Abstract
This study was undertaken to investigate the effect of the Xenon-lamp curing unit (Flipo) on the elemental properties of light curing resin composite by comparison with a halogen-lamp curing unit (XL).
1) The shear bond strengths of resin composite to bovine dentin using each curing unit were measured. The adhesive system and resin composite used in this study were Clearfil Liner Bond II® and Clearfil AP-X® (shades: A 2 and A 4). The irradiation time of XL was 40 seconds as the control, and that of Flipo was 5 seconds (stepped output of 2 seconds at 50% maximal output followed by full output for 3 seconds). The result of the test showed that the shear bond strength produced by Flipo was about equal to that by XL for shade A 2, but for shade A 4 that produced by Flipo was significantly lower than that by XL (p<0.01). Using XL showed high bond strengths independent of shade.
2) The knoop hardness of the resin composite was measured for XL for 40 seconds, Flipo for 5 seconds and Flipo for 10 seconds (2 seconds at 50% maximal output followed by full output for 8 seconds)using Clearfil AP-X® (shades: A 2 and A 4). The result showed that when the shade was A 2, the knoop hardness produced by Flipo for 5 seconds was about equal to that by XL for 40 seconds, and that of Flipo for 10 seconds was significantly higher than those two groups (p<0.01). For shade of A 4, the knoop hardness produced by Flipo for 10 seconds was about equal to that of XL for 40seconds, and that of Flipo for 5 seconds was significantly lower than those two(p<0.01).
3) The dye penetration test was performed for cavities prepared on extracted human premolar and filled with resin under the light curing condition of XL for 40 seconds, Flipo for 5 seconds (two stepped output) and Flipo for 5 seconds of exposure at 100% intensity to evaluate marginal sealing and wall adaptation. The class V cavity with the base at depth of 1 mm in the dentin was prepared on the buccal surface. The group of XL for 40 seconds showed the best marginal sealing and wall adaptation, but when using Flipo at 100% intensity for 5 seconds, the dye penetration score was higher and both the incidence and width of contraction gap were significantly increased. The results of the present experiment proved that using the Xenon-lamp curing unit (Flipo) is effective for hardening a resin composite of shade A 2 less than 2.0 mm-deep with 1/6 of irradiation time needed for the halogen-lamp curing unit (XL). However, if the cavity is deeper than 2.0 mm, sufficient polymerization may not be obtained by using Flipo for 5 seconds, especially for shade A 4, and moreover, using Flipo for 5 seconds at 100% intensity may degrade the marginal seal effectiveness and wall adaptation.
