Abstract
Osteoarthritis of the temporomandibular joint (TMJ) can be described as non-inflammatory arthritic condition that results in degenerative changes of the joint structures. The aim of this study was to evaluate the skeletal morphology of the TMJ in patients with osteoarthritis with severe skeletal malocclusions (Class II and Class III) and patients with Class I occlusion as controls. Cone beam computed tomography images of 45 Class I, 28 Class II and 44 Class III joints of Caucasian patients were assessed for the presence of any degenerative changes in the condyle and fossa/eminence complex as described in the research diagnostic criteria for temporomandibular disorders (RDC/TMD). In all groups, the most commonly observed features were articular surface flattening and subcortical sclerosis. A combination of features that corresponds to a diagnosis of osteoarthritis was observed in 3% Class I, 43% Class II and 20% Class III patient joints. In conclusion, degenerative TMJ changes were more common in patients with skeletal jaw discrepancies, but wide inter-individual variations can be observed even in patients with clinically similar malocclusions.
Like other adult joints, the internal and external morphology of the temporomandibular joint (TMJ) is determined by the biomechanical loads placed on it during growth. As shown previously, various skeletal jaw growth patterns induce differences in stress distribution across the TMJ, which could possibly cause different functional loading of the articular structures. Altered function can lead to TMJ overloading, which is one of the main causes of osteoarthritis, also referred to as degenerative joint disease, a common arthritis affecting the TMJ.
According to research diagnostic criteria for temporomandibular disorders (RDC/TMD), a widely used diagnostic system for TMD, there are numerous scoring options used to evaluate the condition of osseous structures of the TMJ associated with osteoarthritis. The hard tissue components of the TMJ, the mandibular condyle and the fossa/eminence, are assessed for features that indicate remodelling or degenerative changes of the bone. After completing observations, a diagnosis can be made that categorizes the joint as normal, indeterminate or affected by osteoarthritis.
The osteoarthritic features of the TMJ, including changes in bone quantity or quality, can indicate the type of remodelling progressing in the osseous components of the joint.
Functional remodelling is characterized by morphological changes involving the articular structures of the joint that are not associated with any significant alterations in the mechanical function of the joint or occlusion, but dysfunctional remodelling can cause disturbed function of TMJ and unstable occlusion. During functional orthodontic treatment, especially orthognathic surgery, positional changes of the mandibular condyle may occur. More predictable adaptation is expected for joints that can undergo functional remodelling.
Conventional radiography may result in images with superimpositions of the adjacent tissues and overlapping of bony structures, which often makes interpretation difficult. Computed tomography (CT) allows the TMJ to be clearly visualized without the interference of nearby anatomical structures. Several studies confirm that cone-beam computed tomography (CBCT) is similar to conventional CT in diagnosing different osseous conditions and that it provides a cost- and dose-effective diagnostic option.
The aim of this study was to evaluate skeletal morphology of the TMJ in regard to osteoarthritis using RDC/TMD in CBCT images and to compare the results between study groups.
Study was approved by the Committee of Ethics, Riga Stradins University, Latvia.
Materials and methods
This study included 28 patients (mean age 20.3 years, SD 4.1 years), presenting with severe skeletal Class II jaw and angle Class II Division 1 subdivision dental relationship (mean ANB value 6.6°, SD 1.5°), 44 patients (mean age 21.3 years, SD 4.1 years) presenting with severe skeletal Class III and a dental relationship (mean ANB value 4.4°, SD 2.7°) who sought orthodontic and subsequent orthognathic treatment at the Institute of Stomatology and 45 patients (mean age 23.5 years, SD 3.8 years) with Class I skeletal and dental relationship (mean ANB value 2.1°, SD 0.8°) considering orthodontic or surgical treatment because of impacted teeth. Exclusion criteria were the presence of any congenital craniofacial syndrome; previous orthodontic treatment; history of dentofacial trauma or TMD, orofacial pain or mandibular dysfunction; remarkable parafunction; systemic rheumatoid or other type of arthritis.
All patients had CBCT scans at the initial appointment using an iCAT ( iCAT New Generation, Imaging Sciences International, Inc., Hatfield, PA, USA) device, following a standardized scanning protocol (120 kVp, 38 mA, FOV 17 cm, with a resolution of 0, 4 voxel, approximate effective dose = 36 μSv). Using the information from CBCT scans and Dolphin software v.11.5 (Dolphin imaging, CA, USA), cephalometric analyses were performed. Table 1 shows the mean values for the study groups, Fig. 1 illustrates the analyses (ANB angle and Wits appraisal) used to determine the severity of dentofacial deformity.
| Malocclusion type | ANB value (degrees) | SD | Wits appraisal value (mm) | SD |
|---|---|---|---|---|
| Class I | 2.1 | 0.8 | −0.5 | 0.9 |
| Class II | 6.6 | 1.5 | 7.9 | 2.9 |
| Class III | −4.4 | 2.7 | −12.2 | 6.6 |
Two dimensional reconstructions from raw scans were obtained using iCAT Vision (Imaging Sciences International, Inc., Hatfield, PA, USA) software. All examinations were performed by the same operator, an experienced maxillofacial radiologist (LN). Image reconstruction of the skeletal structures of the TMJ, the mandibular condyle and fossa/articular eminence was performed according to the literature. The right and left TMJ were evaluated from reconstructed lateral slices perpendicular to the long axis of the condyle, coronal slices parallel to the long axis and central lateral images of the joint.
