Effects of adhesive, base and diluent monomers on water sorption and conversion of experimental resins.

OBJECTIVES: To establish the relationship of resin composition and resin hydrophilicity (indicated by solubility parameters and logP) to water sorption (WS), solubility, and degree of double bond conversion (DC) of resin mixtures designed for adhesive restoratives by varying the concentration of pyromellitic glycerol dimethacrylate (PMGDM) and various co-monomers. METHODS: Sixteen resin mixtures were prepared with (30-70) mass fraction % PMGDM. At given PMGDM concentrations there were up to five compositions with increasing logP. Polymer disks (13 mm x 0.7 mm) were exposed to 96% relative humidity (RH) to determine water sorption in humid atmosphere (WSH) and subsequently immersed in water for immersion water sorption (WSI) and solubility. DC was assessed by near infrared spectroscopy. RESULTS: WSI was somewhat higher than WSH, which ranged from (2.1 to 5.3) mass fraction %. Both data were positively correlated to PMGDM concentrations [Pearson correlation, p<0.02; R(2)=0.74, 0.73 (WSI)] and solubility (R(2)=0.64), but not to logP. When grouped by structural similarities, i.e., base resins with bisphenol A core (Group B), Group O containing diluent monomers, or Group U containing urethane dimethacrylate, WS within each group was inversely correlated to logP with R(2)=0.98, 0.81, 0.95, and WS/solubility correlation improved with R(2)=0.88, 0.92 and 0.75, respectively. Solubility ranging from 0.3% to 2.3% was inversely related to DC (r=-0.872). Conversion ranging from 41% to 81% was lower for resins with high base monomer concentrations and highest in mixtures with UDMA. SIGNIFICANCE: LogP was a good predictor of WS after grouping the resins according to functional, compositional and structural similarities. WS and conversion were reasonably well predicted from Hoy's solubility parameters and other physical resin properties.

Light-emitting diode curing light irradiance and polymerization of resin-based composite.

BACKGROUND: Light-emitting diode (LED) curing lights are becoming popular; however, questions about their efficiency remain. The authors performed a comprehensive analysis of the properties of resin-based composites cured with LED lights. METHODS: The authors evaluated seven LED lights and one quartz-tungsten-halogen light (control). They measured intensity, depth of cure (DOC), degree of conversion (DC), hardness and temperature rise. They used three shades of a hybrid resin-based composite and a microfill composite, as well as one shade of another hybrid composite. RESULTS: Two LED lights required additional cure time to reach a DOC similar to that of the control light. DC at the top of the samples was independent of the light used. At 2.0 millimeters, the DC for several LED lights was significantly lower than that for the control light and was correlated strongly to the light's intensity. The bottom-to-top ratio for hardness of resin-based composites cured by all but one light was greater than 0.80. All LED lights except one had smaller temperature rise than did the control light. CONCLUSIONS: Six of the seven LED curing lights performed similarly to a quartz-tungsten-halogen curing light in curing resin-based composites. Clinical Implications. While LED curing lights and a quartz-tungsten-halogen light could cure resin-based composites, some resin-based composites cured with LED lights may require additional curing time or smaller increments of thickness.

Network structure of Bis-GMA- and UDMA-based resin systems.

OBJECTIVES: The commonly used dental base monomers 2,2-bis[p-(2'-hydroxy-3'-methacryloxypropoxy)phenylene]propane (Bis-GMA) and 1,6-bis(methacryloxy-2-ethoxycarbonylamino)-2,4,4-trimethylhexane (UDMA) require the use of a diluent monomer, such as triethylene glycol dimethacrylate (TEGDMA). The aim of this study was to measure double bond conversion of UDMA/TEGDMA and Bis-GMA/TEGDMA polymeric systems, determine the leachable portion, and analyze network formation by evaluating crosslinking and pendant double bonds. METHODS: UDMA or Bis-GMA was combined with TEGDMA in systematic increments and irradiated to form light cured polymers. Fourier transform infrared spectroscopy in the near-infrared region was used to measure double bond conversion. The leachable sol fraction was analyzed by 1H NMR. Resin composites were formulated. Flexural strength was measured by three-point bending and volumetric shrinkage was determined with a mercury dilatometer. RESULTS: The amount of base monomer greatly influenced double bond conversion, sol fraction, and crosslinking. Increasing base monomer concentration decreased double bond conversion, increased the leachable fraction, and decreased crosslinking and network formation. At mole fractions higher than 0.125, the UDMA polymers had significantly higher conversion than the Bis-GMA polymers. Bis-GMA polymers had higher leachable amounts of unreacted monomer, while UDMA mixtures had more crosslinking than the Bis-GMA mixtures. In regards to the physical properties of resin composites, increasing the base monomer improved flexural strength and decreased volumetric shrinkage. SIGNIFICANCE: This systematic study for the evaluation of conversion, leachability, crosslinking, and network structure along with physical properties, like volumetric shrinkage and flexural strength, are required for the optimization of competing desirable properties for the development of durable materials.