This study focused on three-dimensional (3D) airway space changes and stability following simultaneous maxillomandibular counterclockwise rotation, mandibular advancement, and temporomandibular joint (TMJ) reconstruction with custom-made total joint prostheses (TMJ Concepts ® ). Cone beam computed tomography (CBCT) scans of 30 consecutive female patients with irreversibly compromised TMJs were obtained at the following intervals: T1, presurgery; T2, immediately after surgery; and T3, at least 6 months after surgery. The CBCT volumetric datasets were analysed with Dolphin Imaging ® software to evaluate surgical and postsurgical changes to oropharyngeal airway parameters. The average changes in airway surface area (SA), volume (VOL), and minimum axial area (MAA) were, 179.50 mm 2 , 6302.60 mm 3 , and 92.23 mm 2 , respectively, at the longest follow-up (T3 − T1) ( P ≤ 0.001). Significant correlations between the amount of mandibular advancement and counterclockwise rotation of the occlusal plane and 3D airway changes were also found ( P ≤ 0.01). The results of this investigation showed a significant immediate 3D airway space increase after maxillomandibular counterclockwise rotation and mandibular advancement with TMJ Concepts total joint prostheses, which remained stable over the follow-up period.
End-stage temporomandibular joint (TMJ) pathology may require surgical replacement with total joint prostheses in order to restore the patient’s function and esthetics. Rheumatoid arthritis, TMJ ankylosis, adolescent internal condylar resorption, and failed previous TMJ surgical intervention are among the indications for TMJ total replacement. Many irreversibly compromised TMJ patients show a high occlusal plane angle, increased anterior lower facial height, and maxillomandibular retrusion. These craniofacial features have been associated with narrower and longer airway space dimensions. Individuals with such altered airway dimensions are more susceptible to obstructive airway disturbances.
The comprehensive treatment of patients with vertical craniofacial growth predominance requires aggressive maxillomandibular counterclockwise rotation and large mandibular advancement in order to increase retroglossal and retropalatal airway spaces, decrease airway length, and improve facial balance as well. However, this surgical procedure has traditionally been considered unpredictable. Also large mandibular advancement associated with counterclockwise rotation of the occlusal plane significantly increases TMJ loading; it has been demonstrated to be a stable procedure for patients with healthy TMJs, but is controversial for individuals with previous TMJ internal derangements. The condition of the TMJ and its capacity to adapt to additional loading have become of paramount importance for the election of this kind of surgical alternative. Owing to this reason, aggressive occlusal plane counterclockwise rotation associated with large mandibular advancements has been adopted only by a few groups, mainly those who address TMJ pathology by simultaneous surgical intervention.
Custom-made TMJ total joint prostheses with CAD/CAM technology, using materials well proven in orthopaedic prostheses, can be used to simultaneously replace the TMJs and promote maxillomandibular counterclockwise rotation and mandibular advancement. Maxillary osteotomies are frequently required to establish optimal functional and aesthetic outcomes, and can be performed at the same operation.
Maxillomandibular advancement (MMA) surgery has been related to significant increases in the oropharyngeal airway, and constitutes one of the most successful approaches to the treatment of obstructive sleep apnea syndrome (OSAS). Moreover, a counterclockwise rotation of the maxillomandibular complex may further increase the oropharyngeal airway space and has been performed for the treatment of high occlusal plane angle patients, with stable results.
The literature indicates that MMA is 75–100% successful in the correction of OSAS. Long-term cephalometric studies have shown good skeletal stability after MMA advancement in these cases. Mehra et al. in a two-dimensional (2D) study, showed that a counterclockwise MMA surgery increased the oropharyngeal airway spaces by 47% in the retropalatal region and 76% in the retroglossal oropharyngeal airway dimension, relative to the amount of mandibular advancement. Other 2D studies have reported airway increases ranging from 42% to 51% in the retroglossal oropharyngeal airway dimension.
Two-dimensional lateral cephalograms have traditionally been used to evaluate airway parameters. However, the value of lateral cephalometric radiographs in analysing the upper airway is limited because they provide 2D images of complex 3D anatomic structures. In contrast, an accurate 3D image of the airway can be obtained using computed tomographic (CT) data in the coronal, axial, and sagittal planes, which may provide reliable and clinically useful information to supplement or possibly replace that provided by 2D cephalograms.
More recently, advances in 3D imaging and surgical techniques have stimulated an interest in CT airway analysis for the diagnosis, treatment planning, and outcome assessment in patients with cranio-maxillofacial deformities and OSAS. The possibility of visualizing the upper airway based on cone beam computed tomography (CBCT) scans and automated computer analysis has been a great aid in understanding normal and abnormal airway conditions and their response to surgery. Moreover, knowledge of the specific airway obstruction and its characteristics based on preoperative studies, allows a more precise surgical treatment plan directed at the areas of restriction.
Although maxillomandibular counterclockwise rotation and mandibular advancement surgery has been shown to increase the oropharyngeal airway space and improve OSAS signs and symptoms, 3D analysis of this procedure associated with TMJ total joint reconstruction is not available. The aim of the present study was to evaluate 3D oropharyngeal airway changes and stability after maxillomandibular counterclockwise rotation and mandibular advancement with TMJ Concepts ® custom-made total joint prostheses, performed at the same operation.
