The purpose of the present study was to investigate the reliability of both
periapical radiographs and orthopantomograms for exact detection of
tooth root protrusion in the maxillary sinus by correlating the results
with cone beam computed tomography.
Material and Methods
A database of 1400 patients scanned with cone beam computed tomography (CBCT)
was searched for matching periapical (PA) radiographs and orthopantogram
(OPG) images of maxillary premolars and molars. Matching OPG images
datasets of 101 patients with 628 teeth and PA radiographs datasets of
93 patients with 359 teeth were identified. Four observers assessed the
relationship between the apex of tooth root and the maxillary sinus per
tooth on PA radiographs, OPG and CBCT images using the following
classification: root tip is in the sinus (class 1), root tip is against
the sinus wall (class 2) and root tip is not in the sinus (class 3).
Results
Overall correlation between OPG and CBCT images scores was 50%, 26% and 56.1%
for class 1, class 2 and class 3, respectively (Cohen's kappa [weighted]
= 0.1). Overall correlation between PA radiographs and CBCT images was
75.8%, 15.8% and 56.9% for class 1, class 2 and class 3, respectively
(Cohen's kappa [weighted] = 0.24). In both the OPG images and the PA
radiographs datasets, class 1 correlation was most frequently observed
with the first and second molars.
Conclusions
The results demonstrated that both periapical radiographs and
orthopantomograms are not reliable in determination of exact
relationship between the apex of tooth root and the maxillary sinus
floor. Periapical radiography is slightly more reliable than
orthopantomography in determining this relationship.
Exact assessment of the relationship between roots of maxillary premolars and
molars and inferior wall of the maxillary sinus is essential in oral and maxillofacial
pathology diagnosis. There are namely many important clinical implications for protrusion
of roots in the maxillary sinus. For example, tooth extraction or endodontic surgery
can lead to the formation of an oroantral fistula or oroantral communication in
a case of presenting tooth root protrusion in the maxillary sinus [1].
Furthermore, the maxillary sinus has been found to be the most significant pathway
of periapical infection spreading for maxillary first and second premolars [2-5].
In addition, increased pneumatization of the maxillary sinus and decreased alveolar
bone thickness can often be observed after extraction of premolars and molars, which
complicates implant placement [6,7]. Spread of periapical infection
from maxillary molars to surrounding structures was previously demonstrated on computed
tomography (CT) images [2]. The influence of root protrusion in
the maxillary sinus floor may evoke tooth roots resorption or tipping during orthodontic
treatment [8,9].
The maxillary tooth root and sinus relationship can be assessed using different
radiographic techniques. Conventional radiographs used in dental clinics include
mainly intraoral periapical (PA) radiographs and to a lesser extent orthopantomograms
(OPG). Virtually every radiographic examination in the dental clinic starts with
a PA radiograph. In contrast, it has been shown in surveys, that up to 95% of dentists
refer their patients solely for an OPG scan before implant placement with only a
relatively small number of referrals for a CT scan [10,11]. It
is interesting to know, that several studies assessed the vertical and horizontal
relationship between the tooth root apex and the inferior wall of the maxillary
sinus using CT diagnostic method [12-16]. It was concluded that
CT is more accurate than OPG in assessing the tooth root and sinus relationship
[17]. Anyhow, two-dimensional radiographs suffer from superimposition
artifacts inherent to the scan method frequently resulting in overprojection of
maxillary teeth roots onto the sinus floor. Authors of two studies correlating CT
scans and OPG images findings confirmed that OPG alone is unreliable in assessing
the relationship between the teeth roots and the maxillary sinus [17-18].
Similarly the reliability of PA radiographs in detection of root penetration in
the maxillary sinus also needs further investigations [19]. Otherwise,
cone beam computed tomography (CBCT) scanning technology, which has been in wide
use in dentistry for the last decade, is advantageous over traditional CT scanning
technology since it provides comparable images at reduced dose and cost [20,21].
CBCT proved to be a reliable technique for visualizing anatomical structures in
the maxillofacial region and for assessing the relationship of teeth roots to adjacent
structures including the maxillary sinus [22-25].
The purpose of the present study was to investigate the reliability of both periapical
radiographs and orthopantograms for exact detection of tooth root protrusion in
the maxillary sinus by correlating the results with cone beam computed tomography
as a reference "gold standard".
