Downloaded from http://journals.lww.com/jcraniofacialsurgery by BhDMf5ePHKbH4TTImqenVAJP5BDjqW51bZyAlL54QIVQ2Dvtd0O3zVBbG70q64XX on 09/01/2020 Copyright © 2020 Mutaz B. Habal, MD. Unauthorized reproduction of this article is prohibited. Changes of Stress Distributions Around Pterygomaxillary Junction With Different Osteotome Angulations Emrah Dilaver, DDS,  Muazzez Suzen, DDS, PhD,  Oguzhan Demir, PhD, z Sedat Iric, PhD, § Ali O. Ayhan, PhD, § and Sina Uckan, DDS, PhD  Abstract: The aim of this study was to investigate how the alteration of the angulation of osteotome at pterygomaxillary junction affects lateral pterygoid plate, maxillary tuberosity, palatal surface of maxilla, palatine bone and body of sphenoid bone. Following recon- struction of 3D modelling of maxilla, Osteotomes’ tip was angulated 45 8 and 90 8 to sagittal plane to simulate pterygomaxillary osteotomy. Finite element analyses (FEA) was performed and Von Misses stress distributions were analyzed for two different angulations. Indepen- dent sample t test was used to compare differences between 45 8 and 90 8 angulations. Von Misses stress values on lateral pterygoid plate were higher in 45 8 angulation (0.71  0.21 MPa) than 90 8 angulation (0.54  0.28 MPa). This difference was statistically significant (P < 0.01). Placement of osteotome’s tip with 90 8 angulation had higher stress value than 45 8 angulation on maxillary tuberosity region. However; difference wasn’t significant (P ¼ 0.44). Stress values on body of sphenoid bone were 0.45  0.17MPa for the case of 90 8 angulation and 0.19  0.09MPa for 45 8 angulation. Difference between these values were statistically significant (P < 0.01). Possi- ble risk of unfavourable lateral pterygoid plate fracture and compli- cations related with body of sphenoid bone during pterygomaxillary osteotomy was remarkably increased in case of narrow angulation (45 8 ). Keeping osteotome at right angle with sagittal plane may avoid these complications. Key Words: Angulation of curved osteotome, finite element analysis, lefort 1 osteotomy, pterygoid plates (J Craniofac Surg 2020;31: 1560–1562) L e Fort I osteotomy technique requires pterygomaxillary separa- tion by curved osteotome before down fracturing of maxilla. 1 Improper positioning of curved osteotome at pterygomaxillary junction may result in undesired fractures on pterygoid bone. 1,2 Due to incomplete separation of pterygomaxillary junction, many complications such as extensive bleeding, fractures of maxillary tuberosity, palatine bone, lateral pterygoid plate and fractures of different levels in base of skull were reported. 3 To reduce unwanted fractures of pterygoid plate, many techniques for formal pterygo- maxillary separation have been proposed, including positioning of osteotome, the use of various micro-oscillating saws and ultrasonic devices. 1,2,4 Different osteotome angulations may result in unfa- vorable fractures in this complicated anatomic area. Computed tomography is routinely taken for virtual planning and assesment of cranial structures before orthognathic surgery. Especially in axial images, it is possible to determine in detail the location of pterygoid plates and pterygomaxillary fissures and angle of osteot- omy. There are only few studies investigating effects of alteration of angle of the osteotome with sagittal plane and they are all anatomical ones 1,3,5 Finite element analysis (FEA) provides visualizing of response of the craniofacial skeleton to forces during osteotomy in three dimensional vision. Advantages of FEA is being non invasive technique and assessing of stress distribution at any given point which is difficult to assess otherwise. The aim of this study was to evaluate stress distributions by finite element analysis (FEA) on lateral pterygoid plate, maxillary tuber- osity, palatal surface of maxilla, palatine bone, body of sphenoid bone on cranial base in different osteotome angulations during separation of pterygomaxillary junction. Results of this study may help to decide ideal ostetome angle and to take precautions during pterygomaxillary osteotomy to prevent potential complications. MATERIAL AND METHODS Computed tomography (CT) was used to obtain mathematical digital model of maxilla and cranium of a healthy adult without skeletal deformity. Three dimensional CT scanning (i-CAT 17 – 19; Imaging Sciences International Inc, Hattfield, PA) was performed with following parameters which are 120 kVp and 20.27 mAs using a 16  6 cm field of view, and 0.30 voxels. DICOM files were converted into STL format (Stereo Lithography) using the Mimics software (Materialise NV, Leuven, Belgium). ANSYS version 10 (ANSYS Inc, Canonsburg, PA), a 3-D modeling and analysis software program, was used to generate solid and finite element models of the maxilla and cranium considered in the study. ANSYS Mechanical APDL was used to generate finite element models of the maxilla and cranium for performing stress analyses. Finite element meshes were generated using tetrahedral elements for the model which consist of 187,597 quadratic elements and 297,992 nodes. Young modulus of model were 13.7 GPa for cortical bone, 1.37 GPa for cancellous bone and 0.069 GPa for sutures. Poisson’s ratio used in the analyses was 0.3 for both cortical bone and cancellous bone and 0.45 for suture. 6,7 Boundary conditions were defined such that the maxilla and cranium surface nodes were constrained in all directions. From the  Department of Oral and Maxillofacial Surgery, Istanbul Medipol University School of Dentistry, Istanbul; z Department of Mechanical Engineering, Bilecik Seyh Edebali University, Bilecik; and § Department of Mechanical Engineering, Sakarya University, Sakarya, Turkey. Received December 20, 2019. Accepted for publication January 21, 2020. Address correspondence and reprint requests to Emrah Dilaver, DDS, Istanbul Medipol University School of Dentistry, Department of Oral and Maxillofacial Surgery, Atatu ¨rk Bulvari No:27, 34083 Unkapani- Istanbul; E-mail: emrahdilaver@gmail.com The authors have no conflicts of interest to disclose. Supplemental digital contents are available for this article. Direct URL citations appear in the printed text and are provided in the HTML and PDF versions of this article on the journal’s Web site (www.jcraniofa- cialsurgery.com). Copyright # 2020 by Mutaz B. Habal, MD ISSN: 1049-2275 DOI: 10.1097/SCS.0000000000006397 ORIGINAL ARTICLE 1560 The Journal of Craniofacial Surgery  Volume 31, Number 6, September 2020