Research diagnostic criteria for TMDs indicate examining the condyle for the presence or absence of the following features: condylar hypoplasia, condylar hyperplasia, articular surface flattening, subcortical sclerosis, subcortical cysts, surface erosion, osteophytes, generalized sclerosis, loose joint body, deviation in form and bony ankylosis. Diagnostic criteria suggest fossa/eminence for articular surface flattening, subcortical sclerosis and surface erosion. The three osseous diagnoses for the TMJ are dependent on features observed in the particular joint. A diagnosis of ‘no osteoarthritis’ requires: normal relative size of the condylar head; and no subcortical sclerosis or articular surface flattening; and no deformation due to a subcortical cyst, surface erosion, osteophytes or generalized sclerosis. A diagnosis of ‘indeterminate for osteoarthritis’ requires: normal relative size of the condylar head; and subcortical sclerosis with or without articular surface flattening; or articular surface flattening with or without subcortical sclerosis; and no deformation due to a subcortical cyst, surface erosion, osteophytes or generalized sclerosis. A diagnosis of ‘osteoarthritis’ requires: deformation due to a subcortical cyst, surface erosion, osteophytes or generalized sclerosis.
On lateral images, the condyle was assessed for the presence of flattening, erosions, osteophytes, and hyper- or hypoplasia of condyle; the fossa/articular eminence was assessed for the presence of flattening and erosion. On coronal images, the condyle was assessed for the presence of flattening, sclerotic changes, deviations in form, and subcortical cysts. To diagnose the previously mentioned features, the following signs must be noted: condylar hypoplasia with normal condylar morphology but decreased size in all dimensions; condylar hyperplasia with normal condylar morphology but increased size in all dimensions; articular surface flattening (a loss of the rounded contour of the surface) ( Fig. 2 ); subcortical sclerosis (any increased thickness of the cortical plate in load-bearing areas relative to adjacent nonload-bearing areas) ( Fig. 3 ); subcortical cyst (a cavity below the articular surface that deviates from normal marrow patterns); surface erosion (a loss of continuity of the articular cortex) ( Fig. 2 ); osteophyte (a marginal hypertrophy with sclerotic borders and exophytic angular formation of osseous tissue arising from the surface) ( Fig. 3 ); deviation in form (a departure from normal shape that is not attributable to flattening) ( Fig. 4 ); erosive changes; osteophytes; hyperplasia or hypoplasia. To validate the presence of these features, hard tissue changes had to be observed in at least three consecutive slices.
Statistics
For all 117 patients who were scanned by CBCT, it was possible to obtain complete bilateral joint images. Each joint was considered as a separate case, and 90 Class I, 56 Class II and 88 Class III joints were used for statistical analysis.
The prevalence of the changes and the number of changes observed by class was assessed using frequency tables. Differences in prevalence were tested using Pearson χ 2 test. The relationship between age group and the number of changes was assessed using ANOVA analysis.
Results
Overall, 42.7% ( n = 100) of TMJs had some visible changes in the osseous components. The number of condyles affected by any of the TMD features is given in Table 2 . Features were more prevalent in the group of patients with Class II skeletal and dental relationship ( P < 0.001). The prevalence of each feature by class is shown in Table 3 .
| Class I | Class II | Class III | Total | |||||
|---|---|---|---|---|---|---|---|---|
| Feature | N | % | N | % | N | % | N | % |
| Absent | 72 | 80.0 | 15 | 26.8 | 47 | 53.4 | 134 | 57.3 |
| Present | 18 | 20.0 | 41 | 73.2 * | 41 | 46.6 | 100 | 42.7 |
| Total | 90 | 100 | 56 | 100 | 88 | 100 | 234 | 100 |
| Class I | Class II | Class III | Total | |||||
|---|---|---|---|---|---|---|---|---|
| Feature | N | % | N | % | N | % | N | % |
| Condylar hypoplasia | 2 | 8.7 | 15 | 19.7 | 6 | 12.3 | 23 | 15.5 |
| Condylar hyperplasia | 0 | 0 | 0 | 0 | 1 | 2.0 | 1 | 0.7 |
| Articular surface flattening | 11 | 47.9 | 25 | 32.9 | 23 | 47.0 | 59 | 39.8 |
| Subcortical sclerosis | 4 | 17.4 | 5 | 6.6 | 1 | 2.0 | 10 | 6.8 |
| Cyst | 0 | 0 | 0 | 0 | 1 | 2.0 | 1 | 0.7 |
| Erosion | 0 | 0 | 8 | 10.5 | 6 | 12.3 | 14 | 9.5 |
| Osteophyte | 3 | 13.0 | 18 | 23.7 | 10 | 20.4 | 31 | 21.0 |
| Deviation in form | 3 | 13.0 | 5 | 6.6 | 1 | 2.0 | 9 | 6.0 |
| Total | 23 | 100 | 76 | 100 | 49 | 100 | 148 | 100 |
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