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ORIGINAL ARTICLE
Year : 2019  |  Volume : 22  |  Issue : 6  |  Page : 771-776

Evaluation of mandibular asymmetry in angle malocclusion samples by posterioanterior cephalometric radiography: A preliminary study


1 Department of Oral and Maxillofacial Radiology, Faculty of Dentistry, Akdeniz University, Antalya, Turkey
2 Department of Oral and Maxillofacial Radiology, Faculty of Dentistry, Ataturk University, Erzurum, Turkey

Date of Acceptance05-Feb-2019
Date of Web Publication12-Jun-2019

Correspondence Address:
Dr. H T Alkis
Department of Oral and Maxillofacial Radiology, Faculty of Dentistry, Akdeniz University, 07058, Antalya
Turkey
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/njcp.njcp_597_18

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   Abstract 


Objectives: The aim of this study was to evaluate the effect of different occlusion types on mandibular asymmetry in different anatomical points using posteroanterior cephalometric radiography. Materials and Methods: This study was retrospectively conducted on 100 patients whose posteroanterior images and malocclusions were registered in a patient database. Asymmetry indices were determined using four linear measurements on images, and the effect of malocclusions, age, and gender on these asymmetry indices was investigated. P <0.05 was considered statistically significant. Results: Right and left horizontal plane gonion distance values varied according to gender, right vertical plane condylar distance and left horizontal plane gonion distance values varied according to age, and right vertical plane condylar distance and left horizontal plane gonion distance values varied according to malocclusions. Conclusion: The measured values of some parameters varied according to age, gender, and malocclusion. Although vertical plane gonion asymmetry index and horizontal plane condylar asymmetry index values varied according to gender, there was no relationship between asymmetry index values of all parameters with age and malocclusion.

Keywords: Facial asymmetry, malocclusion, posteroanterior radiography


How to cite this article:
Alkis H T, Bilge O M. Evaluation of mandibular asymmetry in angle malocclusion samples by posterioanterior cephalometric radiography: A preliminary study. Niger J Clin Pract 2019;22:771-6

How to cite this URL:
Alkis H T, Bilge O M. Evaluation of mandibular asymmetry in angle malocclusion samples by posterioanterior cephalometric radiography: A preliminary study. Niger J Clin Pract [serial online] 2019 [cited 2019 Sep 16];22:771-6. Available from: http://www.njcponline.com/text.asp?2019/22/6/771/260045




   Introduction Top


Facial symmetry is that reference points of the face on both sides of the median sagittal plane are harmonious in terms of size, shape, and location.[1],[2] While the bilateral structures in the vertebrates are like mirror images, perfect symmetry is a theoretical concept; for example, the face has a natural degree of asymmetry.[3] Studies have shown that the maxillofacial area has a minimal amount of asymmetry normally,[4],[5] and the critical threshold for asymmetry is below 4 mm.[6],[7] It is also accepted that at some ages the presence of asymmetry is normal.[8]

The mandible is important due to its direct effect on facial appearance.[2] Mandibular asymmetry may originate from morphological disorders, including abnormal growth speed, hemi-mandibular hypertrophy, hemi-mandibular elongation, condylar hyperplasia, coronoid hyperplasia, trauma, and tumors. Functional causes such as occlusal malformation, muscle dysfunctions, bruxism, and temporomandibular joint dysfunction may also cause mandibular asymmetry.[7],[9] Diagnosis of mandibular asymmetry is complex.[9] While asymmetry can be diagnosed clinically with frontal and side photographs, it can be diagnosed with conventional radiographs[9],[10] or different imaging methods.[11],[12],[13]

The aim of this study was to evaluate the effect of different occlusion types on mandibular asymmetry in different anatomical points using posteroanterior cephalometric radiography (PACR).


   Materials and Methods Top


Data collection

This study was approved by the Akdeniz University, Faculty of Medicine, Clinical Research Ethics Committee, and this study follows the principles of the Declaration of Helsinki.

PACR images of 100 patients who presented for orthodontic treatment to the. University Faculty of Dentistry, Department of Oral and Maxillofacial Radiology, were retrospectively scanned, and four linear measurements were made on images. The following exclusion criteria were used for the study: (1) images wherein anatomical points needed to perform linear measurements were not clearly visualised, (2) trauma, TMJ pathology and midline deviation suspected images and (3) images of patients with systemic disease affecting bone structure.

PACR images were obtained using the same Planmeca ProMax panoramic-cephalometric device (Planmeca Oy, Helsinki, Finland), in accordance with the manufacturer's instructions (a voltage of 64 kVp, a tube current of 5 mA, an exposure time on 18.7 s), by the same X-ray technician. Images were evaluated using the same LED monitor by the same investigator, an expert in dental radiology with 5 years of experience. Evaluation was made in a reduced-light room with tonal adjustments made on images to maximize the view. Only five PACRs were evaluated per a day to prevent investigator fatigue.

The anamnesis and malocclusion data of the patients were reached using the Metasoft Dentasist Programme (version 3.0.448, Eskişehir, Turkey). Patients included in the study were divided into three occlusion groups according to Angle' s malocclusion: class I, class II, and class III, which were each divided into five age groups: 10, 11, 12, 13, and 14 years.

