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Root and Root Canal Mo
Second Molars: A Micro–
Marco Aur�elio Versiani, DDS, MSc, PhD
and Manoel Dami~ao de Sousa-Neto, DD
from a pool of extracted teeth and stored in labeled individual plastic vials
Basic Research—Technology
doi:10.1016/j.joen.2012.03.026
containing 0.1% thymol solution until use.
The external morphology of the specimens was classified into 3 types according
to the divergence of their roots. In type I, palatal roots were widely divergent and
often longer and more tortuous than buccal roots that were less divergent and often
‘‘cow-horn’’ shaped. In type II, roots had blunt apices, run almost parallel to each
other, and were often shorter than type I tooth. In type III, palatal roots were less
divergent and often shorter than buccal roots that were widely divergent. Then,
the size of the mesiobuccal (MB), mesiopalatal (MP), distobuccal (DB), and disto-
From the Department of Restorative Dentistry, Dental
School of Ribeir~ao Preto, University of S~ao Paulo, S~ao Paulo,
S~ao Paulo, Brazil.
Address requests for reprints to Prof. Dr. Manoel Dami~ao de
Sousa-Neto, Rua C�elia de Oliveira Meirelles 350, 14024-070
Ribeir~ao Preto, SP, Brazil. E-mail address: sousanet@forp.usp.br
0099-2399/$ - see front matter
Copyright ª 2012 American Association of Endodontists.
tomography, root canal anatomy, root canal system
 After ethics committee approval (protocol 2009.1.972.58.4, CAAE
0072.0.138.000-09), 25 4-rooted human maxillary second molars were selected
Abstract
Introduction: This study examined the anatomy
of 4-rooted maxillary second molars by using
micro–computed tomography. Methods: Twenty-five
4-rooted maxillary second molars were scanned to eval-
uate the size and curvature of the roots; the distance and
spatial configuration between some anatomical land-
marks; the number of root canals and the position of
apical foramina; the occurrence of fusion of roots and
enamel pearls; the configuration of the canal at the
apical third; the cross-sectional appearance, the volume,
and surface area of the root canals. Data were compared
by using analysis of variance post hoc Tukey test
(a = 0.05). Results: The specimens were classified as
types I (n = 16), II (n = 7), and III (n = 2). The size of
the roots was similar (P > .05), and most of them pre-
sented straight with 1 canal, except the mesiobuccal
that showed 2 canals in 24% of the samples. The config-
uration of the pulp chamber was mostly irregular
quadrilateral-shaped. The lowest mean distance of
the orifices was observed between the buccal roots
(P < .05). Accessory canals were present mostly in the
apical third. Location of the apical foramina varied
considerably. Fusion of roots and enamel pearls
occurred in 44% and 8% of the samples, respectively.
Mean distance from the pulp chamber floor to the furca-
tion was 2.15 � 0.57 mm. No statistical differences
were found in the bi-dimensional and 3-dimensional
analyses (P > .05). Conclusions: All analyzed parame-
ters showed differences between roots, except for the
length of the roots, the configuration of the canals
at the apical third, cross-sectional appearance,
volume, and surface area of the canals. (J Endod
2012;38:977–982)
Key Words
Four-rooted maxillary second molars, micro-computed
JOE — Volume 38, Number 7, July 2012
rphology of Four-rooted Maxillary
Computed Tomography Study
, Jesus Djalma P�ecora, DDS, MSc, PhD,
S, MSc, PhD
It is common knowledge that the goal of endodontic therapy is the thorough cleaningand obturation of the entire root canal system. Therefore, a comprehensive under-
standing of the root and the root canal morphology is imperative to reduce endodontic
failure caused by incomplete root canal preparation and obturation (1). Despite a wide
range of anatomical variations associated with maxillary molars that has been reported
(2), the presence of double palatal roots has been considered as a rare phenomenon
(3–15) most frequently limited to the maxillary second molar teeth (12, 16). The
etiology behind this variation is still unclear, but it is probably related to
disturbances of the Hertwig epithelial root sheath by exogenic or endogenic factors
during the development of the roots (17).
