Several studies reported that the progression and the severity of bony changes on the TMJ increased with age [13,14,15]. On the other hand, our study revealed that the prevalence of bony changes was higher in the groups of 10~19, 20–29, and 50~59 years old than in other age groups (Table 2). This finding was consistent with the former study  that bony changes were more frequent between 20 and 49 years old. Because psychologic status can be a precipitating factor of TMD [17, 18], our finding may be partially related to the stress and the pressure of study for the college entrance examination in Korean teenagers. In addition, young people have a tendency to visit a hospital more often than aged people (Table 2).
The intermediate phase of bony destruction in TMJ lasts on average 6 months to 1 year . In the present study, 48.6% of degenerative condyles were examined within 6 months. We speculated that patients usually visited the hospital in their intermediate phase of DJD, when they might undergo spontaneous joint pain, mouth opening limitation, and/or crepitus .
Generally, bone deformation characterized in DJD is osteophytes, erosion, flattening, sclerosis, and pseudocysts. Each type of bony change occurs in different stages of DJD and has different clinicopathological meanings . As a condyle has adapted to degenerative changes, tissue remodeling has happened and radiographic and/or morphologic appearances of condyles have changed accordingly . Several papers reported the distribution of condylar bony changes and their combinations [10, 13, 14]. These studies presented somewhat different results with the others. Dos Anjos Pontual et al. found flattening to be the predominant findings . Wiese et al. found “flattening + osteophyte + erosion” to be the predominant findings . Campos et al. reported that “osteophytes + erosion” was the most frequent combination and osteophyte was the most common single bony change in the MRI study . We found that erosion + flattening was the most frequent (12.5%), followed by “flattening” (11.5%), “osteophyte + erosion + flattening + sclerosis” (10.4%), and “osteophyte + flattening” (10.1%). The reason for these different results among the studies may be that it was not easy to detect the bony changes definitively, since it is usually a gradual remodeling process [10, 13, 14]. As CBCT has been widely used in assessing TMJ morphology, more specific or detailed guidelines for degenerative bony changes are necessary .
Even though pain has occurred only in one side, degenerative condylar changes can be detected on both sides (Fig. 1). One third of degenerative condyles did not show pain (Table 3). These results can imply that degenerative changes show some degree of inflammation, producing symptoms that resolve with time, while the previous bony changes still remain .
Erosion is a radiographic clue that an active destructive process may be occurring, whereas osteophyte is an indication that the condyle has adapted to degenerative changes produced in the past . In this study, the frequency of erosion was directly proportional to NRS, but the frequency of osteophyte was inversely proportional (Fig. 3). This result demonstrates that the active inflammation of DJD is correlated with the erosion and inversely correlated with the osteophyte.
The prevalence of erosion increased from onset until 2 years and gradually decreased thereafter (Fig. 4). This result suggests “6 months to 2 years” might be a meaningful time point when DJD status changes from the active, unstable phase to the stabilized late phase. The prevalence of osteophyte, erosion, and pseudocyst was increased with age (Fig. 5). Considering these results, we suppose that erosion would have remodeled into osteophyte and/or pseudocyst, as time goes by.
Whereas some previous studies reported that there was poor correlation between bony change and pain [12, 14], our study found that osteophyte and erosion could be pain-related variables in DJD. We speculate that these contradictory results may be due to considering only the existence of bony changes, not the type of bony change in the previous study. There were still controversies about correlation between pain and condylar bony changes [9, 12, 14, 20].
Our study has several limitations such as the limited sample size. Moreover, we evaluated only the first-visit results and excluded the follow-up results. To verify the significant relationships between pain and radiographic findings, further well-organized studies will be needed in the future.