We read with great interest the article in the February issue of the AJO-DO entitled “Midpalatal suture density ratio: a novel predictor of skeletal response to rapid maxillary expansion.” The authors suggested using a qualitative evaluation method of the midpalatal suture to estimate the skeletal response to the rapid maxillary expansion (RME) procedure. This topic is of great interest to orthodontics, because it focuses on a characteristic of the patient that determines the success of the therapy. However, some relevant aspects concerning the methodology of the study should be addressed.

• 1.

  Pretreatment CBCT scans were obtained up to 6 months before the RME. This period of time is sufficient for possible significant dimensional alterations to occur, particularly in patients around 12 years of age (pubertal growth spurt).

• 2.

  Posttreatment CBCT scans were performed, on average, 28.7 months (and even 49 months) after the RME procedure, which was associated with fixed appliance therapy in all patients. By doing so, transverse dimensional differences identified in the sample would actually represent the sum of skeletal effects of RME, orthodontic therapy, and subsequent bone growth, with the latter discussed by the authors in the “Discussion” section.

• 3.

  The areas chosen for measurement of the orthopedic effect of the RME were the least orthopedically susceptible to expansion: the most superior and posterior regions of the maxilla. It is widely known that the most significant effects of RME occur in the anterior and inferior regions of the maxilla.

• 4.

  In the methodology, the variable “prescribed amount of expansion” was used to determine the values of the skeletal effects of RME (greater palatine foramina proportion, GPFp; nasal cavity width proportion, NWp; and infraorbital foramina proportion, IOFp), as shown in Table II. However, quantitative evaluation of RME was performed using as a base the number of activations needed for the correction of crossbites (evaluated on digital casts and recalculated based on intraoral measurements). Perhaps, the experiment would have been more precise if the authors had considered the amount of opening of the hyrax screw at the end of maxillary expansion, because there could have been cases in which the values of the prescribed amount of expansion and the values actually performed were different.