Key words: Analysis - anatomic variation - cephalometry - frontal sinus - radiography
INTRODUCTION
Growth prediction is defined as the estimation of alterations in speed and direction
of future growth.[1 ] The growth patterns of the mandible, maxilla, and other craniofacial structures
should be taken into consideration as essential components to determine the time of
occurrence, duration, and prognosis of malocclusions. Growth prediction can help clinicians
in more accurate diagnosis and treatment planning.[2 ]
Development of craniofacial bones takes place in relation to one another and is influenced
by various factors. The frontal sinus, one of the paranasal sinuses located in the
skull, is formed following pneumatization of the frontal bone, which is directly influenced
by the interactions of the respiratory epithelium and activity of adjacent osteoclasts.[3 ],[4 ] Pneumatization may be absent in frontal bone, resulting in sinus aplasia.[5 ] Since the left and right sinuses are developed independently, asymmetrical sinuses
may also be found. Variations in the extent of pneumatization individualize frontal
sinus morphology and diversity in shape and capacity and symmetry of the frontal
sinus.[6 ] The visibility of the frontal sinus on radiographs depends on the amount of pneumatization.
Frontal sinus anatomy can also help in identification of the deceased by comparing
pre‑ and post‑mortem radiographs.[7 ],[8 ]
Evidence shows that frontal sinus dimensions are multifactorial and related to genetic
factors and weather conditions.[9 ] In 1990, Blaney stated that craniofacial structures affect the morphology of the
paranasal sinuses.[10 ] An association between hypertrophic frontal sinus and overgrowth of the mandible
exists in acromegaly (production of excessive amounts of growth hormone).[11 ] The correlation of frontal sinus anatomy and its dimensions with the mandible in
patients with normal systemic conditions has been previously evaluated.[5 ],[12 ]
[13 ]
[14 ]
[15 ] Rossouw et al .[5 ] suggested the area of frontal sinus as a predictor of mandibular growth pattern
and concluded that a Class III patient with a larger frontal sinus would more likely
need an orthognathic surgery besides orthodontic appliances in the future. They reported
that larger frontal sinuses were associated with skeletal Class III malocclusion,
longer condyles, and wider symphysis.[5 ] Another study on adults with skeletal Class I, II and III relations measured the
area of frontal sinus on their lateral cephalograms (LCs) and indicated that large
frontal sinuses were associated with large mandibles irrespective of their positional
relationship; however, there was evidence that Class III skeletal malocclusions were
more likely associated with larger frontal sinus areas.[12 ] Others have investigated the relationship between the development of the frontal
sinus and the person's height and concluded that frontal sinus can serve as an indicator
for assessment of developmental maturity.[13 ]
[14 ]
[15 ]
Frontal sinus can be evaluated in the sagittal plane using lateral cephalometry and
in the coronal plane using posterior-anterior (PA) cephalometry, which are routinely
ordered for orthodontics patients. This study was designed to assess the possible
associations between the frontal sinus dimensions and craniofacial indices both sagittal
and vertical, using pretreatment LC and PA radiographs in a group of the Iranian population.
MATERIALS AND METHODS
Study population
This retrospective study was approved by the Research Institute of Dental Sciences,
Shahid Beheshti University of Medical Sciences, Tehran, Iran. It was performed on
patients presenting to the Department of Orthodontics, Dental School, Shahid Beheshti
University of Medical Sciences from 2011 to 2013. The included patients were ≥12
years old and had true scale LC and PA radiographs. All these radiographs were taken
using a Cranex D X-ray unit (Soredex, Helsinki, Finland) with exposure settings of
66–70 kVp, 10 mA, and 14.2 s, with patient in centric occlusion and natural head position.
The exclusion criteria were as follows:
Patients with no records of their age or gender
Patients with signs of infection or sinus pathology based on radiographs
Congenital syndromes involving craniofacial bones, palatal clefts, hemifacial microsomia,
or hypertrophy
History of trauma to the nasomaxillary complex
History of orthognathic surgery
Poor quality of radiographs.
