3D direct-printed shape memory aligners in adult anterior open bite: clinical and biomechanical evidence from a scoping review

Abstract

Anterior open bite (AOB) is a complex malocclusion in adult patients, characterized by limited vertical overlap of the incisors and a high risk of relapse. Clear aligner therapy has gained popularity as a non-surgical treatment modality; however, conventional thermoformed aligners exhibit limitations in achieving predictable vertical tooth movements, particularly incisor extrusion and molar intrusion. To evaluate the current evidence regarding the clinical effectiveness, biomechanical performance, and limitations of 3D direct-printed shape memory polymer (SMP) aligners in the management of AOB in adult patients. This scoping review was conducted in accordance with PRISMA-ScR guidelines and established methodological frameworks. The eligibility criteria included studies involving adult patients or relevant in vitro/experimental investigations evaluating 3D direct-printed aligners and/or shape memory polymer aligners in the management of AOB. Studies on conventional thermoformed aligners without direct-printed or shape memory components, pediatric-only populations, non-relevant outcomes, and non-original publications were excluded. Sources of evidence included PubMed/MEDLINE, Scopus, Web of Science, Embase, and the Cochrane Library, supplemented by manual reference screening. Data charting was performed independently using a predefined data extraction framework, capturing study characteristics, intervention type, biomechanical properties, and clinical outcomes. Findings were synthesized narratively due to heterogeneity of the included evidence. The available evidence, predominantly derived from in vitro and experimental studies, suggests that SMPaligners provide improved force consistency, reduced force decay, and enhanced vertical control compared with conventional thermoformed aligners. Their temperature-dependent shape memory behavior enables sustained, low-magnitude force delivery, which may improve the predictability of incisor extrusion and posterior molar intrusion. Additionally, direct 3D printing enhances aligner fit and allows customization of force systems. However, clinical evidence remains limited, with a lack of randomized controlled trials and long-term outcome data. 3D direct-printed aligners demonstrate promising biomechanical advantages for the treatment of AOB in adults. Nevertheless, their clinical effectiveness and long-term stability remain uncertain due to the predominance of preclinical evidence. Further well-designed clinical studies are required before SMP aligners can be considered a reliable alternative to conventional orthodontic approaches.