Degree of conversion of three fissure sealants cured by different light curing units using micro-Raman spectroscopy

Abstract

Background/purpose: Monomer to polymer conversion is important for optimal mechanical properties and resistance to biodegradation of resin-based materials. Incomplete conversion of fissure sealants may account for lower retention and fracture resistance as well as elution of leachable components. The objective of this study was to determine the degree of conversion (DC) of three fissure sealants cured using a conventional quartz-tungsten halogen (QTH) or a high power light-emitting diode (LED) light-curing unit using micro-Raman spectroscopy. Materials and methods: Delton Opaque and Helioseal Opaque and Helioseal Clear were applied to 60 noncarious permanent molars and cured with the QTH or the LED. Micro-Raman spectra were obtained from the top and the bottom surface of each sample. Three-way analysis of variance (alpha = 0.05) was used for data analysis. Results: Top surface DC values were significantly higher than bottom surface in each material irrespective of the light-curing unit (P lt 0.05). LED produced significantly higher DC values than the QTH with all three materials (P lt 0.05). Helioseal Opaque showed significantly lower DC values than Helioseal Clear (P lt 0.05). DC values for Delton and Helioseal Clear were comparable (P > 0.05). Conclusion: Higher DC is achieved with the LED with less exposure time compared with the conventional QTH at top and bottom surfaces of the three fissure sealants, although a lower conversion may be expected in opaque materials.