Minimum size and positioning of imaging field for CBCT-scans of impacted lower third molars: a retrospective study

Abstract

Background Cone-beam Computed Tomography (CBCT) is widely used for preoperative 3D imaging of lower third molars. Hence, for this imaging indication, the present study aimed to define the minimum field-of-view (FOV) size and its optimum placement, to decrease radiation exposure, and highlight the need of computer-assisted FOV centering technique for dental CBCT devices. To facilitate proper placement of image field, lower second molar was chosen as reference. Methods The retrospective study included 50 CBCT-scans of 46 patients with mean age of 34 years. Based on the lower second molar, a three-dimensional coordinate was formed and the location of mandibular canal (MC) and the dimensions and locations of the lower third molars, and possible associated pathological findings were assessed. Accordingly, the FOV size and position for third-molar imaging were optimized, while ensuring encompassment of all relevant structures. Results The minimum cylindrical volume, covering lower third molars and MC, was 32.1 (diameter) × 31.6 (height) mm, placed in relation to the second molar crown, top 2.2 mm above cusp tips, anterior edge 6.7 mm in the front of the most distal point of the crown, and lingual edge 7.9 mm on the medial side of the lingual wall. Conclusions The optimized FOV for lower third molars was smaller than common standard small FOVs. We recommend using FOV volume 3.5∅ × 3.5 cm for third molars without associated pathology. Accurate FOV protocols are essential for development of new CBCT-devices with computer-assisted and indication-specific FOV placement.

The “Dedicated” C.B.C.T. in Dentistry

“…Consequently, it appears necessary to develop a new model of use, which, in compliance with the principle of justification and as low as reasonably achievable (ALARA) and as low as diagnostically acceptable (ALADA), can allow a functional "Dedicated C.B.C.T." exam that is optimized for the individuality of the patient, for treatment planning, and for the improvement of precision and safety of the therapeutic target [3,4,9,18,19,22,25,32,39,40].…”

“…Proper training and recent C.B.C.T. devices with previsualization systems, for the correct placement of the F.O.V., help with this task [32].…”

“…is a commonly encountered event, representing a frequent indication; numerous evidences demonstrate how it is important and useful to significantly limit the irradiation to the patient, and to use adequate exposure parameters of F.O.V. as small as 4 × 4 or smaller [1,17,32]. This has proven to be a favorable optimization strategy in surgical management.…”

“…The low-dose C.B.C.T., especially if associated with a F.O.V. restricted with voxels not below 0.2 mm, can be considered a valid solution in the planning of surgical procedures [1,10,32].…”

Anatomic feasibility of a modified 3-distal site anesthesia injection method for impacted mandibular third molar extraction using cone-beam computed tomography

“…As CBCT can be used as a diagnostic test on impacted third molars in relation to the IAN, CBCT assessment is the main diagnostic tool during anaesthetization in the presurgical phase (32)(33)(34). Among the thousands of cases presented by Luo et al (15), extractions of lower, middle, and high impacted wisdom teeth at mandibular level benefit a lot from CBCT preoperative assessment.…”