Comparative evaluation of tip diameter of different gutta-percha cones according to ISO 6877 measurement method and direct measurement method: an in vitro study

Article information

Restor Dent Endod. 2026;.e42

Publication date (electronic) : 2026 August 3

doi : https://doi.org/10.5395/rde.2026.51.e42

Rémy Balthazard^1,2,, Renaud Giess^1,3, Loïs Martrette⁴, Jean-Marc Martrette^1,5, Marin Vincent^1,6, Éric Mortier^1,2

¹Département de Dentisterie Restauratrice Endodontie, Faculté d’Odontologie de Lorraine, Université de Lorraine, Vandœuvre-lès-Nancy, France

²Université de Lorraine, CNRS, IJL, Nancy, France

³Université de Lorraine, ERPI, Nancy, France

⁴Faculté d’Odontologie de Lorraine, Université de Lorraine, Vandœuvre-lès-Nancy, France

⁵Université de Lorraine, UR 3450, DevAH, Vandœuvre-lès-Nancy, France

⁶Université de Lorraine, CNRS, LEM3, Metz, France

^*Correspondence to Rémy Balthazard, DDS, PhD Departement de Dentisterie Restauratrice Endodontie, Faculté d’Odontologie de Lorraine, Université de Lorraine, 7 avenue de la Forêt de Haye, 54500 Vandœuvre-lès-Nancy, France Email: remy.balthazard@univ-lorraine.fr

Citation: Balthazard R, Giess R, Martrette L, Martrette J, Vincent M, Mortier E. Comparative evaluation of tip diameter of different gutta-percha cones according to ISO 6877 measurement method and direct measurement method: an in vitro study. Restor Dent Endod 2026;51(4):e42.

Received 2026 March 3; Revised 2026 May 13; Accepted 2026 May 17.

Abstract

INTRODUCTION

Root canal obturation aims to achieve a hermetic seal of the endodontic space in order to preserve the aseptic conditions obtained after chemomechanical preparation [1–3]. This critical step, which directly influences the prognosis and long-term success of endodontic treatment, relies on the combination of one or more gutta-percha cones with an endodontic sealer or obturation cement, depending on the obturation technique selected by the clinician.

As a historically established material, gutta-percha was introduced into endodontic practice in the late nineteenth century [4]. Originally derived from the natural latex of Palaquium gutta, a tree native to Southeast Asia, it is now predominantly manufactured from a synthetic polymer, trans-1,4-polyisoprene [5]. Gutta-percha combines biocompatibility, dimensional stability, and thermoplasticity, making it the material of choice for root canal obturation.

The quality of root canal obturation largely depends on the adaptation of the gutta-percha master cone, which must exhibit a tip diameter precisely matched to that of the instrumented apical region. Clinicians therefore require master cones with accurate dimensions to effectively fill the root canal space while minimizing the risks of percolation and microbial proliferation [6–8]. Moreover, optimal adaptation is essential to prevent overfilling or underfilling, both of which are potential contributors to endodontic failure [9–12]. An unsuspecting practitioner, unaware of potential differences between the nominal and actual tip diameters of gutta-percha cones, could face endodontic complications such as postoperative sensitivity, flare-ups, damage to critical anatomical structures, or delayed, impaired, or absent healing of periapical inflammatory lesions [13,14].

The International Standard ISO 6877 (2021) defines the manufacturing requirements for gutta-percha cones by establishing strict criteria regarding tip diameter and taper in order to ensure standardization. However, this standard allows for certain dimensional tolerances, namely ±0.05 mm for tip diameters ≤0.25 mm and ±0.07 mm for diameters >0.25 mm [15]. Although these margins are intended to facilitate industrial manufacturing, they may result in potentially significant variability between the theoretical and the actual diameter. Several studies have confirmed the presence of such dimensional variations, thereby highlighting a possible mismatch between the tolerances permitted by the normative framework and the level of clinical precision required [16–19].

The first objective of this study was to compare the determination of gutta-percha cone tip diameters using the ISO 6877 protocol with a direct measurement method; the second objective was to assess whether commercially available gutta-percha cones compliant with ISO 6877 conform to the nominal dimensions declared by the manufacturers.

