Flame-sprayed strontium- and magnesium-doped hydroxyapatite on titanium implants for osseointegration enhancement

Abstract

Strontium (Sr) and magnesium (Mg) have been reported to promote osteoblastic cell proliferation and to accelerate bone formation. However, the biofunctional effect on osseointegration caused by coating dental implants with hydroxyapatite (HA) incorporating both of these elements has not been investigated to date. The aim of this study was to examine bone formation and osseointegration in Sr- and Mg-doped HA-coated titanium implants. In this study, the flame-spraying technique was used to deposit Sr- and Mg-doped HA onto titanium discs and implants. The biocompatibility and alkaline phosphatase (ALP) activity of human embryonic palatal mesenchymal pre-osteoblasts on titanium discs was evaluated. In addition, the expression of the osteogenesis gene and the protein expression of Runt-related transcription factor 2 (RUNX2), osteopontin (OPN), and osteocalcin (OCN) on titanium discs were determined by using real-time polymerase chain reaction assays, Western blot analysis, and enzyme-linked immunosorbent assays. Ultimately, the effects of Sr- and Mg-doped HA on the osseointegration of implants were examined in beagle dogs. The results showed that of the groups tested, the 5Sr5Mg-HA group exhibited the highest biocompatibility, ALP activity, and mRNA and protein expression of RUNX2, OPN, and OCN. Prominent new bone ingrowth with osteoblasts and osteoid tissue was found in the 5Sr5Mg-HA group at 4 weeks and 8 weeks. In addition, the highest bone-to-implant contact ratio was found in the 5Sr5Mg-HA group compared to other groups at 8 weeks in beagle dogs. The results show the potential of using 5Sr5Mg-HA coating on dental implants for enhanced osseointegration. Statement of SignificanceOsseointegration is assessed according to the extent of bone-to-implant contact and is an indication of implant success. This study is the first to report that flame-sprayed Sr- and Mg-doped HA coatings on titanium surfaces enhance osseointegration and new bone apposition in a beagle dog model. Therefore, the use of titanium implants incorporating Sr and Mg might be advantageous for patients with a low bone density.