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. 2017 Jun;43(3):152-159.
doi: 10.5125/jkaoms.2017.43.3.152. Epub 2017 Jun 28.

Skeletal stability following mandibular advancement: is it influenced by the magnitude of advancement or changes of the mandibular plane angle?

Reza Tabrizi  1 , Mahsa Nili  2 , Ehsan Aliabadi  3 , Fereydoun Pourdanesh  1
Affiliations

Skeletal stability following mandibular advancement: is it influenced by the magnitude of advancement or changes of the mandibular plane angle?

Reza Tabrizi et al. J Korean Assoc Oral Maxillofac Surg. 2017 Jun.

Abstract

Objectives: The aim of this study was to investigate the effects of advancement magnitude and changes in mandibular plane angle on the stability of mandibular advancement.

Materials and methods: This retrospective cohort study evaluated the postoperative stability of mandibular advancement in class II skeletal subjects who underwent bilateral sagittal split osteotomy. Radiographs taken preoperatively, immediately postoperatively and 1 year postoperatively were traced and analyzed using linear and angular measurements. To determine horizontal and vertical relapse, an X-Y coordinate system was established in which the X-axis was constructed by rotating S-N downward by 7° (approximation of the Frankfort horizontal plane) and the Y-axis was defined as a line perpendicular to the X-axis and passing through the point Sella. For certain reference points including point A, point B, pogonion and menton, the perpendicular distance between each point and both axes was determined and cephalometric variables were recorded as X and Y coordinates.

Results: Twenty-five subjects were studied. A significant correlation between the amount of mandibular advancement and relapse in the B point (vertical and horizontal) and the pogonion point was observed (vertical and horizontal, P<0.001). Evaluation of data demonstrated a positive correlation between the mandibular plane angle (SN/ML) change and vertical relapse in the B point (P<0.05). A simple regression model demonstrated that 74% of horizontal relapse and 42.3% of vertical relapse in the B point was related to the amount of mandibular advancement. The receiver operating characteristic test showed that 8.5 mm mandibular advancement is related to a relapse rate of 1 mm or more in the pogonion, vertically or horizontally.

Conclusion: The magnitude of mandibular advancement is a stronger surgical predictor for horizontal rather than vertical relapse at the B point. Changes in mandibular plane angle (SN/ML) during surgery affect vertical, but not horizontal relapse at the B point.

Keywords: Mandible; Mandibular advancement; Orthognathic surgery; Osteotomy.

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Conflict of interest statement

Conflict of Interest: No potential conflict of interest relevant to this article was reported.

Figures

Fig. 1
Fig. 1. Skeletal landmarks used in cephalometric analysis. Refer to Table 1 for the definition of landmarks.
Fig. 2
Fig. 2. Horizontal measurements. Refer to Table 1 for the definition of landmarks.
Fig. 3
Fig. 3. Vertical measurements. Refer to Table 1 for the definition of landmarks.
Fig. 4
Fig. 4. Horizontal relapse in the B point (B2x: dependent factor) related to the amount of mandibular advancement (predictive factor).
Fig. 5
Fig. 5. Vertical relapse in the B point (B2y: dependent factor) related to the amount of mandibular advancement (predictive factor).
Fig. 6
Fig. 6. Vertical relapse in the B point (B2y: dependent factor) related to mandibular plane angle change (predictive factor).
Fig. 7
Fig. 7. Receiver operating characteristic (ROC) test indicates the specificity and sensitivity of 1-mm relapse due to the amount of mandibular advancement. Diagonal segments are produced by ties.
See this image and copyright information in PMC

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