|Year : 2021 | Volume
| Issue : 4 | Page : 193-196
Hard- and Soft-Tissue Cephalometric Landmark Detection when Using a Thyroid Lead Shield
Fatemeh Gorjizadeh1, Roghayeh Panahi2, Milad Masoumi3
1 Department of Orthodontics, School of Dentistry, Yasuj University of Medical Sciences, Yasuj, Iran
2 Department of Oral and Maxillofacial Radiology, School of Dentistry, Yasuj University of Medical Sciences, Yasuj, Iran
3 School of Dentistry, Yasuj University of Medical Sciences, Yasuj, Iran
|Date of Submission||24-May-2021|
|Date of Decision||20-Aug-2021|
|Date of Acceptance||22-Aug-2021|
|Date of Web Publication||21-Dec-2021|
Department of Oral and Maxillofacial Radiology, School of Dentistry, Yasuj University of Medical Sciences, Yasuj
Source of Support: None, Conflict of Interest: None
Introduction: The aim of this study was to assess the detection of some hard- and soft-tissue cephalometric landmarks when using a thyroid lead shield. Materials and Methods: Two study groups were designed, and each group consisted of 50 cephalograms: the first group was without thyroid shield cephalograms and the second group consisted of cephalograms taken using a lead thyroid shield. An observer blinded about the aim of the study was appointed to identify 12 landmarks on the lateral cephalograms. Results: Out of 12 of landmarks, 3 landmarks had a significant relationship with the thyroid shield group. Landmarks of cervical point, second and third vertebrae were not detected in 20%, 30%, and 66% of cases, respectively. Discussion: Two hard-tissue landmarks (second and third vertebrae) and one soft-tissue landmark (cervical point) were masked by the thyroid shield when preparing a cephalogram.
Keywords: Anatomic landmarks, cephalometry, thyroid shield
|How to cite this article:|
Gorjizadeh F, Panahi R, Masoumi M. Hard- and Soft-Tissue Cephalometric Landmark Detection when Using a Thyroid Lead Shield. Dent Hypotheses 2021;12:193-6
| Introduction|| |
When Broadbent developed the first cephalogram in 1931, his goal was studying the changes of anatomy of head and neck over time beside studying craniofacial morphology and helping diagnosis in orthodontics. As then various landmarks and analysis have been developed to evaluate the hard and soft tissues in lateral cephalogram.
In the head and neck area, there are vital organs such as the thyroid gland that are very sensitive to the X-rays. Even diagnostic X-ray exposures can be associated with thyroid cancers. The thyroid gland is located in the anterior of neck and spans the C5-T1 vertebrae. Therefore, this gland is definitely irradiated when preparing a lateral cephalogram. In 1977, the first lead thyroid shield was designed and developed to reduce the absorption dose of radiation by thyroid. It has been shown that these lead shields are very effective in reducing radiation absorption.
We know that the cervical maturity index, by assessing the changes of the second, third, and fourth cervical vertebrae in the cephalogram, determines the skeletal maturity of the individual. This method is also used to determine the best intervention time to get the best results in orthopedic–orthodontic treatments. Some studies have shown that the second and third cervical vertebrae as well as the hyoid bone maybe covered by a lead thyroid shield during preparing a cephalogram. There are also some important soft-tissue landmarks on the throat and neck areas that are important to the orthodontists and surgeons which maybe covered when using a thyroid shield. The purpose of the present study was to assess the possibility of masking some important soft- and hard-tissue landmarks when preparing a cephalogram using a lead thyroid shield.
| Materials and Methods|| |
To conduct this study, 50 cephalograms with thyroid shield and 50 cephalograms without thyroid shield were required. The samples of thyroid shield group were obtained by available sampling method from patients who referred to a maxillofacial radiology clinic in Yasouj and the samples of without thyroid shield group were retrieved from the archival system of the radiology clinic. Patients with syndrome or diseases that affect the head and neck areas or had a history of head and neck trauma or maxillofacial surgeries were excluded from the study. The samples of both study groups were matched in terms of age and sex. The thyroid collar shield that was used in this study was a classic type shield with 0.5-mm-thick lead made by NavidPartoNama Company (Tehran, Iran) available in the area [Figure 1].
Cephalograms were prepared in natural head position and radiography was carried out on a Vatech company direct digital cephalometric unit in one shot mode and medium size images (9 × 10 inch). Exposure parameters were set at tube voltage of 50 to 90 kVp and tube current of 4 to 10 mA. All cephalograms were transferred to a computer system for quality adjustment by EzDent-i software for better landmark detection. An orthodontist and a maxillofacial radiologist determined 12 landmarks that maybe masked by a lead thyroid shield [Figure 2]. An orthodontist was unaware of the purpose of the study was asked to evaluate all the cephalograms of both groups and in pre-prepared forms, mark in front of each landmark whether it was detected or not. The collected data were placed in two separate folders entitled: group with thyroid shield and group without thyroid shield. Data analysis was performed using SPSS software version 16 (IBM Corp., NY, US) and Chi-squared test. The level of significance was set at P < 0.05 with 95% confidence level.
|Figure 2 The landmark used in the study. 1, hard-tissue menton, the most inferior point on the mandibular symphysis; 2, soft-tissue menton; 3, border of mandible (the distance between menton and gonion was considered as border of mandible); 4, gonion, the midpoint of the contour connecting the ramus and body of the mandible; 5, soft palate (the lowest point of the soft palate); 6, lower pharyngeal airway (the distance between intersection of the posterior border of the tongue and inferior border of mandible to closest point on the posterior pharyngeal wall); 7, dorsum of tongue (the most posterior point on the dorsum of tongue closest to the posterior pharyngeal wall); 8, hyoid, most superior-anterior point of hyoid body; 9, cervical point (throat and neck junction); 10, CV2ia, inferior-anterior point of body of second cervical vertebra; 11, CV3ia, inferior-anterior point of body of third cervical vertebra; 12, basion, the lowest point on the anterior margin of the foramen magnum, at the base of the clivus.|
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The study protocol was reviewed by the ethics committee of Yasouj University of Medical Sciences and approved with the ethics ID:IR.YUMS.REC.1399.124.
