteria
• Classified as alpha or beta based on their reaction with hemoglobin molecules on blood agar in a laboratory
• Particularly, those further classified into groups F, G, C, and minority D, were common isolates in endodontic infections (Winkler and Van Amerongen)

E. faecalis

• Gram positive
• Facultative anaerobe
• Exhibits anti-microbial resistance

Evans et al. - E faecalis possesses a proton pump that allows it to adapt to harsh environments.


Bystrom et al. - Proton pump is theorized to contribute to E faecalis’ unique resistance to calcium hydroxide, an intracanal medicament known for its effectiveness against most known endodontic pathogens. Presumably, the proton pump prevents the ionization calcium hydroxide requires for effectiveness.

Love - E faecalis possesses the ability to survive for long periods of time in dentinal tubules without nutrients.

Distel et al. - Found that E. faecalis could form biofilms.

Properties:

• May form biofilms
• Can enter dentinal tubules
• Can survive starvation
• Possesses a proton pulp

Gram negative

Obligate anaerobes

Differentiated in their ability to ferment carbohydrates:

• Prevotella - Saccharolytic
• Porphymonas - Asaccharolytic

Bae et al reported that Prevotella nigrescens was the most common isolate from endodontic infections of those previously categorized as Bacteroides.

Gomes et al reported that Prevotella melaninogenica was commonly associated with painful infections.

Gram positive

Form cohesive colonies often described clinically as "sulfur granules" because of their yellow granular presentation (Sunde).

Common cause of persistent endodontic infection (Nair).

Sunde et al. - Histologic analysis of these “sulfur granules” noted that they indeed contained large quantities of clumped bacteria. 

Nair - Described difficulties in culturing the organism. Modern research methods, on the other hand, more frequently isolate this genus.

Xia and Baumgartner - Noted Actinomyces israelii, Actinomyces naeslundii, and Actinomyces viscosus in infected root canals and aspirates from associated abscesses and cellulitis.

Nair reviewed Actinomyces’ ability to survive and thrive in the periapical area, often called periapical actinomycosis, and cites this entity as a common cause of persistent endodontic infections.

Jeansonne - Recommended treating periapical actinomycosis via a surgical approach along with a relatively long, 6-week course of systemic penicillin.

Gram negative

Anaerobic bacteria with flagella for motility

Difficult to culture, requiring molecular techniques to detect them.

Siqueira et al. - Noted Treponema subspecies in endodontic infections.

Sakamoto et al. -  Identified a variety of Treponema species present in endodontic infections, particulary Treponema denticola, Treponema socranskii, and Treponema maltophilum.

Vianna et al first reported their presence in endodontic infections.

Also known as extremophiles

Known to be present in hot springs and can be localized to the gastrointestinal and vaginal tracts as well as in periodontal plaque.

Baumgartner et al. - Found Candida albicans in primary endodontic infections.

Giardino et al. - Reported a case of an Aspergillus fungal infection associated with extruded zinc oxide–based endodontic sealer in the maxillary sinus potentially related to the zinc, an Aspergillus metabolite, present in the sealer.

Viruses, particularly those in the herpesvirus family, are commonly reported in endodontic infections.

Recent data indicates that viruses may play an active role in pulpal death.

Ferreira et al. - Noted herpes simplex virus (HSV) types 1 and 2; human herpesvirus (HHV) types 6, 7, and 8; and varicella zoster virus (VZV) in aspirated samples of acute apical abscesses.

Sabeti et al. - Reported the presence of Epstein-Barr virus (EBV) and cytomegalovirus (CMV) in periapical lesions, especially larger and symptomatic lesions.

Li et al. - Also reported a possible association of EBV with irreversible pulpitis. 

Goon and Jacobsen - Case report which described devitalization of the dental pulp associated with a trigeminal VZV infection. 

Von Arx et al. - Reported a potential association between feline herpesvirus and cases of invasive cervical root resorption in both humans and cats.

Ferreira et al. - Found human papillomavirus (HPV) in endodontic abscesses. 

Glick et al. - Located HIV in the dental pulp of individuals with clinical AIDS.

Elkins et al. - Found HIV in periradicular lesions of patients known to be carriers of the virus.

NOTE: human immunodeficiency virus (HIV) has not been correlated with the pathogenesis of endodontic disease.

Primary

• Equal numbers of gram positive and gram negative species.
• More anaerobes than aerobes.

Secondary

• Varying ratios of gram positive and gram negative species.
• Equal numbers of anaerobes and facultative species.

Figdor and Sundqvist - Reported differences in the composition of primary versus secondary infections. Primary infections consisted of an equal mix of gram-positive and gram-negative bacteria and contained mostly obligate anaerobes.

Fabricius et al. - Described the progression of primary endodontic infections from largely aerobic species to anaerobic species, a process he termed microbial succession. This results from a reduction in oxygen tension in the necrotic pulp tissue due to aerobic metabolism by early colonizers.

Figdor and Sundqvist - Reported that secondary infections contained mostly gram-positive bacteria with a more equal distribution of facultative and obligate anaerobes.

Murad et al. - Conversely, reported a higher prevalence of gram-negative than gram-positive species in secondary infections, particularly in the presence of a large periapical lesion.

Rôças et al. - Reported that E. faecalis was nine times more likely to be present in secondary than primary infection.

Murad et al. - Using checkerboard DNA hybridization, reported that Enterococcus faecium and Streptococcus epidermidis were the most prevalent species in secondary infections.

Siqueira et al. - Reported an increased prevalence of Fusobacterium in symptomatic infections.

Sassone et al. - Reported an association between T forsythia and painful infections.

Gomes et al. - Noted an increased prevalence of peptostreptococci and P melaninogenica with pain.

Sabeti et al. - Found that EBV and CMV were also associated with painful infections.