Abstract
This study investigated predictive risk factors of condylar remodeling changes after counterclockwise maxillomandibular advancement (CCW-MMA) and disc repositioning surgery. Forty-one female patients (75 condyles) treated with CCW-MMA and disc repositioning had cone beam computed tomography (CBCT) scans taken pre-surgery, immediately after surgery, and at an average 16 months post-surgery. Pre- and post-surgical three-dimensional models were superimposed using automated voxel-based registration on the cranial base to evaluate condylar displacements after surgery. Regional registration was performed to assess condylar remodeling in the follow-up period. Three-dimensional cephalometrics, shape correspondence (SPHARM-PDM), and volume measurements were applied to quantify changes. Pearson product–moment correlations and multiple regression analysis were performed. Highly statistically significant correlation showed that older patients were more susceptible to overall condylar volume reduction following CCW-MMA and disc repositioning ( P ≤ 0.001). Weak but statistically significant correlations were observed between condylar remodeling changes in the follow-up period and pre-surgical facial characteristics, magnitude of the surgical procedure, and condylar displacement changes. After CCW-MMA and disc repositioning, the condyles moved mostly downwards and medially, and were rotated medially and counterclockwise; displacements in the opposite direction were correlated with a greater risk of condylar resorption. Moreover, positional changes with surgery were only weakly associated with remodeling in the follow-up period, suggesting that other risk factors may play a role in condylar resorption.
Postoperative instability of counterclockwise maxillomandibular advancement (CCW-MMA) due to condylar displacement during the surgical procedure and/or subsequent long-term condylar resorption remains an area of concern . Authors have suggested that condylar torque and altered condylar loading may lead to sagittal relapse and an anterior open bite .
There is disagreement in the current literature regarding treatment efficacy and the options for preventing degenerative condylar changes after bimaxillary surgical advancement. Although some investigators believe that orthognathic surgery alone reduces or eliminates temporomandibular joint (TMJ) dysfunction and symptoms , others have reported that performing orthognathic surgery in the presence of a TMJ disorder may cause further harmful effects to the TMJ .
Some studies have shown that the simultaneous surgical correction of coexisting dentofacial deformities and a TMJ pathology by repositioning and stabilizing the articular disc provides high-quality treatment outcomes for most patients . On the other hand, specific condylar displacement changes during articular disc repositioning surgery have been investigated as a potential factor inducing condylar remodeling in the long-term follow-up . Moreover, it has been reported that the degree of mandibular advancement performed may also contribute to skeletal relapse and condylar resorption . Patients with pre-surgical TMJ symptoms requiring large mandibular advancement appear to be at increased risk .
The use of cone beam computed tomography (CBCT) and new three-dimensional (3D) tools allow for a comprehensive analysis of surgical and post-surgical skeletal changes. Such technologies have the potential to identify individual variability and highlight associations between structural changes and the stability of surgical correction .
This study investigated whether age, pre-surgical antero-posterior and vertical facial characteristics, and the magnitude of the surgical procedure and/or condylar displacement changes may predict condylar remodeling after CCW-MMA and disc repositioning surgery.
Materials and methods
De-identified CBCT scans from 41 female patients presenting with disc displacement and TMJ osteoarthritis (OA), who underwent CCW-MMA associated with disc repositioning surgery, were included in this study ( Fig. 1 ). Patients were operated on consecutively by the same surgeon (LMW), using rigid internal fixation. Articular disc displacement was assessed by clinical examination and magnetic resonance imaging (MRI) interpreted by two experienced and calibrated doctors (LMW and JRG). Diagnostic criteria for temporomandibular disorders were used to identify TMJ OA .
The current study utilized CBCT images obtained before surgery (T1), immediately after surgery (3–9 days) (T2), and at an average 16 months post-surgery (T3). Archives from patients presenting with craniofacial syndromes, systemic degenerative conditions such as rheumatoid arthritis, or who had undergone a previous TMJ intervention were excluded.
A total of 82 condyles were analyzed. Seven condyles were excluded due to a history of previous arthroplasty. The final sample was composed of 75 condyles. All patients signed an informed consent form for hospital admission, surgical procedures, and release of information for research purposes. This study was approved by the university institutional review board and was performed in compliance with the Declaration of Helsinki.
Surgical technique
The TMJ and orthognathic surgeries were performed concomitantly, beginning with the TMJ surgery. Articular disc repositioning surgery was performed using the Mitek anchor technique (Mitek Products, Inc., Westwood, MA, USA). The CCW-MMA technique was then performed beginning with the bilateral mandibular sagittal split osteotomies with counterclockwise rotation and stabilization; one bone plate was positioned in the posterior body area and two to three bicortical 2-mm diameter screws were placed in the ascending ramus on each side. The maxillary osteotomies were then performed for counterclockwise rotation and stabilized with four bone plates using 2-mm diameter screws and bone grafting when indicated. A detailed description of the surgical procedure has been published previously .
Image acquisition and 3D analysis
CBCT images were obtained using a 17 × 23 cm extended field of view protocol, with a scan time of 17.8 s and isotropic voxel size of 0.3 mm (i-Cat CBCT, 120 kV, 5 mA; Imaging Sciences, Hatfield, PA, USA). Images were resampled to 0.5-mm isotropic voxel size prior to performing the segmentation of the anatomical structures of interest (CMF Registration, 3D Slicer software, www.slicer.org ). 3D models of the cranial base, maxilla, and mandible were constructed by outlining the cortical boundaries using semi-automated discrimination procedures (ITK-SNAP software, www.itksnap.org ). A 3D cephalometric analysis was conducted to determine the facial skeletal pattern before surgery (T1) and to assess surgical changes (T1–T2) for sample characterization (Q3DC, 3D Slicer software).