METHODS

Gutta-percha cones

Ten commercially available gutta-percha cone brands with two tip diameters and two constant tapers were selected for evaluation (Table 1): tip diameter 0.25 mm with a constant 6% taper (25/.06) and tip diameter 0.30 mm with a constant 4% taper (30/.04).

Table 1.

Gutta-percha cones included in the study

All measurements were performed in the technical platform for dental engineering at the Faculty of Dentistry of Lorraine, an ISO 13485-accredited facility, under controlled environmental conditions (temperature: 21°C ± 1°C). All measurements were performed by the same trained operator to reduce inter-operator variability. The measurements were not repeated. The gutta-percha cones were stored in the laboratory for 1 hour prior to the start of the measurements to allow thermal equilibration.

Only cones without any macroscopically detectable defects were included in the study (Figures 1 and 2). For each brand, ten cones of size 25/.06 and ten cones of size 30/.04 were randomly selected (n = 10). The tip diameters of the gutta-percha cones were subsequently determined according to the ISO 6877 protocol and by means of a direct measurement method, and the results were compared.

Figure 1.

Examples of rolled gutta-percha cones exhibiting manufacturing defects (images acquired using a Micro-Vu Sol 161 profilometer at ×120 magnification). (A) Non-rectilinear cone. (B) Taper defect in the apical region. (C) Apical deformation. (D) Torsional defect. (E) Marked lack of material associated with surface defects. (F) Defect at the apical tip. (G) Multiple calcium silicate agglomerates on the surface. (H) Large surface inclusion.

Figure 2.

Examples of injection-molded gutta-percha cones exhibiting manufacturing defects (images acquired using a Micro-Vu Sol 161 profilometer at ×120 magnification). (A) Large porosities at the apical tip. (B) Apical tip misalignment. (C) Longitudinal defect along its entire length.

Determination of the apical tip diameter according to ISO 6877

The apical tip diameter (D₀) was calculated from the cone diameter measured at 3 mm from the tip (d₃) and the taper (T) using the following formula: D₀ = d₃ − (3T/100).

The taper (T) was determined based on the cone diameters measured at 3 mm (d₃) and 16 mm (d₁₆) from the tip, according to the following formula: T = 100 × (d₁₆ − d₃) / 13 (Figure 3).

Figure 3.

Schematic representation of the measurement points required for the calculation of the apical tip diameter (D₀) of gutta-percha cones according to the ISO 6877 protocol.

The cones were positioned on a millimeter-graduated plate with their tips placed in contact with a fixed stop. For each cone (n = 10), measurements of d₃ and d₁₆ were performed under ×120 magnification using a Sol 161 profilometer (Micro-Vu, Windsor, CA, USA), which provides micrometric accuracy, in accordance with the requirements of ISO 6877. The profilometer calibration was performed in accordance with the quality management system requirements defined by ISO 13485 (calibration certificate C20250227-TF-1-B; MCE, Publier, France). The resulting D₀ values were subsequently recorded using Calc software (Micro-Vu).

Direct measurement of the apical tip diameter

Direct measurement was performed under ×120 magnification using a Sol 161 profilometer (Micro-Vu). To ensure reproducible positioning of the gutta-percha cones under the profilometer, the cones were embedded in a custom-prepared polymethyl methacrylate (PMMA) resin block so that only the first 4 mm of the tip protruded, strictly aligned with the axis of the profilometer (Figure 4). Two PMMA resin blocks measuring 10 mm on each side were prepared.

Figure 4.

Schematic representation of a polymethyl methacrylate resin block with a 25/.06 gutta-percha cone inserted into the prepared canal.

An orthogonal drilling to the upper surface of each block was performed using a 0.40-mm diameter drill mounted on a tensile/compression testing machine (Lloyd Instrument LS; Ametek, Berwyn, PA, USA) coupled with Nexygen software (Ametek).

