Some benefits of the RPE in conjunction with maxillary protraction therapy in treating skeletal class III patients are correction of crossbites often associated with class III malocclusions, anchoring the maxillary dentition against forward movement and anterior constriction, and backward and downward rotation of the mandible [6, 24–27]. Turley  stated that palatal expansion “disarticulates” the maxilla and initiates cellular responses in these circummaxillary sutures, allowing for a more positive reaction to protraction forces potentiating orthopedic effects. Melsen  confirmed these increased cellular responses to RPE.
Kim et al.  in a meta-analysis of the effectiveness of protraction facemasks (based on 14 published articles) concluded that there were no distinct differences between treatments, with or without palatal expansion, except for maxillary incisor angulation, which increased in the nonexpansion treatment group. Similar results were also obtained by Vaughn et al.  that observed no statistically significant differences between groups with or without RPE in any measured variable. They also found no statistically significant differences in overall treatment time or in the time it took to achieve anterior crossbite correction and suggested that, in the absence of objective reasons for expansion such as maxillary width or space deficiencies, expansion will not aid the correction of class III malocclusions with facemask therapy.
Contrary opinion was supported by Yu et al.  using FEA to compare the amount of displacement and deformation of the maxilla, zygomatic arch, and circummaxillary sutures, dependent on whether the midpalatal suture was opened or not, showed there was a decrease in the upward–forward rotation of the maxilla and zygomatic arch with a greater amount of displacement in all-frontal, vertical, and lateral directions, when the midpalatal suture was opened, compared to when there was no opening of the midpalatal suture.
Gautam et al.  verified by FEA that the displacements of craniofacial structures were more favorable for the treatment of skeletal class III maxillary retrognathia when maxillary protraction was used with maxillary expansion. Hence, biomechanically, maxillary protraction combined with maxillary expansion appears to be a superior treatment modality for the treatment of maxillary retrognathia than maxillary protraction alone, in agreement with the present study. However, they did not present a comprehensive description of the mechanical environment within the suture (all principal stresses) and relied on von Mises stress values.
A tendency for constriction at the anterior region of maxillary arch had also been noted using different method approaches. Hata et al. , operating strain gauge transducer systems, analyzed the strain distribution and displacement of the human skull, and Tanne and Sakuda  observed the bones around the zygomaticomaxillary, frontozygomatic, and frontonasal sutures and more prominent compressive stresses with large compressive stresses perpendicular to the frontonasal suture plane.
The effects of micro-implant-assisted rapid palatal expansion showed tension and compression directed to the palate, while showing less rotation and tipping of the maxillary complex, and suggests that causes the maxilla to bend laterally, while preventing unwanted rotation of the complex , and by varying the location of N2 mini-implants and vector of class III mechanics, clinicians can differentially alter the magnitude of forward, downward, and rotational movement of the maxilla .
Our results present a comprehensive analysis of the principal stresses in the midpalatal suture. Since the maxillary expansion and protraction are generally performed in distinct phases and not simultaneously, this study focused only the protraction phase. Simultaneous simulation of the two phases could influence the distribution of stresses, confounding the results for protraction phase. We demonstrated that the potential for treatment benefits in performing RPE adjunctive to maxillary expansion definitely exists because the mechanical environment generated by protraction alone can disrupt or inhibit the normal growth of the midpalatal suture.
The constriction tendency was observed within all the sections of the suture, revealing that all principal stresses were of compressive nature during the maxillary protraction. Moreover, within the compressive stresses, negative on Table 2, the direction of the MinPS in the Fig. 4 a and a’ demonstrates that the highest compressions occur in the opposite direction to the transverse growth of the maxilla. This could aggravate the often already present transverse deficiencies in individuals with class III malocclusion. Hence, biomechanically, maxillary protraction combined with maxillary expansion appears to be a superior treatment modality for maxillary retrognathia than maxillary protraction alone. This forward and downward displacement of the nasomaxillary complex with maxillary protraction with expansion more closely approximates the natural growth direction of the maxilla . Although previous clinical studies failed to provide a measurable benefit, our results show that lack of expansion could promote worsening of transverse relationships. Furthermore, there are potential problems in study design associated with clinical studies, such as power/sample size, patient age, variability of response, actual measurements performed, and other complicating factors that could have prevented significant findings.
Seemingly, the applied parameters did not represent perfectly the complex structure and behavior of the dental, bone and suture tissues. The developing of more detailed parameters is required, so that mathematical equations and computational models could mimic a real biological situation as closely as possible. Notwithstanding, it was assumed that this behavior idealization was suitable to describe theoretically the initial stress distribution of the midpalatal suture in the maxillary protraction therapy.
In the present study, the soft tissue surrounding the bones and teeth were not considered, since the limit definition still were not always possible in computer tomography images. While it is reasonable to assume that mechanical forces of the appliance will greatly overcome the soft tissue resistances, it would be beneficial to investigate the effects of the facial musculature and other soft tissues, and more progressive research with clinical identification of dynamic modeling is required to reinforce these conclusions.