Characterization of facial asymmetry phenotypes in adult patients with skeletal Class III malocclusion using three-dimensional computed tomography and cluster analysis

Abstract

Objective To classify facial asymmetry (FA) phenotypes in adult patients with skeletal Class III (C-III) malocclusion. Methods A total of 120 C-III patients who underwent orthognathic surgery (OGS) and whose three-dimensional computed tomography images were taken one month prior to OGS were evaluated. Thirty hard tissue landmarks were identified. After measurement of 22 variables, including cant (°, mm), shift (mm), and yaw (°) of the maxilla, maxillary dentition (Max-dent), mandibular dentition, mandible, and mandibular border (Man-border) and differences in the frontal ramus angle (FRA, °) and ramus height (RH, mm), K-means cluster analysis was conducted using three variables (cant in the Max-dent [mm] and shift [mm] and yaw [°] in the Man-border). Statistical analyses were conducted to characterize the differences in the FA variables among the clusters. Results The FA phenotypes were classified into five types 1) non-asymmetry type (35.8%); 2) maxillary-cant type (14.2%; severe cant of the Max-dent, mild shift of the Man-border); 3) mandibular-shift and yaw type (16.7%; moderate shift and yaw of the Man-border, mild RH-difference); 4) complex type (9.2%; severe cant of the Max-dent, moderate cant, severe shift, and severe yaw of the Man-border, moderate differences in FRA and RH); and 5) maxillary reverse-cant type (24.2%; reverse-cant of the Max-dent). Strategic decompensation by pre-surgical orthodontic treatment and considerations for OGS planning were proposed according to the FA phenotypes. Conclusions This FA phenotype classification may be an effective tool for differential diagnosis and surgical planning for Class III patients with FA.

Volumetric Analysis of the Jaws in Skeletal Class I and III Patients with Different Facial Divergence Using CBCT Imaging

“…Researchers attributed the etiology of the Class III malocclusion to morphologic or positional disharmony between the maxilla and the mandible during the growth period [ 4 ]. Since there are many variations in Class III morphology, it became a necessity to use the wide applications of 3D imaging in orthodontics to study the volumes of the jaws for a better understanding of the problem [ 5 – 8 ] that may lead to more accurate treatment techniques [ 9 ].…”

Facial Asymmetry Phenotypes in Adult Patients With Unilateral Cleft Lip and Palate and Skeletal Class III Malocclusion Using Principal Component Analysis and Cluster Analysis

“…In addition, 3D facial scan images cannot evaluate asymmetry in the hard tissue. Although PA cephalogram has inevitable errors by the 2-dimensional analysis of a 3D object, 5 it is useful for the initial screening of FA.…”

‘Study of the maxillary yaw on cone beam computed tomography: A preliminary report and comparison between two different dento‐skeletal malocclusions’

“…11 The onset of a mandibular asymmetry in patients affected by prognathism has been also associated with the increased volume of the ipsilateral cranial base, or with lengthening of the ramus and/or of the mandibular body with respect to non-asymmetric patients 8,17 The interest for the asymmetric class III malocclusion has greatly increased in the last years, and Ha et al reported that two-thirds of class III patients who underwent orthognathic surgery were affected by some degree of facial asymmetry. 11,12,14,[18][19][20] In this malocclusion pattern, maxillary yaw develops as a gradual dental compensation, in the attempt to find the best dental intercuspation which may ensure function; especially in age of growth, the dental characteristics of the occlusion (missing teeth, premature contacts, cross bites, etc.) may affect the severity an asymmetric pattern of growth that may affect occlusion and create multiple dental compensations, if not corrected.…”

“…7 The use of cone beam computed tomography (CBCT) in threedimensional diagnosis is boosting the radiographic characterization of different types of facial asymmetry, and the protocols to measure the transverse rotation of the maxillo-facial complex are becoming fast and simple. 7,[11][12][13][14] In this study, we have tested a cephalometric method to assess the yaw on a CBCT three-dimensional reconstructed image of the skull, by evaluating the amount of the maxillary skeletal and dental yawing compensations in two groups of patients clinically affected by a similar malocclusion, a class III with deviation of the lower midline. The aim of the statistical analysis was to compare the measurements of the rotating side with respect to the healthy one in each group, and to analyse if two aetiologically different types of facial asymmetry could significantly affect the transverse maxillary rotation.…”