## 1 Introduction  
Endodontic therapy aims to eliminate bacterial infection from the root canal and maintain the health of the periapical area [1]. Factors such as procedural errors by the operator or tooth-related factors like complex canal anatomy can compromise its outcome [2, 3]. Not every endodontic therapy is successful, with success rates ranging from 86% to 96% [4]. In case of endodontic failure, the first therapeutic choice should always be non-surgical endodontic retreatment [5]. However, even this may have a negative outcome, with a success rate of approximately 78% [4, 6, 7, 8].  
Numerous techniques have been proposed to facilitate non-surgical endodontic retreatment, including stainless steel hand files, the use of gutta-percha solvents, ultrasonics,or NiTi instruments specifically designed for retreatments. Still, none of these techniques guarantees therapy success [9; 10; 11; 12].  
All endodontic treatment techniques are associated with the extrusion of debris into periradicular tissues through the apex, including necrotic pulp tissue, bacteria, irrigants, or dentinal chips [13; 14; 15]. However, in addition to the above factors, the extrusion of root filling materials such as sealer and gutta-percha from the root canal system must be considered in retreatment cases [16; 17; 18]. The extrusion of infected debris into periapical tissues leads to inflammation, causing vessel dilation, increased permeability, and the initiation of inflammatory cell chemotaxis [19; 20]. A clinical consequence of periradicular inflammation is post-operative pain [21; 22; 23]. The intensity of the pain depends on the amount of extruded debris and the virulence of microorganisms [19; 24; 25; 26]. Furthermore, the extrusion of apical debris can lead to delayed healing or even therapy failure due to a foreign body reaction [1; 27]. Although the extrusion of virulent microorganisms into periradicular tissues is recognized as an important causal factor in the development of painful symptoms, even extruded pulp and dentin tissue, though uncontaminated, have the potential to initiate an inflammatory reaction [28; 29; 30; 31].  
It is possible to reduce the extrusion into periapical tissues through various approaches, such as crown-down instrumentation techniques, which gradually provide access to the canal foramen, abundant phases of canal irrigation, or by choosing the correct file size for maintaining apical patency. Nevertheless, the extrusion of a certain amount of debris remains inevitable during canal instrumentation [19; 32; 33; 34].  
The introduction of instruments with reciprocating motion into the market has brought several advantages compared to instruments with continuous rotation, such as improved resistance to instrument fracture or increased instrument durability [35; 36; 37; 38; 39; 40].  
However, it is not clear whether this type of movement results in a difference in the amount of extruded debris during the endodontic retreatment procedure.  
The objective of this systematic review is to evaluate whether, in cases of non-surgical endodontic retreatment, reciprocating instruments cause greater extrusion of debris compared to instruments with continuous rotation. The hypothesis is that, in cases of non-surgical endodontic retreatment, the use of reciprocating instruments compared to instruments with continuous rotation, does not determine a difference in the quantity of extruded debris.