Analysis of skeletal anchored palatal expansion devices in the adult patient

Background: Miniscrew assisted rapid palatal expansion (MARPE) has become a viable option to correct maxillary transversal deficiency in late adolescent and adult patients. The aim of my Ph.D. is to analyze the device-related variables of skeletal anchored palatal expanders by evaluating the stress generated and the number of activations required before deformation or failure across various configurations of reinforced orthodontic expansion screws, connection arms, and OMIs (mini orthodontic implants) through an in vitro investigation. This research aims to assess the current state of the art from an engineering perspective, identify device weaknesses, and optimize its design and components. Furthermore, the study seeks to develop a 3D-printed, sensor-equipped prototype capable of evaluating and comparing future palatal expansion devices by measuring the stress exerted on circum-maxillary sutures, thereby determining their effectiveness. Materials/Methods: This research project provided a comprehensive investigation into the mechanical performance and structural behavior of MARPE (Miniscrew-Assisted Rapid Palatal Expansion) devices for transverse maxillary expansion in adult patients. Through a tripartite experimental approach—compression testing, primary stability analysis, and sensor-integrated 3D-printed modeling—the influence of specific design parameters on clinical outcomes was systematically evaluated. The expansion screws analyzed are produced by the Leone, HDC and Tiger Dental companies for skeletal-anchored expanders. Results and discussion: Compression tests demonstrated that device configuration has a critical impact on the magnitude of forces generated. Expansion screws combined with custom-designed, straight connection arms—produced via 3D laser melting and precision laser welding— exhibited superior structural rigidity and delivered higher force values compared to devices with bent arms. Some configurations exceeded 500 N, well above the clinically relevant threshold of 120 N for midpalatal suture separation in post-adolescent patients. Nevertheless, such high forces may not be clinically desirable, as gradual and controlled loading is preferable to prevent tissue damage and device failure. Primary stability testing revealed that the distance between expansion screw and miniscrew anchorage significantly affects force transmission to the skeletal complex. A reduced distance was shown to improve mechanical stability, especially in cases of low bone density. Bone quality—particularly cortical thickness and medullary density—also played a key role in determining overall stability. The sensor-integrated 3D-printed models enabled both qualitative and quantitative evaluation of stress propagation at the cranio-maxillary sutures. These results reinforced findings from the mechanical tests: devices incorporating robust expansion screws and custom-designed arms showed superior force distribution. Variability in stress localization was observed depending on device geometry, TAD positioning, and anatomical simulation conditions. Conclusions: The project highlighted the critical role of engineering-driven design in optimizing MARPE performance. Key determinants included material selection, manufacturing processes (e.g., laser melting), the geometry of connection arms, and digitally guided TAD insertion protocols. These factors collectively influence the predictability and efficiency of orthopedic expansion in adult patients. The findings of this study lay the groundwork for future optimization of MARPE appliances and support the development of fully customized, digitally planned expansion systems validated through biomechanical simulation and empirical testing. Clinically, these insights provide a solid foundation for the informed selection of devices and protocols, improving therapeutic outcomes and patient safety. Limitations: This is an in vitro study and only some configurations and component elements of MARPE devices were analyzed.