Three-dimensional analysis of maxillary changes associated with facemask and rapid maxillary expansion compared with bone anchored maxillary protraction

Abstract

Introduction: Our objectives in this study were to evaluate in 3 dimensions the growth and treatment effects on the midface and the maxillary dentition produced by facemask therapy in association with rapid maxillary expansion (RME/FM) compared with bone-anchored maxillary protraction (BAMP).

Methods: Forty-six patients with Class III malocclusion were treated with either RME/FM (n = 21) or BAMP (n = 25). Three-dimensional models generated from cone-beam computed tomographic scans, taken before and after approximately 1 year of treatment, were registered on the anterior cranial base and measured using color-coded maps and semitransparent overlays.

Results: The skeletal changes in the maxilla and the right and left zygomas were on average 2.6 mm in the RME/FM group and 3.7 mm in the BAMP group; these were different statistically. Seven RME/FM patients and 4 BAMP patients had a predominantly vertical displacement of the maxilla. The dental changes at the maxillary incisors were on average 3.2 mm in the RME/FM group and 4.3 mm in the BAMP group. Ten RME/FM patients had greater dental compensations than skeletal changes.

Conclusions: This 3-dimensional study shows that orthopedic changes can be obtained with both RME/FM and BAMP treatments, with protraction of the maxilla and the zygomas. Approximately half of the RME/FM patients had greater dental than skeletal changes, and a third of the RME/FM compared with 17% of the BAMP patients had a predominantly vertical maxillary displacement.

Fig 1

Hyrax-type rapid palatal expander with added hooks to receive the protraction elastics: A, before expansion; B, after expansion.

Fig 2

A, FM constructed individually for each patient; B, lateral cephalogram showing the direction of traction.

Fig 3

Intraoral photograph showing the direction of elastic traction with BAMP. The elastic force is delivered directly to the underlying bone, not to the teeth.

Fig 4

RME/FM compared with BAMP changes: frontal view of 3D skeletal color maps of superimpositions of patients treated with RME/FM or BAMP. T2 surface models that were registered on the T1 anterior cranial base display the surface distance color maps with a color code scale of −5 to +5 mm. Red represents outward displacements of the T2 skeletal surfaces in relation to T1; blue represents inward displacements of T2 in relation to T1; green indicates little or no change.

Fig 5

RME/FME changes: lateral view of skeletal changes in 3D superimpositions of patients treated with RME/FM. T2 surface models registered on the T1 anterior cranial base display the surface distance color maps with a similar color code scale as described in Figure 4.

Fig 6

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

Fig 7

Box plots of the growth and response to treatment at each anatomic region for the RME/FM and BAMP groups.

Fig 8

Close-up views of skeletal changes for an RME/FM patient evaluated in the study. The semitransparencies and color maps, respectively, display and quantify the notable forward orthopedic traction, as well as the expansion of the maxilla and the zygomatic bones, and the downward and forward growth of the mandible.

Fig 9

Another example of close-up views of an RME/FM patient with marked forward maxillary protraction: the mandible grew downward and slightly backward.

Fig 10

Example of an RME/FM patient with marked vertical rotation of the maxillary complex and consequently greater vertical displacement of the mandible.

Fig 11

Late mixed dentition patient at cervical vertebral maturation stage 3 at the start of treatment who still demonstrated orthopedic correction of the maxilla after treatment. The T1 and T2 models are registered on the cranial base, and only close-up views are shown to visualize the maxillary displacement in more detail. The mandible was open slightly in the T1 CBCT image; thus, no conclusions can be made concerning the mandibular response, but the profile changes and the maxillary protraction still can be visualized.