Abstract
The purpose of this study was to clarify the correlation between pre-treatment anterior disc displacement and mandibular stability after orthognathic and orthodontic treatment among patients with a skeletal class II malocclusion and without pre-treatment condylar resorption. Thirty-seven patients were included (7 male, 30 female). The mean length of follow-up was 6.76 ± 3.06 years. Patients with condylar resorption before treatment were excluded. Magnetic resonance images and lateral cephalometric radiographs were taken before treatment (T0), after treatment (T1), and at follow-up (T2). Patients were classified according to the degree of disc displacement: −10–10° ‘normal’, 11–50° ‘slight to mild’, ≥51° ‘moderate to severe’. Results showed the condyle moved posterosuperiorly after treatment, and then moved anteriorly to a more concentric location during the long follow-up period. Condylar movement was found not to correlate with disc displacement. The degree of disc displacement before treatment did not correlate with the post-surgical mandibular positional change in either the sagittal or vertical direction. To conclude, the mandibular bilateral sagittal split ramus osteotomy was stable in the long-term after orthognathic and orthodontic treatment. In the absence of pre-treatment condylar resorption, the degree of initial anterior disc displacement did not have a significant influence on the stability of mandibular advancement.
Long-term stability is a major concern when considering orthognathic and orthodontic treatment to correct a skeletal class II malocclusion. Some authors have reported condylar positional change as an important factor contributing to mandibular relapse during follow-up. Others have associated mandibular relapse with condylar resorption related to conditions such as adolescent internal condylar resorption, reactive (inflammatory) arthritis, autoimmune and connective tissue diseases, and end-stage temporomandibular joint (TMJ) pathologies.
Previous studies on patients with skeletal class II malocclusion have shown a high incidence of TMJ internal derangement (anterior disc displacement or other TMJ pathologies). According to the Wilkes staging criteria for internal derangement of the TMJ, there are five stages in the progression of TMJ abnormalities: early, early/intermediate, intermediate, intermediate/late, and late stages. Condylar resorption happens at the late stage. The associated radiological findings can include deformity of the disc and hard tissues, associated with other degenerative arthritic changes. Patients with condylar resorption may exhibit a high angle facial morphology with a short ramus, mandibular retrognathia, open bite, and severe temporomandibular disorder (TMD) syndromes. The stability of the surgical–orthodontic protocol for condylar resorption reported in the literature is controversial. Ongoing condylar changes after the treatment may represent one possible reason for instability.
Various radiographic modalities have been used to evaluate the TMJ structures, including X-ray, computed tomography, and magnetic resonance imaging (MRI). MRI is currently used widely for the quantitative evaluation of the TMJ. This modality is regarded as the gold standard for TMJ examination; it is a non-invasive and non-radiation technique, providing high-resolution images of the articular disc and joint structures. Furthermore, MRI is by far the best way to determine the disc position and presence of condylar resorption. Of note, previous studies have reported that anterior displacement of the TMJ disc on MRI could be a predictor of TMD syndromes.
A retrospective study was performed to determine whether a correlation exists between pre-treatment disc displacement and mandibular stability after a long follow-up among patients with skeletal class II malocclusion and without pre-treatment condylar resorption. To avoid the interference of uncertain condylar resorption progression, this study involved only patients who did not have condylar resorption before treatment. The joint space, horizontal and coronal condylar axial angles, and disc length were evaluated to clarify the surgical and post-surgical TMJ changes.
Materials and methods
Patients
This study included a consecutive series of patients diagnosed with skeletal class II malocclusion identified in the archives. These patients underwent orthognathic and orthodontic treatment between January 2001 and December 2015.
The following inclusion criteria were set: (1) A-point–nasion–B-point (ANB) angle ≥5°, bilateral class II molar relationship, and overjet ≥5 mm; (2) patient had completed orthognathic and orthodontic treatment at least 3 years ago (surgery type was Le Fort I osteotomy, bilateral sagittal split ramus osteotomy (BSSRO), and genioplasty with rigid fixation), and those who had received treatment in recent years and had not reached the 3-year criterion were excluded; (3) availability of a complete series of identical lateral cephalometric radiographs and MRIs (pre-treatment (T0), post-treatment (T1), and follow-up (T2)); and (4) the patient’s stage of internal derangement before treatment did not exceed the intermediate/late stage according to the Wilkes staging criteria for internal derangement of the TMJ and there was an absence of condylar resorption. Patients with congenital craniofacial anomalies, who had undergone post-traumatic treatment, and those for whom data were incomplete were excluded. The same surgeon team and the same orthodontist performed the orthognathic and orthodontic treatments.
The initial group comprised 232 patients. Of these, 45 patients fulfilled the inclusion criteria. Seven of these patients were excluded because of condylar resorption at T0 and one patient was excluded due to evidence of unilateral osteochondroma at T2. Thus 37 patients were included in this study; 7 were male and 30 were female.
At T0, the mean ANB was 9.04 ± 2.21° and mean overjet was 8.17 ± 2.75 mm. The mean age at surgery was 25.95 ± 5.82 years and the mean length of follow-up was 6.76 ± 3.06 years.
Two-jaw surgery was implemented in all patients. Post-surgical orthodontic treatment included the routine use of class II elastics for 6 months. All cases had solid class I occlusal results at T1.
MRI measurements
MRIs were obtained using a 1.5-T imager (Signa; General Electric, Milwaukee, WI, USA) with bilateral 3-inch dual surface coils, according to the routine sequence. Among the horizontal, paracoronal, and parasagittal MRIs obtained, those images with the largest condyle were selected to perform the measurements. Adobe Photoshop and MB-Ruler measurement software were used separately to define the reference planes and obtain parameter values, accurate to 0.01 mm.
A previously described two-step two-circle method was used to transfer the Frankfort horizontal (FH) plane from lateral cephalometric radiographs to MRIs. A condylar head circle was drawn to describe the condylar head outline. Two further circles were drawn to determine the condylar long axis. The first circle passed through the centre of the condylar head and the second circle passed through the first one’s centre; both circles were confined to the contour of the condylar neck. The line linking the centres of the two circles determined the condylar long axis. After tracing the long axis, superimposition enabled FH plane transfer.
The horizontal condylar axial angle was measured on horizontal MRIs of the largest condylar axis. The sagittal baseline was drawn across the nose tip, nasal septum, and centre of the foramen magnum; the horizontal baseline was set perpendicular to the sagittal baseline. The horizontal condylar angle was defined as the angle between the horizontal baseline and the condylar axis ( Fig. 1 a ). The coronal condylar axial angle was defined as the angle between the FH plane and the condylar long axis on coronal MRIs ( Fig. 1 b).
