THE SMEAR LAYER - A PHENOMENON IN ROOT-CANAL THERAPY

When the root canals are instrumented during endodontic therapy, a lay er of material composed of dentine, remnants of pulp tissue and odonto blastic processes, and sometimes bacteria, is always formed on the can al walls. This layer has been called the smear layer. It has an amorph ous, irregular and granular appearance under the scanning electron mic roscope. The advantages and disadvantages of the prescence of smear la yer, and whether it should be removed or not from the instrumented roo t canals, are still controversial. It has been shown that this layer i s not a complete barrier to bacteria and it delays but does not abolis h the action of endodontic disinfectants. Endodontic smear layer also acts as a physical barrier interfering with adhesion and penetration o f sealers into dentinal tubules, in turn, it may affect the sealing ef ficiency of root canal obturation. When it is not removed, the durabil ity of the apical and coronal seal should be evaluated over a long per iod. If smear layer is to be removed, EDTA and NaOCl solutions have be en shown to be effective, among various irrigation solutions and techn iques, including ultrasonics, that have been tested. Once this layer i s removed, it should be borne in mind that there is a risk of reinfect ing dentinal tubules if the seal fails. Further studies are needed to establish the clinical importance of the absence or presence of smear layer.