Anchorage loss evaluation during maxillary molars distalization performed by clear aligners

Maxillary molar distalization is one of the most common strategies to correct Class II molar relationship and it is commonly indicated for patients with maxillary dentoalveolar protrusion or minor skeletal discrepancies. Over time, there have been many types of appliances used for this therapeutic purpose. Cervical headgear has been reported to be effective in maxillary molar distalization and for maxillary growth restriction, with dental movements that are achievable in all planes of space (Cangialosi 1988, Freitas 2008 – Mossaz 2007). However, studies on Class II treatment with cervical headgear combined or not with fixed appliances have shown a postero-inferior redirection of maxillary growth, anterior downward tipping of the palatal plane, opening of the bite, an increase in anterior face height, and downward and backward rotation of the mandible (Freitas 2008, Kim 2001, Schiavon Gandini 2001, Lima 2003). Moreover, this method of Class II correction depends greatly on patient cooperation. To avoid unpredictable results because of varying patient compliance, Hilgers introduced the Pendulum appliance in 1992 (Hilgers 1992). Despite its efficacy for maxillary molar distalization, there are side-effects including increase in lower face height, clockwise mandibular rotation, and extrusion of first premolars (Ghosh 1996, Byloff 1997, Bussick 2000). More recently, an increase in demand for aesthetic, minimally invasive, and more comfortable orthodontic solutions has been seen in adults and growing subjects. Therefore, the orthodontic treatment with removable clear aligners has become a competitive and more hygienic alternative to conventional appliances (Miller 2009). Clear aligners are used for maxillary distalization movement with the advantage of planning the molar backward movement and teeth alignment simultaneously, thus reducing treatment duration (Kravitz 2009). Several articles (Ravera 2016, Simon 2014, Rossini 2015) in the literature analyzed the molar distalization performed by clear aligners treatment, reporting predictable distalization movement up to 3 mm. However, as clear aligners uses dental anchorage, undesirable effects can happen in the same way as with conventional intraoral appliances. Very few studies analyzed the anchorage loss obtained during the upper-molar distalization movement with clear aligners, mainly evaluating this side effect at the end of treatment and none of previous studies observed the anchorage loss at the level of upper premolars and canines at the end of the upper first molar distalization before the retraction of the anterior segment. Therefore, the present retrospective study aims to analyze, using three dimensional (3D) digital casts, the premolar and canine anchorage loss occurring during maxillary molar distalization in young adults presenting with Class II occlusal relationship treated by clear aligners treatment