A. Hasani,2016.pdf

YIJOM-3530; No of Pages 6
Please cite this article in press as: Hasani A, et al. Diagnostic value of cone beam computed tomography and panoramic radiography in
predicting mandibular nerve exposure during third molar surgery, Int J Oral Maxillofac Surg (2016), http://dx.doi.org/10.1016/
j.ijom.2016.10.003
Clinical Paper
Oral Surgery
Diagnostic value of cone beam
computed tomography and
panoramic radiography in
predicting mandibular nerve
exposure during third molar
surgery
A. Hasani, F. Ahmadi Moshtaghin, P. Roohi, V. Rakhshan: Diagnostic value of cone
beam computed tomography and panoramic radiography in predicting mandibular
nerve exposure during third molar surgery. Int. J. Oral Maxillofac. Surg. 2016; xxx:
xxx–xxx. # 2016 International Association of Oral and Maxillofacial Surgeons.
Published by Elsevier Ltd. All rights reserved.
A. Hasani1
, F. Ahmadi Moshtaghin2
,
P. Roohi3
, V. Rakhshan4
1
Department of Maxillofacial Surgery, Dental
Branch, Islamic Azad University, Tehran, Iran;
2
Private Practice, Beaverton, OR, USA;
3
Private Practice, Tehran, Iran; 4
Department
of Dental Anatomy and Morphology, Dental
Branch, Islamic Azad University, Tehran, Iran
Abstract. The aim of this study was to evaluate the diagnostic accuracies of cone
beam computed tomography (CBCT) and panoramic techniques in predicting
inferior alveolar nerve (IAN) exposure. The sample size was determined based on a
pilot study. This prospective clinical series study included 59 third molar extraction
sites with any of seven previously suggested panoramic signs of IAN exposure. The
diagnosis of nerve exposure was done on panoramic and CBCT images. Molars
were extracted and nerve exposure was evaluated clinically. Sensitivity, specificity,
positive predictive value (PPV), and negative predictive value (NPV) of CBCT
method, and sensitivity and PPV of panoramic method were estimated). The
panoramic and CBCT methods correctly classified 67.7% and 93.3%, respectively,
of 60 cases. This difference was statistically significant (x2
= 13.333, P = 0.000).
The sensitivity, specificity, PPV, and NPV for CBCT were 97.4%, 85.7%, 92.7%,
and 94.7%, respectively. The sensitivity and PPV of panoramic radiography were
67.8% and 97.6%, respectively. The signs with the highest sensitivity were
interruption of the mandibular canal border and abrupt canal narrowing. None of the
Pell and Gregory criteria, molar angulations, or three-dimensional canal–apex
relationships was significantly associated with clinically confirmed IAN exposure.
Panoramic radiography may miss about one-third of exposure cases, but a positive
panoramic diagnosis is most likely to be a real exposure and should be taken
seriously.
Key words: cone beam computed tomography;
panoramic radiography; diagnostic value;
impacted third molar; inferior alveolar nerve.
Accepted for publication 7 October 2016
Int. J. Oral Maxillofac. Surg. 2016; xxx: xxx–xxx
http://dx.doi.org/10.1016/j.ijom.2016.10.003, available online at http://www.sciencedirect.com
0901-5027/000001+06 # 2016 International Association of Oral and Maxillofacial Surgeons. Published by Elsevier Ltd. All rights reserved.

The third molars show a high incidence of
impaction, which may cause many con-
ditions, often necessitating their surgical
removal.1–3
The extraction of third molars
is the most common procedure in maxil-
lofacial surgery.1,4
This procedure may be
followed by complications such as neu-
rosensory deficits/dysesthesia,1,4–6
result-
ing from injury to the inferior alveolar
nerve (IAN) bundle, in 0.4% to 8% of
surgeries.2,7–11
The gravity of this condition calls for
preoperative radiographic examina-
tion.2,4,5,9–13
The most widely used tech-
nique is panoramic radiography.1,2,4,5,13,14
However, controversy exists over the effi-
cacy of panoramic features,1,8,10–12,14–16
perhaps because of the inconsistent mag-
nification of panoramic radiography and
its limitations in demonstrating buccolin-
gual depth.1,2,8
Unlike panoramic radiog-
raphy, cone beam computed tomography
(CBCT) can conveniently illustrate buc-
colingual depth without any distortions,
and seems excellent for localizing the
inferior alveolar canal (IAC) and impacted
molars.2,4,5,7
Nevertheless, the only avail-
able study using clinically verified IAN
exposure to investigate the diagnostic val-
ue of CBCT found this not to be different
from the diagnostic value of panoramic
radiography.17
The present study was performed in
view of the importance of the subject
and the small number of studies that have
included direct clinical examination.17
The aim was to assess the diagnostic value
of CBCT and panoramic radiography in
predicting IAN exposure by clinically ver-
ifying the IAN exposure.
