Postsurgical Stability of Temporomandibular Joint of Skeletal Class III Patients Treated with 2-Jaw Orthognathic Surgery via Computer-Aided Three-Dimensional Simulation and Navigation in Orthognathic Surgery (CASNOS)

Abstract

Objective: The aim of this study is to clarify the postsurgical stability of temporomandibular joints in skeletal class III patients treated with 2-jaw orthognathic surgery which was performed utilizing computer-aided three-dimensional simulation and navigation in orthognathic surgery (CASNOS) protocol.

Materials and methods: 23 consecutive nongrowing skeletal class III patients with mandibular prognathism associated with maxillary retrognathism treated with 2-jaw orthognathic surgery between 2018 and 2019 were enrolled in this study. The surgery was planned according to the standardized protocol of CASNOS (computer-aided three-dimensional simulation and navigation in orthognathic surgery). Computed tomography (CT) scans were performed in all patients 3 weeks presurgically and 6 months postsurgically. ITKSNAP and 3D Slicer software were used to reconstruct three-dimensional facial skeletal images, to carry out image segmentation, and to superimpose and quantify the TMJ position changes before and after surgery. Amount of displacement of the most medial and lateral points of the condyles and the change of intercondylar angles were measured to evaluate the postsurgical stability of TMJ.

Results: A total amount of 23 skeletal class III patients (female : male = 12 : 11) with age ranged from 20.3 to 33.5 years (mean: 24.39 ± 4.8 years old) underwent Le Fort I maxillary advancement and BSSO setback of the mandible. The surgical outcome revealed the satisfactory correction of their skeletal deformities. The mean displacement of the right most lateral condylar point (RL-RL') was 1.04 ± 0.42 mm and the mean displacement of the left most lateral condylar point (LL-LL') was 1.19 ± 0.41 mm. The mean displacement of the right most medial condylar point (RM-RM') was 1.03 ± 0.39 mm and the left most medial condylar point (LM-LM') was 0.96 ± 0.39 mm. The mean intercondylar angle was 161.61 ± 5.08° presurgically and 159.28 ± 4.92° postsurgically.

Conclusion: The postsurgical position of TM joint condyles in our study only presented a mild change with all the landmark displacement within a range of 1.2 mm. This indicates the bimaxillary orthognathic surgery via 3D CASNOS protocol can achieve a desired and stable result of TMJ position in treating skeletal class III adult patients with retrognathic maxilla and prognathic mandible.

Figure 1

The superimposition of presurgical (T1, gray area) and postsurgical craniofacial area (T2, orange area). The head was orientated relatively to the Frankfort horizontal (FH) plane which was established by bilateral orbitale and the landmark in the middle of the two porions (mid-Po). The superimpositions of T1 and T2 scans were registered to the cranial base using a voxel-based registration algorithm ((a) the right side; (b) the left side; (c) the bottom view side).

Figure 2

The 3D imaging of the craniofacial area reconstructed with the open-source software. RL (right), LL (left): the most lateral points of the condyles; RM (right), LM (left): the most medial points of the condyles are identified ((a) the presurgical view: T1; (b) the postsurgical view: T2).

Figure 3

The bottom view of the mandible and cranial base. The cutting angle between the axes (intersection between RL-LM and RM-LL: intercondylar angle) was calculated and measured ((a) presurgical intercondylar angle (161.61 ± 5.08°); (b) postsurgical angle (159.28 ± 4.92°); p = 0.061).

Figure 4

(a) The distribution of color zones indicates the means of mandibular position difference between T1 and actual T2 of the subjects. The mandibular mean differences of the patients were distributed in the green and blue zones (green: the absolute value < 0.300 mm; yellow: the absolute value < 1.250 mm). The landmarks of the most medial (RM and LM) and lateral point (RL and LL) were identified. (b) The distribution of color zones indicates the means of mandibular discrepancies on the right and left condylar heads between T1 and T2 of individual subjects. The mean discrepancies of the patients were distributed in the green and blue zones. The landmarks (RM, LM, RL, and LL) were identified from the top and lateral views. All the 3D displacements of the most lateral and medial condylar points are as follows: RL-RL′: 1.04 ± 0.42 mm; LL-LL: 1.19 ± 0.41 mm; RM-RM′: 1.03 ± 0.39 mm; and LM-LM′: 0.96 ± 0.39 mm ((b) the top view and (c) the lateral view; details in Table 4). (c) Lateral view of the condyle heads and the identified landmarks of RL and LL.