Radiation Dosimetry of Extra-oral vs. Intra-oral Bitewing Radiography

Objectives: Extra-oral bitewing radiography is an option in many extra-oral imaging machines which can be used as an alternative to intra-oral bitewing radiography for developmentally disabled patients. This study sought to evaluate the radiation dosages from extra-oral bitewing radiography compared to the conventional intra-oral bitewing radiography.
Methods: Twenty optically simulated dosimeters were placed in tissue-equivalent holders in 20 regions in the head and neck of an adult female phantom to assess the distribution of absorbed radiation dose in various organs.

The intra-oral bitewing radiograph was obtained using the Gendex machine, with the preset exposure factors of 65 kVp, 7 mA, and 0.125 seconds. The phantom was exposed ten times for a left premolar bitewing radiograph and the average recording was reported. The extra-oral bitewing mode in the Sirona ortho xg-plus machine renders four bitewing radiographs in one exposure i.e. with 10 seconds rotation time of the machine and preset exposure factors of 64 kVp and 8 mA, an equivalent of four bitewing radiographs are obtained. Hence, only one round of exposure was performed and the average recording between the four areas (right and left premolar and molar region) was reported.
Results: The effective dose for Sirona ortho xg-plus bitewing was 5.7 μSv while the effective dose for Gendex bitewing was 5.2 μSv. The critical organs include the lens of the eye, brain, and thyroid. The estimated dose for the eye, brain, and thyroid using Sirona ortho xg-plus were 4.9, 15, and 5.5 μGy respectively. The estimated dose for the eye, brain, and thyroid using Gendex were 2.9, 6, and 6 μGy respectively.
Conclusions: Based on the effective dose and the individual organ doses, the extraoral bitewings taken via Sirona emits less radiation for one average bitewing than the intraoral Gendex machine.