Darkening of third molar roots

1. DENTOALVEOLAR SURGERY
J Oral Maxillofac Surg
69:1544-1549, 2011
Darkening of Third Molar Roots:
Panoramic Radiographic Associations
With Inferior Alveolar Nerve Exposure
József Szalma, DMD,* Edina Lempel, DMD,† Sára Jeges, PhD,‡
and Lajos Olasz, MD, DMD, PhD§
Purpose: The aim of the present study was to examine the association between the darkening of the root
on the preoperative panoramic radiograph and intraoperative inferior alveolar nerve (IAN) exposure.
Patients and Methods: In the present study, 116 mandibular third molar surgical extraction cases with
darkening of the third molar roots on the preoperative panoramic radiographs were selected for a case
group, and 193 patients with one or more of the following “high-risk” signs, indicating a close spatial
relationship between the root and dental canal, were selected for the control group: interruption of the
white line, diversion of the canal, and/or narrowing of the canal. The correlation between the radio-
graphic markers and IAN exposure was estimated using bivariate analysis.
Results: The IAN was visible in 47 (15.2%) of 309 intraoperative extractions. Darkening of the third
molar roots was significantly associated with IAN exposure (P Ͻ .001). Those with both darkening and
adjacent “high-risk” radiographic markers present simultaneously had a significantly greater risk of IAN
exposure than those with darkening only (P Ͻ .001) or any other combination of multiple high-risk
factors (P ϭ .001).
Conclusions: Significant differentiation between isolated darkening and darkening with both adjacent
and high-risk signs seems to be essential in predicting IAN exposure.
© 2011 American Association of Oral and Maxillofacial Surgeons
J Oral Maxillofac Surg 69:1544-1549, 2011
Panoramic radiography is probably one of the most
investigated screening methods used before lower
third molar removal.1-3
The significance of different
specific signs indicating a close relationship between
the third molar roots and the dental canal (eg, inter-
ruption of the superior cortical wall, narrowing and
diversion of the canal, darkening of the root, narrow-
ing or deflection of the root) has been well discussed
in published reports.4-8
Some of the earlier studies
showed that panoramic radiography is an accurate
method in the evaluation of these “high-risk” specific
markers,4,5,7
but others have stated that panoramic
radiography is inadequate if a predilection is present
for postoperative inferior alveolar nerve (IAN) pares-
thesia or exposed nerves during surgery.9,10
Several
specialists in the field believe that the absence of
these significant signs on radiographic examination
provides the most reliable information to the surgeon.
Namely, the absence of any of the significant signs
indicates a minimal risk of IAN paresthesia, but the
presence of one or more signs is not a reliable indi-
cation for possible paresthesia.10-12
Darkening of the root has been previously de-
scribed as an increased radiolucency due to impinge-
ment of the canal on the third molar.6,7,13
In contrast,
Mahasintipiya et al14
and Tantanapornkul et al15
showed that darkening can occur on radiographs
without root grooves. Moreover, Tantanapornkul et
*Oral Surgeon, Assistant Professor, Department of Oral and Max-
illofacial Surgery, University of Pécs, Pécs, Hungary.
†Assistant Professor, Department of Conservative Dentistry and
Endodontics, University of Pécs, Pécs, Hungary.
‡Senior Research Professor, Head, Department of Biostatistics
and Medical Informatics, Faculty of Health Sciences, University of
Pécs, Pécs, Hungary.
§Professor, Past President of Hungarian Association of Oral and
Maxillofacial Surgeons, Department of Oral and Maxillofacial Sur-
gery, University of Pécs, Pécs, Hungary.
Address correspondence and reprint requests to Dr Szalma:
Department of Oral and Maxillofacial Surgery, University of Pécs, 5
Dischka Gy St, Pécs H-7621 Hungary; e-mail: jozsef.szalma@
aok.pte.hu
© 2011 American Association of Oral and Maxillofacial Surgeons
0278-2391/11/6906-0006$36.00/0
doi:10.1016/j.joms.2010.09.009
1544

2. al15
stated that darkening of the root can even present
as the thinning of the lingual cortical plate. The re-
view report by Atieh16
showed a pooled sensitivity of
51.2% and a pooled specificity of 89.6% for this sign.
Similar to the results from Blaeser et al4
and Gomes et
al,9
our earlier findings10
affirmed that the darkening
of the third molar root is one of the strongest signs in
the prediction of IAN exposure or paresthesia.
