The Assessment of the Stability in Mandibular Setback Surgery Under Rotational Control of the Proximal Segment
Data from 78 patients who had undergone sagittal split ramus osteotomy for mandibular prognathism were reviewed. The stability of the proximal segment was retrospectively confirmed. Serial cephalograms were used to assess relapse over 1 year. The association between relapse and LeFort I osteotomy as well as the magnitude of setback was assessed.
The statistical analyses were performed with IBM SPSS(version 20.0 for Windows; IBM, Armonk, NY, USA). The reliability of cephalogram tracing was evaluated using the intraclass correlation coefficient (ICC). Differences were considered to be statistically significant at values of P < .05.
The results of this study is that minimal counterclockwise rotation was noted postoperatively, but the proximal segment remained stable for 1 year. Lateral cephalograms were taken before surgery (T0), immediately after surgery (T1), and at 6 weeks (T2), 3 months (T3), 6 months (T4), and 1 year after surgery (T5). The magnitude of setback (SB) was determined by the difference in Bx (X-coordinate of point B) between T0 and T1. The changes in Bx and By (Y-coordinate of point B) were recorded at each time point to assess the horizontal (Bx) and vertical (By) stability of surgery. Ramal inclination (RI) was defined as the angle between the X axis and a line connecting Ar and pGo (the point superior to Go on the curvature of the angle of the mandible defined by the tangent to the posterior border of the ramus). The mean setback was 7.80 ± 3.56 mm in patients who underwent SSRO only and was 8.61 ± 3.53 mm in patients who underwent SSRO with concomitant LeFort I osteotomy (no significant difference; P = .36). RI changed (P < .01) immediately after surgery (T0-T1) but remained stable throughout the follow-up period with the same pattern of change. Patients with less than 7 mm of setback showed greater counterclockwise rotation than other patients (P < .01) at T0-T1, and there was no significant interaction between the magnitude of setback and time (P = .32). Point B showed significant counterclockwise rotation at T2-T3, but it was not affected by LeFort I osteotomy (P = .32 in Bx and P = .71 in By). In patients with less than 7 mm of setback, point B moved posteriorly during the first 6 weeks, but all groups showed anterior movement at T2-T3 and remained stable after 3 months. However, horizontal relapse in patients with less than 7 mm of setback was less than that in patients from the other 2 groups. The vertical change of point B showed the same pattern of change regardless of the magnitude of setback (P = .91), showing superior displacement at T2-T3. Notable forward relapse was shown in the setback of more than 7 mm (P < .01) with resumption of function after 6 weeks, but it was not related with LeFort I osteotomy.
We concluded that relapse was related to the amount of setback and occurred on resumption of function despite rotational control of the proximal segment.
2 References
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