7.1 Introduction
There is no doubt that conventional treatment planning of combined orthodontic-surgical treatment is well developed and can lead to good functional and esthetic results in patients with maxillofacial deformity.
3D imaging and 3D virtual treatment planning, however, enable enhanced diagnostics, more detailed treatment planning, and transfer of the surgical treatment plan to the patient in the operating theatre in combination with unprecedented 3D evaluation of treatment outcome as a quality control. The 3D virtual treatment approach moreover offers a digital communication tool between surgeons and orthodontists, trainer and trainees, and surgeons and engineers to cooperate in a multidisciplinary way to improve patients’ function, facial balance, and harmony.
Although 3D virtual planning has been introduced in daily clinical routine internationally and is becoming state of the art, its efficient integration into the daily clinical workflow remains a problem. In this chapter the entire imaging workflow currently used in the author’s daily practice is presented, and a 10-step protocol for 3D virtual planning of orthognathic surgery is illustrated on a patient.
7.2 Example of treatment using the 10-step protocol
The patient was a 17-year-old woman with a Class III maxillofacial deformity, midfacial hypoplasia, and mandibular asymmetry due to a hemimandibular elongation (HE) at the right side. At the age of 15, she had undergone during growth orthodontic expansion and alignment of the maxillary dental arch for approximately 6 months with braces, which were afterwards removed. She presented with a flattened midface, chin deviation to the left, and a lateral left crossbite (Figs 7-1 to 7-4). In her rest position, the patient had an incisor display of 3 mm, and during spontaneous smiling she had full incisor exposure without gingival display. She had no history of temporomandibular joint (TMJ) dysfunction or pain.
Figs 7-1a to 7-1c Clinical right profile (a) and frontal (b) views of patient in her clinical natural head position (c-NHP) at rest and with cheek retractors (c) at the initiation of combined orthodontic-surgical treatment. Note the flattened midface with lack of infraorbital support and mandibular asymmetry with chin deviation to the left.
Figs 7-2a to 7-2c Presurgical clinical right profile (a), frontal (b), and left profile (c) views of patient in her c-NHP at rest, at the time of the surgical work-up, approximately 3 weeks prior to surgery. Note the flattened midface and mandibular asymmetry with chin deviation to the left.
Fig 7-3 Presurgical clinical frontal view with cheek retractors at the time of the surgical work-up, approximately 3 weeks prior to surgery. Note the 4-mm mandibular midline deviation to the left and that the mandibular midline was clinically aligned with the chin midline.
Figs 7-4a to 7-4e Presurgical intraoral views of the occlusion at the time of the surgical work-up, approximately 3 weeks prior to surgery. Note the important 4-mm mandibular midline deviation to the left with left lateral crossbite.
Bone scintigraphy was performed prior to the surgical work-up and did not show any active condylar growth.
The 10-step protocol for individualized 3D virtual treatment planning1 is based on clinical decision making, starting from the individual patient’s planning head position (PHP). Its aim is to provide the clinician with a standardized and systematic way of using 3D virtual treatment planning in daily clinical routine in order to optimize both the functional and esthetic outcomes of orthognathic surgery.
Figs 7-5a and 7-5b The 3D virtual planning process started with surface rendering of the hard (a) and soft (b) tissues of the head of the patient after proper CBCT image acquisition (i-CAT, Imaging Sciences International, “extended field” mode, field of view [FOV] 17 cm diameter, 22 cm height; scan time 2 × 20 seconds; voxel size 0.4 mm at 120 kV according to DICOM field: 0018,0060 KVP and 48 mA according to DICOM field: 0018,1151 XRayTubeCurrent). The threshold was adjusted to optimize the visualization of the hard and soft tissues, respectively (IPS CaseDesigner v.1.4, KLS Martin). Note the appropriate rendering of both the hard and soft tissues without deformation of the 3D soft tissue mask. Note that there was no distortion of the fronto-temporal soft tissues due to proper position of the head fixation band during CBCT scanning, absence of lip and chin distortion, as well as absence of lip and mentalis muscle contraction.
Figs 7-6a and 7-6b Proper seating of both condyles is crucial prior to 3D virtual planning of orthognathic surgery and needs to be verified both on the sagittal slices and 3D volume-rendered hard tissue representations of the patient. Additional thresholding towards optimal visualization of the condylar-fossa unit can be helpful (IPS CaseDesigner v.1.4). Note the appropriate seating of the right (a) and left (b) condyles in central relation (CR) after CBCT scanning the patient with a wax-bite in CR. Also note the elongation of the right condylar neck due to condylar hyperplasia.
Fig 7-7 Additional image acquisition of the patient’s dentition was performed by direct surface scanning (Autoscan-DS-EX Dental 3D Scanner, Shining 3D) of the all-in-one impression of the maxillary and mandibular arches. The all-in-one impression of the maxillary and mandibular arches was taken using the Alfa Triple Tray (Premier) impression tray in combination with an alternative alginate impression material (AlgiNot, Kerr).
Figs 7-8a and 7-8b 3D representations of the STL files of the maxillary (a) and mandibular (b) arches that were extracted out of the surface scan (see Fig 7-7) of the all-in-one impression of the dentition (3D Infinity).
Figs 7-9a to 7-9c Following surface to image registration (STI), the patient’s head was semi-automatically augmented with accurate occlusal and intercuspidation data generated from the surface scan of the all-in-one impression of the patient’s dentition (see Figs 7-7 and 7-8). The accuracy of registration of the maxillary and mandibular arches in the augmented model (AUM) was then dynamically verified along the dental arches (IPS CaseDesigner v.1.4), eg at the midlines (a), or right (b) and left (c) molar regions.
Figs 7-10a to 7-10c The STL files of the maxillary and mandibular arches were 3D manufactured with a 3D printer (MoonRay D, Sprintray) and additionally surface scanned in final occlusion (Autoscan-DS-EX Dental 3D Scanner, Shining 3D) (3D Infinity). Note that orthodontic wax was used at the inner part of the 3D-printed arches to stabilize the final occlusion that was manually set prior to surface scanning.
Figs 7-11a and 7-11b The STL data of the surface scan of the maxillary and mandibular models in final occlusion (a) were consecutively superimposed (registered) to the STL data of the maxillary and mandibular arches (b) that were registered to the patient scan (see Fig 7-9). Multiplanar reslices along the arches are provided to evaluate the accuracy of the registration process (IPS CaseDesigner v.1.4).
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