Correlation analysis of 3-dimensional changes of hard and soft tissues in Class III orthognathic surgery patients using CBCT

Abstract

Orthognathic surgery combined with orthodontics must enhance facial balance as well as skeletal harmony. Already a paradigm shift has occurred, with orthodontists and patients placing more importance on soft tissue esthetics. Because the facial soft tissues might not reflect the exact changes of the skeleton proportionally, an understanding of the soft tissue response due to skeletal changes from orthognathic surgery is essential during the treatment planning, prediction and treatment processes. The purposes of this study were to examine the correlation between changes of the soft and hard tissues 3-dimensionally in Class III orthognathic patients using CBCT and to provide indicators for the clinical diagnosis and treatment planning of orthognathic surgery.In this study, CBCT images were used within 2 weeks before surgery and at 6 months after surgery in adult Class III patients (9 males and 9 females, mean age 23.5 years) who underwent Le Fort I osteotomy and bilateral intraoral vertical ramus osteotomy (B-IVRO). Subjects were divided into Group 1 with no mandibular asymmetry (less than 2mm of menton deviation from the facial midline) and Group 2 with mandibular asymmetry (over than 4mm of menton deviation from the facial midline). CBCT images were reconstructed and 3D data of landmarks were calculated. Correlations and proportions of changes of the soft tissue to hard tissue were also obtained.1.There were significant correlations of ΔB’ to ΔB and ΔPog’ to ΔPog in both groups on the horizontal axis (P<0.05). The proportions of ΔB’ to ΔB, and ΔPog’ to ΔPog in Group 1 were 0.53 and 0.67, respectively. Those of Group 2 were 0.77 and 0.88, respectively. 2.There were significant correlations of ΔB’ to ΔB, ΔPog’ to ΔPog and ΔMe’ to ΔMe on the sagittal axis in both groups (P<0.05). Correlation coefficients of ΔB’ to ΔB, ΔPog’ to ΔPog and ΔMe’ to ΔMe in Group 2 were greater than in Group 1. The proportions of ΔB’ to ΔB, ΔPog’ to ΔPog, and ΔMe’ to ΔMe in Group 1 were 0.94, 0.84, and 0.96, respectively. Those of Group 2 were 0.95, 0.91, and 1.03, respectively.3.There were no significant correlations between changes in soft and hard tissues on the vertical axis in both groups (P>0.05).4.There were significant correlations of the 3D distances between ΔB’ to ΔB, ΔPog’ to ΔPog and ΔMe’ to ΔMe in both groups (P<0.05). The proportions of ΔB’ to ΔB, ΔPog’ to ΔPog, and ΔMe’ to ΔMe in Group 1 were 0.92, 0.79, and 0.95, respectively. Those of Group 2 were 0.92, 0.88, and 0.97, respectively.In Class III orthognathic patients with mandibular asymmetry, the proportions of ΔB’ to ΔB, ΔPog’ to ΔPog, and ΔMe’ to ΔMe on the horizontal and sagittal axes and the 3D distances were different from patients with no mandibular asymmetry. Because sagittal changes of point A were little, proportions for changes of hard and soft tissues associated with the maxilla and upper lip were not calculated. Clinicians must consider these results in diagnosis and treatment planning of Class III mandibular asymmetry patients.