Using the same tensile/compression testing machine, the two blocks were subsequently prepared with canal-shaping instruments, either size 25/.06 or 30/.04 (HERO Shaper; MicroMega, Besançon, France), mounted on an endodontic motor (Dual Move; MicroMega). The instruments were advanced to a depth of 14 mm, allowing 4 mm to extend beyond the resin block. Finally, to facilitate delineation of the region of interest under the profilometer, the upper surface of the resin blocks was stained black to enhance contrast (Figure 4).

The prepared blocks were placed on a holder aligned with the axis of the profilometer, and the different gutta-percha cones (n = 10) were inserted into their respective blocks (25/.06 or 30/.04) prior to diameter measurement (Figure 4). The directly measured D₀ values were subsequently recorded using Calc software.

RESULTS

Comparison between ISO 6877-based determination and direct measurement

Nonparametric Mann-Whitney U tests for pairwise comparisons revealed the following significant differences between the ISO 6877-based determination and the direct measurement of D₀.

1. Size 25/.06 cones (Table 2)

Table 2.

Comparison, for each commercial reference, of the mean apical tip diameter (D₀) values of 25/.06 gutta-percha cones obtained using the ISO 6877-based determination method and the direct measurement method

• Gutta-percha cones from VDC (p < 0.0001), as well as ROE (p < 0.001) and DEN (p < 0.05), exhibited mean D₀ values determined according to ISO 6877 that were significantly lower than those obtained by direct measurement.

• In contrast, SEP cones (p < 0.0001) showed a mean D₀ value determined according to ISO 6877 that was significantly higher than the value obtained by direct measurement.

2. Size 30/.04 cones (Table 3)

Table 3.

Comparison, for each commercial reference, of the mean apical tip diameter (D₀) values of 30/.04 gutta-percha cones obtained using the ISO 6877-based determination method and the direct measurement method

• Gutta-percha cones from VDC (p < 0.0001), as well as PRO (p < 0.001) and SEP (p < 0.001), exhibited mean D₀ values determined according to ISO 6877 that were significantly lower than those obtained by direct measurement.

• Conversely, ROE cones (p < 0.05) displayed a mean D₀ value determined according to ISO 6877 that was significantly higher than that obtained by direct measurement.

Comparison among manufacturers

Nonparametric Kruskal-Wallis tests with Dunn post hoc correction (α = 0.05) for multiple comparisons revealed the following significant differences.

1. Size 25/.06 cones—ISO 6877-based determination (Table 4)

Table 4.

Inter-brand comparison of the mean apical tip diameter (D₀) values of 25/.06 gutta-percha cones obtained using either the ISO 6877-based determination method or the direct measurement method

• VDC cones exhibited a mean D₀ value that was significantly lower than those of KOM (p = 0.05), SEP (p = 0.0001), FKG (p = 0.0001), RSG (p = 0.01), and KER cones (p = 0.001).

• ROE cones showed a mean D₀ value that was significantly lower than those of FKG (p = 0.0001), RSG (p = 0.01), KER (p = 0.001), and SEP cones (p = 0.0001).

• DEN cones exhibited a mean D₀ value that was significantly lower than those of SEP (p = 0.001) and FKG cones (p = 0.01).

• PRO and VDD cones demonstrated mean D₀ values closest to the nominal diameter.

2. Size 25/.06 cones—direct measurement (Table 4)

• ROE cones exhibited a mean D₀ value that was significantly lower than those of KOM (p = 0.01), FKG (p = 0.0001), RSG (p = 0.01), KER (p = 0.05), and VDD cones (p = 0.01).

• PRO cones showed a mean D₀ value that was significantly lower than that of FKG cones (problem of p = 0.05).

• FKG cones exhibited a mean D₀ value that was significantly higher than that of VDC cones (problem of p = 0.05).

• SEP, PRO, and DEN cones demonstrated mean D₀ values closest to the nominal diameter.

3. Size 30/.04 cones—ISO 6877-based determination (Table 5)

Table 5.

Inter-brand comparison of the mean apical tip diameter (D₀) values of 30/.04 gutta-percha cones obtained using either the ISO 6877-based determination method or the direct measurement method

• VDC cones exhibited a mean D₀ value that was significantly lower than that of VDD cones (p = 0.05).

