Keywords
electronic foramen locator - endodontic - root canal length
Introduction
The precise location of the apical foramen has a significant impact on the success
of endodontic treatment and retreatment. Its definition acts as a guide for professionals
to correctly determine the apical limit to clean, shape, and seal the root canal system,
thereby minimizing damage to the periapical tissues.[1]
[2]
The role of the electronic foramen locator (EFL) in measuring root canal length (RCL)
has been extensively described in the literature.[3]
[4]
[5] Nevertheless, certain clinical conditions have been described as detrimental to
its accuracy. Factors such as limited apical penetration[6]
[7] or lack of apical fit[8] and the impossibility of achieving apical patency[9] have been mentioned as possible factors affecting the accuracy of EFLs. These three
factors seem to affect the relationship between the apical root canal third and the
periapical region.
The mechanism underlying current EFLs depend on the interpretation of impedance, which
in turn depends on two other electrical factors: resistance and capacitance.[10] Resistance is associated with the energy delivered by the instrument tip and is
closely linked to the apical limit.[10] Capacitance, on the other hand, is related to the energy transmitted along the instrument
and is correlated with its adaptation to the root canal walls.[10] It is, therefore, inevitable that clinical conditions that might affect the interpretation
of these factors are likely to influence the accuracy of electronic measuring instruments.
Among EFLs, Root ZX II (J. Morita, Tokyo, Japan) and Raypex 6 (VDW GmbH, Munich, Germany)
have undergone extensive evaluation, yielding results ranging from unsatisfactory
to highly satisfactory, contingent upon clinical conditions.[4]
[9]
[11] These devices interpret impedance at two separately radiated frequencies: the first
as a function of the quotient of impedance (0.4 and 8 kHz), and the second using the
square roots of impedance (0.5 and 8 kHz). Considering the variability in results,
new devices have been developed based on these frequency ranges designed to provide
accurate and reliable measurements regardless of clinical conditions. Therefore, it
is important to evaluate these devices under both ideal and varied conditions.
EPex Pro (MK Life Dental and Medical Products, Porto Alegre, Brazil) and CanalPro
(Coltene/Whaledent GmbH, Raiffeisenstrasse, Germany) are two recently launched devices
operating on similar mechanisms as the aforementioned devices: EPex Pro like Root
ZX II and CanalPro resembling Raypex 6. Although the manufacturers of these devices
claim similarities in operating systems with previous devices, they are equipped with
different electronic components and have a different design (display size, number
of colors on the display, etc.) providing operators with different interpretation
parameters. Possible variations related to these differences remain unknown.
To date, no study in the literature has specifically addressed the precision of different
EFLs under varying foraminal conditions. These anatomical variations undeniably impact
instrument adaptation to canal walls and consequently may affect the accuracy of electronic
determinations. Thus, the aim of this study is to determine the accuracy of Root ZX
II, Raypex 6, CanalPro, and EPex Pro in different foramen morphologies (fully formed
apices, immature foramen with parallel walls, and immature foramen with divergent
walls) with variable apical limit penetration depth (0.0 and −1.0 mm). The null hypothesis
is that there are no differences between the devices and that the differences in foramen
morphology are not significant regardless of apical penetration limit.
Materials and Methods
Sample Collection and Preparation
Prior to the study, the sample size was estimated to determine the number of samples
required. G*Power for Mac version 3.1 (Heinrich Heine; College of Duesseldorf, Duesseldorf,
Germany) was used along with the Wilcoxon-Mann-Whitney test. The data of Vasconcelos
et al[9] were considered in this estimation.
After sample size calculation and approval by the local research ethics committee,
30 healthy human mandibular premolars were collected for the study (n = 30). They were straight teeth with a length ranging from 18 to 22 mm and exhibited
fully formed apices. After standardized coronal approaches with diamond burs (#1012
and #3081; KG Sorensen, Cotia, Brazil) at high speed, the internal anatomy of the
teeth was analyzed. Teeth with two root canals, multiple nonpatent apical foramina
(AF), or a diameter exceeding 250 µm were excluded. Cusp tips were also modified to
provide flat references for positioning the instruments' penetration stops.
Cervical Preparation and Instrumentation
Cervical preparation was performed with #17/.08 files (MK Life Dental and Medical
Products, Porto Alegre, Brazil) activated by a VDW Silver electric motor (VDW GmbH,
Munich, Germany) calibrated to 2N.cm and 800 rpm. Penetration depth was limited to
two-thirds of the provisional RCL. Sodium hypochlorite at a concentration of 2.5%
(Biodinamica, Ibiporã, Brazil) was used as irrigating solution. The apical foramens
were standardized with K-Nitiflex #25 files (Dentsply-Sirona, Ballaigues, Switzerland).