Since the first report on endodontic treatment of maxillary molars with 2 palatal
roots (18), similar cases have been published (3–7, 9–16, 19, 20), and some attempt
has been made to establish its incidence. In a survey of 1200 maxillary second molars,
Libfeld and Rostein (20) found only 0.4% of the sample exhibiting this condition,
whereas in a retrospective study of 520 completed endodontic treatments of maxillary
second molar teeth, Peikoff et al (16) indicated that the frequency of this variation was
nearly 1.4%. Nevertheless, both studies are compromised by lack of methodological
accuracy in the detection of these extra roots, considering that the interpretation
of these morphologic variations in radiographs is difficult and very often impossible
(3, 11, 20). Thus, neither the inspection nor a 2-dimensional (2D) radiograph could
give exact information about the number, location, or morphology of the roots or root
canals in an in vivo situation (11).
In recent years, significant noninvasive technological advances for imaging dental
structures have been introduced, including digital radiography, densitometry, magnetic
resonance imaging, ultrasound, and computed tomography (21). The development of
X-ray micro–computed tomography (micro-CT) has gained increasing significance in
endodontic research because it offers a reproducible technique that can be applied
quantitatively as well as qualitatively for the 3-dimensional (3D) assessment of the
root canal system (22–25).
Although the existence of maxillary secondmolars with 4 separated roots has been
reported by several authors (3–16, 19, 20), no study has been undertaken to evaluate
its anatomy by using micro-CT. Thus, considering the lack of detailed information on
this subject, the aim of this ex vivo study was to investigate the internal and external
morphology of this anatomical variation by using micro-CT.
Materials and Methods
palatal (DP) roots and the distance between the anatomical apexes were measured by
Micro-CT Study of 4-rooted Maxillary Molars 977
using a digital caliper with a resolution of 0.01 mm (Mitutoyo MTI
Corporation, Tokyo, Japan). The direction of root curvature and
the occurrence of fusion and enamel structures at the root were
v.2.1 software (Skyscan) were used for 3D visualization of the speci-
mens (supplemental Video S1 is available at www.jendodon.com).
The results of 2D and 3D analysis as well as the distances between
imal views. Considering the buccal perspective, no curvature was
Figure 1. Buccal and palatal views of 3D reconstruction of 3 4-rooted maxillary second molars, illustrating the classification system based on the divergence of the
roots.
Basic Research—Technology
also evaluated.
After being washed in running water for 24 hours, each tooth was
dried, mounted on a custom attachment, and scanned in a micro-CT
scanner (SkyScan 1174v2; SkyScan N.V., Kontich, Belgium) at an
isotropic resolution of 22.6 mm. Images of each specimen were recon-
structed from the apex to the coronal level with dedicated software
(NRecon v1.6.4; SkyScan), which provided axial cross sections of the
inner structure of the samples. Data Viewer v.1.4.4 software (SkyScan)
was used to evaluate the number and location of root canals, the posi-
tion of the apical foramina, the presence of apical delta, the configura-
tion of the root canal orifices, and the distance from the pulp chamber
floor to the furcation. CTAn v1.11 software (Skyscan) was used for 2D
evaluation (area, perimeter, roundness, major diameter, and minor
diameter) of the root canal 1 mm short of the apical foramen. Volume,
surface area, and cross-sectional appearance, expressedas the struc-
ture model index (SMI), were also measured. CTVox v.2.2 and CTVol
Figure 2. 3D reconstruction of 4-rooted maxillary second molar showing mean di
and distal (B) roots, as well as between anatomical apexes (C).
978 Versiani et al.
observed in the MP root. The MB root curved only distally, whereas
DB and DP roots curved in both mesial and distal directions. From
a proximal perspective, most curvatures were observed in the MP
some anatomical landmarks were statistically compared by using anal-
ysis of variance post hoc Tukey test, with the significance level set as 5%,
by using SPSS v17.0 for Windows (SPSS Inc, Chicago, IL).
Results
Sixteen specimens were classified as type I (64%), 7 as type II
(28%), and 2 as type III (8%) (Fig. 1). Statistical analysis revealed
no difference between the length of the roots (P = .07), whereas the
mean distance between the apexes of MB and DB roots was significantly
lower than MB-MP, MP-DP, and DP-DB distances (P = .0001) (Fig. 2).
Most of the roots presented straight from both buccal and prox-
stance (� SD) from cementoenamel junction to anatomical apex of mesial (A)
JOE— Volume 38, Number 7, July 2012
root. No curvature toward the buccal direction was found in the DB root
(Table 1).
Fusion of roots occurredmore often withMB root (n = 8) and less
frequently with DP root (n = 3) (Fig. 3A–D). In 2 specimens, the pres-
ence of enamel pearl in the furcation area of the palatal roots was
observed (Fig. 3E and F). All roots had 1 main canal except the MB,
which presented 2 canals in 6 specimens (Fig. 3G and H).
