The experimental composites were prepared using a powder to liquid mass ratio of 5: 1. The monomer phase of all experimental composites contained 72 wt% urethane dimethacrylate (UDMA) (DMG, Hamburg, Germany) and 24 wt% PPGDMA (Polysciences Inc, Hirschberg an der Bergstrasse, Germany). 3 wt% 4-methacryloxyethyl trimellitic anhydride (4-META) (Polysciences Inc, Hirschberg an der Bergstrasse, Germany) was added. This may help bind the monomer phase to amine groups and calcium ions in both the composite and dentin. 1 wt% camphorquinone (CQ) (Polysciences Inc, Hirschberg an der Bergstrasse, Germany) was included as initiator.
The glass fillers consisted of 40 nm silica (Azelis, Hertford, UK) combined with two silane treated aluminosilicate glasses (DMG, Hamburg, Germany) with average diameters of 0.7 μm and 7 μm. The mass ratio of 40 nm: 0.7 μm: 7 μm fillers was 1:3:6 to maximize packing. MCPM (53 μm, batch MCP-B26, HiMed, Old Bethpage, NY, USA), β-TCP (34 μm, batch P292 S, Plasma Biotal, Buxton, UK) and PLS (4700 g/mol, 20–50 μm, batch 09010203, Handary S.A., Brussels, Belgium) were used as received. SEM images of filler particles are provided inFig 1 in addition to an image of brushite crystals formed by mixing MCPM and β-TCP with water.
Formulation 1 (F1) and 2 (F2) powders contained 89 wt% and 78 wt% glass respectively. F1 powder also contained 5 wt% MCPM, 5 wt% β-TCP, and 1 wt% PLS whilst F2 powder had 10 wt% MCPM, 10 wt% β-TCP, and 2 wt% PLS. The powder and liquid phase were mixed using a planetary mixer (SpeedMixer, DAC 150.1 FVZ, Hauschild Engineering, Germany) at 3500 rpm for 10 s followed by 2000 rpm for 2 min. Qualitative evaluation of consistency and colour of the mixed pastes were examined visually. Two commercially available dental composites were used as controls; Filtek Z250 (Lot number N519660, Shade B3, 3M ESPE, St Paul, MN, USA) and Gradia Direct Posterior (Lot number 1308132, Shade P-A2, GC, Tokyo, Japan).
Disc specimens were prepared using metal circlips (15 or 10 mm internal diameter and 1 mm in thickness) as moulds. The composite pastes were placed in a circlip and covered with acetate sheets on top and bottom sides. They were then light cured by an LED light curing unit (1,100–1,330 mW/cm2, Demi Plus, Kerr, USA) for 40 s with a circular motion on both sides. Specimens were left at room temperature for at least 24 hr to ensure completion of polymerization. After removal from the circlip, any excesses were trimmed. Specimens were then stored in tubes containing 10 cm3 of deionized water or simulated body fluid (SBF) prepared according to BS ISO 23317:2012 [22 ] at 37°C until the required test time.
The glass fillers consisted of 40 nm silica (Azelis, Hertford, UK) combined with two silane treated aluminosilicate glasses (DMG, Hamburg, Germany) with average diameters of 0.7 μm and 7 μm. The mass ratio of 40 nm: 0.7 μm: 7 μm fillers was 1:3:6 to maximize packing. MCPM (53 μm, batch MCP-B26, HiMed, Old Bethpage, NY, USA), β-TCP (34 μm, batch P292 S, Plasma Biotal, Buxton, UK) and PLS (4700 g/mol, 20–50 μm, batch 09010203, Handary S.A., Brussels, Belgium) were used as received. SEM images of filler particles are provided in
Formulation 1 (F1) and 2 (F2) powders contained 89 wt% and 78 wt% glass respectively. F1 powder also contained 5 wt% MCPM, 5 wt% β-TCP, and 1 wt% PLS whilst F2 powder had 10 wt% MCPM, 10 wt% β-TCP, and 2 wt% PLS. The powder and liquid phase were mixed using a planetary mixer (SpeedMixer, DAC 150.1 FVZ, Hauschild Engineering, Germany) at 3500 rpm for 10 s followed by 2000 rpm for 2 min. Qualitative evaluation of consistency and colour of the mixed pastes were examined visually. Two commercially available dental composites were used as controls; Filtek Z250 (Lot number N519660, Shade B3, 3M ESPE, St Paul, MN, USA) and Gradia Direct Posterior (Lot number 1308132, Shade P-A2, GC, Tokyo, Japan).
Disc specimens were prepared using metal circlips (15 or 10 mm internal diameter and 1 mm in thickness) as moulds. The composite pastes were placed in a circlip and covered with acetate sheets on top and bottom sides. They were then light cured by an LED light curing unit (1,100–1,330 mW/cm2, Demi Plus, Kerr, USA) for 40 s with a circular motion on both sides. Specimens were left at room temperature for at least 24 hr to ensure completion of polymerization. After removal from the circlip, any excesses were trimmed. Specimens were then stored in tubes containing 10 cm3 of deionized water or simulated body fluid (SBF) prepared according to BS ISO 23317:2012 [22 ] at 37°C until the required test time.
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