We praise the authors of the article entitled “Differences in distances between maxillary posterior root apices and the sinus floor according to skeletal pattern” in the December 2017 issue (Ahn NL, Park HS. Am J Orthod Dentofacial Orthop. 2017; 152:811-9) for their involvement in evaluating the relationships between roots and maxillary sinus according to age, sex, and skeletal pattern. This study is a move forward with the cue to research the association between roots and maxillary sinus. We appreciate the authors for publishing data that will initiate more studies. However, this article also has generated some doubts in our mind.

In paragraph 7 of the Discussion, the authors pointed out that patients with a normal cant of the palatal plane (PP) have more protrusion of the roots into the maxillary sinus than do those with an up-canted PP. However, the conclusions showed that hyperdivergent patients seemed to have the smallest distances between the roots and the sinus floor. Many scholars have studied the association between PP cant and facial vertical relationships. Sassouni used the cant of the 4 planes (supraorbital, palatal, occlusal, and mandibular) to evaluate the facial deviation. In an open-bite type, the 4 planes are steep to each other, and the posterior part of the palate is tipped downward. Nahoum showed that if the palate revolves counterclockwise around a point posterior to the anterior nasal spine, then this rotation would decrease the upper face height and increase the lower face height in open-bite patients. The mean angle between the sella-nasion line and the PP in open-bite groups is 4° less than the mean for normal subjects. Since the authors agreed that hyperdivergent patients commonly have an up-canted PP (paragraph 7 of the Discussion), is there a contradiction between the 2 statements?

Thank you for conducting this important investigation.