Two distalization methods compared in a novel patient-specific finite element analysis

Orthodontic mini-implants aid in the correction of distocclusions via direct anchorage (pull from mini-implant to teeth) and indirect anchorage (teeth pulled against other teeth anchored by the mini-implant). The aim of this study was to compare stress levels on the periodontal ligament (PDL) of maxillary buccal teeth in direct and indirect distalization against orthodontic mini-implants and accounting for individual variation in maxillary anatomy and biomechanical characteristics of the compact bone.

A 3D model of the maxilla containing the different components (teeth, PDL, trabecular and cortical bones) was generated from a computed tomographic scan. Cortical bone was divided into several areas according to previously defined zones. Bone stiffness and thickness data, obtained from 11 and 12 cadavers, respectively, were incorporated into the initial model to simulate the individual cortical bone variation at the different locations. Subsequently, a finite element analysis was used to simulate the distalization modalities.

Stresses at the buccal, palatal, mesial, and distal surfaces were significantly different between adjacent teeth under stiffness but not thickness variation. In both distalization modalities, low or no significant correlations were found between stress values and corresponding cortical bone thicknesses. High significant and inverted correlations were observed at the first molar between stress amounts and cortical bone stiffness (direct modality: -0.68 < r < -0.72; indirect modality: -0.80 < r < -0.82; P <0.05).

With the use of a novel finite element approach that integrated human data on variations in bone properties, findings suggested that cortical bone stiffness may influence tooth movement more than bone thickness. Significant clinical implications could be related to these findings.