Keywords
cone-beam computer tomography - gender dimorphism - gender determination - maxillary
sinus index - maxillary sinus volume
Introduction
Personal identification is a key component of forensic investigation, regarded as
one of the most significant priorities in solving criminal cases or evaluating disasters
that are of forensic concern.[1] It may include using pieces of evidence, including body parts or radiographic images,
to make estimates or predictions related to individuals' parameters like stature,
weight, or sex.[1] Anthropometric and radiographic measurements of body parts are therefore important
in forensic or medical-related cases because they can serve as “pieces of evidence”
to use for personal identification. Gender determination is the use of morphological,
physiological, and biochemical differences between males and females in the living
and human remains and makes predictions as to the sex of the individual.[2] It is used in the initial stages in forensics and can also help clinicians in formulating
empirical treatment options.[2] The skull bone is one of the skeletal parts of the body that are used for gender
determination. Maxillary bone and sinuses are known to remain fairly intact even when
the skull bones are badly blemished in severe accidental injuries.[3]
[4] Maxillary sinuses (MSs) are the largest pyramidal paranasal sinuses located in the
maxillary bones.[5]
[6] The location of the MS is below the orbit, and the sinus floor is composed of the
alveolar bone and the apex facing laterally toward the zygomatic bone. Its development
is initiated in the 10th week of intrauterine life and in the 11th week of development,
the mucosa lining the further anterior end of the ethmoid infundibulum exhibits penetrations
into the surrounding mesenchyme, resulting in an independent cavity that represents
the primordium of the MS.[7] The sinus grows rapidly during two developmental periods: from the 17th to the 20th
week and between the 25th and the 28th week.[7] The MS and ethmoidal sinuses begin to form when three horizontal extensions emerge
from the nose's lateral wall and grow in directions. The inferior projection, known
as the maxilla-turbinate, forms the MS.[8] The superior projection known as the ethmoid turbinate forms ethmoidal air cells
and the drainage channels that correspond to them. At birth, the MS are primitive.
After the ninth year, they expand, and they fully manifest throughout puberty, reaching
the adult size around 18 to 20 years of age.[8] MS being the largest of the sinuses has many neurovascular relations like anterior
superior alveolar nerve and arteries and structures in the pterygopalatine fossa.[9] Apart from humidification of inhaled air, reducing the weight of the skull, production
of nitrogen monoxide by the MS is regarded an important function in local immunological
defense mechanisms.[9]
The low frequencies of developmental defects like hypoplasia, etc., seen in the MS
make it a reliable anatomical structure in forensic sciences.[5] In the MS, pneumatization varies from person to person and between the genders.[5] The pneumatization of the MS is the sinus extension toward the alveolar bone, which
is affected by genetic and environmental factors.[6] Its anatomy has been used for identification of skeletal remains and determination
of gender. Various studies have concluded that the measurements of the MS can help
determine the gender in forensic investigation.[2] Individual variations due to the complex anatomy make the paranasal sinuses an area
for exploration in forensics for determining individuals' age and gender.[2]
The conventional radiograph is the most used technique to analyze the MS. However,
it has its limitations when it comes to three-dimensional (3D) structure research.
Cone-beam computer tomography (CBCT), followed by a 3D reconstructions provides valuable
measurements like craniocaudal, transverse, and anteroposterior (AP) diameters; this
has demonstrated consistency with manual measurements of the MS obtained from dry
human skulls.[7] The advantages of CBCT include its providing 3D multiplanar images, a lower radiation
dose than conventional computed tomography (CT), lower costs, and a shorter acquisition
time.[7] The CBCT is now used as a reliable method for evaluating MS volumes (MSVs).[5] The MS index (MSI), determined using the MS height and width, is a relatively new
parameter in the MS evaluation, although not many studies used it for such purpose.[1] The MSI is easier to determine as is calculated by dividing the sinus height with
depth and can be important in the sinus evaluation during implant insertions, diagnosing,
and treating cases of malocclusion, among other pathologies.[1]
Although studies were conducted to provide volumetric parameters of MS, to the best
of our knowledge, only very few studies were conducted that presented the morphometry
of the MS in terms of MSI and MSV among Saudi population. The present study is therefore
aimed at establishing baseline data for these MS parameters (MSI and MSV) among a
population of Saudi adults to supplement the few existing data. More importantly,
the purpose was to investigate the reliability of using MSI, which is a relatively
new and easy-to-use tool used in MS morphometry. Additionally, we want to compare
the degree of accuracy of gender prediction using MSI with that of MSV, which was
well studied for gender determination. This may come handy because obtaining MSI is
much easier since it requires only two-dimensional images, unlike MSV, which would
require 3D images.
