## 5 Discussion  
Contemporary indications for RME comprise maxillary deficiency, often concurrent with Class II or Class III malocclusion [24]. The data presented in the present study offer a comprehensive insight into the clinical parameters and discomfort associated with the use of Haas-type acrylic expanders and fixed orthodontic appliances, stratified by adolescent and adult age groups. This analytical  
Figure 10: (**a**) Changes in the shape of the upper arch in an 18-year-old female reporting headaches during SRME treatment. (**b**) Changes in the shape of the upper arch in a 21-year-old male reporting headaches during SRME treatment. Figure 9: (**a**) Pain during a Haas-type SRME according to CS. (**b**) Pain during FA treatment according to CS. approach facilitates a comprehensive understanding of the impact of orthodontic appliances on different age demographics within the cohort. Our research describes one of few studies referring to pain and discomfort in patients treated with RME devices anchored on acrylic splints (bonded RME) with acrylic extensions on the palate [23; 24; 25; 26; 27]. It is important to underline that most studies refer to RME anchored on two or four separated bands overloading supported teeth [7; 8; 9; 10; 16; 19; 20; 28; 29; 30; 31]. Both the rate of screw turning and the design of the appliance might have an impact on the pain levels reported [5]. The findings of previous studies on pain reported during RME or SRME are presented in Table 3.  
We decided to compare adolescents' and adults' pain perceptions during two potentially painful orthodontic procedures, i.e., SRME (semi-RME) and FA, in the same patients. To our knowledge, this is the first study reporting such a comparison. No consistency exists in the literature referring to the definition of SRME. [PERSON] et al. [16] consider SRME as one quarter-turn activation per day, while [PERSON] and [PERSON] (2010) defined SRME as two quarter turns per day for the first week followed by one quarter turn per day, every other day [23]. In contrast--rapid maxillary expansion (RME) is performed as two to four quarter-turn screw activations per day during the whole treatment [6; 16; 18; 27; 28; 32]. In the present study, an NRS was chosen for its simplicity compared to a VAS [21]. The NRS has been widely used in diverse populations, since pain cannot be directly measured and is believed to range across a continuum of values. The level of pain in the present study can be assumed as moderate grade, as it was equal to 4.00 on the NRS, and only 18.95% of the total group considered pain as the main disadvantage during SRME. The relatively moderate level of pain in our study could be related to a few factors. The first factor might be the design of appliance. Connecting six to eight upper teeth (from first premolar to the first or second molar) increases the support for optimal distribution of the force, instead of devices anchored on two or four bands (as in most studies published), potentially overloading separated, supported teeth. [PERSON] and [PERSON] claim that acrylic splints counteract possible fracture of the buccal bone plate and gingival recessions usually described in the literature [33]. Moreover, the study by [PERSON] et al. reported that the Hyrax expander is more painful than the Haas appliance [20]. The second factor seems to be the rate of expanding the screw. In the present study, it was one quarter turn per day. The activation protocol was chosen following that used by [PERSON] and [PERSON] [22]. Similarly to the present study, [PERSON] et al. used a typical Haas appliance on four bands and acrylic extensions on the palate and found pain or swelling only in 19.15% of patients. On the contrary, [PERSON] et al. used a Hyrax expander on four bands turned four times a day and reported pain, swelling and ulceration in 68% of patients [32]. A more recent study by [PERSON] et al.