Computer-assisted planning and splintless maxillary positioning in complex maxillomandibular surgery

8.1 History and orthodontic pretreatment

This chapter describes the methodologic approach for computer-assisted planning and splintless maxillary positioning in complex maxillomandibular surgery using a clinical example.

A 22-year-old man was referred by an office-based orthodontist for evaluation prior to combined orthodontic and oral surgery therapy. The patient complained of difficulty eating, especially biting down. The following findings were obtained.

Extraoral (Fig 8-1):

midfacial hypoplasia
long lower third of the face
positive lip step
prominent and broad chin
flattened nose tip
visceral swallowing pattern.

Intraoral (Fig 8-2):

skeletal Class III maloclussion
circular open bite with sole support on the second molars
transverse arch discrepancy with narrow maxilla
maxillary and mandibular arches relatively harmonious
minor rotations and rotational positions in the maxilla and mandible
steeply standing mandibular anterior teeth
large tongue.

Radiologic (panoramic radiograph, lateral cephalometric radiograph [LCR]) (Fig 8-3):

mandibular prognathism
maxillary retrognathism
midfacial hypoplasia
circular open bite
retained and displaced maxillary left and mandibular third molars (teeth 28 and 48).

After clinical analysis and treatment discussion with the treating orthodontist, the initial consideration of surgically assisted palatal expansion followed by maxillomandibular surgery was discarded, and a single-stage maxillomandibular procedure was favored.

The median division of the maxilla into two parts for posterior transverse expansion was planned in combination with maxillary advancement and mandibular retraction as well as closure of the open bite via posterior impaction of the maxilla and autorotation of the mandible. Before starting the orthodontic pretreatment, the third molars 28 and 48 were extracted.

The dental arches were shaped as part of the preoperative orthodontic treatment and then the patient was presented again to the oral and maxillofacial surgeon for planning of the maxillomandibular realignment oste-otomy with the existing models.

8.2 Oral and maxillofacial clinical planning of surgical correction of malocclusion

For surgical planning, clinically relevant findings were initially collected. The surgical planning was then performed by means of 3D virtual computer-assisted surgical planning using appropriate planning software (ProPlan CMF, Materialise/DePuy Synthes).

8.2.1 Clinic I

During an initial clinical planning meeting, various clinical measurements were performed. Preoperative panoramic radiography was performed to exclude unforeseen findings, such as impacted third molars, chronic apical periodontitis, or cysts. The preoperative clinical findings and photo documentation were as follows.

Extraoral frontal view (Fig 8-4):

long lower third of the face
no excessive gingival display
horizontal transverse occlusal plane
central chin
straight nose
wide nose.

Extraoral lateral view (Fig 8-4c):

midfacial hypoplasia
positive lip step
prominent and broad chin
moderately pronounced submental fold
nasolabial angle 90 degrees
flattened nose tip.

Intraoral (Fig 8-5):

harmoniously shaped maxillary and mandibular arches
axial position of the maxillary and mandibular anterior teeth
harmonious transverse and sagittal compensation curves
Class III malocclusion with bite position one premolar width mesial
circular open bite with sole support on the second molars
horizontal overlap 7 mm
vertical overlap 6 mm
transverse arch discrepancy with narrow maxilla and crossbite
large tongue.

The clinical findings and the planned displacements of the maxilla and mandible were noted on the findings sheet for orientation (Fig 8-6). The final determination of the displacement distances was made during virtual 3D planning.

Further measures included:

maxillary and mandibular alginate impression for planning model manufacture
bite registration in arbitrary centric condylar position
determination of the skull-related maxillary position by facebow registration.

8.2.2 Laboratory I

Dental technology

Dental casts were created in high-strength stone, followed by arbitrary articulation of the maxillary cast according to the facebow registration and articulation of the mandibular cast using the centric registration (Fig 8-7a).

An initial splint was produced, based on the articulated casts, with slight blocking (approx. 1 to 2 mm) of the articulator (Fig 8-7b).

