In vivo, thyroid and lens surface exposure with spiral and conventional computed tomography in dental implant radiography

Objective. To compare the surface dose exposure to the lens of the eye and the thyroid gland received by patients undergoing spiral and conventional c omputed tomography (CT) examinations during dental implant pretreatment eva luation in critical radiosensitive structures of the maxillofacial region. Study design, Two groups of 10 patients each had a dental implant CT examin ation performed, with 5 patients in each group having maxillary and 5 havin g mandibular examinations. One group was examined with conventional CT and the other with spiral CT. Seven examination parameters were standardized to both types of examinations. Lithium fluoride thermoluminescent dosimeters were placed over the thyroid gland, lateral orbit, and infraorbital foramen of each patient to measure the surface dose. The Wilcoxon rank sum test wa s used to compare doses, with statistical significance set at P < .05. Results, For the maxillary examination, there was a 57.4% reduction in the surface dose at the lateral orbit, 47% at the infraorbital foramen, and 60. 8% at the thyroid when spiral CT was used instead of conventional CT with t he same parameters. Similarly, for the mandibular examination, there was a 57.4% reduction at the lateral orbit, 60% reduction at the infraorbital for amen, and 70.9% at the thyroid. All the dose reductions were statistically significant at P < .05. Conclusion. The use of spiral CT for preimplant evaluation reduces the surf ace absorbed dose in certain critical structures of the maxillofacial regio n compared with conventional CT.