Materials and Methods
Study Setting and Design
The study was conducted at the Dental Clinic of the King Faisal University, Saudi
Arabia. A retrospective cross-section design was employed to obtain the CBCT images
from year 2020 to 2024.
Samples Selection
Two hundred and seventy-five CBCT images were randomly selected from the image databank
of the dental clinic. Images were of male and female adult (20–60 years) Saudi population.
Any obvious anatomical abnormality was excluded before the final selection of images.
Ethical approval (number: KFU:REC:2025-ETHICS:3018) was obtained from the institute's
deanship of scientific and research unit.
CBCT Image Analysis and Measurements
The CBCT machine was a 3D Accuitomo 170 (MORITA, Japan) with 90 Kv, 5 to 8 mA. It
uses an exposure time of 17.5 seconds and a 0.25-mm voxel size. A Vision iCAT imaging
software, downloaded in the personal computer, was used in processing MS images. Axial,
coronal, and sagittal multiplanar image views were used in measuring different MS
dimensions using standard measurements. The image analyses were performed by a radiologist
(with more than 8 years of experience) who helped in the calibrations and obtaining
the images, and a dentist (with 15 years' experience) who did the measurements. [Fig. 1] shows the measurements of the MS height, depth, and width. All measurements were
taken using a line ruler in the software, measurements to the nearest 1.5 mm as follows:
Fig. 1 Cone-beam computer tomography (CBCT) images of maxillary sinus (MS) height (A), width, and depth (B).
-
MS height (H): maximum vertical height from the lowest point on the floor to the roof,
seen on coronal images.
-
MS width (W): maximum distance between the medial wall and the outermost point, seen
on coronal images.
-
MS depth—AP (D): distance from the base to the apex seen in axial images.
-
The MSV was calculated using the formula H*W*D*0.33 mm3.
-
MSI was calculated using the formula H/W.
Statistical Analyses
The variables used for the analysis are the right and left MSV and MSI and the values
obtained were expressed in terms of minimum, maximum, and mean ± standard deviation
(SD). A Kolmogorov–Smirnoff test was performed to test whether or not the variables
were normally distributed. Student's t-test was used for mean comparison between genders and to test for the strength of
gender dimorphism. Discriminant function (DF) analysis was performed for the determination
of gender using MSV and MSI as predictor variables. A DF equation model was obtained
with gender as a classifying variable and MSV and MSI as independent variables. The
analyses were performed using SPSS version 23 (IBM Corporation, for Windows), and
5% (p < 0.05) level of error was considered significant for statistical inference.
Results
The study was conducted over 275 image samples of adult males and females from indigenous
population; the male-to-female ratio was 1.1:1, and the age range was 20 to 60 years
with a mean of 41years ± 10.98 SD. [Table 1] shows the means and SD of the right and left variables. The overall mean of the
MSV was found to be 12.64 cm3 ± 3.47 SD for the right sinus, and 12.04 cm3 ± 3.10 SD for the left. No significant mean difference was found between the right
and left MSVs (p = 0.33). The mean MSI in the right and left were 0.86 ± 0.10 and 0.90 ± 0.12, respectively,
with no statistical difference (p = 0.21).
Table 1
Descriptive statistics of the right and left maxillary sinus volume and index
|
Variable
|
n
|
Min
|
Max
|
Mean
|
Standard deviation
|
p-Value
|
|
RsV (cm3)
|
275
|
9.61
|
21.05
|
12.67
|
3.46
|
0.33
|
|
LsV (cm3)
|
275
|
9.08
|
17.51
|
12.04
|
3.10
|
|
RMSI
|
275
|
0.58
|
1.14
|
0.86
|
0.10
|
0.21
|
|
LMSI
|
275
|
0.58
|
1.24
|
0.90
|
0.12
|
Abbreviations: LMSI, left maxillary sinus index; LsV, left sinus volume; RMSI, right
maxillary sinus index; RsV, right sinus volume.
[Table 2] shows the independent samples t-test done to compare the mean difference of MSV and MSI between the males and females.
The findings showed significant gender dimorphism in all the variables, with males
having significantly higher MSV and MSI (p < 0.001). The trend was similar on both right and left sides.
