The purpose of this study was to investigate the association between coronoid process hyperplasia and temporomandibular joint (TMJ) ankylosis and to analyze the pathological mechanism and clinical significance of coronoid process hyperplasia. Forty-four patients treated for TMJ ankylosis between January 2007 and December 2014 were studied retrospectively; 176 patients with normal TMJs served as controls. The original DICOM data were used to reconstruct the jaw, and a three-dimensional cephalometric analysis (SimPlant Pro software version 11.04) was performed to assess the association between the severity of TMJ ankylosis and the height of the coronoid process. The height of the coronoid process was 20.41 ± 5.00 mm in the case group and 14.86 ± 2.67 mm in the control group; there was a significant difference between the two groups ( P < 0.001). Long-standing TMJ ankylosis contributes to coronoid process hyperplasia. Therefore, attention should be drawn to the coronoid process in patients with TMJ ankylosis. A coronoidectomy together with arthroplasty is recommended in patients with TMJ ankylosis.
Temporomandibular joint (TMJ) ankylosis is a disorder that may be associated with serious functional disability and aesthetic deformity, including limited mouth opening, impaired mastication, poor oral hygiene, and disturbances of facial and mandibular growth. With its unique physical appearance and the use of preoperative computed tomography (CT), it is not difficult to make a correct diagnosis of TMJ ankylosis at the time of patient admission.
Oral and maxillofacial surgeons treating patients with TMJ ankylosis generally concentrate their attention on the condylar region, and the presence of an elongated coronoid process may be overlooked. As a result, unsatisfactory mouth opening may be encountered in some patients with TMJ ankylosis, even when the condylar lesion has been managed appropriately. Anecdotal evidence suggests that a simultaneous coronoidectomy leads to a greater gain in mouth opening. Furthermore, it has been reported in the literature that an elongated coronoid process results in limited mouth opening. Therefore, it is reasonable to speculate that TMJ ankylosis may contribute to coronoid process hyperplasia. There appear to be no reported studies in the literature on the possible association between TMJ ankylosis and coronoid process hyperplasia.
In this study, the coronoid process was assessed and its height estimated by measuring three-dimensional (3D) reconstructions of the mandible using SimPlant Pro 11.04 software. The association between TMJ ankylosis and the development of coronoid process hyperplasia was then analyzed. The management of the different types of TMJ ankylosis and the elongated coronoid process were also explored.
Patients and methods
Forty-four patients treated for TMJ ankylosis at the department of oral and maxillofacial surgery of a university hospital in Kunming, China between January 2007 and December 2014 were studied retrospectively. This study was approved by the necessary ethics committee. Of the 44 patients studied, 20 were male and 24 were female. They ranged in age from 2 to 71 years (mean 22.67 years). Thirty-nine patients (88.6%) had a history of trauma and five (11.4%) had a history of infection; three patients had a surgical history of arthroplasty with a costochondral graft at another hospital. The mean preoperative maximum inter-incisal opening of this group of patients with TMJ ankylosis was 3.4 mm (range 0–17 mm). Based on the preoperative coronal CT image, 32 patients were classified as having unilateral TMJ ankylosis and 12 as having bilateral TMJ ankylosis. The Sawhney and He classification was used to categorize the patients: type I, a dense fibrous adhesion; type II, a bony fusion on the lateral side of the joint (the upper articular surface is undamaged); type III, similar to type II, but the articular disc is intact; type IV, complete bony fusion of the joint. According to this classification, 21 joints were type II, 13 joints were type III, and 22 joints were type IV. The clinical data of the 44 patients are summarized in Table 1 .
|Sex||Age, years||Cause||Sides of TMJA||TMJA type|
n = 24
n = 21
n = 39
n = 32
n = 21
n = 20
n = 23
n = 5
n = 12
n = 13
n = 22
One hundred and seventy-six subjects with normal TMJs and mouth opening were enrolled as controls. The ratio of TMJ ankylosis cases to control cases was 1:4. The control subjects were randomly selected patients matched for age (±2 years) and sex, who displayed symptoms including complicated impacted teeth, supernumerary teeth, maxillary cysts, or oral carcinoma arising from the soft tissue.
A Philips Brilliance iCT 256-slice scanner (Philips Medical Systems Inc., NewTom VG, Verona, Italy) or cone beam computed tomography scanner was used for imaging, except in patients with oral carcinoma in the control group, for whom only the 256-slice CT scanner was used. The CT data of the jaws (DICOM data) were imported into the commercial software program SimPlant Pro version 11.04 (Materialise NV, Leuven, Belgium). A thresholding, draw/erase mask, and segmentation wizard technique was used to extract the contour of the mandible from the CT data. The 3D mandibles were subjected to 3D cephalometric analysis. The following landmarks were identified on the 3D images of the mandibles using the CMF/Simulation and Measure and Analyse applications of the software: inferior gonion point (Go′), which is located at the most inferior point of the posterior border of ramus, the menton point (Me), the sigmoid notch point, and the apex of the coronoid process point ( Fig. 1 ). The mandibular plane (MP) was defined on the basis of three points: Go′L (left gonion), Go′R (right gonion), and Me (Downs analysis). The plane through the sigmoid notch and parallel to the MP was formed. The distance from the apex of the coronoid process to this plane was considered as the height of the coronoid process. This was calculated automatically by the software after the identification of the seven points ( Fig. 1 ).
The data obtained using SimPlant Pro software were collected in MS Excel 2003 and analyzed further using IBM SPSS Statistics version 21.0 software (IBM Corp., Armonk, NY, USA). The age and sex of the patients in the two groups were compared using the χ 2 test . An independent samples t -test was used to compare the height of the coronoid process between the two groups, and the results were expressed as the mean ± standard deviation (SD). Pearson’s correlation coefficient analysis was used to evaluate the relationship between the height of the coronoid process and both the severity and duration of TMJ ankylosis. A P -value of less than 0.05 was considered statistically significant.
There was no significant difference in age or sex between the two groups. No difference in height of the coronoid process was observed between the right and left sides in the control group. The height of the coronoid process was a mean 20.41 ± 5.00 mm in the case group ( n = 56 joints) and 14.86 ± 2.67 mm in the control group ( n = 352 joints) ( P < 0.001). There was a significant difference between the case and control groups for adolescents (≤18 years old) and adults (>18 years old) (both P < 0.001) ( Table 2 ). Furthermore, the height of the contralateral coronoid process in patients with unilateral TMJ ankylosis was significantly greater than the height in the control group ( P < 0.001).