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RADIOGRAPHIC ASSESSMENT OF MANDIBULAR SYMMETRY FOLLOWING RECONSTRUCTION OF SEGMENTAL MANDIBULAR DEFECTS

Restoration of symmetric facial contours after resection of mandibular tumors is one of the requisites of a successful reconstructive surgery. For unilateral mandibular defects and using the “mirroring” feature available in many surgical simulation software, it is possible to restore the undistorted mandibular contours and bend the reconstruction plate prior to surgery. The aim of this study: is to assess whether pre-bent mandibular reconstruction plates using computer-assisted techniques for post tumor-ablation defects are good enough at restoring mandibular symmetry radiographically. Patients and Methods: eight patients with segmental mandibular post-tumor resection defects, to whom a computer assisted planning and pre-bending of the reconstruction plates were performed; were included in this study. For each patient, on the 3D reformatted image, a midsagittal plane was constructed and the perpendicular distances were measured from the midsagittal plane to the titanium reconstruction plate and to the contralateral intact side on the axial cuts. The mean differences calculated and statistically analyzed. Results: The mean of the differences between the intact and reconstructed sides of the mandible showed normal data distribution. Overall mean among all patients was 0.7225 mm ± 0.24467. Onesample t test against a hypothetical mean difference of 0 mm revealed an extremely statistically significant difference between the intact and reconstructed sides with a p-value < 0.0001. Conclusion: Computer-assisted precontoured mandibular reconstruction plates can be considered to offer a very good degree of symmetry during mandibular reconstruction procedures. (3108) Adel Hamdy Abou-ElFetouh and Yasmine Ahmed Nassar E.D.J. Vol. 63, No. 4 A tumor-affected mandible is usually deformed to a significant degree that precludes the possibility of intraoperatively bending a reconstruction plate onto the mandible prior to accomplishing the resection. Attempts to contour a reconstruction plate after the resection is completed might risk improper seating of the condyle in the glenoid fossa with resultant malocclusion and temporomandibular disorders. To overcome this problem, some authors recommended the use of various types of condylarpositioning devices (CPDs) to maintain the condyle in place while a reconstruction plate is being adapted and fixed2,3. However, CPDs add to the overall cost and length of the surgery. It was not until the introduction of computerassisted techniques to the field of oral and maxillofacial surgery that a true solution for this problem has been proposed. For unilateral mandibular defects and using the “mirroring” feature available in many surgical simulation software, it is possible to restore the undistorted mandibular contours followed by fabrication of a physical model by additive manufacturing techniques for pre-bending a mandibular reconstruction plate4, 5, 6. Through this study, we aim to assess whether pre-bent mandibular reconstruction plates using computer-assisted techniques for post tumorablation defects are good enough at restoring mandibular symmetry radiographically. PATIENTS AND METHODS Patients were selected for inclusion in this study during the period from January 2013 to August 2017 from the department of Oral and Maxillofacial Surgery, Cairo University. The inclusion criteria were: segmental unilateral mandibular defects; either right or left side; and restoration of mandibular continuity using a titanium reconstruction plate. Whereas exclusion criteria were: free-hand bent and adapted reconstruction plates, patients with resultant soft tissue defects and patients with missing postoperative computed tomography (CT) or whose CTs were not available in a Digital Imaging and Communication in Medicine (DICOM) format. Eight patients could be identified who fulfilled the applied criteria. For these patients, DICOM data of their postoperative CTs were imported into a surgical simulation software*. The CT data were then realigned based on the Frankfurt plane. On the 3D reformatted image, a midsagittal plane was constructed (fig 1). Subsequently, perpendicular distances were measured from the midsagittal plane to the titanium reconstruction plate and to the contralateral intact side on the axial cuts (fig 2). The difference between the two recorded measurements was calculated. Three measurementswere recorded along the anteroposterior (AP) plane and the differences calculated. A mean of the three calculated measurements differences was obtained for each patient. The means were checked for normality using the Shapiro Wilk test7. Assuming perfect symmetry between both sides of a mandible, a hypothetical mean difference of zero millimeters was assumed between the intact and reconstructed sides against which the obtained results were analyzed using a one-sample t test. Fig. (1) Mid-sagittal plane construction on the reformatted 3D image of the skull. * Mimics 15.0, Materialise Software, Leuven, Belgium RADIOGRAPHIC ASSESSMENT OF MANDIBULAR SYMMETRY (3109)