• PRO, DEN, and KER cones demonstrated mean D₀ values closest to the nominal diameter.

4. Size 30/.04 cones—direct measurement (Table 5)

• ROE cones exhibited a mean D₀ value that was significantly lower than those of KOM (p = 0.01), FKG (p = 0.001), PRO (p = 0.001), KER (problem of p = 0.05), DEN (p = 0.01), and VDD cones (problem of p = 0.05).

• RSG cones exhibited a mean D₀ value that was significantly lower than those of FKG (problem of p = 0.05) and PRO cones (problem of p = 0.05).

• VDC, KER, and SEP cones demonstrated mean D₀ values closest to the nominal diameter.

Graphical analysis of D₀ values

Graphical representations of D₀ values for each 25/.06 and 30/.04 gutta-percha cone (Figures 5 and 6) allowed several observations to be made.

Figure 5.

Graphical representation of D₀ values (mm) for each 25/.06 gutta-percha cone obtained using the ISO 6877-based determination method and the direct measurement method.

Figure 6.

Graphical representation of D₀ values (mm) for each 30/.04 gutta-percha cone obtained using the ISO 6877-based determination method and the direct measurement method. Brand codes are defined in Table 1.

1. Size 25/.06 cones (Figure 5)

• The majority of D₀ values were located within the ISO tolerance range. However, KOM, FKG, KER, and DEN cones occasionally exhibited values outside the ISO-defined limits.

• The ISO 6877-based determination method showed a greater number of cones with tip diameters outside the accepted tolerance range compared with those obtained by direct measurement.

• With the exception of KOM, RSG, and VDD cones, the values obtained by direct measurement were homogeneous across all tested brands.

• Except for VDC cones, the results obtained using the ISO 6877-based determination were more heterogeneous than those obtained by direct measurement.

2. Size 30/.04 cones (Figure 6)

• With the exception of ROE cones, all other cones fell within the ISO tolerance range.

• For ROE cones, although the values were homogeneous, 60% of the cones exhibited D₀ values outside the ISO tolerance range.

• Except for ROE, DEN, and VDD cones, the values obtained by direct measurement were homogeneous.

• As observed for the 25/.06 cones, the ISO 6877-based determination method yielded more heterogeneous results than direct measurement, with the exception of VDC cones.

In summary, according to the ISO 6877 method and within the limitations of this study, the 25/.06 gutta-percha cones with tip diameters closest to the nominal value were ranked in descending order as follows: [PRO, KOM, VDD] > [RSG, KER, DEN, SEP] > [FKG, VDC, ROE]. According to the direct measurement method and within the limitations of this study, the ranking in descending order was: [PRO, SEP, DEN, VDC] > [KER, VDD, RSG, KOM] > [FKG].

According to the ISO 6877 method and within the limitations of this study, the 30/.04 gutta-percha cones with tip diameters closest to the nominal value were ranked in descending order as follows: [DEN, KER, PRO, FKG, KOM] > [SEP, VDD, RSG, VDC, ROE]. According to the direct measurement method and within the limitations of this study, the ranking in descending order was: [VDC, KER, SEP, VDD, DEN] > [KOM, PRO, FKG] > [ROE].

The cones with tip diameters closest to the nominal value were the rolled PRO cones, whereas those with tip diameters farthest from the nominal value were the rolled ROE cones.

DISCUSSION

The results of the present study demonstrate variability in the diameters of gutta-percha cones. This dimensional variability, which has already been reported in the literature [16–19], represents a clinical concern, as proper master cone adaptation directly influences three-dimensional sealing of the apical region and, consequently, the prognosis of endodontic treatment [12].

As the study was designed as a comprehensive benchmark analysis, no a priori sample size calculation was performed. Given the exploratory and multifactorial design of the present in vitro study, the sample size was selected in accordance with previous dimensional studies evaluating the variability of gutta-percha cones [16]. Furthermore, the inclusion of 10 manufacturers, two ISO sizes, two tapers, and two measurement methods resulted in a substantial overall number of experimental conditions and measurements.

