We believe that the interpretation of the discussion on bone regeneration around dental implants inserted immediately after maxillary sinus lift without the addition of bone substitutes is important. The development of new biomaterials via tissue engineering is the basis for studies in the field of bone regeneration. It is undisputed that the maxillary sinus cavity after a sinus lift is highly conducive to the regeneration process, initially with the formation and development of the blood clot, followed by the development and maturation of the connective tissue and finally with mineralization and bone remodelling. Our recently published study showed that the sinus membrane lift with immediate implant placement, supporting the buccal wall as the new maxillary sinus roof, promoted satisfactory bone neoformation around the implants, which was shown after 51 months of clinical and computed tomography follow-up.

We agree that the Schneiderian membrane presents osteogenic potential and contributes to the process of bone regeneration, as evidenced by in vivo and in vitro studies. We believe that the Schneiderian membrane supplies viable cells for bone regeneration, and also promotes the migration of osteogenic cells to differentiate into osteoblasts. With the sinus lift technique and implant placement described in our study, the membrane was responsible for bone regeneration, especially in the peri-implant palatal region. However, taking into account the displacement of the anterior wall of the maxillary sinus along with the sinus membrane, thereby leading to the development of a new maxillary sinus roof, the space corresponding to the dental implants in the buccal, mesial, and distal regions remained distant from the Schneiderian membrane. Thus, we believe that in large areas of the peri-implant region, formation of new bone tissue was influenced by the blood clot that filled the defect, and by the periosteum, which also provides osteogenic cells, and not so much by the Schneiderian membrane. This assertion is supported by the results of a study by Lundgren et al., who observed spontaneous bone formation after removal of a cyst in the maxillary sinus, even without the sinus membrane.

We have not investigated the actual role of the sinus membrane, clot, and periosteum in bone regeneration around implants, nor could we find any published data related to this. Therefore, we plan to perform in vivo studies (on the maxillary sinus of rabbits) to compare the bone regeneration process between implant placement with sinusectomy and that without.