Key words:
Cone beam computed tomography - maxilla - root canal anatomy
INTRODUCTION
Knowledge of internal morphology of the root canal system is the main part of planning
and performing endodontic treatments.[1] The main purpose of endodontic treatments is to perform mechanical and chemical
debridement of the whole length of the canal and fill it with biocompatible materials.[2] On the other hand, inability to properly identify, debride, and fill all canals
of a tooth is considered as the main cause of endodontic treatment failure.[3] Due to the more complex anatomy and common morphological variations, especially
the presence of second mesiobuccal (MB2) canal and its various forms, attempts have
been made in various studies to focus more on the MB root of maxillary molars.[2]
[4]
[5]
[6]
[7]
[8]
[9]
[10]
[11]
[12] The high incidence of endodontic treatment failure in maxillary first molars is
probably due to the inability to find and fill the MB2 canal. Finding the location
of MB2 is therefore the most important aspect of treatment of these canals.[13] Several factors including the race and age as well as variations in the research
methods are responsible for the widespread variations in the frequencies reported
for MB2 in maxillary molars.[2] Methods of root canal morphology evaluation include tooth clearing and staining,
analog radiography, digital radiography, microcomputed tomography (CT), cone beam
CT (CBCT), CT, and modified tooth clearing and staining.[2] Lack of anatomical superimpositions provides higher diagnostic accuracy for CBCT
compared to digital and conventional periapical radiographies.[14] In addition, in comparison with the conventional CT, CBCT has higher accuracy, higher
resolution, less scan time, and low absorption dose.[15] Multiple demographic studies have used CBCT for evaluation of the root shape and
root canals in different teeth.[2]
[3]
[13]
[15]
[16] Furthermore, several studies have been carried out on the root canal morphology
of the Iranian population using CBCT images.[5]
[7]
[8]
[17]
[18] Results of the mentioned researches are fairly inconsistent possibly due to the
variations in the racial characteristics of different populations even in the same
country. Hence, the present study was aimed at evaluating the MB root canal(s) anatomy
in the maxillary first and second molar teeth of a northern Iranian population as
well as determining the frequency of MB2 canals’ association with the patients’ sex
and the buccopalatal dimension of the roots.
MATERIALS AND METHODS
In this cross sectional study, CBCT images of 280 maxillary first and second molar
teeth (145 first molars and 135 second molars) were used. The images belonged to patients
who either attended the dental faculty of Rasht, Iran, or a private maxillofacial
radiology center in Rasht, Iran, in the years 2016 and 2017. These images were previously
acquired for different purposes including implant site assessment or impacted tooth
surgery. CBCT images were acquired by the same device ( New Tom, Verona, Italy) and
with the following exposure parameters: voxel size: 0.2–0.24 mm, field of view: 10
cm × 10 cm for standard zoom mode and 22.5 cm × 22.5 cm for full zoom mode. The ethical
approval code of this research was IR.GUMS.REC.1395.299 (registered by Guilan University
of Medical Sciences). All of the images had to be of proper quality and include the
upper jaw of the patients so that examination of the maxillary first and second molars
would be possible. Images of the maxillary first and second molars with severe caries
extended to the cervical or intermediate portion of the root and also endodontically
treated teeth in which the root canal treatment procedure had disrupted the original
morphology of the root canal system were excluded from the study. Furthermore, first
and second molar teeth with two roots were not included in the examination.
Axial and cross sectional CBCT views with 1 mm slice thickness and 1 mm slice interval
were evaluated by scrolling the images from the pulp chamber to the apex for each
first and second molar tooth [Figures 1] and [2]. Two maxillofacial radiologists individually evaluated the CBCT images. Presence
of MB2 canal within the MB roots of maxillary first and second molar teeth was assessed.
Root canal configuration was determined according to the classification of Weine[19] which describes the root canal types as follows: Type I – a root canal extending
from the pulp chamber to the apex, Type II – two root canals that connect near the
apex, Type III – two root canals leading to two distinct apical foramens, and Type
IV – a root canal that is divided into two canals and ends at two distinct apical
foramens. In addition to determining the number and shape of the MB root canals of
the maxillary first and second molars, the relationship between the number of canals
and patients’ sex as well as the buccopalatal dimension of the MB roots at the level
of cementoenamel junction where the canal orifice begins was evaluated. Chi square
test was used to examine the relationship between the number of MB canals and sex
and Mann–Whitney analysis was used to define the relationship between the number of
canals and the buccopalatal dimension of the MB roots. Level of statistical significance
was considered to be <0.05. The level of interobserver agreement was assessed with
Kappa test.
Figure 1: Axial cone beam computed tomography view shows two distinct canals in the mesiobuccal
root of the maxillary right first molar tooth
Figure 2: Axial and cross–sectional cone beam computed tomography views demonstrate two canals
associated with the mesiobuccal root of an endodontically treated maxillary right
first molar tooth
RESULTS
In this study, a total of 280 teeth, including 145 maxillary first molars (51.79%)
and 135 maxillary second molars (48.21%), were evaluated using CBCT images of an Iranian
population.