Measuring sinus dimensions
Sinus dimensions were measured on PA radiographs and LC of patients before orthodontic
treatment by Dolphin Imaging Software (Dolphin Imaging, Chatsworth, CA, USA) [Figure 1a ] and [b ]. Briefly, sinus borders were marked excluding the crista galli by an experienced
orthodontist. Extension of the superior orbital rim was considered as the lower limit
of sinus, in cases in whom the inferior sinus border was not detectable.[16 ],[17 ] Measurements of the maximum height, width, and area of the frontal sinuses were
made by AutoCAD 2007 software (Autodesk Inc., San Rafael, CA, USA) with 2.5% error
in both sagittal and frontal planes by two examiners [Figure 1c ] and [d ].[18 ] The mean values of measurements made by the two examiners were reported for each
patient. Intraclass correlation coefficient was measured to assess the interexaminer
reliability.
Figure 1: A sample case of frontal sinus measurement and cephalometric analysis. (a) Landmarks
on lateral cephalogram. (b) Frontal sinus traced on posterior?anterior cephalogram.
(c) Measurement of sinus dimensions on the sagittal plane. (d) Measurement of sinus
dimensions on the coronal plane
Cephalometric analysis
Anatomical landmarks were identified through Dolphin software, and their accuracy
was ensured by an orthodontist [Figure 1a ]. Fifteen cephalometric variables representing maxillofacial growth pattern in both
vertical and anterior-posterior dimensions were calculated [Tables 1 ]and[ 2 ].[19 ]
Statistical analysis
Descriptive values (mean and standard deviation) were reported for each parameter.
Normal distribution of data was confirmed by Kolmogorov–Smirnov test (P > 0.05). Student's t -test for independent samples was used to compare sinus dimensions between males
and females. The relationship between sinus dimensions and cephalometric indices
was assessed by the Pearson's correlation coefficient. To control for the effect
of age and gender on this relationship, a linear regression model was applied. Statistical
analysis was performed using SPSS version 21 software (SPSS Inc., IL, USA) at a significance
level of 0.05.
Table 1:
Definition of the cephalometric landmarks used in the study
Landmark
Definition
Sella (S)
Midpoint of sella
Nasion (N)
The most anterior point of the frontonasal suture
Porion (Po)
Uppermost point of the external auditory meatus
Orbitale (Or)
Lowermost point of the bony orbit
Articular
Intersection of the images of the posterior margin of the ramus and the outer margin
of the cranial base
Gonion (Go)
Intersection of the lines tangent to the posterior border of the ramus and the lower
border of the mandible
Anterior nasal spine (ANS)
The most anterior point of the tip of the anterior nasal spine
Posterior nasal spine (PNS)
Intersection of the continuation of the anterior wall of the pterygomaxillary fissure
and the nasal floor
Menton (Me)
The most inferior point of the outline of the symphysis
Gnathion (Gn)
The most anterior inferior point on the bony chin
Pogonion (Pog)
The most anterior point of the symphysis
A‑point
The deepest point on the outer contour of the maxillary alveolar process
B‑point
The deepest point on the outer contour of the mandibular alveolar process
RESULTS
A total of 144 subjects were enrolled; of which, 78 were female and 66 were male.
The mean age of patients was 19.26 ± 4.66 years (range: 13–31 years). The intraclass
correlation coefficient for interexaminer reliability was 0.83, which is considered
excellent.
Frontal sinus dimensions
[Table 3 ] reports the average dimensions of the frontal sinus. The average dimensions of the
frontal sinus in both sagittal and frontal planes in males were greater than those
in females. However, according to the independent t ‑test, this difference was only significant in the transverse dimension in the frontal
plane (P = 0.032).
Cephalometric indices
The mean values of cephalometric indices are presented in [Table 4 ]. The average measurements on LC were not significantly different between males and
females except for the ANB angle, which was 0.56° ± 4.93° in males and 3.32° ± 3.96°
in females (P = 0.048).