The aim of the study was to conduct a broad comparative benchmark including all major industrial manufacturers of gutta-percha cones, as well as the two most commonly used ISO standardized sizes (0.25 mm and 0.30 mm) and tapers (4% and 6%). This approach inherently resulted in a high number of experimental conditions and a large overall sample size.

The tolerances permitted by the ISO standard (±0.05 mm to ±0.07 mm, depending on the nominal diameter) allow for dimensional discrepancies whereby a cone that is compliant from a normative standpoint may prove clinically unsuitable [16]. For 25/.06 cones, a tolerance of ±0.05 mm corresponds to a diameter range from 0.20 mm to 0.30 mm, which, for a 6% taper, translates into an approximate length variation of ±0.83 mm relative to the established working length. For 30/.04 cones, a tolerance of ±0.07 mm corresponds to a diameter range from 0.23 mm to 0.37 mm, which, for a 4% taper, translates into an approximate length variation of ±1.75 mm relative to the established working length. The deviations observed in our results relative to the nominal diameter (Tables 2–5 and Figures 5 and 6) illustrate instances of under- or overdimensioning, which may compromise apical adaptation of the master cone.

Furthermore, another explanation affecting the apical adaptation of the cone lies in its proper placement at working length, where lateral friction against the canal walls occurs despite a tip diameter smaller than the apical preparation diameter [20].

These dimensional variations were observed across all tested gutta-percha cone brands and were confirmed regardless of the method used to assess the apical tip diameter, whether ISO 6877-based determination or direct measurement. These findings underscore the need for a reassessment of conformity criteria in order to ensure optimal clinical reliability.

In the present study, VDC, ROE and DEN 25/.06 gutta-percha cones exhibited mean D₀ values determined using the ISO 6877 protocol that were significantly lower than those obtained by direct measurement (p < 0.0001, p < 0.001, and p < 0.05, respectively), whereas SEP cones showed significantly higher D₀ values when determined according to the ISO method (p < 0.0001) (Table 2).

For the 30/.04 cones, mean D₀ values determined using the ISO 6877 protocol were significantly lower than those obtained by direct measurement for VDC, PRO, and SEP cones (p < 0.0001, p < 0.001, and p < 0.001, respectively), while ROE cones exhibited significantly higher ISO-determined D₀ values compared with direct measurements (p < 0.05) (Table 3).

Taken together, for both tested nominal diameters, the differences observed between the two assessment methods suggest an inherent approximation associated with the ISO 6877 protocol, even though this discrepancy is not systematically statistically significant. Several factors may account for this variability. First, the ISO protocol assumes a constant taper between 3 mm and 16 mm from the tip and requires the use of this theoretical taper to determine D₀ from the d₃ measurement. Second, the ISO standard allows measurements to be performed in a single plane only, without three-dimensional consideration. As the morphology of gutta-percha cones is frequently irregular, as illustrated in Figure 1, it is likely that measured values vary depending on the measurement plane.

Moreover, when cones of identical nominal size were inserted into the PMMA resin blocks, they did not protrude to the same extent. Although differences in apical tip diameter may partly explain this finding, some cones exhibited greater protrusion despite similar measured D₀ values, suggesting variability in taper among the tested cones.

The viscoelastic and thermosensitive nature of this material makes it particularly susceptible to mechanical and thermal stresses encountered during the manufacturing, handling, transportation, and storage stages [21]. These fluctuations can induce expansion or shrinkage phenomena, which may at least partially explain the variability observed in our results [22]. Furthermore, the differences in chemical composition and crystalline structure of gutta-percha cones among different manufacturers represent an additional factor that may influence the dimensional stability of the cones and contribute to the discrepancies observed between nominal and actual dimensions [23]. In this context, maintaining gutta-percha cones under stable conditions appears essential to preserve their dimensional integrity [17,22]. Moreover, improved standardization of manufacturing processes, together with stricter control of material composition, may further contribute to reducing such variability [23].

