Importantly, the periapical status is more closely related to the underlying infectious condition than to the presence of the metallic fragment per se.

The potential consequences of overestimating the value of retrieval are illustrated by the cases shown in Figure 2A–2C. In each example, attempts to remove a separated instrument resulted in substantial radicular damage, despite the absence of apical radiolucency. These cases emphasize that procedural “success” should not be pursued at the expense of root integrity, and that the threshold for retrieval should be higher when preoperative findings do not indicate apical disease. Accordingly, when the biological benefit of removal is uncertain, conservative management, including retention of the fragment and clinical monitoring, may represent the more prudent and structurally protective strategy.

These clinical examples emphasize the need to differentiate technical success, defined as mechanically retrieving the fragment, from biological success, defined as achieving effective infection control and periradicular healing. Although retrieval may be technically feasible in many cases with contemporary magnification and ultrasonic techniques, successful fragment removal does not necessarily translate into improved biological prognosis (Suter et al., 2005; Parashos and Messer, 2006). Conversely, the dentin removal required to gain access, together with canal transportation or perforation during retrieval attempts, may weaken the root and reduce long-term tooth survival despite apparent procedural “success”.

Accordingly, removal of a separated instrument should be considered primarily in situations in which the fragment directly compromises access to infected tissues that are essential to eliminate for disease resolution. In all other scenarios, a more conservative strategy, including leaving the fragment in situ, bypassing the obstruction, or monitoring the case over time, may represent a more biologically sound and structurally protective approach (Ricucci et al., 2026).

This biologically driven framework supports a selective, case-specific approach to fragment management and challenges the routine assumption that retrieval is inherently beneficial. Instead, clinical decision-making should be guided by the likelihood that removal will materially improve disinfection and healing, balanced against the mechanical and structural risks associated with the procedure (Parashos and Messer, 2006).

Criteria for assessing clinical complexity

Assessment of clinical complexity is central to determining whether retrieval of a separated instrument is both biologically justified and technically reasonable. The decision to attempt removal should not be based solely on the presence of a fragment, but rather on a comprehensive evaluation of anatomical, mechanical, and biological variables that influence both the feasibility of retrieval and the risk of iatrogenic damage (Suter et al., 2005; Terauchi et al., 2022).

Factors to consider include:

• Presence or absence of apical pathology
• Fragment location within the canal space (coronal, middle, apical third)
• Fragment length and diameter
• Visualization of separated fragments and the influence of canal curvature
• Instrument type and characteristics
• Type and metallurgical properties of the instrument
• Operator experience and availability of specialized retrieval devices and techniques

Presence or absence of apical periodontitis

Apical periodontitis is a disease of microbial origin that results from infection and colonization of the root canal system (Siqueira and Rôças, 2022). Although physical or chemical insults may contribute to transient periradicular inflammation, extensive experimental and clinical evidence consistently demonstrates that microbial infection is the primary etiological factor in the initiation, progression, and persistence of apical periodontitis (Kakehashi et al., 1965; Bergenholtz, 1974; Sundqvist, 1976; Möller et al., 1981). These infections typically arise when the natural defense mechanisms of the pulp–dentin complex are compromised following pulp necrosis caused by carious exposure, trauma, periodontal disease, or operative injury, or after deliberate pulp extirpation during root canal treatment.

Bacteria exist predominantly in the form of biofilms within the root canal system. Biofilms are structured microbial communities adherent to canal walls and protected by an extracellular polymeric matrix (Ricucci and Siqueira, 2010). Once a periapical lesion becomes radiographically detectable on periapical radiographs or CBCT imaging, it can be inferred that the canal system has been colonized by bacteria. The apical extent of infection may vary considerably, with biofilms in some cases extending to the apical foramen and into apical ramifications and accessory canals (Ricucci and Bergenholtz, 2004). In contrast, in the absence of radiographic evidence of periapical pathology, the radicular pulp is generally presumed to be vital or minimally infected. In such a scenario, the likelihood of an established apical biofilm is substantially lower.

This distinction has direct implications for the management of separated instruments. In cases in which no apical radiolucency is present and the fragment is located in the most apical portion of the canal, particularly beyond a curvature and without direct visual access, the biological justification for aggressive retrieval is limited. Under such circumstances, the recommended approach is to avoid removal attempts, to inform the patient of the incident, and to institute periodic clinical and radiographic monitoring. Uncritical attempts to remove fragments located beyond canal curvatures, without appropriate biological diagnosis and anatomical assessment, may lead to significant complications, including excessive dentin removal, secondary instrument fracture, root perforation, and vertical root fracture (Hashem, 2007).