Frequency of second mesiobuccal in the mesiobuccal roots of maxillary first and second
molars
Nearly 44.8% of the maxillary first molars were shown to have MB2 and 55.2% had only
one canal in the MB roots. In the maxillary second molars, it was revealed that 18.5%
of the teeth had MB2 in the MB roots and 81.5% had a single canal in the mentioned
roots. It should be noted that none of the samples were found to have more than two
canals in their MB roots.
Frequency of root canal types
The highest and lowest frequencies of the canal types in the MB roots of the maxillary
first molars were related to Type I (55.2%) and Type IV (2.8%), respectively. Similarly,
in the maxillary second molars, Type I with the frequency of 81.5% and Type IV with
the frequency of 0.7% had the highest and lowest frequencies, respectively [Table 1].
Table 1:
Frequency distribution of canal types in the mesiobuccal root of maxillary first and
second molars
|
Tooth
|
MB canal type
|
Total(n)
|
|
Type I, n (%)
|
Type II, n (%)
|
Type III, n (%)
|
Type IV, n (%)
|
|
MB: Mesiobuccal
|
|
Maxillary first molar
|
80 (55.2)
|
17 (11.7)
|
44 (30.3)
|
4 (2.8)
|
145
|
|
Maxillary second molar
|
110 (81.5)
|
7 (5.2)
|
17 (12.6)
|
1 (0.7)
|
135
|
Relationship between the number of mesiobuccal root canals and sex
The CBCT images evaluated in the current study belonged to 182 women (65%) and 98
men (35%). [Table 2] shows the number of MB root canals in the maxillary first and second molars according
to the patients’ sex. No significant relationships were obtained between the number
of MB root canals and sex in both the first and second molar teeth.
Table 2:
Frequency distribution of number of mesiobuccal root canals in the maxillary first
and second molar teeth according to gender
|
Tooth
|
Number of MB root canals
|
Gender
|
Total
|
P*
|
|
Male, n (%)
|
Female, n (%)
|
|
*Chi-square. MB: Mesiobuccal
|
|
Maxillary
|
1
|
26 (32.5)
|
54 (67.5)
|
80
|
0.455
|
|
first molar
|
2
|
25 (38.5)
|
40 (61.5)
|
65
|
|
|
Maxillary
|
1
|
41 (37.3)
|
69 (62.7)
|
110
|
0.209
|
|
second molar
|
2
|
6 (24)
|
19 (76)
|
88
|
|
Relationship between root dimensions and the number of canals in the mesiobuccal roots
According to the findings of [Table 3], a significant relationship existed between the buccopalatal dimension of the MB
roots measured at the onset of the orifice and the number of MB root canals in the
maxillary first and second molars (P < 0.001) so that the mean buccopalatal dimension of the MB roots tended to be greater
in the roots containing two canals.
Table 3:
Frequency distribution of number of mesiobuccal root canals according to root dimensions
|
Number of MB root canals
|
Number of teeth
|
Mean±SD of root dimension (mm)
|
P*
|
|
*Mann-Whitney. SD: Standard deviation, MB: Mesiobuccal
|
|
1
|
190
|
6.04±0.80
|
<0.001
|
|
2
|
90
|
6.80±0.64
|
|
DISCUSSION
The present study was mainly aimed at determination of the frequency of MB2 canals
and their configuration types according to the classification of Weine[19] in the first and second molar teeth of the maxilla in a northern Iranian population.
Besides, assessment of any possible relationships between the presence of MB2 canals
and the buccopalatal dimension of the MB roots as well as the patients’ sex was performed.
Using CBCT images, the frequency of MB2 canals was calculated to be 44.8% in the first
molar and 18.5% in the second molar teeth. Regarding the configuration of canals based
on the classification of Weine,[19] the most encountered type of the MB canals was Type I. Possibility of the presence
of two canals in the MB roots was higher in roots with greater buccopalatal dimensions.
No sex predilection was found associated with the presence of MB2 in both the first
and second maxillary molar teeth.
Successful nonsurgical root canal treatment requires mechanical and chemical debridement
and three dimensional filling of the root canals.[20] Due to the more complex anatomy, particularly the presence of a MB2, various studies
and researches have focused on the MB roots of maxillary molars by different methods.[2]
[3]
[4]
[5]
[6]
[18] The ideal method should have definite criteria including accuracy, simplicity, and
applicability for in vivo conditions.[3] Today, CBCT has been used as a comparative method for studying the roots and root
canal anatomy of human teeth for in vivo environments and numerous studies have benefited from this imaging technique for
evaluation of the root form and root canal anatomy in different teeth.[2]
[3]
[4]
[6]
[7] It has been shown that in order to find the MB2 canal of the maxillary molar teeth,
CBCT is a reliable method in comparison with the gold standard of tooth sectioning.[13]
Results of the present study indicated that 44.8% of the first molars and 18.5% of
the second molars had MB2 canals. Furthermore, with respect to the root canal type
in accordance to the classification of Weine,[19] the obtained frequencies in descending order were as follows: Type I, Type III,
Type II, and Type IV. Rouhani et al.[7] investigated the root canal morphology of a number of extracted maxillary first
and second molar teeth of an Iranian population via CBCT imaging. According to the
classification of Vertucci, they found out that the most frequent canal type in all
the three roots of both the first and second molar teeth was Type I. On the contrary,
evaluation of the CBCT images of another Iranian population by Khademi et al.[8] revealed that in both the first and second molar teeth of the maxilla, Type II of
the Vertucci classification had the highest frequency in the MB roots. They also found
the frequency of MB2 canals to be 70.2% in the first molars and 43.4% in the second
molars. Another investigation on the Iranian population performed by Naseri et al.[17] came upon a frequency as great as 86.6% for MB2 canals in the maxillary first molar
teeth. The variations that are encountered in both the frequency and type of the MB2
canals in the mentioned studies are best explained by the racial characteristics of
the populations selected from the different regions of Iran, worthy to mention that
none were previously performed on the northern population as our research did.
