Development of SiYAlON Glaze for Improved Osteoconductivity of Dental Implants

Objectives: The novel bioceramic, silicon nitride, has been utilised for clinical applications in orthopaedic implant devices due to its superior mechanical properties and osteoconductive capacity. However, surface modification is required to further enhance its osteoconductivity. Our research group has successfully developed a glaze layer of silicon yttrium aluminium oxynitride (SiYAlON) on a silicon nitride base. In this study, using spectroscopic analysis methods, we investigated whether SiYAlON-glazed silicon nitride possesses a greater osteoconductivity than untreated silicon nitride.
Methods: The human osteoblast cell line Saos-2 was seeded on various culture substrates (1: Untreated silicon nitride, 2: SiYAION-glazed silicon nitride, 3: Titanium alloy), and was cultured in a bone differentiation-inducing medium for 7 days. Hydroxyapatite deposited on the substrate was measured using Raman spectroscopy and EDX spectroscopy. Furthermore, the expression of the bone matrix protein, osteocalcin, was examined using fluorescence microscopy.
Results: Raman spectroscopic analysis showed a greater deposition of hydroxyapatite in the SiYAlON-glazed silicon nitride group than in the untreated silicon nitride or titanium alloy groups. Additionally, EDX showed higher calcium and phosphorus signals in the SiYAlON group than in the untreated silicon nitride group. Immunostaining showed that the SiYAlON group had greater cell adhesion and osteocalcin expression than the untreated silicon nitride group.
Conclusions: SiYAlON-glazed silicon nitride is believed to have promoted biomineralization by forming hydroxyapatite-like crystals called N–apatite, a compound containing Y₅Si₃O₁₂N, in the glaze layer. Furthermore, coating with SiYAION is expected to confer the remineralization and antibacterial properties of SiYAION to bioinert dental materials such as cement and polymer. With its high osteoconduction and antibacterial properties, SiYAlON-glazed silicon nitride can be expected to provide robust osseointegration and prevent periimplantitis. It is, thus, a highly promising novel implant material.