Callus formation and remodeling at titanium implants.

Titanium is biocompatible with bone tissue, and during the healing process bone makes intimate contact with the implant surface. Although much is known about the long-term healing of implants, less is known about the callus formation at implants. In this study, the histology of bone healing was studied during the period between 4 and 14 days. Incisions were made in rat tibia. Some incisions were simply left to heal, while in others titanium discs were implanted. Smooth implants as well as implants with different porosities were used. After 4, 7, and 14 days of healing, the sites of bone incisions were retrieved, decalcified, sectioned, and stained. The aim was to compare normal fracture healing with implant healing and to see whether implant properties influenced the short-term healing process. Similarities between fracture healing and implant healing were evident. In both cases, inflammation, soft and hard callus formation, and remodeling had taken place during the period investigated. Between 7 and 14 days substantial bone resorption occurred around the implants. While after 14 days the marrow was almost completely reconstituted during normal wound healing, at the implants a thin layer of bone remained in close contact with the surface. Results from bone-implant contact measurements indicate that the surface properties of the implants do not have a significant influence on the early bone formation, since there were no significant differences between the smooth surface and any of the porous surfaces.

Implantation of hydrophilic and hydrophobic titanium discs in rat tibia: cellular reactions on the surfaces during the first 3 weeks in bone.

In a previous study, a method for evaluation of short-time (1-8 days) healing of titanium implants in rat tibiae was described (J. Biomed. Mater. Res. 66A(3) (2003) 662). The implants were disc-shaped and cells and tissue on the surface were investigated, not the adjacent tissue. In this study healing during the first 3 weeks in bone was examined and the healing response between hydrophilic and hydrophobic titanium was compared. Immunofluorescence techniques were used to detect signs of bone formation on the surfaces. Cell viability, alkaline phosphatase (ALP) activity, presence of osteocalcin and cells positive for bone morphogenetic protein-2 (BMP-2) and vascular endothelial growth factor (VEGF) were investigated. Both viable and non-viable cells were found on both surfaces during the first week. Only initially was there a difference between them; 4% viable cells on hydrophilic discs compared to 56% on hydrophobic ones. More BMP-2 positive cells were found on hydrophilic discs than on hydrophobic ones after 1 week. VEGF was detected after 8 days on both surfaces. Osteocalcin positive cells were found from 2 weeks. ALP positive cells were found after 8 days, while at 2-3 weeks ALP positive tissue was abundant on both surfaces. In conclusion, signs of bone formation were detected during the period investigated. Surface energy appeared to be of more importance initially, with higher surface energy resulting in more rapid cell activation and differentiation than lower.