Distalizing mandibular molars may be indicated for patients with minor skeletal Class III discrepancies or in Class III subjects with mild crowding. Traditionally, mandibular molar distalization was accomplished using elastics, open coils, and the multiloop edgewise archwire technique. In recent years, several techniques have been developed to reduce the dependence on patient compliance, such as skeletal anchorage. Recently, several reports have been published on mandibular distal movement using miniscrews and some case reports have shown the possibility of obtaining Class III correction with sequential mandibular distalization in non-growing subjects by means of clear aligners. However, a sound clinical judgment should always be made on the basis of a higher level of evidence. Therefore, the purpose of the present prospective study is to provide a detailed analysis of the underlying skeletal and dental changes determined by mandibular distalization therapy with the sequential Invisalign protocol in permanent dentition. This will be accomplished by testing the following null hypothesis: mandibular molar distalization is not achievable with aligners without the application of TADs.

Class III malocclusion is considered one of the most challenging maxillofacial disorders in clinical practice characterized by an antero-posterior discrepancy with mandibular protrusion, maxillary retrusion, or a combination of both. In adult patients, managing this condition is further complicated by the absence of residual skeletal growth, limiting therapeutic options to orthodontic interventions and, in some cases, surgical procedures. Diagnosis in Class III adult patients requires distinguishing between skeletal malocclusion and dento-alveolar discrepancy. The combination of orthognathic surgery and orthodontic therapy represents the gold standard for more severe skeletal Class III disharmonies, leading to an improvement of both function and aesthetics. On the other hand, in Class III cases characterized by a prevalent dental component or mild skeletal discrepancy, the malocclusion can be addressed with a dento-alveolar compensation. In these cases, the clinical objectives are to achieve a correct sagittal, canine and molar Class I relationship, as well as ideal values of overjet and overbite. The non-surgical orthopedic approach involves the application of Class III elastics or the distalization of the lower molars, which can improve the sagittal occlusal relationship. As a matter of fact, mandibular distalization allows the increase of lower arch length along with the achievement of the necessary space to correct a Class III relationship. However, bone density and root anatomy make lower molar distalization difficult to achieve. In addition, one of the most frequent adverse effects is represented by the anterior anchorage loss with a worsening of lower incisor proclination and overjet values. Traditional appliances feature the use of open coil springs, inter arch elastics, and lip bumper device combined with fixed appliances. Nowadays, the development of clear aligner technology provides new opportunities even in the management of complex malocclusion cases, including Class III discrepancies. In particular, molar distalization movements and intermaxillary elastics have been proposed as a valid clinical strategy to improve the occlusal relationship without requiring skeletal anchorage devices. During the sagittal mechanics, over-corrected movements should be planned in order to obtain more bodily movements of the lower molars. Moreover, the best accuracy and predictability of distalization movements are supported by the sequential staging and the presence of attachments on the tooth surfaces. Nowadays, scientific evidence on this topic is limited and it is influenced by restrictions in terms of sample size, retrospective design, and lack of long-term observation. Hence, the aim of the present study was to evaluate the efficacy and efficiency of intermaxillary elastics combined with lower molar distalization by means of clear aligners in the treatment of Class III malocclusion in adult patients. More specifically, a randomized controlled trial (RCT) was conducted to evaluate the antero-posterior correction induced by Class III elastics combined with lower distalization movements and the application of Class III elastics alone. The possibility of achieving satisfying clinical outcomes without the use of skeletal anchorage was considered to avoid an invasive orthodontic approach

Inclusion Criteria:

• adult age (≥19 years)
• permanent dentition including second permanent molars
• skeletal Class I or slight Class III (-2° < ANB < +2°)
• normal skeletal divergency pattern (SN^GoGn, 27°-37°)
• Class III canine and molar relationship at baseline (T0), moderate lower arch crowding (≤ +4 mm)
• good compliance with aligners and elastics (≥ 20 hours/day)

Exclusion Criteria:

• severe skeletal Class III malocclusion (ANB < -2°)
• transversal maxillary deficiency
• use of Temporary Anchorage Devices (TADs)
• extraction treatments other than third molars
• periodontal disease or temporomandibular disorders (TMDs).