An Automatic Voxel-Based Method for Optimal Symmetry Plane Generation for the Maxillofacial Region in Severe Asymmetry Cases

Abstract

Symmetry is representative of aesthetics and health in all kinds of vertebrates, especially the human face. Therefore, to automatically locate the appropriate symmetry plane is crucial. The aim of this study was to develop an automatic and reliable method to determine the symmetry plane of the maxillofacial region. We compared the proposed method of determining the symmetry plane by assessing landmark-based and surface-based methods by way of quantitative symmetry assessments. Statistical analysis was applied to evaluate whether significant difference existed among these three kinds of symmetry planes. Twenty cases who had a diagnosis of severe facial asymmetry were evaluated retrospectively. The results showed that searching for the symmetry plane using a voxel-based method, named the optimal symmetry plane (OSP), achieved the most representative symmetry according to the outcomes of the trials. The OSP was significantly more symmetrical than the other two planes, as determined by other methods. The paired-voxel computation method proposed in this research is a robust and reliable method for identifying the unique symmetry plane for patients with severe facial asymmetry. Symmetry is of crucial significance for all kinds of vertebrates, including its clinical implications for surgical planning in orthognathic surgery.

Establishment of the mid-sagittal reference plane for three-dimensional assessment of facial asymmetry: a systematic review

“…A semi-automatic technique that involves digital landmarking was employed for cephalometric and morphometric MSP construction in nine studies [23,24,28,31,32,40,[47][48][49], whereas a fully automated and landmark-independent technique for morphometric MSP and symmetry plane construction was reported in seven studies [3,16,21,25,9,33,50]. The fully automated MSP construction method was reported to accurately measure the degree of asymmetry and achieve satisfactory skeletal symmetry, as asserted by the authors in their respective studies (Table 3).…”

“…Between 2005 and 2023, a total of 42 studies were identified, focusing on estimating the mid-sagittal plane in patients with facial asymmetry. Out of the selected 42 studies, eight were computational studies [1,3,[21][22][23][24][25][26]; six were observational [14,15,[27][28][29][30]; 21 studies used retrospective analytical design [4,9,9,12,[31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47]; three were experimental studies [17,48,49], and one study was ambispective in nature [50]. The age range of the patients in all the included studies was 7-57 years.…”

“…The majority of the included studies [12, 14, 27-31, 9, 32, 36, 37, 39-49, 51-53] constructed a cephalometric MSP, while eight studies computed a morphometric MSP [3, 17, 21-24, 34, 38] for the assessment of asymmetry (Table 3). In addition, five studies employed both cephalometric and morphometric MSP construction methods [4,15,25,35,50], while four studies assessed asymmetry using a symmetry plane [1,26,9,33]. For the cephalometric MSP construction, N-S was the most consistently used landmark combination [12,28,35,39,40,43,47,48].…”

A Symmetry-Based Superposition Method for Planning and Surgical Outcome Assessment

“…The median plane of the CT gantry region is set to the initial guess plane of the OSP. The OSP is found by the plane that minimizes f [ 24 ].…”

“…Hence, this paper introduces a computerized voxel-based method to automatically locate the unique symmetry plane of an object, called the optimal symmetry plane (OSP). The symmetry ratio quantifies the degree of asymmetry of an object and determines the OSP, which is more reliable than the landmark-based and surface-based symmetry plane [ 24 ].…”