Longitudinal Observation of Thin Hydroxyapatite Layers Formed on Anodic Oxide Titanium Implants after Hydrothermal Treatment in a Rat Maxilla Model

Purpose: Highly crystalline thin hydroxyapatite (HA) layers deposited on the surface of commercially pure titanium (cpTi) by discharge anodic oxidation and hydrothermal treatment (SA treatment) enhance the value of cpTi as endosseous implants in clinical dentistry. In particular, the SA treatment affects the osteoconductive properties of cpTi. Determining whether this HA layer retains its chemical stability during osseous wound healing is crucial for its use in implants. In this study, we characterized the morphological, chemical, and structural features of HA layers on SA-treated cpTi implants in rat maxilla. Materials and methods: SA-treated cpTi implants (diameter: 1.0 mm, length: 2.0 mm) were placed in the maxilla of 8-week-old Wistar rats. After 14, 21, and 28 days, the maxilla were harvested and the implant surfaces were analyzed by scanning electron microscopy (SEM), electron probe microanalysis (EPMA), and x-ray photoelectron spectroscopy (XPS). Results: SEM analysis revealed precipitated HA crystals on the implant surface; the crystals had a typical single hexagonal columnar shape and they were highly crystalline. Implantation up to 28 days changed neither the morphology nor the crystalline features of the thin HA layer. EPMA revealed an even distribution of P and Ca in the HA layers before and after implantation in the maxilla, while XPS indicated no change in the binding energies of P and Ca in the HA crystals. Conclusion: The thin HA layer formed on the SA-treated cpTi implants remained stable during the process of