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Table of Contents   
ORIGINAL RESEARCH  
Year : 2012  |  Volume : 23  |  Issue : 5  |  Page : 698-699
Utility of lead thyroid collar in cephalometric radiography


1 Department of Oral Medicine and Radiology, Vidya Shikshan Prasarak Mandal's Dental College and Research Center, Digdoh Hills, Nagpur, Maharashtra, India
2 Department of Oral Medicine and Radiology, TIFAC CORE in Interventional Radiology, AVBRH, Pune, Maharashtra, India
3 Department of Oral Pathology, Bharti Vidyapeeth, Dhanakwadi, Pune, Maharashtra, India
4 Department of Oral Medicine and Radiology, Sharad Pawar Dental College and Hospital, DMIMSU, Sawangi (M), Wardha, Maharashtra, India
5 Department of Pedodontia, Bharti Vidyapeeth, Dhanakwadi, Pune, Maharashtra, India

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Date of Submission14-Feb-2011
Date of Decision11-Aug-2011
Date of Acceptance06-Sep-2011
Date of Web Publication19-Feb-2013
 

   Abstract 

Objective: To investigate whether the application of thyroid collars (TCs) affects the results of cephalometric study.
Study Design: The Steiner cephalometric analysis of the patients was performed using lateral cephalometric radiographs, which were taken twice for each patient: Once using TCs (TC group; n0 = 50) and once without using TCs (NTC group; n = 50). A randomized and observer-blinded diagnostic study with head films taken from the two aforementioned groups was performed and results were evaluated with the t-test and Z-test, using GraphPad® Prism 4 software.
Results : Statistical analysis using t-test was performed. The values of the line angles used in Steiner cephalometric analysis were compared for which values of each angle remained unchanged when done using TCs and without TC to the same samples.
Conclusions : Lead shielding of the thyroid gland does not affect landmark identification or the specific measurements of the angulations traced during cephalometric analysis. TCs should be routinely applied during cephalometric radiography if cephalometric analyses are limited to the structures above the second cervical vertebra.

Keywords: Cephalometric radiograph, Steiner analysis, thyroid collar

How to cite this article:
Choudhary AB, Motwani MB, Banode PJ, Chaudhary MB, Degwekar SS, Bhowate RR, Chaudhary SM. Utility of lead thyroid collar in cephalometric radiography. Indian J Dent Res 2012;23:698-9

How to cite this URL:
Choudhary AB, Motwani MB, Banode PJ, Chaudhary MB, Degwekar SS, Bhowate RR, Chaudhary SM. Utility of lead thyroid collar in cephalometric radiography. Indian J Dent Res [serial online] 2012 [cited 2020 Jan 19];23:698-9. Available from: http://www.ijdr.in/text.asp?2012/23/5/698/107442
It has been reported that dental radiology represents the most frequent diagnostic radiological examination, and intraoral radiographs are the most frequent X-ray examinations in humans. Several radiosensitive organs such as the thyroid, the esophagus, and vertebral bone marrow are located in the neck region. The extent to which these organs are exposed to ionizing radiation under real-life conditions has not been reported. In the case of the thyroid, exposure can vary from person to person due to variability in the position of the gland. Although radiation exposure to the gonads and thyroid glands may be negligible in properly conducted radiographic examinations, radiation dose to the thyroid is considered the largest component of the effective dose in dental radiography. [1] Several major dose surveys in diagnostic radiology have been performed in developed countries but, in developing countries, basic information is still lacking. [2]

Cephalometric radiography is used to study dental occlusion, skeletal growth pattern, and the sagittal relationship of jaws in orthodontic diagnosis and therapy. Since the majority of orthodontic patients are children who are relatively more sensitive to the detrimental effects of radiation, shielding of radiosensitive organs such as the thyroid gland is mandatory and is achieved by using collimation and external lead shielding. The lead thyroid collar (TC) used in cephalometric radiography was introduced in 1977 with the aim of avoiding unnecessary thyroid exposure and the induction of neoplasms in later life. Cephalometric doses are typically low and the sample sizes required to detect a risk are often impractically substantial. [3] The degree of exposure of the thyroid gland to ionizing radiation depends on various factors. There is person-to-person variability in the position of the thyroid [4],[5] due to the age-dependent caudal movement of the thyroid through puberty. [6] Exposure may also be influenced by the clinician's request regarding what should be visualized on the radiograph [7] and by differences in radiographic practices.

It has been thought that thyroid shields are commonly used in modern dentistry, but these assertions are inconsistent as seen on various surveys. [8],[9],[10] The main drawback of the TC is that it may affect cephalometric analysis. The aim of the present study was to investigate whether the application of TCs affects the results of cephalometric study and consequently interferes with the diagnostic process of cephalometric analysis radiography.


