finite element analysis model: osteotomy design to detect palatal expansion

Analysis of Expansion Patterns from SARPE Using Finite Element Models

Surgically assisted rapid palatal expansion (SARPE) is a commonly used technique for transversely expanding the maxillary bony structure and the dental arch in skeletally mature patients1. The surgery involves a LeFort I osteotomy, a mid-palatal corticotomy, and, optionally, the release of the pterygoid-maxillary fissure2. However, undesired expansion patterns from SARPE, such as uneven expansion between left and right hemimaxillae3 and dentoalveolar process buccal tipping/rotation4, have been reported, which could lead to failure of SARPE, and sometimes, even requiring additional surgeries for correction5. Previous studies have indicated that the variation in circum-maxillary osteotomies may play a significant role in post-SARPE expansion pattern2,3, as the collisions between the bone blocks at the Le Fort I osteotomy sites can contribute to the uneven resisting force of lateral expansion of the hemimaxillae and to the rotation of the hemimaxillae with the alveolar edges below the cut moving inwards while the dentoalveolar process expands3,4. Therefore, there is a need to investigate the effects of different osteotomy directions, especially the buccal osteotomy, on post-SARPE expansion patterns.
Several finite element analysis (FEA) models have been set up to evaluate the force distribution during SARPE. However, the amount of expansion set in these models is limited to up to 1 mm, which is far below the required clinical amount6,7,8,9,10,11,12. Inadequate expansion in FEA models can lead to erroneous predictions of post-SARPE outcomes. More specifically, the collision between the bones at the osteotomy site, as reported by Chamberland and Proffit4, may not be demonstrated if the expander is not adequately turned, which may not reflect the true clinical reality. With the limited amount of expansion built in the previous models, the outcome evaluations of these models were focused on stress analysis. However, the stress analysis of FEA in dentistry is usually conducted under static loading with the mechanical properties of materials set as isotropic and linearly elastic, which further restricts the clinical relevance of the FEA studies13.
Furthermore, most of these studies did not consider the thickness of the surgical instrument at the osteotomy site6,7,8,10,11,12, often setting friction to zero at the cuts as part of the boundary conditions. However, this setting oversimplifies the contacts between the hard and soft tissues. It may significantly impact the distribution of force and the resulting expansion pattern of the hemimaxillae.
Nevertheless, no available literature has investigated the effect of osteotomy on post-SARPE asymmetry using finite element analysis (FEA) models. All the current studies employed models with symmetrical osteotomy patterns6,7,8,9,10,11,12,14, which do not reflect the reality of clinical practice where the osteotomies may differ on each side of the skull. The lack of literature examining the effect of asymmetrical osteotomies on post-SARPE asymmetry represents a significant knowledge gap that must be addressed.
Therefore, the goal of this study is to develop a novel FEA model of SARPE that can truly mimic the clinical conditions, including the expansion amount and osteotomy gap, and investigate the expansion patterns of the hemimaxillae in all three dimensions with various designs of the osteotomy. Such an approach would provide valuable insight into the mechanics underlying post-SARPE expansion patterns and serve as a useful tool for clinicians in the planning and execution of SARPE procedures.

Author Spotlight: Development of a Novel Finite Element Analysis Model for Improved Orthognathic Surgical Techniques 

Finite Element Analysis Model for Assessing Expansion Patterns from Surgically Assisted Rapid Palatal Expansion

SARPE is commonly used for maxillary expansion in skeletal immature patients. However, asymmetric expansion has been reported with unknown etiologies. This study aims to develop a novel FEA model of SARPE that can truly mimic the clinical conditions, and to investigate the expansion patterns of the hemi-maxilla in all three dimensions.Finite element analysis has been used in the dental and bioengineering field to allow in vitro simulation of surgeries, such as SARPE. In this study, four software were utilized to set up the FEA model and to predict expansion pattern. The most challenging part, which most previous studies link, is to simulate forces at the wound healing site across osteotomy surface.To achieve this, springs were set in our pilot study and is considered a novel design for SARPE FEA. This unified element model focused on its patient patterns, making it more realistic SARPE simulation through osteotomy gap creation and experience inclusion. It presents significant potential as the clinical tool for branding and its guiding SARPE procedures.Our interdisciplinary group will work diligently to develop cutting-edge 3D models that can provide valuable insights into personalized treatment strategies to analyze and improve orthognatic surgical technique by utilizing an engineering-assisted approach and to improve communication and collaboration between orthodontists and oral maxillofacial surgeons through engineering-assisted 3D imaging system.

Watch this Scientific Journal Video about Finite Element Analysis Model: Osteotomy Design to Detect Palatal Expansion at JoVE.com

Finite Element Analysis Model: Osteotomy Design to Detect Palatal Expansion  

To begin, launch the SolidWorks software to create a one-millimeter thick plane from the piriform aperture towards the infra-zygomatic crest. Now open the Insert menu, then click on Reference Geometry and Plane options. From the osteotomy plane, select three feature points and click OK to create the O1 plane.Navigate to the plane again by clicking on Insert and Reference Geometry. This time, choose the osteotomy plane and set an offset distance of one millimeter. Click OK to create a lower cutting plane marked O2.Now navigate to split by selecting Insert, followed by Features, and choose the O1 and O2 planes in Trim Tools.Select the target bodies and press Cut Bodies to create a cutting preview. Next, tick the check boxes in the Resulting Bodies section and press OK to separate the maxillary complex. Then click on the body between the O1 and O2 planes, right-click, and press Delete under the Body section.To export the models with different buccal osteotomy angles, first click on File, then Save As, and choose Parasolid x_t from the file type list. Finally, click Save to export the models for finite element analysis software. The demonstrated analysis used the cone-beam computed tomography image of a 47-year-old female with maxillary deficiency to generate a model.For accurate surgery simulation, the nasal septum, lateral nasal cavity walls, and pterygomaxillary fissure were separated.

