Unexpected Spontaneous Bone Formation Beyond the Boundary of the Grafted Area Following Lateral Maxillary Sinus Floor Augmentation: A Report of Four Cases

Maxillary sinus floor elevation (MSFE) is a common procedure to address insufficient bone height in the posterior maxilla for implant placement.In MSFE, bone substitute grafting is commonly employed to create space for new bone formation, which is typically confined to the grafted area.Conversely, this case study demonstrates unexpected spontaneous bone formation (SBF) beyond the grafted region.In four patients, lateral MSFEs with or without simultaneous implant placement were performed.Sinus membrane perforation was not detected during MSFE.Cone-beam computed tomography (CBCT) was obtained pre-operatively, at 1 week, at prosthesis delivery, and during follow-up.Early CBCT revealed significant sinus mucosal swelling and varying graft particle dispersion, without clinical signs of infection.Subsequently, new bone formed beyond the grafted region, particularly along the lateral sinus wall, with progressive maturation and cortical thickening.All implants achieved functional stability.These findings suggest that post-operative events such as bleeding, transient mucosal thickening, or possible undetected membrane perforation may create additional space beyond the grafted area, which subsequently undergoes bone formation.The clinical impact of SBF may be limited, but it provides insight into the osteogenic potential of the sinus environment.