The smear layer in endodontics – a review

Abstract

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.

Effect of endodontic chelating solutions on the bond strength of endodontic sealers

“…8 A combination of NaOCl and EDTA solutions is recommended for the efficient removal of the smear layer from the surface of the root canal wall. 19 However, this combined irrigation regimen can lead to erosion of the dentin surface.…”

“…7 Over the years, several methods have been tested to improve adhesion of root canal sealers to radicular dentin. Removal of the smear layer is one of these techniques, 8 and numerous irrigation solutions/regimens have been recommended for that purpose. 9 Chelating solutions are able to remove the smear layer, and expose a large number of dentinal tubules, 10 which in turn may promote adhesion due to an increased contact area that would ensure a better adaptation between the sealer and root canal dentin.…”

Comparación in vitro de la capacidad de remoción del barrillo dentinario con rc-prep (Premier), glyde (Dentsply), kelfar (Eufar), durante la limpieza y conformación de los conductos radicales

“…Violich y Chandler, en su artículo de revisión, justifican la importancia de la remoción del barro dentinario para la eliminación de tejido necrótico, bacterias y sus productos presentes en el conducto; estas condiciones permiten la multiplicación y supervivencia de ellas en los túbulos dentinales, limitando y bloqueando la penetración y acción de las sustancias irrigantes; también actúa como barrera entre el material de obturación y las paredes del conducto. Por esto, muchos estudios han demostrado la necesidad de usar agentes quelantes en conjunto con sustancias irrigantes, como el hipoclorito de sodio al 5,25%, para poder asegurar así la eliminación del componente orgánico e inorgánico y obtener una superficie libre de desechos [15,16]. La preparación biomecánica de las muestras en este estudio se realizó mediante el sistema de limas Protaper.…”

Effect of cementation protocol on push-out bond strength of fiber posts to root canal

“…According to manufacturers, these resin-based materials do not require any pretreatment of the dental surfaces and their main adhesive mechanism is attributed to a chemical reaction between phosphate methacrylates and hydroxyapatite [8,[20][21][22]. However, the formation of a thick and dense smear layer during the root canal instrumentation [23] impairs a proper contact between the acidic methacrylates of self-adhesive cements and the underlying dentin, compromising the bond strength [24,25].…”