Materials and methods
This retrospective study evaluated CBCT scans of 30 consecutive female patients from a single practice, from December 2008 through October 2009, who underwent maxillomandibular complex counterclockwise rotation and mandibular advancement with TMJ total joint prosthesis reconstruction. The mean patient age at the time of surgery was 44 years (range 13–62 years). Criteria for study inclusion were: bilateral TMJ reconstruction associated with maxillary osteotomies for counterclockwise rotation of the maxillomandibular complex and mandibular advancement using total joint prostheses (TMJ Concepts system); use of maxillary and mandibular rigid fixation; and all surgical procedures performed by one surgeon (LMW). Patients were rejected based on the following criteria: craniofacial syndromes, previous oropharyngeal surgery, and inadequate or poor quality records.
CBCT scans were performed with the iCAT™ Cone Beam 3D Imaging System (Imaging Science International, Hatfield, PA, USA) on each awake subject seated upright with the Frankfurt plane (trago-infraorbital rim line) parallel to the ground. The patients were instructed to remain still and not to swallow. The mandible was positioned in centric relation and the lips were relaxed. For all scans, the 23-cm extended field of view setting was used during an 8.9 s scan, with a 0.3 mm resolution. Presurgical (T1) records were taken 1 day (range 1–2 days) before the surgery; immediate postsurgical (T2) records were taken 5 days (range 3–9 days) after surgery; and the longest follow-up (T3) records were taken on average 8.7 months after surgery (range 6–19 months).
CT scan data were acquired and a 3D plastic model of the patient’s jaw and cranial base structures was manufactured. A surgical predicting tracing was developed from a lateral cephalometric radiograph to determine the desired final position of the maxilla and mandible. The surgeon then repositioned the mandible to its predetermined new position. The custom-made total joint prostheses were then manufactured using CAD/CAM technology on the 3D model to fit the patient’s specific anatomical requirements and mandibular advancement needs. Prior to surgery, the mandibular movements done on the 3D models were duplicated accurately on anatomically mounted dental casts, and an intermediate splint constructed to determine mandible repositioning during surgery. The maxillary cast was then sectioned and repositioned to achieve the best occlusal relationship.
Surgery was performed under general anaesthesia via nasal endotracheal intubation. The TMJs were approached via a modified endaural or preauricular incision, and condylectomy and joint debridement were performed. Through a submandibular incision, the masseter and medial pterygoid muscles were reflected off the mandibular ramus. A subperiosteal tunnel was created on the ramus to connect to the base of the temporal bone. A coronoidectomy was performed and the temporalis muscle was reflected from the coronoid process to allow advancement and lengthening of the ramus. The mandible was then mobilized and repositioned using the intermediate splint and intermaxillary fixation. The fossa component was inserted through the endaural or preauricular incision and stabilized to the zygomatic arch with three to four 2-mm diameter bone screws. The mandibular prosthetic component was inserted through the submandibular incision and fixed to the ramus with eight to nine 2-mm diameter bicortical screws ( Fig. 1 ). Fat was harvested from the suprapubic or umbilicus region of the abdomen or from the buttocks, and packed around the fossa/mandibular component to help prevent fibrosis and heterotopic bone formation postsurgery. The extraoral incisions were closed in a layered fashion.
Multiple maxillary osteotomies were performed to establish the best possible functional and aesthetic result. The maxilla was stabilized with bone plates. Bone grafts and/or porous block hydroxyapatite grafts (PBHA, Interpore 200, Interpore Inc., Irvine, CA, USA) were used when necessary ( Fig. 2 ).
The CBCT volumetric datasets were imported in DICOM file format into Dolphin Imaging ® software version 11.0 (Dolphin Imaging and Management Solutions, Chatsworth, CA, USA). Once imported, the volumes were initially segmented to reduce interference from noise and voxel averaging. Segmentation was manually adjusted for each volume, limited to the software capabilities.
After segmentation, the 3D volume was oriented. In the coronal view, the mid-sagittal plane was oriented to the midline of the subject, considering crista galli and anterior nasal spine alignment. In the sagittal view, the Frankfurt horizontal plane (FH) was parallel to the axial plane ( Fig. 3 ). The external auditory meatus were levelled in the axial plane.
Once the image was properly oriented, the software was used to create a 2D simulated lateral cephalometric image with a ray-sum technique ( Fig. 4 ). A custom cephalometric analysis consisting of three linear and eight angular measurements was performed for the purpose of this study ( Fig. 5 ). The airway parameters are defined in Table 1 .
|Upper airway length||UAL||mm||1D||Length parallel to the long axis of the airway, between a horizontal plane tangent to the superior aspect of the hyoid bone and a horizontal plane tangent to the posterior palate|
|Sella to epiglottis distance||S–Epig||mm||1D||Sella to epiglottis distance|
|Lateral dimension of the retroglossal airway||LAT||mm||1D||Greater lateral dimension of the cross-section of the airway in the middle of the retroglossal area (between the base of the epiglottis and the inferior aspect of the soft palate)|
|Antero-posterior dimension of the retroglossal airway||AP||mm||1D||Greater antero-posterior dimension of the cross-section of the airway in the middle of the retroglossal area (between the base of the epiglottis and the inferior aspect of the soft palate)|
|Ratio of the lateral to the antero-posterior dimensions||LAT/AP||NA||Ratio||Ratio of AP and lateral dimensions|
|Volume||VOL||mm 3||3D||Volume of the airway from the tip of the epiglottis to a line parallel to the FH and tangent to the basion point|
|Surface area||SA||mm 2||2D||Surface area of the airway|
|Minimum axial area||MAA||mm 2||2D||Lowest cross-sectional area of the airway|
Initially, the region of interest was set with the aid of a clipping box and seed point. The software airway analysis tool was used to determine volume (VOL), surface area (SA), and minimum axial area (MAA). Structures and landmarks were taken as reference in order to establish the limits of the oropharynx, as seen in Fig. 6 .