https://omlc.org/~prahl/pubs/pdfx/schneider08a.pdf

Influence of photoinitiator type on the rate of polymerization, degree of conversion, hardness and yellowing of dental resin composites

The ratio of the double-bond content of monomer to polymer, i.e. degree of conversion (DC) has been used frequently as a convenient means of comparing the behavior and properties of dental composites and adhesives. The purpose of this investigation was to study the relationship of photopolymerization processes, bulk properties, and structure using model dentin adhesives cured in the presence of different ethanol content as an example. There was little difference in the DC of model BisGMA-based adhesives cured in the presence of ethanol concentrations ranging from 0 to 40 wt %, but there were substantial differences in the mechanical properties. Ultimate tensile strength (UTS) and modulus of elasticity decreased with an increase in ethanol content. Polymer structure was revealed by thermal behavior in the glass transition temperature (Tg) region; these measurements were obtained by modulated temperature differential scanning calorimetry (MTDSC) technology, which removes the competing irreversible effects associated with release of volatiles and residual curing. Glass transition temperature of model adhesives decreased substantially with an increase in ethanol content. The DC based on the quantity of remaining double bond has been used extensively to characterize and provide a relative assessment of the quality of dentin adhesives and dental composites. Since polymers differing in linearity, and therefore crosslink density, may have a similar degree of conversion, the measurement of monomer/polymer conversion does not necessarily provide complete representation of the quality or durability of the polymer structure.

Relationship of solvent to the photopolymerization process, properties, and structure in model dentin adhesives

Physical properties of current dental nanohybrid and nanofill light-cured resin composites

Thermal expansion coefficient of dental composites measured with strain gauges

The effect of fiber orientation on the thermal expansion coefficients of fiber-reinforced composites.

Summary

Selected commercial and experimental composites and resin systems have been evaluated by thermal analysis techniques of Differential Scanning Calorimetry, Thermogravimetric Analysis and Thermomechanical Analysis. Important thermal data such as heat of cure, coefficient of thermal expansion, dimensional changes over selected temperature ranges, filler weight percent, onset temperature of decomposition, temperature of peak decomposition rate, temperature of the end of decomposition, etc. have been determined. Heat of cure, thermal expansion coefficient and dimensional changes appear to follow an inverse linear regression fit with filler fraction in the composite. Thermal expansion changes and exothermic reactions with temperature indicate secondary cure during postcure heating. The thermally-induced decomposition occurs in multiple stages indicating presence of different structural species in the resin matrix.

Y. Wang

Papers

Thermoanalytical characterization of visible light cure dental composites