Vertical Effects in Class II Patients Treated With Distalization: Comparison Between Multibracket Conventional Therapy and Clear Aligners

Class II malocclusion presents a major and common challenge to orthodontists. Treatment of Class II malocclusion is one of the most investigated and controversial issues in contemporary orthodontics because of the extensive variability of treatment strategies addressing the morphological characteristics of this malocclusion. The therapeutic approaches include tooth extractions, orthopedic appliances and extraoral or intraoral distalizing appliances. 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. One of the most used devices is Pendulum appliance, introducted by Hilgers in 1992. It is a tooth-tissue-borne appliance that includes a Nance button on the palate for intraoral anchorage and titanium-molybdenum coils that deliver a mild and continuous force to the maxillary molars. Despite its efficacy for maxillary molar distalization, there are side-effects, including labial/mesial tipping and protrusion of the maxillary incisors and premolars, distal tipping of the maxillary molars, increase in lower anterior face height, clockwise mandibular rotation, and extrusion of the first premolars. Consequently, these side-effects have to be corrected during the following fixed appliance treatment phase.

In the last decades, the orthodontic treatment with removable clear aligners has become an increasing common choice because of the growing number of adult patients who ask for aesthetic and comfortable alternatives to conventional fixed appliances.

In 1997, Align Technology (Santa Clara, Calif) adapted and incorporated modern technologies to introduce the clear aligner treatment (CAT). Only few investigations have focused on the predictability of orthodontic tooth movement with CAT. A systematic review by Rossini et al. pointed out that among the dental movements analyzed in 11 studies, the bodily distalization was the most predictable.

Simon et al. reported a high accuracy (88%) of the bodily movement of upper molars with aligners when a mean distalization movement of 2.7 mm was prescribed. The authors reported the best accuracy when the movement was supported by the presence of an attachment on the tooth surface. Furthermore, they underlined the importance of staging in the treatment predictability.

Ravera et al. showed that clear aligners are effective in distalizing maxillary molars in non-growing subjects without significant vertical and mesiodistal tipping movements. The authors reported that the lower facial height did not change at the end of the treatment. Therefore, clinicians can consider the use of aligners in treatment planning for adult patients requiring 2 to 3 mm of maxillary molar distalization.