The purpose of this study was to test the precision and accuracy of three-dimensional (3D) linear measurements for Le Fort I osteotomy, obtained from multi-slice computed tomography (MSCT) and cone beam computed tomography (CBCT) scans. The study population consisted of 11 dried skulls submitted to 64-row MSCT and CBCT scans. Three-dimensional reconstructed images (3D-CT) were generated, and linear measurements ( n = 11) based on anatomical structures and landmarks of interest for Le Fort I osteotomy were performed independently by two oral and maxillofacial radiologists, twice each, using Vitrea software; this allows true 3D measurement on 3D-CT images. The results demonstrated no statistically significant differences between the inter-examiner and intra-examiner analyses, and physical and true 3D linear measurements using MSCT and CBCT images. Regarding examiner accuracy, no statistically significant differences were found for the comparisons among the physical and the MSCT and the CBCT linear measurements by either examiner. For examiners 1 and 2, the analysis intra-examiner correlation coefficient ranged from 0.87 to 0.96 and 0.82 to 0.98, respectively, using MSCT, and from 0.84 to 0.98 and 0.80 to 0.98, respectively, using CBCT, indicating almost perfect agreement for all analyses performed. 3D linear measurements obtained from MSCT and CBCT images were considered precise and accurate for Le Fort I osteotomy and thus accurate and helpful for Le Fort I osteotomy planning.
Currently available three-dimensional (3D) software has been developed specifically to assist in the diagnosis, treatment planning, and prediction of outcomes related to orthognathic surgery and to prevent perioperative complications such as haemorrhage, permanent neural disorders, and unplanned fractures, especially for the Le Fort I osteotomy involving the pterygoid process. However a large number of parameters are involved that could influence the surgeon’s analysis and consequently compromise the surgical outcome, such as different computed tomography image acquisition (multi-slice computed tomography – MSCT, and cone beam computed tomography – CBCT), different reconstruction algorithms, and different forms of linear measurement method.
The purpose of this study was to test the precision and accuracy of 3D linear measurements for Le Fort I osteotomy obtained from MSCT and CBCT scans.
Materials and methods
The study population consisted of 11 intact human skulls (eight male and three female, aged 19–56 years), provided by the institution’s department of anatomy. Approval was granted by the institutional review committee/human specimens committee. There was no ethnic or gender preference when selecting the sample, and no history of bone disease was identified in the medical records.
Before scanning the skulls, the mandibles were fixed to the skulls in central occlusion using tape. The skulls were placed in a plastic bucket with water for MSCT and in a bulk bag with water for CBCT, for beam attenuation and to mimic the soft tissues, in accordance with previously published methods. The skulls were then placed in the equipment to keep them in a position similar to that of the clinical situation for the MSCT and CBCT.
The specimens were first submitted to a 64-row multi-slice CT procedure (Aquilion; Toshiba America Medical Systems Inc., Tustin, CA, USA). The boundaries of the imaging area were set superior to the vertex and extended inferiorly to below the mandible. High-resolution contiguous images were obtained following the acquisition image protocol (0.5 mm thick axial slices, 0.3 mm of reconstruction interval per 0.4 s of time, 512 × 512 matrix, 120 kVp and 300 mA, and 24.0 cm field of view), associated with a low frequency filter (bone filter). Subsequently, the skulls were submitted to a CBCT scan (i-CAT Cone Beam 3D Dental Imaging System, Imaging Sciences International, Hatfield, PA, USA) at 0.25-mm voxel size for 40 s to acquire raw data. The field of view (FOV) was a 20-cm height and 16-cm diameter cylinder. The grey-scale range of the acquired images was 14 bits. After the original image was acquired, these data were recorded and stored in DICOM format (Digital Imaging Communication in Medicine) to avoid data loss.
Multiplanar (MPR; axial, coronal, and sagittal) and 3D-CT reconstructed images using the bone protocol were obtained simultaneously, based on the original axial slices, and were generated in Vitrea version 3.8.1 software (Vital Images Inc., Plymouth, MN, USA) installed in a Dell 650 Precision independent workstation (Dell Computer Corp., Round Rock, TX, USA) running the Windows XP operational system (Microsoft, Redmond, WA, USA). Two oral and maxillofacial radiologists, with extensive experience in interpreting CT and knowledge of the software tools, were calibrated prior to study commencement.
Linear measurements of the 3D coordinates used for this study were obtained using the anatomical structures described in Table 1 . Most of the bone structures were selected expressly, instead of using the traditional craniometric points, since analysis of these structures is highly relevant in the planning of the Le Fort I osteotomy ( Table 1 ).