An FEM Analysis Comparing the MiRPE and Conventional RPE

Objectives: Orthodontic palatal expansion appliances have been widely used with satisfactory and, most often, predictable clinical results. Recently, clinicians have successfully utilized mini-implants with palatal expander designs to work as anchors to the palate to achieve more efficient skeletal expansion and to decrease undesired dental effects. The purpose of the study was to use Finite Element Method (FEM) to determine the stress distribution and displacement within the craniofacial complex when simulated conventional and mini-implant supported rapid palatal expansion (MiRPE) expansion forces are applied to the maxilla. The simulated stress distribution produced within the palate and maxillary buttresses, in addition to the displacement and rotation of the maxilla could then be analyzed to determine if mini-implants aid in skeletal expansion. 

Methods: A 3-dimensional mesh model of the cranium with associated maxillary sutures was developed using CT images and Mimics modeling software. To compare transverse expansion stresses in RPE and MiRPE, expansion forces were distributed to differing points on the maxilla and evaluated with ANSYS simulation software. 

Results: The stresses distributed from forces applied to the maxillary teeth are distributed mainly along the trajectories of the three maxillary buttresses. In comparison, the MiRPE showed tension and compression directed to the palate, while showing less rotation, and tipping of the maxillary complex. In addition, the conventional hyrax displayed a rotation of the maxilla around the teeth as opposed to the midpalatal suture of the MiRPE. This data suggests that the MiRPE causes the maxilla to bend laterally, while preventing unwanted rotation of the complex.

Conclusions: The MiRPE may be beneficial for hyperdivergent patients, or those that have already experienced closure of the midpalatal suture, who require palatal expansion and would worsen from buccal tipping of the teeth or maxillary complex.