The direct measurement method, by contrast, yielded predominantly homogeneous results (Tables 2–4; Figures 5 and 6). In addition, the mean D₀ values obtained by direct measurement were more closely aligned with the nominal values. This finding suggests that manufacturers generally comply with the specified apical tip diameters, whereas cone taper appears to be more irregular. Nevertheless, the difficulty in precisely defining the region of interest with this direct measurement technique makes it highly operator dependent.

The homogeneity of the D₀ values obtained by direct measurement for VDC cones, particularly for the 30/.04 size, may be partly explained by the presence of a flat apical tip rather than an ogival one. As demonstrated by Lopes et al. [24], a flat-ended apical design facilitates more accurate assessment by limiting measurement errors associated with the tapered geometry of conventional cone tips.

Furthermore, the industrial manufacturing process used for these cones, based on molding, may contribute to a closer adherence to the declared taper, resulting in more consistent and homogeneous D₀ values when determined using the ISO protocol.

VDC cones are indeed produced through an injection molding process of gutta-percha into standardized molds, in contrast to the cones from the other manufacturers included in this study, which are manufactured by rolling. It may therefore be assumed that the industrial standardization of the process and the intrinsic precision of injection techniques allow improved control over both tip diameter and taper.

However, for VDC cones, slightly higher mean D₀ values than the nominal diameter were observed using direct measurement (0.265 mm for 25/.06 and 0.302 mm for 30/.04), whereas the corresponding values determined according to the ISO protocol were lower (0.197 mm and 0.271 mm, respectively). In addition, the D₀ values obtained by direct measurement were statistically higher than those derived from the ISO 6877-based determination (p < 0.0001).

The higher values observed with the direct measurement method may be attributed, at least in part, to the presence of minor morphological irregularities at the cone tip, which were frequently identified in VDC cones and could locally increase the measured diameter, thereby affecting measurement accuracy (Figure 2A and B).

With regard to the results obtained using the ISO protocol, the presence of a “parting line” (Figure 2C), which may induce local irregularities in taper between d₃ and d₁₆ due to imperfect alignment of the two mold halves during the injection process, likely contributes to the discrepancies observed.

It should be emphasized that the demolding process of gutta-percha cones following injection molding may induce irreversible deformation, affecting both the apical tip diameter and the taper of the cones [25]. In addition, limitations in mold accuracy, combined with progressive mold wear over time, could represent a further source of dimensional variability [19,26]. Optimizing mold design, combined with rigorous monitoring of wear and the implementation of regular maintenance or replacement protocols, could thus help improve the dimensional accuracy of manufactured cones [27].

As demonstrated by the present results, for a given determination method, numerous statistically significant differences were observed among cones of the same nominal diameter, regardless of the manufacturer evaluated. The presence of such statistically significant differences (p < 0.05) is noteworthy, as manufacturers are expected to provide equivalent products with apical tip diameters calibrated according to standardized specifications. One possible explanation for these findings may lie, once again, in the challenges associated with achieving dimensional accuracy within industrial manufacturing processes.

In this context, some manufacturers have implemented advanced metrological quality-control procedures, including laser-based analysis. Such non-destructive techniques allow for the assessment of cone morphology, both in terms of apical tip diameter and taper, thereby promoting closer adherence to the declared dimensional specifications.

When using direct measurement, statistically significant differences in mean D₀ values were not more frequent for 25/.06 cones than for 30/.04 cones.

In contrast, when applying the ISO 6877 protocol, statistically significant differences were markedly more frequent among 25/.06 cones. For 30/.04 cones, only a single statistically significant difference was identified, between VDC and VDD cones (p = 0.05). In agreement with previous reports, these findings suggest that a 4% taper may be associated with fewer manufacturing-related deviations than a 6% taper, and that apical tip diameter accuracy does not appear to be greater for cones with a nominal diameter of 0.25 mm compared with those of 0.30 mm [19,28].

