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ePaper created 2015-11-17, 15:11:47 | version 1.38.0
Volume 1 | Issue 1/2015 43Journal of Oral Science & Rehabilitation Os teopon ti n e xpre ssi o n i n ano rgani c bovi ne bo ne and intramembranous ossification.14 It has also been reported to enhance osteoblastic differen- tiation and proliferation and increase alkaline phosphatase activity.15 Increased OPN expres- sion at injuryor infection sites likelyresults from the release of growth factors (e.g., platelet-de- rived growth factor) or cytokines (e.g., inter- leukin1) that activate different transcription fac- tors, such as Fos and Jun, which are capable of upregulatingOPNtranscription.16 Hence, besides promoting bone formation, OPN has been implicated in bone resorption.17 Various mechanisms have been proposed to un- derlie this biological function. Phosphorylation of OPN appears necessary for the inhibition of biological crystal formation and for the forma- tion of calcium carbonate crystals.7 OPN is a po- tent inhibitor of the mineralization process, be- cause it is binding to hydroxyapatite (HA), in- hibits the formation of HA crystals18 and the growthofHAcrystals,19 andpromotestheinhibi- tion of bone mineralization.20 OPN plays an im- portant role in osteoclastogenesis and osteo- clast activity. Its expression is upregulated during the maturation of monocytes into macrophages,21 a process that presumably oc- curs as circulating monocytes extravasate and migrate through the tissue.16 Parathyroid hor- mone-induced RANKL signaling normally aug- mentsthe numberand activation ofosteoclasts, but this increase is disrupted in the absence of OPN.22 TheneutralizationofOPNsuppressesos- teoclastogenesis in vitro, whereas its addition enhances osteoclastogenesis in OPN-/- cells.23 However, Chellaiah et al. reported an increase in the number of osteoclasts in OPN-/- mice as a compensatorymechanismforthe decreased ac- tivity of OPN-/- osteoclasts, because OPN-defi- cient osteoclasts do not migrate and are unable toresorbbone.24,25 Hence,bone-resorbingactiv- ity could only partially be restored by exogenous OPN,24 indicating that autocrine OPN is impor- tantforosteoclastactivity.26 Anorganic bovine bone (ABB) is a depro- teinized, sterilized bovine cancellous bone com- prising calcium-deficient carbonate apatite.27 ABB is frequently utilized as a bone substitute in maxillary sinus lift procedures when insufficient autogenous cortical bone (ACB) is available for the graft.28 ABB particles are similar to human cancellousboneincrystallineandmorphological structure.29 They are natural, osteoconductive bone substitutes that promote bone growth in periodontal and maxillofacial osseous defects. The particles provide a scaffold and a matrix for bone cell migration and are integrated into the natural physiological remodeling process. It has been suggested that deproteinized cancellous bovine bone can induce new bone formation through osteoinductive mechanisms.30 It has also been reportedthatthe application ofABB in a collagenous matrix induces the formation of membranousandendochondralboneinvivoand thatABBexertshighangiogenicactivity.31 Inpre- vious studies, however, no OPN was detected in bovineboneslices,andnostainingwasobserved inosteocytes,bloodvessels,cementlinesortyp- icalsitesofOPNexpression.32 Inananimalstudy, Araújo et al. described OPN expression in ABB particles during earlyhealing ofthe post-extrac- tion socket.13 Ourgroup described a similarphe- nomenon in humans during late healing after sinus grafting, observing OPN expression not only in the ABB particles, but also within their canalicular system. These observations differ from previous findings in ultrastructural studies in a rat modelthat suggestedthat OPN accumu- lated at the mineral front and was progressively incorporateddeeperintothebone,butbythefur- therdepositionofnewbonematrix.33 The objectives of this studywere to examine OPN expression in bone and ABB in maxillary sinus grafts after six months of healing and to study its relationship to morphological and im- munohistochemical results and to patient vari- ablesandhabits. Materials&methods Stu dy de si gn and su bj e ct re cru i tme nt This clinical case series was reviewed and ap- proved by the institutional review board of the University of Granada Faculty of Dentistry (Spain) prior to subject recruitment. The study was conducted accordingtothe principles ofthe Declaration of Helsinki for experimentationwith humansubjects.34 Totallyorpartiallyedentulous patients need- ing a sinus liftwere screened and included in the studyiftheymet the following inclusion criteria: agebetween18and85years,PhysicalStatusIor II accordingtotheAmerican SocietyofAnesthe- siologists,35 absence of uncontrolled systemic disease or a condition known to alter bone me- tabolism(e.g.,osteoporosisordiabetesmellitus), O’Leary plaque score of ≤ 20%,36 and ≤ 5 mm of