Material and methods

This retrospective study sample was composed of CBCT scans and clinical records from patients who had CMMA by the same surgeon (L.M.W.). Inclusion criteria were (1) osteotomies performed and stabilized with rigid internal fixation; (2) female patients at least 15 years old and male patients at least 17 years old; (3) patients with no TMJ abnormalities and with TMJ disc displacement assessed in clinical examinations and on magnetic resonance imaging interpreted by 2 experienced and calibrated doctors (L.M.W. and J.R.G.); and (4) CBCT scans acquired at 3 time points: before surgery (T1), immediately after surgery (T2), and at least 6 months postsurgery (T3). The exclusion criteria were patients with (1) craniofacial syndromes, (2) systemic degenerative conditions, (3) severe facial asymmetry, (4) previous TMJ surgery, and (5) previous arthroscopy, arthrocentesis, or viscosupplementation.

Records from 226 subjects consecutively treated from October 2008 to January 2011 were evaluated. One hundred nine patients were excluded for having undergone total prostheses of the TMJ. Thirty-eight patients were excluded for not having CBCT scans at all 3 time points (12 had TMJ articular disc repositioning surgery using the Mitek anchor technique (Mitek Products, Westwood, Mass), and the other 26 had no TMJ intervention). Therefore, 79 patients matched the inclusion criteria for this study.

A total of 158 condyles were analyzed; 16 condyles were excluded due to previous arthroplasty. The final sample included 142 condyles divided into 3 groups: group 1 (n = 105), condyles of patients diagnosed with symptomatic presurgical TMJ articular disc displacement who underwent articular disc repositioning concomitantly with CMMA. Many condyles in this group had osteoarthritis, showing severe flattening of the condylar surface, subchondral cysts, erosions, and osteophytes, causing considerable deformation of the condylar structure. In group 2 (n = 23), the condyles were of patients with clinical verification of presurgical bilateral TMJ articular disc displacement, mostly without osteoarthritic signs or symptoms, who underwent only CMMA. In group 3 (n = 14), the condyles were of patients with healthy TMJs who had CMMA. 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 institutional review board of the University of Michigan and complied with the Helsinki Declaration.

If indicated, articular disc repositioning surgery was performed using the Mitek anchor technique. This is an open-joint procedure performed simultaneously with the orthognathic surgery. Only salvageable discs were indicated for this surgery. A modified endaural incision was used to access the TMJ. The superior joint space was entered by incising the capsular ligaments, and the inferior joint space was entered with an incision just above the lateral pole of the condyle. The hyperplasic bilaminar tissue was wedge resected. The disc was mobilized and passively positioned over the condyle, with the lateral pterygoid muscle attachment preserved. The Mitek anchor with two 0 Ethibond sutures (Ethicon, Somerville, NJ) attached was inserted in the posterolateral surface of the condylar head, approximately 8 mm below the condylar top. The Ethibond sutures were attached to the posterior aspect of the posterior band of the disc for stabilization. The joint was then irrigated and the incision closed.

After the TMJ surgery, the orthognathic surgery was performed. Counterclockwise rotation and advancement of the maxillomandibular complex was routinely performed on these patients that included bilateral mandibular ramus osteotomies and multiple maxillary (LeFort 1) osteotomies. Bilateral mandibular ramus sagittal split osteotomies were performed; the mandible was placed into its final position with an intermediate splint and intermaxillary fixation, and internal rigid fixation using bone plates and screws. Maxillary osteotomies were then performed, internasal procedures were completed if indicated, a palatal splint was inserted, intermaxillary fixation was placed, and rigid fixation was applied using 4 bone plates fixated with 2.0-mm diameter screws.

The protocol for image acquisition was carried out with the patients sitting upright, keeping the Frankfort horizontal plane (trago-infraorbital) parallel to the ground. The mandible was positioned in centric relationship with the lips relaxed, and the patients were instructed not to swallow. CBCT images were obtained in the same machine (i-CAT CBCT, 120 kV, 5 mA; Imaging Sciences International, Hatfield, Pa) using a 17 × 23-cm extended field of view protocol, during a 17.8-second scan, with a 0.3-mm isotropic voxel size. Records were taken 1 day (range, 1-2 days) before the surgery (T1), 5 days (range, 3-9 days) after surgery (T2), and in the longest follow-up (T3), on average, 15.4 months after surgery (range, 6-52 months).

The CBCT images were reformatted to 0.5-mm isotropic voxel size for the segmentation of the anatomic structures of interest. Three-dimensional models of the cranial base, maxilla, and mandible were constructed by outlining the cortical threshold using a semiautomatic procedure (ITK-SNAP software; www.itksnap.org ).

The ITK-SNAP software was also used for cropping the cranial base model. This model indicated the registration program (CMF registration, 3DSlicer), the specific place where we wanted the different time-point models to be superimposed. The cranial base was used as the reference for registration because it remains stable over time and does not change with surgical treatment. By using an automated voxel-wise rigid registration method that allowed 6 degrees of freedom, the program compared and matched different time point images considering the intensities of the voxel grey scales at the cranial base.

Three-dimensional cephalometric analysis was used to determine the facial skeletal pattern before surgery and to assess the surgical changes (T1-T2) and postsurgical stability (T2-T3) (Q3DC, 3DSlicer). First, landmarks were positioned in specific places in the cranium as described in Table I . Then the software automatically calculated the SNA and SNB angles to express the anteroposterior positions of the maxilla and mandible, respectively, relative to the cranial base. The SN.GoMe angle was also calculated to show the mandibular plane inclination ( Fig 1 ).