Nevertheless, it is noteworthy that gutta-percha cones from the PRO and KOM brands, manufactured by Sure Dent Corporation (Seongnam, Korea), consistently ranked among the most dimensionally accurate in the present study. Although these cones are produced using a rolling process, a high level of precision was observed, as no statistically significant differences in mean D₀ values were identified for either 25/.06 or 30/.04 cones. Moreover, these cones were characterized by a generally well-rectilinear geometry and exhibited virtually no defects upon profilometric examination. Taken together, these observations suggest that the manufacturing process alone is not sufficient to predict the dimensional accuracy of gutta-percha cones.

Beyond measurement and calculation considerations, which revealed substantial variability in D₀ values, numerous surface and morphological defects were observed during the analysis of the gutta-percha cones. Apical irregularities, morphological defects, impurities, and dye inclusions were identified (Figures 1 and 2). Similar observations were previously reported by Goldberg et al. [29].

In line with the present findings, several recent studies have emphasized the need to reconsider the manufacturing processes of gutta-percha cones in order to improve their dimensional standardization [18,28]. The production of undersized cones followed by calibrated trimming, as well as the use of injection molding techniques ensuring greater geometric stability, represent realistic approaches.

Accordingly, it may be beneficial to encourage reflection on the ISO 6877 standard concerning stricter tolerance limits and more direct measurement methods, in order to better align industrial standards with current clinical requirements. Furthermore, systematic laser-based quality control prior to commercialization could enhance the accuracy of both apical tip diameters and tapers of gutta-percha cones available on the market.

However, such developments may be associated with increased manufacturing costs, which would likely be passed on to clinicians. Nevertheless, the clinical implications of apical fit justify encouraging a reassessment of the current standard and the implementation of stricter dimensional tolerance criteria.

Further studies are warranted to expand upon these findings. Our work was limited to the evaluation of gutta-percha cones of sizes 25/.06 and 30/.04, as these dimensions correspond to the most commonly used final instruments in contemporary root canal shaping sequences. However, a wide range of gutta-percha cone sizes, in terms of both tip diameter and taper, may be used in clinical practice, which therefore represents a potential limitation of this study. Future investigations should include larger sample sizes and a broader range of manufacturers. In addition, incorporating the assessment of actual taper, alongside apical tip diameter measurements, appears essential for a comprehensive evaluation of gutta-percha cone quality. Although apical adaptation primarily depends on the accuracy of the tip diameter, excessive taper may prevent the cone from reaching the working length, thereby directly compromising obturation quality [30]. However, our study is limited to the evaluation of strictly dimensional parameters and does not assess the impact of potential mismatches between the final shaping instrument and the corresponding gutta-percha cone on apical sealing. Therefore, a direct clinical extrapolation of the results cannot be made.

Finally, the use of micro-computed tomography could enable three-dimensional morphological analyses, allowing for precise apical tip diameter measurements as well as detailed characterization of the true geometric properties of gutta-percha cones.

In the absence of further industrial improvements, the dimensional variability of gutta-percha cones should be taken into consideration by clinicians in daily practice. To ensure optimal master cone adaptation, clinicians are advised to select a cone with a diameter slightly smaller than that of the prepared canal and subsequently calibrate it using an endodontic gauge. This approach allows for precise adjustment of the apical tip diameter and significantly reduces the risk of over- or under-obturation. However, accurate gauging of the apical constriction diameter remains a critical prerequisite for the effectiveness of this strategy.

CONCLUSIONS

This study compared apical tip diameter determination according to the ISO 6877 protocol with a direct measurement method and evaluated the conformity of gutta-percha cones with nominal diameters. The findings demonstrated substantial dimensional variability among cones from different manufacturers and between the two determination methods. Direct measurement yielded values that appeared to more closely reflect the actual apical tip diameters, whereas ISO 6877-based determination was influenced by morphological irregularities and taper variations, potentially leading to under- or overestimation of D₀.

These results suggest that further consideration may be warranted regarding the tolerance limits defined in the current ISO 6877 standard, with a view to better aligning industrial specifications with clinical requirements. The adoption of advanced manufacturing processes and systematic metrological controls may enhance the accuracy and reliability of gutta-percha cones. Finally, the direct measurement approach evaluated in this study may represent a valuable complementary tool for assessing apical tip diameter accuracy alongside the ISO determination method.

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