The primary purpose of orthognathic surgery is to correct disharmony between the maxilla and mandible with occlusion and aesthetic improvement. The fundamental prerequisite for this is the stabilization of the TMJ. In cases where the resorption of the mandibular condyle is pronounced, patients may experience occlusion issues, TMJ dysfunction, pain, facial asymmetry, mandibular retraction, and anterior open bite [7, 16]. In this regard, this paper holds significance. In this retrospective study, we compare the 2 measurements and analyze the change in condyle volume and condyle position immediately after BSSRO and approximately 6 months after surgery in patients with skeletal Class II and III malocclusion. Remodeling and displacement of the mandibular condyle in relation to orthognathic surgery are relatively common. To date, the precise mechanism and underlying cause of mandibular condyle resorption remain unclear. However, as a physiological adaptation process of the TMJ, it is postulated that resorption of the mandibular condyle begins when the external force exceeds the capacity of the joint [17]. For example, occlusal adjustments including prosthetic and orthodontic treatments may change the position of the condyle before and after treatment due to the application of different pressure to the joint than before treatment. This can lead to resorption of the mandibular condyle, but the extent is not usually significant enough to change the occlusion [18]. Patients with TMD were excluded from this study. In patients with TMD, abnormal condyle shape and volume, even if the condyle is repositioned within the glenoid fossa during surgery, the condyle's position within the glenoid fossa may misalign due to muscle reactivation, potentially leading to pathological condylar resorption [19, 20]. Many factors are causes known to increase the risk of resorption of the mandibular condyle. These include local factors, such as trauma, orthodontic treatment, and orthognathic surgery [21,22,23,24,25], and systemic factors, such as chronic steroid use, lupus erythematosus, and systemic sclerosis [26,27,28].

This study focused on orthognathic surgery as one of the potential factors contributing to the resorption of the mandibular condyle. In this study, a significant reduction in the volume of the mandibular condyle occurred in both patients with Class II and Class III malocclusion. When comparing the measurement taken immediately after BSSRO and at 6 months after surgery, the mean condyle volume immediately after surgery was 2301.12 ± 620.31 mm3 and 6 months after surgery was 2235.15 ± 640.49 mm3, showing a statistically significant decrease of 2.91%. da Silva et al. showed 3.84%, a larger average volume loss compared to the results in this study. When only a decrease of 10% or more is considered, the mean volume reduction was 12.11% in 12.5% of the mandibular condyles. da Silva et al. showed a mean volume reduction of 23.2% of the initial volume in 33.3% of the condyles.

This difference may be due to the use of data with an average follow-up period of 18 months, which is significantly longer than the 6 months in this study [29]. Moreover, although none surpassed 10%. volumetric increase in certain condyles was observed 6 months after surgery compared to immediately after surgery. Similar findings were noted in studies conducted by R.J. da Silva et al. and You Na Lim et al. These results imply that new bone formation is possible even after endochondral growth has ended in adults, and it is presumed to originate from the adaptive process through repositioning of the mandibular condyle after orthognathic surgery [29, 30]. Further research in this area is needed.

Notably, compared to immediately after surgery, the SJS and MJS showed a statistically significant decrease 6 months after surgery, suggesting that the mandibular condyle moved superiorly and medially in the mandibular glenoid fossa. da Silva et al. mentioned that changes in the position of the mandibular condyle appear to be related to other factors apart from condylar remodeling [29]. Chen et al. highlighted the possibility for intra-articular edema caused by manipulation of the mandibular proximal segment and subsequently, early-stage downward positioning of the condyle, and condylar sagging by using splints and muscle relaxants under general anesthesia [31]. In contrast, Kawamata et al. and Alder et al. reported that the displacement of the mandibular condyle is in an upward and backward direction [11, 32]. However, in these studies, the displacement of the mandibular condyle was measured using a 2-dimensional analysis method rather than a 3-dimensional method, which consequently may have affected the precision in measuring medial movements. The disparity between the findings from previous studies and the results in our study may be related to the inherent limitation in accurately quantifying the extent of inward movements.

Overall, there was no statistically significant correlation between the volume change and positional relationship of the mandibular condyle immediately after surgery and approximately 6 months after surgery, implying that they should be regarded as independent phenomena, with each may be related to distant underlying mechanisms.

Finally, a significant correlation was detected between the amount of mandibular advancement and AJS in the Class II malocclusion group, and also between the amount of mandibular setback and PJS in the Class III malocclusion group (Table 2). This result is consistent with the findings of existing studies [33, 34]. These anatomical correlations may be due to the pull of the pterygomasseteric sling caused by lengthening or stretching of the muscle fibers after BSSRO. With the amount of mandibular movement increases, there is the potential for a regressive phenomenon to occur.

This study acknowledges the limitation of the relatively small patient sample size, which may impose constraints on the generalizability and reliability of the findings. Future research efforts with larger sample sizes are required to draw more robust conclusions.