Authors: McComb D, Smith DC.
Title: A preliminary scanning electron microscopic study of root canals after endodontic procedures.
Journal: J Endod
Date: Jul 1975
Citation: 1(7):238-42
Category: Access and Canal Instrumentation
Evidence-based Ranking: 5
Purpose/Objectives: To contribute to the development of more rational root canal therapy through the investigation and improvement of the procedures involved in chemomechanical preparation of the canal.

Materials and Methods: Recently extracted single rooted teeth were used in the study. The first series used reamers, files, Hedstrom files, and giromatic reamers with distilled water. The second series used files and reamers in conjunction with different irrigants. This included 1% and 6% NaOCL, 6% NaOCL and 3% H2O2, REDTA, RC Prep, and polyacrylic acid. The third series had certain solutions sealed in the canal up to 24 hours. Two teeth from each group were studied with a SEM. Results: Water irrigation- pulps removed with barbed broach showed an overall appearance that was sound with superficial debris. Instrumentation with other instruments was similar, however, at higher magnification a surface layer was evident occluding the tubules. Reaming and filing alternatively resulted in a more uniformed canal. Chemomechanical instrumentation- 6%NaoCL showed an extremely smooth and clean canal, but the smear layer was still present. NaOCL with H2O2 was similar to water irrigation. REDTA resulted in a clean canal with the removal of the smear layer. RC Prep resulted in more debris than water irrigation especially when used with NaOCl. 20% Polyacrylic acid was the other solution that removed the smear layer. Chemical treatment- REDTA for 24 hrs showed the cleanest canal surfaces of the study free of debris and the smear layer. There was no significant discussion on the other irrigants that were sealed were 24 hrs.

AuthorÂ’s Conclusions: Currently accepted methods of root canal preparation are inadequate for the purposes of producing a clean canal. ReviewerÂ’s Comments: There were many questions concerning this study, for example the method of hand instrumentation and the small sample size. With all the inadequacies, however, the paper at the time did give a preliminary description of what different irrigant solutions do. I assume it was one of the first studies to use a SEM for descriptive work, and to look at what actually removes the smear layer. It reminded me of work done by Baumgartner at a later date, which seemed to be more organized and detailed.