Key words: Anatomy - cone-beam computed tomography - endodontics - root canal treatment
INTRODUCTION
Lack of recognition of the anatomical complexities is one of the main causes of clinical
failure in the root canal treatments.[1 ] Recent and more detailed three-dimensional radiographic examinations are gaining
crescent popularity due to possibility of understanding the anatomy of root canal
system in advance. The methods used for studying endodontic anatomy can be divided
into ex vivo, performed on extracted teeth, and in vivo, performed directly on patients.
For many years, the “gold standard” for ex vivo methods was the clearing technique.[2 ] In recent years, the use of micro-computed tomography (CT) gained popularity. Micro-CT
is a three-dimensional X-ray technique that can identify the slightest anatomical
details with greater accuracy than the clearing technique.[3 ] However, this technique is time-consuming and expensive and can be also used only
on extracted teeth.[4 ]
The in vivo techniques for investigating the endodontic space are based on X-ray examinations.
Radiology is an essential tool in endodontic practice since it provides a clinician
with information otherwise not accessible. For a long time, the only available radiographic
method was difficult to interpret because of its two-dimensional nature: The overlap
of teeth and surrounding dentoalveolar structures allows to detect only few aspects
of their true three-dimensional configuration.[5 ]
[6 ]
The limits of traditional radiography have been largely overcome by the introduction
of cone-beam CT (CBCT), which is capable of providing three-dimensional images of
the teeth and their surrounding structures, i.e., images that are related to each
other according to the three orthogonal planes in space.[7 ]
[8 ]
[9 ]
CBCT is proving itself a reliable and nondestructive method for the in vivo study of teeth and can be used in the preoperative phase for diagnosis and treatment
planning, as well as for investigating endodontic anatomy.[10 ]
[11 ]
[12 ]
The mandibular first molar is the tooth that most frequently undergoes endodontic
treatment and its mesial root is characterized by a complex and variable root canal
anatomy.[13 ]
[14 ] This can affect the quality of instrumentation procedures and the incidence of iatrogenic
errors. Although many anatomical studies were conducted to analyze the root canal
morphology of mandibular first molar mesial root, no study evaluated the confluences
and the different trajectories of the two confluent canals. Therefore, these characteristics
were evaluated in the present study by means of CBCT.
MATERIALS AND METHODS
A total of 200 first mandibular molars, selected from the CBCT examinations of 130
patients, were examined. Seventy patients out of 130 had both left and right molars,
for a total of 140 teeth out of 200. The sample of patients consisted of 76 males
and 124 females, with an age ranging between 18 and 79 years. The examined CBCTs were
previously performed for surgical and implant placement reasons.
The following parameters were evaluated:
Number of canals
Root canal system configuration (using as a reference Vertucci classification)
Presence of apical confluences
Distance between confluences and apical foramina
Canal with a higher degree of curvature
Symmetry between left and right elements in the same individual.
Through the use of iCatVision™ software (Imaging Sciences International, Hatfield,
PA, USA), three-dimensional reconstructions were analyzed to evaluate the parameters
of interest.
The parameters evaluated first were number of root canals, presence of apical confluences,
and root canal system configuration according to the Vertucci classification. The
axial projections were examined by scrolling the images in coronal-apical direction;
the parasagittal ones were analyzed by reducing the thickness of the section to the
minimum (0.2 mm, voxel size) and checked from mesial to distal.
In regard to three-dimensional reconstructions, the cursor was aligned in such a way
as to intersect both canals so as to provide even in this case a vision from the mesial
side of the dental element.
The distance between apical confluences and apical foramina was measured on parasagittal
and three-dimensional reconstructions using the tool for distance measurement present
in the same software. When a root had an accentuated curvature on the mesial-distal
plane, it was not observable in its entirety in individual parasagittal frames. In
this case, it was impossible to directly measure the distance between confluences
and apical foramina; therefore, another method was used: The frame corresponding to
the root apex and the first frame in which appeared evident the union of the two canals
were identified, and taking into account that the distance between each frame and
the next was 0.2 mm, the distances between the frames were summed to obtain the value
of the distance between the confluence and the apex.
The identification of the canal with a higher degree of curvature in mesial vision
was based on the visual assessment by the operator, not being possible to apply any
of the geometrical methods that can be used to measure the mesial-distal curvature
on two-dimensional radiographs. In cases of doubt, the canal with the higher degree
of curvature was chosen as the longest one, in consideration of the geometric principle
that a circumference arc has a greater length than its subtended chord. The two canals
were signed by different colors, using the red one for the most difficult one, the
green for the easiest, and the blue for the confluences [Figures 1 ] and [2 ].
Figure 1 : Visualization of canal trajectories and (blue) confluences in three different first
molars (a, b, c). The most difficult canal is drawn in red.
Figure 2 : Visualization of canal trajectories and (blue) confluences in two molars (a, b)
presenting a more coronal confluence than teeth in Figure 1. The most difficult canal
is drawn in red.
