Root canal treatment is a non-surgical procedure used to treat two distinct endodontic disease entities: (1) vital, but irreversibly inflamed pulp or (2) the non-vital or dying, infected pulp, associated with apical periodontitis (European Society of Endodontology 2006). Non-surgical root canal therapy has become a routine procedure in modern dentistry. Recent techniques and novel materials resulted in saving of millions of teeth that would otherwise be lost (Hargreaves et al. 2011). The principal goal of endodontic treatment is to render the root canal system bacteria-free and to prevent the invasion of bacteria and their byproducts from the root canal system into the periradicular tissues (Tsesis et al. 2012).
There are several materials have been used to fill the root canals: resilon, silver point and the most popular is the gutta-percha in conjunction with different sealers. However, gutta-percha has two significant drawbacks: its poor sealing ability and its inability to further strengthen the teeth (Marfisi, K. et al.2010).
Post-treatment failure is associated with the persistence of microorganisms in the root canal system due to untreated canals, inadequate filling, insufficient cleaning, iatrogenic events or recolonization of the root canal space by bacteria following coronal or apical micro-leakage (Nair et al. 1999; Siqueira 2001). Furthermore, During retreatment procedures mechanical mishaps, missed canals, and radicular subcrestal fractures were revealed (Ruddle CJ. 2004).
Non-surgical endodontic retreatment is a procedure to remove the filling material from the root canals system entirely, followed by cleaning, shaping and obturation of the canals (Friedman et al. 1990, Bodrumlu et al. 2008). Retreatment of the previously filled root is the preferred treatment option after endodontic failures; It aims to improve the disinfection of root canal system by complete removal of root canal obturation material to uncover the remnant necrotic tissues and bacteria that may be responsible for periapical failure and inflammation (Pirani et al. 2009).
Retreatment of a root canal system is more challenging and time-consuming compared with the initial treatment leading to many procedural errors ( Kasam, S. 2016; Duncan & Chong 2008).
Different methods have been followed to gain this goal; these include H-files, rotary files, solvents (Pirani et al. 2009; Somma et al. 2008; Oliveira et al. 2006), Gates Glidden burs, heat, ultrasonic instruments (Wilcox 1989) and laser (Viducic et al.2003). Regardless of technique, gutta-percha is best gradually removed from a root canal to prevent inadvertent displacement of irritants periodically. Gutta-percha may be initially removed from the canal in the coronal third, then the middle third, and finally from the apical third. Single cones in larger and straighter canals can be removed with one instrument in one motion (Ruddle CJ.2002). Studies have shown that none of the retreatment procedures can completely remove gutta-percha from the canal walls (Vidal et al. 2016; Khalilak et al. 2013), particularly in the apical third where microorganisms are commonly present (Preetam et al. 2016).
The removal of gutta-percha using hand files with or without solvent can be a complicated procedure and time-consuming process especially when the root filling material is well compacted (Oliveira et al. 2006). Therefore, the use of NiTi rotary instruments in root canal retreatment is faster and more efficient than Hedstrom hand files and might decrease patient and operator fatigue (Tasdemir et al. 2008; Khalilak et al. 2013; Fariniuk et al. 2017 ). That may be due to the frictional heat of engine-driven file which might plasticize gutta-percha and ease its removal (Betti & Bramante, 2001).
Also, it has been reported that NiTi files are more efficient in the removal of filling material at the cervical and middle one-third as well as Hedstrom hand files at the apical region (Preetam et al. 2016).
The ProTaper Universal retreatment files (D1, D2, and D3) are invented to remove filling materials from the root canal before the reshaping procedures. They have different tapers and diameters at the tip. The D1 designed to remove the filling materials from the coronal third, D2 from the middle third and D3 from the apical third. Similar to the shaping and finishing instruments they have a convex cross-section, the D1 has a working tip that facilitates its initial penetration into filling materials (Gu et al.2008).
