Use of a Modified Expander During Rapid Maxillary Expansion in Adults: An In Vitro and Finite Element Study

Purpose: This preliminary study was performed to evaluate a proposed maxillary expansion treatment method for adults with fused intermaxillary sutures. Materials and Methods: This study was performed in three Thiel-fixed skulls from older female cadavers with a microimplant-supported expansion screw. This modified expansion screw was mounted on the palatine process with microimplants and activated every 15 to 20 seconds with an activation key until the intermaxillary suture ruptured. A strain gauge was bonded to the expansion screw and calibrated so it could be used as a force sensor device. Rupture of the intermaxillary suture was indicated by a sudden drop in the registered force, through visible opening of the suture, and via computed tomographic data. Finite element simulations were performed, which led to the experimental testing. Results: Rupture of the intermaxillary suture was achieved in all three experiments with the microimplantsupported screw. The strain measurement on one of the expansion screws resulted in an expansion force of 86 N. Finite element simulations showed a high tensile stress concentration exerted by the microimplantsupported expansion screw on the intermaxillary suture. Conclusion: The applied expansion force led to high tensile stress concentrations, mainly on the intermaxillary sutures, resulting in the opening of fused intermaxillary sutures. This method may help adults to be treated by an orthodontist, thereby avoiding surgical intervention.