Three-dimensional cone beam computed tomography analysis of temporomandibular joint response to the Twin-block functional appliance

Abstract

Objective: To propose a three-dimensional (3D) method for evaluating temporomandibular joint (TMJ) changes during Twin-block treatment.

Methods: Seventeen patients with Class II division 1 malocclusion treated using Twin-block and nine untreated patients with a similar malocclusion were included in this research. We collected their cone beam computed tomography (CBCT) data from before and 8 months after treatment. Segmentations were constructed using ITK-SNAP. Condylar volume and superficial area were measured using 3D Slicer. The 3D landmarks were identified on CBCT images by using Dolphin software to assess the condylar positional relationship. 3D models of the mandible and glenoid fossa of the patients were constructed and registered via voxel-based superimposition using 3D Slicer. Thereafter, skeletal changes could be visualized using 3DMeshMetric in any direction of the superimposition on a color-coded map. All the superimpositions were measured using the same scale on the distance color-coded map, in which red color represents overgrowth and blue color represents resorption.

Results: Significant differences were observed in condylar volume, superficial area, and condylar position in both groups after 8 months. Compared with the control group (CG), the Twin-block group exhibited more obvious condyle-fossa modifications and joint positional changes. Moreover, on the color-coded map, more obvious condyle-fossa modifications could be observed in the posterior and superior directions in the Twin-block group than in the CG.

Conclusions: We successfully established a 3D method for measuring and evaluating TMJ changes caused by Twin-block treatment. The treatment produced a larger condylar size and caused condylar positional changes.

Keywords: Computed tomography; Functional; Temporomandibular joint; Three-dimensional cephalometrics.

Figure 1. Technical route of the experiment. 1, Construction of the three-dimensional (3D) segmentations of the mandible and glenoid fossa. 2, Performing condylar segmentation. 3, Generating the surface model and performing volumetric measurements of the condyle. 4, Measuring the joint space by using 3D landmarks. 5, Performing the statistical analysis. 6, Registering the condyle-fossa based on the voxels. 7, Visualization of condyle-fossa modifications using the distance color-coded map.

Figure 2. Condylar volume increases significantly 8 months after treatment (T1) compared to before treatment (T0) in both control (A) and experimental groups (B).

Figure 3. Condylar superficial area increases significantly 8 months after treatment (T1) compared to before treatment (T0) in both control (A) and experimental groups (B).

Figure 4. The absolute increases in condylar volume (A) and superficial area (B) are significantly higher in the experimental group (EG) than in the control group (CG) after 8 months of treatment.

Figure 5. One example of six-directional views of superimposition in the control (A) and experimental (B) groups (CG and EG, respectively). More obvious skeletal remodeling is observed in the superior and posterior directions of the condyle in the EG than in the CG. All the skeletal superimpositions are visualized on a color-coded map and measured using the same scale, in which red color represents overgrowth and blue color represents resorption.

Ant, Anterior; Post, posterior; Sup, superior; Inf, inferior.

Figure 6. The superior view of all condylar superimpositions in the control (A) and experimental (B) groups (CG and EG, respectively). More obvious skeletal remodeling is observed in the superior direction of the condyle in the EG than in the CG. All the skeletal superimpositions are visualized on a color-coded map and measured using the same scale, in which red color represents overgrowth and blue color represents resorption.

Figure 7. The posterior view of all condylar superimpositions in the contol (A) and experimental (B) groups (CG and EG, respectively). More obvious skeletal remodeling is observed in the posterior direction of the condyle in the EG than in the CG. All the skeletal superimpositions are visualized on a color-coded map and measured using the same scale, in which red color represents overgrowth and blue color represents resorption.

Figure 8. All superimpositions of the left and right glenoid fossa in the control (A) and experimental (B) groups (CG and EG, respecitvely). More obvious skeletal resorption is observed in the superior direction of the glenoid fossa in the EG than in the CG. All the skeletal superimpositions are visualized on a color-coded map and measured using the same scale, in which red color represents overgrowth and blue color represents resorption.