Cellular responses to titanium surfaces blasted with TiO2 particles

Abstract

A major determinant of successful osseointegration of endosseous implants is the surface topography of the implant, which influences the cellular response of the surrounding tissues. This series of experimental studies investigated cellular responses to surface modifications of titanium implant material. With machined (turned) surfaces as controls, the topography was altered by blasting with Ti02 particles of varying size. Surface roughness increased with increasing particle size, up to 106- 180 µm. Further increasing particle size to 300 gm did not significantly increase surface roughness.

Cellular response was studied in two cell types: primary cultures of human gingival fibroblasts and osteoblast-like cells. The following responses were investigated: attachment, proliferation, differentiation and production of transforming growth factor beta1 (TGF-beta1) and prostaglandin E2 (PGE2).

In study I, turned surfaces favored fibroblast attachment, least attachment occurring on the surfaces blasted with 63-90 µm particles, whereas in study II, turned surfaces and those blasted with 63-90 gm particles provided the most favorable attachment for osteoblast-like cells. This strongly suggests that in contact with implant surfaces, bonederived cells behave differently from fibroblasts. Hence the results highlight the importance of using the relevant cell system for evaluation of dental implant material. Blasting with larger particles (300 gm) did not further enhance the initial attachment of osteoblast-like cells compared to the turned surfaces (study III).

Studies III & IV concerned the effect of surface roughness on attachment, proliferation and differentiation of human osteoblast-like cells, as well as the production of two factors known to have potent effects on tissues surrounding an implant: TGF-beta1, and PGE2. Incorporation of [3H]-thymidine and osteocalcin synthesis were significantly increased on all blasted surfaces compared to the turned surfaces. The production of TGFbeta1, and PGE2 was also higher on the blasted surfaces.

In study V, the different surfaces subjected to cell culture tests were characterized by electrochemical impedance spectroscopy and X-ray photoelectron spectroscopy. Compared to the turned surfaces, the effective surface area is several times larger on the blasted surfaces, with less carbon contamination. Corrosion resistance was unaffected by blasting the normal machined titanium surfaces with titanium dioxide particles or exposing the samples to the culture conditions for 28 days. Osteoblast-like cells enhance ion incorporation and precipitation processes, whereas the amount of calcium absorption is independent of surface roughness.

In summary, the results show that the technique used for isolation of human osteoblast-like cells from mandibular bone is useful for investigating the biocompatibility of dental implant materials in vitro. Attachment of fibroblasts may be enhanced on turned surfaces and inhibited on surfaces roughened by blasting. Surface roughness, achieved by blasting titanium surfaces with various sizes of Ti02 particles significantly favored proliferation, differentiation and production of TGFbeta1 and PGE2. Increasing surface roughness to this range may modulate the activity of cells interacting with an implant, thereby enhancing tissue healing and implant success.