Influence of Molecular Structure of Fluorescent Probe on Sensitivity for Cure Monitoring of Bonding Resin
K Komatsu, Francis W. Wang, K Nemoto
The structure of a fluorescent probe's rotating group is expected to affect the sensitivity of its response to the resin microviscosity. The purpose of this study was to investigate the influence of the molecular structure of a fluorescent probe that is dissolved in a photocured bonding resin on the change of its fluorescence emission spectrum during the polymerization of the resin. Therefore, we investigated how the chain length of the substituents on the amino group of a fluorescent probe (ANEPPS) affects the relationship between the degree of monomer conversion and the change in the fluorescence spectrum of the probe. The photocured bonding resin consisted of a mixed monomer (HEMA and BisGMA), a photoinitiator (CQ and 4EDMAB), and 0.1 mmol/L ANEPPS. Three ANEPPS probes with different chain lengths for the substituents on the amino group were used. After the bonding resin was out into a silicone mold, a specimen was prepared by exposing the bonding resin to a curing light for up to 120 s. The fluorescence spectrum of the specimen was then measured at an excitation wavelength of 520 nm. The DC of the bonding resin was obtained from the concentration of available C=C bonds determined from nearinfrared spectra. The fluorescence spectra of the ANEPPS probes showed not only an increase in fluorescence intensity, but also a blue shift in peak wavelength from 655 nm to 608nm. For each ANEPPS probe, the fluorescence intensity ratio, the ratio of the intensities at the peak wavelengths for the cured and uncured resins, was a piecewiselinear function of the DC with a transition occurring near 60 % of DC. A strong correlation was obtained in the relationship between the DC and the intensity ratio for each of the ANEPPS probes. The slope of the linear relation between the intensity ratio and the DC was used as a measure for the sensitivity of each probe for cure monitoring. For each ANEPPS probe, the slope of the linear equation below the transition was higher than the slope beyond it. In addition, the chain length of an ANEPPS probe did not affect the slope of the equation below the transition. However, the slope of the equation beyond the transition increased with the increase in the chain length of the ANEPPS probe.