Three-dimensional cephalometric analysis.

For analyzing specific mandibular condylar displacement changes, superimposed models were simultaneously cropped (Easy Clip, 3DSlicer). All left condyles were mirrored in the sagittal plane to form right condyles. Then condylar models were compared by subtraction to compute the surgical (T1-T2) and postsurgical (T2-T3) changes by using the shape correspondence analysis (SPHARM-PDM, 3DSlicer).

A mesh with 4002 correspondent points was generated by the shape correspondence analysis via spherical mapping and parameterization of each volume. 3DSlicer tool was then used to calculate the 3D point-wise linear distances between each time-point model (model to model distance, 3DSlicer).

Semitransparent overlays and vector maps were used to visually compare condylar displacement changes. The magnitudes of the computed 4002 differences were displayed on the condyle surface, and vector images pointed out the direction of the change.

Shape correspondence made it possible to mark the interest regions in 1 condyle alone (at T1) and propagate such regions for the other surgical time points (T2 and T3), obtaining x, y, and z coordinates for each point (Pick ‘n Paint module, 3DSlicer) ( Fig 2 ). Then the Q3DC module in the 3D Slicer software allowed measuring both translational and rotational displacements ( Fig 3 ). Positive or negative signs indicated displacement directions ( Table II ).

Example of lateral pole propagation considering correspondent surface mesh points: A, T1; B, T2; C, T3.

Rotational and translational measurements used to assess condylar changes; A, yaw, rotation around the y-axis (axial view); B, roll, rotation around the z-axis (coronal view); C, pitch, rotation around the x-axis (sagittal view); D, anteroposterior displacement (sagittal view); E, vertical displacement (coronal view); F, lateral displacement (coronal view).

Results

Three-dimensional cephalometric analysis showed high intraobserver and interobserver reproducibilities for all diagnostic variables (ICC ≥0.9) ( Table III ). The method used to measure condylar displacement changes also showed high intraobserver and interobserver reproducibilities (ICC ≥0.8) ( Table IV ). Demographic characteristics of the sample are listed in Table V . The 3 groups had similar mean ages, follow-up periods, and craniofacial patterns ( P ≥0.05). The patients on average had high mandibular plane angles and bimaxillary retrusions.

The amounts of counterclockwise rotation and maxillary advancement were similar in the 3 groups. However, patients in groups 1 and 2 experienced greater mandibular advancement compared with group 3 ( P ≤0.01) ( Tables VI and VII ).

For condylar translational changes during surgery, it was observed that, on average, the condyles moved backward and medially in the 3 groups. Patients having disc repositioning surgery (group 1) showed, on average, downward condylar displacement, whereas the condyle moved upward in groups 2 and 3 ( P ≤0.001).

Regarding mean condylar rotational changes, lateral yaw, medial roll, and upward pitch were observed in the 3 groups. However, group 1 showed a greater upward pitch compared with group 2 ( P ≤0.05) and group 3 ( P ≤0.01). Medial roll was also significantly larger in group 1 relative to group 3 ( P ≤0.01) ( Tables VIII and IX ).

Table VIII

Descriptive statistics and 1-way analysis of variance for comparing condylar linear and rotational displacements during surgery (T1-T2)

Condylar displacement ∗ (T1-T2)	Group 1 (n = 105)					Group 2 (n = 23)					Group 3 (n = 14)
	Mean	SD	Med	Min	Max	Mean	SD	Med	Min	Max	Mean	SD	Med	Min	Max	P value
AP (mm)	0.6	1.2	0.6	−3.2	3.5	0.7	0.7	0.6	−1.0	2.4	0.9	1.1	0.7	−0.4	3.2	0.523
Vert (mm)	0.9	1.2	0.9	−2.3	5.0	−0.1	0.8	−0.3	−1.2	1.9	−0.3	0.9	−0.2	−2.0	0.8	0.000
Late (mm)	1.5	1.7	1.3	−2.5	7.3	1.0	1.4	0.7	−1.4	4.8	0.9	1.3	1.2	−1.1	2.6	0.243
Yaw (°)	4.0	5.5	3.6	−11.8	18.3	3.2	5.1	3.0	−10.6	12.1	3.8	5.1	2.9	−5.0	11.6	0.797
Roll (°)	−5.5	6.6	−5.3	−30.5	8.7	−2.4	5.4	−1.6	−13.5	6.1	−0.3	5.3	0.3	−12.3	8.9	0.005
Pitch (°)	−7.7	7.6	−7.8	−32.3	14.0	−3.3	5.5	−2.1	−18.6	7.9	−1.4	4.6	−1.6	−8.5	10.7	0.001

Only gold members can continue reading. Log In or Register to continue

Share this:

• Click to share on Twitter (Opens in new window)
• Click to share on Facebook (Opens in new window)

Related

Related posts:

1. Orthodontic appliances and oral hygiene: Are we asking the right questions?
2. Vertical position of the maxillary canines and smile esthetic perceptions
3. Erratum
4. Factors affecting treatment decisions for Class I malocclusions
5. Maturational changes of the normal occlusion: A 40-year follow-up
6. Extreme maxillomandibular discrepancy in unilateral cleft lip and palate: Longitudinal follow-up in a patient with mandibular prognathism

Stay updated, free dental videos. Join our Telegram channel

Join