Table 2:
Definition of assessed cephalometric indices
Index
Definition
SN-FH
Angle between anterior cranial base (SN) and Frankfurt plane (Po-Or)
Saddle
Angle between anterior cranial base (SN) and sella to articular
Articular
Angle between sella to articular and articular to gonial
Gonial
Angle between articular to gonial and mandibular plane (Go-Me)
Sum of posterior
Sum of saddle, articular and gonial angles
Facial angle
Angle between nasion to pogonion and Frankfurt plane (Po-Or)
Occ-SN
Occlusal plane angle in relation to anterior cranial base (SN)
Pal-SN
Palatal plane (ANS-PNS) angle in relation to anterior cranial base (SN)
Man-SN
Mandibular plane (Go-Me) angle in relation to anterior cranial base (SN)
SNA
Anteroposterior position of A-point
SNB
Anteroposterior position of B-point
ANB
Anteroposterior relationship between A-point and B-point with respect to nasion
Wits
Distance between a line constructed from Point A perpendicular to the occlusal plane
and a line constructed from Point B perpendicular to the occlusal plane
Y-axis
Angle between Y-axis (S-Gn) and anterior cranial base (SN)
Jarabak index
Posterior facial height (S-Go) to anterior facial height (N-Me) ratio (%)
Correlation between the frontal sinus size and maxillofacial dimensions
Assessment of the relationship between the dimensions of the frontal sinus and cephalometric
indices revealed a significant association of SN?FH and SNA angles with frontal sinus
size [Tables 5 ]. In males, the SN?FH, sum of posterior angles, Pal?SN, and Jarabak index had
significant associations with the size of the frontal sinus [Tables 6 ]; while in females, only SN?FH and gonial angles were significantly correlated with
frontal sinus dimensions [Tables 7 ].
A regression model was applied adjusted for age and gender. The results showed a significant
correlation between sinus dimensions and SN?FH, sum of posterior angles, and Jarabak
index [Tables 8 ]. Neither age nor gender affected the correlation between frontal sinus dimensions
and cephalometric indices.
Table 3:
The average dimensions of the frontal sinus in two planes (width and height in cm
and area in cm2 . Sample size: 144)
Minimum
Maximum
Mean
SD
SD: Standard deviation
Lateral cephalometry
Width
0.43
2.00
1.1530
0.39104
Height
1.18
3.36
2.3182
0.58847
Area
83.00
193.00
129.3864
23.86222
Posteroanterior cephalometry
Width
0.47
7.41
5.1757
1.44574
Height
0.72
4.34
2.8282
0.74522
Area
88.00
191.00
123.6136
18.71104
Table 4:
Average cephalometric indices (all indices in degrees except for Wit’s [mm] and Jarabak
index [ratio]. Sample size: 144)
Minimum
Maximum
Mean
SD
SN‑FH
1
18
7.30
3.764
Saddle
109
137
123.30
7.473
Articular
135
162
144.20
5.987
Gonial
114
142
129.91
6.994
Sum of posterior
383
412
399.22
6.293
Facial angle
72
95
86.55
4.791
Occ‑SN
3
31
17.95
5.754
Pal‑SN
2
17
8.57
4.411
Man‑SN
21
54
37.25
7.980
SNA
69
91
79.86
4.921
SNB
71
87
77.55
4.123
ANB
−7
11
2.32
4.487
Wits
−14
6
−2.66
5.374
Y‑axis
60
80
69.34
4.870
Jarabak index
0.3630
0.8521
0.659179
0.0851843
Table 5:
Significant correlations between the dimensions of the frontal sinus and cephalometric
indices in total
Index
Sinus dimension
R
P
R: Relationship (Pearson’s)
SN‑FH
Sinus width (lateral view)
−0.483
0.001
Sinus height (lateral view)
−0.479
0.001
Sinus width (frontal view)
−0.492
0.001
Sinus height (frontal view)
−0.426
0.004
SNA
Sinus height (frontal view)
−0.323
0.032
DISCUSSION
Growth of the maxilla and nasal cavity is closely related to the development of paranasal
sinuses and all these structures ultimately determine the final morphology of the
face.[20 ] Studies conducted on twins have shown that the shape of sinuses is mainly determined
by genetics;[16 ],[21 ] however, environmental factors, trauma, allergies, acquired conditions, nutrition,
and drug use can also affect the development of sinuses.[22 ] Genotype and growth of maxillofacial structures are two major factors that affect
frontal sinus dimensions.[21 ] Considering the multifactorial size of the frontal sinus, the current study assessed
the relationship between the cephalometric indices and frontal sinus dimensions in
a group of Iranian patients. The results revealed good correlations between some cephalometric
indices and frontal sinus size.
