What is the impact of root canal disinfection on treatment outcomes?
This summary is based on information found in Disinfection of Root Canal Systems: The Treatment of Apical Periodontitis (Wiley Publishing, 2014)
- Disinfection of the root canal system and its general effect on endodontic outcomes is a complex issue, parts of which have been studied widely, but its specific effect is not well documented in clinical trials with high levels of clinical evidence.
- It is understood that if a canal system can be filled after a negative culture is obtained, the outcome is better (1).
- The steps that produce a canal system with a low level of bacteria remaining are of some dispute, and what level is critical to produce a significantly higher outcome is not known.
- Using real-time polymerase chain reaction, it was found that root canals with primary infections contain higher bacterial loads and that chemomechanical root canal preparations can reduce bacterial counts by at least 95% (7).
- Irrigation is one of the most important steps in endodontic therapy, carrying out many functions including tissue dissolution, lavage, killing of microorganisms, removal of debris, lubrication of the canal for instrumentation, and smear layer removal (8).
- The most widely used irrigating solutions are sodium hypochlorite, chlorhexidine, and iodine potassium iodide; and EDTA.
Clinical evidence to assess the effects of irrigants used in the nonsurgical root canal treatment of teeth
- Although there are many studies on irrigants used in endodontics, documentation of the effect of the irrigants on clinical outcomes is lacking.
- NaOCl and chlorhexidine are the commonly used irrigating solutions, but there is uncertainty as to which solution is the most effective.
Effects of various concentrations of solutions
- The ultimate concentrations of these various irrigating solutions have been investigate.
- One study found that the volume of irrigant used was more important than the solution and recommended using the most biologically acceptable irrigating solution (53).
- There is general agreement that copious volumes of irrigation during treatment are important for many reasons, especially for the lavage of the area.
Effect and efficacy of the delivery of irrigating solutions
- Another factor to be considered is how the irrigating solution is delivered to the canal.
- If the irrigating needle can reach the apical few millimeters of the canal, irrigation is more effective in debris removal (54, 55).
- A brush-covered irrigating needle produced cleaner coronal thirds than conventional irrigation, as found in one study (61).
- Sonic and ultrasonic irrigation, especially passive ultrasonic irrigation, has been found to help eliminate debris and bacteria from instrumented root canals, and is effective in the removal of tissue and debris from isthmus areas (62–67).
- Many investigations have found negative pressure irrigation to be superior in terms of both debris removal and elimination of bacteria, particularly in the apical aspect of the canal (71–75).
- It is recognized that negative pressure irrigation is safer than other forms of irrigation with respect to decreasing or eliminating the possibility of apical extrusion of irrigants (79–81).
Calcium hydroxide and other interappointment medicaments
- Calcium hydroxide is the most widely used intracanal medicament in addition to other medications that have been used in endodontics, including phenolic compounds, essential oils, aldehydes, halogens, quaternary ammonium compounds, antibiotics, and steroids.
- A 7-day application of calcium hydroxide in teeth undergoing endodontic therapy effectively eliminated bacteria from the root canal system (87).
- Calcium hydroxide has also been reported to dissolve tissue, and the tissue-dissolving effect of NaOCl is enhanced with pretreatment with calcium hydroxide (90).
- Although there is controversy over the effectiveness of calcium hydroxide as an interappointment medicament, it remains the primary medicament to reduce, or at least contain, the number of bacteria between appointments.
Apical preparation size
Two opposing views:
- The rationale for instrumenting to a larger apical size is to remove more bacteria, infected dentin, necrotic tissue, and debris, thus decreasing the risk of posttreatment apical inflammation and/or infection.
- The rationale for instrumenting to a smaller apical size is to conserve dentin and decrease the risk for subsequent root fracture (101, 102).
- Despite multiples lines of evidence from preclinical studies that suggest that larger apical sizes result in more efficient root canal disinfection in the apical aspect of the canal, data do not exist from clinical studies to support the idea that this translates into more successful clinical outcomes.
- There is debate in the endodontic community as to the ideal length to which canals should be instrumented and obturated. The rationale for instrumenting and obturating to a longer length is to ensure that the most apical extent of the canal has been cleaned and sealed.
- The rationale for instrumenting and obturating to a shorter length is to preserve the integrity of the apical tissues and avoid debris extrusion or overfilling the canal.
1 versus 2 visits
- There is great debate in the field of endodontics about the number of visits in which root canal treatment should be completed.
- There is consensus that a tooth with a vital pulp may have root canal therapy completed in one visit (if time permits) and if the canals are not infected.
- There is also consensus that teeth should not be obturated when the patient has swelling or the canal cannot be dried because of exudate seepage from the apical tissues.
- There is disagreement on whether necrotic teeth with asymptomatic apical periodontitis, symptomatic apical periodontitis, or a chronic apical abscess should be treated with single- or multiple-visit root canal therapy. At the core of this debate are the principles of disinfection of the root canal system.
- The preoperative diagnosis has repeatedly been shown to have a significant effect on outcome.
- Teeth with preoperative apical radiolucencies have a poorer prognosis than teeth without preoperative apical radiolucencies.
- Teeth with an apical radiolucency are believed to be infected, whereas teeth without an apical radiolucency may or may not be infected, So those with an apical radiolucency would be more difficult to disinfect than teeth with intact apical tissues.