Cephalometric measurements

The landmarks and planes used in the study were determined according to Almasan et al.[7] as follows:

Condylion (Co): the most superior point of the condyle.

Gonion (Go): the most inferior posterior point of the mandible angle.

Menton (Me): the most inferior point of the anterior mandibula.

Anterior nasal spine (ANS): the center point at the base of the nose.

Internal sphenoid margin (ISM): internal edge of sphenoid bone.

O point: midpoint of the line connecting left and right ISM.

Horizontal plane: horizontal plane passing from left to right ISM and O point.

Vertical plane: vertical plane passing from O point, ANS, and Me.

The linear measurements used in the study were as follows: vertical plane condylion distance (VPCD), vertical plane gonion distance (VPGD), horizontal plane condylion distance (HPCD), and horizontal plane gonion distance (HPGD) [Figure 1].
Figure 1: The linear measurements used in posteroanterior cephalometric radiographic images

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All measurements were performed on the right and left sides and were automatically calibrated with the Planmeca Romexis 4.0 software program developed for the Planmeca ProMax device (Planmeca Oy) as per the manufacturer's instructions. After 4 weeks, all measurements were repeated in 20 randomly selected patients and intraobserver variability was assessed. Vertical plane condylion asymmetry index (VPCAI), vertical plane gonion asymmetry index (VPGAI), horizontal plane condylion asymmetry index (HPCAI), and horizontal plane gonion asymmetry index (HPGAI) were determined using the formula developed by Habets et al.:[14]

Asymmetry Index = [(Right − Left)/(Right + Left)] × 100

Statistical analysis

Data were statistically analyzed using SPSS (version 23.0; SPSS Inc., Chicago, IL, USA). Kolmogorov–Smirnov method was used for the evaluation of normality assumption. While the normal distribution of the data was tested by performing independent samples t-test, Mann–Whitney U-test was used for data not displaying a normal distribution. For dependent variables, paired t-test was used for data displaying a normal distribution, whereas Wilcoxon signed-rank test was used for data with non-normal distribution. For analysis of differences between data of more than two groups, parametric analysis of variance was used for data with a normal distribution and nonparametric Kruskal–Wallis test was used when data were not normally distributed. Statistical significance was determined using Scheffe's test used for paired comparisons. Relationships between data were evaluated using nonparametric Spearman's correlation test or parametric Pearson's correlation test. A P value of <0.05 was considered statistically significant. Intraobserver reliability was assessed by intraclass correlation coefficient (ICC).


   Results Top


Of the 100 patients in this study, 51 (51%) were female and 49 (49%) were male, and 24 were class I, 37 were class II, and 39 were class III. The age of the patients ranged between 10 and 15 years with a mean age of 12.03 ± 1.06 years.

When the right and left values were compared, the right HPCD value was found to be significantly greater than that of the left, and the right HPGD value was found to be significantly greater than that of the left. [Table 1] shows the mean, number, standard deviation, minimum, maximum, and P values of left and right measurements, and [Table 2] shows the comparison of the right and left values according to gender. Right HPGD and left HPGD values were significantly greater in males than females.
Table 1: Right and left values of the parameters

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Table 2: The relationship between gender and the right and left values of the parameters

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When the relationship between the type of occlusion and the right and left values of the parameters was examined, the right VPCD and left HPGD values demonstrated differences depending on the type of occlusion, and the P values were 0.029 and 0.015, respectively. The type of occlusion responsible for these differences is shown in [Table 3].
Table 3: The type of occlusion responsible for the differences

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When the relationship between age and the right and left values was examined, the right VPCD and the right and left HPGD values demonstrated differences depending on the age, and the P values were, respectively, 0.001, 0.01, and 0.005. The age responsible for these differences is shown in [Table 4].
Table 4: The age responsible for differences in right VPCD, right HPGD, and left HPGD

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[Table 5] shows the AI values obtained as a result of the AI formula, and [Table 6] shows the relationships between the AI values and gender. VPGAI was significantly greater in males than females, and HPCAI was significantly greater in females than males.
Table 5: Asymmetry index mean, standard deviation, minimum, and maximum values

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Table 6: The relationships between the asymmetry index values and the gender

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When the relationships between the AI values and the type of occlusion was examined, none of the parameters demonstrated a statistically significant relationship [Table 7]. Furthermore, none of the parameters demonstrated a statistically significant relationship with age.
Table 7: The relationships between the asymmetry index values and the type of occlusion

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Intraobserver variability was assessed with ICC, and this correlation coefficient was found to be above 0.90 in all parameters (ICC > 0.90).


