Evaluation in vitro and in vivo of biomimetic hydroxyapatite coated on titanium dental implants

Abstract

Among several materials used as dental implants, metals present relatively high tensile strengths. Although metals are biotolerable, they do not adhere to bone tissues. On the other hand, bioactive ceramics are known to chemically bind to bone tissues, but they are not enough mechanically resistant to tension stresses. To overcome this drawback, biotolerable metals can be coated with bioactive ceramics. Various methods can be employed for coating ceramic layers on metal substrates, among them ion sputtering, plasma spray, sol–gel, electrodeposition and a biomimetic process [E.C.S. Rigo, L.C. Oliveira, L.A. Santos, A.O. Boschi, R.G. Carrodeguas. Implantes metálicos recobertos com hidroxiapatita. Revista de Engenharia Biomédica, vol. 15 (1999), números 1–2, 21–29. Rio de Janeiro]. The aim of this work was to study the effect of the substitution of G glass, employed in the conventional biomimetic method during the nucleation stage, by a solution of sodium silicate (SS) on the chemical and morphological characteristics, and the adhesion of biomimetic coatings deposited on Ti implants. The obtained coatings were analyzed by diffuse reflectance FTIR spectroscopy (DRIFT) and scanning electron microscopy (SEM). Titanium implants were immersed in synthetic body fluid (SBF) and SS. All implants were left inside an incubator at 37 °C for 7 days, followed by immersion in 1.5 SBF and taken back to the incubator for additional 6 days at 37 °C. The 1.5 SBF were refreshed every 2 days. At the end of the treatment, the implants were washed in distilled and deionized water and dried at room temperature. To check the osseointegration, titanium implants coated with biomimetic method were inserted in rabbit's tibia, remaining there for 8 weeks. During the healing period, polyfluorochrome sequential labeling was inoculated in the rabbits to determine the period of bone remodeling. Results from DRIFT and SEM showed that, for all processing variants employed, a HA coating was always obtained on the Ti implants. Besides, G glass employed during the nucleation stage can be effectively substituted by a sodium silicate solution according to these results. The presence of implants stimulated the bone growth in the medullar region and the use of polyfluorochrome sequential labeling allowed the identification of the period of bone deposition and bone reorganization.