Materials and methods
Sample
In this prospective clinical series study,
60 extraction sites were selected in
patients attending the department of max-
illofacial surgery of a university dental
center and a private surgery clinic. The
research committee of the university ap-
proved the protocol in accordance with
the Declaration of Helsinki, and the
patients provided signed written consent.
The inclusion criteria comprised (1) indi-
cation for the extraction of an impacted
mandibular third molar and (2) patient age
between 16 and 40 years. The exclusion
criteria were the absence of any panoram-
ic features suggesting IAN exposure,
any systemic or local diseases/cysts, the
occurrence of uncontrollable post-extrac-
tion bleeding, or any other surgical events
or problems.
Radiographic evaluation
Patients with an indication for the extrac-
tion of an impacted mandibular wisdom
tooth were referred to a single radiology
center for panoramic radiography (Proline
XC; Planmeca, Helsinki, Finland). The
radiographs were evaluated by a maxillo-
facial radiologist with more than 15 years
of experience. If the radiograph showed
signs of proximity of the IAC and molar
root, the patient was referred to a single
radiology center to obtain CBCT volumes.
The CBCT images were obtained with a
Promax-3D unit (Planmeca) with a flat
receiver of 12 12 cm2
and a field of
view of 8 8 cm2
, emitting pulsated rays
(20 m/s each pulse) for 18 s. The same
radiologist examined the CBCT scans.
Radiographic diagnosis of IAN exposure
All panoramic and CBCT images were
scrutinized independently regarding the
topographic relationship between the im-
pacted third molar and the IAC. The ab-
sence or presence of direct contact on the
panoramic radiographs was evaluated
through consideration of the following
seven features, all of which have been
reported to be suggestive of close contact
between the tooth root and the mandibular
canal: (1) interruption of one or both bor-
ders of the IAC, (2) darkening of the root,
(3) diversion of the IAC, (4) abrupt root
dilaceration, (5) narrowing of the root, (6)
darkening and divarication of the apex, and
(7) narrowing of the canal.1,8,10–15,17–19
The diagnosis of canal exposure was per-
formed by an experienced radiologist,
based on the above criteria.
These criteria (excluding root/apex
darkening) were also used and documen-
ted when assessing the CBCT scans for the
diagnosis of IAC exposure, as well as the
lack of cortication between the IAC and
dental socket. The diagnosis was made by
the same radiologist through an evaluation
of volumetric reconstructions, as well as
axial, panoramic, and cross-sectional
images prepared from the tomography
volumes.11
Impaction status
The depth of impaction (classes A, B, and
C as the deepest) and molar horizontal
position (classes I, II, and III as the most
posterior) were determined on panoramic
images according to the criteria of Pell and
Gregory.3,20
The angle of impaction
(mesioangular, distoangular, vertical, hor-
izontal) was also documented based on
panoramic images.
Canal position relative to the tooth
CBCT images were used to determine the
position of the canal in relation to the root:
buccal, lingual, or none (underneath the
tooth).
