Although sagittal split ramus osteotomy (SSRO) and intraoral vertical ramus osteotomy (IVRO) are the prevalent orthognathic surgical procedures for correcting mandibular position, they both share some disadvantages. For instance, SSRO induces condylar resorption (de Lima et al., 2018; He et al., 2019), interference of bone segments (Yang et al., 2010), temporomandibular disorder (TMD), and skeletal relapse due to inappropriate bone fixation (Harada et al., 1996). In addition, the fixation may induce medial rotation of the proximal segment (Park et al., 2012), followed by medial rotation of the condylar head. In contrast, long-term maxillomandibular fixation (MMF), limited indication, and blind osteotomy are the principal disadvantages of IVRO (Tuinzing and Greebe, 1985). Moreover, the segments are completely overlapped in IVRO, resulting in the lateral swinging of the proximal segment. This implies that the condylar head may change its position after surgery, although some reports have shown that IVRO either decreased or did not induce TMD after treatment (Park et al., 2012).

To overcome these impediments in both procedures, the physiological positioning strategy (PPS), a new treatment strategy for mandibular jaw deformity, has been advocated in previous studies (Ohba et al., 2014a, 2014b). Briefly, modified SSRO, also known as the Hunsuck-Epker method or short lingual osteotomy (SLO) (Hunsuck, 1968; Epker, 1997), was performed, and the segments were not fixed after mandibular osteotomy. Subsequently, an occlusal splint was set with MMF. The MMF wire was replaced with elastics. Jaw exercises with elastics were initiated on the second postoperative day (Fig. 1). According to previous studies (Ohba et al., 2014a, 2014b, 2020), SSRO without fixation followed by postoperative management with PPS (nonfix-SSRO) provides skeletal stability comparable to that of conventional SSRO with fixation (conv-SSRO) and IVRO. However, few TMDs were found after nonfix-SSRO. This implies that the proximal segments, including the temporomandibular joints (TMJs), are placed in a physiologically ideal position for postoperative jaw movement after surgery in nonfix-SSRO. Consequently, it was hypothesized that nonfix-SSRO could minimize the adverse effects on the proximal segment position after surgery.

The positional changes of the condylar head with the above-mentioned treatment procedures may affect the incidence of TMD after treatment. The condylar head, however, showed little translational movement after SSRO and IVRO as reported in previous studies (Park et al., 2012; Ohba et al., 2016). Thus, the condylar rotation may influence TMD after mandibular osteotomy.

The aim of the study was to clarify the effects of orthognathic surgical treatment procedures on the proximal segments after mandibular osteotomy. The incidence of TMD and the angle of the condylar long axis were evaluated using three different procedures for mandibular setback in skeletal class III: conv-SSRO, IVRO without fixation (IVRO), and nonfix-SSRO (Fig. 2) (see Fig. 3).