Electron Spin Resonance (ESR) Spectroscopy Studies of Compomer Type Dental Restoratives

Abstract

Electron spin resonance (ESR) spectroscopy was used to evaluate the curing kinetics of compomer type dental restoratives, determining rate constants and half-life of radicals. Physical strength measurements of the compomers were also determined for correlation with the ESR results. Compoglass (Ivoclar-Vivadent), Dyract (Dentsply), ANA (Nordiska) and Luxat (DMG) compomers were used in the study. Specimens, 3. 2 mm diameter x 6. 6 mm length, were cured in a plastic mold for 2 minutes, using an Elipar lamp. Immediately after curing, samples were examined by ESR, establishing time zero. The influence of conditioning at 37°CC in water, 0.1M lactic acid, and 75% ethanol was examined. A Varian (E—9 X-band) ESR spectrometer was used to follow radical decay in all dental compomers studied. Peak intensities decrease during storage under dark conditions, accelerated by solution sorption which causes the matrix to swell, bringing about faster radical decay. Rate constants and half-lives of the radicals were calculated from the average of n=3. Each system showed bi-exponential decay with one long lived half-life and one short lived half-life component. Radical decay rates for the four systems differ markedly, depending on their water sorption or conditioning method. Luxat and ANA were found by ESR and physical strength measurements to be structurally more homogeneous and water resistant than the other two compomers. Luxat exhibited the greatest half-life, i. e., longest radical decay profiles, on exposure to all conditioning methods, suggesting it would be the most stable compomer in dental applications. But, Luxat would be expected to release less fluoride in the oral cavity than Compoglass or Dyract.