Study on Experimental LED Curing Light Unit

Abstract

 Purpose: We experimentally prepared a novel LED curing unit (MI-head) with a small tip (diameter: 2.1 mm) capable of irradiating light close to the gingival wall. In this study, we compared the MI-head and a conventional LED light curing unit, Pen Cure, to investigate the influence of the curing unit on adhesion to the gingival wall of class II cavities.
 Methods: Dentin adherend surfaces were prepared on extracted bovine teeth. Clearfil Mega Bond (MB) was applied to the surface, followed by light irradiation using Pen Cure or the MI-head at various irradiation distances and durations. Resin paste was then applied, and tensile bond strength (TBS) was measured after the specimens were placed in a 37°C water bath for 24 h. Class II cavities were prepared in extracted human teeth. After setting the matrix, MB was applied to the tooth surface, followed by light irradiation from the cuspal side using Pen Cure, or from the gingival wall side of the cavity using the MI-head. Resin paste was then incrementally filled and thermal stress was applied. Each sample was immersed in 5% basic fuchsin solution for 24 h, and marginal leakage was observed under an optical microscope. A class II cavity was prepared on the mesial side of the left first molar in an artificial mandibular model, and the light intensities of Pen Cure and the MI-head were measured under the same irradiation conditions as employed in the marginal leakage test.
 Results: Although TBS was significantly higher when irradiated with MI-head, marginal leakage could not be prevented. The light intensity of Pen Cure was significantly higher than that of the MI-head.
 Conclusion: The results of this study suggest that improvements in the irradiation method and prolonged irradiation are necessary to achieve adequate bond strength by the bonding agent applied to class II cavities using the MI-head.