Mixed-reality simulation for orthognathic surgery

Abstract

Background: Mandibular motion tracking system (ManMoS) has been developed for orthognathic surgery. This article aimed to introduce the ManMoS and to examine the accuracy of this system.

Methods: Skeletal and dental models are reconstructed in a virtual space from the DICOM data of three-dimensional computed tomography (3D-CT) recording and the STL data of 3D scanning, respectively. The ManMoS uniquely integrates the virtual dento-skeletal model with the real motion of the dental cast mounted on the simulator, using the reference splint. Positional change of the dental cast is tracked by using the 3D motion tracking equipment and reflects on the jaw position of the virtual model in real time, generating the mixed-reality surgical simulation. ManMoS was applied for two clinical cases having a facial asymmetry. In order to assess the accuracy of the ManMoS, the positional change of the lower dental arch was compared between the virtual and real models.

Results: With the measurement data of the real lower dental cast as a reference, measurement error for the whole simulation system was less than 0.32 mm. In ManMoS, the skeletal and dental asymmetries were adequately diagnosed in three dimensions. Jaw repositioning was simulated with priority given to the skeletal correction rather than the occlusal correction. In two cases, facial asymmetry was successfully improved while a normal occlusal relationship was reconstructed. Positional change measured in the virtual model did not differ significantly from that in the real model.

Conclusions: It was suggested that the accuracy of the ManMoS was good enough for a clinical use. This surgical simulation system appears to meet clinical demands well and is an important facilitator of communication between orthodontists and surgeons.

Keywords: Computed tomography; Dental compensation; Facial asymmetry; Mixed-reality simulation; Motion tracking; Orthognathic surgery.

Fig. 1

Mixed-reality surgical simulation system

Fig. 2

Reference splint

Fig. 3

3D craniofacial model with reference spheres

Fig. 4

Dento-skeletal model

Fig. 5

3D motion tracking and digitizing equipment. a ① Transmitter; ② box-type receiver; ③ stylus receiver; ④ universal joint. b Geometrical location of the stylus receiver to the titanium reference sphere

Fig. 6

Facial photographs (initial record) in case 1

Fig. 7

Oral photographs (initial record) in case 1

Fig. 8

Reference coordinate system for 3D diagnosis. a Cranial global coordinates. b Mandibular local coordinates MLB

Fig. 9

3D diagnosis in cranial coordinates in case 1. a Frontal view. b Inferior view

Fig. 10

3D diagnosis in mandibular local coordinates MLB in case 1. a Inferior view. b Superior view

Fig. 11

Upper dental or maxillary compensation for mandibular asymmetry. a Inferior view. b Posterior view

Fig. 12

3D simulation in case 1. a Original model. b Simulated model. Mandible: SSRO. Maxilla: unilateral RME assisted by Le Fort I corticotomy

Fig. 13

Treatment progress in case 1. a Facial photographs of pre- and post-treatment. b Oral photographs at initial, 6 months (pre-surgery), 7 months (2 weeks after surgery), and 1 year 1 month (post-treatment)

Fig. 14

Photographs (just before surgery) in case 2. a Facial photographs. b Oral photographs

Fig. 15

3D diagnosis and simulation in case 2. a Original model. b Superimposition of the simulated model on the original one (solid line). ManMoS demonstrates that the skeletal midline of the mandible is moved toward the right while the left half of the mandible is moved antero-inferiorly. Note that the right condylar position is not changed so much

Fig. 16

Unilateral SSRO

Fig. 17

Virtual cephalometric image (VCI). a VCI reconstructed from 3D craniofacial model. b VCI of original model. c VCI of simulated model

Fig. 18

Treatment progress in case 2. a Facial photographs of pre and post treatment. b Oral photographs at initial, post-surgery, and post-treatment

Fig. 19

Ramus positioning. a Flaring out of the condylar proximal segment. b Superimposition of the simulated model on the original one