## 4 Discussion
[PERSON] et al., evaluating full-arch prostheses with the All-on-Four method in the mandible, reported an average marginal bone loss of 1.72 mm and 2.32 mm at 10 and 15 years, respectively; higher values, i.e., greater than 3 mm, were associated with smoking (OR = 2.72), previous failure of a contiguous implant or biological complication. Similar results were also obtained in the upper jaw [52; 53]. To test the hypothesis of a time-dependent variation of marginal bone levels, a MANOVA (repeated measures ANOVA) test was performed with the within factor (time) alone. The test showed a significant difference between the values of bone marginal levels as a function of time, F (1, 45) = 2229.18, \(p\) < 0.001. In agreement with the statistical analysis, [PERSON] et al., in their prospective clinical study, evaluated clinical and radiographic outcome mandibular full-arch fixed prostheses supported on four implants with either axial or tilted distal implants, reporting a marginal bone loss at years 1, 2, and 3 of 1.11 \(\pm\) 0.4 mm, 1.26 \(\pm\) 0.42 mm and 1.40 \(\pm\) 0.41 mm, respectively, representing a significant (\(p\) < 0.001) continuing time-dependent annual reduction [54]. In addition to the assessment of marginal bone loss obtained with intra-oral radiographs, the aid of cone beam CT enabled the thickness of the bony cortical to be assessed to highlight any dehiscence. In agreement with the results obtained, both at the maxillary and the mandibular levels, the thickness of the bony cortical progressively increased in the apical direction. Our results agree with those of [PERSON] et al., who reported that avoiding cantilever loading during the healing period prevented implant micromovements from adversely affecting implant stability, thus allowing the preservation of cortical bone in full-arch rehabilitation [55]. Furthermore, as suggested by several authors, implant planning with second-level examinations, coupled with exploitation of the basal bone with placement of the fixtures in the vestibulo-palatal or vestibulo-lingual direction (in order to avoid fenestrations or leakage at the thinner vestibular wall) could promote implant stability over time [56; 57]. Concerning muscular and articular complications, the results of this study showed statistically significant differences between the mean values recorded in male and female subjects, while the most frequently encountered problems during the clinical evaluation were the presence of joint clicks and pain in the masseter muscles. Two of the patients examined showed problems with mandibular latero-deviation and prosthetic fracture. Edenutlous patients rehabilitated with implant-supported fixed prostheses demonstrated a greater degree of muscular activity during clenching and chewing [24]; in addition, as reported by [PERSON] et al., an improvement in masseter muscle activity and maximum bite force could also be recorded [58]. Precisely, an increase in the activity of the masseter muscles more than the temporalis [57] could justify a greater incidence of pain in these muscles. With regard to prosthetic complications, [PERSON] et al., in their retrospective clinical study in which they described the clinical outcomes and complications related to provisional prostheses after full-arch implant-supported rehabilitation by means of an immediate loading protocol, reported that fracture of the provisional prosthesis was the more common finding [59]. In contrast, [PERSON] et al. reported the detachment of an element of the definitive prosthesis as the most frequent prosthetic complication of rehabilitations with a reduced number of implants [60]. [PERSON] et al., in their 5-year follow-up, in accordance with the results obtained in this study, recorded the following prosthetic complications (reported in order of incidence): fracture or detachment of one or multiple acrylic teeth in temporary prosthesis, definitive and minor acrylic fractures in the temporary and definitive prosthesis [61].