The thought-provoking article by Nguyen et al in the December issue reported on an assessment of maxillary protraction with bone anchorage. Comprehensive methods to treat maxillary deficiency are available in the orthodontic literature, but we thank the authors for opening new doors and concepts in the field. We have the following questions regarding their study.
What about the force vector direction, since the maxillary plates were placed below the center of resistance of the maxilla? This will tend to rotate the maxilla downward in the posterior part and upward in the anterior part; this is not ideal in Class III patients. The mandibular plates were placed between the canines and the lateral incisors, again anterior to the center of resistance of the mandible, which will tend to rotate the mandible in a counterclockwise direction and is contraindicated in Class III patients.
The authors selected I-type plates, although it is well proven in the 3-dimensional studies by Lee et al and Cha and Ngan that the Y-type of plate has a distinct advantage over the I-type.
The maximum amount of traction force applied by the authors was 250 g per side, but, for any kind of orthopedic correction, especially protraction of the maxilla, the minimum amount of force should be 400 to 450 g per side.
The authors did not have any panoramic radiographs to show the actual position of the plates in the maxilla and the mandible.
Only the Wits appraisal was used for assessment of the correction. How did the authors determine that the maxilla was protracted or the mandible was retracted, because the traction force is coming from the mandible?
The authors haven’t considered or discussed the possible effects of opening or loosening of the circummaxillary sutural system, which could facilitate the orthopedic effect.