The aim of the present study was to focus on one of
the most important panoramic signs and to estimate
the differences between isolated (darkening as a sin-
gle observation without adjacent “high-risk” radio-
graphic markers on the radiographs) and darkening
plus other signs (darkening sign together with other,
previously mentioned, “high-risk” signs) and IAN ex-
posure to determine the adjacent factors on pan-
oramic radiographs that would improve the risk as-
sessment in patients with darkening of the third molar
roots.
Patients and Methods
STUDY DESIGN
In the present retrospective study, a case-control
model was constructed. A total of 116 patients who
underwent mandibular third molar surgical extraction
and had had darkening of the third molar roots on the
preoperative panoramic radiographs were selected
for the case group. A total of 193 patients without
darkening were selected for the control group. The
inclusion criteria for the control group were the pres-
ence of one or more “high-risk” panoramic signs (eg,
interruption of the white line, diversion of the canal,
and/or narrowing of the canal). The control group
was selected with the following criteria: homologic
age, gender, and impaction depth, with respect to the
case group.
The patients with root darkening were divided into
2 groups according to the panoramic findings. The
first group had isolated darkening. That is, darkening
of the root was present as an isolated preoperative
panoramic radiographic finding. No adjacent pan-
oramic signs were present. The second group had
darkening plus other signs. That is, darkening of the
root and one or more of the adjacent panoramic
radiographic signs (diversion of the canal, narrowing
of the canal, and interruption of the superior cortical
line) were present simultaneously.
The control cases were also divided into 2 groups
according to the panoramic findings. The control
cases were separated into groups 3 and 4. Group 3
patients had an isolated, single, “high-risk” sign,
with the exception of darkening of the root. Group
4 had the simultaneous presence of 2 or more
“high-risk” signs, with the exception of darkening
of the root.
All the patients were selected and underwent sur-
gery at the Department of Oral and Maxillofacial Sur-
gery (University of Pécs, Pécs, Hungary) from Decem-
ber 2006 to December 2009. Before surgery, each
patient provided full informed consent. The Regional
Research Ethics Committee of the Medical Center,
Pécs approved the present study (reference number
3795.316-7851/KK4/2010). The examined radiographic
markers and the surgical technique of removal were
the same as described in our previous study.10
The
IAN visualization was documented after extraction.
The sockets were irrigated with 20 mL sterile saline
solution at room temperature combined with precise
focused suction. The exposed IAN bundles were ex-
amined under loupe magnification using a headlight.
The direct visualization of the suspected neurovascu-
lar bundle was considered IAN exposure, when the
following criteria were partially or totally fulfilled:
mesiodistal oriented tubular and/or pale or whitish
structure at the expected level of the socket (esti-
mated according to the panoramic radiographs). Non-
tubular, lingually observed, soft tissues without mesi-
odistal orientation were considered lingual plate
perforations and were not included in the present
study.6,11
IMAGING AND IMAGE ANALYSIS
The preoperative radiographs were analyzed by 2
of us (J.S., E.L.). Conventional panoramic radiographs
were taken before surgery (Planmeca Proline PM
2002 CC, Helsinki, Finland). The images were ana-
lyzed with a light box, and loupe magnification was
available for the observers. Three months later, 50
radiographs were examined again. The intraexaminer
and interexaminer reliability were calculated.
STATISTICAL ANALYSIS
The data collection and statistical analysis were per-
formed using the Statistical Package for Social Sciences,
version 17.0 (SPSS, Chicago, IL) and StatsDirect, version
2.7.2 (StatsDirect, Altrincham, UK).
The association of isolated darkening and multiple
symptoms in the cases and controls with the presence
of nerve exposure was tested using the Pearson chi-
square test. Univariate odds ratios of the variables
associated with IAN exposure were calculated. P Ͻ
.05 was considered significant. Cohen’s kappa statis-
tic was used to calculate the intra- and interobserver
agreement. A kappa value of Ͻ0.40 was considered to
show poor agreement; a value of 0.40 to 0.59 was
deemed a fair agreement; a value of 0.60 to 0.74 was
seen as good agreement; and a value of 0.75 to 1.00
was considered excellent agreement.
