## 4 Discussion  
The present study investigated parameters assessed by clinical head and neck muscle palpation and instrumental examinations by sEMG and kinesography in the evaluation of TMJ involvement in patients with JIA. These tools do not replace the gold standard of diagnosis, which remains nuclear magnetic resonance imaging (MRI) [41], but may help clinicians to identify patients at higher risk of TMJ involvement and those who are more likely to benefit from screening or early therapeutic intervention [42; 43; 44]. Muscle palpation, sEMG and kinesography can therefore be considered functional indicators of muscle activity and jaw movements since they show the tendency to support experimental hypotheses. The presence, however, of statistically significant parameters confirms the possibility of demonstrating the validity of these diagnostic aids. Muscle palpation analysis (Table 2) showed a statistically significant difference between the JIA group and the control group in the MM and SCM evaluation on both sides (\(p<0.05\)) and in the TA only on the right side (\(p<0.05\)). Pain on palpation of the orofacial regions is one of the clinical signs detected by a task force investigating clinical orofacial examination in JIA [24], in agreement with the results of our study. These results indicate that there is higher pain in the masticatory and neck muscles in the JIA group compared to healthy controls [45; 46]. Due to condylar erosion, masticatory muscles force the mandibular bone to rotate backwards with respect to the anterior skull base, thus generating dentoalveolar deformities. This might cause an overload of the masticatory muscles (which become painful on palpation) and of the joint structures, leading to muscle imbalances and possible intracapsular disorders. On the left TA, higher pain was recorded in the JIA group compared to the control group; statistical significance, however, was lacking, probably due to the low sample size. Another explanation of these results might be found in the prevalence of jaw deviation on the right side observed in the JIA group, where, indeed, 29 out of 32 JIA subjects showed jaw deviation towards the right side. Finally, the significant results found in SCM highlight the link existing between chewing muscles and neck muscles and therefore the need to take into consideration the involvement of neck muscles in addition to chewing muscles in patients with JIA [47]. Statistical analysis of sEMG data showed a positive correlation between the pathological ratio (MM/TA \(<1\)) and JIA, with an \(\chi^{2}\) value of 2.006 (Table 4). However, since this correlation was present, but it was not statistically significant (\(p=0.157\)), frequencies in terms of percentage were calculated. A higher frequency of the pathological ratio (MM\(\backslash\)TA \(<1\)) in the test group (65.2%) compared with the control group (53%) was observed. The prevalence of the pathological ratio in the group of patients indicates that JIA subjects showed an incorrect function of the masticatory muscle system. The masticatory muscle alteration observed in sEMG data confirmed the results extracted from palpation, where greater pain was observed in the JIA group. The progressive erosion suffered by TMJ structures in JIA patients involves masticatory muscles which must readapt the masticatory pattern to ensure the function of the stomatognathic system. This adaptation leads to muscle dysfunction and pain, as shown by sEMG and muscle palpation data. It is therefore reasonable to assume that if no intervention on the stomatognathic system is performed, muscle alteration and pain could progressively become worse as the erosion on TMJ structures continues [48; 49; 50]. Kinesiographic statistical analysis (Table 5) showed a statistically significant difference both in the maximum mouth opening width and jaw deviation at maximum mouth opening between cases and controls. Regarding mouth opening, the results of the present work disagree with a previous study by [PERSON] et al.