Methods for evaluation of early bone healing at titanium implants

Abstract

Titanium has for a long time been the implant material of choice when in need for abilities as strength, biocompatibility and stability. Although numbers of studies have been done, little is known about the early events in implant healing. The primary aim in this thesis was to develop methods for evaluating bone healing around implants. We used common histological methods but also time-of-flight secondary mass spectrometry (TOF-SIMS) to evaluate the implant healing. This method has previously been used for inorganic materials but can, thanks to new ion sources, be efficiently utilized for analysis of biological compounds. With the Bi3+ cluster ion source used, it is possible to detect high mass fragments of hydroxyapatite (HA) which was applied in the last paper. HA within an area of 40µm from the implant was measured and a correlation between histology and TOF-SIMS was found. We think that TOF-SIMS as a method may be suitable for studying high mass HA fragments. The interface zone was another area we wanted to elucidate using TOF-SIMS technique. Bone formation and resorption and the relationship between those two during the first weeks have been of interest in this thesis. Our hypothesis is that understanding of the bone resorption phase could be a crucial step in influencing the bone healing around implants. After 7 days bone was in close contact with the implant but from this day and evident after 14 days resorption was seen. The initially formed bone was then resorbed and replaced by mature lamellar bone. Our findings indicate that healing around implants starts primarily in the periphery growing toward the implant. Early callus formation and resorption are crucial steps in these early phases and possibly the net bone production is influenced by these factors. Findings in the fourth paper indicate that magnesium coatings decrease resorption and increase net bone production.Porosity together with Magnesium coating seems to positively influence bone growth. We detected formation of adhering bone around all the implants after 7 days through measuring HA. After 4 days there was a zone at the interface without mineralization despite light microscopy (LM) detected bone formation. This has not been reported before. Decalcification and sectioning were used in one paper which gave an opportunity to study the relation between bone and the titanium implant in thin sections giving a good LM resolution. The most porous surface only had the third highest HA coating which indicated that other factors influence implant healing except porosity. TOF-SIMS was used pre implantation to characterize the surfaces. It was then possible to see that during the oxidation process different compounds, like sulphur, phosphor and fluoride, are built into the oxide.