Clinical diagnosis of IAN exposure
The mandibular third molar was removed
surgically by a maxillofacial surgeon
who has been in practice for more than
15 years. The patients were treated under
local anesthesia (lidocaine 2% and
1:100,000 epinephrine) administered to
the inferior alveolar, long buccal, and
lingual nerves. Each patient received
two carpules of anesthesia. The patient
could receive additional dose(s) according
to their need or upon request, to ensure a
painless surgery. A mucoperiosteal pocket
was incised and everted to gain access to
the third molar; osteotomy and dental
sectioning (using rotary instruments) were
performed when necessary. In the case of
bleeding that was not easily controllable,
the patient was excluded from the study,
treated appropriately, and replaced with a
new participant. IAN exposure was eval-
uated by the maxillofacial surgeon after
surgically removing the mandibular third
molar, irrigating the socket, and inspecting
all socket walls/floor. Following this, the
bone edges were smoothed and the flap
was sutured. Patients were given ibupro-
fen 400 mg for pain control and were
instructed to take one dose every 4 h plus
additional doses if the pain persisted.
Patients were monitored for 3–4 days
for any signs of infection. Their sutures
were removed at 1 week post-surgery.
Study variables and statistical analyses
The main predictor was the indication of
IAN exposure according to CBCT and
panoramic imaging, diagnosed on the ba-
sis of the criteria given above. Other in-
dependent variables were the Pell and
Gregory depth of impaction, horizontal
position of the molar, angle of impaction,
and three-dimensional (3D) position of the
canal in relation to the root. The outcome
variable was the direct visualization of
the neurovascular bundle at the time of
molar extraction.13
The sample size was
predetermined based on a pilot study; a
minimum of 40 extraction sockets with
clinically confirmed IAN exposure was
required to obtain a test power
above 90% (effect size = 40%, a = 0.05).
The specificity, sensitivity, negative pre-
dictive value (NPV), and positive predic-
tive value (PPV) of panoramic
2 Hasani et al.
j.ijom.2016.10.003

radiography and CBCT features were cal-
culated. The data were analyzed by x2
and
x2
goodness-of-fit tests using IBM SPSS
Statistics version 20.0 software (IBM
Corp., Armonk, NY, USA). The level of
significance was set at 0.05.
Results
Fifty-nine third molars (in 41 patients)
with panoramic signs of a close relation-
ship to the IAC were evaluated surgically.
Finally 40 sockets with true IAN exposure
were sequentially included. In addition, a
socket with no panoramic risk factors (in
one of the 41 patients undergoing CBCT)
was later found to be clinically positive
and was also included. The remaining 19
sockets that were positive on panoramic
radiography but clinically negative were
included as negative controls. The average
age of the 41 patients enrolled was
26.1 4.1 years. Of the 60 sockets includ-
ed, 24 were in female patients and 36 were
in male patients; 30 sockets were on the
right side and 30 were on the left.
The sensitivity, specificity, PPV, and
NPV of the CBCT method were 97.4%,
85.7%, 92.7%, and 94.7%, respectively.
The sensitivity and PPV for panoramic
radiography were 67.8% and 97.6%, re-
spectively (Table 1). Overall, panoramic
radiography classified 67.7% of 60 sockets
correctly, while CBCT classified 93.3% of
the 60 alveoli correctly. This difference
was statistically significant (x2
= 13.333,
P = 0.000).
In the panoramic radiographs of the 41
extraction sockets with real (clinically
confirmed) IAN exposure, the most com-
mon radiographic sign was discontinua-
tion of the upper border of the IAC, which
was observed in 28 of the 41 clinically
confirmed IAN exposures (sensitivi-
ty = 68.3%). The second most common
radiographic sign was abrupt narrowing
of the canal, with a sensitivity of 19.5%
(observed in eight out of 41 sockets). The
other signs were IAC diversion (observed
in three cases; sensitivity = 7.4%), dark-
ening of the root (one case; sensitivi-
ty = 2.4%), and superimposition of the
root on the IAC (one case; sensitivi-
ty = 2.4%). The PPV, sensitivity, and
specificity for abrupt IAC narrowing to-
gether with root darkening were 72%,
87.8%, and 26.3%, respectively. The
PPV, sensitivity, and specificity for the
rest of the panoramic signs combined were
50%, 12.2%, and 73.7%, respectively.
A x2
goodness-of-fit test was used to
compare the radiographic status of impac-
tion with the value 19:41. None of the Pell
and Gregory criteria or 3D canal–apex
relationships was significantly associated
with the presence of real (clinically con-
firmed) IAN exposure (Table 2).
