## 4 Discussion
However, in clinical practice, we try to level the posterior dental cant but do not intend to make it 0 degrees, but rather coordinate with other parameters for symmetric and harmonious positioning of the maxillomandibular complex. The posterior dental cant was revealed in the range of \(-\)0.88-2.68, matching our clinical purpose (Table 3). For the same reason, the midline was easier to align by moving and rotating the maxillomandibular complex. Hence, the anatomic landmarks were more significantly centered and symmetric when undertaking the two-jaw surgery (Table 3). A large amount of maxillary advancement could cause problems such as postoperative instability, a high relapse rate, velopharyngeal insufficiency, or inadequate blood supply. The limitation of LeFort I maxillary advancement was suggested as 10 mm for non-cleft patients, but the amount was advised to be conservative and no more than 6 mm in patients with cleft [23; 24; 25; 26; 27; 28]. It was suggested that if the maxillomandibular discrepancy was more than 6 mm, bone graft, a combined mandibular setback osteotomy or distraction osteogenesis should be considered. In the present study, the maxilla was advanced by an average of 7.46 mm in the one-jaw design and 4.80 mm in the two-jaw design, respectively (Tables 2 and 3, A-N perpendicular). Two-jaw surgery with mandibular setback compensated for the amount of maxillary advancement by an average of 2.66 mm. When completing one-jaw surgery, 26 patients (63%) needed maxillary advancement of more than 6 mm which was an unfavorable condition causing possible relapse (Table 4). Only 15 patients (37%) with moderate maxillary advancement were suitable and qualified for one-jaw surgery design for the correction of anteroposterior discrepancy in this study cohort. Although the regular amount of maxillary advancement was adequate to achieve positive overjet and acceptable occlusion, the skeletal relationship was still a prognathic profile with a mean ANB angle 0.25\({}^{\circ}\) (Table 4). Patients would complain of inadequate correction of facial appearance in our practice. By completing the two-jaw surgery, the maxillomandibular complex was allowed to rotate clockwise in the pitch direction in order to increase the ANB angle with A point forward and B point backward in order to achieve skeletal class I appearance with a better facial profile. An average gain of 3.28\({}^{\circ}\) (0.25\({}^{\circ}\)-3.53\({}^{\circ}\)) in ANB angle by the clockwise rotation was achieved in the present study (Table 4). Therefore, the mandibular setback osteotomy was not only able to compensate for the amount of maxillary advancement, but also to improve the jaw relationship by the clockwise rotation in cases of minor sagittal discrepancy (Figure 3). Patients with a unilateral cleft lip and palate tend to have a more asymmetrical face compared to the normal population, not only showing in the nasomaxillary region, but also in the lower facial skeleton [20, 29, 30, 31]. It is consistent with the results of this study that both maxillary and mandibular midline landmarks were significantly deviated from the midsagittal plane compared to norms (Table 2). The deviation and asymmetry could only be improved by the two-jaw approach but not the one-jaw surgery (Table 3). The asymmetry index (ASI) was first proposed for assessing right and left ramal height symmetry in 2-dimensional orthopantomograms [18]. ASI was then used to evaluate the extent of 3-dimensional asymmetry of facial skeletons [19, 32], and applied in cleft orthognathic surgery planning [20]. The present study showed that in comparison with ASI, the two-jaw design obtained more symmetry in both the maxilla and mandible (Figure 1). By undertaking a two-jaw surgery, the U1 in the maxilla and all midline landmarks in the mandible were significantly improved (Table 5). In the one-jaw OGS simulation, the maxillary symmetry could get worse, and the mandibular asymmetry remained the same (Table 5).