The maxillary sinus gradually expands after birth and becomes fully pneumatized with the eruption of all permanent teeth. Although the physiological cause and maxillary sinus pneumatization are largely unknown, it is believed that genetics, atmospheric pressure, and hormones are involved in it. This sinus is closely related to the root apex of the premolar and molar teeth, and it is either separated from the teeth by a thin layer of bone or its mucous membrane is in direct contact with the teeth. The pneumatization of the maxillary sinus and the reduction in the bone wall thickness resulting from the loss of teeth is attributed to atrophy caused by a reduction in stimulation to the bone. It is also believed that physiological effects of the mucous membrane of the maxillary sinus as well as factors such as osteoclasts and loss of tooth root resistance to atmospheric pressure in the maxillary sinus are considered to play a role [1–3].

When an implant is placed in the maxillary molar region with atrophy, the maxillary sinus floor is close to the alveolar crest. Thus, some cases may require bone grafting for maxillary sinus floor augmentation. Initially, the gold standard for bone grafting material used to perform this procedure was autogenous bone. The advantages of autogenous bone graft are that it has osteogenic, osteoinductive, and osteoconductive properties. It has been reported that the release of growth factors, such as platelet-rich plasma and transforming growth factor-β and early vascularization from the donor bone enables remodeling within 4–6 months after implant placement. Although the transplanted bone used in maxillary sinus floor augmentation varies, it has been reported that approximately 1.5 cm³ is required to elevate the sinus floor by 10 mm. This requires donor sites with sufficient bone mass (e.g., the mental region and mandibular ramus in the oral cavity or the iliac crest and tibia outside the oral cavity), and it places great stress on both the practitioner and the patient [4, 5]. In recent years, maxillary sinus floor augmentation has been introduced using various bone grafting materials to decrease invasiveness. In Japan, xenogeneic bone grafts are not permitted for ethical reasons; instead, synthetic bone grafting agents that are not derived from animals, such as hydroxyapatite (HA) and β-TCP, have been used. However, unlike nonabsorbable materials such as HA, β-TCP has properties to get absorbed in the body and to be replaced by the bone; in addition, its usefulness has been reported in orthopedic surgery and maxillofacial surgery [6, 7]. We have achieved good outcomes using β-TCP as the bone grafting material for maxillary sinus floor augmentation. However, the predictability of the material and the change in absorption of the transplanted material mass remain largely unknown.