Effect of Lithium and Strontium Substitutions Into 58-S-Bioactive Glass in Regenerative Dentistry

Objectives: Both lithium and strontium have been substituted into bioactive glasses (L-BG and S-BG) in order to achieve specific biological properties such as proliferation and alkaline phosphatase (ALP) activity of cells as well as antibacterial activity. The first aim of this study was to clarify how individually substitution of Li and Sr in the range of 0 to 10 mol% with quite reverse effect on BG's solubility, retard the bioactivity of L-BG, S-BG. Second, the variation influence of Li and Sr on in vitro formation of nano-size hydroxyapatite, proliferation and ALP activity of osteoblast cell line MC3T3-E1 as well as antibacterial activity of sol-gel synthesized 58S-BG were investigated.
Methods: The Li-containing-BG and Sr-containing-BG were synthesized through so-gel method. characterization techniques such as, thermal analysis, X-ray diffraction, Fourier transform infrared spectroscopy, inductively coupled plasma atomic emission spectrometry and scanning electron microscopy were applied. Furthermore, the proliferation rate and ALP activity of MC3T3-E1 treated with L-BG and S-BG were studied and compared together.
Results: The obtained results confirmed that various radius of Li⁺ and Sr²⁺ compared to Ca²⁺ resulted in a higher and lower oxygen density in L-BG and S-BG, respectively which leaded to higher and lower structure compactness. Our observation suggests two possible mechanisms for lowered bioactivity: lower supersaturation for nucleation of apatite in L-BGs and blocking of the active growth sites of calcium phosphate by Sr²⁺ in S-BGs. 3-(4,5dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide and ALP assay showed that all synthesized L-BGs and S-BGs with exception of 58S-BG with 10 mol % SrO, exhibited statistically significant increase in both cell proliferation and alkaline phosphatase activity, respectively.
Conclusions: The 58S-BG with 5 mol % Li₂O was considered as a potential biomaterial in regenerative dentistry with maximum biocompatibility, the highest ALP activity, acceptable bioactivity and the most efficient antibacterial activity against methicillin-resistant Staphylococcus aureus bacteria among all synthesized L-BGs and S-BGs.