Synthesis, characterization, shrinkage and curing kinetics of a new low-shrinkage urethane dimethacrylate monomer for dental applications.

OBJECTIVES: The aim of the study was to synthesize and characterize an isophorone-based urethane dimethacrylate (IP-UDMA) resin-monomer and to investigate its shrinkage and curing kinetics. METHODS: The IP-UDMA monomer was synthesized through the reaction of polyethylene glycol 400 and isophorone diisocyanate followed by reacting with HEMA to terminate it with methacrylate end groups. The reaction was followed using a standard back titration method and FTIR spectroscopy. The final product was purified and characterized using FTIR, (1)H NMR, elemental analysis and refractive index measurement. The shrinkage-strain of the specimens photopolymerized at circa 700mW/cm(2) was measured using the bonded-disk technique at 23, 35, and 45 degrees C. Initial shrinkage-strain-rates were obtained by numerical differentiation of shrinkage-strain data with respect to time. Degree-of-conversion of the specimens was measured using FTIR spectroscopy. The thermal curing kinetics of the monomer were also studied by differential scanning calorimetry (DSC). RESULTS: The characterization methods confirmed the suggested reaction route and the synthesized monomer. A low shrinkage-strain of about 4% was obtained for the new monomer. The results showed that the shrinkage-strain-rate of the monomer followed the autocatalytic model of Kamal and Sourour [Kamal MR, Sourour S. Kinetic and thermal characterization of thermoset cure. Polym Eng Sci 1973;13(1):59-64], which is used to describe the reaction kinetics of thermoset resins. The model parameters were calculated by linearization of the equation. SIGNIFICANCE: The model prediction was in a good agreement with the experimental data. The properties of the new monomer compare favorably with properties of the commercially available resins.

PMMA-grafted nanoclay as novel filler for dental adhesives.

OBJECTIVE: The aim of this study was to investigate the benefits of incorporation of poly(methyl methacrylate)-grafted-nanoclay on the bond strength of an experimental one-bottle dentin bonding system. The effect of the modification on the stability of the nanoparticle dispersion in the dilute adhesive was also studied. MATERIALS AND METHODS: Poly(methyl methacrylate) was grafted onto the pristine Na-MMT nanoclay (Cloisite Na(+)) through the free radical polymerization of methyl methacrylate in an aqueous media in the presence of ammonium persulfate as initiator. A reactive surfactant (AMPS) was also used in the reaction recipe to provide active sites on the surface of the nanoclay. The grafting polymerization reaction was carried out at 70 degrees C. The PMMA-g-nanoclay was then coagulated in methanol and filtered. The resulting PMMA-g-nanoclay was characterized using FTIR, TGA, X-ray diffraction (XRD) and particle size distribution analysis. The modified nanoclay was added to an experimental dentin bonding system as filler and the morphology of the nanoclay layers in the adhesive matrix was studied using TEM and XRD. Shear bond strength of the adhesives containing different filler contents was tested on the caries-free extracted human premolar teeth. The mode of failure was studied by scanning electron microscopy. The stability of the nanoclay dispersion in the dilute adhesive was also studied using a separation analyzer. The results were then statistically analyzed and compared. RESULTS: The grafting of poly(methylmethacrylate) onto the nanoclay was confirmed and the results revealed a partially exfoliated structure for the PMMA-g-nanoclay. Incorporation of the modified nanoclay provided a dentin bonding system with higher shear bond strength. The dispersion stability of the modified nanoparticles in the dilute adhesive was also increased more than 40 times in comparison with the pristine nanoclay. SIGNIFICANCE: The grafting modification provided nanoclay particles with higher dispersion stability than pristine Na-MMT nanoclay in a dilute dentin bonding system. Incorporation of the modified nanoclay into the bonding system provided higher shear bond strength. The finding would be beneficial in producing nano-filler containing adhesive systems.