A clinical microscope (Alliance, Campinas, Brazil) with 16x magnification was used
to determine the baseline RCL. Files were inserted into the canals until their tips
were visible in the AF opening. The distance between the rubber stop, aligned with
the occlusal reference, and the file tips was measured with a digital caliper (0.001 mm;
Mitutoyo, Suzano, Brazil) (RCL1).
Electronic Measurements
Electrical conductivity was facilitated using an alginate model (Jeltrate II; Dentsply
Brasil, Teresópolis, RJ, Brazil). The sample was divided into five subgroups of six
samples each for electronic measurements (EM); each subgroup underwent measurements
for no more than 30 minutes. Measurements were performed in triplicate by a single
operator using matched files at the desired depths. Instruments were used sequentially
and alternated for each repetition. Initially, the instrument was inserted to a depth
of 1.0 mm just before the AF (−1.0 mm), and file insertion halted upon this depth
being indicated on the instrument displays (EM1/-1). Subsequently, the rubber stops
were standardized based on occlusal references, files were removed from the root canals,
and length was measured with a digital caliper. Measurements were then taken at the
level of the foramen (EM1/0.0), indicating when AF was reached (0.0 mm).
For immature tooth tips, 3.0 mm of the apical portion was resected using a Zecrya
bur (Dentsply-Sirona) activated at high speed and under abundant irrigation to replicate
immature teeth with parallel AF walls. RCL2 was determined as before. EMs were taken
1.0 mm anterior to the AF (EM2/-1) and at the level of the foramen (EM2/0) following
the same parameters as for the full apex.
Finally, to mimic a tooth with an immature apex and divergent AF walls, a retrograde
preparation was performed by inserting #17/.08 instruments 4.0 mm in the apical–cervical
direction. RCL3 was determined, and EMs for both apical limits (EM3/-1 and EM3/0)
were performed as previously described. [Fig. 1] illustrates the tested foramen morphologies.
Fig. 1 Micro-computed tomography images presenting root canal morphologies: fully formed
apices (A); immature apical foramen with parallel canal walls (B); and immature apical foramen with divergent canal walls (C).
Calculation and Statistical Analysis
Mean errors between RCLs and EMs were calculated for two predefined penetration depth
limits (0.0 mm and −1.0 mm) using the formulas: Standard error (0.0 mm) = EMx/0-RCLx/0;
Standard error (−1.0 mm) = EMx/-1-(RCLx − 1.0 mm).
Statistical analysis involved considering both positive and negative values for measurements
beyond and below the AF, respectively. Absolute values of mean errors were utilized.
The Shapiro–Wilk test confirmed nonparametric distributions of the data. The Kruskal–Wallis
and Dunn tests were applied to determine potential differences between devices based
on foramen morphology and/or apical limit. Significance was set at 5.0%.
Results
[Table 1] presents the means, standard deviations, and medians of errors recorded by the EALs
across various AF morphologies and apical limits. Comparison between EFLs within each
foramen morphology/apical limit revealed a significant difference solely in measurements
at the foramen level (0.0 mm) with divergent canal walls. EPex Pro exhibited superior
performance, significantly surpassing Raypex 6 (p < 0.05).
Table 1
Mean, standard deviation and median of error (mm) provided by each device electronical
measurement in different foraminal conditions and penetration levels
|
Device
|
Complete apex
|
Immature apex
|
|
Parallel apical foramen walls
|
Expulsive apical foramen walls
|
|
0.0
|
−1.0
|
0.0
|
−1.0
|
0.0
|
−1.0
|
|
Mean[*]
|
SD
|
Median[*]
|
Mean[*]
|
SD
|
Median[*]
|
Mean[*]
|
SD
|
Median[*]
|
Mean[*]
|
SD
|
Median[*]
|
Mean[*]
|
SD
|
Median[*]
|
Mean[*]
|
SD
|
Median[*]
|
|
Root ZX II
|
0.26
|
0.14
|
0.25[a]
[A]
|
0.30
|
0.18
|
0.27[a]
[A]
|
0.25
|
0.13
|
0.28[a]
[A]
|
0.36
|
0.27
|
0.30[a]
[A]
|
0.34
|
0.23
|
0.31[ab]
[A]
|
0.38
|
0.33
|
0.31[a]
[A]
|
|
Raypex 6
|
0.27
|
0.14
|
0.29[a]
[A]
|
0.35
|
0.21
|
0.32[a]
[A]
|
0.29
|
0.18
|
0.31[a]
[A]
|
0.41
|
0.26
|
0.33[a]
[A]
|
0.49
|
0.33
|
0.46[b]
[B]
|
0.49
|
0.33
|
0.36[a]
[A]
|
|
EPex Pro
|
0.28
|
0.16
|
0.26[a]
[A]
|
0.32
|
0.21
|
0.30[a]
[A]
|
0.29
|
0.18
|
0.29[a]
[A]
|
0.42
|
0.27
|
0.38[a]
[A]
|
0.34
|
0.23
|
0.30[a]
[A]
|
0.39
|
0.24
|
0.41[a]
[A]
|
|
CanalPro
|
0.28
|
0.16
|
0.27[a]
[A]
|
0.29
|
0.20
|
0.27[a]
[A]
|
0.31
|
0.20
|
0.32[a]
[AB]
|
0.41
|
0.31
|
0.40[a]
[A]
|
0.43
|
0.25
|
0.39[ab]
[B]
|
0.49
|
0.30
|
0.39[a]
[A]
|
Abbreviation: SD, standard deviation.
