## 1 Introduction  
Juvenile idiopathic arthritis (JIA) is characterized by the onset of arthritis of an unknown etiology before the age of 16 that persists for longer than a six-week duration. JIA is the most common rheumatic disease of childhood [1, 2, 3]. The progression and course of disease in JIA is unpredictable. It is self-limiting in some patients while in other circumstances it can be persistent with joint resorption. Depending on the timing of onset and severity of disease, JIA may cause growth disturbances, permanent joint damage, functional limitations, and short- or long-term disability [4]. The temporomandibular joint (TMJ) is one of the more frequently involved synovial joints in JIA patients and in some cases may be the only joint involved [5; 6]. The TMJ is affected in 30-45% of JIA patients, with all JIA subtypes at risk for TMJ involvement [7; 8]. Despite the high percentage of JIA patients that have TMJ arthritis and a high prevalence of associated morbidity, TMJ arthritis is an underdiagnosed component of JIA [9]. This is due in part to the challenges associated with traditional radiography and clinical examination of the TMJ, as well as the fact that TMJ symptoms are frequently absent or unreliable [9; 10; 11; 12]. Even with radiographic evidence of condylar lesions, a significant percentage of JIA patients do not report any TMJ symptoms and may have a benign clinical TMJ examination [5; 13; 14]. Despite these challenges, early diagnosis and treatment of TMJ arthritis is critical, as the risk of craniofacial growth alterations is thought to increase in cases of earlier age of onset and results in longer duration of disease activity [9; 15]. As TMJ involvement may be present without any clinical signs or symptoms, MRI is the gold standard for diagnosis of TMJ involvement [14]. This imaging technique is capable of detecting 63-91% of inflammatory changes, ranging from active arthritic changes as well as the sequelae of chronic arthritis [10]. Higher percentages of TMJ involvement are found when Gadolinium-enhanced magnetic resonance imaging (Gd-MRI) is employed, compared to ultrasound, computed tomography (CT), cone-beam-computed tomography (CBCT), or traditional radiography (i.e., panoramic radiographs) [5; 11; 16; 17; 18]. The anatomy of the TMJ makes it particularly susceptible to damage from arthritis [5]. Unlike other synovial joints, the primary center for mandibular growth is the mandibular condylar cartilage that lies under a thin layer of fibrocartilage on the head of the condyle [5]. Due to its superficial position, it is susceptible to damage or resorption in the presence of chronic inflammation of the TMJ, and subsequently, TMJ arthritis may have destructive effects on the growth of the mandible [19; 20]. JIA patients with TMJ involvement may present with altered craniofacial morphology, including micrognathia, mandibular retrognathism, decreased total mandibular length, decreased posterior face heights, increased anterior face heights, skeletal anterior open bite, posterior mandibular rotation with hyperdivergent mandibular plane angle and occlusal plane angle, obtuse gonal angle, gonal noticing, convex facial profile, and facial asymmetry with chin deviation in cases of unilateral joint destruction [5; 6; 13; 15; 21; 22; 23; 24; 25; 26; 27]. In one study, retrognathia was seen in 82% of JIA patients that had TMJ involvement diagnosed using the panoramic radiograph but was also seen in 55% of patients that did not show any signs of radiographic TMJ involvement. Those patients who did have TMJ involvement had a cephalometric A point-nasion-B point (ANB) angle that averaged 1.8 degrees greater than those without TMJ involvement [6]. It has been shown that even a small degree of condylar damage can be associated with significant alterations in craniofacial morphology [13]. In recent years, CBCT has become a commonly used imaging modality in dentistry and orthodontics.