Abstract
Objectives:
To determine age- and sex-related changes in mastoid air cells volume in orthodontic malocclusions (class 1, class 2, class 3) in cone beam computed tomography (CBCT), morphometric analysis, and age prediction on the basis of mastoid air cells.
Methods:
In total, 150 3D CBCT scans of study subjects having class 1, class 2, and class 3 malocclusions have been analyzed retrospectively for the estimation of volume of mastoid air cells by Dolphin imaging software V11.9, and measurement data of volumes have been recorded and analyzed using SPSS software 24.v.
Results:
The volume of mastoid air cells was highest in age group of 14–28 years which was statistically not significant (P value >.05). The volume of mastoid air cells in the right side of cranium is greater than mastoid air cells in the left side. The mastoid air cell volume was higher in males than females. The volume of mastoid air cells (right side) was highest in class II malocclusion (2404.53 ± 1737.50 mm3) followed by class III and was least in class I malocclusion (1842.09 ± 1263.78 mm3). However, the volume of mastoid air cells in the left side was highest in class III malocclusion (2368.03 ± 1853.00 mm3) followed by class II and was least in class I (1920.52 ± 1285.34 mm3).
Conclusions:
The volume of mastoid air cells varies in different class of orthodontic malocclusions. The mastoid air cells volume is higher in males than females. On the basis of mastoid air cells volume, we are able to predict the age, sex, and class of orthodontic malocclusion.
Keywords: 3D CBCT, malocclusion, mastoid air cells
INTRODUCTION
Pneumatization refers to the development of air-filled cavities in bone. These accessory air cells which are common in paranasal sinuses are observed in many bones including the temporal bone.[1] Air cells in the zygomatic extension of the temporal bone are referred to as zygomatic air cell defect or pneumatized articular tubercle (PAT).[2] PAT structurally weakens the roof of the glenoid fossa resulting in a fragile temporomandibular joint (TMJ)[3] in which infections, tumors, or fractures may progress more easily.[4] Any surgical intervention on the articular eminence may also have an increased risk for perforation.[5] PAT is recommended as a prognostic factor that can be used to detect extensive pneumatization of the mastoid air cells and therefore tomographic examination is recommended before surgical procedures.[6] However, no volumetric research has been done till date. A decreased number of mastoid air cells are common in chronic otitis media. There are two theories. The environmental theory suggests that frequent inflammatory changes in the upper respiratory tract, Eustachian tube, and middle ear cavity hamper the development of the air cells of mastoid or calcify the existing air cells. The hereditary theory suggests that congenitally poor air cells in the mastoid do not provide a good air buffer for the middle ear cavity leading to the development of chronic otitis media.[7] It is not unusual that the space in the external auditory cavity is smaller in chronic otitis media subjects who have only sensorineural hearing loss, tinnitus, dizziness, or trauma. This difference can be explained by the mastoid air cell theories. There are also insufficient data to analyze this. Till date, none of the study has been conducted to establish co-relation between malocclusions and mastoid air cells pre- and post-orthodontics treatment and its co-relation with otitis media and hearing loss. The present study has been conducted to determine mastoid air cell volumes in malocclusions in 3D cone beam computed tomography (CBCT) and age- and sex-related changes in mastoid air cell volume in malocclusions. The research hypothesis for the study is that the volume of mastoid air cells decreases with age and type of malocclusions (class 1 malocclusion has greatest volume while class 3 has least volume). The present study has been conducted to predict the age- and sex-related changes in mastoid air cells volume in class 1, class 2, and class 3 malocclusions and also to compare mastoid air cells volume in class 1, class 2, and class 3 malocclusions with normal healthy individuals.
MATERIAL AND METHODS
The present study has been conducted retrospectively and has been approved by Institutional Ethics Committee (Ref code 101st ECM IIA/P12, 784/Ethics/2020 dated 01/09/2020). CBCT images having typical mastoid air cells will be included in the study [Figures 1a-c and 2a-c]. However, CBCT with undetectable zygomatic extension due to technical errors, trauma, infection, and anomaly history in maxillofacial region will not be included in the present study. Low field of view images that did not present mastoid air cells will be excluded from the sample.
Figure 1.
(a-c) Showing volume measurement of mastoid air cells in class 1, class 2, and class 3 malocclusion (right side)
Figure 2.
(a-c) Showing volume measurement of mastoid air cells in class 1, class 2, and class 3 malocclusion (left side)
Statistical analysis
In total, 150 3D CBCT scans of study subjects having class 1, class 2, and class 3 malocclusions were analyzed for volumes of mastoid air cells retrospectively using Dolphin imaging software V11.9. The measurement data of volumes were recorded in Microsoft Excel sheet and analyzed using SPSS software 28v. 0 (IBM Corp, Armonk, NY, USA). A P value of < 0.05 was considered statistically significant.
