We thank the readers for their comments regarding our article (Echchadi ME, Benchikh B, Bellamine M, Kim SH. Corticotomy-assisted rapid maxillary expansion: a novel approach with a 3-year follow-up. Am J Orthod Dentofacial Orthop 2015;148:138-53). We also thank the editor for allowing us to reply to the letter.
In the methodology we used for the computed tomography scans, the standardization of the equipment, the image-acquisition settings, and the patient’s head posture position in all 3 planes allowed comparison of the images before and after expansion. The pretreatment buccal cusp tips of the maxillary first molars and premolars were at the same level, and our reference plane was an axial section parallel to the palatal plane, at the level of maxillary first molar furcation (Fs). Since the roots had about 11 mm in average length and the slice thickness was about 1 mm, the alveolar bone thickness measurements were made at the middle of the root at Fs + 4 mm, and for the root apex at Fs + 9 mm. However, to obtain a proper occlusion, the canines were extruded; hence, we used the buccolingual root diameter as a reference for the canines to obtain comparable sections between pretreatment and posttreatment.
Superimposition of the computed tomography scans showed noticeable increases in bone thickness, especially in the canine and premolar areas. Also, the alignment of the 4 maxillary incisors resulted in an increase of the interradicular bone volume.
The comparison of pretreatment and posttreatment maxillary posterior tooth inclinations showed increases in the axial inclinations of the premolars and right molars, which had a significant impact on the transverse linear dimensions. In addition, the use of fixed appliances simultaneously with the expander offered overcorrection control. Moreover, tooth movement occurred with the alveolar bone and not through it.
In this patient, alveolar bone regeneration and posterior tooth inclinations contributed in the same way to the maxillary arch expansion. However, buccal bone apposition, observed in this patient, cannot necessarily be extrapolated for other patients.