In contrast, when a periapical lesion is present, the biological rationale for intervention is stronger. In such cases, a separated instrument may obstruct access to infected canal segments and limit the delivery of irrigants and intracanal medicaments to the apical portion of the root canal system, thereby compromising disinfection. Under these circumstances, efforts should be directed toward bypassing the fragment or, when anatomically and biologically justified, implementing appropriate retrieval strategies. The technical considerations and management options for these scenarios are addressed in the following sections.

Fragment location within the canal space (coronal, middle, apical third)

The location of a separated instrument within the root canal system is one of the most influential determinants of both clinical complexity and biological justification for retrieval. Fragment position directly affects accessibility, the amount of dentin removal required to achieve straight-line access, and the risk of iatrogenic damage. As fragment depth increases, the balance between potential biological benefit and structural risk progressively shifts in favor of conservative management (Suter et al., 2005; Terauchi, 2012; Terauchi et al., 2022). 

Fragments located in the coronal third of the canal are generally associated with the highest likelihood of successful retrieval and the lowest risk of structural compromise. These fragments are more readily visualized under the operating microscope and require minimal dentin removal to achieve access. As a result, controlled ultrasonic techniques can often be applied with a relatively favorable risk–benefit profile (Ward et al. 2003). In such cases, retrieval is more likely to be both technically feasible and biologically acceptable, particularly when access to infected canal segments is required.

Fragments located in the middle third of the canal represent an intermediate level of complexity. Although visualization and access may still be possible, retrieval often requires more extensive dentin removal to create a staging platform and to straighten the canal path. This increases the risk of canal transportation and thinning of the root walls, particularly in teeth with narrow or curved roots (Ward et al., 2003; Hashem, 2007). Accordingly, middle-third fragments require careful case selection, with retrieval attempts justified primarily when there is a clear biological indication, such as persistent apical disease or obstruction of infected canal segments.

Fragments located in the apical third of the canal present the greatest clinical challenge and carry the highest risk of iatrogenic damage. Visualization is frequently limited or impossible. Access usually requires substantial dentin removal, particularly in curved canals. These anatomical constraints markedly increase the likelihood of canal transportation, strip perforation, and excessive weakening of the apical root structure (Suter et al., 2005; Terauchi, 2012; Terauchi et al., 2022). As a result, retrieval of apical third fragments should be approached with particular caution and generally reserved for cases in which a compelling biological indication exists and alternative strategies such as bypassing or surgical management are not feasible.

The clinical relevance of fragment location is illustrated in Figure 3. Figure 3A shows a mandibular second molar with a fractured instrument in the coronal third, where access and visualization are favorable. Figure 3B demonstrates a fragment in the middle third of a mandibular second molar, highlighting the increased complexity associated with deeper canal locations. Figure 3C illustrates a maxillary first molar with a fragment located in the apical third, exemplifying a scenario in which retrieval is technically demanding and associated with a heightened risk of structural compromise. Figure 3D shows a mandibular second molar in which the fracture lentulo spiral is partially located within the canal space and partially extending into the periodontal tissues. Such a scenario represents an additional layer of complexity that may further limit nonsurgical retrieval options.

Collectively, these examples emphasize that fragment location should be regarded as a primary stratification variable in clinical decision-making. As fragment depth increases, the threshold for attempting retrieval should likewise increase. Greater emphasis should be placed on biological necessity, preservation of root structure, and consideration of alternative management strategies. This location-based framework reinforces the central principle that anatomical feasibility must be carefully balanced against biological benefit, and that apical third fragments, in particular, demand a highly selective and conservative approach.

Case study

A representative clinical case is presented in Figure 4 to illustrate the complex interplay between biological indications, anatomical constraints, and procedural risks in the management of separated instruments. This case exemplifies how decision-making must extend beyond technical feasibility and incorporate a comprehensive assessment of root canal anatomy, infection status, and the potential for iatrogenic damage.

