Abstract
The purpose of this study was to evaluate the accuracy of surgical splints and an external reference point to reposition the maxilla during orthognathic surgery. Before surgery, a radiological marker was inserted inside the orthodontic bracket of the first right maxillary molar. A surgical splint was utilized to reposition the maxilla in the sagittal and coronal planes after the osteotomy. The vertical position was established by measuring the distance between a Kirschner wire inserted at bony nasion and the orthodontic wire. Preoperative and postoperative cephalometric radiographs were obtained and manually traced. The radiological marker and the tip of the right maxillary incisor were used as specific landmarks. Their displacement on the pre- and postoperative radiographs was measured. The actual surgical movement of the maxilla was compared to the initial surgical planning. 23 patients met the inclusion criteria to participate in the study. The mean difference between the planned and executed movements of the maxilla was 0.1 mm ( p = 0.71). The difference was not statistically significant for any given movements of the maxilla. The use of surgical splints made from model surgery combined with an external reference point at bony nasion is accurate methods for repositioning the maxilla during orthognathic surgery.
Surgical interventions for the correction of malocclusion and craniofacial anomalies are invasive procedures. They are elective operations and every effort should be made to achieve the best dental occlusion, excellent facial aesthetic and have a low rate of complications. Although it is now possible to have surgical guides fabricated through the use of three-dimensional (3D) virtual simulation with cone-beam computed tomography (CBCT), most orthognathic procedures are still performed using intermediate and final surgical splints obtained after model surgery. This technique is generally considered less time consuming, less expensive and requires fewer logistics.
Correct positioning of the maxilla is the cornerstone of orthognathic surgery. Failure to do so can lead to poor aesthetic results, facial asymmetry or malocclusion. This is particularly true when rotation of the maxillo-mandibular complex is performed, as this could have an impact on the position of the central incisors and the chin. An intermediate splint is generally used to establish the horizontal movement of the maxilla and the vertical dimension is ascertained with an external or an internal reference point.
The goal of this project was to evaluate the precision of surgical splints generated through model surgery and an external reference guide to position the maxilla correctly during orthognathic surgery. The authors’ hypothesis is that this technique yields a precision range of 1 mm of the planned displacement.
Materials and methods
Patients requiring a Le Fort I osteotomy, in combination or not with a bilateral sagittal split osteotomy or a genioplasty, were included in this study. To be enrolled, patients had to: have a craniomaxillofacial anomaly requiring a Le Fort I osteotomy; undergo presurgical orthodontic decompensation of the teeth; consent to participate in the study. Patients with a cleft deformity were excluded. The Centre Hospitalier Affilié Universitaire de Quebec institutional review board approved this study and all participants signed an informed consent agreement.
A preoperative cephalometric radiograph was obtained 2 weeks before and immediately after the operation. Before the first X-ray was taken, a radiological marker made of a stainless steel wire was inserted inside the bracket of the first right maxillary molar to measure the displacement of the posterior maxilla ( Fig. 1 ). All radiographs were recorded with the same appliance with the head of the patient in a standardized position. Using the preoperative X-ray, information from clinical examination and dental models, the desired movement of the maxilla was determined.
All osteotomies were performed based on the technique described by Bell. In cases where a concomitant mandibular osteotomy was necessary, an intermediate dental splint indexed to the teeth was fabricated and used at the time of surgery to execute the desired displacement of the maxilla correctly. The splint was constructed after analytical model surgery.
In brief, models were mounted on a semi-adjustable articulator after face-bow and centric relation registration. Preoperative measurements were recorded on central incisors, canines and second molars with an Erickson’s vertically mounted electronic calliper. The maxillary model was cut simulating a Le Fort I osteotomy and moved to its desired position using the same dental landmarks to measure the movements. With the maxillary model in its final position relative to the mandibular model, an intermediate splint was fabricated. In cases of isolated Le Fort I osteotomy, the occlusion was established intra-operatively by using a final dental splint. This splint was simply fabricated with dental models in the best possible dental occlusion. For all cases, vertical positioning of the maxilla was confirmed intraoperatively by measuring the distance between a Kirschner wire inserted at bony nasion and the orthodontic wire between the two central incisors.
Preoperative and postoperative cephalometric radiographs were traced manually by the same surgeon (CB) with these specific landmarks: line CLP-NA, a line from the superior aspect of the posterior clinoid process to bony Nasion; point M6, the radiological marker on the first molar; point I1, the tip of the right maxillary central incisor; point M6′, the intersection of a perpendicular line from point M6 to CLP-NA; point I1′, the intersection of a perpendicular line from point IL to CLP-NA ( Fig. 2 ).