Accessory canals were located mostly in the apical third of the
roots, and no furcation canals were found (Table 2). The location of
the apical foramina varied considerably, tending to the buccal aspect
of the MP roots (48%), to the palatal aspect of the DP roots (28%),
and to the distal aspect of the MB (40%) and DB roots (24%)
(Table 3). Apical delta was observed only in 8% of the MP (n = 2)
and 4% of the DB (n = 1) roots.
The spatial configurations of the orifices in relation to the pulp
chamber floor were classified as type A (irregular quadrilateral-
shaped, 56%), type B (trapezoid-shaped, 24%), type C (lozenge-
shaped, 12%), and type D (kite-shaped, 8%). Mean distance between
the buccal orifices (3.48 � 2.43 mm) was significantly lower than
MP-MB orifice distance (5.09 � 1.34 mm) (P < .05) (Fig. 4), and
the thickness of the pulp chamber floor ranged from 1.20–3.13 mm
(2.15 � 0.57 mm). 2D evaluation of the root canal 1 mm short of
TABLE 1. Percentage Distribution (n) of Direction of Root Curvature Observed in Both Buccal and Proximal Views of 25 4-rooted Maxillary Molars
Direction of curvature
Roots (buccal view) Roots (proximal view)
MB MP DB DP MB MP DB DP
None (straight) 64 (16) 100 (25) 80 (20) 84 (21) 84 (21) 88 (22) 96 (24) 80 (20)
Toward distal 36 (9) – 8 (2) 12 (3) – – – –
Toward mesial – – 12 (3) 4 (1) – – – –
Toward palatal – – – – 8 (2) 4 (1) 4 (1) 4 (1)
Toward buccal – – – – 8 (2) 8 (2) – 16 (4)
Basic Research—Technology
Figure 3. 3D reconstructions of 4-rooted maxillary second molars showing frequ
and internal anatomy of MB root presenting 1 (G) and 2 (H) root canals.
JOE — Volume 38, Number 7, July 2012
ency and location of fused roots (A–D), presence of enamel pearls (E and F),
Micro-CT Study of 4-rooted Maxillary Molars 979
the apical foramen (area, perimeter, roundness, major diameter, and
minor diameter) as well as volume, surface area, and SMI analysis
showed no statistical differences between the roots (P > .05; Table 4).
Discussion
The most extensive study published on the anatomy of 4-rooted
maxillary second molars classified 22 molars into 3 types (I–III)
according to the separation level and divergence of the roots (19).
Whereas type I consisted of teeth in which the palatal roots were
more divergent than the buccal ones, types II and III were based on
the size and fusion of roots. In the present study, a new classification
system based only on the divergence of the roots is proposed,
TABLE 2. Percentage Distribution (n) of Sample That Presented Accessory
Canals
Root third
Roots
MB MP DB DP
Cervical – – – –
Middle 4 (16) 2 (8) 2 (8) 2 (8)
Apical 9 (36) 6 (24) 6 (24) 7 (28)
Total 13 (52) 8 (32) 8 (32) 9 (36)
TABLE 3. Percentage Distribution (n) of Apical Foramen Position in Roots of
25 4-rooted Second Maxillary Molars
Foramen position
Roots
MB MP DB DP
MB – – – 8 (2)
MP 8 (2) – 16 (4) –
DB 4 (1) 8 (2) 4 (1) 8 (2)
DP 16 (4) 4 (1) 8 (2) 4 (1)
Buccal 8 (2) 48 (12) 16 (4) 12 (3)
Palatal 8 (2) 16 (4) 16 (4) 28 (7)
Mesial 16 (4) – 16 (4) 20 (5)
Distal 40 (10) 24 (6) 24 (6) 20 (5)
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Figure 4. Coronal view of 3D reconstruction of pulpal chamber floor of 4-rooted
mean distance (� SD) between them.
980 Versiani et al.
maxillary second molars showing 4 spatial configurations of canal orifices and
JOE— Volume 38, Number 7, July 2012
is of
ng
–0.
–2.
–0.
–1.
–0.
–9.
–44
–4.
Basic Research—Technology
considering that fusion might occur in different levels of all roots
(4, 10, 11), making this proposal not feasible. Thus, Christie’s types
II and III were combined into one category (type II), and a new
variation was described as type III. The average size of the roots
ranged from 12.13–13.07 mm, similarly to a previous study in
which the mean sizes of MB, DB, and palatal roots of 220 3-rooted
maxillary second molars were 12.3, 13.0, and 13.6 mm, respectively
(26). The analysis of the external surface of the roots also showed the
presence of enamel pearl in the furcation area of 2 specimens as well
as Christie et al (19), who observed its presence in 3 specimens during
the radiographic examination of 16 4-rooted maxillary second molars.