In the current study, PA radiographs and LC were used to assess the dimensions of
the frontal sinus. LCs provide an optimal view to examine the PA walls of the frontal
sinus, and the sinus area is visible on PA radiographs.[23 ],[24 ] The previous studies have shown that physiological changes in the size of the frontal
sinus after the age of 12 are minimal;[21 ],[23 ],[24 ] thus, only patients over 12 years of age were enrolled in this study. A noteworthy
result was that the dimensions of the frontal sinus were larger in males compared
to females; however, this difference was not statistically significant. Similarly,
previous studies reported larger frontal sinus in men compared to women,[25 ],[26 ] and this difference was not significant in some of them.[16 ],[23 ],[27 ]
In total population of the study, a significant inverse correlation was found between
– angle and the dimensions of the frontal sinus, especially its height in sagittal
and frontal planes. The increase in the size of frontal sinus resulted in the lower
inclination of the anterior cranial base from the horizontal plane. It could be justified
that the nasion point, which is the anterior landmark of the SN plane, is influenced
by the dimensions of the frontal sinus. An inverse correlation between the – angle
and sinus dimensions was also observed when analyzing females and males separately.
This provides strong evidence for the influence of frontal sinus on the inclination
of anterior cranial base.
Table 6:
Significant correlations between the dimensions of the frontal sinus and cephalometric
indices in males
Index
Sinus dimension
R
P
R: Relationship (Pearson’s)
SN‑FH
Sinus height (lateral view)
−0.720
0.002
Sinus width (frontal view)
−0.657
0.006
Sinus height (frontal view)
−0.642
0.007
Sinus area (frontal view)
−0.689
0.003
Sum of posterior
Sinus area (frontal view)
0.541
0.031
Pal‑SN
Sinus area (lateral view)
−0.504
0.046
Jarabak index
Sinus width (lateral view)
−0.544
0.029
Sinus height (lateral view)
−0.623
0.010
Table 7:
Significant correlations between the dimensions of the frontal sinus and cephalometric
indices in females
Index
Sinus dimension
R
P
R: Relationship (Pearson’s)
SN‑FH
Sinus width (lateral view)
−0.549
0.002
Sinus height (lateral view)
−0.378
0.048
Sinus width (frontal view)
−0.470
0.012
Gonial
Sinus area (lateral view)
0.425
0.024
Table 8:
Linear regression model adjusted for age and gender, showing significant correlations
between the dimensions of the frontal sinus and cephalometric indices
Index
Sinus dimension
Parameter
R
P
SN‑FH
Sinus width (lateral view)
Gender
0.467
0.657
Age
0.096
0.372
Sinus width (lateral view)
−3.360
0.016
Sinus height (lateral view)
Gender
0.589
0.566
Age
0.090
0.390
Sinus height (lateral view)
−2.419
0.003
Sinus width (frontal view)
Gender
1.425
0.168
Age
0.181
0.079
Sinus width (frontal view)
−1.275
<0.001
Sinus height (frontal view)
Gender
0.813
0.436
Age
0.118
0.260
Sinus height (frontal view)
−1.859
0.004
Sum of posterior
Sinus area (frontal view)
Gender
−1.761
0.402
Age
−0.149
0.549
Sinus area (frontal view)
0.189
0.006
Jarabak index
Sinus width (lateral view)
Gender
0.014
0.610
Age
0.001
0.731
Sinus width (lateral view)
0.112
0.011
Only one correlation was found between the anterior?posterior growth of skeletal structures
and dimensions of the frontal sinus. This correlation was Significant correlations
between the dimensions of the frontal sinus and cephalometric indices in females found
between the SNA and height of the sinus in the frontal plane and might indicate a
tendency for maxillary retrognathism in individuals with increased height of frontal
sinus. On the other hand, the ANB and Wits indices showed no significant relations
with the dimensions of the frontal sinus. Therefore, according to the results presented
here, the skeletal relation of the maxilla and mandible in the sagittal plane was
not influenced by the dimensions of the frontal sinus. The results did not show any
correlation between the Linear regression model adjusted for age and gender, showing
significant correlations between the dimensions of the frontal sinus and cephalometric
indices size of the frontal sinus and Angle classification in the studied population.