SZALMA ET AL 1545

3. Results
The study sample consisted of 309 patients, 144
men and 165 women, with a mean age of 26.7 Ϯ 7.9
years (range 21 to 59). Overall, 116 patients pre-
sented with root darkening on the panoramic radio-
graphs (groups 1 and 2), and 193 patients had other
“high-risk” panoramic signs indicating a close spatial
relationship between the third molar root and dental
canal (groups 3 and 4). Of the 309 extractions, the
IAN was visible in 47 cases (15.3%), 32 (27.6%) of the
116 with isolated darkening and 15 (7.8%) of the
193 with other signs (control patients; Table 1).
Visible IAN injury or excessive bleeding during
surgery was not documented in the present study.
Of the 47 patients with the IAN visible, reversible
paresthesia occurred in 4 (8.5%), and the paresthe-
sia had resolved at the latest within the first 4
months in all 4 patients.
The presence of IAN exposure in the study groups
is listed in Table 2. According to the bivariate analysis,
darkening (as either a single or a multiple sign) was
significantly associated with IAN exposure (P Ͻ .001,
chi-square test; univariate adjusted odds ratio 4.52,
95% confidence interval 2.32 to 8.79). The risk of IAN
exposure was significantly greater (P ϭ .001, chi-
square test; odds ratio 5.15; 95% confidence interval
1.8 to 14.65) in group 2 (multiple signs plus dark-
ening) than in group 1 (only darkening). Moreover,
the risk of IAN exposure was significantly greater
(P Ͻ .001, ␹2
test; odds ratio 5.58; 95% confidence
interval 2.4 to 12.93) in group 2 (multiple signs
plus darkening) than in group 4 (multiple high-risk
signs without darkening). Both the interexamina-
tion (0.84 and 0.81) and intraexamination (0.77)
reliability results were considered excellent in the
present study. Representative cases are presented
in Figures 1 and 2.
Discussion
Panoramic radiography has proven to be an essen-
tial preoperative diagnostic tool in several studies.4-8
However, in conjunction with Gomes et al,9
we con-
cluded in an earlier study10
that panoramic radio-
graphs do not provide images reliable enough for
predicting nerve lesions. The limitations of 2-dimen-
sional panoramic radiography (which provides infor-
mation only on the position of the inferior alveolar
canal in the vertical plane, with variable magnification
and lingually positioned structures that are projected
upward to produce a sharp image layer [focal trough]
of limited width) is well known.2,12,17-19
Perhaps
the most accepted agreement is that the absence of
these specific signs on radiographic examination
provides the most reliable information, but that
the presence of any of these signs does not make
Table 1. CHARACTERISTICS OF STUDY GROUPS AND
THEIR RELATIONSHIP TO IAN EXPOSURE AFTER
THIRD MOLAR SURGERY
Variable
Control
Group
(n ϭ 193)
Case
(Darkening)
Group
(n ϭ 116)
P
Value
Age (yr) NS
Range 21 to 59 23 to 56
Mean Ϯ SD 26.4 Ϯ 8.6 26.9 Ϯ 7.2
Gender (n) NS
Male 91 (47.1) 53 (45.7)
Female 102 (52.9) 63 (54.3)
Impaction degree (n) NS
Fully erupted 11 (5.7) 6 (5.1)
Partially erupted 87 (45.1) 51 (44.0)
Fully impacted 95 (49.2) 59 (50.9)
IAN exposure (n) 15 (7.8) 32 (27.6) Ͻ.001*
Abbreviations: IAN, inferior alveolar nerve; NS, not sig-
nificant.
Data in parentheses are percentages.
*␹2
test.
Szalma et al. Darkening of Third Molar Roots. J Oral Maxillofac
Surg 2011.
Table 2. PRESENCE OF IAN EXPOSURE IN STUDY GROUPS
Group
IAN Exposure
Group Total Overall TotalYes No
Root darkening 116
Group 1 5 (10.9) 41 (89.1) 46 (100)
Group 2 27 (38.6) 43 (61.4) 70 (100)
Control
Group 3 6 (5.8) 98 (94.2) 104 (100) 193
Group 4 9 (10.1) 80 (89.9) 89 (100)
Total 47 262 309
Abbreviation: IAN, inferior alveolar nerve.
Data in parentheses are percentages.
Szalma et al. Darkening of Third Molar Roots. J Oral Maxillofac Surg 2011.
1546 DARKENING OF THIRD MOLAR ROOTS

4. them authentic markers for the prediction of IAN
injury.