RESULTS
Categorical variables were presented in number and percentage (%) and continuous variables were presented as mean ± SD and median. Quantitative variables were compared using unpaired t-test between two groups and ANOVA between three groups. Qualitative variables will be compared using Chi-Square test/Fisher’s exact test as appropriate. Pearson correlation coefficients were used to determine the relationship of age between different parameters, while correlation was defined as a measure of the strength of a linear relationship between two variables.
The study population consists of 150 subjects having different class of malocclusions. The study subjects were in age from 10 to 24 years [Table 1]. The study population consists of 90 males and 60 females [Table 2]. In the study population, class I malocclusion was most common (52%) followed by class II malocclusion (26%); however, class III malocclusion (22%) was least [Table 3]. The volume of mastoid air cells in the right side (2136.02 mm3) of cranium is greater than mastoid air cells in the left side (2098.66 mm3) [Table 4]. In the study population, volume of mastoid air cells is compared in age groups by applying one-way ANOVA test for significance. In the right and left side of cranium, volume of mastoid air cells was highest in the age group of 14–28 years which was statistically not significant (P value >.05) [Table 5]. In the study population, volume of mastoid air cells is compared in different class of malocclusions by applying one-way ANOVA test for significance. The volume of mastoid air cells (right side) was highest in class II malocclusion (2404.53 ± 1737.50 mm3) followed by class III and was least in class I malocclusion (1842.09 ± 1263.78 mm3). This association was statistically highly significant (P value <0.001). However, the volume of mastoid air cells in the left side was highest in class III malocclusion (2368.03 ± 1853.00 mm3) followed by class II and was least in class I (1920.52 ± 1285.34 mm3). This association was highly significant (P value < 0.001) [Table 6]. The unpaired t-test is used to know the variability of mastoid air cell volume in males and females. The mean mastoid air cells volume (right side) was greater in males (2195.12 ± 1388.78 mm3) than females (2046.20 ± 1640.51 mm3). However, in the left side, the mastoid air cells volume was higher in males (2166.46 ± 1437.09 mm3) than females (1988.31 ± 1508.96 mm3). The volume of mastoid air cells (right side and left side) was statistically not significant in both males and females (P value > 0.05) [Table 7]. The co-relation between age and volume of mastoid air cells was estimated by Pearson correlation coefficient and a mathematical equation is derived on the basis of which the age of a subject can be estimated if volume of mastoid air cells is known [Table 8].
Table 1.
Showing age groups in study population
| Age groups | Frequency | Percent |
|---|---|---|
| 10-14 years | 11 | 7.3 |
| 14.1-18 years | 65 | 43.3 |
| 18.1-24 years | 74 | 49.3 |
| Total | 150 | 100.0 |
Table 2.
Showing gender wise distribution of study population
| Gender | Frequency | Percent |
|---|---|---|
| Male | 90 | 60.0 |
| Female | 60 | 40.0 |
| Total | 150 | 100.0 |
Table 3.
Showing malocclusion-wise distribution of study population
| Class of malocclusion | Frequency | Percent |
|---|---|---|
| Class I | 78 | 52.0 |
| Class II | 39 | 26.0 |
| Class III | 33 | 22.0 |
| Total | 150 | 100.0 |
Table 4.
Showing the volumes of mastoid air cells
| Mean (mm3) | SD | Median | n | |
|---|---|---|---|---|
| Mastoid air cells right side | 2136.02 | 1489.14 | 1696.00 | 126 |
| Mastoid air cells left side | 2098.66 | 1461.79 | 1684.00 | 134 |
Table 5.
Showing volume of mastoid air cells in age groups
| 10-14 years | 14.1-18 years | 18.1-24 years | F | P | |
|---|---|---|---|---|---|
| Mastoid air cells volume (mm3) right side | 1449.90±1209.54 | 2282.50±1634.23 | 2103.80±1391.15 | 1.119 | 0.330 |
| Mastoid air cells volume (mm3) left side | 1027.00±863.99 | 2178.40±1480.16 | 2156.70±1467.60 | 2.336 | 0.101 |
Table 6.