The knowledge of the direction of curvature of each root is of
particular importance, especially when the curvature is toward the
buccal or palatal direction, because it could not be visualized in radio-
graphs (26). In the present study, most of the roots presented straight
from both buccal and proximal perspectives and most of the curvatures
toward mesial or distal. Special attention should be given in relation to
MP roots by considering that from a proximal perspective, most curve
toward buccal (20%). Similarly, eccentric placement of the apical
foramina was recognized in all specimens, and its location varied
considerably, as observed in other studies (27, 28).
A new classification system based on the configuration of the canal
orifices in relation to the pulp chamber floor was also proposed. The
TABLE 4. 2D Analysis of Canals at 1 mm from Major Foramen and 3D Analys
MB MP
Mean ± SD Range Mean ± SD Ra
2D analysis
Area (mm2) 0.09 � 0.11 0.02–0.56 0.08 � 0.08 0.02
Perimeter (mm) 1.12 � 0.56 0.41–3.14 1.0 � 0.49 0.28
Roundness 0.61 � 0.13 0.40–0.83 0.61 � 0.10 0.39
Major diameter
(mm)
0.41 � 0.19 0.15–1.03 0.37 � 0.19 0.11
Minor diameter
(mm)
0.27 � 0.15 0.07–0.82 0.25 � 0.13 0.02
3D analysis
Volume (mm3) 2.41 � 1.61 0.66–7.31 2.66 � 2.18 0.13
Surface area
(mm2)
20.83 � 7.52 9.44–35.82 20.34 � 9.62 4.0
SMI 2.71 � 0.49 1.7–3.66 2.83 � 0.53 1.63
Analysis of variance (P > .05).
shortest distance observed between the canal orifices of buccal roots
might be explained by considering that most of the sample comprised
type I configuration. Besides, the position of the canal orifices observed
in the present study suggests that the access cavity on 4-rooted maxil-
lary molars should be wider than usual on the palatal aspect (3), with
the access outline to be trapezoidal rather than triangular or square
(3). This is especially important in divergent palatal roots (type I)
because the MP canal orifice might be difficult to visualize (19).
Such classifications are expected to be valuable for making proper
treatment plansand help the clinician to diagnose and negotiate the
root canal anatomy.
There is a wide range of variation in the literature with respect to
the number of canals in maxillary molars (2, 26–32). In the present
study, all roots had only 1 main canal (2), except the MB root that pre-
sented 2 canals in 26% of the sample. This frequency, however, was
lower than previous reports that showed a percentage of 2 canals in
the MB roots of 3-rooted maxillary second molars to be higher than
40% (26–28). This difference might be related to the small sample,
but it is supported by most of previous reports in which authors
JOE — Volume 38, Number 7, July 2012
failed to find a second canal in theMB root of 4-rooted maxillary molars
(3–16, 19, 20).
In the present study, furcation canals were not found (29), and
the mean thickness of the pulp floor (2.15 � 0.57 mm) was similar
to a previous study in which the distance from the furcation to the
pulp floor in maxillary molars has been shown to be #3 mm
(33). In this context, the risk of accidental furcation perforation
should be considered.
Accessory canals were observed mostly at the apical third of the
root, and its frequency was higher (38%) than a previous study
(23.3%) that evaluated 3-rooted maxillary second molars (29). This
dissimilarity might be explained by considering differences of the
samples and methods used to evaluate the root canal morphology.
Effective canal debridement relies on accurate determination of
the working length and adequate apical canal enlargement, because
it can overcome the potential limits of irrigation in the apical area, opti-
mizing root canal disinfection (34). In this way, the knowledge of the
diameter of the canal in the apical third might enable the clinician to
provide a more predictable root canal preparation. In the present
study, the major diameter of the canal 1 mm short of the apical foramen
averaged 0.4 mm, which means that debridement in the apical third
could be improved with a larger instrument than an ISO size 40.
