The antimicrobial effect of calcium hydroxide in root canals pretreated with 5% iodine potassium iodide Molander A, k i t C, Dahlen G. The antimicrobial effect of calcium hydroxide in root canals pretreated with 5% iodine potassium iodide. Endod Dent Traumatol 1999; 15: 205-209. 0 Munksgaard, 1999. Abstract -Calcium hydroxide (CH) is often used as a routine interappointment dressing during the endodontic treatment of teeth with apical periodontitis. However, it fails to consistently produce sterile root canals. The present study was set up to find out whether an antimicrobial strategy including the use of C H could be made more effective if: 1) canals were pretreated with 5% iodine potassium iodide (IPI), and 2) the dressing period was extended up to 2 months. Fifty human teeth, with radiographically verified apical periodontitis, were microbiologically sampled. After chemomechanical preparation the canals were pretreated with IPI for 3-7 days. Teeth where microorganisms persisted were then treated with C H for 2 months. Following instrumentation and dressing with IPI, 43 bacterial strains were recovered in 22 of the teeth. Samples obtained after the C H dressing period disclosed growth of 13 facultative and two strict anaerobic strains in 10 teeth. Enterococcus faecalis was identified in two specimens. In conclusion, the present study gave no evidence for an increased antimicrobial effect of C H if it was left for longer periods in the root canal. Although pretreatment with IPI from a quantitative point of view did not seem to add antimicrobial power, it might reduce the frequency of persisting strains of E. faecalis.The aim of modern endodontic treatment of teeth with apical periodontitis is total elimination of intracanal microbes. Data show that relatively few root canals will be bacteria free following only mechanical instrumentation (l), and that an interappointment dressing therefore is needed. Calcium hydroxide paste (CH) is considered the most effective dressing currently in use. However, it fails to consistently produce sterile root canals (2, 3). Few microorganisms will survive when directly exposed to CH, but several factors may impair its antimicrobial potency in the root canal. For example, complex anatomy will make it difficult to satisfactorily pack the whole canal system with C H paste (4, 5). Therefore, longer periods of time than those usually recommended (1-2 weeks) A. Molanderl, C. Reit', 6. Dahlen2