A 30-year-old woman was referred for specialist management of a mandibular right first molar with a history of previous root canal treatment complicated by instrument separation. According to the clinical history, multiple retrieval attempts had been performed prior to referral, and the patient sought further care because of persistent concern regarding the retained fragments and the long-term prognosis of the tooth. The pre-referral interventions were relevant to case complexity because they likely altered canal anatomy and reduced remaining dentin thickness, thereby increasing the risk of procedural complications during subsequent management.

Figure 4A shows the mandibular right first molar at the initial specialist visit, with three fractured instrument fragments located within the mesial canals. The fragments were positioned partly within the root canal system and partly extending into the periapical tissues, reflecting a highly complex anatomical and procedural scenario. This configuration immediately places the case in a high-risk category for nonsurgical retrieval, with the likelihood of limited visibility, restricted access, and the need for substantial dentin removal to engage the fragments.

Further assessment revealed significant procedural challenges after removal of the root filling material (Figure 4B). Placement of a Hedström file into the mesiobuccal canal demonstrated severe apical transportation (Figure 4C). This indicated that the original canal anatomy had already been compromised. The finding is clinically important, as it highlights how prior instrumentation errors and canal deformation can further increase the risks associated with fragment retrieval and reduce the margin for safe dentin removal.

Subsequent attempts resulted in successful removal of two lentulo spiral fragments. However, the third fragment was displaced into the periapical tissues (Figure 4D). This outcome illustrates an important procedural hazard associated with retrieval in complex cases, namely the potential for fragment displacement beyond the canal system. Such a mishap may further complicate management and introduce additional biological and surgical considerations.

Despite these procedural challenges, root canal filling was completed using a bioceramic sealer and gutta-percha (Figure 4E). At the 6-month follow-up, radiographic examination demonstrated complete regeneration of the periapical bone (Figure 4F) that is indicative of favorable biological healing. This outcome illustrates that even in highly complex cases involving multiple fragments and procedural complications, biological success may still be achieved when adequate disinfection and sealing are ultimately accomplished.

Fragment length and diameter

Fragment size materially influences both the degree of canal obstruction and the choice of management strategy. In general, the larger the diameter, taper, and overall cross-sectional footprint of a fractured instrument, the greater the likelihood that it will substantially occlude the canal lumen. This is particularly so for round-shaped canals. Under these circumstances, controlled dentin modification with ultrasonic tips is often required to create access and establish a staging platform to improve visibility and enable subsequent retrieval.

In contrast, a bypass strategy is often more appropriate if cone-beam computed tomography (CBCT) or periapical radiographs suggest that the fragment has a relatively small diameter or does not occupy the full cross-sectional area of the canal (Madarati et al., 2013). This situation may be encountered with instruments whose design leaves free space within the canal lumen, such as Lentulo spirals, XP-endo Shaper (FKG Dentaire SA, La Chaux-de-Fonds, Switzerland), XP-endo Finisher (FKG Dentaire SA), the self-adjusting file (ReDent Nova GmbH & Co. KG, Berlin, Germany), and similar instruments. In such cases, careful negotiation of a small file alongside the fragment can establish a glide path, permitting subsequent canal preparation and, when biologically justified, a later attempt at fragment removal.

Fragment length is a critical factor in determining retrieval complexity. While short fragments (1–3 mm) may involve less surface contact with dentin, they frequently occur within or beyond canal curvatures, areas of maximum structural stress. A short fragment wedged beyond a curvature represents one of the most challenging scenarios, as achieving straight-line access for retrieval often requires significant and potentially hazardous removal of dentin. In the clinical case illustrated in Figure 5A, although the fragment was short, its visibility under the operating microscope was the decisive factor. Once direct visualization was achieved, ultrasonic techniques alone were sufficient for retrieval, with limited dentin sacrifice (Figures 5B–C). Consistent with this clinical experience, Terauchi reported that fragments shorter than 4.5 mm may often be removed with ultrasonics alone within approximately 10 seconds during the retrieval phase (Terauchi, 2012).

In contrast, longer fragments (greater than 4.5 mm long), particularly those fractured within curved canals, are frequently bent rather than straight. These bent fragments increase both engagement with canal walls and resistance to ultrasonic vibration (Figure 6A). In such situations, two broad approaches may be considered. One approach involves removing dentin circumferentially around the fragment to disengage it and allow it to straighten, after which an attempt at removal can be made. Although this strategy may facilitate mechanical retrieval, it often requires substantial dentin sacrifice and may compromise root strength, thereby placing long-term tooth survival at risk.

