The maxillary step osteotomy technique is a modification of Le Fort I osteotomy. A major advantage of the step osteotomy is that it can provide pure anteroposterior maxillary movements7. The main focus of the current study was to analyze the probable advantages of the step osteotomy technique in postoperative stability.
Prior to evaluation of the difference between LO and SO, skeletal stability of the Le Fort I osteotomy done in the current study was compared with those in previous studies. The present study showed that mean postoperative changes at point A were less than 1 mm, both horizontally and vertically (differences in hA and vA between T1 and T3). Horizontal changes (differences in hA between T1 and T3) were −0.94 mm (mean, SD = 1.23) in the LO group, and −0.79 mm (mean, SD = 1.01) in the SO group. Previous studies have reported that postoperative changes greater than 2 mm are clinically significant and are considered as skeletal relapse11,12,13,14. Dowling et al.15 reported that skeletal relapse (≧2 mm) occurred in 14% of the patients who underwent Le fort I advancement. Chen et al.16 reported that maxillary relapse occurred in 16.7% of the included patients. In the present study, relapse (changes exceeding 2 mm) was observed in 19.2% (5 of the 26) and 11.5% (3 of the 26) patients in LO and SO groups, respectively. Meanwhile, vertical changes (differences in vA between T1 and T3) were −0.76 mm (mean, SD = 1.49) in the LO group, and 0.20 mm (mean, SD = 1.24) in the SO group. Politi et al.17 reported that the mean postoperative vertical change was −0.24 mm at point A in patients who underwent combined maxillary advancement and mandibular setback with rigid internal fixation. The maxillary postoperative changes seen in the patients in the present study were comparable to those in the previous studies15,16,17, indicating that the stability of repositioned maxilla was the same, regardless of the method of osteotomy.
Mandibular postoperative stability in the present study was also comparable to a previous report by Park et al.18. The setback distances of the LO and SO groups in the current study were approximately 8.67 mm and 6.75 mm, respectively (differences in hB between T0 and T1). Postoperative horizontal changes (differences in hB between T1 and T3) were as minimal as 0.395 mm in LO and −0.264 mm in SO, that represented 4.56% and 3.9% of the above setback distance, respectively. Park et al.18 studied 20 cases combining Le Fort I maxillary with bSSRO mandibular setback using rigid fixation and showed that the average horizontal relapse was 0.85 mm of 7.72 mm mean setback distance, representing a relapse rate of 11.1%. Mean vertical movements of the mandible measured at point B were 2.43 mm in the LO group and 1.68 mm in the SO group. Postoperative changes (differences in vB between T1 and T3) were 1.62 mm and 1.18 mm that represented 66.6% and 70.2% of the above movements, respectively. In a study by Park et al.18, wherein conventional bimaxillary surgery was performed, the average vertical relapse was 2.744 mm of 4.096 mm mean superior movement, representing a relapse rate of 67.0%. Based on the above observations, it was considered that the stability of the postoperative mandibular position in the current study was similar to that of the previous study.
To investigate the probable difference in skeletal stability after conventional linear osteotomy and modified step osteotomy, the above-mentioned horizontal and vertical changes were compared between the LO and SO groups. Statistically significant differences were observed between the two groups in the measurements of hM, vB, and vM, in the early postoperative period (within 3 months postoperatively). The differences in hM, vB, and vM were 1.25 mm, 0.42 mm, and 0.61 mm, respectively. However, the differences were not consistently observed throughout the duration of follow-up (up to 1 year postoperatively). Thus, the difference between LO and SO was minor and temporary to be clinically significant11,12,13,14. There was limited clarity regarding the occurrence of statistical differences between the two groups in the early postoperative period alone, as well as the difference being observed only in the mandible. Pertaining to the latter observation, it may be speculated that slight maxillary clockwise or anticlockwise rotation might be amplified in the mandible. Lee et al.19 studied skeletal stability after modified quadrangular Le Fort I osteotomy (MQLI), and no statistically significant of skeletal stability was reported between LO and MQLI.
The current study also examined the probable influence of occlusal cant correction on the stability in both groups. Statistically significant difference between LO and SO was observed only in the group without occlusal cant correction (Group AC and Group BC). In the group without occlusal cant correction, the difference (1.01 mm) in vB was statistically significant during the entire duration of follow-up. Without occlusal cant correction, the variation in the measurement of vB is small because the direction of the relapse is simple, and the difference between LO and SO may be reflected to cause a significant difference in the amount of post-operative change in vB. In orthognathic surgery, osteosynthesis devices17,19 have been developed since Bennett and Wolford reported the maxillary step osteotomy technique7. Therefore, it is possible that the disadvantages of the conventional Le Fort I osteotomy may have been improved by use of structurally strong miniplates and locking type miniplates20.
The current study is associated with some limitations. First, only two-dimensional skeletal changes were assessed with the use of cephalometric radiographs. Ideally, computed tomography (CT) should be utilized to measure the three-dimensional skeletal changes. Second, the sample size in the present study was small and the design was retrospective in nature. Third, homogeneity of patients and the surgical technique are fundamental for critical analysis of the multi-factorial nature of postoperative changes21. In the present study, the same surgeon performed the surgeries and all patients underwent Le Fort I osteotomy and sagittal split ramus osteotomy stabilized with titanium plates and screws, although the plates and screws were provided by two companies. However, multiple orthodontists performed the orthodontic treatment. Forth, the observation was a 1-year follow-up period in the present study. Profitt et al. described the period of follow-up for Class III patients as: short-term (1 year) and long-term (1 to 5 years)22. Previous studies have indicated that relapse was observed after 2 years of follow-up23,24. Long-term (1–5 years) stability after LO vs SO in bimaxillary surgery needs to be evaluated in the future.
In conclusion, statistically significant differences were observed between the original Le fort I osteotomy and step osteotomy techniques at the point B and menton; however, the changes were minimal to be clinically significant. Although there was limitation to evaluate the stability after LO vs SO for Class III over the long-term follow-up, the results suggest that both procedures are not associated with significant difference in the skeletal stability after 1-year follow-up.