A wide range of functional appliances have been designed across the years to obtain a supplementary growth of the mandible by its forward posturing to correct mandibular retrusion. In a review published by Cozza et al., the efficiency of functional appliances used in healthy humans in terms of supplementary growth of the mandible per month of treatment, was measured. The Herbst appliance had the highest coefficient of efficiency (0.28 mm per month) followed by the Twin-block device (0.23 mm per month).~Different authors claimed that functional treatment by removable appliances may be effective in treating Class II malocclusion with clinically relevant skeletal effects if performed during the pubertal growth phase. However, the growth pattern in JIA patients is more complicated and difficult compared to the treatment groups in the above-mentioned studies. The pattern is not only characterized by a decrease in mandibular length, but also by a decreased ratio between the posterior and the anterior face height, due to a failure in the vertical growth of the condyles The favorable effect of functional orthopedic appliances in JIA cases is therefore, besides advancing the mandible, an anterior (counter clockwise) rotation with a possible increase of the posterior face height, if possible. The efficacy of the functional orthopedic appliance in the correction of open bite has been demonstrated by Ibitayo et al.~To date, different types of removable orthopedic appliances have been proposed into the scientific literature for management of deformities in skeletally immature patients with JIA, in particular the activator and the distraction splint. Although functional orthopedic treatment is recommended, literature is still lacking studies on this important topic.~Recently a mandibular advancement device (MA) was implemented by Align TechnologyTM (San José, CA, USA) on clear aligners, for the treatment of skeletal Class II in growing patients. Similarly, to the principle applied in Twin Block, MA is composed by two pairs of lateral inclined planes (precision wings), positioned buccally in the posterior area of aligners, which come into contact each time the patient closes his mouth determining a mandibular forward position.~Regarding the above-mentioned novel therapeutic approach, accurate bibliographic research performed on June 2022 showed that, the scientific literature needs further studies evaluating the skeletal effects produced by the Mandibular advancement with clear aligner since there is limited literature on its efficiency, consisting mostly of case studies. Recent longitudinal studies reported very promising results, when used in the pubertal growth phase. The short-term effects of Mandibular Advancement feature are dento-skeletal with additional growth of the mandible and improvement in facial convexity. The MA clear aligner treatment in JIA patients could bring countless benefits. The main ones are the possibility of performing a class II functional therapy with the same ability of a distraction splint or activators in promoting mandibular growth and at the same time controlling the vertical dimension with a programmed intrusion/extrusion of the teeth. Moreover, these therapeutic approaches should be more aesthetic, less bulky, and annoying appliances which can therefore guarantee greater collaboration from the patient. The latter would be reinforced by the fact that during functional therapy there would be a concomitant dental alignment with positive implications in patients whose facial aesthetics are already partially compromised, the face is one of the most salient and relevant social stimuli humans encounter and automatically evokes neural responses, facial deformity must not be underestimated. Moreover, clear aligner therapy is associated with minimal adverse events related to the periodontal structures compared to fixed appliances, this is of relevant interest in JIA subjects who often suffer from moderate or severe periodontitis.
There is currently no information on how mandibular advancement therapy could influence three-dimensionally the condylar and mandibular morphology in growing patients affected by Juvenile Idiopathic Arthritis (JIA). Therefore, the aim is to assess the three-dimensional morphological mandibular changes produced by the Invisalign® Mandibular Advancement (MA) (Align Technology, San José, CA, USA) in growing subjects affected by juvenile idiopathic arthritis with unilateral and bilateral JIA and to compare them with not-JIA control subjects