Effect of thyroid shields on the quality of digital lateral

Considering the possible damage of thyroid in radiographic examinations, use of thyroid shields has been recommended but there is general concern about the effects of thyroid shields on the diagnosis of anatomical landmarks, which was addressed in this study.
In this descriptive-analytic study two groups of lateral cephalograms, consisting of 50 lateral cephalograms without a thyroid shield and 50 lateral cephalograms with a thyroid shield, retrieved from an oral radiology center archives in Isfahan were evaluated. The lateral cephalograms had been taken with a Cranex-D Ceph (Soredex, Finland) direct digital radiography system. A total of 15 landmarks were identified on the lateral cephalograms by 2 blinded observers. Inter-observer variance was analyzed with Mann-Whitney test (α = 0.05).
All the 15 landmarks on lateral cephalograms without the use of a thyroid shield were identified by 2 observers. Only 12 of the 15 landmarks were identified in patients with a thyroid shield, with no significant differences between the two observers (p value > 0.05).
The landmarks that were covered by thyroid shield were the hyoid bone and the second and third cervical vertebrae. However, these landmarks are used for the analysis of skeletal maturity index (SMI). Therefore use of thyroid shields is recommended during cephalometric radiography.