Table 2
Independent t-test comparison of MSV and MSI between males and females
|
Variables
|
Males
|
Females
|
t-Test
|
p-Value
|
|
n
|
Mean
|
SD
|
n
|
Mean
|
SD
|
|
RsV (cm3)
|
144
|
13.64
|
3.22
|
131
|
10.03
|
1.96
|
20.14
|
0.001
|
|
LsV (cm3)
|
144
|
12.14
|
2.90
|
131
|
9.25
|
1.69
|
30.21
|
0.001
|
|
RMSI
|
144
|
0.919
|
0.08
|
131
|
0.80
|
0.10
|
10.74
|
0.001
|
|
LMSI
|
144
|
0.961
|
0.10
|
131
|
0.84
|
0.11
|
9.10
|
0.021
|
Abbreviations: LMSI, left maxillary sinus index; LsV, left sinus volume; MSI, maxillary
sinus index; MSV, maxillary sinus volume; RMSI, right maxillary sinus index; RsV,
right sinus volume; SD, standard deviation.
The DF test performed using MSVs (right and left) to predict gender is summarized
in [Table 3]. One hundred and twenty-four of the 144 males were correctly classified by the DF
model as males, and 107 of the 131 females were correctly classified as females. This
gives a sensitivity of 85% and a specificity of 84%. Conversely, when the DF was performed
using MSI as predictors ([Table 4]), 118 out of the 144 males and 92 out of the females were correctly classified.
This gives a sensitivity of 83% and specificity of 70% of the function using sinus
index, which is slightly lower than that for sinus volume.
Table 3
Discriminant function test using maxillary sinus volume as predictors for gender
|
Predicted group
|
Total
|
|
Original count
|
Male
|
Female
|
|
|
Male
|
122
|
22
|
144
|
|
Female
|
24
|
107
|
131
|
|
%
|
|
Male
|
84
|
16
|
100
|
|
Female
|
15
|
85
|
100
|
Table 4
Discriminant function table using maxillary sinus index as predictor for gender
|
Predicted group
|
Total
|
|
Original count
|
Male
|
Female
|
|
|
Male
|
119
|
25
|
144
|
|
Female
|
39
|
92
|
131
|
|
%
|
|
Male
|
83
|
17
|
100
|
|
Female
|
30
|
70
|
100
|
[Table 5] summarizes the effect sizes and the strength of prediction power by using both MSV
and MSI as predictors. The Wilks' lambda shows a lower value (0.507) when MSV is used
as predictors for gender determination than the value obtained (0.696) when MSI was
used. This indicates that MSV gives a better model with stronger discriminating power
for gender prediction. Both models are, however, statistically significant (p < 0.001).
Table 5
Effect sizes and discriminating power of the DFT for gender prediction
|
Variable
|
Wilks' lambda
|
Standardized coefficient
|
Canonical coefficient
|
p-Value
|
|
RsV
|
0.507
|
0.481
|
0.177
|
0.0001
|
|
LsV
|
0.564
|
0.233
|
|
RMSI
|
0.696
|
0.455
|
8.733
|
0.0001
|
|
LMSI
|
0.346
|
2.271
|
Abbreviations: DFT, discriminant function test; LMSI, left maxillary sinus index;
LsV, left sinus volume; RMSI, right maxillary sinus index; RsV, right sinus volume.
The standardized DF coefficient shows that MSV has more explanatory power with overall
coefficients of 0.53 than MSI with a coefficient of 0.401. This may indicate that
MSV is a better predictor than MSI for gender prediction. The DF equations for the
two models are found to be statistically significant (p = 0.001).
The DF equation for MSV was determined to be D = 0.177*RV + 0.233*LV – 4.390, with values toward 0.759 (> 0) to be classified as
males and values toward −0.880 (< 0) to be classified as females. On the other hand,
the DF equation for MSI was determined to be D = 8.73*RMSI (right MSI) + 2.271*LMSI (left MSI) – 9.27, with values toward 0.607
(> 0) classified as male and −0.604 (< 0) to be classified as female.