   Materials and Methods Top


This randomized, observer-blinded, diagnostic study was carried out in the Department of Oral Medicine and Radiology, Sharad Pawar Dental College and Hospital, DMIMSDU (Datta Meghe Institute of Medical Sciences, Deemed University) Wardha, Maharashtra, India, after obtaining the approval of the institutional ethical committee. The study population included 50 randomly selected patients (31 females and 19 males) in the age-group of 10-30 years. Each patient underwent cephalometric radiography twice: Once with the TC [Figure 1]a and b and once without the thyroid collar [Figure 2]a and b. Planmeca Proline CC ® panoramic X-ray machine with cephalostat (Planmeca Oy, Helsinki, Finland) was used, with exposure parameters 68 kVp and tube current 12 mA for 0.8 seconds. Radiographs were taken according to the standard protocol. Each radiograph [Figure 3] and [Figure 4] was traced by an expert orthodontist and Steiner analysis was applied for the values obtained, which were then compared with Student's t test using GraphPad ® Prism 4 software.
Figure 1: (a and b). Patient positioned on Cephalostat without thyroid collar

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Figure 2: (a and b). Patient with TC positioned on cephalostat

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Figure 3: Cephalogram without thyroid collar

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Figure 4: Cephalogram with thyroid collar (arrow indicates the TC)

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   Results Top


The Z test and the t test, using GraphPad ® Prism 4 software, was performed on the data collected which was estimated on the various line angles obtained by tracing according to Steiner cephalometric analysis. On applying the Z test to the data obtained we found that there was no significant difference in the measurements of angles for Steiner analysis after tracing both the films: One with TC and other without TC [[Table 1] and [Graph 1]] [Additional file 1], indicating that there was no change in the skeletal as well as the soft tissue anatomic landmarks. The t-test when applied to the various angles evaluated in Steiner analysis also showed a nonsignificant difference [Table 2], the P value being more than 0.05 (i.e., P > 0.05).
Table 1: Measurement of angles using Z - test in Steiner analysis in TC and non - TC group, with mean angle and standard deviation

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Table 2: Measurement of angles in Steiner analysis using t test

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   Discussion Top


Though studies have shown that the use of the TC affects the landmark reproducibility on cephalometric radiographs, it is necessary to evaluate whether any of the measured differences are of clinical significance. Another issue is whether the amount of error legitimates the refusal to use the TC in clinical practice.

The present study was undertaken with the aim of determining whether the use of the lead TC has an influence on Steiner cephalometric analysis. The results obtained show that the values of the angles used in cephalometric analysis remained unchanged even when the TC was used. Wiechmann et al.[3] investigated whether the application of TCs affects cephalometric landmark identification using 100 radiographs with TC and 100 without TC and concluded that though lead shielding of the thyroid gland affects landmark identification, the overall clinical effect is negligible. In our study, there were no changes observed in the angles used in Steiner analysis, as well as the hard tissue landmarks which are joined by lines passing through those landmarks to form the specific angles specifically used in Steiner analysis.

In view of these results we suggest that leaded collars should be used whenever practical to minimize any unnecessary radiation exposure. Leaded TCs are strongly recommended for use in pediatric patients because children's thyroid tissue is highly susceptible to X-rays. There is contradictory evidence in the literature as to whether dental radiography causes exposure to significant doses. On the one hand, there are extensive human and animal studies denying that a risk exists for radiation-induced effects following dental radiography and, on the other hand, epidemiological data suggests that exposure to dental X-rays during pregnancy may be responsible for human fetal growth retardation. [11],[12],[13] However, small differences in radiation doses exist and which option has the greatest benefit for the patient must be carefully considered.

With regard to orthodontic patients, it must be remembered that children and adolescents are considerably more sensitive to radiation-induced damage than adults and that children have a longer life expectancy in which to express risk. Unless there has been some acute pathologic condition, an adolescent's first exposure to diagnostic radiation usually occurs as part of orthodontic treatment. Thus, in an individual in need of orthodontic treatment X-ray exposure may start between the ages of 6 and 10 years, a time when the thyroid gland is highly susceptible to radiation exposure. Current guidelines like the 'Radiation protection guidelines for the practicing orthodontist,' a summary of dental X-ray guidelines from the US National Council on Radiation Protection and Measurements, Report No. 145, [14] are rather vague as far as the orthodontist is concerned, inasmuch as neither the use of TCs for cephalometric radiography nor recommendations for eliciting the pregnancy status of a female patient are mentioned. Similar conditions, for example, 'lack of unequivocal guidelines in the use of thyroid shielding,' were seen as a factor contributing to the anticipated general underutilization of them. [13]

The findings of a recent study from the University of Washington indicate that between 1973 and 2003 the overall share of TC use at the Department of Orthodontics was 19.2% of total patients. [4] In 619 of 763 assessed cephalometric head films without the presence of a TC, the exposure field was increased up to the fifth cervical vertebra, indicating direct irradiation of portions of the thyroid gland. [4] A possible explanation for the findings for radiation exposures to thyroid in children may be the unproven hypothesis that the thyroid is positioned higher in the neck of children than of adults [15] and that the skull and the neck of children and females are smaller than those of adults and males. [4] The landmark set used in this study does not represent the whole range of available analysis, but it is the standard analysis followed for all patients irrespective of the other analyses and it would make less sense to use landmarks of regions unlikely to be subject to interference from the TC.