In this study, the images obtained at the different time-points were superimposed using two specific voxel-based registration methods (CMF Registration, 3D Slicer software). Cranial base registration was applied to assess condylar displacement changes , and regional registration was used to analyze condylar remodeling . Both procedures were conducted through 3D Slicer software (CMF Registration, 3D Slicer software).
All left condyles were mirrored in the sagittal plane to form right condyles to facilitate the outcomes analysis. Superimposed models were simultaneously cropped (Easy Clip, 3D Slicer software) and compared by subtraction to compute surgical (T1–T2) and post-surgical (T2–T3) changes between corresponding surface meshes using shape correspondence analysis (SPHARM-PDM, 3D Slicer software).
Shape correspondence made it possible to mark the regions of interest (ROI) in one condyle and propagate such regions for the other surgical time-points, obtaining x , y , z coordinates for each point (Pick ’n Paint, 3D Slicer software). Then, mathematical formulas were applied to each coordinate of correspondent points in the condylar surface, which allowed the measurement of both translational (antero-posterior, vertical, and lateral) and rotational (pitch, roll, and yaw) displacements. Each condylar translational displacement was measured in millimeters and each rotational change in degrees. Positive and negative signs indicated the direction of displacement ( Fig. 2 ).
Five specific ROI were selected as representative of each condylar surface, i.e., superior, anterior, posterior, medial, and lateral surfaces. Thirty-seven correspondent points were used to analyze changes in the anterior, superior, and posterior surfaces, whereas 19 points were selected as representatives for the analysis of changes in the lateral and medial surfaces ( Fig. 3 ). The referred ROI were marked in the post-surgical 3D models and propagated to the respective follow-up models (Pick ’n Paint, 3D Slicer software). 3D point-wise linear distances between each time-point were then used to calculate remodeling changes in millimeters (Model to Model Distance, 3D Slicer software). Positive and negative signals represented outward and inward movement, respectively. Thus, positive values indicated bone apposition and negative values indicated bone resorption. Condylar volume changes were also calculated in cubic millimeters using the ITK-SNAP software.
Statistical analysis
Descriptive statistics were used to report clinical characteristics before surgery (T1), as well as surgical (T1–T2) and post-surgical changes (T2–T3). Pearson product–moment correlations were used to determine the relationships of clinical and surgical factors with condylar remodeling in the follow-up period. Stepwise multiple linear regression analysis was used to identify the independent variables that best predict condylar remodeling at specific sites. A significance level of P ≤ 0.05 was applied. The statistical analyses were performed using SPSS version 16.0 software (SPSS Inc., Chicago, IL, USA).
3 Results
Patient demographic and clinical characteristics are listed in Table 1 . The sample was composed mostly of hyperdivergent retrognathic patients. Fifteen percent of the subjects presented a sella–nasion to mandibular plane (SNGoMe) angle of <33.2° and/or sella–nasion to B-point (SNB) angle of >79°. The maxilla was often retruded as well. All patients underwent mandibular advancement and counterclockwise rotation of the maxillomandibular complex simultaneously with disc repositioning surgery. The mean counterclockwise rotation and advancement at B-point were 5.6° ± 3.1° and 6.0° ± 2.3°, respectively. Descriptive statistics for the surgical displacement changes are shown in Table 2 .
| Age, years | Follow-up (months) | Before surgery (T1) | |||
|---|---|---|---|---|---|
| SNGoMe (°) | SNA (°) | SNB (°) | |||
| Mean | 26.4 | 16.1 | 40.9 | 79.1 | 74.4 |
| SD | 12.5 | 8.2 | 7.4 | 3.7 | 4.6 |
| Min | 16.0 | 6.0 | 25.1 | 69.5 | 59.4 |
| Max | 58.0 | 52.0 | 61.0 | 85.8 | 81.6 |
| Percentile | |||||
| 15th | 16.0 | 10.0 | 33.2 | 75.1 | 71.1 |
| 50th | 21.0 | 14.0 | 41.4 | 79.4 | 74.9 |
| 85th | 41.9 | 23.9 | 46.3 | 83.2 | 79.0 |
| Magnitude of the surgical procedure | Condylar displacement changes | ||||||||
|---|---|---|---|---|---|---|---|---|---|
| SNGoMe (°) a | SNA (°) b | SNB (°) c | AP (mm) d | Vertical (mm) e | Lateral (mm) f | Yaw (°) g | Roll (°) h | Pitch (°) i | |
| Mean | 5.6 | −3.3 | −6.0 | 0.6 | 1.0 | 1.5 | 4.5 | −5.2 | −7.5 |
| SD | 3.1 | 2.0 | 2.3 | 1.3 | 1.3 | 1.8 | 6.0 | 7.3 | 8.0 |
| Min | 0.7 | −7.4 | −12.6 | −3.2 | −2.3 | −2.5 | −11.8 | −30.5 | −32.3 |
| Max | 14.6 | 1.2 | −1.8 | 3.5 | 5.0 | 7.3 | 18.3 | 8.7 | 14.0 |
| Percentile | |||||||||
| 15th | 2.3 | −5.5 | −8.4 | −0.6 | −0.2 | −0.6 | −1.2 | −11.4 | −14.5 |
| 50th | 5.4 | −3.1 | −5.7 | 0.8 | 0.9 | 1.2 | 3.5 | −4.4 | −7.8 |
| 85th | 7.9 | −1.4 | −3.4 | 1.8 | 2.4 | 3.4 | 12.0 | 1.8 | −1.3 |
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