ANALYSIS OF DENTAL COMPOSITES BY NEAR INFRARED SPECTROSCOPY.

Collaborative research among the American Dental Association, the University of Colorado, and NIST led to an improved method to analyze dental composites. Vinyl resin based composites are increasingly being used as alternatives to amalgam fillings. The durability and biocompatibility of dental restoratives materials, however, may be affected by the thoroughness to which they polymerize and how much water they will absorb in the oral environment. The collaborative work exploited near infrared (NIR) spectroscopy, which uses clinically relevant sized specimens, to provide information on both vinyl group conversion and water uptake on the same composite specimen. Owing to the nondestructive nature of this analytical technique, these properties can be monitored versus time and aqueous exposure. With NIR spectroscopy, it now becomes possible to assess the influence of the type and amount of filler phase of the composite on conversion and water absorption. In contrast to conventional gravimetric water absorption stu dies, NIR spectroscopy allows differentiation between free or unbound water and hydrogen-bonded water, thereby aiding in elucidating how water interacted with the polymer network. Recent studies have extended the use of NIR spectroscopy to monitor the conversion of the oxirane group in new types composites utilizing epoxy resin binders.