Three-dimensional analysis of maxillary protraction with intermaxillary elastics to miniplates

Abstract

Introduction: Early Class III treatment with reverse-pull headgear generally results in maxillary skeletal protraction but is frequently also accompanied by unfavorable dentoalveolar effects. An alternative treatment with intermaxillary elastics from a temporary anchorage device might permit equivalent favorable skeletal changes without the unwanted dentoalveolar effects.

Methods: Six consecutive patients (3 boys, 3 girls; ages, 10-13 years 3 months) with Class III occlusion and maxillary deficiency were treated by using intermaxillary elastics to titanium miniplates. Cone-beam computed tomography scans taken before and after treatment were used to create 3-dimensional volumetric models that were superimposed on nongrowing structures in the anterior cranial base to determine anatomic changes during treatment.

Results: The effect of the intermaxillary elastic forces was throughout the nasomaxillary structures. All 6 patients showed improvements in the skeletal relationship, primarily through maxillary advancement with little effect on the dentoalveolar units or change in mandibular position.

Conclusions: The use of intermaxillary forces applied to temporary anchorage devices appears to be a promising treatment method.

Fig 1

Modified titanium miniplates used as TADs.

Fig 2

Intermaxillary elastics to customized attachment hooks on modified titanium miniplates.

Fig 3

Segmentation process: defining anatomic boundaries in all 3 planes to create 3D surface model with the open-source ITK-SNAP program.

Fig 4

Three-dimensional superimposition visualization tools. With the color map tool, areas on the red end of the spectrum have positive values of mean surface distance between the T1 and T2 models, and represent surfaces with outward movement. Areas on the blue end of the spectrum have negative values of mean surface distance between the T1 and T2 models, and represent surfaces with inward movement. Areas that are green have little or no change in surface distance between the T1 and T2 models. With the semitransparency tool, the T1 model is solid red, and the superimposed T2 model is a semitransparent gray mesh to allow qualitative assessment of change.

Fig 5

Color maps of 3D superimpositions for all 6 patients.

Fig 6

Semitransparency of 3D superimpositions of all 6 patients. The 3D models have been manipulated so that the maxilla and the mandible are viewed from above.

Fig 7

Color maps of 3D superimpositions for all 6 patients. The 3D models have been manipulated so that the maxilla and the mandible are viewed from the posterior.

Fig 8

Color maps of 3D superimpositions for all 6 patients. The 3D models have been manipulated to view the cranial base and the glenoid fossae from below.

Fig 9

Semitransparency of 3D superimpositions for all 6 patients. The 3D models have been manipulated to view the soft-tissue changes in profile.

Fig 10

Location of the miniplate relative to the zygomaticomaxillary suture. Note that this figure is only for visualization purposes as this is a skull of an adult, and the anatomic contour of the zygomatic process of the maxilla changes with age.