Asymmetry Index From Photogrammetric Analysis

Overview

We propose a transversal observational study, to be performed on three-dimensional images acquired through photogrammetry of patients who will undergo orthodontic treatments. The aim of our research consists in the evaluation of facial asymmetry through a graph built on three degrees of Asymmetry Index (symmetry, slight asymmetry, asymmetry) in an Italian population that meets the criteria of absence of craniofacial deformities and that has not undergone surgery or orthodontic treatment. For the analysis, images acquired via photogrammetry are used, then analyzed with the Geomagic Control 2014 program (64 bit).

Facial symmetry is considered one of the most significant factors in the perception of facial attractiveness. A slight degree of asymmetry is common in the human face and often does not require any treatment\], as it is camouflaged by the presence of soft tissue, dental compensation or change in head posture . However, the problem of asymmetry is difficult to manage for the dentist and, in particular, for the orthodontist. In fact, there are many etiological factors related to the development of facial asymmetry and asymmetries that share the same etiology can have different characteristics, as they are influenced by other factors, such as individual growth and compensation. In fact, at the very moment of the physical examination, it is often not easy to identify the degree of severity of the patient's facial asymmetry. During the clinical examination, dental and skeletal asymmetry can be evaluated: facial asymmetry can be investigated by simple observation of the patient . However, the aid of instrumental radiological examinations has always been considered the choice for determining the degree of asymmetry. Orthopantomography is one of the first diagnostic tests that is performed, thanks to its low cost and low radiation dose. The analysis of teleradiographs appears to be, however, the most reliable and most used means over time for the diagnosis of asymmetry. Traditional radiographic examinations, however, (PA and SV projection teleradiographs) have limitations in determining the diagnosis of asymmetry as they make a three-dimensional image two-dimensional, which can lead to distortions and errors in image projection . The development of computed tomography (CT), cone beam (CBCT) and stereophotogrammetry have brought about a new era in the field of asymmetry diagnosis . 3D images have greatly reduced the magnification and projection errors common in conventional radiographs while providing an important aid in the evaluation of asymmetry. They can also offer accurate and more detailed information for diagnosis and treatment planning by allowing quantitative measurements and comparisons between the right and left sides of the face. The introduction of non-invasive three-dimensional image acquisition via photogrammetry has made it possible to view the patient's face from different angles providing the possibility to perform accurate measurements of lengths, areas, angles and volumes. Although the nature of the asymmetry is complex and the characteristics are different, there have been some attempts to create a systematic classification of facial asymmetry.