STATEMENT OF PROBLEM

Various solutions used to irrigate root canals and remove the smear layer prior to obturation of a root canal affect surface topography and may influence the sealing ability of endodontic therapy, retention of endodontic dowels, and restoration survival.

PURPOSE

This study microscopically evaluated the effects of varying dilutions of lactic acid on the removal of the smear layer created by hand instrumentation in the coronal, middle, and apical thirds of root canals. Lactic acid solution was compared with other solutions deemed to be suitable root canal irrigants.

MATERIAL AND METHODS

Thirty-five extracted human single-rooted teeth were manually shaped with files (K-flex) using the step-back technique. ISO size 50 files were used as master apical files. The teeth were equally divided into 7 test groups according to the canal irrigant used. While the teeth were cleaned and shaped, the root canals were irrigated with 3 mL of 1 of the following irrigants between each file size and as a final flush: no irrigant (control), 5% hydrogen peroxide, 5% sodium hypochlorite, a combination of 5% hydrogen peroxide and 5% sodium hypochlorite, 15% ethylenediaminotetraacetic acid (EDTA), 10% lactic acid, or 20% lactic acid. Specimens were critical-point dried and freeze-fractured for scanning electron microscope analysis at 3 sites (cervical, middle, and apical).

RESULTS

Scanning electron micrographs showed no differences between the cervical, middle, and apical levels of the specimens tested with any of the irrigants used. Also, no difference was found within individual groups. The surface of the control specimens had a smear layer that contained smear plug material. Hydrogen peroxide and sodium hypochlorite used separately and in combination consistently produced surfaces with a smear layer. Lactic acid solutions and EDTA, however, removed the dentinal smear layer but left remnants of smear plugs in the dentinal tubules.

CONCLUSIONS

Within the limitations of this study, differences related to the type of irrigant used were found in the characteristics of the pulpal dentin surface. Although lactic acid effectively cleaned and smoothed the dentin walls of root canals of endodontically prepared teeth, further study is needed before this procedure can be recommended for routine clinical use.