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

Summary

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.

Abstract

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.

Introduction

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 add....

Protocol

This study utilized a pre-existing, de-identified, pre-treatment CBCT image of a patient who had SARPE as part of the treatment plans. The study was conducted in accordance with the Declaration of Helsinki and approved by the Institutional Review Board (protocol #853608).

1. Sample acquisition and tooth segmentation

1. Acquire a human CBCT image of the head in a natural head position that includes the patient's maxillary complex, including the maxillary basal bone.......

Discussion

The direction of the buccal osteotomy in SARPE can be either a horizontal cut from the nasal aperture before stepping down at the maxillary buttress area or a ramped cut from the piriform rim towards the buttress corresponding to the maxillary first molar, as described by Betts². Either way, the osteotomy extends well below the zygomatic process of the maxilla. However, most current FEA studies on SARPE use a horizontal cut extending posteriorly at the same level as the piriform rim

Materials

Name	Company	Catalog Number	Comments
Ansys	Ansys	Version 2019	Ansys is a software for finite element analysis that can solve complicated models based on differential equations. The expansion results of different buccal osteotomy angles were analyzed through this software.
Geomagic Studio	3D Systems	Version 10	Geomagic Studio is a software for reverse engineering that can generate digital models based on physical scanning points. This study built cancellous bone and periodontal ligaments through this software.
Mimics	Materialise	Version 16	Mimics is a medical 3D image-based engineering software that efficiently converts CT images to a 3D model. This study reconstructed a maxilla complex through the patient's DICOM images.
SolidWorks	Dassault Systèmes	Version 2018	SolidWorks is a computer-aided design software for designers and engineers to create 3D models. A Haas expander was designed and drawn through this software in this study.