Polymerization kinetics stability, volumetric changes, apatite precipitation, strontium release and fatigue of novel bone composites for vertebroplasty

Abstract

PurposeThe aim was to determine effects of diluent monomer and monocalcium phosphate monohydrate (MCPM) on polymerization kinetics and volumetric stability, apatite precipitation, strontium release and fatigue of novel dual-paste composites for vertebroplasty.Materials and methodsPolypropylene (PPGDMA) or triethylene (TEGDMA) glycol dimethacrylates (25 wt%) diluents were combined with urethane dimethacrylate (70 wt%) and hydroxyethyl methacrylate (5 wt%). 70 wt% filler containing glass particles, glass fibers (20 wt%) and polylysine (5 wt%) was added. Benzoyl peroxide and MCPM (10 or 20 wt%) or N-tolyglycine glycidyl methacrylate and tristrontium phosphate (15 wt%) were included to give initiator or activator pastes. Commercial PMMA (Simplex) and bone composite (Cortoss) were used for comparison. ATR-FTIR was used to determine thermal activated polymerization kinetics of initiator pastes at 50–80°C. Paste stability, following storage at 4–37°C, was assessed visually or through mixed paste polymerization kinetics at 25°C. Polymerization shrinkage and heat generation were calculated from final monomer conversions. Subsequent expansion and surface apatite precipitation in simulated body fluid (SBF) were assessed gravimetrically and via SEM. Strontium release into water was assessed using ICP-MS. Biaxial flexural strength (BFS) and fatigue properties were determined at 37°C after 4 weeks in SBF.ResultsPolymerization profiles all exhibited an inhibition time before polymerization as predicted by free radical polymerization mechanisms. Initiator paste inhibition times and maximum reaction rates were described well by Arrhenius plots. Plot extrapolation, however, underestimated lower temperature paste stability. Replacement of TEGDMA by PPGDMA, enhanced paste stability, final monomer conversion, water-sorption induced expansion and strontium release but reduced polymerization shrinkage and heat generation. Increasing MCPM level enhanced volume expansion, surface apatite precipitation and strontium release. Although the experimental composite flexural strengths were lower compared to those of commercially available Simplex, the extrapolated low load fatigue lives of all materials were comparable.ConclusionsIncreased inhibition times at high temperature give longer predicted shelf-life whilst stability of mixed paste inhibition times is important for consistent clinical application. Increased volumetric stability, strontium release and apatite formation should encourage bone integration. Replacing TEGDMA by PPGDMA and increasing MCPM could therefore increase suitability of the above novel bone composites for vertebroplasty. Long fatigue lives of the composites may also ensure long-term durability of the materials.

Physical/mechanical and antibacterial properties of orthodontic adhesives containing Sr-bioactive glass nanoparticles, calcium phosphate, and andrographolide

“…The glass transition temperature ( T g ) of UDMA (− 35.3 °C), which was the primary base monomer in the experimental material, is lower than that of Bis-GMA (− 7.7 °C). The polymer containing monomers with a low glass transition temperature ( T g ) usually attains a higher level of monomer conversion compared to polymers consisting of high- T g monomers 37 , 38 . A higher monomer conversion was expected to reduce the risk of monomer release 39 .…”

Physical/Mechanical and Antibacterial Properties of Orthodontic Adhesives Containing Calcium Phosphate and Nisin

“…It was proposed that MCPM may be disproportionated and reprecipitated with a different phase of calcium phosphates [58], such as dicalcium phosphates [59]. The new calcium phosphate precipitation may help fill the voids and prevent crack propagation and failure of the composites [10]. Future work should focus on the long-term mechanical properties (>6 months) to ensure the sufficient durability of the materials.…”

“…Materials with the ability to promote apatite formation are expected to enable bottom-up or top-down remineralization in the demineralized tooth structure. Previous studies have incorporated monocalcium phosphate monohydrate (MCPM; 10-40 wt %) into dental composites to promote mineralizing actions for the materials [9][10][11][12][13]. MCPM is a commercially available calcium phosphate compound with excellent ion-releasing and hydroxyapatite formation abilities [14].…”

Effects of Color Modifier on Degree of Monomer Conversion, Biaxial Flexural Strength, Surface Microhardness, and Water Sorption/Solubility of Resin Composites

“…The degree of monomer conversion is primarily governed by the chemical structures of monomers [26], the concentration and type of photoinitiators [27], translucency and shade of materials [28], and the irradiance of light-curing units [29]. A high degree of monomer conversion after light curing may generally help ensure good physical and mechanical properties in the restored composites [30].…”