DISCUSSION
In the present study, we investigated the root canal anatomy of mandibular first molar
mesial roots by means of CBCT. CBCT is a three-dimensional radiological method that
is able to overcome the limitations of traditional radiology and is gradually changing
the way endodontic treatment is prepared and executed.[4 ]
A systematic review of literature shows the presence, in the mesial root, of two canals
in 94.2% of cases; such canals would present a Vertucci Type IV configuration in 52.3%
of cases and a Type II configuration in 35% of cases.[14 ]
The root canal configurations of mandibular first molars reported in literature, however,
show great variability related to the different populations examined and the different
methods used.
A 2013 study carried out by means of CBCT on an Asian population reported a 76.86%
of Type IV configuration, followed by a 20.21% incidence of Type II configuration
and 1.81% of Type I configuration.[15 ]
Another study, on an Italian population, reported a 71.6% incidence of Type IV configuration
and a 28.4% incidence of Type II configuration.[16 ]
A study carried out on an American population reported a highly variable canal morphology
in the mesial root, in which the most frequent configuration found was Type V (22.7%).[17 ]
In the present work, 100% of the examined teeth showed the presence of two canals.
In 59% of cases, there was a Type IV Vertucci configuration, and in the remaining
41% of cases, there was a Type II configuration, numbers that appear congruent with
the statistics reported by de Pablo et al .[14 ]
The presence of apical confluences (i.e., the presence of multiple canals that become
a single canal in the apical-middle thirds of the root) and its relation to canal
curvature were evaluated in the present study. No studies so far have evaluated apical
confluences in these roots even if their recognition is clinically very relevant.
Confluent canals often result in abrupt curvatures that may overstress instruments
and cause their intracanal breakage.
This iatrogenic error, however, can be easily avoided by treating and filling the
straighter canal up to its apical end and the other canal only up to the junction
point.[1 ] Unfortunately, in the majority of cases, a preoperative radiograph cannot show confluence
and also which canal is the more straight one.
In the present study, all canal confluences were detected in the apical third or between
the middle third and the apical third of the root. Therefore, the number of elements
having apical confluences matched the number of elements having a Type II Vertucci
configuration.
The average distance between confluences and root apex was 2847 mm. These data are
clinically relevant because the apical portion of the canal is always more challenging.
An abrupt confluence in the last 3 mm can easily overstress an endodontic instrument,
which already accumulated metal stress in coronal and middle curvatures. Moreover,
confluent canals are very rarely identified through preoperative two-dimensional radiology,
making CBCT a key instrument for better planning of the therapy.
In the present work, we also investigated which canal (the MB or the ML) had a higher
degree of curvature when observed from a mesial point of view. Literature is quite
unanimous in this regard: Vertucci,[1 ] for example, has stated that the vestibular canal is usually the more curved one;
another 2015 study observed that the degree of curvature is significantly higher in
the MB canal compared to the ML one.[18 ] These observations were confirmed by the results of this study: in 85% of cases
(considering the entire sample analyzed), the canal with a higher degree of curvature
was the MB one.
However, no studies related the canal curvature and apical confluences. In the present
study, MB canals were the most curved canal in 78% of cases. Therefore, in the presence
of a confluence, the percentage of cases in which the ML canal is more curved than
the MB is higher than expected.
Symmetry between left and right mandibular first molars of the same patient was analyzed.
Few studies in the literature examined symmetry between contralateral molars, and
most of them focused on the number of roots and canals without analyzing in detail
the canal trajectories. A 2013 study on an Italian population showed symmetry (in
relation to the number of roots and canals) between contralateral molars in 70.6%
of cases;[19 ] another work,[20 ] published in 2015 and referring to an Indian population, observed symmetry between
the left and right first molars in 78.6% of cases, always in reference to the above
parameters.
In the present study, we aimed at gaining a much more detailed picture of the actual
root canal symmetry of contralateral teeth. Two roots may present the same number
of canals, but these canals may have different configurations, and also, the canal
with a higher degree of curvature may not be the same.
The results showed that symmetry was present in 88% of cases, but a more in-depth
analysis highlighted that in 74% of cases, the mesial roots of left and right molars
of the same patients presented the same Vertucci configuration and the same canal
with a higher degree of curvature; in 14% of cases, the canals had the same configuration,
but the canal with a higher degree of curvature was different; in 9% of cases, both
the Vertucci configuration and the curved canal were different; finally, in 3% of
cases, the root canal configuration was different, but the canal with a higher degree
of curvature was the same.
These data clearly show that there may be different degrees of symmetry between endodontic
anatomies of two similar dental elements belonging to the same individual.
CONCLUSIONS
Hence, we may conclude that apical confluences in mesial roots of mandibular molar
can be present in a significantly high number of cases: their recognition and the
evaluation of complexities in the trajectories of the different canals are essential
to prevent iatrogenic errors during canal instrumentation.
Financial support and sponsorship
Nil.
