Effectiveness of Clear Aligner Therapy in Maxillary Molar Distalization for Class II Malocclusion: A Systematic Review of Clinical Studies

Abstract

Aim: Addressing skeletal Class II (CII) malocclusion often involves molar distal movement (Dx). While traditional methods like headgear face challenges related to patient compliance, clear aligner therapy (CAT) is considered an appealing alternative, although its effectiveness in molar Dx is an ongoing study area. This systematic review (SR) seeks to review the recent studies on the efficacy of CAT for effecting molar Dx. The aim of this SR was to assess the effectiveness of CAT in achieving molar Dxs in individuals with sagittal CII malocclusion.

Materials and methods: A comprehensive search in five electronic databases (Scopus, PubMed, Google Scholar, Cochrane, and Web of Science) for relevant articles till December 2023 was performed. The population, intervention, comparision, outcome and study design criteria included subjects with CII malocclusion intervened with CAT, the control was no treatment or fixed appliance therapy using traditional methods of molar distalization, and the outcomes assessed were molar Dx, achieved vs. predicted movements, molar tipping, and rotation. Only prospective trials, retrospective studies, randomized controlled trials (RCTs), and controlled clinical trials were included. The principal measure of Dx was millimeters. The risk of bias (ROB) assessment of the included studies was conducted using the Newcastle-Ottawa scale and ROBINS-I tool. Preferred reporting items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines were adopted for data reporting and synthesis. The SR was registered in the PROSPERO database (registration number CRD42024531205).

Results: Out of 547 studies identified, 11 papers were included in the present SR. Eight of them were retrospective, and three were prospective studies. The sample size ranged from a minimum of seven to 49 patients. A total of 278 patients were assessed in all the studies. Invisalign^® system CA was used in all studies. Five studies reported predicted vs. achieved tooth movements. Two studies reported the use of attachments, and one study reported the use of microimplants for preventing anchorage loss along with Class I elastics. Dx ranged from 0.67 ± 0.5 mm to 2.54 ± 0.12 mm. When compared to the predicted Dx, the achieved Dx for M6 was 36.48-75.5%; for M7, it was 41.94-72.2%, and the accuracy of derotation of molars was 62.7-77.5%. Quantitative analysis could not be performed owing to the heterogeneity in the included studies. Six included studies had a low ROB, and two of them had a moderate ROB. Three studies were ranked low quality on the Newcastle-Ottawa scale. The strength of evidence for the included studies was judged as moderate on assessment with the Agency for Healthcare Research and Quality criteria.

Conclusion: The available moderate-quality evidence suggests that CAT can achieve molar Dx up to 2 mm with good accuracy. However, the included studies were mainly retrospective with lesser samples without adequate controls; also, there was a wide variation in measurement methods and evaluation times. Well-designed RCTs are required to validate these findings and provide more robust evidence.

Keywords: CAT; Class II malocclusion; Class II molar; clear aligner therapy; distalization; molar distal movements; orthodontic aligners.