The irruption of digital technology in the planning of orthognathic surgery cases has been a revolution in the field of maxillofacial surgery, being the origin of a paradigm shift. Thus, the possibility of planning in 3D makes it possible to preview surgeries with high levels of detail and with precise control of condylar position.
Intermaxillary occlusal splints (FO), which take the occlusal opponent as a reference for positioning the osteomized fragment, are the universal transfer system, although they can introduce errors that are impossible to control at the time of surgery, leaving the vertical control and positioning of the mandibular condyles in the hands of the professionals, which can condition the correct positioning of the mandibular fragment.
The aim of this article is to present and evaluate the accuracy of a new positioning system that replaces the FO, based on the use of a supported bone-guide and a customized mini-plate.
The maxillary fragment is positioned independently of the antagonist maxillary position, minimizing the consequent transfer errors of articular movements, simplifying the procedure and reducing surgical times by avoiding intermaxillary fixation, mini-plate shaping and the need for intraoperative measurements.
A customized mini-plate, designed on the skeletal surface of an orthognathic surgery case plan, already integrates the necessary information to fix the maxillary fragment in its position in the bone. The SPO is designed and fabricated by laser synthesizing commercial pure titanium powder, seeking biomechanical properties similar to those of the maxillary cortical bone.
Material and methods used for guides and mini-plates in orthognathic surgery
Prospective observational study on ten patients recruited according to these inclusion criteria, with adult candidates for orthognathic surgery. The minimum postoperative follow-up was six months. The protocol followed for the planning, design and fabrication of the SPO was as follows:
- Records: maxillofacial computed tomography (CT).
- Reverse virtual surgical planning
- Design of the customized mini-plate
- Design of the cut-groove guide
- Fabrication of the guide and custom plate
1.1 Precision study
Four weeks after surgery a second CT scan was performed with the same machine, protocol and technician, eventually creating a 3D model of the patient’s skull.
1.2 Surgical protocol
A second premolar to second premolar approach was performed at the maxillary level. Prior to the osteotomy, the bone-supported guide was adapted and fixed with two osteosynthesis screws. Subsequently, directed broaching and marking of the osteotomy was performed, culminating with the fragment/descent of the maxilla. Mobilization of the maxilla must be complete to allow its repositioning without tension. This requires careful removal of bony and cartilaginous interference and release of the palatal pedicles from their bony canals.
This action allows the maxilla to be positioned and the osteosynthesis to be performed simultaneously.
Results of the study of guides and mini-plates for orthognathic surgery
The SPO was successfully used in all ten bimaxillary surgery cases without any remarkable incidences. The cutting guides directed the brocades and osteotomies in a simple, precise and controlled manner, and the customized mini-plates adapted perfectly to the surface of the four maxillary buttresses.
At the same time, surgical times were shortened, especially in the fragmented case, as intermaxillary fixation, intraoperative measurements and manual remodeling of the mini-plates were avoided. The operative evolution was favorable, with no signs of intolerance to the material. In patients with sleep apnea, sleep architecture was normalized, with a postoperative apnea-hypopnea index of less than 10 in 87.5% of cases.
There are several alternative systems to the classic FO to perform the intraoperative transfer of the virtual surgical plan. These protocols are usually applied to position the upper jaw or to facilitate condylar centric relation, and could be classified into two groups according to the osteosynthesis system used:
- Group 1: exclusive repositioning group: use of different splints applied at different times or assisted by navigation to position the maxillary fragment, subsequently osteosynthesis is performed with conventional miniplates.
- Group 2: simultaneous repositioning and osteosynthesis using customized titanium mini-plates with the aid of brocade guides or navigation systems, as explained throughout this text.
Conclusions of the study of guides and mini-plates in orthognathic surgery
The SPO has made it possible to significantly simplify the procedure and reduce surgical times by avoiding intermaxillary fixation, mini-plate casting and the need for intraoperative measurements. These customized osteosynthesis systems may be a future option that evolves in parallel to the technological field, and that will increase the safety of the procedure.
They require exhaustive planning, which must take into account the possible eventualities that may occur during surgery, detecting bone contacts and fixing the osteosynthesis screws in safe areas with good bone quality.
For more information, consult a specialist in Oral and Maxillofacial Surgery.
** Brunso J, Prol C, Franco M, De Carlos F, Martin JC, Santamaria JA. Rev Esp Oral Cir Maxillofacial 2017;39:7-14.