Standard and low-dose cone beam computer tomography protocol for orthognatodontic diagnosis: a comparative evaluation.

Considering the diagnostic capability offered by cone-beam computed tomography (CBCT), nowadays orthodontists often use this exam for treatment planning, especially in cases of impacted teeth, maxillary ipoplasia, orthognathic surgery etc. The aim of this study was to compare the radiation doses related to a conventional CBCT setting and that of a low dose protocol, usable in orthodontic practice. The absorbed organ doses were measured using an anthropomorphic phantom loaded with thermo-luminescent dosimeters related to sensitive organs (brain, bone marrow, salivary glands, thyroid, esophagus, oral mucosa, extrathoracic airways, lymph nodes). The device used was a MyRay Hyperion X9-11x5. The standard setting of the apparatus was 90 Kv, 36 mAs, CTDI/Vol 4.09 mGy, instead the low dose one was 90 Kv, 27 mAs, CTDI/Vol 2.89 mGy. Equivalent and effective doses have been calculated; the measurement of the effective doses was based on the ICRP recommendations. For the assessment of image quality, five readers, independent and experienced orthodontists, were asked to state if the images were sufficient enough to perform an orthodontic diagnosis. The lowest organ dose (5.01 microSv) was received by the esophagus during low dose CBCT acquisition. The highest mean organ dose instead (1227.67 microSv) was received by the salivary glands during conventional setting CBCT acquisition. Image quality has been considered sufficient for orthodontic diagnostic needs for both CBCT protocols. CBCT low dose setting should be preferred over the standard one in orthodontic practice, because it provides a significant lower radiation dose to the patients ensuring a good image quality. However, further studies are necessary to evaluate the opportunity of CBCT exams in orthodontic treatment planning.

Comparison of linear transverse measures between plaster and resin printed digital models.

The aim of this study was to test for dimensional variations between plaster models recorded with alginate impression and printed 3D physical replicas from an .stl file digitized with an intra-oral scanner. Eighty arches (maxillary and mandibular) from 40 different patients were analyzed. Classic alginate impressions and digital recordings with an intraoral scanner were taken on the same day, for both arches of each patient. Digital recordings were then printed into resin models. The linear intercanine (IC) and intermolar (IM) distances were measured with a manual electronic caliper and then compared. The measurements were repeated twice for each distance to verify repeatability with the intraclass correlation coefficient (ICC). The Student’s t test for paired data was used to compare the two sets of impressions. The repeatability of the measures was assessed as ICC values were higher than 0.98. The values of the IC and IM lengths showed a statistically significant difference, but not clinically significant as it was less than 0.1 mm, between the two techniques.