Two participants were unavailable to attend the testing at 1–2 weeks after the provisional restoration had been inserted, which resulted in missing data.

Overall descriptive analyses yielded the following observations for the four tests.

Occlusal contact and approximate maximum bite force were significantly increased 3 months after implant rehabilitation because of the adjustment of provisional occlusion, with the bite force gradually building up by 72% compared with that at stage one (prior to implant rehabilitation). Prior to implant surgery, when participants were wearing complete dentures for the lower or upper jaw, none expressed satisfaction with their dentures when we asked about them. However, occlusal contact and approximate maximum bite force varied widely among subjects but steadily increased in the individual participants (bite force, range 16.4–339.80 N, SD = 103.89; occlusal contact area, 0.4–9.63 mm², SD = 3.31). The occlusal contact area was increased right after implant surgery (p < 0.005) and 3 months after wearing implants (p < 0.005). At the same time, maximum bite force also increased on these occasions (p < 0.001 and p < 0.005) (Fig. 2a, b). There was a positive and significant correlation between occlusal contact area and approximate maximum bite force (r = 0.91, p < 0.001). Our findings on occlusal contact and bite force were 7.96 ± 3.55 mm² and 254.3 ± 76.4 N, respectively, after 3 months of wearing implant-support prostheses.

The obtained glucose data varied considerably between before and immediately after implant surgery (before, 0–180.7 mg/dl, SD = 62.9 mg/dl; day 0, 23.0–258 mg/dl, SD = 73.92 mg/dl). In contrast, masticatory efficiency was not significantly different among the four periods (Wilcoxon test) (Fig. 2c). Overall, the masticatory efficiency increased by 46% immediately after surgery, stabilizing at around 40% 3 months after implant rehabilitation. This parameter was decreased in two participants at 3 months after wearing implants, one of whom also showed decreases in both occlusal contact and bite force.

We also obtained data on the healthy control group (n = 11), with an age similar to that of the experimental participants (age average ± SD, 65 ± 9; glucose data average ± SD, 25.5 ± 77.6). The findings for our experimental participants under all conditions were lower than those for the control group (Fig. 2c).