Commentary

Endodontic treatment is essentially directed toward the prevention and control of pulpal and periradicular infections. Given the relevance of micro-organisms in the pathogenesis of these lesions, it is clear that the outcome of endodontic therapy depends on their reduction or elimination. Complete chemo-mechanical preparation is considered an essential step in root canal disinfection. Total eradication of bacteria (sterility) is a difficult task to accomplish1 but the use of intracanal medications such as calcium hydroxide has long been thought to maximise the chances of eradicating pathogens from micro-endodontic systems.

The basic theory behind the use of calcium hydroxide is that endodontic pathogens will be unable to survive in the alkaline environment it creates. Indeed, several studies showed total eradication of several bacterial species commonly found in infected root canals when in direct contact with this treatment.2 Its antimicrobial activity is related to the release of hydroxyl ions in an aqueous environment; these are highly oxidising free radicals that show extreme reactivity with many biomolecules.

However, this direct contact is not always possible. At is difficult for calcium hydroxide to dissolve and diffuse in the root canal system and thus its cytotoxicity is limited to the tissues with which it is in direct contact. Its low solubility and diffusibility may make it difficult to cause the rapid and significant increase in pH that would eradicate bacteria located at distant anatomic sites.3

Although the pharmacokinetics of this compound have been well-characterised, this pharmacodynamic problem seems to be overlooked, in turn affecting our understanding of its efficacy in vivo. The effect of buffering systems, acids, proteins, carbon dioxide and dentine chips might all affect the bioavailability of hydroxide ions to diffuse.4 In addition, the interaction between calcium hydroxide and the biofilms coating dentine walls is not well-characterised; it might be hypothesised in this case, as in others, that cells located at the periphery of the biofilm protect those located distant from the surface.

Another unknown in the pharmacodynamics of calcium hydroxide is the period required to optimally disinfect the root canal system. Studies of this have given conflicting results, ranging from 3 months to 2 weeks.5, 6 Negative culture findings do not always indicate sterile root canals, either, because of the limited accessibility to these ‘micro anatomic’ systems, as well as the fact that the sensitivity limit of these cultures is 103–105 cells/ml.

This review aimed to determine the efficacy of calcium hydroxide intracanal medication in eliminating bacteria from human root canals, comparing the effect of treatment with the same canals before treatment. This was measured using bacterial cultures as the outcome for systematic review and meta-analysis. As such, this is a welcome addition to the existing literature. The data extraction was carried out using a standardised data extraction sheet. The inclusion criteria were well-defined and appropriate for the purpose of the study. The insignificant difference between pre- and postmedication in positive cultures adds more evidence of the limited effect of calcium hydroxide in eradicating bacteria from human root canals. Nevertheless, these findings do not discount the use of calcium hydroxide as intracanal medication, particularly in cases where chemomechanical debridement cannot be carried out optimally, such as apexification and perforation repair.

Practice points

Calcium Hydroxide has limited effectiveness in eliminating bacteria from root canals.