Root canal therapy has shown satisfactory results for patients, but failures do occur with a rate of 10% to 15% (Wong 2004). The main contributory factor for the endodontic failure is microbial infection persistent in the root canal system and the periapical region. Chemical and mechanical preparation may not reach every corner of the complex root canal system. Bacteria in isthmuses, ramifications, irregularities and dentinal tubules may persist and some necrotic tissue substance may also remain. Bacteria may gain access to the periapical region if complete sealing is not obtained, leading to pathological lesions (Lin 1991; Siqueira 2001).

According to the Appropriateness of Care and Quality Assurance Guidelines (AAE 1998) of the American Association of Endodontists, when such failures happen, retreatment of the root canal is the choice. With the introduction of new technologies, such as ultrasonic instruments, the dental operative microscope and nickel titanium instruments, some cases which could not be handled with conventional root canal therapy as a result of the complexity of the root canal system, inadequate instrumentation, or presence of a physical barrier, can now be treated satisfactorily. When teeth cannot be treated appropriately by root canal treatment or retreatment, periapical surgery (which usually consists of periapical curettage, root end resection, root end preparation and root end filling (Gutmann 2004) is needed to save the teeth. el‐Swiah and Walber (el‐Swiah 1996) classified reasons for such a surgery into three kinds: biological (teeth with periapical lesions that do not respond to proper endodontic therapy, calcified canals etc.), technical (teeth that have a crown or a post etc.) and a combination of the two.

The aims of the periapical surgery are to remove the pathogenic agents and establish an environment facilitating the regeneration of the wounded tissue. In a retrospective study (Harty 1970), it was reported that the apical seal was the single most important factor in achieving success in such surgery. Root end filling materials are used to establish the barrier between the root canal system and the surrounding supportive tissue (Gutmann 1991). An ideal material to seal the root end cavities should be non toxic, non carcinogenic, biocompatible and bioconductive as well as having good sealing ability (Andreasen 1993; Gartner 1992).

For many years, amalgam has been accepted as the material of choice for root end filling. It has the advantage of being easily available, inexpensive and easy to handle. The clinical application has shown reasonable success. However in recent years, the appropriateness of amalgam for its initial marginal leakage, corrosion, moisture sensitivity, mercury contamination of periapical tissue, especially mercury hazard (Eley 1993; Gartner 1992), has been questioned. The disadvantages associated with amalgam led to the use of alternative materials. Gutta‐percha, zinc oxide engerol (super EBA and IRM), polymers, glass ionomer cements, composite resin and MTA have been employed and several cases have been reported (Hauman 2003). However in most studies the sample size was small and some of the results were conflicting (Dalal 1983; Jesslen 1995).

A systematic review has been conducted by Niederman (Niederman 2003) for an evaluation of various materials used in retrograde (root end) obturation (filling). There are however some restrictions to this review. The languages of the included articles were limited to only English, German and French. The search strategy was not specific or sensitive enough to retrieve all relevant articles and the inclusion criteria were not precise, the systematic review included all articles which had an experiment and a control group without demanding root end filling materials be used in both groups. In fact, the included articles which compared orthograde (occlusal to apical) filling with retrograde (apical to occlusal) filling were not addressing the question: which material is more suitable for root end filling?

In light of the variability in clinical practice and some conflicting study results, a comprehensive systematic review is needed to integrate the small sample size trials and clarify the effectiveness of different materials for retrograde filling in root canal therapy.