| Strontium-substitued hydroxyapatite(Sr-HA) has higher solubility and better biocompatability because of the incorporation of strontium, comparing to the pure HA and pure titanium. Additionally, low dose-strontium stimulates bone formation and reduces bone resorption. The strontium ranelate have been successfully used to treat osteoporosis, and is considered a safe and reliable treatment.Our group has developed a MAO-treated strontium-substituted hydroxyapatite (Sr-HA) coating with different doses of strontium on titanium dental implants in order to sustained release strontium ions in bone defects. The aim of the study is based on the preliminary observation of the properties of the films, to explore the osseointegration effects of strontium in vivo, and to select an optimum strontium concentration for clinical application.Objective:Detect the properties of the films, including surface morphology, element composition and phase component of the coatings.Investigate the strengthening mechanisms of bone bonding of crystalline hydroxyapatite (HA) with incorporation of strontium in vivo. Explore the osteogenic activity of the Sr-HA coating developed to enhance the osseointegration of titanium dental implants.Compare the osteogenic and osteocondusive differences among Sr-HA coatings with different strontium concentrationsto provide experimental evidence for clinic uses.Methods:The surface morphology of the coatings was analyzed by scanning electron microscope (SEM).The element composition and phase component were analyzed with energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD).24 imlpants were inserted into the metaphysis of rabbits tibias and femurs using polyfluorochrome sequential labeling. After implantation periods of 4 and 12weeks, the morphology and chemical composition of the bone-implant interfaces were evaluated by histological examination and energy-dispersive X-ray.Fifteen adult New Zealand white rabbits were selected in this study. Three different kinds(5%,10%,20%)of Sr-HA titanium implants were inserted into the metaphysis of tibias and femurs using polyfluorochrome sequential labeling. After implantation periods of 4 weeks, 8weeks and12 weeks, animals were sacrificed. We use micro-CT, histological, biomechanics examination to evaluate new bone formation on the bone-implant interfaces, the degradation of Sr-HA coating, and the stability of dental implant. The tubiform area (radii of 0.5mm) from the bone implant surface was defined as the region of the interests (ROI). The bone volume fraction (BVF), trabecular thickness (Tb.Th), trabecular number (Tb.N),and trabecular spacing(Tb.Sp) were analyzed in ROI by Micro-CT. The bone implant contact (BIC) and mineral apposition ratio (MAR) were analyzed in histological examination; and the maximum force (Fmax) and shear strength were compared among the three groups.Results:1. The XRD patterns showed that the diffraction peaks of HA shift to lower 2θvalues with Sr-addition, consequently, decreases in lattice energy and then crystallinity. Under SEM observation, Sr-HA coating presented a microporous structure.2. Sr-HA coating exhibited osteogenic activity at the early stage of bone healing period and new bone mineral apposition ratio was significantly higher than that of the control group. An apatite layer was observed at the interface of bone-(Sr-HA) coating determined by light microscopy observation and energy-dispersive X-ray analysis, then the apatite layer was precipitated and formed new bone which became mature bone and bonded tightly to the Sr-HA coating at 12 weeks.3. Micro-CT analysis showed that bone volume/tissue volume(BV/TV), trabecular thickness(Tb.Th) of 10%Sr-HA group were significantly higher than those in 5% and 20%Sr-HA group; however, trabecular spacing(Tb.Sp) of 10%Sr-HA group was significant lower than that in 5% and 20%Sr-HA group, at all implant peroids.4. Histological examination: 10%Sr-HA coating exhibited osteogenic activity at the early stage of bone healing period and the quantity and density of newly formed bone around the implant were much better than that in 5, 20%Sr-HA group. Histomorphometry analysis showed the BIC and MAR of 10%Sr-HA group were significantly higher than that of the 5, 20%Sr-HA group.5. Biomechanics test indicated that implant-bone bonding power increased with time duration, the maximum tensile force of the 10%Sr-HA group was significantly larger than that of the 5% and 20%Sr-HA group at each time period(P<0.05).Conclusions:1. MAO-treated strontium-substituted hydroxyapatite (Sr-HA) coating shows high biological activity and osteoconductivity, hence a promising implant surface treatment.2. The promoting action of strontium increases solubility of HA, accelerates the biological apatite formation at the bone-implant interfaces. Incorporation of strontium in hydroxyapatite coating enhances the osseointegration of titanium dental implants.3. The most suitable concentration of strontium in HA is about 10%. 10%Sr-HA coating has the following advantages: it shows osteogenic activity at early stage of bone healing period; it promotes osseointegration process; it significantly enhances implant-bone bonding power. Thus, the MAO-treated 10%Sr-HA coating is a promising surface modification method for Ti-based dental implants.
|
PDF Full Text Request