A comparative study of cone beam computed tomography and conventional radiography in diagnosing the extent of root resorptions
Alamadi et al. Progress in Orthodontics
A comparative study of cone beam computed tomography and conventional radiography in diagnosing the extent of root resorptions
Elham Alamadi 0 2
Hisham Alhazmi 0 2
Ken Hansen 0 2
Ted Lundgren 1
Julia Naoumova 0 2
0 Specialist Clinic of Orthodontics, University Clinics of Odontology, Public Dental Service Västra Götaland Region , Gothenburg , Sweden
1 Department of Pediatric Dentistry, Institute of Odontology at Sahlgrenska Academy, University of Gothenburg , Gothenburg , Sweden
2 Specialist Clinic of Orthodontics, University Clinics of Odontology, Public Dental Service Västra Götaland Region , Gothenburg , Sweden
Background: Root resorptions are assessed and diagnosed using different radiographical techniques. A comparison of the ability to assess resorptions on two-dimensional (2D) and three-dimensional (3D) radiographs is, hitherto, lacking. The aims of this study were to evaluate the accuracy of 2D (periapical radiographs, PA and panoramic radiograph, PAN) and 3D (cone beam computed tomography, CBCT) radiographic techniques in measuring slanted root resorptions compared to the true resorptions, a histological gold standard, in addition to a comparison of all the radiographic techniques to each other. Methods: Radiographs (CBCT, PA, and PAN), in addition to histological sections, of extracted deciduous canines from thirty-four patients were analyzed. Linear measurements of the most and least resorbed side of the root, i.e., “slanted” resorptions, were measured using an analyzing software (Facad ®). For classification of slanted root resorptions, a modified Malmgren index was used. Results: PAN underestimated the root length on both the least and most resorbed side. Small resorptions, i.e., low modified Malmgren scores, were more difficult to record and were only assessed accurately using CBCT. The root resorption scores were underestimated using PA and PAN. In assessment of linear measures, PAN differed significantly from both CBCT and PA. Conclusions: CBCT is the most accurate technique when measuring and scoring slanted root resorptions.
Accurate diagnosis and assessment of the extent of root
resorption is important in orthodontic treatment and
treatment planning. The diagnosis of root resorptions
mainly depends on radiographic examinations.
Conventional two-dimensional (2D) radiographical techniques
are the most commonly used methods for diagnosis of
root resorption. These methods, however, have
limitations such as superimposition of structures onto the
two-dimensional plane, distortion projection errors, and
blurred images [
]. Furthermore, the conventional
radiographs are inadequate in grading resorption lesions
and in detecting resorption dimensions [
2, 6, 7
During the 1990s, cone beam computed tomography
(CBCT) was introduced and is now widely used. Studies
have shown that CBCT imaging is a more reliable tool
for detection of small resorptions compared to
conventional panoramic (PAN) radiograph [
When periapical (PA) radiographs were compared to
CBCT images, root lengths were underestimated by an
average of 2.6 mm compared to 0.3 mm underestimation
in CBCT images. In a comparison of the accuracy of
CBCT and PA radiographs in detecting small periapical
resorptions, CBCT showed poor accuracy in detecting
simulated resorptions smaller than 0.8 mm in diameter
and excellent when the lesions were larger than 1.4 mm
in diameter. On the other hand, PA radiographs
demonstrated poor accuracy for all simulated resorption sizes.
A higher accuracy was reported with PA radiographs
when lesions were larger (2 to 5 mm) in diameter [
Linear measurement is usually used for measuring root
length and the resorption level. Several studies have
investigated the accuracy of linear measurements in CBCT.
Findings indicate that these measurements are highly
Malmgren root resorption scoring system with index
scores from 0 to 4 is commonly used to classify the
severity of horizontal root resorption. In order to assess
slanted root resorptions, a modified Malmgren index is
]. A thorough comparison of various
radiographic techniques and their ability to detect horizontal
and slanted resorptions is, hitherto, lacking. To our
knowledge, no study has compared slanted root
resorptions on PA, PAN, or CBCT in relation to a true
histological gold standard. The aims of this study were to
evaluate the accuracy of three radiographic techniques:
CBCT, PA, and PAN in measuring slanted root
resorptions compared to a true histological gold standard, in
addition to determining which technique is most precise
in detecting slanted root resorption by comparing PA,
PAN, and CBCT to each other.