* Mean error and median calculated in terms of absolute values of the determinations.
a,b Different lower case letters indicate statistically significant differences according
to the Kruskal–Wallis and Dunn tests (p < 0.05), considering the devices in each condition and penetration level.
A,B Different upper case letters indicate statistically significant differences according
to the Kruskal–Wallis and Dunn tests (p < 0.05), considering each device at different conditions taking in account each penetration
level.
Regarding individual EFL performance across different foramen morphologies, notable
differences were observed. Raypex 6 accuracy varied significantly with divergent canal
walls compared to other morphologies (p < 0.05). Similarly, CanalPro's accuracy significantly differed between divergent
canal walls and complete apices (p < 0.05). However, no significant differences were noted when considering the apical
penetration limit for each device (p > 0.05).
[Tables 2] and [3] depict the distribution of EFL measurements across the three foramen morphologies.
Acceptable measurements were those falling within a tolerance margin of ± 0.5 mm.
At the foramen level (0.0 mm), the accuracy of EFLs was notably influenced by foramen
morphology. Measurements were less accurate for immature AF with divergent walls (60–80%)
compared to complete apices or immature with parallel root canal walls (90–100%).
When inserted 1.0 mm below the AF, in general, all EFLs demonstrated reduced accuracy
compared to the values obtained at 0.0 mm, except for Root ZX II in complete AF (86.7%).
Across other EFLs/morphologies, accuracy remained below 80%, with no significant differences
observed in foramen morphologies.
Table 2
File tip position relative to the apical foramen for measurements performed to 0.0
|
Distance from apical foramen (mm)
|
Root ZX II
|
Raypex 6
|
EPex Pro
|
CanalPro
|
|
Complete apex
|
Immature apex
|
Complete apex
|
Immature apex
|
Complete apex
|
Immature apex
|
Complete apex
|
Immature apex
|
|
Parallel walls
|
Expulsive walls
|
Parallel walls
|
Expulsive walls
|
Parallel walls
|
Expulsive walls
|
Parallel walls
|
Expulsive walls
|
|
n
|
%
|
n
|
%
|
n
|
%
|
n
|
%
|
n
|
%
|
n
|
%
|
n
|
%
|
n
|
%
|
n
|
%
|
n
|
%
|
n
|
%
|
n
|
%
|
|
< −0.51[a]
|
3
|
10
|
0
|
0
|
6
|
20
|
4
|
13.3
|
2
|
6.7
|
12
|
40
|
3
|
10
|
3
|
10
|
6
|
20
|
3
|
10
|
2
|
6.67
|
10
|
33.3
|
|
−0.50 to −0.01[a]
|
26
|
86.7
|
22
|
73.3
|
21
|
70
|
24
|
80
|
19
|
63.3
|
17
|
56.7
|
24
|
80
|
19
|
63.3
|
22
|
73.3
|
27
|
90
|
19
|
63.3
|
20
|
66.7
|
|
0.00
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
1
|
3.3
|
0
|
0
|
|
0.01 to 0.50
|
1
|
3.3
|
8
|
26.7
|
3
|
10
|
2
|
6.7
|
9
|
30
|
1
|
3.3
|
3
|
10
|
8
|
26.7
|
2
|
6.7
|
0
|
0
|
8
|
26.7
|
0
|
0
|
|
> 0.51
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
a Negative value indicates file position short (or coronal) to the apical foramen.