Recently, XP-endo Finisher (FKG Dentaire, La Chaux de Fonds, Switzerland) was introduced for use as a last supplementary step to enhance the root canal cleaning during root canal treatment. The file displays a core diameter of ISO 25 and zero tapers (25.00) they produced using an exclusive FKG alloy, the highly flexible NiTi MaxWire (Martensite-Austenite-electropolish-fleX) that reacts at different temperature levels. At room temperature, the file is straight in their M-phase. While within the root canal system the file exposed to the body temperature and adjust its shape to A-phase that has a C-shape at the apical half. Due to their unique sickle shape, the file can expand up to 6mm in diameter to reach and clean areas that are otherwise impossible to approach with standard instruments (Silva et al. 2017).
After the innovation of XP-endo Finisher in 2015, FKG Dentaire SA continues its marketing and innovate the XP-endo Finisher R targeting the removal of filling material. It is a nontapered instrument and has a core diameter larger than XP-endo Finisher (30.00) making it slightly stiffer and more efficient in the removal of gutta-percha and sealer (Silva et al. 2017). Currently, there is no sufficient data available on the removal of gutta-percha after using XP-endo Finisher R.
There is a study comparing the efficacy of XP-endo Finisher and the XP-endo Finisher R ?les in the removal of residual root ?lling material from straight oval-shaped canals, both were equally effective, but none of them can completely remove gutta-percha from the root canal system (Silva et al. 2017). Other studies showed the superior result of the XP-endo finisher when used as a final irrigation step procedure on the removal of debris and smear layer (Elnaghy et al. 2017) and in the removal of calcium hydroxide past from root canal (Hamdan et al. 2017).
In root canal retreatment solvent as chloroform, eucalyptol or orange oil are often used as an aid for gutta-percha removal (Bodrumlu et al. 2008; Martos et al. 2011). Chloroform one of the most commonly used solvents since it dissolves the gutta-percha rapidly and has a long history of clinical use (Hargreaves et al. 2011). But due to its potential carcinogenicity, the US Food and Drug administration forbade its use in drug and cosmetic (United States Drug Administration 1976). The carcinogenicity of chloroform in humans is suspected based on sufficient evidence of carcinogenicity in experimental animals (McDonald & Vire, 1992). But with careful use, its toxicity may be excluded as a risk factor for both the patient and the operator (Chutich et al. 1998; Allard & Andersson, 1992). So, their use should be avoided if possible; however, a solvent is usually required to remove well-condensed gutta-percha (Hargreaves et al. 2011). Antibacterial effect of chloroform has been reported (Edgar et al. 2006).
Several in vitro methods were used to detect the residual filling material after canal retreatment including: stereomicroscope ( Nair et al. 2017; Khalilak et al. 2013 ), postoperative radiograph (Preetam et al. 2016), micro-CT device (Silva et al. 2017), and scanning electron microscope (Horvath et al. 2009).
A study using scanning Electron microscope revealed that solvents led to more remnant of gutta-percha and sealer on root canal walls and dentinal tubules (Horvath et al. 2009). Another Study reported that there was no significant difference among chloroform, orange oil, and eucalyptol in the removal of the filling material, but superior retreatment was achieved without the use of solvents (Scelza et al. 2008). Therefore, authors recommend that the only indication for the solvent is the inability to reach working length without it during retreatment (Horvath et al. 2009).
During retreatment, the amount of extruded debris, gutta-Percha, and tissue remnants beyond the apical foramen is associated with all retreatment instrument (Keskin et al. 2017).
It has been shown that Hedstrom hand files are associated with more debris extrusion compared with rotary instruments (Lu et al. 2013). Moreover, a previous study stated that that lower taper files could lead to a removal of more debris in the coronal direction and resulted in less debris extrusion (Koçak et al. 2017) as showed in XP- endo finisher files.
Also, it has been published that the use of solvent significantly reduced apically extruded debris compared to the non-solvent group (Keskin et al., 2017). Reduction in debris extrusion during canal debridement is desirable since apical extrusion of foreign material has been linked with periapical inflammation, flare-ups, postoperative pain, and delay periapical healing (Seltzer & Naidorf 1985; Siqueira et al. 2002; Siqueira 2003; Burklein & Schafer 2012).