This study collected data related to clinically recorded orofacial signs and patient-reported subjective symptoms in a comprehensive cohort of patients with JIA, referred for specialist dental examination, at a mean of 2.9 years after disease onset. ILAR categories and disease activity during the last two years were assessed. Panoramic radiographs performed at the study visit, were available for half of all patients. Records from three clinics, with geographically distinct catchment areas and with patients referred over a period of several years, were examined to ensure accuracy. Orofacial signs and symptoms were common, varied between categories, and were related to the disease activity. Condylar alterations were not associated with other variables, such as ILAR category, clinical signs, symptoms or disease activity.
A strength of the study was the fairly large cohort, with objective as well as subjective variables involved and with radiological findings as an end point. What percentage of all patients diagnosed with JIA that was referred for orofacial issues is not known. Although the cohort of referrals was relatively sizeable, in contrast with many previously described case series, the number of patients in some of the ILAR categories was small, which weakens the results. Above all, the basic data were not population-based, were collected retrospectively and only discussed in relation to previous studies. Register studies, like the present one, run the risk of selection bias with overrepresentation of severe cases possibly illustrated by the high disease activity among the referrals. Although only one dentist summarized the standardized clinical and anamnestic protocols, a group of experienced but non-calibrated examiners were involved in the original data collection. This implies a weakness, in terms of both validity and reliability.
Some differences in patient characteristics between the sites were observed, partly reflecting variations in clinical routines. The merged study cohort was representative of the ILAR categories, gender and age in a distribution resembling cohorts from epidemiological studies [3, 18–20].
Different methods of collecting data regarding temporomandibular signs and symptoms have been used over the years. Helkimo’s dysfunction, Di, and anamnestic, Ai, indices are coarse quantifications of signs and symptoms in the orofacial area, but the standardized evaluations facilitate comparisons between patients and conditions. The indices have acceptable levels of reproducibility, not only for the same observer but also between different observers [16, 21], and are strongly correlated with other indices . Di and Ai have been widely used in epidemiological contexts concerning temporomandibular disorders (TMDs) , also among children and adolescents .
TMDs with signs and symptoms similar to those in JIA also occur in the healthy, general population. Signs and symptoms have been found to be less frequent in children than in adults in general . Examination of randomly selected samples of 3, 5, 10 and 15-year-old children in a Swedish city, using Helkimo’s indices, revealed a low prevalence of severe TMD signs and symptoms . Severe clinical signs, Di, were rare, also in a longitudinal series of Finnish children . Signs of, at most, mild dysfunction have thus been found in only a few percent among healthy, young children , but increase with age [28–30]. The prevalence of self-reported TMD in a large cohort of Swedish youths, 12–19 years of age, was 4.2% , and other studies have reported similar figures [32, 33]. Most of the patients in the present case series were afflicted in the orofacial area. Cases with severe dysfunction, Di III, were found in all but one of the diagnostic categories. Severe symptoms; Ai II, occurred in all categories. Orofacial engagement in young JIA patients, as found in this study, thus exceeds that in comparable, healthy groups. Severe signs and symptoms among JIA patients, according to Helkimo’s indices, have been presented earlier but all the categories were not represented .
In the present study, the prevalence of orofacial signs, as assessed by the specialist dentists, was higher than the prevalence of self-reported orofacial symptoms in all JIA categories, which is in agreement with epidemiological surveys of TMD . Patients may be unaware of, used to or not disturbed by certain clinical findings. The significant correlation between signs and symptoms, as found in the present study, is supported by findings in other studies .
The distribution of clinical signs and reported orofacial discomfort in this cohort differed significantly between the ILAR categories. That differences exist are in line with earlier investigations but the results have varied between studies. Pedersen et al.  found most TMJ involvement in the polyarticular category, Twilt et al.  in the systemic category and Cannizzaro et al.  in the extended oligoarticular category. In the present study, both signs and symptoms were significantly more frequent in the psoriatic arthritis category than in several other categories, despite similar disease activity. Clinical signs were found in almost all psoriatic arthritis patients and symptoms were also common. One reason may be that psoriatic arthritis engages not only the synovium, but also the surrounding tissues [35–37].
Moreover, the RF-positive category had very few patients without any orofacial signs. It is known that the RF factor contributes to joint involvement [10, 11, 38, 39], but as the number of patients in this category was limited, it is difficult to draw confident conclusions.
This study found significant associations between orofacial signs and symptoms, assessed at the study visit, and overall disease activity, assessed for the most recent years. The findings were perhaps not unexpected, as the TMJ is a joint among others and a high disease activity affects articular as well as periarticular structures.
The radiographs mirror previous arthritis in contrast with instant clinical and subjective examinations. Panoramic radiography has obvious shortcomings in TMJ diagnostics. Only condylar changes can be evaluated with any confidence, and have acceptable reliability and specificity, but low sensitivity compared with more advanced radiological techniques . For example, joint fluid and synovial enhancement can not be demonstrated with panoramic radiography. Magnetic resonance imaging (MRI) is the most superior technique to detect ongoing inflammation [12, 15]. Orofacial signs and symptoms might be related to ongoing inflammation but this is uncertain. However, panoramic examinations are simple, inexpensive, and easily accessible at most clinics, involve low radiation levels and require no sedation in young children. The method is used to get an overview of the jaws and is often performed before more sophisticated imaging examinations are performed. The reasons for the panoramic examinations in our study may have varied and patients with higher disease activity were examined more often, which entails a possible bias. The frequency of condylar alterations in this study was somewhat lower than previously reported for similar patient cohorts [9, 10], and were not related to any clinical or subjective variables, ILAR category or disease activity over the last years. Pedersen et al. , on the other hand, reported that condylar resorption had the highest prevalence in children with JIA of the polyarticular type as judged from panoramic radiographs. The median disease duration in their study was 4.4 years. Also using panoramic radiographs in patients with JIA, Billau et al.  found no relation between condylar lesions, diagnostic category or disease activity after a median disease duration of 2.96 years in agreement with our results.