## 1 Introduction  
Rapid and slow expansion of the maxillary arch are classical methods for increasing the perimeter of the arch. Rapid expansion of the upper jaw is achieved by applying heavy forces that can split the palatal suture [1]. This expansion results from a combination of skeletal [2; 3; 4; 5; 6; 7; 8; 9; 10] expansion and dental (orthodontic) inclination and displacement. The development of CAD/CAM technology allowed the fabrication of customized RME appliances that are very accurate, with dental or hybrid skeletal-dental attachment and action [11; 12; 13; 14; 15]. The ratio between skeletal and dental effects depends on the type of expansion method used and the maturation of the palatal suture. The goal of rapid maxillary expansion is to achieve maximal skeletal effect with minimal tooth movement, allowing physiological adaptation of the suture during expansion. The expansion of the maxilla with an RME appliance is a reliable and proven method for increasing the maxillary width and managing the transversal dimensions. The pattern of opening the midpalatal suture has been deeply investigated and described in the literature [16; 17]. An appropriate time must be chosen for treatment with the RME appliance--most adequate results are achieved before midpalatal suture ossification, and the cervical vertebral maturation (CVM) method for determining the craniofacial skeletal maturational stage of an individual is an effective tool for clinical decision [18; 19]. The best skeletal effects are achieved when the RME appliance is used before the growth spur (stages 1 to 3 of the cervical vertebral maturation (CVM) method) [18; 19]. The expansion achieved with RME has an additional effect on the surrounding structures. The nasal cavity and the entire upper jaw are influenced by widening the airways [20; 21; 22; 23; 24; 25; 26]. According to a systematic review, there was a statistically significant increase in oropharyngeal and nasopharyngeal dimensions and an improvement in airway patency in cases treated with RME appliances [21]. Also, this type of therapy can eliminate obstructive sleep-breathing disorders and restore and enhance normal nasal airflow. Often, RME treatment also contributes to the correction of mouth breathing by changing the anatomical structures--the maxillary palatine process and the palatine bone, which form the roof of the oral cavity and the floor of the nasal cavity. By increasing the surface of these structures during expansion, the volume of the nasal cavity is increased, and the breathing process is affected [25; 27; 28; 29; 30; 31]. [PERSON], in a review, shows the increase in nasal and oropharyngeal space volumes and a decrease in airway resistance in growing children and adolescents that occur immediately after RME and at 3, 6, and 12 months follow-up [24]. This is due to the fact that more air is breathed in and out when the airways are wider and have an enlarged volume. The method is highly effective and favors mouth-breathing patients and patients diagnosed with sleep apnea [21; 30; 31]. The condition of sleep apnea is improved by relieving respiratory function. All of the described effects make the RME appliance a contemporary tool for treatment with clinical implications, which is the reason for many authors from different fields to continue with their investigations of the achieved results and effects. Another consequence that has been observed is posterior rotation of the mandible after RME treatment, which has been described by [PERSON] [32]. In a systematic review, [PERSON] [33] also concluded that the application of RME in the maxilla leads to posterior mandibular rotation. The mandible is shifted downwards and backwards, which increases the lower facial height. Observations were made immediately after RME treatment and favor treatment of skeletal class III. In patients with skeletal class II, medialization of the mandible is observed 6 months and more after treatment with an RME appliance [34; 35].