ANALYSIS OF THE EFFECTIVENESS OF XP-ENDO FINISHER R IN ORTHOGRADE ENDO-DONTIC RETREATMENT

SUMMARYBackground: Removal of the root canal filling material in the course of the endodontic retreatment is achieved by the use of various instruments and techniques. Purpose: The aim of this article is to systematically analyze published in vitro investigations over a five-year period of time (2018-2022), assessing the efficacy of the XP-Endo Finisher R file as a supplementary approach in orthograde endodontic retreatment. Materials and methods: The literature data was acquired through PubMed - MEDLINE, The Cochrane Li-brary and Science Direct database and hand web search, then the articles were assessed by three independent reviewers. Results: An overall number of eighteen papers out of 108 titles met the eligibility criteria and were finally chosen for quantitative synthesis. Most of the studies af-firmed the effectiveness of XP-Endo Finisher R by means of microcomputed tomography. Shaping with the file is not able to guarantee root canal walls free of remnants. Conclusions: XP-Endo Finisher-R is an effective supplementary approach in endodontic retreatment procedures. Nonetheless, it is rarely reported to achieve the complete removal of the root canal filling material. Micro-CT is a reliable, non-invasive analytical tool that can accurately measure the volume and the percentage of the remaining root canal fillings.

duced photoacoustic streaming, and various combinations of these methods [4]. The majority of dental clinicians opt for engine-driven endodontic systems rather than manual instrumentation due to their improved efficacy and the shortened chair time of the appointments [3,6,7]. Nevertheless, none of the specifically designed NiTi retreatment files renders root canals completely free of filling material [8,9]. Thus, supplementary techniques following retreatment procedures would be beneficial to cover larger and difficult to reach root canal areas and enhance the action of the disinfecting irrigants [10].
Recently, the XP-endo Finisher-R (FKG, La Chauxde-Fonds, Switzerland) was introduced to the market as an improved variant of the XP-endo Finisher. It is a non-tapered file with a larger core diameter (30/.00). The instrument is manufactured from the novel MAX-wire (MartensiteAustenite ElectropolishFleX), which allows it to expand at body temperature and upon pressure, to adopt a "spoon-like" shape of the final millimeters of its working part. Due to this, the file abrades the dentine surface with an improved distance of 6 mm in diameter and cleans areas that were previously impossible to reach by the standard instruments of the same size. Additionally, the instrument provides agitation of the irrigants due to the turbulence resulting from its action [11][12][13][14][15][16].
The aim of this article was to analyze and summarize the recently published studies investigating the efficacy of XP-endo Finisher-R (XP-FR) as a supplementary retreatment approach.

Eligibility criteria
The review process was performed on articles assessing the in vitro effect of the novel file XP-Endo Finisher R on samples prepared from extracted, fully formed permanent human teeth without any root canal caries, cracks, fractures or other defects.

Exclusion criteria
Studies focusing solely on debris extrusion, microbial flora assessment, removal of root canal medications, registration of the morphological changes of the instruments after use, case reports, review articles, thesis, articles not in English or only about XP-Endo Finisher files were not included in the systematic review. https://doi.org/10.5272/jimab.2022282.4371 Literature search and data extraction A thorough literature search was done on PubMed -MEDLINE, The Cochrane Library, Science Direct database and own manual search on the web. The following keywords were used: XP-endo finisher R, retreatment, supplementary, removal, root filling material, remnant/s. The data search was applied for in vitro studies investigating the ability of XP-Endo Finisher-R to enhance the removal of root canal filling material, released in the period from 2018 to 2022. The language was restricted to English.

Screening and selection
Three independent reviewers judged the relevance of each paper to the criteria based on its title and/or abstract. Case reports, letters, reviews, and theses were not included in the search. A detàiled, full-text reading of the article was initialized when the keywords were present either in the title and/or the abstract. Those papers that ful-filled all of the selection criteria were processed for data extraction. Any conflicts between the three reviewers were resolved by a discussion.
From the collection of papers that met the eligibility criteria, data were extracted and summarized in tables.

RESULTS
In the PubMed -MEDLINE database, 20 articles were obtained with the combination of the keywords. The total number of papers found through Cochrane Library, Science Direct and manual search was: 2, 11 and 75, respectively. After removing duplicates for searches and identifying relevant studies, 108 unique papers were selected for further systematic review. A total number of 18 articles were finally chosen for quantitative synthesis (Fig.1). Table 1 shows the characteristics of the reviewed studies concerning the efficacy of the XP-FR file as a supplementary instrument.