Showing volume of mastoid air cells in malocclusions
| Class of malocclusion |
F | P | |||
|---|---|---|---|---|---|
| Class IMean±SD | Class IIMean±SD | Class IIIMean±SD | |||
| Mastoid air cells right side | 1842.09±1263.78 | 2404.53±1737.50 | 2364.20±1498.79 | 15.936 | <0.001* |
| Mastoid air cells left side | 1920.52±1285.34 | 2160.05±1349.24 | 2368.03±1853.00 | 17.839 | <0.001* |
Table 7.
Showing gender wise volume of mastoid air cells
| Gender |
t | P | ||
|---|---|---|---|---|
| Male Mean±SD | Female Mean±SD | |||
| Mastoid air cells right side | 2195.12±1388.78 | 2046.20±1640.51 | 0.548 | 0.585 |
| Mastoid air cells left side | 2166.46±1437.09 | 1988.31±1508.96 | 0.684 | 0.495 |
Table 8.
Showing mathematical equations for age prediction for volume of mastoid cells
| Parameters | R | P | Mathematical equations |
|---|---|---|---|
| Mastoid air cells right side | 0.081 | 0.366 | Y=000x Mastoid air cells right side+17.946 |
| Mastoid air cells left side | 0.124 | 0.154 | Y=000x Mastoid air cells left side+17.792 |
DISCUSSION
CBCT is used as a reliable technique in volume measurement research because it eliminates the disadvantages of 2-dimensional conventional imaging methods (e.g., magnification and superposition) and has advantages including a low radiation dose compared to computed tomography (CT), low costs, and a short scanning time.[8] Lima et al.[9] stated that the volumetric analysis of mastoid air cells plays a key role in understanding the mastoid physiology and pathogenesis, and CT is the best way to determine mastoid pneumatization. Due to its low dose of radiation and rapid imaging, CBCT has recently emerged as an alternative to CT to evaluate anatomical structures in the maxillofacial region.[10] The mastoid air cells also serve as a gas reservoir that compensates for changes in pressure in the middle ear and provides insulation against heat changes.[11] Magnuson[11] described temporal bone pneumatization into five compartments, that is, accessory air cells in the middle ear, mastoid process, peri-labyrinth, petrous apex and squamous, zygomatic, occipital, and styloid fragments. These air cells reduce the weight of the skull, provide sound resonance during phonation, and control and moisturize the air inhaled during respiration.
Adışen and Aydoğdu[12] compared mastoid air cell volumes in patients with or without a PAT on CBCT images. The patients with PAT and those without PAT had a mean mastoid volume of 6.31 ± 2.86 cm3 and 3.25 ± 1.99 cm3, respectively. There were statistically significant differences in mastoid air cell volumes between patients with and without PAT regardless of sex and mastoid air cell side (P < 0.05). Orhan et al.[13] reported a prevalence of pneumatized articular eminence as 3.42% in individuals with orthodontic malocclusions which is quite high when compared to general population studies. Distribution of individuals with PAT revealed the highest number/rate in class I (25/666), followed by class II (15/447) and class III (10/292).
Ladeira et al.[5] estimated the prevalence and characteristics of pneumatization of the temporal bone by CBCT to determine pneumatization in the articular eminence (PAT) and roof of the glenoid fossa (PGF). Age and gender were recorded for all patients and for the cases of pneumatization, laterality and type (unilocular or multilocular) were noted. Its prevalence was correlated with gender, age, and laterality by statistical analyses. 21.3% of individuals presented with PAT and 38.3% presented with PGF. Considering the TMJ, PAT was 15.5% and PGF 30.2%. Of PAT cases, 54.3% were unilateral and 45.7% bilateral; 3.4% were unilocular and 96.6% were multilocular. In the PGF cases, 42.5% were unilateral and 57.5% bilateral; 0.02% was unilocular and 99.8% were multilocular.
Demirel et al.[14] used the following grading system for pneumatization in craniofacial region: “grade 0 as pneumatization limited to the mastoid process, grade 1 as pneumatization between the mastoid process and the glenoid fossa, grade 2 as pneumatization between the deepest point of the glenoid fossa and the tip of the articular eminence, and grade 3 as pneumatization extending beyond the crest of the articular eminence, to reveal that out of the 500 investigated areas, 32.4% had grade 0 pneumatization, 55.4% had grade 1, 8.6% had grade 2, and 3.6% had grade 3.” There were no significant correlations between pneumatization grade and age of patients.
CONCLUSION AND FUTURE CONSIDERATIONS
Our study is the first study which has predicted age of patients based on volume of mastoid air cells. The volumes of mastoid air cells vary in different class of orthodontic malocclusions. Till date, no study has been conducted to find out the relation between malocclusions and mastoid air cells pre- and post-orthodontics treatment and its co-relation with otitis media and hearing loss.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
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