The patient in this study is from a previous prospective
randomized trial on interceptive treatment of palatally
displaced canines (PDCs) by extracting the deciduous
canine. Details about the patients, their recruitment,
inclusion, and exclusion criteria are described in this study
]. Sixty-seven patients (40 girls, mean age ± SD
11.3 ± 1.1, 27 boys mean age ± SD 11.4 ± 0.9) with
eighty-nine PDCs were randomized by block randomization
method with allocation concealment in consecutive
numbers of sealed envelopes. Patients were
randomized to have either extraction of a deciduous canine
or non-extraction. The extraction group was included
in the present study, which consisted of forty-four
children: 20 boys (11.5 ± 1.2) and 24 girls (11.2 ± 1.2),
with forty-five PDCs. Eleven teeth were excluded due to
either missing PA radiographs and due to patient’s wish to
keep the extracted deciduous canine (Fig. 1).
The study was approved by the research ethics
committee of Sahlgrenska Academy at the University of
Gothenburg, Sweden, and by the radiation protection
committee. Parents and patients have received verbal
and written information, in addition to informed consent
provided by the patient or the parent in accordance with
the Declaration of Helsinki.
All patients had a set of radiographic images before
extraction of deciduous canines. These radiographs
included, at least, two PA, one PAN, and one CBCT. The
PAN and CBCT were taken on the same day as the
extraction of the deciduous canine, while the PA
radiographs were taken not more than 3 months before the
PA radiographs were taken by the general practitioners
in the public dental clinics, in bisecting angle and
parallel techniques. At least two radiographs on each tooth in
a different angle to detect the position of the permanent
canine were taken. All PA radiographs were scanned in
high resolution (2000dcm). PAN were taken at the
Department of Oral and Maxillofacial Radiology at the
Institute of Odontology at Sahlgrenska Academy, with
1.7-degree magnification (Scanora, Soredex, Finland).
CBCT was performed at the Department of Oral and
Maxillofacial Radiology at the Institute of Odontology at
Sahlgrenska Academy, with 3D Accuitomo FPD (J. Morita,
Kyoto, Japan) with a 360-degree rotation. The volume used
was 60 × 60 mm. Primary data reconstructions were made
by acquisition software (i-Dixel-3DX, 3D Version 1.691, J
Morita Mfg Corp) at the Accuitomo workstation, providing
axial, frontal, and sagittal views. Secondary reconstruction
was then made using the i-Dixel software. A sagittal
radiographical view of the deciduous canine was performed with
a Sectra Imtec IDSS multiplanar reconstruction program
with a reference line placed at the middle of the pulp
chamber and another intersecting line with a 45-degree angle.
This was made in order to obtain 3D CBCT images
comparable to 2D periapical images.
Extracted deciduous teeth were stored in 5% buffered
formaldehyde. Before embedding, the teeth were washed
several times in 70% ethanol, with a final wash in
absolute ethanol. Then, the teeth were embedded in
epoxyresin (Epofix®; Electron Microscopy Sciences, Fort
Washington, PA), and each tooth was cut sagittally, in a
bucco-lingual direction into halves in a Leitz low-speed
saw microtome. From the central part of the teeth, three
sections were cut with a thickness of 110 μm. All
sections were photographed with fiber-optic surface
illumination in a Nikon SMZ800 microscope equipped with
a Nikon Digital Sight DS-F1 camera. The slanted root
resorption evident on the most central cut of the tooth
was used as gold standard (Fig. 2).
Root resorption measurements
Radiographical (PA, PAN, and CBCT) and histological
images of 34 patients, in total 136 images, were coded
with a numeric sign, and the order of the images was
randomized in www.random.org. The radiographical and
histological images were imported into an analyzing
software (Facad version 3.0, Ilexis AB, Linköping, Sweden)
and were calibrated regarding magnification. Assessment
of the most resorbed and the least resorbed root side
was made on each image by two calibrated examiners
(EA and HAL). Two linear measurements were done on
each image. The most resorbed (MR) side of the root
was defined as the distance from cemento-enamel
junction to the most resorbed point on the root. The less
resorbed (LR) side of the root was defined as the distance
from the cemento-enamel junction to the least resorbed
point on the root surface. This was considered a
“slanted” resorption (Fig. 2). The original Malmgren
index used for classification of root resorptions was
completed with additional scores [
]. For classification
of slanted root resorption, a modified Malmgren index,
now comprising of six scores, was used (Fig. 3). When
the apex of the tooth was intact, but a resorption was
evident on the root side, the resorption was defined as
“middle” resorption. Middle resorptions were measured
from the most cervical resorption point to the most
apical resorption point in a linear line (Fig. 3, score 6).
