## 1 Introduction  
The prevalence of maxillary transverse deficiency is highly present in all age populations [1, 2, 3]. During primary and mixed dentition and early permanent dentition, rapid maxillary expansion (RME) is a simple procedure with high success rates. It is a stable procedure in the short and long term, regardless of the type of expander used [4; 5]. Tooth-supported RME is not used in skeletally mature patients with a fused palatal suture because of the side effects and complications involved, such as buccal crown tipping, alveolar bone bending, alveolar bone dehiscence, gingival recession, reduction in buccal bone thickness, and marginal bone loss [6; 7]. In adults, the surgically assisted RME (SARME) is the main alternative for the treatment of maxillary transverse discrepancies [8; 9]. Recently, nonsurgical RME using miniscrew anchorage has been identified as another possibility for the treatment of adult maxillary transverse deficiency [10; 11]. This novel bone-borne maxillary expansion technique is known as miniscrew-assisted RME (MARME). Whereas conventional rapid maxillary expanders have questionable effects on the maxillary basal bone, MARME avoids this issue by using a rigid element to deliver an expansion force directly to the basal bone. Compared to a bicortical miniscrew placement, a monocortical placement provides lower force resistance and stability, but higher cortical bone stress [12]. Clinically relevant dimensions of bone available for a palatal mini-implant anchorage include both cortical layers, i.e., the outer cortical layer of the oral hard palate and the nasal floor. Clinicians should consider bicortical anchorage when a high orthodontic load is expected. In addition to the bicortical anchorage consideration, the effects of the number, position, and length of miniscrews in the palatal bone for expansion treatment should be deliberated [13]. The effects of the monocortical and the bicortical miniscrew placement were investigated by [PERSON] et al. in 2020 [14]. The results showed that the bicortical placement technique increases the stability of miniscrews. The bicortical insertion of the miniscrews decrease the risk of screw deformation. Moreover, the bicortical placement techniques should be performed, producing the good clinical outcome. The midpalatal suture opening was influenced by treatment protocol. The reference indicates that the bicortical miniscrew placement could promote a more favorable parallel displacement of the maxillpolatal structure, which obviously represents different expansions in shape between bicortical and monocortical placements [14]. The evidence has confirmed the contribution of the bicortical miniscrew placement, if the parallel displacement of a maxillary suture is needed. The midpalatal suture opening was discovered to have two types of parallels, and wedge widening using different treatment conditions of the rapid maxillary expansion, resulting in the midpalatal suture opening being displayed in the study by [PERSON] et al. [15]. The material effect of the miniscrews also influences the midpalatal suture opening. The previous literature indicates that miniscrews in stainless steel have significantly higher values of fracture torque and flexural strength than in titanium alloy [16]. Hence, the toughness in the stainless steel miniscrews is expressively greater than in titanium alloy miniscrews. The stiffer miniscrews seem to provide a better outcome in regard to the midpalatal suture opening when using rapid maxillary expansion. The finite element analysis (FEA) is a useful resource for performing a virtual biomechanical assessment of possible clinical outcomes. The three-dimensional (3D) FEA is used to simulate maxillary expansion and to evaluate the stress distribution and displacement of the maxillofacial complex [17; 18; 19]. However, FEA is rarely used to evaluate the role of bone-borne expanders requiring heavy anchorage in maxillary orthopedic expansion.