| Results|| |
All 12 landmarks were identifiable in the group of unshielded thyroid cephalograms. The landmarks of basion, border of mandible, menton of soft tissue, menton of hard tissue, and the lowest part of soft palate were detected in all the samples of shielded group. But gonion, dorsum of tongue, lower airway, and hyoid landmarks were not detected in 2%, 4%, 8%, and 10% of shielded group cases, respectively. There was no association between groups and these landmarks (P>0.05). The landmark of cervical point was not detected in 20% of cases and had a statistically significant relationship with shielded group (P<0.001). Also landmarks of second and third vertebrae which were not detected in 30% and 66% of cases, respectively; had a statistically significant relationship with shielded group (P<0.0001) [Figure 3]. In the shielded group there was an association between third vertebrae and sex (P-value<0.05), this landmark was more undetectable in men than women at the presence of lead thyroid shield.
|Figure 3 The detection percentage of three landmarks that were affected by thyroid shield.|
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| Discussion|| |
The present study was performed to evaluate the possibility of covering some landmarks of the neck and lower part of the face and skull by lead thyroid shields on cephalometric radiographs. The first result of this study was that in the unshielded thyroid group all 12 landmarks were observed, which was to be expected. In the group with thyroid shield, the landmarks of Basion, border of mandible, menton of soft tissue, menton of hard tissue, and the lowest part of soft-palate tissue were detected in 100% of cases, which means that the thyroid shield does not interfere with the detection of these landmarks at all. This finding is consistent with the findings of a study by Choudhary et al. The study showed that the use of thyroid collar had no particular effect on the identification of landmarks and linear angles used in Steiner cephalometric analysis.
Gonion, dorsum of tongue, lower airway, and hyoid were the other landmarks investigated in the present study and the results showed that there was no association between these landmarks and the shielded group; these landmarks were undistinguishable in less than 10% of cephalograms of shielded group. In the study of Sansare et al., the land mark “the deepest depression in the mandibular trunk versus the master muscle,” which is close to the landmark of gonion in our study, was examined. In that study, as in our study, this landmark was not affected by thyroid shield.
We found that the hyoid landmark was detectable in 90% of cases which used a shield. This finding contradicts the results of Sansare et al.’s study. They concluded that detection of this landmark is affected by thyroid shield. In anatomy books, the position of the hyoid bone relative to the vertebrae is stated at the level of the third vertebra; some new researchers have found its position even lower at the level of the fourth vertebra. However, it should be noted that most of these studies have been performed on patients in the supine position and we know that the position of the hyoid changes from the supine to the standing position. It has also been suggested that the distance of the hyoid bone to the cranial base, maxilla, mandible, and cervical vertebra increases with age. This means that the hyoid position changes as the craniofacial and cervical posture change over time. Sağlam and Uydas also showed that the hyoid bone position is higher and more posterior in women than men. In general, it seems that many factors may affect the position of the hyoid bone that should be considered when studying this landmark.
The cervical point is the junction of the throat and neck. In the present study, this landmark was not detectable in 20% of the cases in thyroid shielded group. It is worth noting that this is the only soft-tissue landmark that has been affected by thyroid shield and has not been studied or mentioned in similar previous studies. This landmark is important to maxillofacial surgeons during genioplasty or doublechin surgery or mandibular surgery in classes II and III patients. Sn–Gn’–C angle, which is examined in most studies of soft-tissue changes, may alter during surgery. This landmark is also important in determining the chin–throat–neck angle or cervical angle. In the study of Arroyo et al., this angle has been used as one of the important angles for analyzing the lower third of the face.
Two other landmarks were also undetectable in the neck region in the shielded thyroid group, inferior-anterior point of the body of the second and third cervical vertebrae in 30% and 66% of cases were masked by thyroid shield, respectively. It should be noted that among all the landmarks considered in the present study, the highest rate of nondiagnosis is related to the third cervical vertebra, so when using a thyroid shield, the probability of not detecting this landmark is high. In the study of Sansare et al., the second and third cervical vertebrae in most cases (more than 90%) were not detectable, and hence, both vertebrae were almost invisible when using a thyroid collar. This result is consistent with our study, but our study showed that the probability of covering the third vertebra is much higher than the second vertebra (66% vs. 30%), whereas in the Sansare study, both vertebrae were almost equally indistinguishable.
We also evaluated the relationship between gender and landmarks in shielded thyroid group. The results showed that the landmark of third cervical vertebra was more undetectable in men than women. This result maybe related to the differences between the neck anthropometry of men and women. Vasavada et al. concluded that male and female necks are not geometrically similar and vertebral heights were significantly smaller in women for vertebrae C3–C5.
Limitations of the study
There was no age limit for participants in the present study. Although patients in both groups were age matched, we know that during growth, neck length changes, consequently, the position of landmarks changes. Age classification is suggested in future studies to eliminate this confounding factor.
| Conclusion|| |
The present study showed that the second and third cervical vertebrae maybe masked with thyroid lead shield when preparing cephalometry. The cervical point landmark, which indicates the soft tissue junction of the throat and neck, may also be masked by the shield. Third vertebra was more undetectable in men than women.
The authors thank Dr Narges Roustaei, PhD of Biostatistics at School of Health and Nutrition Sciences at Yasuj University of Medical Sciences for her help with statistical analysis of the data.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3]