Three lateral osteotomy designs for bilateral sagittal split osteotomy: biomechanical evaluation with three-dimensional finite element analysis

Abstract

Background: The location of the lateral osteotomy cut during bilateral sagittal split osteotomy (BSSO) varies according to the surgeon's preference, and no consensus has been reached regarding the ideal location from the perspective of biomechanics. The purpose of this study was to evaluate the mechanical behavior of the mandible and screw-miniplate system among three lateral osteotomy designs for BSSO by using three-dimensional (3-D) finite element analysis (FEA).

Methods: The Trauner-Obwegeser (TO), Obwegeser (Ob), and Obwegeser-Dal Pont (OD) methods were used for BSSO. In all the FEA simulations, the distal segments were advanced by 5 mm. Each model was fixed by using miniplates. These were applied at four different locations, including along Champy's lines, to give 12 different FEA miniplate fixation methods. We examined these models under two different loads.

Results: The magnitudes of tooth displacement, the maximum bone stress in the vicinity of the screws, and the maximum stress on the screw-miniplate system were less in the OD method than in the Ob and TO methods at all the miniplate locations. In addition, Champy's lines models were less than those at the other miniplate locations.

Conclusions: The OD method allows greater mechanical stability of the mandible than the other two techniques. Further, miniplates placed along Champy's lines provide greater mechanical advantage than those placed at other locations.

Figure 1

Schematic of the three lateral osteotomy designs for bilateral sagittal split osteotomy (BSSO). (A) In the Trauner-Obwegeser (TO) method, the lateral osteotomy cut was made horizontally from the distal region of the second molar to the posterior border well above the mandibular angle. (B) In the Obwegeser (Ob) method, the lateral osteotomy cut was made from the distal region of the second molar to the midpoint of the mandibular angle. (C) In the Obwegeser-Dal Pont (OD) method, the lateral osteotomy cut was made vertically from the distal of second molar to the lower border of the ascending ramus.

Figure 2

Miniplate locations. The baseline location was along Champy's lines; the miniplate was applied along Champy's lines of ideal osteosynthesis as close to the alveolar border as possible (the upper miniplates). (A) The miniplate was placed in translation 5 mm inferior to the baseline location. (B) The miniplate was placed 20° in clockwise rotation to the baseline location. (C) The miniplate was placed 20° in counterclockwise rotation to the baseline location.

Figure 3

The 12 finite element analysis (FEA) miniplate fixation models. TO-1 to 4, the Trauner-Obwegeser method; Ob-1 to 4, the Obwegeser method; OD-1 to 4, the Obwegeser-Dal Pont method. The miniplates were fixed as described in Figure 2.

Figure 4

Establishing the constraints and loading. (A) The bilateral temporomandibular joints were completely constrained. (B) For incisal loading, a 66.7-N compressive load was applied to the central incisors perpendicular to the occlusal plane. (C) For contralateral molar loading, a 260.8-N compressive load was applied to the occlusal surface of the right first molar perpendicular to the occlusal plane.

Figure 5

The displacement fields in the mandibles in the OD-1, Ob-1, and TO-1 methods. The displacement fields in the mandibles of the Champy's lines models were determined following (A) incisal loading and (B) contralateral molar loading.

Figure 6

Regional distributions of von Mises bone stress in the vicinity of the screws in the OD-1, Ob-1, and TO-1 methods. The highest concentration of bone mechanical stress was found at site 3 bilaterally in all three methods on (A) incisal loading and (B) contralateral molar loading.

Figure 7

Regional distributions of von Mises stress on the bilateral screw-miniplate systems in the OD-1, Ob-1, and TO-1 methods. The site 3 screws and miniplates demonstrated very high tensile stresses in all three methods on (A) incisal loading and (B) contralateral molar loading.