Quantitative appraisal of bilateral sagittal split osteotomy impact on the loading of temporomandibular joint

Bilateral sagittal split osteotomy is one of the most frequently performed operations in orthognathic surgery. The health of the temporomandibular joint (TMJ) is an important prerequisite for its functionality. The aim of this finite element study was to assess the developed stresses during mouth opening after bilateral sagittal split osteotomy. Different osteotomy gap widths and disc positions were evaluated. Computed tomography and magnetic resonance data of a dentulous cadaver head were used in order to create two finite element models simulating split distances of 5 and 10 mm, respectively. The fixation of the distal and proximal segments was made by a four- or a six-hole titanium mini plate and four monocortical screws respectively. For both models, three different situations of the articular disc were created: a physiological disc position, anterior disc displacement and posterior disc displacement. The mandible was vertically displaced in the midline in order to simulate a mouth opening of 20 mm. The simulation showed high stresses in the area of the titanium plates (up to 850 MPa), implying an increased risk of material failure. High stresses were found within the discs in the models with normal disc position and anterior disc displacement as well (up to 8 MPa), indicating a higher risk of developing craniomandibular disorders. Regarding the stresses within the fixation screws, the highest values were recorded in the area of the upper thread. The degree of mandibular advancement after a bilateral sagittal split osteotomy affects the stress balance in the mandible and the articular discs during mouth opening.