Table 3
File tip position during measurements performed short of the apical foramen (−1.0 mm)
|
Distance from apical foramen (mm)
|
Root ZX II
|
Raypex 6
|
CanalPro
|
EPex Pro
|
|
Complete apex
|
Immature apex
|
Complete apex
|
Immature apex
|
Complete apex
|
Immature apex
|
Complete apex
|
Immature apex
|
|
Parallel walls
|
Expulsive walls
|
Parallel walls
|
Expulsive walls
|
Parallel walls
|
Expulsive walls
|
Parallel walls
|
Expulsive walls
|
|
n
|
%
|
n
|
%
|
n
|
%
|
n
|
%
|
n
|
%
|
n
|
%
|
n
|
%
|
n
|
%
|
n
|
%
|
n
|
%
|
n
|
%
|
n
|
%
|
|
< −1.51[a]
|
1
|
3.4
|
1
|
3.4
|
7
|
23.3
|
0
|
0
|
0
|
0
|
8
|
26.7
|
0
|
0
|
0
|
0
|
5
|
16.7
|
1
|
3.34
|
2
|
6.7
|
10
|
33.3
|
|
−1.50 to −1.01[a]
|
10
|
33.3
|
7
|
23.3
|
16
|
53.3
|
13
|
43.4
|
7
|
23.3
|
11
|
36.7
|
8
|
26.7
|
3
|
10
|
13
|
43.3
|
13
|
43.3
|
10
|
33.3
|
16
|
53.3
|
|
−1.00
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
|
−0.50 to −0.01
|
16
|
53.3
|
12
|
40
|
6
|
20
|
10
|
33.3
|
12
|
40
|
7
|
23.3
|
16
|
53.3
|
12
|
40
|
9
|
30
|
10
|
33.3
|
8
|
26.7
|
2
|
6.7
|
|
> 0.00
|
3
|
10
|
10
|
33.3
|
1
|
3.4
|
7
|
23.3
|
11
|
36.7
|
4
|
13.3
|
6
|
20
|
15
|
50
|
3
|
10
|
6
|
20
|
10
|
33.3
|
2
|
6.7
|
a Negative value indicates file position short (or coronal) to the apical foramen.
Discussion
In this study, the accuracy of four EFLs (Root ZX II, Raypex 6, EPex Pro, and CanalPro)
was evaluated during EMs across different foramen morphologies (complete apex, immature
foramen with parallel root canal walls, and immature foramen with divergent root canal
walls). The impact of the apical limit of penetration on measurements was also assessed.
The findings indicate no substantial differences among the evaluated EFLs. However,
it is evident that the accuracy of EFLs may diminish in cases of immature AF teeth
with divergent root canal walls, which is crucial information for clinicians during
procedures. Regarding the apical limit of penetration, it did not significantly influence
the accuracy of the tested EFLs. Thus, the null hypothesis was partially rejected.
To achieve the study's objectives, the alginate model was employed,[12] emphasizing the importance of prior cervical preparation[13] and AF standardization.[8]
[9] The alginate method already has it clinical relevance previously ensured.[14] These procedures aimed to minimize distortions associated with instrument apical
adaptation.[8]
[9]
[13] Considering the differences in foraminal morphology, apicoectomy was performed to
simulate immature teeth with wide AF and parallel root walls. Tapered instruments
were utilized to create wide AF with divergent canal walls in extreme conditions.
Regarding the results, all four tested EFLs demonstrated satisfactory accuracy and
safety. Irrespective of the apical limit or foramen morphology, the lowest and highest
standard errors were 0.26 (Root ZX II, 0.0 mm) and 0.46 mm (Raypex 6, 0.0 mm, immature
apex with divergent AF walls), respectively. Both Root ZX II and Raypex 6 exhibited
mean errors comparable to those observed in previous studies when tested on fully
formed complete apices.[15]
[16] EPex Pro and CanalPro had not been previously evaluated; nevertheless, their results
aligned with those of previously tested devices.
The presence of large AFs did not significantly affect the accuracy of the electronic
devices. This confirms findings from studies indicating good accuracy of EMs with
matched files in teeth with incomplete/enlarged apices[17]
[18]
[19] or deciduous teeth.[20]
[21] Discrepancies in EFL accuracy may occasionally stem from a lack of apical fit of
the instrument, especially in wide AFs, potentially interfering with capacitive impedance.
However, in AFs with divergent canal walls, achieving apical fit becomes impossible,
leading instruments to compensate for the reduction in capacitive factor. In this
study, the tested EFLs exhibited similarity; however, Raypex 6 and CanalPro, utilizing
similar mechanisms, displayed reduced accuracy with divergent AFs. This suggests that
these electronic devices' mechanisms are impacted by compromised interpretation of
the capacitive factor, resulting in a broader measurement error range.
Consequently, it can be inferred that EPex Pro and CanalPro offer a suitable accuracy
akin to that provided by Root ZX II and Raypex 6. They stand as dependable tools for
EMs even in nonideal foramen morphology scenarios. Concerning Raypex 6 and CanalPro
interpretations, clinicians should consider their limitations when encountering anatomical
variations like expansive apical foramen walls. Hence, endodontists must meticulously
approach EMs in teeth with immature apices and divergent canal walls, where the use
of EFLs might encounter limitations.
Conclusion
Considering the study conditions, it was possible to conclude that the four EFLs tested,
Root ZX II, Raypex 6, CanalPro, and EPex Pro, are reliable tools for determining the
apical limit during endodontic treatment, regardless of the desired apical limit.
However, unlike the others, Raypex 6 and CanalPro demonstrated an increase in precision
related to foraminal morphology.