A first set of measurements was blinded; thus, root
resorption measurements were performed by each
operator on each radiographic image without comparing
the image to the gold standard. In a second not
blinded measurement set, the root resorption level in
each radiographic image was compared to gold
standard. The data from the blinded and not blinded
measurement sets was analyzed by each operator in a
2 months’ interval period.
Two root resorption measurements were performed for
each tooth; one measured by examiner EA and the other
by examiner HAL. The mean of the two measurements
was used for the statistical analysis. Paired t tests were
used to compare the blinded and the not blinded data
sets. p values < 0.05 was considered statistically
significant. The inter-examiner reliability was assessed with
Cohen’s kappa with less than 5% deviation from the gold
standard. The Malmgren classification of the gold
standard sections was compared to the radiographic sections
using Mann-Whitney test. All statistical tests were
performed using the statistical package in Excel.
Comparison of root length to gold standard
For both blinded and not blinded measurements, PAN
underestimated the root length on the least and most
resorbed side. However, measurements with CBCT and
PA were similar to gold standard (Fig. 4).
Comparison of modified Malmgren classification to gold standard
There was a statistically significant difference between
the root scores for the PAN and PA images compared to
the gold standard, while CBCT values did not differ.
Also, blinded and not blinded recordings did not differ
statistically. Small resorptions were more difficult to
record than large resorptions, except for middle
resorptions, i.e., grade 6. Resorption grade 1 was recorded
accurately only with CBCT. On the contrary, resorption
grade 5 was accurately recorded even on PAN
radiographs. Resorption grade 6 was severely underestimated
by all techniques. Most of grade 6 resorptions were
detected on CBCT. Grade 6 resorptions in the apical third
were misdiagnosed on the PA and PAN radiographic
images as grade 1 or grade 2 (Fig. 5).
Comparison of root length as measured by the radiographic techniques
In assessments of linear measures, there was no
difference between CBCT and PA in either blinded or not
blinded measurements. PAN, however, differed
statistically significant from both CBCT and PA, both blinded
and not blinded, in this sense (Fig. 6).
Comparison of modified Malmgren as measured by the radiographic techniques
A statistical significant difference was detected for
not blinded PA images compared to CBCT and for
both blinded and not blinded PAN compared to
CBCT (Fig. 7).
The inter-examiner reliability, as assessed by Cohen’s
kappa, differed for the radiographic techniques. For
PAN, the kappa value was 1.0, i.e., a perfect agreement.
For PA images, the kappa value was 0.71, i.e., a
substantial agreement, and, finally, for CBCT, the kappa value
was 0.44 demonstrating a moderate agreement. The
inter-examiner agreement for the modified Malmgren
root index was 0.88, demonstrating a good agreement
between the two examiners.
This study shows that CBCT is the most accurate
radiographical technique when measuring root length and
root resorptions, using a modified Malmgren score, in
deciduous maxillary canines. In this study, for the first
time, the most common routine radiographs, i.e., PAN
and PA radiographs and CBCT, were compared to gold
standard histology of true resorptions on extracted teeth.
Orthodontic diagnosis and treatment planning is
essentially influenced by radiographic interpretations of
the site and severity of root resorptions. Periapical
radiographs and PAN are the most commonly used
conventional radiographic techniques in orthodontics although
they have limitations [
]. CBCT, which was presented
in the early 1990s, has been showed to be superior to
other radiographic methods. However, the diagnostic
measures of CBCT requires validation through
comparison with different conventional radiographic methods, in
addition to a gold standard [
To determine the degree of root resorption, different
approaches have been employed, being linear
measurements, scoring of horizontal root resorption degree, or
using scales to describe mesial, distal, buccal, and lingual
]. In orthodontic patients, slanted root
resorption has been found in up to 15% on the palatal
root surfaces as measured with CBCT . Since none
of the abovementioned indices describes slanted
resorptions, a modified six-scaled Malmgren index for various
types of slanted resorption was developed.