Alternatively, the fragment may be retrieved coronally by securing its coronal portion under dry conditions, typically with a loop device to enable controlled traction while minimizing additional dentin removal. This loop-assisted strategy was used in the clinical case. Figure 6B shows the canal space immediately after successful fragment removal, demonstrating patency and the regained access created by retrieval. Following subsequent preparation, Figure 6C shows the completed obturation of the MB1 and MB2 canals. 

Among commonly used loop (lasso) systems are EndoCowboy (Köhrer Medical Engineering GmbH, Baden-Baden, Germany; Figure 7A), BTR Pen (CERKAMED Medical Company, Stalowa Wola, Poland; Figure 7B), and Yoshi Loop (DELabs – Dental Engineering Laboratories, Tokyo, Japan; Figure7C). Because loop-based retrieval can reduce the need for aggressive dentin removal, it is generally preferred as a second-line strategy when ultrasonic removal is unsuccessful, or when fragment length increases the likelihood of ultrasonic failure. Loop systems are indicated for retrieval of fragments longer than 4.5 mm, or when ultrasonic attempts exceed 10 seconds without progress (Terauchi et al., 2022).

Visualization of separated fragments and the influence of canal curvature

Nickel–titanium instruments are more susceptible to fracture in curved root canals. This feature represents the combined effects of cyclic fatigue and torsional stress in anatomically constrained canals (Farid et al., 2013). During clinical evaluation under an operating microscope, a separated fragment may be fully visible, partially visible, or not visible. This visibility spectrum is clinically important because visualization and accessibility are among the strongest predictors of retrieval success (Nevares et al., 2012).

When a fragment is clearly visible, particularly when it is short (less than 4.5 mm) and located within a relatively straight portion of the canal, retrieval is often achievable with limited dentin removal and a favorable risk–benefit profile. In such cases, ultrasonic techniques under magnification can typically be applied in a controlled manner, with a relatively low likelihood of canal deviation or excessive weakening of the root (Nevares et al., 2012; Terauchi, 2012).

Partially visible fragments are frequently encountered when the canal is filled with irrigating solutions. This phenomenon is attributable to optical refraction at interfaces with different refractive indices, which can create the impression of partial visibility along the instrument surface. In these cases, the clinician must decide whether to convert partial visibility into direct visualization under dry conditions. Achieving this typically requires selective dentin removal to improve straight-line access, often along the inner wall of the canal curvature. In thin root areas, even modest dentin sacrifice may substantially reduce remaining root thickness and increase the risk of structural compromise (Garg and Grewal, 2016).

Case-specific risk assessment using CBCT is advisable prior to undertaking dentin modification in these scenarios. Detailed evaluation of canal curvature, remaining dentin thickness, and proximity to external root surfaces is essential to avoid excessive dentin removal and to minimize complications such as perforation, strip defects, and structural weakening. In practical terms, CBCT-derived assessment helps define the “safe envelope” for dentin removal and clarifies whether the anticipated gain in visibility is likely to justify the inadvertent loss of intraradicular dentin.

The most challenging scenario involves fragments that are not visible under the microscope. Retrieval success for non-visible fragments has been reported to be substantially lower than for fragments that are directly visualized, and attempts to create straight-line access beyond a curvature are generally not recommended because of the high risk of over-enlarging the canal and compromising root integrity (Nevares et al., 2012). In such cases, a conservative strategy is often more rational, with primary emphasis placed on bypassing the fragment. This approach involves careful negotiation and preparation along the obstruction to regain access to the apical canal space. This procedure is followed by a limited and minimally invasive attempt at retrieval only if it becomes feasible without excessive dentin sacrifice. 

A limitation of this study is the follow-up period of 1–2 years in some cases. Although 1 year is the minimum observation period, favorable outcomes may reverse if infection or reinfection occurs (European Society of Endodontology 2006). While the majority of healing typically occurs within the first year (Orstavik 1996), apexification failures are most likely to happen within the first three years (Burns et al., 2023), emphasizing the importance of regular monitoring during this critical time.

In conclusion, the simplicity and reliability of apexification in cases with open apices, especially those requiring intracanal posts, including in retreatments. The results reinforce apexification as a predictable and effective treatment option, with a high likelihood of long-term survival, particularly when supported by a permanent coronal restoration and regular monitoring.