MATERIAL AND METHODS
Data collection
In this retrospective study the database of patients scanned with CBCT at the
Department of Oral Radiology, University of Amsterdam was examined. The initial
selection criteria were: patients older than 18 years and the presence of one or
multiple posterior maxillary teeth with a fully visible inferior maxillary sinus
wall. Initial screening with these criteria resulted in the inclusion of 1400 CBCT
patient's images. The images were made with the NewTom 3G CBCT system (QR SLR, Verona,
Italy) using the 9'' field of view (FoV) selection and 110 kVp and 8 mA. Subsequently,
the patients' records database was searched for matching conventional OPG images
and intraoral PA radiaographs. Only those OPG images and PA radiographs were included
in the study, where the relationship of teeth roots to the maxillary sinus floor
could be adequately assessed. First, a dataset of matching OPG images of 101 patients
(33 males and 68 females; aged 18 to 77 years; mean age = 49 years) with 628 maxillary
premolars and molars was obtained. A second dataset of matching PA radiographs of
93 patients (37 males and 56 females; aged 23 to 74 years; mean age = 51 years)
with 359 maxillary premolars and molars was also identified and included in this
study. The OPG images were performed using the Cranex Tome unit (Soredex, Tuusula,
Finland) and the PA radiographs using a fixed intraoral unit (Heliodent MD, Siemens,
Erlangen, Germany) and size 2 phosphor-plate films (Digora, Tuusula, Finland).
Data analysis
Four dentists following a master course in maxillofacial radiology at the Department
of Oral Radiology were recruited as observers for this study. The datasets were
collected by one investigator (maxillofacial radiologist, Department of Oral Radiology,
University of Amsterdam) who did not participate in the observations. The observers
were blinded to the patients' biographic data including name, gender and age. The
observers were calibrated by training them in the radiographic features for identifying
the relationship of the teeth roots to the inferior wall of the maxillary sinus.
The identifying radiographic feature in all imaging modalities was to assess whether
the apical root tip of right and left first and second premolars, first, second
and third molars is over (in), against (doubtful) or under (out) the white line
depicting the inferior border of the maxillary sinus. The observers assessed first
the conventional PA radiographs and OPG and then the CBCT images. All measurements
were made with consensus among the four observers. Radiographs were displayed under
standardized lightening conditions of reduced dim light on a 21-inch flat-panel
screen (resolution 1680 x 1050, Philips Brilliance, Amsterdam, Netherlands). The
PA radiographs and OPG images were displayed using Emago imaging software (v.5.4,
Amsterdam, Netherlands) (Figure 1). The CBCT images datasets were
reviewed using the NewTom 3G software (v.2.17, Verona, Italy). Multiplanar reformatted
reconstructions in the axial, coronal and sagittal planes were created and the relationship
of the teeth root tip to the maxillary floor was assessed in all three reconstruction
planes on all slices (Figure 2). Voxel size in CBCT images were
0.3 mm with no inter-slice thickness (contiguous dataset). Image manipulation by
changing contrast/brightness levels, sharpness filter and magnification was permitted
to enhance visibility.
An example of no protrusion of tooth #27 palatal root tip (arrow) in the maxillary
sinus according to cone beam computed tomography scans assessment: A = axial
slice; B = coronal slice; C = sagittal slice. Tooth root #27 overprojection
onto the maxillary sinus floor using orthopantomogram images (D) and periapical
radiographs (E).
An example of tooth #26 palatal root protrusion in the maxillary sinus according
to cone beam computed tomography scans multiplanar reformatted images: A
= axial slice; B = sagittal slice; C = coronal slice.
A single score was obtained for each tooth whether single or multirooted for
each imaging technique with the following classification: at least one root tip
is in the sinus (class 1); at least one root tip is against the sinus wall (class
2) and all roots tips are not in the sinus (class 3).
Statistical analysis
All measurements were entered and analyzed using SPSS software (v.16, SPSS Benelux,
Gorinchem, Netherlands). A two-sided Chi square test and Cohen's weighted kappa
coefficient were used to correlate the OPG images and PA radiographs measurements
with the CBCT assessment scores. A univariate analysis of variance (ANOVA) was also
conducted to assess any possible correlation between the proportion of presence
of root in the sinus and patients' age and sex. Differences were considered as statistically
significant when P values were < 0.05.
