Negative Effect of Rapidly Resorbing Properties of Bioactive Glass-Ceramics as Bone Graft Substitute in a Rabbit Lumbar Fusion Model

Background

Bioactive glass-ceramics have the ability to directly bind to bones and have been widely used as bone graft substitutes due to their high osteoconductivity and biocompatibility. CaO-SiO₂-P₂O₅-B₂O₃ glass-ceramics are known to have good osteoconductivity and are used as bone graft extenders.

Methods

This study aimed to evaluate the effects of the resorbing properties of glass-ceramics in bone fusion after producing and analyzing three types of CaO-SiO₂-P₂O₅-B₂O₃ glass-ceramics with high osteoconductivity that had enhanced resorption by having an increased B₂O₃ content. The three types of CaO-SiO₂-P₂O₅-B₂O₃ glass-ceramics with B₂O₃ contents of 8.0, 9.0, and 9.5 weight % were designated and grouped as P20B80, P10B90, and P5B95, respectively. Glass-ceramic types were tested for fusion rates and bone formation by employing the lumbar 5-6 intertransverse process fusion model in 51 New Zealand male rabbits. Bioactivity was assessed by soaking in simulated body fluid (SBF).

Results

In vitro study results showed sufficient hydroxycarbonate apatite layer formation occurred for P20B80 in1 day, for P10B90 in 3 days, and for P5B95 in 5 days after soaking in SBF. For the rabbit lumbar spine posterolateral fusion model, the autograft group recorded a 100% fusion rate with levels significantly higher than those of P20B80 (29.4%), P10B90 (0%), and P5B95 (14.3%), with high resorbing properties. Resorbing property differences among the three glass-ceramic groups were not significant. Histological results showed new bone formation confirming osteoconductivity in all three types of glass-ceramics. Radiomorphometric results also confirmed the resorbing properties of the three glass-ceramic types.

Conclusions

The high resorbing properties and osteoconductivity of porous glass-ceramics can be advantageous as no glass-ceramics remain in the body. However, their relatively fast rate of resorption in the body negatively affects their role as an osteoconductive scaffold as glass-ceramics are resorbed before bony fusion.