A new removable connecting device for MARPE expander with non-common path of insertion

Maxillary transverse deficiency is a common malocclusion frequently observed in orthodontic clinics. Miniscrew-assisted rapid palatal expansion (MARPE) not only produces greater skeletal expansion but also offers advantages such as simple miniscrew implantation without flap elevation, enhanced patient comfort, and an expanded age range and indications for palatal expansion. However, the fixed connection between the expander and the miniscrews makes the expander difficult to remove, significantly hindering its clinical application. This study aims to employ a non-common path of insertion connection device-comprising 3D-printed miniscrew caps and silk fibroin (SF) electrospun membranes-to optimize the clinical operation of non-co-located MARPE in orthodontic expansion.

The removable connection device for non-common path of insertion MARPE consists of 3D-printed miniscrew caps and SF electrospun membranes. First, the miniscrew cap was measured using reverse engineering software (Geomagic Wrap) to generate optimal fit data, and designed with the 3D creation program Cinema4D to form an internal cylinder and an external protective ring, with the design saved as a STL file. The data were then imported into Voxelddance Tango software to design a virtual base scaffold, and the cap was fabricated using a 3D printer. Subsequently, SF and polyethylene oxide (PEO) were electrospun at various mass ratios to form SF electrospun membranes. The morphology was observed using scanning electron microscope (SEM), and Fourier-transform infrared (FTIR) spectroscopy was used to analyze the secondary structural conformation of both the miniscrew cap and the SF electrospun membranes. Tensile and compression tests were conducted to evaluate their mechanical properties, and the sealing performance of the removable connection device (with and without the SF electrospun membrane) was compared. In addition, cell compatibility was assessed by co-culturing the miniscrew caps and SF electrospun membranes with mouse embryonic fibroblasts (NIH 3T3), using a live/dead cell staining kit and the cell counting kit-8 (CCK-8). Finally, a 13-year-old male patient at palatal suture stage D was selected. Pre-implantation cone beam computed tomography (CBCT) measured the palatal soft and hard tissue thickness at the planned insertion site, and 2 miniscrews were implanted at the optimal bone density site between the second premolar and the first molar. An intraoral scan model was used to integrate teeth 13 and 23 into a tooth-bone hybrid-supported expander, which was customized. The miniscrew caps were trial-fitted, and the expander was adjusted until it fitted perfectly without interference. The expander was then bonded, with the SF electrospun membrane wrapped around and covering the miniscrews, and the miniscrew cap applied. Light-cured resin was used to connect the expander and the miniscrew caps. The patient was instructed to perform expansion once daily for a total of 28 sessions, with close monitoring of the expansion process to obtain pre- and post-expansion data and assess expansion efficacy.

The friction force and load pressure of the miniscrew caps were (54.7±9.57) N and (148.61±15.29) N, respectively. Among SF electrospun membranes prepared with 10%, 20%, and 30% PEO, the 20% PEO membrane exhibited the most uniform fiber diameter and the most continuous, stable electrospinning process. Degradation experiments revealed no significant weight changes for all SF electrospun membranes at days 1, 3, and 7. FTIR analysis showed that all membranes exhibited similar characteristic bands; thus, the 20% PEO SF electrospun membrane was selected for further study. Under wet conditions, the maximum tensile stress of the 20% PEO membrane was (2.46±0.26) N. In in vitro simulations, both macroscopic observations and SEM showed excellent sealing between the miniscrew caps and the electrospun membranes. NIH 3T3 cells co-cultured with the SF membrane and miniscrew caps, when stained with a live/dead assay, exhibited typical fibroblast morphology and high viability. CCK-8 results showed that by day 3, cell viability in the SF membrane group reached 111.46%, suggesting an increasing trend in cell activity. Finally, in a 13-year-old male patient at palatal suture stage D, after non-common path of insertion MARPE with the removable connection device, a 2.5 mm gap was observed between teeth 11 and 21. Six months later, CBCT re-examination showed significant widening of the palatal suture, confirming successful expansion.

The removable connection device for non-common path of insertion MARPE demonstrates excellent mechanical properties and biocompatibility, effectively opening the palatal suture at stage D. With its simple operation and promising clinical application prospects, this device offers an optimized approach for orthodontic palatal expansion.