Soungjun Yoon, Dong-Yul Lee, Seok-Ki Jung

Influence of changing various parameters in miniscrew-assisted rapid palatal expansion: A three-dimensional finite element analysis.

- Korean J Orthod 2019;49:150–160

We want to express our appreciation to the authors for this interesting as well as enlightening article. Miniscrew-assisted rapid palatal expander (MARPE) has been on the center stage of attention among orthodontic specialists for various well-deserved reasons, and this investigation has certainly provided answers to some of our curiosities. Having said so, we would also like to request the authors' expert opinions regarding the following aspects of the investigation:

Q1. The results of this study were based on the premise of physical properties summarized in Table 1. Though authors have listed related references concerning the choice of Young's modulus for periodontal ligament, the basis for some of other physical property factors were somewhat lacking. Thus, I feel it would be beneficial for authors to mention briefly how those property figures were determined especially when their variation exists depending on different publications.

Q2. How would the authors anticipate the present results to be modified by the factors, such as immature palatal sutures in growing patients, increasing or decreasing diameters of the miniscrew anchors, and less-than-rigid hook extension from MARPE to miniscrews?

Q3. As stated by the authors, reduced risk of dehiscence may be one of advantages of MARPE. We hope to ask the authors' opinion if such a statement is supported by the results of this study after considering effects of other combination of tooth- and bone-borne rapid palatal expander (RPE) models reported in the literature.

Q4. Comparisons of groups 3, 5, and 6 showed that, while anterior positioning of MARPE increased transverse expansion in the posterior region, positioning MARPE in the opposite direction resulted in reduction of expansion in the posterior region. This finding, to us, was somewhat counterintuitive since, if expansion force is applied closer to the hinge, more expansion may be expected to be produced away from the hinge, which is in the anterior region in group 6, given that greater resistance to RPE tends to come from posterior sections of the maxilla, such as pterygomaxillary sutures and surrounding structures. I would appreciate authors' comments in this area.