## 4 Discussion  
New materials, new techniques and dental implant modifications, as well as many other factors related to implant prosthodontic treatment innovations, need thorough in vitro investigation before their safe clinical utilization [27; 28; 29]. Due to a lack of studies on interface stress from implants on bone, which determines the strain level within the loaded bone, in vitro studies to predict clinical outcomes and marginal bone loss from peri-implant bones are crucial. Potential microfractures and bone remodeling can occur when displacement during elastic deformation exceeds 150 microns [32]. The bone first compensates for loads by forming more bone. Repeated stress with \(\geq\)3000 microstrains increases the micro-damage and can overwhelm bone reparatory mechanisms [33]. The bone bed and the MDI material do not have the same modulus of elasticity, which has a significant impact on peri-implant stress. Higher stiffness or higher elastic modulus of the implant will result in a greater amount of periimplantbone loss. Roxolid(r) alloy (Tl85 Zr15) shows higher strength and resistance to fatigue compared to other titanium alloys [34; 35]. The Roxolid(r) alloy amortizes part of the forces with elastic deformation during loading, thus reducing stress in the peri-implant bone [36]. Different numbers and positions of Ti90 Al6V4 mini-implants supporting the mandibular OD have been studied in vitro [37]. [PERSON] et al. [37] converted microstrains into lateral forces through calibration. Lateral forces were higher in the model with two MDIs inserted in the previous canine sites and in the four-MDI model compared with the one-MDI model and the two-MDI model with MDIs inserted in the positions of previous lateral second incisors. The applied loading force was only 49 N. Fewer mini-implants resulted in less lateral stress on mini-implants, which was ascribed to increased mucosal support when the number of mini-implants was reduced. However, a reduced number of implants caused a greater transfer of forces to the bearing area, resulting in a greater load on the bone. On the contrary, our study revealed lower amounts of peri-implant strains with increasing numbers of implants. Lower strains in the posterior dedentulous area were recorded when more MDIs were present, which is in line with [PERSON] et al. [37] (higher strains in the edentulous area with reduced numbers of implants). [PERSON] et al. [22] found that peri-implant microstrains were 1.5 times higher when two Ti-6 Al-4V mini-implants supporting a mandibular OD (2.6 mm wide, 10 mm long) already had peri-implant marginal bone loss than when there was no marginal bone loss. The pressure on the posterior denture-bearing area was higher under the complete denture than under the two mini-implant-supported OD, as well as the displacement of the denture base. No significant differences in the posterior pressure and denture displacement were registered between MDIs with peri-implant marginal bone loss and those without marginal bone loss. Our study revealed higher strains both at the bone-implant interface and in the edentulous area in the one- and two-MDI models than in the three- and four-MDI models. Increasing the number of implants lowered the strains in the edentulous area under the same loading forces. [PERSON] et al. [38] emphasized a positive correlation between compressive forces and the number of implants. According to their study, the highest compressive forces were achieved with four MDIs that retained a mandibular OD, followed by three and two MDIs. In the case of bilateral loading, the compressive forces were distributed symmetrically, while in the case of unilateral loading, higher compressive forces were recorded on the side where the load was applied. With unilateral loading, a compressive force was observed on the distal side of the posterior MDI on the loaded side while a tensile force was observed on the mesial side in the model with four MDIs.