DISCUSSION
XP-Endo Finisher-R facilitates the removal of root canal filling materials after the initial retreatment procedures [16]. Nevertheless, almost all of the investigations noted the existence of remnants in the specimens after their upplementary use [5,11,12,15,[17][18][19][20][21][22][23][24][25][26][27][28]. These findings corroborate with earlier studies where no retreatment strategy was able to clean the root canal walls completely [8,9]. In the study of Campello et al., total removal of filling remnants was achieved only in two out of thirty-two roots after shaping with XP-FR [14]. Machado et al. reported thorough cleanliness of mesial canals of lower molars after their retreatment with D-Race, followed by XP-endo Shaper, SAF and TRUShape -70%, 55% and 30% of the specimens, respectively. The supplementary step with the XP-endo Finisher R instrument was associated with additional filling material removal, and six more canals were rendered free of filling material after using this finishing instrument [13].
The effectiveness of XP-FR has been assessed for a variety of root canal filling materials and techniques. The majority of the experiments tested the ability of XP-FR in the removal of epoxic resin-based endodontic sealers [5, 11-14, 20, 21, 24, 27, 28]. AH Plus (Dentsply De Trey, Konstanz, Germany) is considered to be a 'gold standard' sealer for its excellent physiochemical properties and good biocompatibility [17]. Additional shaping with the file resulted in a significant reduction of gutta-percha and AH Plus sealer [5,15,17,20,22,24,27,28]. Retreatment of bioceramic sealers is often a great challenge and might cause the blockage of the apical portion of the root canal Reports from scientific data have been inconsistent regarding the use of solvents during the retreatment procedures. Despite the manufacturer's recommendation of using solvent for the XP-endo Finisher R file, it was included in the protocol of a few of the reviewed articles [14,15,20,23]. This might be explained by the possible formation of a thin layer of softened gutta percha which adheres to the root canal walls and hinders the removal of root canal filling material, resulting in a longer procedure [5,11,15,29,30]. However, Iriboz et al. outlined the effectiveness of Resosolv in combination with XP-FR [15]. A recent study by Ferreira et al. demonstrated the favourable effect of an additional solvent mixture of Methyl ethyl ketone/ Tetrachlorethylene that increased the efficiency of filling materials removal regardless of the agitating instruments employed, IrriSafe or XP endo Finisher R. These findings refute the results reported by Campello et al. who found that the use of eucalyptol did not improve filling material removal from Vertucci's type II molar mesial canals and isthmuses [14].
The removal of root canal filling materials has been analyzed by several methods such as tooth splitting [15,17,23,28], diaphanization [11,31], conventional and digital radiography [32], dental operating and stereomicroscope images [11,17,23,28], scanning electron microscopy (SEM) analysis [15], and CBCT [7,33]. To date, microcomputed tomography is the most preferred approach for its non-destructive nature and accuracy in qualitative and quantitative analysis of the retreatment procedures [5,19]. This technique provides longitudinal observation of the same sample throughout the experiment at different time points [5,12,34]. Moreover, it reduces the risk of sample selection bias by choosing teeth with minimal anatomical differences that have almost the same volume or aspect ratio of the root canals [20].
There are no unified criteria in terms of sample selection in in vitro investigations on the removal of root canal filling material by supplementary approaches. Researches usually choose oval-shaped root canals due to their noncircular anatomy, representing a challenge in retreatment cases [5,12,25,[35][36][37]. The sharpened notch of the oval extensions is a site accumulated with a residue of filling material, debris and bacteria. The amount of root canal filling remnants in oval canals has been observed to be higher [38] than in round canals [39]. The expansion of the XP-FR during its action enables the instrument's tip to touch and dislodge root filling material from the canal walls even in these inaccessible areas, which may be further removed by various irrigation solutions [12].
LIMITATION The major databases were used for the literature search. A possible limitation of this systematic analysis is that papers which are not listed in these sources might have been omitted. The current review includes articles published in the English language, which may have neglected potentially valuable scientific data.

CONCLUSION
XP-Endo Finisher-R is an effective supplementary approach in endodontic retreatment procedures. Nonetheless, it is rarely reported to achieve the complete removal of the root canal filling material. Further efforts should be focused on the design of new instruments that can improve the cleaning and disinfection of the root canal system during retreatment.
Micro-CT is a reliable, non-invasive analytical tool that can accurately measure the volume and the percentage of the remaining root canal fillings.