In Vivo Study Of Different Topography Of Titanium Dental Implants Coated With Strontium-substituted Hydroxyapatite

Osseointegration is the key point in implant prosthesis. The surfacecomposition and topography may play important roles. Our previous study alsoshows that the titanium surface coated with strontium-substituted hydroxyapatite(Sr-HA) by micro-arc oxidation technique promotes osseointegration greatly.Through various in vivo and in vitro experiments with different concentration ofstrontium, we find the most preferable concentration is10percent whichdemonstrates finest osteogenesis. Besides, the topography changes with differenttime of micro-arc oxidation. Here, we prepare the samples as previous showswith different micro-arc oxidation time and study the topography of them.Moreover, we implant the samples into animal models to observe the impacts onosteogenesis and test the strength of the conjunction in order to find out the mostbiocompatible topography of materials to better osseointegration. Objective:1. Observe the topography of strontium-substituted hydroxyapatite (Sr-HA)by micro-arc oxidation technique with different oxidation time.2. Use animal experiment to explore thedifferent titanium implants onosseointegration and generally infer the possible mechanism.3. Compare the conjunction strength of different titanium coated withstrontium-substituted hydroxyapatite through pull-out test andstereomicroscope observation for the hope of selecting proper micro-arcoxidation time in clinical application.Methods:1. The samples were prepared by micro-arc oxidation technique as describedin previous studies with the oxidation time of5min,10min, and15min.The surface morphology was qualified by the scanning electronmicroscope and quantified by optical profilometer.2. The titanium implants with different oxidation time were separated intothree groups and inserted into metaphysis of rabbits femurs and tibias.After operation, we usedpolyfluorochrome sequential labeling technique.The bone-implant interfaces tissues were obtained in4weeks,8weeks and12weeks and evaluated through histological examination, Bone ImplantContact and Mineral apposition ratio.3. The materials were implanted into dogs ilium bone and undergone pull-outtest in4weeks,8weeks,12weeks. The maximum force and shear strengthwere recorded. We also observed the surface of materials bystereomicroscope. Results：1. The coating surface presented a micro porous feature that dense insideand rough outside. The roughness increased whenthe oxidation time waslong and themorphology demonstrated a volcano-like multi-level porousstructure.2. All the three groups presented high osteogenic activity. In12weeks, thenew bone mineral apposition ratio showed no significantly differencebetween three groups which indicated that the bone genesis was up tothe maximum amount. Nevertheless, the15min and10min groups boneimplant contact were higher than any other groups while the two groupsshowed no difference which demonstrated that the bone implant contactwas influenced by both the time and roughness.3. The pull-out test exhibited that the bone implant conjunction wasstrengthened by both the oxidation time and the period afterimplantation. Stereomicroscope indicated that the tissue residualdecreased by the oxidation time which proved that long oxidation wouldenhance osseointegration.Conclusions:1. The surface roughness is increased with the oxidation time. The15min groupshows the most complicated surface that provides sufficient space forosteoblasts adhesion.2. In vivo study proves that the osteogenic activity is trigged by the surfacecoating. Bone implant conjunction is strengthened by both the oxidation time and the period after implantation. The bone mineral apposition ratio and boneimplant contact are affected by both material roughness and the time afterimplantation.Above all, we recommend that when the micro-arc oxidation time is15mintogether with10percent strontium concentration will form a proper surfacetopography which can largely improve osseointegration.