RESULTS
In the assessment of 628 teeth included in the OPG images dataset (Table
1), sixty eighth teeth (10.8%) were identified as class 1, 50 (8%) class 2 and
510 (81.2%) class 3. Within the 359 teeth included in the PA radiographs dataset
(Table 2), sixty six teeth (18.4%) were identified as class 1,
19 (5.3%) class 2 and 266 (76.3%) class 3. Table 1 shows the classifications,
proportions, sensitivity, specificity and Cohen's weighted kappa coefficient results
between (OPG) images and CBCT scans for protrusion of roots in the maxillary sinus
per tooth. Overall correlation between OPG and CBCT assessments scores independently
of tooth type was 50%, 26% and 56.1% for class 1, class 2 and class 3, respectively
(Cohen's kappa [weighted] = 0.1). Overall correlation between PA radiography and
CBCT assessments scores (Table 2) independently of tooth type
was 75.8%, 15.8% and 56.9% for class 1, class 2 and class 3, respectively (Cohen's
kappa [weighted] = 0.24). There was no statistically significant correlation between
the proportion of root protrusion in the maxillary sinus and age (P = 0.32) or sex
(P = 0.40) in both datasets.
Classificationa of maxillary premolars and molars roots relationship to the maxillary sinus floor according to cone beam computed tomography scans and orthopantomogram images assessment results
Maxillary
teeth
N
Cone beam computed
tomography
(n [%])
Orthopantomography
(n [%])
True
positive
True
negative
False
positive
False
negative
Sensitivity
Specificity
Kappa
coefficient
Class 1
Class 2
Class 3
Class 1
Class 2
Class 3
First
premolar
148
0
1 (0.7)
147 (99.3)
32 (21.6)
24 (16.2)
92 (62.2)
0
62.2
21.8
0
0
74
0.01
Second
premolar
146
2 (1.4)
6 (4.1)
138 (94.5)
40 (27.4)
21 (14.4)
85 (58.2)
100
60
24.6
0
100
70
0.05
First
molar
144
34 (23.6)
17 (11.8)
93 (64.6)
51 (35.4)
25 (17.4)
68 (47.2)
41.2
47.3
30.1
52.9
45
61
0.01
Second
molar
145
26 (17.9)
25 (17.2)
94 (64.8)
51 (35.2)
29 (20)
65 (44.8)
57.7
50
33
26.9
68
60
0.16
Third
molar
45
6 (13.3)
1 (2.2)
38 (84.4)
13 (28.9)
9 (20)
23 (51.1)
50
51.1
26.3
50
50
66
0.11
Total
(n [%])
628 (100)
68 (10.8)
50 (8)
510 (81.2)
187 (29.8)
108 (17.2)
333 (53)
0.1
aClass 1 = at least one root tip is in the sinus; Class 2 = at least one root tip is against the sinus wall; Class 3 = all roots tips are not in the sinus.
Classificationa of maxillary premolars and molars roots relationship to the maxillary sinus floor according to cone beam computed tomography scans and periapical radiographs assessment results
Maxillary
teeth
N
Cone beam computed
tomography
(n [%])
Periapical radiography
(n [%])
True
positive
True
negative
False
positive
False
negative
Sensitivity
Specificity
Kappa
coefficient
Class 1
Class 2
Class 3
Class 1
Class 2
Class 3
First
premolar
90
3 (3.3)
1 (1.1)
86 (95.6)
8 (8.9
7 (7.8)
75 (83.3)
0
84.9
8.1
66.7
0
91
0.05
Second
premolar
88
8 (9.1)
8 (9.1)
72 (81.8)
17 (19.3)
19 (21.6)
52 (59.1)
25
63.9
16.7
50
59
79
0.12
First
molar
90
28 (31.1)
6 (6.7)
56 (62.2)
71 (78.9)
2 (2.2)
17 (18.9)
92.9
28.6
69.6
3.6
96
29
0.16
Second
molar
83
27 (32.5)
4 (4.8)
52 (62.7)
59 (71.1)
4 (4.8)
20 (24.1)
81.5
32.7
63.5
11.1
88
33
0.13
Total
(n [%])
359 (100)
66 (18.4)
19 (5.3)
266 (76.3)
155 (44.3)
32 (8.9)
164 (46.8)
0.24
aClass 1 = at least one root tip is in the sinus; Class 2 = at least one root tip is against the sinus wall; Class 3 = all roots tips are not in the sinus.
In both PA radiographs and OPG images datasets, class 1 relationship in which
the root penetrated the sinus wall was most frequently observed with the first and
second molars (Tables 1 and 2). Class 2 relationship in which
the root was against the sinus wall, was observed in a relatively small number of
cases and was also most frequently associated with the first and second molars.