A statistically significant difference was found in
modified Malmgren scores for PA images and PAN compared
to gold standard. On the other hand, CBCT did not
differ from gold standard. It was evident that grade 6
resorptions with intact apex were the most difficult to
detect, especially on 2D x-rays due to superimposition of
structures. Large resorptions were easily interpreted
with all techniques, while low resorption grades,
especially grade 1 could be interpreted only on CBCT
images. Other studies have, as well, showed that
CBCT is a superior diagnostic tool in determining
location and dimension of small root resorptions
compared to PA radiographs [
20, 22, 23
]. CBCT is
also more sensitive than PA images in detecting
small simulated lesions drilled on extracted teeth.
Small root resorptions less than 0.3 mm can be
detected using CBCT while resorptions of 0.6 mm in
diameter and 0.3 mm in depth are not detectable on
PA radiographs [
8, 22, 24
Furthermore, when linear measurements were assessed
and compared to histology, CBCT was once again found
to be the most accurate technique. Interestingly, linear
root length measurements of the most resorbed side
made on PA images were close to gold standard, while
the least resorbed side was somewhat overestimated.
PAN, however, underestimated the root length in both
blinded and non-blinded measurements. Several other
studies have also reported the limits with PAN for
assessing root resorptions [
8, 25, 26
To overcome the difficulties in identifying tooth
structures due to superimposition of 3D structures onto a 2D
plane, distortion projection errors, and blurred images,
blinded and not blinded assessments of root length and
resorptions were performed. This has important clinical
relevance since the root resorption detection on the
radiograph is considered blinded. Interestingly, the linear
root length measurements and index scoring did not
differ regardless if it was blinded or not. Even when the
assessments were done not blinded, PAN underestimated
compared to histology but also when it was compared to
CBCT. This clearly demonstrates that PAN is not an
accurate method to detect root resorption in the canine
region. Similarly, PA differed in assessing resorptions
with Malmgren scores; however, in linear measurements,
it did not differ. When the different radiographic
techniques were compared to each other, PAN was found
least accurate in blinded as well as not blinded
measurements compared to CBCT and PA [
none of these studies have compared the results to a
gold standard as done in the present study.
The inter-examiner reliability test in the present study
showed better agreement with the least accurate
radiographic techniques, i.e., PA images and PAN, as it
showed lower kappa values with the CBCT which was
the most accurate technique. In the literature, other
results, with better inter-examiner reliability for CBCT
than for both PA and PAN, have been presented. A
reason for this difference might be the use of a modified
Malmgren score in the present study. This shows that it
is easier to have a high agreement between two
observers using a less accurate technique [
23, 28, 29
Thus, CBCT can be useful in the detection of small root
resorption and to evaluate the severity of the resorption.
In addition, CBCT was the technique most accurate in
comparison to gold standard, i.e., histology. Moreover, in
clinical practice, CBCT gives a 3D image which provides
the clinicians with a multitude of data. However, since
the radiation exposure of CBCT is higher than the
conventional radiographic methods, it is important to
consider factors including the probability of obtaining the
diagnostic information that is sought from it, its risks,
and costs. Therefore, practitioners should always follow
the ALARA principle (As Low As Reasonably
Achievable), which dictates that every precaution should be
taken to minimize radiation exposure to patients [
CBCT is the most accurate technique, both blinded and
not blinded, when measuring root length and detecting
root resorptions using a modified Malmgren score. PA
images were comparable with CBCT for blinded and not
blinded root length measurements but were not accurate
when assessing root resorptions using the modified
Malmgren score. PAN is not a good diagnostic tool for
measuring blinded and not blinded root length and root
resorptions. A better kappa agreement was seen for the
least accurate technique, i.e., PAN.
This research was supported by the Local Research and Development Board
for Gothenburg and Södra Bohuslän, Health and Medical Care Committee of
the Regional Executive Board for Västra Götaland Region, and the Gothenburg
JN conceived of the study, its design and coordination, collected all the
material and drafted the manuscript. EA and HA carried out all the
measurements, re-measurement and drafted the manuscript. TL carried out
the histological images, participated in the design of the study, performed
the statistical analysis and drafted the manuscript. KH participated in the
design of the study and created the analyzing programme in FACAD in order
to measure all the images. All authors read and approved the final
The authors declare that they have no competing interests.
Springer Nature remains neutral with regard to jurisdictional claims in
published maps and institutional affiliations.
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