In both females and males, associations were found between the frontal sinus size
and vertical cephalometric indices. After controlling for the confounding factors
of age and gender, a significant correlation was found between frontal sinus size
and SN–FH, sum of posterior angles and Jarabak index. In males, the sum of posterior
angles showed a positive correlation with the sinus area. In cases with larger sinus
area, a larger anterior facial height can be expected. The negative correlation between
the Jarabak index and sinus dimensions in the lateral view supports this finding.
A poor inverse correlation was also observed in males between the Pal-SN angle and
the sinus area. This finding could again be justified by the influence of frontal
sinus on the location of nasion and the inclination of cranial base as well as clockwise
rotation of the maxilla, which could result in increased anterior facial height. Similar
to males, a correlation was found in females between the sinus area and the gonial
angle, which supports increased steepness of the mandible.
Some controversies exist when comparing our findings with those of previous studies.[5 ],[12 ] As previously described, there were no significant associations between the position
of the maxilla and mandible in the sagittal plane with frontal sinus dimensions, other
than the weak tendency for maxillary retrognathism in the present study, while in
other studies, larger frontal sinus was correlated with excessive mandibular growth
and Class III skeletal malocclusion.[5 ],[12 ] Rossouw et al .[5 ] assessed the association between the area of the frontal sinus and excessive mandibular
overgrowth by comparing fifty skeletal Class I and 53 skeletal Class III patients.
The only radiograph used in their study was the LC, and the area of the sinus was
measured using a digitizer connected to a microcomputer. They claimed that sinus
area can serve as a predictor of abnormal mandibular growth according to the measurements
of mandibular length, symphysis width, porion location, ramus position, and condylar
axis. Among the anteroposterior angles, only ANB was used for the analysis. ANB was
the common variable measured in both studies; however, a negative correlation between
ANB and sinus area was reported by Rossouw et al .[5 ] concluding that larger sinus areas are associated with skeletal Class III malocclusion.
No correlations were reported in their study between the frontal sinus size and the
facial angle, indicating that a large frontal sinus may be present in vertical growers.
While, there was a significant association between increased vertical dimension and
sinus size in the current study. Prashar et al .[12 ] also demonstrated that larger sinus areas were strongly associated with larger mandibles,
with a tendency for Class III skeletal malocclusion. However, smaller sinus areas
did not indicate a Class II skeletal malocclusion.
The inherent limitation of conventional two? dimensional radiographs for measuring
the volume of complex three?dimensional anatomical structures is considered as a limitation
of the present study. A computed tomography scan of the frontal sinus would enable
more accurate analysis of sinus dimensions; however, the aim of this study was to
identify expected associations between the frontal sinus anatomy and craniofacial
structures on LC and PA radiographs routinely ordered by orthodontists. Furthermore,
patient malpositioning or slight movements when taking radiographs could cause inaccuracies
in the measurement of frontal sinus size and cephalometric indices. In this study,
radiographs with any sign of distortion were excluded.
To generalize the results to the clinical setting, it should be noted that prediction
of growth of craniofacial structures in the diagnosis phase can help achieve stable
and favorable outcomes in orthodontic patients, and clinicians should use all the
tools available for this purpose.[5 ] Dimensions of the frontal sinus, which are visible on routine orthodontic radiographs,
may be used as an indicator to assess the vertical growth. However, the current study
was a cross?sectional study and growth prediction could not be concluded. The results
showed an association between frontal sinus size and some cephalometric indices in
adult patients. Based on these results, the authors could only suggest that in young
adults, in whom the frontal sinus has reached its maximum size (while the vertical
growth continues), larger frontal sinus might be associated with future vertical growth.
To confirm this, longitudinal studies are required.
CONCLUSION
Considering the limitations of the present study, greater dimensions of the frontal
sinus might be associated with decreased inclination of theanterior cranial base (SN).
There was also a correlation between frontal sinus dimensions and increased anterior
facial height (sum of posterior angles, Pal-SN, and Jarabak index) in males and increased
gonial angle in females.
Financial support and sponsorship
Nil.