8.2.3 Clinic II

During a second clinic appointment, a multislice computed tomography (MSCT) scan of the facial skull was obtained with the initial splint in situ. This involved:

inserting the initial splint and checking the fit in the maxilla, the mandible, and in occlusion
MSCT of the entire facial skull as planning CT for computer-assisted planning with incorporated initial splint
reconstruction of the MSCT scans in 1-mm slices.

8.2.4 Laboratory II

Dental technology

A duplicate maxillary cast was medially split between teeth the maxillary central incisors (Fig 8-8a) (note that if no division of the maxilla is necessary for planning purposes, this step is omitted).

Maxillofacial surgeon

Manual adjustment and fixation of the models in target occlusion in Class I dentition took place after consultation between the oral and maxillofacial surgeon and orthodontist. In this case, Futar D Fast (Kettenbach Dental) was used (Figs 8-8b and 8-8c).

Currently, the combination of digital planning and analog occlusion adjustment under haptic control is the most effective way to perform surgical planning. Fully digital occlusion simulations are possible but very time consuming. With the routine use of powder-free and accurate intraoral scanners, this is likely to shift in favor of impression- and model-free virtual occlusion adjustment in the future.

Dental technology

Optical 3D scan of the fixed maxillary and mandibular models in planned target occlusion (Fig 8-9).
Creation of the new split maxillary cast (Fig 8-10).
Isolated optical 3D scans of the new maxillary as well as the mandibular cast (Fig 8-11).
Articulation of the maxillary cast in target occlusion based on the already articulated mandible (Fig 8-12a).
2-mm blocking of the occlusion and fabrication of the target splint in target occlusion (Fig 8-12b).
Production of a palatal reinforcement plate. This facilitates correct transverse expansion during surgery and stabilizes the two maxillary segments in relation to each other postoperatively (Fig 8-13a).
Exclusion and removal of interfering contacts between the target splint and the palatal reinforcement plate (Fig 8-13b).

8.3 Virtual computer-assisted surgical planning

In principle, there are three planning options for virtual computer-assisted surgical planning:

Complete in-house planning. Here, both the operation of the planning software and the complete planning of the jaw relocation, including the preparatory measures (see below), are carried out by the clinician. For this purpose, the planning software must be available and it must be possible for the clinician to operate it safely.
Partially independent planning. Here, the preparatory measures (see below) up to the actual planning are carried out by the cooperating company. The planning of the jaw relocation is carried out independently by the dental practitioner. The planning software must also be available for this purpose and the clinician must be able to operate it safely. In this case, the DICOM data record of the CT of the case to be planned as well as the optical model scans must be transmitted in advance to the cooperating company via FTP server over the Internet. After the preparatory measures have been carried out, the planning data set is transmitted back to the surgeon for further surgical planning.
Online operation planning in cooperation with a medical engineer of the cooperating company. Before the start of the online meeting, all preparatory measures (see below) are carried out by the company so that only the isolated planning of the jaw relocation takes place during the online meeting. In this case, the engineer operates the planning software according to verbal instructions from the surgeon. There is no operation of the software by the surgeon at any time. Here, too, the DICOM data record of the CT of the case to be planned as well as the optical model scans (maxilla in initial situation and in simulation, mandible in initial situation and simulation, if applicable, maxilla/mandible in target occlusion) must be transmitted to the cooperating company via FTP server in advance.

In the illustrated case, complete self-planning was performed by the surgeon.

8.3.1 Preparatory measures

Before starting the surgical planning with determination of the arch displacements, the following preparatory steps must be taken.

Import of DICOM data of the planning CT into planning software

Import of the DICOM data of the planning CT into the planning software and conversion into the software-specific file format as well as orientation of the data set in terms of right/left, top/bottom, anterior/posterior. In the illustrated case, planning was performed using ProPlan CMF software (Materialise/DePuySynthes).

Segmentation of the CT dataset

Segmentation of the CT dataset and creation of a virtual model for surgery plannin (Figs 8-14 and 8-15)
Segmentation of the entire facial skull in the soft tissue window (Fig 8-14a)
Segmentation of the entire bony skull (Fig 8-14b)
Segmentation of the mandible (Fig 8-14c)
Segmentation of the facial skull without the mandible via a so-called Boolean operation. In practice, the mandible is subtracted from the entire segmented bony skull (Fig 8-14d).