Discussion
The findings of this study indicate that
CBCT may have excellent diagnostic ac-
curacy. Panoramic radiography also
showed an excellent PPV, meaning that
the presence of at least one of the seven
risk factors evaluated (particularly IAC
narrowing and root darkening) should
be taken seriously. The molar position,
angulation, and impaction depth were
not associated with IAN exposure, consis-
tent with the findings of an earlier study.12
The risk of occurrence of IAN exposure
during third molar surgery is high at up to
43%.17
Important features that should be
evaluated on panoramic images include
darkening of the root, deflected roots,
narrowing of the root, dark and bifid roots,
interruption of the opaque line(s),
and diversion/narrowing of the
IAC.4,7,11,14,21–23
Diversion of the IAC,
darkening of the root, and interruption
of the white line might be significantly
related to nerve injury.4,8,12,14,21,24
Previ-
ous studies have shown the most important
panoramic radiographic signs to be inter-
ruption of the white line and darkening of
the roots.1,8,10,14,15,25,26
For panoramic
images, the highest sensitivity has been
found for interruption of the cortical
lines.10,11,23
Darkening of the third molar
roots where the mandibular canal is super-
imposed has been reported to be sugges-
tive of a close relationship between the
root and canal in several stud-
ies.11,13,14,18,27
In a few cases, darkening
of the roots could be associated with thin-
ning or perforation of the lingual cortex by
the tooth roots, rather than being related to
‘true contact’ between the mandibular ca-
nal and the tooth roots.1,7,11,23,28
However,
not all of these cases lead to nerve inju-
ry.1,15
The main panoramic signs identi-
fied in different studies include the
following: interruption of the cortical
lines,1,8,10,11,14,15
root darkening,11,13,14,18
IAC diversion,12,14,15
and narrowing of the
mandibular canal.14
Nevertheless, some
authors have failed to observe a high
Predicting nerve exposure in third molar surgery 3
j.ijom.2016.10.003
Table 2. Distribution of real (clinically confirmed) IAC exposure according to radiographic
features (angulation, anteroposterior position, and depth of the tooth, as well as the position of
the IAC).a
Mesioangularb
Vertical Horizontal
Positive 26 (43.3%) 7 (11.7%) 8 (13.3%)
Negative 8 (13.3%) 5 (8.3%) 6 (10.0%)
P-value 0.306 0.458 0.370
Class I Class II Class III
Positive 24 (40.0%) 16 (26.7%) 1 (1.7%)
Negative 11 (18.3%) 8 (13.3%) 0
P-value 0.972 0.863 –
A B C
Positive 8 (13.3%) 20 (33.3%) 13 (21.7%)
Negative 6 (10.0%) 6 (10.0%) 7 (11.7%)
P-value 0.370 0.345 0.751
Buccal Lingual Below
Positive 18 (30.0%) 18 (30.0%) 5 (8.3%)
Negative 7 (11.7%) 8 (13.3%) 4 (6.7%)
P-value 0.691 0.919 0.411
IAC, inferior alveolar canal.
a
P-values were calculated by comparing each ratio with the ratio 41:19.
b
There were no distoangular cases.
Table 1. Contingency tables showing the efficacy of panoramic and CBCT methods.
Method Radiographic diagnosis
Clinically confirmed IAC
exposure (gold standard)
Positive Negative
Panoramic radiography Positive 40 (66.7%) 19 (31.7%)
Negative 1 (1.7%) 0
CBCT Positive 38 (63.3%) 1 (1.7%)
Negative 3 (5.0%) 18 (30.0%)
CBCT, cone beam computed tomography; IAC, inferior alveolar canal.

