As grafting materials for maxillary sinus floor augmentation, autogenous bone, which is considered as the gold standard and reported first by Boyne et al. using iliac bone graft, has been used as the first-choice material. In terms of osteogenic, osteoinductive, and osteoconductive properties, autogenous bone is considered ideal; however, the use of autogenous bone places great physical stress on patients because of the need for surgery at the donor site. Synthetic bone substitutes such as β-TCP are clinically very beneficial because donor site surgery can be avoided. Moreover, in the 1996 Sinus Consensus Conference, these materials were concluded as having highly predictable outcomes. Although there are many related factors, no difference in the success rate has been observed according to the grafting material [14].

Artzi et al. conducted a comparative experiment of bovine bones and β-TCP to fill defect areas in dogs. They reported that β-TCP was absorbed within 24 h and replaced by autogenous bone, whereas with bovine bone, approximately 30 % granules remained [15]. Thus, β-TCP is considered the ideal grafting material.

The permanence of the new bone formed within the maxillary sinus has been primarily evaluated in humans using radiography. The clinical assessment and short-term and long-term investigations have also been conducted using panoramic radiography and conventional CT [8–12]. Panoramic radiography analysis does not have the shortcomings of radiation risk and expensive CT equipment; therefore, images can generally be obtained frequently. However, its limitations include the ability to assess two-dimensional height, and various magnifications or errors, such as distortion, must also be taken into consideration. In the past, evaluations during implant treatment were primarily performed using panoramic radiography and conventional CT. Recently, however, the use of preoperative and postoperative CBCT has gained popularity, and radiographic assessment by CBCT for volumetric changes in graft bone in maxillary sinus floor augmentation has also been reported [16]. According to our radiographic analysis by CBCT of dental implantation using β-TCP in the present study, we found that the graft volume decreased over time, both at 6 months after surgery and even at 2.5 years after surgery. The result of 54.9 % graft volume change of 2.5 years after surgery is similar to previous reports [17]. Loads were applied to the implant only 6 months after surgery. Nevertheless, the results suggested that it is difficult to control maxillary sinus pneumatization by exerting implant occlusive load. Zijderveld et al. conducted a 5-year radiographic study using panoramic radiography to evaluate periodic changes in β-TCP [20 patients: 10 patients with autogenous bone (taken from the mental region) and 10 patients with β-TCP]. They reported that the majority of β-TCP absorption occurred within the first 7.5 months and that very little change was observed after 1.5 years [12]. Furthermore, in 2004, Hatano et al. used a 2:1 mixture of autogenous bone-to-bovine bone and reported that the maxillary sinus floor was situated at the same height or lower than the implant tip in most patients [11]. These results are similar to our study that maxillary sinus pneumatization continues to progress ≥1 year after surgery; it stabilizes 3 years after surgery and the implant tip protruded beyond the maxillary sinus floor in approximately 70 % implants (41/58 implants) in patients who were followed up 2.5 years after surgery. However, there were no clinical abnormalities, such as maxillary sinusitis. With regard to liner valuables (RBH, IL, SW, iBH) in the present study, the results suggested that it is difficult to control maxillary sinus pneumatization. There was no significant difference in the change in bone height according to SW, and this result is inconsistent with previous reports [18]. There was a limited number of subjects in this study; we believe it is necessary to conduct long-term tests of larger numbers of subjects in the future.