Osseointegration- biomaterial modulation of bone immunobiology

15400 ORAL COMMUNICATION BASIC RESEARCH

Background

Osseointegration, the basic phenomenon allowing the clinical anchorage of oral implants, is the result of a bone reaction to materials such as titanium. Despite much research being done on this topic, the mechanisms leading to osseointegration are still unknown. It has been demonstrated that a specific immune-inflammatory reaction occurs around titanium over time, when compared to a sham site healing, i.e. natural healing of the bone.

Aim/Hypothesis

The current study explores the bone immune reaction to different materials, in order to investigate how a specific immune modulation may contribute to determine whether a material osseointegrates or not.

Materials and Methods

Copper and PEEK implants (test materials known for not osseointegrating) were compared to Titanium (control) in an in vivo study in the rabbit tibia. Of a total of twelve rabbits, six were studied at each time point of 10 and 28 days, respectively within the inflammatory stage of the normally described healing period, and the post-inflammatory period. At each time point, the implants were removed from the bone and samples collected from five animals for gene expression analysis of immunological and bone resorption markers through PCR, as well as samples from six animals for tissue histological evaluation.

Results

Copper and PEEK demonstrated a higher immune activation than titanium at both time points, revealing a prolonged pro-inflammatory peri-implant environment over time. Cu developed a soft tissue encapsulation, even if showing initial bone demarcation of the implant at a distance (distance osteogenesis), over time showing a significant down-regulation of RANKL and up-regulation of OPG; whereas PEEK failed to osseointegrate through an immune regulated (sharp up-regulation of PPAR-gamma and M-CSF) adipose tissue proliferation instead of bone formation in the implant vicinity. Results for PEEK at 28 days must read with caution, since only two out of the five animals allowed for mRNA collection around PEEK; however, both animals showed a similar trend and the biological markers correspond to the tissue histology.

Conclusion and Clinical Implications

The results suggest that different implant materials lead to a specific modulation of the immune system, when placed in bone. This immune modulation seems to correlate with the biology of the effector tissue cells and determine the ultimate tissue formation around an implant. Two possible mechanisms for clinical osseointegration failure are suggested by the results.