The cross-sectional appearance of the root canal, round or more
Root Canals of 25 4-rooted Second Maxillary Molars
Roots
P
value
DB DP
e Mean ± SD Range Mean ± SD Range
38 0.07 � 0.06 0.02–0.25 0.09 � 0.11 0.02–0.56 .821
72 1.02 � 0.50 0.33–2.20 1.0 � 0.54 0.22–2.80 .825
78 0.55 � 0.17 0.22–0.82 0.64 � 0.15 0.30–0.90 .116
11 0.39 � 0.21 0.14–0.90 0.36 � 0.17 0.08–0.89 .821
57 0.25 � 0.16 0.02–0.85 0.27 � 0.17 0.02–0.82 .959
79 1.88 � 1.32 0.22–5.56 2.64 � 2.25 0.36–8.44 .436
.25 16.52 � 6.52 4.93–30.27 19.12 � 9.65 6.35–38.09 .163
06 2.25 � 0.53 1.83–3.31 2.79 � 0.38 1.84–3.43 .777
ribbon-shaped, is expressed as roundness. This index varies from
0 (parallel plates) to 1 (perfect ball). In this study, the average round-
ness of the root canal 1 mm short of the apical foramen ranging from
0.55–0.64 indicated that the canals of 4-rooted maxillary second
molars are oval-shaped in this region, in accordance with a previous
publication that demonstrated similar configuration of the canals in
the apical third of 3-rooted maxillary second molars (35).
Algorithms used in micro-CT evaluation allow further measure-
ment of basic geometric parameters such as volume and surface area
as well as additional descriptors of canal shape such as SMI. The SMI
describes the plate- or cylinder-like geometry of an object and is deter-
mined by an infinitesimal enlargement of the surface, whereas the
change in volume is related to changes of surface area, that is to the
convexity of the structure. If a perfect plate is enlarged, the surface
area does not change, yielding an SMI of 0. However, if a rod is
expanded, the surface area increases with the volume and the SMI is
normed, so that perfect rods are assigned an SMI score of 3 (23). In
the present study, the mean SMI results indicated that the root canals
of the 4-rooted maxillary second molar teeth had a cylinder-like
Micro-CT Study of 4-rooted Maxillary Molars 981
geometry. Nonetheless, the results of volume and surface area cannot be
compared because there is no information on this subject in the
literature to date. Thus, the clinical relevance of such findings is still
to be determined.
8. Deveaux E. Maxillary second molar with two palatal roots. J Endod 1999;25:
571–3.
9. Di Fiore PM. A four-rooted quadrangular maxillary molar. J Endod 1999;25:695–7.
10. Gopikrishna V, Reuben J, Kandaswamy D. Endodontic management of a maxillary
first molar with two palatal roots and a single fused buccal root diagnosed with
Basic Research—Technology
The number and morphology of the root canal system can vary
considerably among teeth. The frequency of 2 palatal roots in maxillary
secondmolars has been reported to be very low, but it should not be left
out of consideration during endodontic treatment (11). An important
tool for detecting variations of the root canal in maxillary molars has
been the radiograph (3–5, 8, 9, 13, 19); however, superposition of
the anatomical structures in this region might result in failure to
diagnose a second palatal root. In this condition, a root canal might
be left untreated, which could result in failure. Therefore, other
diagnostic methods such as spiral and cone-beam CT, as well as the
surgical operative microscope, could be useful (3, 10, 21, 30–32),
supporting the clinicians within the diagnosis and treatment of
4-rooted maxillary second molars.
Conclusions
Considering the evaluation of the external and internal anatomy of
4-rooted maxillary second molars, it can be concluded that most of the
samples were classified as type I. Fusion of roots and enamel pearls
were observed. Most of the roots presented straight with 1 main canal,
except the MB root, which presented 2 canals in 24% of the samples.
There were no furcation canals. Accessory canals were located mostly
in the apical third of the roots, and apical delta was observed in 12% of
the roots. The location of the apical foramina varied considerably.
Fifty-six percent of the samples presented an irregular quadrilateral-
shaped orifice configuration. The mean distance from the pulp
chamber floor to the furcation was 2.15 � 0.57 mm. No difference
was observed between roots by considering their length, the configura-
tion of the root canal in the apical third, the SMI, the volume, and the
surface area of the root canals.
Acknowledgments
The authors deny any conflicts of interest related to this study.
Supplementary Material
Supplementary material associated with this article can be
found in the online version at www.jendodon.com (doi:10.1016/
j.joen.2012.03.026).
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JOE— Volume 38, Number 7, July 2012
	Root and Root Canal Morphology of Four-rooted Maxillary Second Molars: A Micro–Computed Tomography Study
	Materials and Methods
	Results
	Discussion
	Conclusions
	Acknowledgments
	Supplementary Material
	References