In the study of Baratto Filho et al.,[1] which was aimed at investigating the internal morphology of the maxillary first
molars, 54 teeth were examined using CBCT. It was shown that 37.05% of three rooted
teeth had four canals. In 90.90% of the teeth with four root canals, only one apical
foramen was seen which could be considered analogous to the Type I of Weine’s classification.[19] Results of this study were quite close to ours in terms of frequency and type of
MB2 canals in the first molar teeth of the maxilla.
Lin et al.[4] estimated the frequency of MB2 canals to be 56% in the first molar and 7.7% in the
second molar teeth of a Taiwanese population using CBCT images. Another study performed
by Celikten et al.[6] on the CBCT images of a Turkish population revealed that the frequency of MB2 canals
was 50.6% and 22.8% in the maxillary first and second molar teeth, respectively, which
is approximately close to the results of our study. They also reported that on the
basis of Vertucci classification, Type I in the first molars and Type II in the second
molars were the most frequent varieties.
Shetty et al.[10] evaluated the CBCT images of endodontically treated maxillary first and second molar
teeth in an Indian population. They reported that the frequency of MB2 canals was
86.63% in the first molar and 29.4% in the second molar teeth. Based on their findings,
77.19% of the MB2 canals of the first molars and 90% of them in the second molars
had been missed during the root canal treatment procedure and subsequently 72.7% of
the first molars and 88.8% of the second molars showed to have periapical radiolucencies.
Zheng et al.[15] evaluated the root form and root canal anatomy of maxillary first molar teeth using
CBCT images in a Chinese population. They reported that the frequency of MB2 canals
was 52.24%. The frequency of MB2 canals in this study was highly consistent with the
findings of the studies performed on a selected population of Greece (53.4%)[12] and the Asian populations of Thailand (65%)[21] and Japan (58%),[22] but obviously lower than the frequencies reported for a Turkish (93.5%)[23] and a Pakistani (70.6%) population.[11]
Silva et al.[24] reported that the frequency of MB2 canals was 42.63% in the maxillary first molar
and 34.32% in the maxillary second molar teeth using CBCT images in a Brazilian population.
Furthermore, regarding the root canal types based on the Weine’s classification, they
claimed that Type I and Type III were the most frequently detected varieties, a finding
in complete agreement with the results of our study as well as the study of Neelakantan
et al. that investigated the root canal morphology of maxillary first and second molar
teeth in an Indian population via CBCT images.[3]
The wide variations that are observed among different studies on the frequency and
types of the MB2 canals in the maxillary molar teeth could be explained by the differences
in ethnicity, sample size, study design (including exclusion/inclusion criteria and
whether it is conducted clinically or experimentally), and method of root canal detection
and evaluation.
In the current study, no significant relationships were found between the patients’
sex and the number of MB2 canals in the maxillary first and second molar teeth (P = 0.829), a finding that is consistent with the study results of Celikten et al.,[6] Gomes Alves et al.,[9] and Zheng et al.,[15] however in contradiction with the results of the study of Sert and Bayirli.[23] On the other hand, Kim et al.[25] concluded that although no significant relationship is seen between gender and presence
of MB2 in the maxillary second molar teeth, it seems that men have higher rates of
MB2 canals in their maxillary first molars.
Mohammadzadeh Akhlaghi et al.[18] assessed the thickness of the MB roots in the maxillary first molar teeth and arrived
at the conclusion that in the roots with a single canal, the mesial and distal aspects
of the root have the least thickness and in the roots containing two root canals,
the thinnest parts are the distobuccal and the distopalatal sides. According to the
findings of the present study, a significant relationship was found between the presence
of MB2 canals in the maxillary first and second molars and the buccopalatal dimension
of the MB roots measured at the orifice level. The mean buccopalatal dimension of
the MB roots at the onset of the canal orifices tends to be greater in roots having
two root canals.
CONCLUSION
In the present study, MB2 canals did not show a very high frequency in the maxillary
first and second molar teeth, which is highly associated with the racial features
of the population. With respect to the canal types according to the classification
developed by Weine, Type I and Type III had the highest frequencies. There was no
relationship between sex and the frequency of MB2 canals; on the contrary, the mean
buccopalatal dimension of the MB roots showed to be interrelated with the number of
root canals.
Financial support and sponsorship
Nil.
