An accurate maxillary superior repositioning technique without intraoperative measurement in bimaxillary orthognathic surgery

Abstract

This article describes a simple and accurate technique for maxillary superior repositioning without any intraoperative measurement using reference points that can be the source of error in bimaxillary orthognathic surgery. A bilateral straight locking miniplates (SLMs)/screw system secured to the maxilla and mandible maintains the three-dimensional relationship between the mandible and the skull base precisely like the incisor pin of an articulator in model surgery. The maxilla can then be accurately moved into the planned position identical to that in model surgery by the SLMs technique.

Inaccurate positioning of the maxilla leads to less than ideal functional and aesthetic outcomes in orthognathic surgery. Previously reported techniques for positioning the maxilla required intraoperative measurement using internal and external reference points. These intraoperative measurement techniques have been shown to be clinically reliable, but for accurate repositioning, intraoperative measurement often has to be repeated several times until the maxilla is moved into the planned position, which is time-consuming and troublesome. It is still difficult to exclude the possibility of error incidental to the measurement procedure, even if it is performed by experienced surgeons with the utmost care, especially during multidirectional moves.

The authors introduced a simple technique with straight locking miniplates (SLMs) for accurate maxillary superior repositioning without any intraoperative measurement. This technique is based on the principle that three-dimensional (3D) positioning of the maxilla can be achieved precisely if the vertical dimension from skull base to mandible is kept constant during splint fabrication in model surgery and transoperative time. During model surgery, the incisor pin of the articulator maintains the vertical dimension from the skull base to the mandible, and during surgery, SLMs secured to the maxilla and mandible maintain the vertical dimension like the incisor pin of the articulator.

Technique

The centric relation of the condyle (CR) is confirmed by radiographs (Schüller) and a CR-guiding interocclusal wafer is fabricated preoperatively. The models are mounted on a semi-adjustable articulator by face-bow transfer. Maxillary model surgery is performed. The maxillary cast is moved in 3D planes within the articulator according to the predictive tracings. The surgical splint is fabricated by filling the space created on maxillary movement between the maxillary and mandibular casts, which are fixed in the centric condylar position. This splint is used as an intermediate during surgery.

Before down-fracture, the maxillo-mandibular complex with interpositioning wafer guiding CR position is fixed by SLMs bilaterally. The plates are fixed to the zygomatic buttress above the Le Fort I osteotomy borderline and the proximal segment of the mandible, and secured with two screws on each side ( Fig. 1 ). SLMs maintain the vertical distance between the skull base and the mandible and can reproduce centric condylar positioning throughout the surgery.

Fig. 1
During surgery, bilateral straight rocking miniplates (SLMs) secured to the maxilla and mandible maintain the 3D relationship. SLMs act like the incisor pin of an articulator in model surgery. TMJ, temporomandibular joint; CR, centric relation.

After removal of SLMs, a standard Le Fort I maxillary down-fracture is performed. The maxilla is then mobilized. Bone that interferes with desired repositioning of the maxilla is removed with a small round bur. The maxilla is placed in the planned position using an intermediate splint. SLMs are fixed bilaterally only on the side of the mandible. If any further bony interference is present, SLMs cannot be fixed to the previous position on the side of the maxilla ( Fig. 2 ). In that case, additional bone removal should be carried out until the screw holes of the SLM match with the corresponding holes drilled previously on the zygomatic buttress. When SLMs are secured with two screws bilaterally, the maxilla can be moved into the planned position accurately as in the model surgery. SLMs act as temporary fixation of the maxilla, keeping it in the new position without manual control. The maxilla is fixed with 2.00 mm L-shaped, short, straight miniplates at the piriform rim and anterior wall bilaterally ( Fig. 3 ).

Fig. 2
If any bony interference is present, SLMs cannot be fixed to the previous position on the side of the maxilla. When the maxilla can be moved accurately into the planned position as in model surgery, the screw holes of the SLM match the corresponding holes drilled previously on the zygomatic buttress.
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Jan 26, 2018 | Posted by in Oral and Maxillofacial Surgery | Comments Off on An accurate maxillary superior repositioning technique without intraoperative measurement in bimaxillary orthognathic surgery
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