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89 Views.  University of Pennsylvania. To begin, launch the SolidWorks software to create a one-millimeter thick plane from the piriform aperture towards the infra-zygomatic crest. Now open the Insert menu, then click on Reference Geometry and Plane options. From the osteotomy plane, select three feature points and click OK to create the O1 plane.Navigate to the plane again by clicking on Insert and Reference Geometry. This time, choose the osteotomy plane and set an offset distance of one millimeter. Click OK to create a l...

Video: Finite Element Analysis Model: Osteotomy Design to Detect Palatal Expansion  

Surgically assisted rapid palatal expansion (SARPE) was introduced to release bony resistance to facilitate skeletal expansion in skeletally mature patients. However, asymmetric expansion between the left and right sides has been reported in 7.52% of all SARPE patients, of which 12.90% had to undergo a second surgery for correction. The etiologies leading to asymmetric expansion remain unclear. Finite element analysis has been used to evaluate the stress associated with SARPE in the maxillofacial structures. However, as a collision of the bone at the LeFort I osteotomy sites occurs only after a certain amount of expansion, most of the existing models do not truly represent the force distribution, given that the expansion amount of these existing models rarely exceeds 1 mm. Therefore, there is a need to create a novel finite element model of SARPE that could perform a clinically required amount of expander activation for further analysis of the expansion patterns of the hemimaxillae in all three dimensions. A three-dimensional (3D) skull model from cone beam computed tomography (CBCT) was imported into Mimics and converted into mathematical entities to segment the maxillary complex, maxillary first premolars, and maxillary first molars. These structures were transferred into Geomagic for surface smoothing and cancellous bone and periodontal ligament creation. The right half of the maxillary complex was then retained and mirrored to create a perfectly symmetrical model in SolidWorks. A Haas expander was constructed and banded to the maxillary first premolars and first molars. Finite element analysis of various combinations of buccal osteotomies at different angles with 1 mm clearance was performed in Ansys. A convergence test was conducted until the desired amount of expansion on both sides (at least 6 mm in total) was achieved. This study lays the foundation for evaluating how buccal osteotomy angulation influences the expansion patterns of SARPE.

A set of novel finite element models of surgically assisted rapid palatal expansion (SARPE) that could perform a clinically required amount of expander activation with various angles of buccal osteotomy was created for further analysis of the expansion patterns of the hemimaxillae in all three dimensions.

Surgically assisted rapid palatal expansion (SARPE) was introduced to release bony resistance to facilitate skeletal expansion in skeletally mature ...

Expansion Assessment Using Finite Element Analysis from Surgically Assisted Rapid Palatal Expansion (SARPE)

To begin, launch the Ansys software to import the material parameters of the maxillary complex model into the software. Next, click and drag the static structural in the toolbox to create an analysis workspace. Double click on engineering data, followed by linear elastic under toolbox, and set the Young's modulus and Poisson's ratio for all the materials in properties.Now, double click on geometry, followed by file, then select import external geometry file, and click generate to import the maxillary complex model. Then click create, followed by Boolean, and generate the cortical and periodontal ligament Boolean with cancellous bone and teeth. To set up the finite element analysis model, double click on the model, then select geometry to determine the material properties for each part.Next, right click on mesh and press generate mesh to build the model elements. Now, click connections and assign the soft or small part in contact bodies, and the stiff or large part in target bodies, then assign the contact type and friction coefficient in definition. Next, right click connections and select insert, then press spring to connect the upper and lower parts of the osteotomy plane.Set the springs to one millimeter length with a spring constant K set at 60 newtons per millimeter. Place one spring at each grid node. After setting a clinically acceptable force along the X axis, right click the static structural option.Press insert, followed by fixed support to render the structure on the palatal plane as immovable. To apply force on the acrylic plate away from the medial line, click on static structural, then insert and set the force to 150 newtons. Then right click solution followed by insert, deformation, and total to monitor the expansion deformation.Finally, to carry out a convergence test, select solve in the toolbars and wait until the force convergence level reaches the force criterion. Then click on solution information, followed by total deformation to display the expansion results. The demonstrated model used the cone beam computed tomography image of a 47-year-old female with maxillary deficiency to create a model.For accurate surgery simulation, the naval septum, lateral nasal cavity walls, and pterygo-maxillary fissure were separated. A preliminary test performed on both the left and right sides of the model with symmetric, zero degree cuts, showed that 150 newtons of force caused more than eight millimeters of expansion. Additionally, a variety of angles were built to mimic different clinical conditions.The right and left expansions were visible as a before and after color map of the maxilla models.