UCLA

Objectives: The purpose of this study was to use Finite Element Method (FEM) to simulate various clinical protocols for maxillary protraction with micro-implants, which can provide skeletal changes without the use of surgery. We aim to analyze how location and direction force alters the skeletal effect. Analysis of the skeletal effects can be used to improve clinical protocols for treating class III patients.

Methods: A 3-dimensional cranial mesh model with associated maxillary sutures was developed from CT images and Mimics modeling software. Utilizing ANSYS simulation software, protraction forces were applied at different locations and directions to simulate conventional facemask therapy; seven different maxillary protraction protocols utilizing micro-implants. Stress distribution and displacement were analyzed. Video animations and superimpositions were created to illustrate the skeletal effect from varying location and direction of force application.

Results: Conventional facemask and facemask from anterior micro-implants at 15� below and 30� above the occlusal plane result in counter-clockwise rotation of the maxillary complex. In contrast, maxillary protraction at 45� below the occlusal plane with anterior or posterior micro-implants displayed clockwise rotation of the maxilla. At 30� below the occlusal plane, Facemask with palatal or anterior micro-implants translated the maxilla downward and forward, while protraction from posterior micro-implants closely resembled pure anterior protraction of the maxilla. Facemask without micro-implants resulted in higher internal stresses, suggesting force dissipation to bone rather than to the sutures.

Conclusion: Location of micro-implant placement and direction of pull altered the skeletal response, changing the upward or downward displacement of the maxillary complex, maxillary incisor upward or downward movement, and amount of protraction. Brachyfacial class III patients with a deep bite would benefit from counter-clockwise rotation of the maxilla, resulting in bite opening. Dolicofacial patients with open bite tendency require protraction that minimizes maxillary downward movement. As a result, class III growth modification treatment with micro-implants can be customized for each patient to maximize clinical effectiveness.