Change in height of bone surrounding the implant (height from the maxillary sinus floor to the implant tip): Immediately after surgery, all patients had grafted bone between the implant tip and the maxillary sinus floor, with a mean of 2.00 ± 1.51 mm. This height decreased to 0.73 ± 1.33 mm at 6 months after surgery and −0.72 ± 1.11 mm at 2.5 years after surgery (Fig. 5). 41/58 implants had developed pneumatization 2.5 years after surgery and had no bone around the implant tip. The overall mean reduction in bone height was 2.72 ± 1.27 mm: (i) the mean reduction from immediately after surgery to 6 months afterward was 1.28 ± 1.05 mm and (ii) that from 6 months after surgery to 2.5 years after surgery was 1.44 ± 1.45 mm (Table 6, Fig. 6).

The liner parameters: mean RBH, IL, and SW were 4.48 ± 1.51 mm, 6.50 ± 1.88 mm, and 10.32 ± 2.29 mm with a mean value, respectively (Table 7). In addition, on examining the 10 patients (20 implants) with multiple long-term data of ≥1 year after surgery, the height reduction was found to have progressed to the same extent from approximately 1–2 years after surgery, after which there was only a slight change (Fig. 5).

Radiographic evaluation items were statistically analyzed: (a) a significant decrease in graft volume (BV) was observed over time (p < 0.00) and there was no statistically significant effect of age or gender and (b) a significant decrease in bone height (BH) was observed over time (p < 0.001) and there was no statistically significant effect of age or gender. We found that this change of BH was affected by RBH (p = 0.003) and IL (p = 0.001); the thicker the RBH, the less the decrease of BH; the longer the IL, the more the decrease of BH over time. We determined that the higher the immediately postoperative bone height (iBH) was, the higher the subsequent total height would be. We also observed that the coefficient for the interactive items tended to have negative values and that the higher the postoperative bone height was, the larger the amount of decrease was. There was no significant difference in the change in bone height according to SW and also no significant difference according to implant site (Wald chi-square value = 1.221, P = 0.748) (Table 8).