Three-dimensional assessment of mandibular and glenoid fossa changes after bone-anchored Class III intermaxillary traction

Abstract

Introduction: Conventional treatment for young Class III patients involves extraoral devices designed to either protract the maxilla or restrain mandibular growth. The use of skeletal anchorage offers a promising alternative to obtain orthopedic results with fewer dental compensations. Our aim was to evaluate 3-dimensional changes in the mandibles and the glenoid fossae of Class III patients treated with bone-anchored maxillary protraction.

Methods: Twenty-five consecutive skeletal Class III patients between the ages of 9 and 13 years (mean age, 11.10 ± 1.1 year) were treated with Class III intermaxillary elastics and bilateral miniplates (2 in the infrazygomatic crests of the maxilla and 2 in the anterior mandible). The patients had cone-beam computed tomography images taken before initial loading and at the end of active treatment. Three-dimensional models were generated from these images, registered on the anterior cranial base, and analyzed by using color maps.

Results: Posterior displacement of the mandible at the end of treatment was observed in all subjects (posterior ramus: mean, 2.74 ± 1.36 mm; condyles: mean, 2.07 ± 1.16 mm; chin: mean, -0.13 ± 2.89 mm). Remodeling of the glenoid fossa at the anterior eminence (mean, 1.38 ± 1.03 mm) and bone resorption at the posterior wall (mean, -1.34 ± 0.6 mm) were observed in most patients.

Conclusions: This new treatment approach offers a promising alternative to restrain mandibular growth for Class III patients with a component of mandibular prognathism or to compensate for maxillary deficiency in patients with hypoplasia of the midface. Future studies with long-term follow-up and comparisons with facemask and chincup therapies are needed to better understand the treatment effects.

Fig 1

Elastics are fixed for 24 hours a day between the extensions of the maxillary and mandibular miniplates.

Fig 2

Three-dimensional skeletal color map of the superimposition of the mandible registered on the anterior cranial base. The image of the isolines on the posterior border of the mandible shows regions with a displacement equal to or greater than a preset value. The red color of the posterior border of the ramus corresponds to a posterior displacement of 4 mm.

Fig 3

Three-dimensional skeletal semitransparency superimposition registered on the anterior cranial base. The 3-dimensional image in red is from the CBCT image at T1, and the transparent overlay is from the CBCT image at T2 of the bone-anchored maxillary protraction protocol. The condyles moved posteriorly.

Fig 4

Three-dimensional skeletal color map of the superimposition of the glenoid fossa at T1 over the image at T2 registered on the anterior cranial base with a scale of −3 to +3 mm shows bone apposition at the anterior eminence (red) and resorption of the posterior wall (blue). The green color corresponds to surfaces without displacement.

Fig 5

A, Three-dimensional skeletal color map and B, semitransparency superimposition registered on the anterior cranial base shows a slight asymmetric displacement of the chin to the patient’s right side after unilateral elastic traction for about 5 months; C, asymmetric movement of the condyles corresponds to asymmetric modeling of the left and right glenoid fossae.

Fig 6

Three-dimensional skeletal semitransparency superimposition registered on the anterior cranial base. The green volume is before treatment, and the transparent overlay is after treatment, illustrating a slight swing-back of the ramus and closure of the gonial angle with a small reduction of the mandibular plane angle. This results in restriction of the forward projection of the chin.