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ePaper created 2015-11-17, 15:11:47 | version 1.38.0
the scaffold surface and mayenhance cytokine adsorption.46 The interconnectivity of the pores in ABB particles and their hydrophilic properties explain the presence of OPN within the lacuno-canalicular system. This explana- tion is supported by the distribution of OPN found in our samples from the surface to the core of the particles, with the lacuno-canalicu- lar system ofthe remnantABB particles clearly depicted by the staining. Although the biologi- cal relevance of this finding remains unclear, it may be related to the cellular recolonization and revascularization ofABB that has been ob- servedaftersixmonthsofhealing.31 Inthispre- vious study, a direct correlation was found be- tween OPN expression in osteocytes and CD34-positive endothelial cells (rho coeffi- cient = 0.828, p = 0.042, Spearmantest).As al- ready noted, one of the functions of OPN is re- lated to angiogenesis,5 which is impaired in OPN-deficient mice.47 Images of ABB particles aftersix months ofgraft maturationwere com- patible with neovascularization and central re- sorption, implying the integration of this bio- material within the functional and biomechan- ical system ofthe neoformed bone. Whereas most noncollagenous proteins are more or less homogeneously dispersed through- out bone, ultrastructural immunocytochemical studies have consistently found OPN to be pre- dominantlydistributed at cement lines in remod- elingboneandatlaminaelimitans.48,49 Thesesites represent matrix–matrix and cell–matrix bound- aries, respectively, and are therefore important in the bone formation process.6 Cement lines de- marcate the boundary between older and newer bone and characteristicallyhave a high OPN con- tent.TheoriginofOPNinthecementlinehasbeen controversial,32,50 andosteoclastsandosteoblasts maybothbeinvolved.OPNmayinitiallyplayarole inosteoblastadhesionorearlycalcificationevents inthecementlayer.51 Subsequently,themoredif- fusedistributionofOPNthroughoutthebonema- trix may influence osteoclast activity during re- sorption and the transformation of woven and lamellarbone.6 Ourfindingssupportthisproposi- Volume 1 | Issue 1/2015 47Journal of Oral Science & Rehabilitation Os teopon ti n e xpre ssi o n i n ano rgani c bovi ne bo ne Fig. 3 Fig. 3 (a) Immunohistochemical expression of OPN in osteocytes and cement lines in pristine bone (micropolymer- peroxidase-based method, 10×). (b) Detail of OPN expression in osteocytes (micropolymer- peroxidase-based method, 20×). (c) Immunohistochemical expression of CD56 in osteoblasts around trabecular bone (micropolymer- peroxidase-based method, 10×). (d) Immunohistochemical expression of TRAP in osteoclasts around ABB particles (micropolymer- peroxidase-based method, 40×). a b c d