Utility of thyroid collars in cephalometric radiography

A study was carried out to investigate the rationale that use of a thyroid collar (TC) in cephalometric radiography hampers the diagnostic and descriptive quality of lateral cephalogram.

A randomized observer blinded study was designed. The study consisted of two groups. The first group data were retrieved from the oral radiology archival system having lateral cephalogram without a TC. The second group was selected from the oral radiology department of patients where lateral cephalogram was taken using a TC. Lateral cephalogram was taken on direct digital system, the Kodak 9000 unit (Eastman Kodak, Rochester, NY). 2 observers blinded about the aim of the study were appointed to identify 15 sets of landmarks on the lateral cephalogram. Interobserver variance was also analysed for the study.

50 lateral cephalograms in each group were studied. Out of 15 sets of landmarks, 12 were identified consistent with the TC group. Three landmarks, namely the hyoid bone, second cervical vertebra and third cervical vertebra could not be identified on the TC group. There was no significant difference in the interobserver markings on lateral cephalogram.

TCs do mask a few landmarks on the lateral cephalogram. These landmarks are mainly used for analysis of skeletal maturity index (SMI). Lead TCs are probably the most convenient and easily available means to protect the thyroid from unwanted radiation while taking lateral cephalogram. It is therefore encouraged to use a TC during routine cephalometric radiography where SMI information is not needed.