Affidabilità delle sovrapposizioni trimensionali nel trattamento distalizzante dei molari superiori

Objectives

The aim of the study was to establish an easy method to obtain three-dimensional superimposition of Cone Beam tomographies on stable anatomical landmarks in growing patients.

Materials and methods

Two patients in Class II molar relationship were selected and subjected to the tomographic exam before and immediately after the distalization of the first upper molars with two different appliances: the Hilgers’ Pendulum and the MGBM System. The results were compared with bidimensional superimposition, done with two methods: the “Best Fit” and the structural method by Bjork. The exam consists in a Cone Beam tomography at low radiation dose with the ILUMATM tomography machine, set at 0.3 mm³ voxel dimension. The realization process was divided in three steps. The first is the image orientation, in order to orient each volume at the same position. The second step is the volume segmentation, to reconstruct the three-dimensional images of every anatomical structure that will be superimposed. The last process is the localization of the same landmarks on the two volumes.

Results

The result obtained by the superimposition method proposed may be considered acceptable since the variation between the two volumes corresponds to the dental and skeletal changes induced by treatment with the appliances used. Further confirmation comes from the comparison with the two-dimensional superimposition. The final result is not completed because it cannot be used to quantify the extent of growth or displacement induced by treatment. The comparison with the two-dimensional superimposition has also highlighted the limitations of the conventional teleradiography and the great advantage of the CBCT. The teleradiography has some basical errors that do not permit an accurate and unique landmarks localitazion. CBCT, instead, allow to evaluate every anatomical structure at 360° with no images superimposition and no magnification, the sagittal and vertical variations in the two different patient's sides, the condilar position and the dental root position in the alveolar bone.

Conclusions

The progress is trying to convert all the diagnostic tools in three-dimensions and this method can be a starting point to create a system accessible to all the orthodontists.