Root canal instrumentation produces a layer of organic and inorganic material called the
smear layer that may also contain bacteria and their by-products. It can prevent the penetration of intracanal medicaments into dentinal tubules and influence the adaptation of filling materials to canal walls. This article provides an overview of the
smear layer, focusing on its relevance to
endodontics. The PubMed database was used initially; the reference list for
smear layer featured 1277 articles, and for both
smear layer dentine and
smear layer root canal revealed 1455 publications.
Smear layer endodontics disclosed 408 papers. A forward search was undertaken on selected articles and using some author names. Potentially relevant material was also sought in contemporary endodontic texts, whilst older books revealed historic information and primary research not found electronically, such that this paper does not represent a 'classical' review. Data obtained suggests that
smear layer removal should enhance canal disinfection. Current methods of smear removal include chemical, ultrasonic and
laser techniques - none of which are totally effective throughout the length of all canals or are universally accepted. If smear is to be removed, the method of choice seems to be the alternate use of
ethylenediaminetetraacetic acid and
sodium hypochlorite solutions. Conflict remains regarding the removal of the
smear layer before filling root canals, with investigations required to determine the role of the
smear layer in the outcomes of root canal treatment.