Histological and Histochemical Analyses of Cell-mediated Resorption of Anorganic Bovine Bone Matrix at the Site of Sinus Floor Augmentation in Humans

Abstract

Sterilized particles of anorganic bovine bone matrix (ABBM: Bio-Oss^®), widely used for sinus floor augmentation, are characterized by high bone conductivity and long persistence due to slow resorption. Here we report the histological and histochemical features of ABBM particles applied for bone augmentation in 5 adult patients with special reference to the mode of osteoclastic resorption of xenogenic material. Bone cores retrieved at 6 months after surgery contained densely packed ABBM particles fully or partially encapsulated by the newly induced bone and showed immunoreactivity for osteopontin (OPN) at the bone/ABBM boundary. Multinuclear cells showing enzymatic reactions for tartrate-resistant acid phosphatase (TRAP) were in contact with 48.26±9.43% of the ABBM surface but only 2.13±0.84% of that of induced bone. TRAP-positive multinuclear cells attached to the ABBM particles were enriched with mitochondria but, with a few exceptions, lacked a ruffled border and immunoreactivity for cathepsin K. These data indicate that a predominantly large proportion of TRAP-positive cells at the graft site are hypofunctional osteoclasts or osteoclastic cells at 6 months after surgery, and explain the long persistence of grafted ABBM particles despite the abundance of TRAP-positive multinuclear cells. Graft samples retrieved at 2 weeks from the extraction socket suggested the role of tiny ABBM fragments for the induction of TRAP-positive multinuclear cells in the early postoperative phase. Due to the limited availability of samples, how grafted xenogenic material is involved in bone remodeling in later time periods is yet to be determined.