We have shown, using a comparative cross-sectional multicenter design, that around one third of participants with JIA in this cohort had TMD. Half of children and adolescents with JIA reported pain during jaw movements and pain on palpation of the masticatory muscles and TMJs as compared to one fourth of their healthy peers; palpatory pain was associated with sDMARDs and bDMARDs treatment, and children and adolescents with JIA had a significantly lower mean vertical jaw movement. Moreover, TMJ-related clinical signs and vertical jaw movement ≤40mm had the highest association to the JIA group.
The reported prevalence of TMD in children with JIA varies between 38% to 83% according to the definitions and methods of ascertainment used, to the cohort examined and to differences in populations (15, 32–35). Ferraz and colleagues, in their study of fifteen children with JIA, age ranged between six and twenty-eight years and mean age 16.3 years, reported a high prevalence of 83%, however, without describing the method of ascertainment, eg. whether the figures were based on self-reporting or on clinical examination [29]. A previous study from Rongo and colleagues based on fifty participants with JIA aged between nine and sixteen years, found the prevalence of TMJ damage from 100 joints to be 74% as assessed on magnetic resonance imaging (MRI) [34]. Others have reported prevalences of 55% based on a questionnaire [32] and of 72% based on clinical signs [33]. Both studies are not based on DC/TMD, and the children were older than those in our study. In contrast, a longitudinal study by Zwir et al, including seventy-five children, revealed a prevalence of 38% based on symptoms and 47% based on clinical examination [30]. Their results are in line with ours.
In our study, the prevalence of TMD, either based on symptoms or clinical signs, in the healthy peers were quite high, 28 and 29%. It was higher than in earlier studies among adolescents, reported by Graue and collegues (7 and 12%) and Østensjø and collegues (7%) [9, 10]. A combination of both symptoms and clinical signs for TMD, was more in line with the mentioned studies. Studies from Finland and Brazil confirm our results with a high prevalence of TMD in the normal population. Vierola et al [35] presented a TMD prevalence of 35% (mean age 7.9 years) and de Paiva Bertoli 34% (mean age 11.0 years) [36]. Reasons for the difference in TMD prevalence in the normal population of children and adolescents are probably due to the use of different diagnostic used tools, number of participants, age in the studied population, different countries involved and different study design. In studies from Norway, Graue and collegues [10] used two screening questions for pain related to TMD [11] and DC/TMD [26] form for symptoms and clinical signs in a population of 210 children and adolescents, age 12-19 years. Østensjø et al [9] used the same two screening questions of TMD symptoms [11] for screening in a population of 560 adolescents, age 13-19 years, and then a modified research diagnostic criteria for TMD (RDC/TMD) examination [37] in those that answered yes to 1) having pain in the temples, face, temporo- mandibular joints, or jaws once a week or more, and 2) having pain when open the mouth wide or chew once a week or more. The Finish group [35] used RDC/TMD [37] form for clinical signs on 483 children of 6-8 years and the Brasilian group [36] used the American Academy of Orofacial Pain [38] form for screening and RDC/TMD [37] for clinical examination on a population of 934 children between 10-14 years. It is clear that it can be difficult to get an exact figure on the prevalence of TMD in the normal population. A previous meta-analysis conducted by da Silva and colleagues revealed the overall prevalence of intra-articular joint disorder of 16% [39].
In our study, approximately half of the JIA subjects had clinical findings consistent with TMD, with no differences according to JIA category. Since the numbers for three of the categories, including systemic arthritis, rheumatoid factor positive polyarthritis, psoriatic arthritis were relatively low, these results should be interpreted with caution.
he sensitivity and specificity of the clinical orofacial examination in relation to TMJ has been debated, as displacement of the disc, although eliciting a clicking sound, may be asymptomatic [40–42]. Based on the DC/TMD criteria, asymptomatic TMJ clicking is still defined as TMD. However, several studies have shown that pain-free clicking represents a normal variant, typically seen in girls during puberty [16]. Recently, a clinical examination protocol for JIA was developed by the Temporomandibular joint juvenile arthritis working (TMJaw) group. This examination protocol focuses on three general items: TMJ symptoms, TMJ dysfunction, and dentofacial deformity in JIA and shows acceptable reliability and construct validity [7].
We found, in accordance with other studies, that the TMJ area and the masseter muscle region were common locations for pain in JIA [32]. However, a recent study from Koos and colleagues revealed a lower frequency of masticatory pain on palpation [16], and Kristensen and colleagues stated that masticatory pain complaints could develop over time [43]. In the present study, more than half of the participants with JIA revealed clinical signs in the TMJ region and in the masseter region, and more than one-fourth of the participants with JIA had TMD. A longitudinal multicenter approach could elucidate the development of masticatory muscle pain, as Kristensen and collegues have pointed out [43].
The vertical unassisted jaw movement has been widely used as a valid marker for TMJ arthritis [44]. We showed that participants with JIA have lower vertical movements as compared to their healthy peers, however, the differences were relatively small, questioning its clinical significance. Differently viewed, for children and adolescents aged <11 years, the cutoff value 40mm ranges as normal vertical jaw movement [45]. Further, our findings suggest that lateral movement did not differ significantly between the two groups, which is in line with Twilt and colleagues [46] and by Küseler and colleagues (22). In the latter study, fifteen children with JIA with a mean age of 12 years, recorded decreased lateral movements ≤ 5 mm with no significant relevance [20].
We found no statistically differences in the presence of TMD to JIA categories. However, we found a significantly higher occurrence of clinical signs in participants with JIA currently on DMARDs medication (whether synthetic or biologic) than in those off such medication. A high risk of developing clinical signs of TMD was associated with a severe disease course, indicated by the use of DMARDs.
The strengths of the study is the relatively large number of participants, that the study groups were well matched and the meticulous standardization of the clinical TMJ assessment performed prior to and during the study period. However, the large number of participants should not hide the fact that we are dealing with an underpowered sample size with a lack of 75 participants. There are some more limitations to the study. The overall response rate of 63%, although considered acceptable, might have influenced the results because the group which not participated, on average, was slightly younger and had a slightly lower proportion of girls. Secondly, the shortened version of DC/TMD used in this study is not directly comparable with studies having used the full DC/TMD score. In the present study children and adolescents with JIA with TMD involvement were defined based on self-reported pain and clinical examination. Further studies may focus on the role of imaging on the diagnosis of TMJ arthritis in children with JIA. This is particularly important in JIA with non-symptomatic TMJ involvement since hard tissue loss in the condyle may hinder the growth of the mandible and subsequently affect chewing function and cause aesthetic problem [16].