Treatment of moderate-to-severe Class III malocclusion frequently requires a combination of orthodontics and orthognathic surgical procedures. Therefore, it is important for the clinician to be able to predict soft-tissue changes resulting from alterations of the hard tissue.

The soft-tissue changes following orthognathic surgery (OGS) depend on various factors, such as variability in soft-tissue thickness, degree of deformity, and tonicity of the musculature (Legan and Berstone, 1980). The thickness of the soft tissue covering the bone and dentition is highly variable. Consequently, soft-tissue thickness affects not only the amount of lip protrusion but also the total facial profile (Hu et al., 1999). For example, thicker lips appear to respond less to incisor movement after premolar extraction in orthodontic movement (Alkadhi et al., 2019).

Many studies have investigated the relationship between the soft-tissue profile changes and hard-tissue movement by using two-dimensional (2D) lateral cephalometric analysis (Hu et al., 1999; Arnett et al., 1999; Marşan et al., 2009; Gunaid et al., 2012; Yeo et al., 2019). Most of these studies reported significant associations between horizontal soft tissue and corresponding hard-tissue changes (Yeo et al., 2019; Lin and Kerr, 1998). Some retrospective studies have claimed that sex is a factor influencing soft-tissue changes (Hu et al., 1999; Lin and Kerr, 1998), while others have observed that the effects of age on changes in soft tissue are nonsignificant (Naoumova et al., 2008). However, 2D images may not represent the anisotropic behavior of soft tissues accurately; moreover, the presentation of a complex 3D craniomaxillofacial structure in 2D is difficult. Cone-beam computed tomography (CBCT) has been increasingly used for imaging of both soft and hard tissues, and for assessing surgical outcomes by evaluating the 3D facial changes based on the underlying bone movement (Paula et al., 2013). Few studies have evaluated soft-tissue and hard-tissue changes by using 3D imaging (Hajeer et al., 2004; Choi et al., 2021).

Several studies have reported that soft-tissue morphology varies by vertical facial pattern. Celikaglu et al. reported that, in women, the high-angle group had thinner lower anterior face soft tissue compared with the normal-angle group (Celikoglu et al., 2015). Ahmed et al. compared the soft-tissue responses among three facial patterns. They concluded that skeletal parameters were highly correlated with soft-tissue parameters in long faces (Ahmed et al., 2016). However, these studies investigated soft-tissue changes by using 2D cephalograms. Choi et al. compared the changes in soft-tissue thickness between normal- and high-angle facial patterns after bimaxillary surgery, and discovered that the thickness of the soft-tissue pogonion (Pog) increased slightly with mandibular plane angle preoperatively (Choi et al., 2021).

The number of studies comparing soft-tissue changes following OGS by using 3D images among vertical facial types is limited. For this reason, our study compared soft-tissue changes in relation to the underlying hard tissue and the changes in soft-tissue thickness among three vertical facial types in patients with mandibular prognathism. The null hypothesis was that the soft-tissue thickness changes and the ratio of soft-tissue to hard-tissue changes would not differ significantly among the three vertical facial types.