   Discussion Top


Asymmetric function and activities of the jaws cause different developments in the right and left sides of the mandible.[15],[16],[17],[18] Mandibular asymmetry is important because it directly affects facial aesthetics and can cause functional problems due to its stomatognathic role.[2]

Asymmetry is often detected radiographically with panoramic radiography, lateral cephalometric radiography, posterioanterior radiography, 45° oblique radiography of the mandible,[9] and submentovertex radiography[10] or by computed tomography,[12] cone-beam computed tomography,[13] and magnetic resonance imaging.[2],[11] Asymmetry determination is frequently performed on panoramic radiographs. Agrawal et al.[9] compared linear measurements between panoramic radiography and PACR and concluded that there was a strong correlation between these radiographs. PACR has been used for orthodontic diagnosis, orthognathic diagnosis, and surgical planning for asymmetry treatment.[9],[19] PACR provides mediolateral information which is useful for the evaluation of facial asymmetry.[9] PACR can be used as the first choice in the diagnosis of facial asymmetry because it allows comparison of the left and right sides of the face.[7],[20] However, both types of radiography are affected by head position or beam angulation.[9] While head position change causes a small effect in vertical measurements, it causes greater effect in horizontal measurements at vertical plane. On the other hand, head position change causes greater effect in vertical measurements than horizontal measurements at transverse plane.[21],[22] The position in which the Frankfort plane is parallel to the ground and the patient look directly or slightly downward is considered to be the appropriate position for radiography.[23] The superposition of other structures makes it difficult to determine anatomical landmarks in PACR.[24],[25] It is recommended to repeat the analysis to reduce the detection and measurement errors of the landmarks in the cephalometric measurements.[26] PACR was used to detect mandibular asymmetry in this study. In this study, the measurements were made by the same experienced investigator and all measurements were repeated in randomly selected patients. Intraobserver variability was assessed with ICC, and this correlation coefficient was found to be above 0.90 in all parameters (ICC >0.90).

Some techniques have been developed to evaluate mandibular asymmetry and the most common are the Kjellberg technique[27] and Habets technique.[14],[28] While the Kjellberg technique[27] compares the ratios of condylar and ramus height between the right and left sides of the mandibule, the Habets technique[14] uses a linear calculation formula for mandibular asymmetry. Both these techniques are based on the use of panoramic radiography.[28]

In 1988, Habets et al.[14] developed a formula to evaluate the mandibular condyle and mandibular ramus at panoramic radiography. According to this formula, a 3% index rate may originate from a 1-cm displacement in head position during panoramic radiography, whereas a >3% difference indicates the existence of asymmetry. The Habets technique may be used for patients with temporomandibular joint dysfunction, class II and class III malocclusions, and different skeletal and occlusal samples.[29] In 2013, Almaşan et al.[7] conducted a study in patients with temporomandibular joint disorder and they adapted Habets technique to PACR. They assessed 14 linear and angular measurements on the PACR and found significant differences in the AI for 10 of the 14 evaluated measurements. In this study, Habets technique was adapted to PACR in angle malocclusion samples. Four linear measurements were assessed bilaterally on PACR images and AI values of these parameters were calculated.

While Farkas and Cheung,[30] Ferrario et al.,[31] Shah and Joshi,[32] and Peck et al.[1] showed that the right side of the face was more dominant than the left, Vig and Hewitt[33] indicated that the left side of the face was more developed than the right side. This study showed that the maesured values of the right sides were greater than the left sides in HPCD and HPGD parameters. Other parameters did not show a significant difference between values for the right and left sides.

There is a significant correlation between facial asymmetry and type of malocclusions, age, and type of dentition.[3] In this study, while a statistically significant difference was found between patients with class II malocclusion and class I malocclusions in right VPCD and class II malocclusions and class III malocclusions in left HPGD, other parameters did not show a significant difference and there was no significant difference between malocclusion and the AI values.

The presence of asymmetry is considered normal in some ages. Although it has been reported that mandibular asymmetries are a common feature in growing patients, a size difference greater than 2–3 mm between both sides of the mandible is considered to be asymmetry.[8] In this study, while it was found that there was a statistically significant difference between the right VPCD, right and left HPGD values, and age, there was no correlation between age and AI values. In addition, when the relationship between gender and the right and left values of the parameters was examined, the right HPGD and left HPGD were found to be significantly higher in male patients. While the VPGAI value was significantly higher in male patients, HPGAI was significantly higher in female patients.

In this study, the relationship between right and left measurement values and the relationship between measurement values and age, gender, and malocclusions were examined in detail. In addition, the relationship between age, gender, malocclusions, and AI values were investigated. There is no such detailed study in the literature to our knowledge.

This study was conducted using patient records on the type of occlusion from the database. This may be a limitation of this study due to the lack of knowledge about the frequency of class II division 1, class II division 2, class II subdivision, unilateral posterior crossbite, and bilateral posterior crossbite. In addition, this study was considered a preliminary study, because only few parameters were used.

In summary, the measured values of some parameters varied according to age, gender, and malocclusion. Although VPGAI and HPGAI values varied according to gender, there was no relationship between AI values of all parameters with age and malocclusion. This study may be a preliminary study and it is thought that further studies will provide more accurate outcomes.

Acknowledgements

The authors would like to thank Dr. Ebru Kaya Basar for statistical analysis. This original article was presented in “1st International Congress on Sports, Anthropology, Nutrition, Anatomy and Radiology” on 3–5 May 2018 in Nevsehir, Turkey, as poster presentation.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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    Figures

  [Figure 1]
 
 
    Tables

  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6], [Table 7]



 

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