Three-dimensional assessment of maxillary changes associated with bone anchored maxillary protraction

Abstract

Introduction: Bone-anchored maxillary protraction has been shown to be an effective treatment modality for the correction of Class III malocclusions. The purpose of this study was to evaluate 3-dimensional changes in the maxilla, the surrounding hard and soft tissues, and the circummaxillary sutures after bone-anchored maxillary protraction treatment.

Methods: Twenty-five consecutive skeletal Class III patients between the ages of 9 and 13 years (mean, 11.10 ± 1.1 years) were treated with Class III intermaxillary elastics and bilateral miniplates (2 in the infrazygomatic crests of the maxilla and 2 in the anterior mandible). Cone-beam computed tomographs were taken before initial loading and 1 year out. Three-dimensional models were generated from the tomographs, registered on the anterior cranial base, superimposed, and analyzed by using color maps.

Results: The maxilla showed a mean forward displacement of 3.7 mm, and the zygomas and the maxillary incisors came forward 3.7 and 4.3 mm, respectively.

Conclusions: This treatment approach produced significant orthopedic changes in the maxilla and the zygomas in growing Class III patients.

Fig 1

Skull illustrating the anatomic locations of the bone anchors.

Fig 2

Intermaxillary elastics to anchors with a bite plate retainer to assist with bite opening.

Fig 3

The isolines, displayed as a black circle or a dot, show the regions with the greatest displacement (positive in red; negative in blue) between the T1 and T2 superimpositions. These isolines measure the closest distance between the superimpositions. The top image shows the isolines representing the regions of greatest outward displacement in the maxilla and zygomas, and the bottom image illustrates the regions with maximum inward displacement.

Fig 4

Box plots of the growth and response to treatment at each anatomic region.

Fig 5

Three-dimensional skeletal color maps of superimpositions of T2 over T1 registered at the anterior cranial base with a scale of –5 to +5 mm. Red represents outward displace of T2 in relation to T1; blue represents inward displacement of T2 in relation to T1.

Fig 6

Lateral views of the skeletal semitransparency superimpositions for 9 patients. T1 models are represented by solid red; superimposed T2 models are shown as semitransparent white mesh.

Fig 7

Frontal views of 3D soft-tissue color maps of superimpositions for 9 patients showing a large range of responses.

Fig 8

Lateral views of the soft-tissue semitransparency superimpositions for 9 patients. Note the range of soft-tissue responses from 1 patient to another.

Fig 9

Distraction of circummaxillary sutures at T2 (red arrows). Note the opening of the zygomaticofrontal, zygomaticotemporal, zygomaticomaxillary, and transverse palatine sutures.