## 4 Discussion  
The null hypothesis was that stress distribution in two unilateral RPDs could be similar if supported by a posterior implant in the distal part and without the implant. The results showed that the presence of the implant increases the stress on the partial denture and the risk of fracture, while the implant-supported denture is exerting less pressure on the mucosa and subjacent bone, thus rejecting the hypothesis. Various researchers have tried to find the best solution for solving the unilateral free-end saddle equation. Some authors recommend special care in choosing and positioning the artificial teeth in order to adequately stabilize the abutment tooth and denture base of unilateral RPD [10]. [PERSON] et al. compared stresses under different loads in a unilateral RPD and a classical RPD, both with three artificial teeth (second premolar, first molar and second molar) and found similar physiological values [11]. In our study, on the second premolar, values obtained on the bone are not clinically relevant, considering the fact that the denture is completely supported by the attachment under the second premolar. With regard to the second molar, and also clinically speaking, association with a distal implant decreases the maximum von [PERSON] stresses values on the two molars, especially on the second one, on the bone area. This is the most important area for the long-term success of the prosthetic treatment because it prevents the tilting of the saddle that accentuates during the use of the denture trough bone resorption. A prior study that aimed to compare a mandibular class I Kennedy removable partial denture (RPD) with ball attachments, in two designs--teeth supported only, and implant and teeth supported--demonstrated that associating an implant for each free-end saddle significantly reduces the maximum von Mises stress and the maximum displacement values in the RPD [12] and decreases the risk of bone resorption. In this study, in the case of unilateral RPDs, association with distal implants increases the risk of fracture for the denture, but it is also decreasing the risk of resorption of the bone, which is important for maintaining the vertical dimension of occlusion, masticatory efficiency and comfort. Another FEA study revealed differences between the stress distribution pattern of implant-supported RPD and that of implant-tissue-supported RPD; the highest maximum displacement value was found in the model tooth-tissue-supported RPD, while the lowest value was in the implant-supported RPD [13]. Another study analyzed how the free-end saddle length influences the behavior of unilateral partial denture supporting structures and found a different stress distribution on the abutment teeth and the attachment, determined by physiological forces; stress level  
Figure 6: Maximum von Mises stress in unilateral RPD with implant when the forces were applied on the PM2: (**a**) full analyzed assembly; (**b**) metallic reinforcement. values in the abutment teeth and the attachment were far lower than the marginal ones [14]. In our study, values obtained for the metal reinforcement above the attachment are greater for the implant supported denture only on the second premolar. Studies found in the literature showed that association between implants and RPDs is beneficial for the teeth and tissues because the implant receives the majority of the load and reduces the stress on the abutment and the displacement of the denture; the amount of stress in the implant and the periodontal ligament of the abutment teeth decreases when the implants are placed in the first molar area [15,16]. The implant position affects the stresses level around implant such that a distal position recorded higher stresses than a mesial implant position [17]. Another benefit of the association between the implant and the mandibular free-end saddle is that it significantly improves masticatory function which occurs, regardless of the position chosen for the implant [18]. In our study, the implant was positioned under the second molar.