MARKERS OF PRIMARY MINERALIZATION ARE CORRELATED WITH BONE-BONDING ABILITY OF TITANIUM OR STAINLESS-STEEL IN-VIVO

Critical events in the adaptation of osseous tissues to implant materi als involve initial calcification of the newly synthesized bone. Previ ous studies indicated that bone-bonding but not nonbonding glass ceram ics increase the matrix vesicle number, thereby compensating for delay ed maturation of the extracellular organelles. The present study asses sed whether this was also true for metal implants commonly used in ort hopaedics and oral medicine. Bone-bonding titanium (Ti) or nonbonding stainless steel (SS) implants were placed in the right tibias of Sabra rats following ablation of the marrow. At 3, 6, 14, and 21 days posti njury, newly formed endosteal bone in the treated and contralateral li mbs was removed and matrix vesicle-enriched membranes isolated. Alkali ne phosphatase and phospholipase A(2) specific activities and phosphat idylserine (PS) content were determined and compared with those of a n onsurgical control group. Results show that matrix vesicle alkaline ph osphatase and phospholipase A(2) activity and PS content was increased in the Ti-implanted limbs at 6 (peak), 14, and 21 days, although at l evels less than observed in normal healing. Alkaline phosphatase activ ity remained elevated throughout the healing period, In contrast, thes e parameters were markedly inhibited in the SS-implanted limbs with re spect to Ti or to normal healing. Both implants altered the systemic r esponse associated with marrow ablation, but in an implant-specific ma nner. The results support the hypothesis that cells adjacent to bone-b onding materials can compensate for negative effects on primary minera lization during osteogenesis, whereas cells adjacent to nonbonding mat erials either do not compensate or are further depressed. The data sup port the use of the rat marrow ablation model as a tool for rapid, ini tial assessment of biomaterials in bone.