<SUP>1</SUP>H stray-field long spin-echo trains and MRI: novel studies on the photopolymerization of a commercial dental resin

Photopolymerization of a commercial dental resin has been investigated by ¹H stray-field (STRAFI) magnetic resonance. The resin is a visible light-cured system, included in a new generation adhesive, which is used to bond the restorative material to enamel or dentin. Different methods were used to follow the curing reaction, which involve long and short spin-echo train acquisitions to obtain one-slice and one-dimensional data, respectively. The echo attenuation, in the limit of very short time delays, could be described as the sum of two exponentials. While the intensity of the early echoes in the train appeared mainly governed by spin-spin relaxation, the decay of the last echoes seemed to depend also on spin-lattice relaxation in the rotating frame. The relative amplitude of the long-time component was found to decrease from 84% to 10% with the photopolymerization progress, and a STRAFI degree of conversion of 74% could thus be suggested. The influence of the curing protocol was observed in STRAFI profiles.