How useful is root canal culturing in predicting treatment outcome?

Microbial control--fundamental to healing of apical periodontitis--is central to endodontic practice. The effectiveness of antibacterial measures is generally monitored (in clinical research studies) by microbiological root canal sampling (MRS), which is often used as a predictor for healing. This article addresses the question of the extent to which positive or negative cultures at time of obturation are able to predict treatment outcome. To date only one small clinical study has attempted to relate the treatment outcome to intraradicular bacterial status (p = 0.025, Fisher's exact test): the strength of the association was not great, with a wide confidence interval (odds ratio = 6.8; 95% CI: 1.5 to 32). The extent to which current canal sampling techniques accurately reflect the bacterial status of the canal space must also be taken into account. False positive and negative cultures may adversely affect the performance of MRS. These conditions emphasize how potentially error-prone MRS can be. As currently practiced, intracanal sampling techniques suffer from deficiencies that limit their predictive value. This article in no way questions the role of intracanal bacteria in causing apical periodontitis, nor the central role of bacterial control in endodontic treatment. Rather, it emphasizes the need for more detailed clinical studies of bacterial status and healing, as well as refinement of techniques for microbial sampling of canals.