7.1 Relapses Following the Surgery-First Approach for Patients with Class III Malocclusions: Intraoral Vertical Ramus Osteotomy (IVRO) Versus Sagittal Split Ramus Osteotomy (SSRO)
Since the introduction of Intraoral Vertical Ramus Osteotomy (IVRO) and Sagittal Split Ramus Osteotomy (SSRO) as mandibular setback surgery methods in the 1950s, extensive research on their postoperative stability has been conducted. Since the 1990s, several studies have shown that SSRO is prone to both anterior and upward relapses, after initial mandibular setback, and in the same direction for late relapse. In the case of IVRO, there are some differences among the studies, but initial relapses show posterior mandibular movement of mandible. In cases of late relapse, anterior and upward movement of the mandible is observed, similar to the aspect after SSRO (Fig. 7.1). However, the values are clinically acceptable and both procedures show very stable results [1–3].
How does the stability achieved after the surgery-first approach differ from that of conventional mandibular setback surgery? In the early postoperative period, the segmental changes initiated by the dislocation of proximal and distal segments mostly affect initial relapses. These are caused by an imbalance of forces generated by the stomatognathic system associated with the distal segments. Intraoperative distal and lateral displacement of the proximal segments can cause this type of imbalance. At the late stage, the proximal and distal segments are mostly joined and the mandibular movement is generated from the muscles of the pterygomasseteric sling responding to a single united segment. In the surgery-first approach, there is the possibility of another stage between the early and the late stages; this stage is called the middle postoperative orthodontic stage. During this stage, how much does the incomplete occlusion affect the surgical stability?
A study comparing the postoperative mandibular relapse patterns after conventional orthognathic surgery and those following the surgery-first approach showed that the mandibular forward relapse was slightly larger following the surgery-first approach [4–7]. This was common for both the SSRO and the IVRO groups (Fig. 7.2) . This was likely the case because, in the surgery-first approach patients, surgical occlusion may have induced transient temporary bite openings due to premature contact with the posterior teeth. As mentioned in the previous chapter, this is because the position of the mandible, which has been moved forward and upward, is the position that was initially planned in the surgical treatment objective. Therefore, these mandibular movements would be more appropriately called predicted or planned mandibular seating .
Case Report 7.1: 20 years 9 months old female patient having complaints of mandibular prognathism, long face and facial asymmetry. Two-jaw surgery was planned and performed with surgery-first approach. The superimposition of lateral cephalometric radiographs shows relatively good stability after 39 months of surgery