Discussion
Examination of the skull, pelvic bone and long bones can give up to 90.0 to 95.0%
accuracy in sex determination.[9]
[10] Both conventional CT scan and CBCT have been reported to be reliable methods in
the estimation of different dimensions of the MS.[11] Studies have also shown that measurements of the MS sizes obtained from skull measurements
were similar and consistent to those obtained by CT scans.[12]
[13]
[14] It may, therefore, be reasonable to assume that CBCT is a reliable method for measuring
the dimensions of the MS. Apart from being an easy tool to be used in forensic analysis,
knowing the MSI and MSV may be useful in planning sinus graft procedures, which are
frequently conducted to rebuild and restore the edentulous posterior maxilla that
has been affected by alveolar bone loss, following extraction and sinus pneumatization.[15]
[16] During surgical procedures an elevated risk of hemorrhage is caused by the varied
position of the vascularization of the Schneiderian membrane—which can be perforated—and
the posterior-lateral projection of the sinus walls.[17] A thorough understanding of the MS vascular network is therefore necessary to prevent
any difficulties during sinus lift surgery.[17] In approximately 10 to 30% of cases, the posterior superior alveolar artery, which
is situated on the MS lateral wall, is present where the lateral window is formed
for sinus floor elevating procedures.[18]
In this study, we used CBCT images to obtain MSV and MSI, provided reference ranges
for both, and used statistical methods to predict gender of the subjects using these
dimensions. We found a statistically significant difference between males' and females'
MSV and MSI. The study also found that DF tests can be used to predict gender using
MSV and MSI with a moderate accuracy, and that using MSV gives a better prediction.
Studies have differed in their findings concerning gender dimorphism in MS dimensions.
While we found a statistically significant gender difference in the mean MSV and MSI,
many have found no such difference. Najem et al found no gender dimorphism in MS height
and width among a population of adult Egyptians, using CBCT.[19] They examined a sample of only 86 images and measured only the height and width.
Similarly, Hettiarachchi et al[20] and Ghada et al[21] found no gender difference in MSV among CBCT images of adults. Both these studies
were also conducted on a relatively small sample of 20 and 67, respectively, and the
latter study used conventional CT rather than CBCT, which was used for this study.
On the other hand, there are studies that show significant gender differences similar
to our findings.[22]
[23]
[24] Vidya et al in a study on 30 dry skulls of South Indians, found that the MSV of
the males was slightly more than those in the females.[25] Furthermore, although not many studies evaluated the effect of MSI on gender determination,
Khaitan et al[1] and Chalkoo and Salma[26] observed that MSI is significantly different in males than in females. Both of these
studies used lateral X-ray cephalogram in measuring the sinus dimensions. In Europe,
a study about gender determination found that the volume of MS was significantly larger
and wider in males than in females.[27]
The DF test we performed on the samples was able to predict and classify 122 males
correctly out of 144 and 107 out of 131 of females correctly, giving a sensitivity
of 85%. This is when MSV was used as a predictor. A similar study conducted by Uthman
et al found that 74.4% of males and 73.3% of females were correctly classified using
MS dimensions.[28] Similarly, Chandra et al have found that MS area and perimeter by lateral cephalogram
could be used accurately in gender determination. The correct predictive accuracy
they found was 70.8% in males and 62.5% in females.[29] Some investigators in Egypt conducted a study to predict gender from some radiologic
measurements of the MS using multidetector CT and came up with a predictive accuracy
of 70.8% in males and 62.5% in females.[4]
Similar to our study, Prabhat et al examined the MS of a sample of 30 adults' CT scans
in the Indian population. They conducted DF tests and the method was able to predict
gender with an accuracy of 80.0% in males and 86.7% in females, with an overall accuracy
rate of 83.3%.[30]
This study found that MSV was a better predictor of gender than MSI with both the
right and left MS dimensions added in the DF equation. Not many studies were conducted
on comparing the two variables for gender determination in the same population. Prabhat
et al conducted DF test to obtain an overall accuracy rate of 83.3% with three MS
parameters entered into the model.[30] Our DF equation is simple and fairly accurate (85%) with only two variables entered.
This could be because of a larger sample size (275) in our population, the use of
CBCT, and/or the variable volume we used in the equation.
Conclusion
The study provided a normative value for MSV and MSI in Saudi Arabian population using
CBCT. It concluded that the two variables are sexually dimorphic and that both are
good predictors for gender determination, with MSV being a better predictor. The DF
equation performed provided a high predictive accuracy, which was comparable if not
higher than many studies.
Recommendations
The probability of surgical problems could be significantly decreased with accurate
diagnosis, appropriate treatment planning, and familiarity with the surrounding anatomy.
It is important to understand that the size of the MS varies between men and women.
Surgeons may provide patients with more individualized care as a result of this knowledge.
When diagnosing sinusitis, contemplating orthodontic procedures, carrying maxillofacial
surgeries, or implanting dental prosthesis, understanding these distinctions is essential
to getting good results. Future research might examine the surgical consequences of
MS measurements in greater detail, in relations to neighboring anatomical structures.
It is therefore possible to look into the effects of these variations on associated
surgical specialties such as ophthalmology and neurosurgery.