diagnostic value for IAC diversion,1,11
IAC border interruption,16
IAC narrow-
ing,1
and any of the seven panoramic
features.15
The results pertaining to the sensitivity
values are also quite controversial. For
instance, the sensitivity values for inter-
ruption of the cortical border reported in
three studies were 75%,13
80%,12
and
100%,17
and ranged between 65% and
74% for root darkening and between
22% and 50% for IAC diversion (Table
3).12,13,17
However, regardless of the vari-
ation in values, it appears that interruption
of the radiopaque borders is the most
prevalent sign in actual cases of IAN
exposure, followed by root darkening. A
meta-analysis aggregating the raw data
from previous studies calculated a sensi-
tivity of 53.5% for interruption of the
cortical border, 51.2% for darkening of
the root, and 29.4% for canal diversion.19
The present study also indicated interrup-
tion of the cortical border to be the pre-
dictor of IAN exposure with the highest
sensitivity (68.3%) . However, unlike the
above-mentioned studies, the other pan-
oramic features had low sensitivities in the
present study; the signs of root darkening
and IAC diversion were not highly preva-
lent among true IAN exposure cases. In-
stead of root darkening (which was found
previously to be the panoramic trait with
the second highest sensitivity), IAC nar-
rowing had the second highest sensitivity
in this study (19.5%). Nevertheless, its
sensitivity does not appear to be clinically
useful.
A high PPV means that if a case is
identified radiographically as having the
signs of IAN exposure, it will very proba-
bly be an actual case of nerve exposure .
The PPV might be a more clinically useful
indicator for identifying important diag-
nostic risk factors. The results of the pres-
ent study showed a 72% PPV for the
combination of IAC narrowing and root
darkening, indicating a high risk of IAC
exposure upon observing these traits. The
item root darkening is consistent with the
literature reporting this to be a critical risk
factor. Nevertheless, the factor IAC nar-
rowing has not been recognized as one of
the important traits in most of the previous
studies. Ghaeminia et al. reported the
panoramic sign diversion of the canal to
be the best diagnostic marker, followed by
root darkening and IAC interruption.17
Much lower PPVs were reported by Seda-
ghatfar et al.13
(Table 4). Although all
PPVs were low in this latter study, the
same order of importance held.13
Similar-
ly, Blaeser et al. reported IAC diversion,
root darkening, and IAC border interrup-
tion as important panoramic signs12
(Table 4). A meta-analysis aggregating
previous data demonstrated PPVs of
24% and 28% for root darkening and canal
diversion, respectively, compared to 2%
for interruption of the cortical border.19
The considerable variations observed in
different studies might be attributable to
anatomical variations present in the dif-
ferent samples and methodological varia-
tions, such as in the quality and resolution
of radiographs and computer screens, as
well as the expertise and eyesight of the
evaluators.
Volumetric examination is recom-
mended when specific panoramic traits
are seen.1,12,14,16,18
When preoperative ex-
amination identifies a risk factor, the sur-
geon may consider the use of special
surgical approaches to decrease the risk
of IAN injury.4,5,14,28
In particular, dark-
ening of the root is associated with cortical
bone loss and/or grooving of the
root.4,7,29–31
Furthermore, interruption of
the radiopaque borders has been attributed
to the loss of cortical structure of the canal.
Diversion of the mandibular canal is in-
dicative of a nerve running between the
roots, or a nerve sandwiched between the
root and the mandibular cortical Plate 4.
The different prevalence rates of lingually
and buccally positioned IACs calls for
volumetric evaluation.7,11,23
Volumetric
assessments allow a better management
of severe cases.1
The true relationship of
the root and the IAC is best visualized in
volumetric examinations.1,16,25,26,28,32
The presence of two or more signs on a
panoramic radiograph may indicate an
increased risk of IAN exposure or inju-
ry.1,8,12,15–18,32,33
When specific panoram-
ic signs are observed, 3D examination is
highly recommended.1,12,14,16,18,25,28,32,33
The predictive value of 3D assessments
for post-surgical IAN injury has been
reported to be about 20–30%.4,34–38
Volumes can be viewed either as 3D
reconstructed models, or as cross-sections
(preferably coronal slices) through the
IAN area if reconstruction software is
not available.4,35
Such cross-sections are
useful for the assessment of the cortical
status of the IAC. High-risk signs on
panoramic radiographs are highly associ-
ated with the absence of cortication be-
tween the third molar and the IAC.4,11,29
The absence of cortication might strongly
suggest nerve injury.4,16,22,35,39
The shape
of the IAC is also an important indicator of
the proximity of the IAC to the impacted
molar.4,35,39,40
Preoperative 3D examination is now
considered a critical assessment tool for
third molar surgery. Nevertheless, it has
some drawbacks: it does not necessarily
detect all exposure cases due to sparse
trabeculations in some mandibles or other
technical factors such as image resolution
or observer eyesight. There is also a need
for standardized eligibility criteria for 3D
examination.4,41,42
Moreover, the higher
costs and the limited availability of ad-
vanced radiography units in many regions,
plus the higher X-ray dose required, are
other obstacles to the use of volumetric
imaging in molar surgery.1,2
The results of
this study indicate that CBCT is an excel-
lent method for the detection of IAC ex-
posure in terms of all the diagnostic
measures assessed. It was significantly
superior to the panoramic method. The
only similar study available in the litera-
ture found no significant difference in
accuracy between the panoramic and
CBCT methods in predicting IAN expo-
sure.17
This might be due to methodologi-
cal differences such as the devices used,
sample sizes, or operator expertise.
