Simon S. Jensen Reinhard Gruber Daniel Buser Dieter D. Bosshardt Osteoclast-like cells on deproteinized bovine bone mineral and biphasic calcium phosphate: light and transmission electron microscopical observations Authors’ affiliations: Simon S. Jensen, Reinhard Gruber, Daniel Buser, Dieter D. Bosshardt, Department of Oral Surgery and Stomatology, School of Dental Medicine, University of Bern, Bern, Switzerland Simon S. Jensen, Department of Oral & Maxillofacial Surgery, Copenhagen University Hospital (Rigshospitalet), Copenhagen Ø, Denmark Reinhard Gruber, Laboratory of Oral Cell Biology, School of Dental Medicine, University of Bern, Bern, Switzerland Dieter D. Bosshardt, Robert K. Schenk Laboratory of Oral Histology, School of Dental Medicine, University of Bern, Bern, Switzerland Corresponding author: Simon S. Jensen, DDS, Research fellow, Consultant oral and maxillofacial surgeon Department of Oral & Maxillofacial Surgery Copenhagen University Hospital (Rigshospitalet), Blegdamsvej 9, DK-2100 Copenhagen Ø, Denmark Tel.: +45 35 45 20 02 Fax: +45 35 45 23 64 e-mail: simon.storgaard@jensen.mail.dk Key words: biphasic calcium phosphate, bone regeneration, degradation, deproteinized bovine bone mineral, osteoclast Abstract Objectives: The occurrence of multinucleated giant cells (MNGCs) on bone substitute materials has been recognized for a long time. However, there have been no studies linking material characteristics with morphology of the MNGCs. The aim was to analyze the qualitative differences of MNGCs on two commercially available calcium phosphate bone substitute materials retrieved from bone defects. Material and methods: Six defects were prepared bilaterally in the mandibular body of three mini pigs. The defects were randomly grafted with either deproteinized bovine bone mineral (DBBM) or biphasic calcium phosphate (BCP). After a healing period of four weeks, bone blocks were embedded in LR White resin. Three consecutive sections per defect were analyzed as follows: two with light microscopy using toluidine blue and tartrate-resistant acid phosphatase (TRAP) staining and one with transmission electron microscopy. Results: Multinucleated giant cells appeared on both biomaterials. On BCP, MNGCs had a flat morphology and were not observed in resorption lacunae. On DBBM, the MNGCs appeared more round and were often found in shallow concavities. MNGCs on both biomaterials demonstrated a varying degree of TRAP staining, with a tendency toward higher staining intensity of MNGCs on BCP. At the ultrastructural level, signs of superficial dissolution of BCP together with phagocytosis of minor fragments were observed. MNGCs on the surface of DBBM demonstrated sealing zones and ruffled borders, both features of mature osteoclasts. Conclusion: MNGCs demonstrated distinctly different histological features depending on the bone substitute material used. Further research is warranted to understand the clinical implications of these morphological observations. In the search for the ideal bone substitute material (Bohner 2000), a key characteristic has been the ability of the material to sup- port new bone formation (Hjorting-Hansen 2002). Bone substitute materials should facil- itate bone healing by osteoconduction or undergo resorption or degradation to be replaced by new bone. This highlights the role of osteoclasts in orchestrating the pro- cess of graft consolidation (Henriksen et al. 2011). Understanding the impact of a bone substitute material on the formation and activity of mature osteoclasts is thus relevant in biomaterial research. A mature osteoclast originates from a hematopoietic progenitor and is a function- ally polarized multinucleated giant cell (MNGC). It attaches to a mineralized surface by forming a tight ringlike zone of adhesion, the sealing zone, into which protons and pro- teases are secreted, causing the surface to dissolve (Schenk 1998; Boyle et al. 2003; Kartsogiannis & Ng 2004). This phenomenon results in a resorption lacuna in the mineral- ized surface. The cytoplasm of osteoclasts contains multiple vacuoles and stains posi- tive for tartrate-resistant acid phosphatase (TRAP). The foreign body giant cell (FBGC) develops from macrophages and may also be found on calcium phosphate (CaP) surfaces (Anderson et al. 2008). However, in contrast to the osteoclast, the FBGC in general is TRAP negative (TRAPÀ) and does not Date: Accepted 22 February 2014 To cite this article: Jensen SS, Gruber R, Buser D, Bosshardt DD. Osteoclast-like cells on deproteinized bovine bone mineral and biphasic calcium phosphate: light and transmission electron microscopical observations. Clin. Oral Impl. Res. 00, 2014, 1–6 doi: 10.1111/clr.12376 © 2014 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd 1