Alça de correção radicular modificada para a verticalização de molares inferiores com intrusão

Abstract

The uprighting of lower molars is a frequently required procedure in orthodontic practice and presents a certain complexity when the molar’s extrusion is not indicated, which happens in most of the cases. A difficulty is to establish a stable and efficient anchorage unit. This study suggests a new uprighting spring called “Modified Root Correction Spring” (MRCS), which has an individualized activation to reach the ideal forces and moments for the uprighting with intrusion. A plaster model and a tomography of a young adult patient who had an inclined second molar was selected. Orthodontic accessories were bonded in the model for evaluation of the forces released by the springs using a dynamometer. The tomography was used to obtain a three-dimensional model for discretization and simulation using the Finite Element Method. Three springs were tested: the Burstone’s Modified Root Correction Spring (with activation indicated by Marcotte), the spring developed by Sander and Wichelhaus, and the MRCS. The tendency of molar uprighting and intrusion was verified in all the springs. The MRCS showed, when compared with the Sander’s Spring, only 40% of top maximum principal stress in the anchorage unit and 58% in relation to the Marcotte´s spring. The activation of the uprighting spring considering the distance between the tooth rotation center and the forces’ line, as done with the MRCS, may present fewer side effects in the anchorage unit, favoring its clinical application and making the use of mini implants not needed in some cases.