This study had some limitations. The
sample size was rather small; however,
this was based on power calculations and
a pilot study. Furthermore, due to the lack
of sockets that were negative on panoram-
ic radiography, it was not possible to
4 Hasani et al.
j.ijom.2016.10.003
Table 3. Sensitivity values reported in some previous studies.
Study
IAC
interruption
Root
darkening
Root
narrowing
IAC
diversion
Ghaeminia et al.17
100% 74% – 22%
Sedaghatfar et al.13
75% 71% 50% 42%
Blaeser et al.12
80% 65% – 50%
IAC, inferior alveolar canal.
Table 4. PPV values reported in some previous studies.
Study IAC diversion Root darkening IAC interruption
Ghaeminia et al.17
93% 61% 48%
Sedaghatfar et al.13
19% 24% 12%
Blaeser et al.12
34% 31% 25%
PPV, positive predictive value; IAC, inferior alveolar canal.

calculate the specificity and NPV for the
panoramic method. However, enrolling
patients with sockets that are negative
on panoramic radiography and subjecting
them to CBCT examination without any
treatment need would result in an unnec-
essary X-ray dose that would not be ethi-
cally justifiable.43
Future studies should
also evaluate different radiographic fea-
tures separately in the CBCT scans. Also
the vertical position of the canal in rela-
tion to the root (apical, middle, coronal)
should be assessed in future studies, as
this might influence the risk of iatrogenic
damage. A broader age range might
improve the generalizability of the find-
ings, as patients who are older than 40
years can also experience post-surgical
difficulties. However, it is recommended
that third molar extraction surgeries are
performed in those aged 16 to 40 years,
because of the better systemic health and
jaw bone density/flexibility of these
patients.3
Therefore, the age range was
not extended in this study in order to have
a more uniform sample.
In conclusion, CBCT was able to iden-
tify most of the nerve exposure cases, as
well as those without nerve exposure,
precisely. The high PPV of the panoramic
radiography technique is valuable and
implies a high probability of IAN expo-
sure upon observing at least one of the
seven signs evaluated, particularly IAC
narrowing and root darkening, which
had the highest PPVs. The panoramic
feature with the highest sensitivity was
interruption of the IAC border.
Funding
This study was self-funded.
Competing interests
The authors declare no competing inter-
ests or conflicts of interest.
Ethical approval
Ethical approval was obtained. The inter-
nal review board of the university ap-
proved the thesis on which this study
was based.
Patient consent
Not required. The article does not include
any identifiable patient images.
Acknowledgement. AH conceived and
designed the study, performed the surger-
ies, and supervised the thesis. FAM
searched the literature and participated
in the experiments. PR searched the liter-
ature, performed the experiments, collect-
ed the data, and wrote the thesis. VR
analyzed the data, searched the literature,
and wrote/revised/submitted the article.
The authors wish to express their sincere
gratitude to Dr. Masoud Varshosaz for
radiographic examinations.
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Address:
Farnam Ahmadi Moshtaghin
17145 SW Oak St.
Beaverton
OR 97007-3920
USA
E-mail: farnammoshtaghin@gmail.com
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