Organic-inorganic hybrid precursors for dental restorative resins.

S. ASMUSSEN; C. VALLO

Ghent University

Simposio; Baekeland 2007 Symposium - Thermosets, 100 years after Bakelite , 23-26 September 2007, Gent- Belgium; 2007

Ghent University

Silsesquioxanes are increasingly being considered in applications were high wear resistance is required. The synthesis of organic-inorganic hybrid precursors for the preparation of dental composites is described. The classic formulation for organometallic silica gel generation comprises four components: an alcoxysilane, water, an acidic or basic catalyst, and a solvent to provide compatibility between the normally immiscible alcoxysilane and water.  In the present study, organic-inorganic precursors were prepared from hydrolysis and condensation of methacryloxypropyltrimethoxysilane (MPTMS) using formic acid as catalyst.  The formic acid serves as solvent, water source and catalyst for both hydrolysis and condensation. Water need not be present as an initial reactant; it is generated in situ during the reaction and MPTMS and formic acid are miscible so the reaction was carried out in the absence of solvent. In addition the hydrolysis condensation reaction of MPTMS was carried out in the presence of dimethacrylate monomers. The methacrylate monomer consisted of blends of {2,2-bis[4-(2-hydroxy-3-methacryloxyprop-1-oxy)phenyl]propane} (Bis-GMA)and triethy lene glycol dimethacrylate (TEGDMA) at mass fractions 70:30. For comparison, the reactions of MPTMS alone, and MPTMS with Bis-GMA/TEGDMA blend were studied under similar conditions.  The components were mixed at room temperature and the hydrolysis condensation reaction was carried out at 70 °C using formic acid 98 wt%.  The reaction products were characterized by mid-infrared spectroscopy and gel permeation chromatography (GPC). The resins were activated for visible light polymerization by the addition of Camphorquinone (CQ) and ethyl-4-dimethylaminobenzoate (EDMAB) in molar proportion CQ/EDMAB=1. The photo-polymerization reaction was monitored by NIR spectroscopy. The specimens were irradiated at regular time intervals equal to 10 s, by manually controlling the curing light and the conversion profiles were calculated from the decay of the absorption band located at 6165 cm-1.  The light source employed to cure the resins was a LED unit with a wavelength range 410-530 nm and light intensity of 400 mW/cm2.