TIBIAL IMPLANT MINERALIZATION IN RATS IS INVERSELY RELATED TO SERUM OSTEOGENIC CAPACITY

In this study, the correlation between the mineralization of healing b one defects and the osteogenic capacity of the serum was tested in rat s. The purpose of the study was to test the hypothesis that during cal lus formation, some serum factors are consumed. The bone defects in th e tibia contained two different implant types, and all sustained juxta -implant fractures. One implant type was the coral Porites and the oth er was its recrystallized version (Interpore-200), which exhibit diffe rent mineralization rates during fracture healing. Use of these two im plant types permitted generation of an expanded mineralization spectru m suitable for regression analysis. Mineralization was assessed by mea suring the mineral content change (MCC) using dual-energy X-ray absorp tiometry. Osteogenic capacity of sera of the implanted rats was assess ed by its ability to increase specific alkaline phosphatase (ALP) acti vity in stromal cell cultures. The MCC was followed for 5 weeks in the Porites and Interpore-200 implants, and it was found that the MCC in Interpore-200 implants exceeded that of the Porites implants. Thus, th e two implant types generated a wide mineralization spectrum. Inductio n of ALP in stromal cell culture was lower for sera derived from rats implanted with Interpore-200 than for sera derived from rats implanted with Porites. Two weeks after implantation, the change in serum ALP i nduction correlated inversely with the MCC of bone defects. This indic ates that during callus formation, the mineralization rate is reciproc ally related to the serum osteogenic capacity. The decreased serum ost eogenic capacity may be interpreted by the hypothesis that callus form ation consumes certain serum osteogenic factors.