## 4 Discussion  
The success of surgical hard palate closure in UCLP and BCLP is dependent on the availability of tissue in relation to the cleft area that needs to be closed. In wider clefts it is imperative to mobilize the tissue adjacent to the cleft more extensively, which leads to a wider tissue wound and tissue reparation rather than regeneration [51]. This situation may interfere with the normal growth and development of the midface and dentition [12; 52]. The growth in patients with clefts remains a challenge regardless of which surgical protocol is applied. Applying adjuvant therapies before surgery can alleviate the problems of tissue deficiency to some extent by approximation of the palatal shelves using active presurgical orthopedics [53] or passive plate therapy [17], which facilitate tissue closure across the cleft area. However, the stocks of bone and soft tissue still remain deficient since such therapies do not aid in the regeneration of local tissue. Therefore, in this study we tested a contrasting strategy based on increasing the bone and soft tissue prior to cleft surgical repair by means of magnetic periosteal distraction. It aims for true generation of the deficient ostee-mucoperiosteal tissue\(-\)thus, tackling the inherent palatal tissue deficiency which is a basic feature of the cleft malformation that does not disappear over time. With this intention, we analyzed the in silico stress distribution induced by magnetic strips placed on the cleft palatal shelves in newborns with UCLP and BCLP. We tested the hypothesis that magnets can generate bone inducing strains in UCLP and BCLP newborns. Analyses of load transfer, by studying the distribution of stresses and strains, are a prerequisite before in vivo testing since incorrect loading or overloading may lead to disorganized tissue structures, eventually leading to tissue necrosis. Determining these stresses and strains in vivo is not feasible in newborns for ethical reasons, and so 3D in silico models were deemed a valid alternative approach. Although our experiments were confined to tissue generation by means of stresses induced by magnetic periosteal distraction, there is increasing evidence that magnetic fields can further promote bone regeneration directly by attracting growth factors, hormones and polypeptides to the implantation site [54]. The length of the magnetic strips was defined as 23 mm since the average length of hard palate at birth is 25.6 mm \(\pm\)1.6 mm [55]. Previous tests on the magnetic attraction forces across porcine palatal mucosa (rugae) tissue allowed the simulation of the thickness of mucosa in the newborns [44]. In the present study we found that applying 5 N attraction forces using magnetic strips induced stresses in the UCLP and BCLP models mainly at the vomer edge and the palatal shelf ridges of the greater and lesser segments (left and right columns, Figure 3). Areas of tissue generation were delineated by applying the principles of [PERSON]'s Mechanostat theory, which states that mechanical loading influences the bone structure by changing the mass (amount of bone) and architecture (arrangement of surrounding tissues) if the induced strain exceeds 1500 us strain. This implies that periosteal tissue regeneration will be induced at sites where the strain in the underlying bone exceeds 1500 us strain, as the periosteum is mechanically subservient to the bone [56] (Figure 4). The area of periosteal tissue that was subjected to at least 1500 us strain was larger in the UCLP model than the BCLP model, which could be due to differences in material properties of the bone and anatomical variations. In the two FE models there is more low-density bone type 3 present in BCLP than in the UCLP model (Figure 2). Moreover, the direction of the magnetic forces is also more horizontally oriented in BCLP model compared to the UCLP model.