   Conclusion Top


The application of a lead TC for cephalometric radiography was previously thought to be associated with an increase in landmark placement error. The number of errors and the differences between the TC group and the non-TC group are too small to have meaningful effects on cephalometric landmarks and, thereby, on the overall diagnosis and treatment planning. The lead TC is a low-cost and easy-to-use device that protects the thyroid gland against direct irradiation and extraoral X-rays. Personal lead shielding with a TC is currently the most efficient way to reduce exposure during cephalometric radiography to the practical minimum. Hence, keeping in mind the principles of radiation protection and ALARA (as low as reasonably achievable), we recommend that the use of the lead TC be made routine for cephalometric radiographs also.

 
   References Top

1.ADA Council on Scientific Affairs. An update on radiographic practices: Information and recommendations. ADA Council on Scientific Affairs. J Am Dent Assoc 2001;132:234-8.  Back to cited text no. 1
[PUBMED]    
2.Mortazavi SM, Shareghi A, Ghiassi-Nejad M, Kavousi A, Jafari-Zadeh M, Nazeri F, et al. The need for national diagnostic reference levels: Entrance surface dose measurement in intraoral radiography. Iran J Radiat Res 2004;2:127-33.  Back to cited text no. 2
    
3.Wiechmann D, Decker A, Hohoff A, Kleinheinz J, Stamm T. The influence of lead thyroid collars on cephalometric landmark identification. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2007;104:560-8.  Back to cited text no. 3
[PUBMED]    
4.Hujoel P, Hollender L, Bollen AM, Young JD, Cunha-Cruz1 J, McGee M, et al. Thyroid shields and neck exposures in cephalometric radiography. BMC Medical Imaging 2006;6:6.  Back to cited text no. 4
    
5.Gray H, Standring S, Ellis H, Collins P, Wigley C, Berkovitz BK. Gray's anatomy: The anatomical basis of clinical practice. Vol. 20, 39 th ed. Edinburgh; New York: Elsevier Churchill Livingstone; 2005. p. 1627.  Back to cited text no. 5
    
6.Crelin ES. Functional anatomy of the newborn. Vol. 12, New Haven: Yale University Press; 1973. p. 87.  Back to cited text no. 6
    
7.Seedat AK, Forsberg CD. An evaluation of the third cervical vertebra as a growth indicator in Black subjects. SADJ 2005;60:156, 158-60.  Back to cited text no. 7
    
8.Lockhart PB, Brennan MT, Sasser H, Ludlow J. Antepartum dental radiography and low birth weight. JAMA 2004;292:1020.  Back to cited text no. 8
    
9.Reiman RE. Antepartum dental radiography and low birth weight. JAMA 2004;292:1019.1019.  Back to cited text no. 9
    
10.Boice JD, Stovall M, Mulvihill JJ, Green DM. Dental X-rays and low birth weight. J Radiol Prot 2004;24:321-3.  Back to cited text no. 10
    
11.Brent RL. Commentary on JAMA article by Hujoel et al. Health Phys 2005;88:379-81.  Back to cited text no. 11
    
12.Buch B, Fensham R. Orthodontic radiographic procedures. How safe are they? SADJ 2003;58:6-10.  Back to cited text no. 12
    
13.Hujoel PP, Bollen AM, Noonan CJ, del Aguila MA. Antepartum dental radiography and infant low birth weight. JAMA 2004;291:1987-93.  Back to cited text no. 13
    
14.Mupparapu M. Radiation protection guidelines for the practicing orthodontist. Am J Orthod Dentofacial Orthop 2005;128:168-72.  Back to cited text no. 14
    
15.Gijbels F, Sanderink G, Wyatt J, Van Dam J, Nowak B, Jacobs R. Radiation doses of collimated Vs non-collimated cephalometric exposures. Dentomaxillofac Radiol 2003;32:128-33.  Back to cited text no. 15
    

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Correspondence Address:
Anuraag B Choudhary
Department of Oral Medicine and Radiology, Vidya Shikshan Prasarak Mandal's Dental College and Research Center, Digdoh Hills, Nagpur, Maharashtra
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0970-9290.107442

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