The majority of the other cases were identified as class 3 in which there were no
contact between the root and the sinus floor and this was most frequently observed
with the first premolar (Tables 1 and 2).
DISCUSSION
The present investigation was conducted to assess the reliability of PA and OPG
radiographs in detection of tooth root protrusion of the maxillary sinus inferior
wall. The correlation results with CBCT measurements, per tooth and overall, demonstrated
low reliability of both OPG scans and PA radiographs for detection of tooth root
protrusion (Tables 1 and 2). Due to the super-imposition of anatomical
structures on conventional two-dimensional radiographs, the roots of the premolars and molars were overprojected on the wall
of the maxillary sinus. There was better correlation between CBCT scans and PA radiographs
scores than between CBCT scans and OPG images scores. This may be due to the use
of paralleling technique for intraoral radiographs with the aid of a film holder
and a beam indicating device that both the film and the long axis of the root were
parallel to each other with the x-ray beam passing perpendicularly to both root
and film [26]. It is noteworthy that a standardized paralleling
technique is routinely used in our institute unless a contraindication favors the
use of the bisecting angle technique instead. Therefore, the results could differ
somewhat from private dental clinics.
The present study results revealed, independently on applied radiographic method,
that the maxillary first premolar tooth did not perforate the sinus wall in most
cases while first and second molars were the most frequent teeth to penetrate the
maxillary sinus wall (Tables 1 and 2). This is in agreement with
previous findings [16,18]. There were many false positives in
both techniques. The largest number of false positives was with the maxillary second
molar (33%) for OPG while it was the first molar (69.6%) for PA. It was previously
found that the least thickness of the sinus floor is at the maxillary second molar
area and that the average distance of the root apex from the sinus floor was the
longest in the first premolar area and shortest in the second molar area [15,27].
Several classifications for the relationship of the teeth to the maxillary sinus
floor were previously suggested. Freisfeld et al. [28] suggested
a classification applicable for both panoramic images and CT scans based on the
first molar. Kwak et al. [16] suggested an elaborate classification
for the vertical relationship of the tooth root apex on CT scans and the results
were compared to histological findings. They found that the inferior wall of the
sinus was located above the level connecting the buccal and lingual roots apices
in the first and second molars region in 54.5% and 52.4% of cases respectively.
Sharan et al. [18] extended Freisfeld's et al. [28]
classification and made this applicable to both OPG images and CT scans. The classification
used in present study was a reduced version of that of Sharan et al. [18]
classification. Sharan et al. [18] found that in 80 subjects
with 422 maxillary roots, there was high agreement of 86% to 96% between CT scans
and OPG images for roots that did not project on the sinus floor. While only 39%
of the roots that projected on the sinus cavity in OPG images showed protrusion
into the sinus on CT scans. Their results also demonstrate that OPG images cannot
provide the clinician with sufficient information about the true relationship between
the sinus floor and root tips when the root is projected on the sinus. The results
of this study corroborate those findings and additionally suggest that PA radiography
could be a more reliable technique than OPG in detecting root protrusion in the
sinus.
Present study was limited that two separate databases where employed to assess
the accuracy of OPG and PA radiography. A common database with a sufficient sample
size for statistical analysis in which the patient has matching CBCT, OPG and PA
radiographs could not be identified. CBCT was used in this study as a "gold standard"
since the tomographic nature and inherently high image contrast of this imaging
modality compared to conventional projection radiography permits better assessment
of the relationship between the root apex and the sinus wall. However, CBCT image
artifacts and increased noise levels might occasionally mask the root and the sinus
wall rendering precise assessment difficult. The reliably of the "reference standard"
is thus limited by the spatial resolution and contrast of the system used. Additionally,
this study focused mainly on the vertical relation of the root to the maxillary
sinus and the horizontal relationship was not assessed.
CONCLUSIONS
The results of present study demonstrated that both periapical radiographs
and orthopantomograms were not reliable in determination of exact relationship between
the apex of tooth root and the maxillary sinus floor. Periapical radiographs were
slightly more reliable than orthopantomograms in determining this relationship.
ACKNOWLEDGMENTS AND DISCLOSURE STATEMENTS
The author would like to thank Dr. Jamshed Tairie, Department of Oral
Radiology, Academic Centre for Dentistry Amsterdam (ACTA), for his support with
data analysis and Dr. Hans Verheij, Department of Oral Radiology, Academic Centre
for Dentistry Amsterdam (ACTA), for his support with the statistical analysis.
The author declares that there is no conflict of interest of any kind in this
study.