If one performs mandibular surgery first, rigid fixation is mandatory.
Counterclockwise rotation is easier to do when operating the mandible first.
Clockwise rotation is easier when operating the maxilla first.
Accurate bite registration is critical when performing maxillary surgery first.
In the future, virtual planning will make model surgery efforts and sequence less critical.
Adequate planning and technical accuracy during clinical evaluation and model surgery is critical in achieving positive outcomes when performing orthognathic surgery, especially when one is performing double-jaw surgery. The sequence in which the bimaxillary surgery will be done is dictated by the previous model surgery and fabrication of intermediate splints in the laboratory. There has always been controversy among practitioners about the best way to perform simultaneous double-jaw surgery.
This article critically reviews the indications and contraindications of performing mandibular surgery first versus maxillary surgery first in a double-jaw procedure, knowing that either of the surgical sequences can produce similar outcomes when properly planned and executed.
The traditional way of performing double-jaw surgery has always been to perform the maxilla first, stabilize it, and then finish with the mandibular surgery. The reason that this sequence has historically been done is that the maxilla was the only jaw that could be made stable in the days when wire fixation was all that was available. With the implementation of stable internal fixation devices, Buckley and colleagues described a technique for performing mandibular surgery first. In 1994, Cottrell and Wolford presented a technique to perform model surgery for surgery of the mandible first that “may decrease laboratory time and improve the accuracy and predictability of the surgical outcome.”
It is important to emphasize again that properly planned and executed either sequence can provide accurate positioning of the jaws.
The case for mandibular surgery first
There are some prerequisites to performing mandibular surgery first. The most important is the need to perform stable internal fixation of the mandible after the osteotomy. The maxilla lends itself to be repositioned and stabilized as an initial step in bimaxillary cases, as in the years of wire fixation; this was followed by intermaxillary fixation as the last step after the mandibular osteotomy was completed. The factor that has allowed surgical repositioning of the mandible as an initial step is the availability of stable internal rigid fixation.
The sagittal split osteotomy is perhaps the most commonly used mandibular procedure for surgical repositioning of the mandible. Fortunately, it readily lends itself to the application of plates and/or screw fixation. Bicortical screws, bone plates, or a combination of them can provide stable internal fixation of the sagittal ramus osteotomy ( Fig. 1 ). However, if one choses a different osteotomy, such as a vertical ramus osteotomy, one must be capable of rigidly stabilizing the segments if the mandibular osteotomy is to be performed first. Situations when performing the mandible first may be advantageous are reviewed next.
When performing a segmented maxillary surgery or an unstable cleft maxilla in conjunction with a Bilateral Sagittal Split Osteotomy (BSSO), we have traditionally relied on an intermediate splint that fits between the mobilized maxilla and the unoperated mandible. The splint is fabricated in the laboratory out of a difficult multiply segmented maxilla that is usually hard to accurately position in space ( Fig. 2 ).
Multiple measurements, usually at the level of the central incisors, cuspids, bicuspids, and last molars, need to be done from the teeth to the vertical and horizontal reference lines of the maxillary cast. Then the segmented pieces are oriented against the mandible to obtain adequate transverse and occlusal relationship and new measurements are done to position the new maxilla in space as a unit mimicking the previously planned cephalometric prediction tracing. Adequate placement in all three planes taking into consideration pitch, roll, and yaw is an arduous and inaccurate task, as previously reported by Ellis. The model surgery is usually done with expensive tools (Erickson model marking tool) to be precise and predictable ( Fig. 3 ).
This may necessitate duplication and double mounting of the models. The technique requires extensive laboratory time and two splints (interim and final, a piggy-back technique) and at surgery may require additional time performing intraoperative measurements.
However, when the mandibular osteotomy is performed first, the multiple maxillary segments can easily be placed into intermaxillary fixation against the already operated and stable mandible in maximal intercuspation, and fixated without complications, leaving only the vertical repositioning of the maxillomandibular complex to be measured intraoperatively. The model surgery involved with moving the mandible first is a much easier task. It can be accomplished without the use of a model surgery platform using a few key measures usually done at the level of the first molars, pogonion, and central incisors.
A similar situation could be encountered in the patient with cleft palate requiring orthognathic bimaxillary surgery, because of their tendency to fracture through the cleft during surgery, making their maxilla behave like a multipiece osteotomy ( Fig. 4 ).
Counterclockwise rotation and downgrafting of the posterior maxilla
Class II skeletal relationship are the most common deformity a maxillofacial surgeon in the United States encounters. Usually this deformity benefits esthetically not only from a horizontal advancement but also from a counterclockwise rotation that projects pogonion even more ( Fig. 5 ).
The other situation when this occurs is in the setting of a very steep occlusal plane angle, such as in the case of condylar degeneration or agenesis. The correction of this deformity usually requires a posterior maxillary downgrafting. Model surgery with the traditional surgical sequence creates a transient anterior open bite, requiring a thick intermediate splint that during surgery requires a large opening rotation of the mandible. This can cause the condyles to translate, creating malposition of the maxilla ( Fig. 6 ). If the mandible is instead operated first, a posterior open bite is created in the interim position. This is readily closed by performing a maxillary osteotomy and dropping the posterior maxilla into occlusion with the mandibular dentition ( Fig. 7 ).