The cited frequency of IAN exposure during man-
dibular third molar surgical removal has been 5% to
8%, and the direct visualization of an intact IAN bun-
dle indicates a subsequent risk of paresthesia of 20%
to 40%.11,20
However, Susarla et al21
found neither
temporary nor permanent damage in their study of
FIGURE 1. A, Partially erupted mesioangular lower left third molar
representing “single” root darkening on panoramic radiograph. B,
IAN visible intraradicularly (green arrow). C, Slight groove on
lingual surface of buccal root seen (blue arrow).
Szalma et al. Darkening of Third Molar Roots. J Oral Maxillofac
Surg 2011.
FIGURE 2. A, Partially erupted mesioangular lower left third molar
representing “multiple” root darkening from panoramic radio-
graph. Darkening of root present, together with diversion of inferior
alveolar canal and narrowing of root (latter sign not investigated in
present study). B, Intraoperative photograph showing exposure of
IAN (blue arrow indicates neurovascular bundle). C, Intraradicular
groove formation visible on extracted tooth.
Szalma et al. Darkening of Third Molar Roots. J Oral Maxillofac
Surg 2011.
SZALMA ET AL 1547

5. nerve exposure. In the present study, the incidence of
IAN visualization was 15.3% (47 of 309 extraction
cases), greater than that previously reported. A possi-
ble explanation might be that mainly high-risk cases
that had been referred to our department were in-
volved in the present study. In contrast, the lower
incidence of paresthesia in those with IAN exposure
(8.5%; 4 with paresthesia of 47 with IAN exposure)
could be partially explained by the observation of
Pogrel et al22
in their anatomic study. They found
from examination of the exact structure of the infe-
rior alveolar neurovascular bundle that the vein laid
on the top of the nerve was in the 12-o’clock position
in all examined cases and suggested that the possibil-
ity of direct injury of the IAN would be rare without
injury to the vein.22
Bleeding from the neurovascular
bundle was not registered in the present study; thus,
that the vein had not been injured might have re-
sulted in the lower incidence of nerve paresthesia in
those with an exposed IAN bundle.
Darkening of the root was determined in some
previous studies to be the single most important
warning sign of IAN exposure or injury4-7,9
; how-
ever, other researchers have failed to confirm these
results. Valmaseda-Castellon et al13
found that only
the deflection of the mandibular canal was signifi-
cantly associated with IAN injury. Tantanapornkul
et al18
reported that only the interruption of the
canal wall was significant. Nakagawa et al23
stated
that the absence of the superior canal wall on the
panoramic images demonstrated direct contact be-
tween the third molar roots and the mandibular
canal. Finally, Susarla and Dodson24
found that
none of the panoramic radiographic signs was as-
sociated with an increased risk of IAN injury.
Darkening of the root was defined by Bundy et al6
as follows: this radiographic sign occurs because of
intimate contact between the tooth and canal causing
radiographically evident loss of tooth root density.
Öhman et al19
stated that a dark band is an indicator
of grooving of the tooth by the canal, although it
could be present without this radiographic sign. How-
ever, Tantanapornkul et al15
stated that this sign re-
flects cortical thinning or perforation of the lingual
cortical plate (in 80% of cases) rather than grooving of
the tooth (occurring in just 20% of cases).
Several investigators have previously demonstrated
that the simultaneous presence of 2 or more signs on
the panoramic radiograph results in an increased risk
for IAN exposure or injury.4,5,10
However, the signif-
icance of a different combination of these signs has
not been previously investigated. The results from the
present study have suggested that darkening of the
third molar root, together with adjacent “high-risk”
signs, results in the greatest risk of IAN exposure—
significantly more than the darkening of a single
root or when other “high risk” signs are present
without darkening of the root. Our findings corre-
late with those from Tantanapornkul et al15
: when
1 or more adjacent “high-risk” signs were present
with root darkening, IAN exposure might be pre-
dicted even though darkening was the only the sign
of lingual cortical perforation.
In conclusion, we suggest that cases of root dark-
ening and one or more adjacent “high-risk” panoramic
signs (interruption of the superior cortical wall, nar-
rowing and diversion of the canal) simultaneously
present on the panoramic radiographs have the great-
est risk of IAN exposure. According to our findings,
the presence of darkening of third molar roots on the
panoramic radiograph should be classified into single
and multiple darkening categories before mandibular
third molar extraction creates a more accurate esti-
mate of the risk of IAN exposure.
Acknowledgments
We would like to thank Alexandra Forsayeth Sieroslawska for the
English language revision of this report.
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SZALMA ET AL 1549