Large maxillomandibular advancements
If the maxilla is first advanced in large bimaxillary advancements, the occlusion in the intermediate position has a large overjet, creating a very large and thick anterior intermediate splint making intermaxillary fixation difficult. If instead the mandible is first advanced, the intermediate position is more conducive to securing intermaxillary fixation.
When correcting anterior open bites with bimaxillary surgery
When correcting open bites with double-jaw surgery the most common movement one makes is a counterclockwise rotation of the mandible, with a decrease of the occlusal plane. This requires thick intermediate splints if the maxilla is done first ( Fig. 8 ).
By doing the mandible first, the mandible is positioned against the maxilla, closing the open bite and using the anterior teeth as a guide (this visual aid is extremely helpful to set the model). The intermediate splint is simplified because the anterior teeth are almost touching and closed to each other decreasing the thickness of the splint and therefore inaccuracies in the acrylic. Furthermore, the relationship of the anterior teeth is much more favorable and the application of maxillo mandibular fixation (MMF) is greatly facilitated. Once the mandibular osteotomy has been stabilized, the posterior open bite is readily closed by performing a maxillary osteotomy and dropping the posterior maxilla into occlusion with the mandibular dentition (see Fig. 8 ).
Rigid fixation of maxilla versus mandible (type of bone)
Some maxillae have very thin bone and this is not usually discovered until during surgery. If the maxillary osteotomy is performed first and stabilized, it can become loosened when the mobilized mandible is brought into occlusion after its osteotomy, especially if the advancement of the mandible is large. This is a disaster because now both jaws are free-floating and accurate positioning becomes extremely difficult ( Fig. 9 ).
When the mandible is instead performed first, it is set against a stable nonmobile maxilla with no possibility for inaccuracies because of maxillary mobility. Because of the thicker bone in the mandible, stable internal fixation is guaranteed and it is unlikely that it would become unstable when subsequently bringing the mobilized maxilla into occlusion with it.
Stability of Le Fort I versus BSSO
Because the mandible rotates and translates in the temporomandibular joint (TMJ), there is potentially a higher risk of slight inaccuracies (condylar malposition) when repositioning the mandible in general. When inaccuracies are detected during surgery it requires that the surgeon resets the fixation until the mandible rotates into the proper occlusion. Sometimes very small discrepancies (1 mm or less) may be difficult to correct no matter how many times the surgeon repositions the mandibular fixation. Leaving this condition translates into occlusal discrepancies that may be problematic.
The maxilla, however, is set against the skull base with no articulation and it remains in place unless the type of fixation used is put to extreme forces. The errors that may be inadvertely created by doing the mandible first would potentially be eliminated and not translated to the occlusion if the maxilla is done last. This was corroborated by Béziat and colleagues in 2009 when they found that changes in the anteroposterior direction were discovered after BSSO in 74% of the time, with average amplitude of 0.32 mm. However, the maxilla had much smaller amplitude of error of 0.19 mm and happened less frequently in 54% of cases. They found that the average error in the anteroposterior direction was 0.02 mm without a difference in 92% of the cases.
Concomitant temporomandibular joint surgery
Wolford and coworkers state that “The TMJs are the foundation for orthognathic surgery. If the TMJs are not stable and healthy (pathologic), orthognathic surgery outcomes may be unsatisfactory relative to function, aesthetics, stability, and pain. Orthognathic surgery to correct dentofacial deformities cannot ‘fix’ or eliminate coexisting TMJ pathology.” When performing concomitant TMJ and orthognathic surgery, one has two options. The first option is to do the maxilla first, then the TMJ surgery, and finish with the mandibular osteotomy. This option requires two sets of instruments to avoid contamination of the clean and sterile TMJ. The second option is to perform the TMJ surgery first, followed by the orthognathic component; this allows for one set of instruments to be used. In this scenario the mandible must be performed before the maxillary osteotomy because of the change of the condylar position that will accompany the joint surgery.
If during maxillary hardware application one of the condyles is out of the fossa and the discrepancy is overlooked this introduces an error in the final maxillary position and mandibular position that requires loosening of all hardware and restart of the surgery. By doing the mandible first this is avoided and if the condyles are out of the fossa at the time of maxillary repositioning the error is detected immediately after cutting MMF as a shift on the midlines or a slight open bite that can be corrected without the need to change or reopen the mandibular osteotomies and incisions.
A major concern for many surgeons in reference to concomitant TMJ and orthognathic surgery is condylar position and control. The condylar position, size, and/or morphology can be significantly altered, affecting the position of the mandible, with the following surgical factors:
Repositioning the articular disk (usually displaces the condyle and mandible downward and forward; Fig. 10 )